Effect of bigger wheels on fuel mileage.
11-28-2012, 01:03 AM
#1
Instructor
Thread Starter
Effect of bigger wheels on fuel mileage.
So, I finally ran a full tank after installing the 215/65/17 winter tires on the car. The tank returned me 406 miles on the trip meter.
Since the car does not know that she has bigger tires or, the mileage is understated. So I decided to do some maths.***
R (factory rim+ tire)= 12", measured mine with a tape measure when they are off the car, don't go anal.
R (snow rims+ 17 inch wheels)= 14".
Circumference of factory wheels= 2*3.14*12= 75.36"
Circumference snow wheels= 2*3.14*14= 87.82"
Revolutions of factory wheel per mile= 1/(( 75.36*1/12)*1/5,280)=840.76433.
Revolutions of factory wheel for a full tank= 406*840.76433= 341,350.3184713483.
Mileage covered by the snow wheel= 341,350.3184713483*87.82*(1/12)*(1/5,280)=473.66 miles.
So, unless I missed something... increasing the size of my wheels actually increased the useful range of the car. The mileage was recorded on the mix of city/highway driving. 473 miles puts me at 29.5 MPG in the mixed cycle.
***My biggest assumption in this calculation is that the car cannot determine the size of the wheels it has on it, and odometer/trip meter continue counting the miles based on the dimensions of the factory wheel/tire package specific to the car.
Since the car does not know that she has bigger tires or, the mileage is understated. So I decided to do some maths.***
R (factory rim+ tire)= 12", measured mine with a tape measure when they are off the car, don't go anal.
R (snow rims+ 17 inch wheels)= 14".
Circumference of factory wheels= 2*3.14*12= 75.36"
Circumference snow wheels= 2*3.14*14= 87.82"
Revolutions of factory wheel per mile= 1/(( 75.36*1/12)*1/5,280)=840.76433.
Revolutions of factory wheel for a full tank= 406*840.76433= 341,350.3184713483.
Mileage covered by the snow wheel= 341,350.3184713483*87.82*(1/12)*(1/5,280)=473.66 miles.
So, unless I missed something... increasing the size of my wheels actually increased the useful range of the car. The mileage was recorded on the mix of city/highway driving. 473 miles puts me at 29.5 MPG in the mixed cycle.
***My biggest assumption in this calculation is that the car cannot determine the size of the wheels it has on it, and odometer/trip meter continue counting the miles based on the dimensions of the factory wheel/tire package specific to the car.
Last edited by AZsilverTl; 11-28-2012 at 01:10 AM.
11-28-2012, 08:54 AM
#2
Senior Moderator
The speedometer is calibrated for the stock wheel dia. That is roughly 25.5 to 25.7 or around 809 rev's per mile (going by the stock 205/60/16 / 215/50/17.) I'm not sure how you got to your measurements?
The car cant and doesn't know that the overall dia of the tire increased, how would it know? This is why when people upgrade rims and tires they try to stay within the stock dia. If you don't it will throw off the speedometer like yours is. Your snow tires are too big with them being a 65 series profile. Why did you purchase the wrong size? Your speedo is way off and so is your mileage.
The car cant and doesn't know that the overall dia of the tire increased, how would it know? This is why when people upgrade rims and tires they try to stay within the stock dia. If you don't it will throw off the speedometer like yours is. Your snow tires are too big with them being a 65 series profile. Why did you purchase the wrong size? Your speedo is way off and so is your mileage.
Last edited by fsttyms1; 11-28-2012 at 09:12 AM.
11-28-2012, 09:18 AM
#3
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So, unless I missed something... increasing the size of my wheels actually increased the useful range of the car. The mileage was recorded on the mix of city/highway driving. 473 miles puts me at 29.5 MPG in the mixed cycle.
***My biggest assumption in this calculation is that the car cannot determine the size of the wheels it has on it, and odometer/trip meter continue counting the miles based on the dimensions of the factory wheel/tire package specific to the car.
***My biggest assumption in this calculation is that the car cannot determine the size of the wheels it has on it, and odometer/trip meter continue counting the miles based on the dimensions of the factory wheel/tire package specific to the car.
Speedometer calibration is done based on factory wheels/tires. Any change to wheel or tire size not in proportion to stock size will throw off the speedo and hence the mileage/mpg.
Me thinks you need to re-read geometry and physics 101.
11-28-2012, 10:17 AM
#4
MechEng
iTrader: (9)
It's just not possible to increase you gas mileage by going to a larger, heavier tire. The engine will have to work much harder to rotate the increased mass and diameter. Your math is flawed somehow.
11-28-2012, 12:15 PM
#7
Senior Moderator
It doesnt matter what ecu you have, they ran the same dia tires the tl did. Go back and read my post. The speedo is calibrated for the 25.7 overall dia. It doesnt matter if you have 15s or 19s on the car if the overall dia is similar to the stock tire the speedo/odo will remain accurate.
Last edited by fsttyms1; 11-28-2012 at 12:17 PM.
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11-28-2012, 06:31 PM
#8
Instructor
Thread Starter
Fsttyms1, I am well aware that speedometer will be thrown off, hence the reason for the calculation. Speed and trip/odometer reading will be understated. Wheels are purchased for a reason- lift the car. Diameter increase- more ground covered for each revolution.
NSXNEXT, speedometer calibration is done for factory wheels. Bigger diameter wheels do throw off the odometer and speedometer. In my case, they HAVE increased the mileage. Here is the explanation: increasing the diameter of the wheels has the same effect as gearing down the car; IE going from 4.10 rear to 3.73. The result of the increased diameter is that my car stays at lower RPM when cruising, and reaches the cruising speed at LOWER RPM- result is the increased fuel mileage. Added rotational mass of the bigger tire is negated by the lower weight of the wheels. Or you are going to dispute that car cruising at 70MPH while at 1,800 RPM will use less gas than the car cruising at 70MPH while at 2,000 RPM?
03Tl, you can do the math and look into this. The wheels I have are 17", not 24". Any gain from the tire weight is negated by the lighter weight of the wheels. Your logic with heavier/bigger wheels works on going from 17" to a 22" wheel/tire sets. I am far from that. With my combination I am dropping my crusing RPMs, hence the gas saving. All four tires are pumped to 40 PSI, so that helps with reduced rolling resistance. The only time I could be losing on the mileage, is in the heavy start/stop traffic, but this cannot be measured.
NSXNEXT, speedometer calibration is done for factory wheels. Bigger diameter wheels do throw off the odometer and speedometer. In my case, they HAVE increased the mileage. Here is the explanation: increasing the diameter of the wheels has the same effect as gearing down the car; IE going from 4.10 rear to 3.73. The result of the increased diameter is that my car stays at lower RPM when cruising, and reaches the cruising speed at LOWER RPM- result is the increased fuel mileage. Added rotational mass of the bigger tire is negated by the lower weight of the wheels. Or you are going to dispute that car cruising at 70MPH while at 1,800 RPM will use less gas than the car cruising at 70MPH while at 2,000 RPM?
03Tl, you can do the math and look into this. The wheels I have are 17", not 24". Any gain from the tire weight is negated by the lighter weight of the wheels. Your logic with heavier/bigger wheels works on going from 17" to a 22" wheel/tire sets. I am far from that. With my combination I am dropping my crusing RPMs, hence the gas saving. All four tires are pumped to 40 PSI, so that helps with reduced rolling resistance. The only time I could be losing on the mileage, is in the heavy start/stop traffic, but this cannot be measured.
Last edited by AZsilverTl; 11-28-2012 at 06:39 PM.
11-28-2012, 07:19 PM
#9
Senior Moderator
Fsttyms1, I am well aware that speedometer will be thrown off, hence the reason for the calculation. Speed and trip/odometer reading will be understated. Wheels are purchased for a reason- lift the car. Diameter increase- more ground covered for each revolution.
NSXNEXT, speedometer calibration is done for factory wheels. Bigger diameter wheels do throw off the odometer and speedometer. In my case, they HAVE increased the mileage. Here is the explanation: increasing the diameter of the wheels has the same effect as gearing down the car; IE going from 4.10 rear to 3.73. The result of the increased diameter is that my car stays at lower RPM when cruising, and reaches the cruising speed at LOWER RPM- result is the increased fuel mileage. Added rotational mass of the bigger tire is negated by the lower weight of the wheels. Or you are going to dispute that car cruising at 70MPH while at 1,800 RPM will use less gas than the car cruising at 70MPH while at 2,000 RPM?
03Tl, you can do the math and look into this. The wheels I have are 17", not 24". Any gain from the tire weight is negated by the lighter weight of the wheels. Your logic with heavier/bigger wheels works on going from 17" to a 22" wheel/tire sets. I am far from that. With my combination I am dropping my crusing RPMs, hence the gas saving. All four tires are pumped to 40 PSI, so that helps with reduced rolling resistance. The only time I could be losing on the mileage, is in the heavy start/stop traffic, but this cannot be measured.
NSXNEXT, speedometer calibration is done for factory wheels. Bigger diameter wheels do throw off the odometer and speedometer. In my case, they HAVE increased the mileage. Here is the explanation: increasing the diameter of the wheels has the same effect as gearing down the car; IE going from 4.10 rear to 3.73. The result of the increased diameter is that my car stays at lower RPM when cruising, and reaches the cruising speed at LOWER RPM- result is the increased fuel mileage. Added rotational mass of the bigger tire is negated by the lower weight of the wheels. Or you are going to dispute that car cruising at 70MPH while at 1,800 RPM will use less gas than the car cruising at 70MPH while at 2,000 RPM?
03Tl, you can do the math and look into this. The wheels I have are 17", not 24". Any gain from the tire weight is negated by the lighter weight of the wheels. Your logic with heavier/bigger wheels works on going from 17" to a 22" wheel/tire sets. I am far from that. With my combination I am dropping my crusing RPMs, hence the gas saving. All four tires are pumped to 40 PSI, so that helps with reduced rolling resistance. The only time I could be losing on the mileage, is in the heavy start/stop traffic, but this cannot be measured.
11-28-2012, 07:46 PM
#10
Senior Moderator
Also to add to the above, lower rpm doesn't necessarily mean better mpg. If that were the case they would have made the engine run at 1000 rpm on the hwy. The cars engine has to have the power and efficiency to be able to push the car thru the air at hwy speed and at that rpm. For instance my TL with the CL 6 speed in it gets the same mileage as it did with the auto in it BUT it is revving 750 rpm higher on the hwy. Like I said. Unless you know EXACTLY how far and fast yout are now driving you cat accurately say you are getting better mileage. Also your calculations are off for the overall factory tire dia. It's 25.5 dia or roughly 819 revolutions
11-28-2012, 08:21 PM
#11
Instructor
Thread Starter
Why would I care for speed I am driving at now?
RPM is the key in to this. Car is shifting up earlier, and I am staying at lower RPM with the traffic flow; speed I am driving is irrelevant- lower RPM is what counts. Try this, place your car in SS and in D5 at 40 MPH and mash the gas; torque converter will allow slippage to raise the RPM to try to move the car. When I am driving in D5 on cruise, RPM is sitting at 1,300 RPM without the fluctuation UP- and this fluctuation WOULD occur if car was sensing that it needed more torque to move itself or if it senses that the car is lacking power. If the engine was not running efficiently, I would get the RPM fluctuation due to cruise control constantly adjusting the RPM/Trans to the road condition (same was as it does when you start driving up hill). I am driving the car, and I am telling you that in the mixed cycle the car returned better mileage than before. Knowing the diameter of the stock and snow wheels is ALL that is needed to find out the exact distance I traveled based on the trip meter readings. Even if I apply your calculation of amount of revolutions, I will still end up with 455 miles covered on the new wheels.
Wheel wise, I went from the stock wheels with the mix of tires previous owner had them on; Raiken Raptor and something else. Current it has Bridgestone Blizzak tires on.
Unsprung weight concept is of NEGLIGIBLE value here. You can read up on someone doing extensive testing to see if getting a much lighter wheel/tire combination gave him a better acceleration. http://www.nsxprime.com/forum/showth...-their-results
Judging by his results, and by my mileage so far I can say with numbers backing me that getting bigger tires produced NO penalty for mileage in MY case. Again, you are bringing in the theory of unsprung weight being removed from the center of the wheel, without giving the concrete numbers for my case. You are not considering the higher inertia+ less rolling resistance that can negate that.
Last point on drag. TL is not an SUV, there is nothing sticking out from the bottom; so again, the "theoretical" increase in drag will NOT be noticed. I can make a same point about removing a rear spoiler, as it creates drag- hence removing it will largely improve your fuel economy.
And most important point here is the mileage. On average my car was getting between 400-475 miles to a tank since I had. Low 400s when driving in mixed driving, higher numbers when on the road trips. So far after one mixed trip the mileage is higher than any previous mixed runs, with only variable being- bigger tires. The only logical conclusion is that bigger tires gave me better mileage, for the reasons listed earlier.
RPM is the key in to this. Car is shifting up earlier, and I am staying at lower RPM with the traffic flow; speed I am driving is irrelevant- lower RPM is what counts. Try this, place your car in SS and in D5 at 40 MPH and mash the gas; torque converter will allow slippage to raise the RPM to try to move the car. When I am driving in D5 on cruise, RPM is sitting at 1,300 RPM without the fluctuation UP- and this fluctuation WOULD occur if car was sensing that it needed more torque to move itself or if it senses that the car is lacking power. If the engine was not running efficiently, I would get the RPM fluctuation due to cruise control constantly adjusting the RPM/Trans to the road condition (same was as it does when you start driving up hill). I am driving the car, and I am telling you that in the mixed cycle the car returned better mileage than before. Knowing the diameter of the stock and snow wheels is ALL that is needed to find out the exact distance I traveled based on the trip meter readings. Even if I apply your calculation of amount of revolutions, I will still end up with 455 miles covered on the new wheels.
Wheel wise, I went from the stock wheels with the mix of tires previous owner had them on; Raiken Raptor and something else. Current it has Bridgestone Blizzak tires on.
Unsprung weight concept is of NEGLIGIBLE value here. You can read up on someone doing extensive testing to see if getting a much lighter wheel/tire combination gave him a better acceleration. http://www.nsxprime.com/forum/showth...-their-results
Judging by his results, and by my mileage so far I can say with numbers backing me that getting bigger tires produced NO penalty for mileage in MY case. Again, you are bringing in the theory of unsprung weight being removed from the center of the wheel, without giving the concrete numbers for my case. You are not considering the higher inertia+ less rolling resistance that can negate that.
Last point on drag. TL is not an SUV, there is nothing sticking out from the bottom; so again, the "theoretical" increase in drag will NOT be noticed. I can make a same point about removing a rear spoiler, as it creates drag- hence removing it will largely improve your fuel economy.
And most important point here is the mileage. On average my car was getting between 400-475 miles to a tank since I had. Low 400s when driving in mixed driving, higher numbers when on the road trips. So far after one mixed trip the mileage is higher than any previous mixed runs, with only variable being- bigger tires. The only logical conclusion is that bigger tires gave me better mileage, for the reasons listed earlier.
Last edited by AZsilverTl; 11-28-2012 at 08:27 PM.
11-28-2012, 11:25 PM
#12
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This article is based on the assumption that you are plus-sizing the wheels/tires, maintaining the correct aspect ratio which you are not.
http://www.caranddriver.com/features...d-tires-tested
http://www.caranddriver.com/features...d-tires-tested
The aesthetic appeal of larger wheels and tires is undeniable, but what about the alleged performance benefits? In general, larger wheels are heavier, and additional weight hinders performance. To examine the effects of installing larger wheels and tires, also known as “plus-sizing,” we tested five wheel-and-tire combinations—ranging from 15 to 19 inches—on a 2010 Volkswagen Golf and got a good sense of what is gained and lost in the process.
The plus-size concept basically works like this: As the wheel gets larger in diameter, the size of the tire’s sidewall must shrink to maintain the tire’s overall diameter. Keeping the overall tire diameter roughly the same is crucial to keeping the gearing the same and the speedometer accurate, as well as for making sure the wheels and tires fit within the fenders. But larger-diameter wheels and tires are often available only in enlarged widths as well. For more information on plus-sizing and details on what will and won't fit your car, call the folks at Tire Rack (800-981-3782) or visit tirerack.com.
Our test employed nearly identical Goodyear Eagle GT ultra-high-performance all-season tires in all five sizes, inflated to manufacturer-recommended pressures. We say that the tires were nearly the same because the 15-, 16-, and 17-inchers have a lower speed rating (V, or a top speed up to 149 mph) than the 18- and 19-inch tires’ W-rating (up to 168 mph). This, however, was as close as we could get to testing the same tire in every size. We used the stock steel wheels for the 15-inch test and went to the aftermarket for the larger wheels, as most owners would do. The aftermarket wheel we chose was a cast-aluminum ASA GT1, which is available in 16- to 19-inch sizes on the Golf. It’s obvious from the test that as wheels and tires grow in size, they also grow in weight. Here’s how the test shook out:
What’s immediately apparent from the results is that as the wheel-and-tire packages get larger and heavier, acceleration and fuel economy suffer. Neither is a huge surprise, but we measured a 10-percent drop in fuel economy and a four-percent degradation in 0-to-60-mph acceleration from the 15s to the 19s, which is worth considering should you be thinking about “going big.” Increasing wheel diameter and width, in turn, requires wider tires with shorter and stiffer sidewalls, which we found will increase skidpad grip, but as our test shows, there is a limit to this assertion. The 19-inch package came with the widest tires (235/35R-19) mounted to the widest wheels (8.5 inches), but this setup had less grip around the skidpad than the narrower 225/40R-18s on 8.0-inch-wide wheels. We asked the folks at Goodyear why that might be, and they postulated that the added width may have given the outside tire more grip, which would increase body roll and could therefore decrease the load on the inside tire enough to lose 0.01 g on the skidpad.
Surprisingly, the 225/40R-18s showed a big skidpad advantage compared with the 225/45R-17s (0.89 g versus 0.85 g). We suspect the difference is due to the grippier compound (lower wear rating) of the W-rated 18s. Goodyear does offer a W-rated GT in the 225/45R-17 size, which is what we intended to use, but Goodyear sent us the V-rated version for our test.
Subjectively, both the 17-inch and 18-inch wheels and tires were in the sweet spot of grip, braking performance, ride comfort, and steering feel. Moving from 17-inchers to 18s barely degrades ride quality, and the additional grip is welcome. We’d guess that a W-rated Eagle GT in the 17-inch size would come close to matching the grip of the W-rated 18, but we can’t say for certain without testing. Even with V-rated rubber, the per-formance of the 17s felt similar to that of the 18s. But since the 18-inch setup costs only $112 more than the 17-inch package, we’d probably opt for the 18s if we lived in a region with smooth roads and looks were a priority.
We do know that the heavy, 19-inch setup suffered from the most impact harshness and seemed to tax the suspension the most. In contrast, the two smallest wheel-and-tire combos showed a propensity for more understeer on the skidpad but provided a more controlled and supple ride. And although it didn’t register on the dBA-meter, the 15- and 16-inch arrangements had a more pleasant sound quality than the larger tires.
The 19-inch wheels definitely look the coolest. But the 17- and 18-inch setups offer a better compromise of grip, acceleration, price, and ride harshness, so we’re not surprised VW uses 17- and 18-inch sizes on its hot Golf, the GTI. If it’s acceleration you’re after, stick with the smaller, lighter wheels and tires. And remember, unless you believe it is better to look good than to feel good, take our advice and stay away from extremely low-profile sidewalls and massively heavy wheels.
The plus-size concept basically works like this: As the wheel gets larger in diameter, the size of the tire’s sidewall must shrink to maintain the tire’s overall diameter. Keeping the overall tire diameter roughly the same is crucial to keeping the gearing the same and the speedometer accurate, as well as for making sure the wheels and tires fit within the fenders. But larger-diameter wheels and tires are often available only in enlarged widths as well. For more information on plus-sizing and details on what will and won't fit your car, call the folks at Tire Rack (800-981-3782) or visit tirerack.com.
Our test employed nearly identical Goodyear Eagle GT ultra-high-performance all-season tires in all five sizes, inflated to manufacturer-recommended pressures. We say that the tires were nearly the same because the 15-, 16-, and 17-inchers have a lower speed rating (V, or a top speed up to 149 mph) than the 18- and 19-inch tires’ W-rating (up to 168 mph). This, however, was as close as we could get to testing the same tire in every size. We used the stock steel wheels for the 15-inch test and went to the aftermarket for the larger wheels, as most owners would do. The aftermarket wheel we chose was a cast-aluminum ASA GT1, which is available in 16- to 19-inch sizes on the Golf. It’s obvious from the test that as wheels and tires grow in size, they also grow in weight. Here’s how the test shook out:
What’s immediately apparent from the results is that as the wheel-and-tire packages get larger and heavier, acceleration and fuel economy suffer. Neither is a huge surprise, but we measured a 10-percent drop in fuel economy and a four-percent degradation in 0-to-60-mph acceleration from the 15s to the 19s, which is worth considering should you be thinking about “going big.” Increasing wheel diameter and width, in turn, requires wider tires with shorter and stiffer sidewalls, which we found will increase skidpad grip, but as our test shows, there is a limit to this assertion. The 19-inch package came with the widest tires (235/35R-19) mounted to the widest wheels (8.5 inches), but this setup had less grip around the skidpad than the narrower 225/40R-18s on 8.0-inch-wide wheels. We asked the folks at Goodyear why that might be, and they postulated that the added width may have given the outside tire more grip, which would increase body roll and could therefore decrease the load on the inside tire enough to lose 0.01 g on the skidpad.
Surprisingly, the 225/40R-18s showed a big skidpad advantage compared with the 225/45R-17s (0.89 g versus 0.85 g). We suspect the difference is due to the grippier compound (lower wear rating) of the W-rated 18s. Goodyear does offer a W-rated GT in the 225/45R-17 size, which is what we intended to use, but Goodyear sent us the V-rated version for our test.
Subjectively, both the 17-inch and 18-inch wheels and tires were in the sweet spot of grip, braking performance, ride comfort, and steering feel. Moving from 17-inchers to 18s barely degrades ride quality, and the additional grip is welcome. We’d guess that a W-rated Eagle GT in the 17-inch size would come close to matching the grip of the W-rated 18, but we can’t say for certain without testing. Even with V-rated rubber, the per-formance of the 17s felt similar to that of the 18s. But since the 18-inch setup costs only $112 more than the 17-inch package, we’d probably opt for the 18s if we lived in a region with smooth roads and looks were a priority.
We do know that the heavy, 19-inch setup suffered from the most impact harshness and seemed to tax the suspension the most. In contrast, the two smallest wheel-and-tire combos showed a propensity for more understeer on the skidpad but provided a more controlled and supple ride. And although it didn’t register on the dBA-meter, the 15- and 16-inch arrangements had a more pleasant sound quality than the larger tires.
The 19-inch wheels definitely look the coolest. But the 17- and 18-inch setups offer a better compromise of grip, acceleration, price, and ride harshness, so we’re not surprised VW uses 17- and 18-inch sizes on its hot Golf, the GTI. If it’s acceleration you’re after, stick with the smaller, lighter wheels and tires. And remember, unless you believe it is better to look good than to feel good, take our advice and stay away from extremely low-profile sidewalls and massively heavy wheels.
Last edited by NSXNEXT; 11-28-2012 at 11:28 PM.
11-29-2012, 09:38 AM
#14
Don't forget to calculate the 2% loss for winter blend gas.
Hey this would make a good MythBusters episode!
Hey this would make a good MythBusters episode!
11-29-2012, 09:38 AM
#15
Senior Moderator
11-29-2012, 09:59 AM
#16
Do you guys know that even with stocn rim tire setup the speedo is off by some ? Back in a day they did accurate test on different car and hondas were off more than others... lets say your speedo tells u your are driving 60mph but you are actually doing only 56mph
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11-29-2012, 01:02 PM
#19
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11-29-2012, 04:17 PM
#20
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I think factory speedos are overstated to err on the side of caution. Better to have a speedo read 60 mph at 56 mph, than 56 mph at 60 mph.
I know the 7G Accord had a speedo/odo that was off by ~3%. There was a big stink about it because of issues just out of warranty, etc.
Fatty, if you have OP's range on his summer tires, the diameter of the summer tires and winter tires, actual range on winter tires should be easy to calculate.
I know the 7G Accord had a speedo/odo that was off by ~3%. There was a big stink about it because of issues just out of warranty, etc.
Fatty, if you have OP's range on his summer tires, the diameter of the summer tires and winter tires, actual range on winter tires should be easy to calculate.
11-29-2012, 07:03 PM
#21
Instructor
Thread Starter
Neuronbob: bigger tires are there for a reason, I need higher ground clearance as I use my TL to go everywhere in AZ, which includes trails, mud, and snow. Go through my threads if you want the details. Next on my list is the actual 2" lift all around, so car is as trail ready as she can be. I took her through everything AZ had, and she took like a boss. It is a big modern misconception among people that FWD car, or even any 2WD cannot go off-road. Some short 25 years ago, FWD cars were competing and winning in Dakar Rally, going through the roughest terrain in the world.
With TL not once did I have to back off from driving anywhere, ground clearance being my only problem. In my country you don't need 4x4 to drive on leaves, as is the case in USA.
Mr.Marco, no winter gas in Phoenix as ... it is always summer here.
just, I need to grab mine and do a test at different speeds and see the deviation. Local speed signs in 35MPH zones show my speedo being 4-6 miles slow. IE when my speedo shows 30MPH, I am actually doing 35MPH.
With TL not once did I have to back off from driving anywhere, ground clearance being my only problem. In my country you don't need 4x4 to drive on leaves, as is the case in USA.
Mr.Marco, no winter gas in Phoenix as ... it is always summer here.
just, I need to grab mine and do a test at different speeds and see the deviation. Local speed signs in 35MPH zones show my speedo being 4-6 miles slow. IE when my speedo shows 30MPH, I am actually doing 35MPH.
11-29-2012, 07:44 PM
#22
Senior Moderator
There are a few basic principles that come to play here:
1. The more weight something has, the more energy is required to move it.
2. The further the weight is from the point of rotation (Axis) the more energy is required to move it. (the energy required is exponential for every amount of increase)
3. Increasing the diameter of a circular object will DECREASE the amount of revolutions the circular object takes in a given distance.
4. Any tire combination will have it's limitations due to the ECU and the nature of a gas engine W/ a transmission.
So the goal here is to increase MPG and this can be accomplished in a few ways. I'm not going to go into a 100% thought out explanation with equations and numerous examples.
#1: Move the bulk of the weight closer to the hub of the wheel. You can do this by getting a smaller diameter wheel with a tire with a larger sidewall. The weight of the rubber on the increase in sidewall is going to be a lot less than the weight of metal for a rim. So basically if you have a 22" rim with a tire that's like rubber band vs a rim that's 18" with a larger tire (both have the same overall diameter), the 18" rim combo will require less energy to move since the weight is closer to the axis of rotation (The hub)
#2: Reduce the rotational mass! The less you mass you have, the less energy will be required to move it. So if you reduce the weight of your wheel and tire combination, you will require less energy to move them.
#3: If you put larger tires on your car you are essentially "gearing UP" your car thus making the engine rev lower for a given speed. For example if your car has factory tires, etc it revs at 1500 RPM at 50MPH (Actual speed). If you increase the tire size to make the circumference larger, then the engine will now rev at 1400 RPM's at 50MPH (actual speed). Your speedometer and instrumentation to measure MPG that's built into the car will be off and will have an innate error since they were programmed with the factory tire size and not the new one. Doing this has it's limitations as explained below.
Limitations: A car's engine will only produce a certain amount of power at a given RPM. As well the ECU can only retard the timing and cut fuel to a certain extent to match the car's needs. In a factory senario, the car will be cutting or adding fuel to make enough power to drive the wheels. What sizing up the tire does, or reducing weight, etc is shift the car's power needs to a lower number.
So I'm going to make up a senario to explain this. Take an engine that makes 40HP at 1000 RPM's, 50HP at 1500 RPMs, 60HP at 2000 RPMS and so on and so forth in 10HP increments per 500 RPMs. But this engine has a Computer that calculates the fuel needed (PGM-FI) and will inject the necessary amount of fuel.
So your driving along at 50MPH (actual speed) revving at 1500 RPMS making 50HP to drive the factory wheels on your car. You stop at discount tire and buy a new set of wheels and tires, and this new set has a LARGER overall diameter. You get it put on and decide to take a trip! Well now your car is revving at 1400 RPM's going 50MPH and the CAR is making 46.66 HP at 1400RPMs. Since the engine is revving 100 RPMs less it THEORETICALLY requires less fuel!
If your new tire/rim combo requires MORE energy to rotate, then the PGM-FI system will dump more fuel into the engine to produce extra power (advance the timing, etc). So in this senario you may end up HURTING your fuel economy.
So you come back from your trip and see the ADV.1 has a new lightweight wheel/tire combo that you like and you buy it and put it on your car and everything is close to factory specs as far as sizing goes. Now your driving along and once again your are doing 1500 RPM's @ 50MPH producing 50HP. But since your new wheels are lighter they require less energy to move, so the PGM-FI system cuts back on the fuel and the engine's timing is retarded to produce say 40HP to drive the new lighter wheels. This is when you start saving money and getting better gas mileage!
TL;DR: It's all really based on the amount of energy required to move a certain tire/wheel combo. Upsizing tires doesn't guarantee you better MPG. Reducing the weight doesn't either. It depends on the distance and the weight.
Just to make it easy to see:
Energy Required = 1/2 * Mass * Radius^2 * Angular Velocity
11-29-2012, 08:27 PM
#23
Senior Moderator
This is correct to an extent! The physics involved in this are fairly basic engineering physics with rotational mass and "work" and "energy" expanded to move a rolling cylinder (to an extent).
There are a few basic principles that come to play here:
1. The more weight something has, the more energy is required to move it.
2. The further the weight is from the point of rotation (Axis) the more energy is required to move it. (the energy required is exponential for every amount of increase)
3. Increasing the diameter of a circular object will DECREASE the amount of revolutions the circular object takes in a given distance.
4. Any tire combination will have it's limitations due to the ECU and the nature of a gas engine W/ a transmission.
So the goal here is to increase MPG and this can be accomplished in a few ways. I'm not going to go into a 100% thought out explanation with equations and numerous examples.
#1: Move the bulk of the weight closer to the hub of the wheel. You can do this by getting a smaller diameter wheel with a tire with a larger sidewall. The weight of the rubber on the increase in sidewall is going to be a lot less than the weight of metal for a rim. So basically if you have a 22" rim with a tire that's like rubber band vs a rim that's 18" with a larger tire (both have the same overall diameter), the 18" rim combo will require less energy to move since the weight is closer to the axis of rotation (The hub)
#2: Reduce the rotational mass! The less you mass you have, the less energy will be required to move it. So if you reduce the weight of your wheel and tire combination, you will require less energy to move them.
#3: If you put larger tires on your car you are essentially "gearing UP" your car thus making the engine rev lower for a given speed. For example if your car has factory tires, etc it revs at 1500 RPM at 50MPH (Actual speed). If you increase the tire size to make the circumference larger, then the engine will now rev at 1400 RPM's at 50MPH (actual speed). Your speedometer and instrumentation to measure MPG that's built into the car will be off and will have an innate error since they were programmed with the factory tire size and not the new one. Doing this has it's limitations as explained below.
Limitations: A car's engine will only produce a certain amount of power at a given RPM. As well the ECU can only retard the timing and cut fuel to a certain extent to match the car's needs. In a factory senario, the car will be cutting or adding fuel to make enough power to drive the wheels. What sizing up the tire does, or reducing weight, etc is shift the car's power needs to a lower number.
So I'm going to make up a senario to explain this. Take an engine that makes 40HP at 1000 RPM's, 50HP at 1500 RPMs, 60HP at 2000 RPMS and so on and so forth in 10HP increments per 500 RPMs. But this engine has a Computer that calculates the fuel needed (PGM-FI) and will inject the necessary amount of fuel.
So your driving along at 50MPH (actual speed) revving at 1500 RPMS making 50HP to drive the factory wheels on your car. You stop at discount tire and buy a new set of wheels and tires, and this new set has a LARGER overall diameter. You get it put on and decide to take a trip! Well now your car is revving at 1400 RPM's going 50MPH and the CAR is making 46.66 HP at 1400RPMs. Since the engine is revving 100 RPMs less it THEORETICALLY requires less fuel!
If your new tire/rim combo requires MORE energy to rotate, then the PGM-FI system will dump more fuel into the engine to produce extra power (advance the timing, etc). So in this senario you may end up HURTING your fuel economy.
So you come back from your trip and see the ADV.1 has a new lightweight wheel/tire combo that you like and you buy it and put it on your car and everything is close to factory specs as far as sizing goes. Now your driving along and once again your are doing 1500 RPM's @ 50MPH producing 50HP. But since your new wheels are lighter they require less energy to move, so the PGM-FI system cuts back on the fuel and the engine's timing is retarded to produce say 40HP to drive the new lighter wheels. This is when you start saving money and getting better gas mileage!
TL;DR: It's all really based on the amount of energy required to move a certain tire/wheel combo. Upsizing tires doesn't guarantee you better MPG. Reducing the weight doesn't either. It depends on the distance and the weight.
Just to make it easy to see:
Energy Required = 1/2 * Mass * Radius^2 * Angular Velocity
There are a few basic principles that come to play here:
1. The more weight something has, the more energy is required to move it.
2. The further the weight is from the point of rotation (Axis) the more energy is required to move it. (the energy required is exponential for every amount of increase)
3. Increasing the diameter of a circular object will DECREASE the amount of revolutions the circular object takes in a given distance.
4. Any tire combination will have it's limitations due to the ECU and the nature of a gas engine W/ a transmission.
So the goal here is to increase MPG and this can be accomplished in a few ways. I'm not going to go into a 100% thought out explanation with equations and numerous examples.
#1: Move the bulk of the weight closer to the hub of the wheel. You can do this by getting a smaller diameter wheel with a tire with a larger sidewall. The weight of the rubber on the increase in sidewall is going to be a lot less than the weight of metal for a rim. So basically if you have a 22" rim with a tire that's like rubber band vs a rim that's 18" with a larger tire (both have the same overall diameter), the 18" rim combo will require less energy to move since the weight is closer to the axis of rotation (The hub)
#2: Reduce the rotational mass! The less you mass you have, the less energy will be required to move it. So if you reduce the weight of your wheel and tire combination, you will require less energy to move them.
#3: If you put larger tires on your car you are essentially "gearing UP" your car thus making the engine rev lower for a given speed. For example if your car has factory tires, etc it revs at 1500 RPM at 50MPH (Actual speed). If you increase the tire size to make the circumference larger, then the engine will now rev at 1400 RPM's at 50MPH (actual speed). Your speedometer and instrumentation to measure MPG that's built into the car will be off and will have an innate error since they were programmed with the factory tire size and not the new one. Doing this has it's limitations as explained below.
Limitations: A car's engine will only produce a certain amount of power at a given RPM. As well the ECU can only retard the timing and cut fuel to a certain extent to match the car's needs. In a factory senario, the car will be cutting or adding fuel to make enough power to drive the wheels. What sizing up the tire does, or reducing weight, etc is shift the car's power needs to a lower number.
So I'm going to make up a senario to explain this. Take an engine that makes 40HP at 1000 RPM's, 50HP at 1500 RPMs, 60HP at 2000 RPMS and so on and so forth in 10HP increments per 500 RPMs. But this engine has a Computer that calculates the fuel needed (PGM-FI) and will inject the necessary amount of fuel.
So your driving along at 50MPH (actual speed) revving at 1500 RPMS making 50HP to drive the factory wheels on your car. You stop at discount tire and buy a new set of wheels and tires, and this new set has a LARGER overall diameter. You get it put on and decide to take a trip! Well now your car is revving at 1400 RPM's going 50MPH and the CAR is making 46.66 HP at 1400RPMs. Since the engine is revving 100 RPMs less it THEORETICALLY requires less fuel!
If your new tire/rim combo requires MORE energy to rotate, then the PGM-FI system will dump more fuel into the engine to produce extra power (advance the timing, etc). So in this senario you may end up HURTING your fuel economy.
So you come back from your trip and see the ADV.1 has a new lightweight wheel/tire combo that you like and you buy it and put it on your car and everything is close to factory specs as far as sizing goes. Now your driving along and once again your are doing 1500 RPM's @ 50MPH producing 50HP. But since your new wheels are lighter they require less energy to move, so the PGM-FI system cuts back on the fuel and the engine's timing is retarded to produce say 40HP to drive the new lighter wheels. This is when you start saving money and getting better gas mileage!
TL;DR: It's all really based on the amount of energy required to move a certain tire/wheel combo. Upsizing tires doesn't guarantee you better MPG. Reducing the weight doesn't either. It depends on the distance and the weight.
Just to make it easy to see:
Energy Required = 1/2 * Mass * Radius^2 * Angular Velocity
11-29-2012, 09:43 PM
#24
Instructor
Thread Starter
BUT it may take more throttle to maintain said speed at that rpm in turn would require more fuel. Just because the throttle is open more does not mean that the rpm would be higher as the op tried to point out earlier. Also his idea is flawed as well in his using ss mode or the rpm jumping up or down as he stated the car needing more power. For the most part under a certain throttle input the torque converter stays locked, there by keeping the trans in said gear and the rpm stable BUT throttle can be open more to sustain/maintain speed its traveling. Part of the "SS" mode is keeping the torque converter locked. You wont get the unlocking and locking of the torque converter with it. One would have to have a live data scanner or a device to monitor the actual throttle position.
When you place the shifter in the SS (tip tronic mode) on the TL in 5th gear at low speed 35-40 MPH it will NOT lock down the TC. If you try to go full throttle at that speed while in D5, the TC will allow slippage where RPMs will be be at 3k RPM. During my normal driving with larger diameter tires I get upshifts at lower RPM, and car's RPM do not fluctuate when I set cruise at 45MPH in 5th gear, they stay planted at 1,300 RPM.
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