Everything else being equal (such as combined wheel/tire weights), what is the effect of a change in overall wheel and tire circumference on acceleration (i.e. 0-60 times and 1/4 mile)?

For example, the 19X8 Versus Campionato SS7s are listed at 25lbs on autocarparts.com, which is about equal to stock, if I were to go with these wheels with 235/35/19 rubber, how would my acceleration be affected since the tire calculator shows a minimal increase in overall circumference over stock? (I'm even guessing that the total wheel/tire weight may drop slighty since these tires should be lighter than the stock ones.)

 

^^^

OK, I'm figuring that there's no way these wheels will hurt acceleration, but all I hear is that 19s WILL hurt performance. Someone has to have a better explanation, other than the weight factor.

 

Ok! This is a simplified explanation. Our final gear ratio is 4 something. If you put on larger wheels that ratio drops to 3 something. Higher top speed but slower off line and mid-range! I certainly wouldn't put 19in. wheels on plus with my Eibachs they would rub. Hope this helps!

 

Rod,

It has to do more with rotational inertia. Once you're moving, then the acceleration is not too bad, but off the line, it will hurt you.

Although your tire/wheel combo may be lighter than stock, most of the weight is not centralized, but rather spreads out radially. Thus, it's takes more work to rotate an object when its mass is more towards the edge.

I believe EricL has a link to the formula for calculating the ideal weight of larger rim/tire that will give the same rotational inertia as the stock. I believe that to achieve the same effect it had to be ~ 19-20lbs rim...or something like that. EricL, your input please.

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Frank
01-S White/Parchment
Comptech Sways & Springs

 

So a 16" wheel would be better then a 17" of the same weight???

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2001 Silver 3.2CLS
Muds, Spoiler, Hardwire 8500, Polarg M-6 lamps, K&N filter #33-2178,
Comptech Headers, Sways, mufflers
Planning: SSR 17X7.5 GT1 Wheels, Brembo Brakes.

 

Thanks, this makes more sense to me now, but I'm figuring since the difference in the rolling radius or overall circumference between the 2 wheel/tire combinations I'm comparing is extremely minimal, about a .04% increase over stock, the effect on acceleration should also be minimal. It was just a question out of curiosity since I've heard so many negative things about going with 19s.

 

You betcha. I had a set of 17 x 7 SSR Integral on my Lude Si a while back. At the time, I was running 16.2 in the 1/4 mile. I then switched to the stock 15 x 6.5 rims, and guess what, time was better with the stock ~ 15.9-16.0. The weight for both the stock and SSR was ~ 17lbs.



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Frank
01-S White/Parchment
Comptech Sways & Springs

 

I heard that going to 18's cut around 10hp to the wheels......

At least that has been posted on this list in multiple Dyno threads.....ymmv



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2001 Silver 3.2CLS
Muds, Spoiler, Hardwire 8500, Polarg M-6 lamps, K&N filter #33-2178,
Comptech Headers, Sways, mufflers
Planning: SSR 17X7.5 GT1 Wheels, Brembo Brakes.

 

Yeah, usually 5-10HP; however, if you have a light 18" set up like Astroboy's Volks SE-37, you may be able to pick up 5-10HP depending on your mods.

A local speed shop where I live did a test on a Civic with Intake/Headers/Exhaust and 15" stock rims vs 17" SSR rims weighing a good 10lbs less. Result showed the Civic with 17" gained 5-6 HP peak over stock.



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Frank
01-S White/Parchment
Comptech Sways & Springs

 

Taken from a post I made months ago:

http://www.acura-cl.com/ubb/Forum1/HTML/003193.html

Some basic math to help with the idea, basic lever concept:

AT = Axle Torque
GT = Torque at the pavement
R = Tire/Wheel Radius

GT = (12 / R) * AT

Or as with a stock Tire/Wheel radius of 12.732 and an example axle torque of 200 lb/ft:

12 / 12.732 = 0.943
0.943 * 200 = 188.5

So 188.5 Lb/Ft actually make it to the pavement. So go a little bit smaller diameter, say 215/40 series on the same rim:

12 / 11.886 = 1.010
1.010 * 200 = 202

So by going smaller you actually get more of the present torque to the pavement. But this does not take into account the gearing changes that would also affect performance as the transaxle will be shifting at a different MPH

 

Link is gone -- I figured out the 19-20 lbs for a 18" based on a simple physics model.

If the 18" wheel was constructed exactly the same as the stock CLS wheel, the formula works out to require an 18" wheel to be around 18-20lbs to not require more energy to spin up and/or down that the stock wheel.

I would have to look up the formulas again, and repost.

The wheel weight does make a huge difference. I got more speed over the entire range with the 50lb loss in wheel weight, than I did with the headers and CAI.

(You drop 50 lbs of static weight AND 50 lbs of rotational weight.)

The hard part about making "rules" is the assumption that the bulk of the mass is concentrated in the rim -- this is just an assumption that I made to get a "ball park" idea of how heavy (or how light) an eighteen inch wheel should be to not loose HP.

The 18" Volks wheels Astroboy has would probably use LESS energy than the stock wheels.

Light weight wheels also help with braking. An object at rest tends to remain at rest, and an object in motion tends to remain in motion. This law applies to rotational inertia. So lighter wheels cut stopping distances, and will spin-up easier at any speed.


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Silver 2001 CL-S with NAVI

• Mud guards
• Wheel locks
• Toyo T1S 235/45ZR17-97W* Proxies on 17x8" SSR Competition wheels (48lbs less than stock)
• Kevlar/SS Brake lines w/Brembos?
• Comptech headers & sways
• Silver AEM CAI
• 10 coats of Zaino magic

 

Thanks for all the great info, but I still want 19s if I decide to go with aftermarket wheels. I don't really race or anything, more into the appearance thing with this car, but I didn't want to completely kill performance either.