Motomano

Yesterday I installed Cooper Discoverer 245/60 on stock 18" wheels, but a question comes out: if I ever need to use the smaller diameter spare, it will damage the SHAWD system? This because a couple of days ago, got a flat on the right front, used the spare, it had low pressure, so I drove a few yards by making a U turn, ( steering felt weird BTW ) and warnings for ABS, VSA, SHAWD showed immediatly, I entered a gas station, set the spare tire pressure to 60 psi, drove out, lights went off.
Another related issue: the only warning didn't show was the TPMS after the flat was in the trunk...

justnspace

iTrader: (1)

a spare is for temporary use.
I think the acura engineers would account for the spare being smaller for a short amount of time.

Motomano

That is my thinking, and being familiar with 4WD vehicles, I know the weird U turn sensation was because of the larger radius on the smaller tire, my guess is this triggered the warnings, I hope never need to use the spare with the new tires, as a matter of fact I surfed for a bigger spare say 175/80, instead of the 165/80, but not even found a dealer who has temporary use tires.
Thanks for your input Justnspace.

mrgold35

I've never been too crazy about putting a donut spare on the front for Honda/Acura because they are mostly fwd because:
- front wheels have most/all of the power from engine (RDX mostly fwd)
- fronts do most of the braking
- the fronts have to do the steering.

I did see a guy spin out on a curve in a Ford Taurus with a donut on the rear (he was driving waaaaay to fast even for a Taurus).

Lucky for me, all my flats have been the rear tires on my TSX and RDX. I upgraded my rims on all three vehicles and kept the OEM rims to use as full size spares. I still keep the donuts in the trunk for the TSX and RDX since they are in-town commuter cars. If it will take a few days/weeks to get a replacement tire, I usually switch to the full size spare in the garage. I would really take it easy since braking/steering/traction is limited.

justnspace

iTrader: (1)

right, because of the different rolling diameter on the front (one spare and one regular sized wheel) it caused an imbalance when U-turning..

to solve this; move the the spare to the rear, so that your driving wheels(the front) will always be a match.

Motomano

Thanks, both of you were very helpful, so in the event I need to use the soare It will be on the rear, for the shorter distance I could, hopefully not on a looong time, but who knows?
Anyway ai do carry a small air compressor and a Fix-a-flat can just in case, so spare will be the last choice. a couple of days ago a nasty bump on the side wall exploded of sudden a day after I orderer the new tires and a day before they arrived.

mrgold35

I don't know if you can use fix-a-flat because of the TPMS. The goo might ruin the sensor, I'm not 100% sure on this or what you can use. You might have to plan on replacing the TPMS sensor if you have no choice to use fix-a-flat.

I would only worry about moving to the rear if it is going to be a few days before you can replace the tire. It is hard to flip/flop two tires in the middle of no-where with one jack.

The TPMS saved me a few times with slow leaks and I was able to repair in time because of the M.I.D. warning. Another time I ran over road debris and put a dime size hole in the tire. The TPMS gave me enough warning to slow down, check TPMS, and pull off the hwy at the next exit before it went 100% flat. I put my donut spare on the RDX, drove home, and switch out with my full size spare. It took about a week before my replacement tire came in (Conti DWS).

NBP04TL4ME

Rotating the donut to the rear axle is the way to go.

In terms of Fix-a-Flat, it does work but at the same time it typically does destroy your TPMS sensor. It covers the entire interior of the tire and rim (and TPMS sensor) with a sealing film. Depending on our situation (think snow or rain storm or dark unlight roadside or even a family member who doesn't know or isn't physically capable), Fix-a-Flat and a new sensor may be the safer or easier way to go vs. changing your tire.

Motomano

I forgot about the TPMS sensor inside the wheel, no Fix a Flat unless it would be no other choice, all of you guys are very helpful, now I do have clear what to do in any situation.
Thanks a lot!

BigHatch

first question, why would you do that with tire size? ...but that's besides the point.

WRONG!!! DO NOT PUT THE SMALLER SPARE ON THE REAR WITH OVERSIZED TIRES!!

Spare must match up or you are damaging internal parts, causing much uneccessary wear.

Being that you currently don't have a choice, keep it on the front axle that at least has an open differential.

...or if you like, go ahead and put that on the rear and see what happens to the SHAWD... feel like being a guinea pig??

BigHatch

for those concerned about handling and braking with a donut up front... Its a donut. Don't keep it there long, and don't be a jackass while its on there.

problem solved.

Motomano

I wanted a larger sidewall, since often I go to maintown with cobblestone paved streets, also need to take a dirt road sometimes; that was the reason for the bigger tires; actually I was looking for a bigger donut size to match the 245/60's, knowing there could be some SHAWD issues, but found nothing, unless I pick a motorcycle tire, ( some guys install a car tire on a motorcycle rear wheel, but I don't want to be the first to try this, I understand what an open diff is, and thanks to your input I know it will be better having the donut on the front, and will be very careful, if I have the choice I will fix the flat or put air with my compressor to avoid the use of the donut.
Will keep the search for a bigger donut anyway, just for peace of mind, but can't keep at wondering how all the guys with bigger wheels/ tires managed this issue?
Thanks BigHatch,

BigHatch

ken b found a bently spare tire to size up and over his brakes... maybe they might have something taller for ya.

Motomano

Thanks BigHatch,
I am not aware of Ken B, but I researched a little and the VW Touareg/ AudiQ7 compact spare tire has the same circumference minus 7mm, ( 195/80R17) , than the new tires; according to the pictures, tire comes compacted with no air, both the VW and the Audi has an air outlet to inflate the tire when needed, I guess it would fit the spare rim, and it would even give me more storage on trunk...

NBP04TL4ME

Are you implying that the SH-AWD system doesn't have an open differential on the rear axle? If so then please explain torque vectoring and how Acura accomplishes this?

Tomtwtwtw

Acura Media Newsroom - Technical - 2009 Acura RDX - Powertrain

Direct Electromagnetic Clutch Systems

Located on either side of the hypoid gear that drives the rear axle, two identical direct electromagnetic clutch systems control the amount of drive torque that reaches each rear wheel, and provide limited-slip differential function. These clutch systems can be controlled as a pair to alter the front/rear torque split, or be controlled independently, to allow up to 100-percent of the total rear axle torque to go to one side of the vehicle.

An electric coil controls the pressure in each clutch device, which slows the sun gear in a planetary gear set to modulate the torque sent to the wheel. The amount of available rear axle torque transmitted to each rear wheel can vary continuously, between zero and 100-percent, depending on the conditions. Since the clutches are electromagnetically operated, the amount of drive torque delivered to each rear wheel can be controlled quickly and precisely, reducing wheel slip in low traction conditions.

The clutch packs and friction material are specially designed to withstand the small amount of continuous slip between front and rear axles (created by the 1.7-percent speed differential), while ensuring the expected level of Acura durability. An oil-temperature sensor allows the ECU to estimate the clutch plate coefficient of friction (which changes with heat) in each clutch pack and then adjusts voltage sent to the electromagnetic coil that controls each clutch to compensate. To ensure that the amount of torque transmitted remains optimized as miles accumulate a coil provides a feedback loop that the ECU uses to adjust voltage to the electromagnetic clutches to compensate for any clutch wear.

NBP04TL4ME

Thanks Tomtwtwtw. I knew that (not in that level of detail) and was looking for BigHatch to explain how this was possible without an open differential...........
And one of the takeaways here is that this is a temporary situation. I can't imagine ( but could be wrong) that someone is going to be driving on a donut for hundreds of miles.

Motomano

Indeed, shall be a temporary solution, the minor distance required to the next gas station or tire repair shop, anyway I learned more how the SHAWD works, thanks you both, being used to more traditional 4WD, from the stiff front diff on the old Cherokee Sport from the 90's to the more modern from Toyota trucks, I knew little about this system developed from Honda, so good than I read somewhere than Audi will use it after an agreement among both makers.

NBP04TL4ME

The SH-AWD system is arguably the best modern system on the road today.

BigHatch

cool info.

to my statement, its Honda magic, like pushing the car backwards and producing kittens from the tailpipe. being that I don't pretend to know how it works id still say keep it on the front where at least you know it has an open differential. as independent as the rear is, there appears to be a bajillion sensors that monitor everything even to the extreme of accounting for temperature.

...if temp is that important, don't you imagine a significant change in diameter will have an impact? the computer thinks things have operated one way, yet they've actually done something else. id just prefer to not chance making the computer go haywire.

...but let us know how it goes when you do it.

NBP04TL4ME

I thought when you said "WRONG!!! DO NOT PUT THE SMALLER SPARE ON THE REAR WITH OVERSIZED TIRES!!" and referred to the front axle being an open one, you had personal knowledge or had a bad experience with the rear axle or something.
I'm not sure which axle would be least invasive in terms of putting a smaller diameter tire would be, but based on the front bias of the AWD and braking systems, I believe I would still put it on the rear.
Fortunately for me, having a flat isn't anything I have had to deal with in years althought the is a can of Fix-A-Flat in the trunk of the car my kids use.

Motomano

Re- reading Tomtwtwtw post again, It describes pretty well the way the rear axle works with the planetary gear and the clutches, my guess is this should be the same on the front, since sometimes when driving in twisties and the display on the SH-AWD mode, I watched both left, or right wheels get more traction than the oposite pair...