Tire Size and AWD [Merged 5-7] diameter radius rolling different sizes size

[King Salami]

Gurus - I've got an 92 TSi AWD that I recently had to replace a tire on. All other tires are about 20% worn. Will the difference in tire diameters (due to wear; tire brand & size for the new tire is the same) cause any harm to my transfer case/AWD system?
I know wheel/tire size differences are very important on an AWD, but would 20% wear on 3 tires vs. 1 new make a difference? Since I rotated my tires, I'm experiencing an odd low-pitched "hum" or "grumble", especially when downshifting or raising off the throttle.
I've asked the guys at Discount Tire and my local Audi dealer, but they didn't seem too concerned.

 

[Zenja]

I'm running the same setup as you and it seems to work fine. I have different brands though. I guess it's a good idea to make sure that they're identical circumference/diameter just in case. If they're a little different you can probably compensate with different tire pressures.

 

[CowPimp]

Originally posted by Rob98GST

Everything was just fine for the time I ran that setup. I even rotated the tires (225/50/16 front, 205/55/16 rear). I would be more concearned with running the spare tire if I were to ever have a flat with the AWD....

I had to use the donut spare after a car accident on the way to visit someon. I had to drive 250 miles back home. My car feels just as good as it did when I bought it now that the necessary body work was taken care of and I got new tires.

 

[AWDPetmitsu]

I would think that the engineers designed some amount of tolerance in the center diff to account for different tread depths? All four tires will wear differently. If you say that we are supposed to rotate them, I never heard Mitsu stressing it.

 

[ARTSUPRA]

Derived from http://www.miata.net/garage/tirecalc.html

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
205/55-16 4.4in 12.4in 24.9in 78.2in 811 0.0%
225/50-16 4.4in 12.4in 24.9in 78.1in 811 -0.1%

 

[Defiant]

Originally posted by Rob98GST
I ran this exact same setup on my 91 AWD for a little over 2 years over 20k miles (sold the car two months ago).

Your customer is over in the Drivetrain forum asking about parts and failures. Something about crappy DSMs.

:laugh:

 

[SDSGSX]

hey guys heres the deal....im runnin stock gsx 17 rim with stock good year tires. i was planning on buying rims and tires this summer to replace them because i want wider tires and am tired of bending rims. Anywayz i got a nail in my tire and they found another so they said it couldn't be fixed. under road hazard they are helpin me pay for one so i went ahead and bought the other so i would have two new tires. My question is am i hurting my car at all by runnin 2 new tires in the front or back and then the two old ones? i read somewhere that the VC may not like that.. thanks guys

 

[PogiTSI]

errr I dunno dude, I know Left and Right Size tires will break shit. But I dont know how much a diffrence is alowed in the front and rear. now I know theres give in the VC. like 2-4 Mph or something. I dont think same size new fronts, and Same size old tires in the rear will make a diffrence. I mean The tred on tires isnt that tall, The main size of the tires is the Sidewall height.

Wait for someone to chime in on this though.

 

[SDSGSX]

thanks for the reply i was hoping that was the case....i really dont wanna buy 4 new tires if i plan on upgrading in the summer but id rather do that than hurt the car ..thanks alot for your answer tho you have made me feel a lil better about doin it

 

[91awd]

If they are within 2/32 of tread of the rears than you are ok but if it's more than 2/32's of tread it will ruin your transfercase.

 

[SDSGSX]

2/32??? whoa...i just picked up my car and it seems to be that the rear (new tires) have about 50% more tread than the old (front now) tires. so your saying ill mess things up..my question is will i be okay to drive it back to school (70 miles) away tomorrow than let it sit till ig et new tires or will i blow something up on the way?

 

[mustg5]

got that right, AWD vehicles need to have tires almost exactly the same tread depth, or the transfer case will be screwed.......i work in a tire shop so take my word for it.......we will not put 2 new tires on an AWD vehicle becuase of it, the customer either has a choice for us not to do any work, or put 4 new on........liability reasons, if u do any new, DO 4 NEW

 

[mustg5]

dont drive at all........unless its to the tire shop

 

[PokinatchaPunk]

I had the same problem just about two weeks ago...I came back from Iraq to find that my front left tire had a "slow" leak....well I went to breakfest and on my way driving back it felt real sluggish. Pulled into the next gas station and the tire was coming of the rim. Kinda sucked....long story short. ABout 95% of tire shops will tell you if you have a AWD car that they are required to change all four. Makes sense....

 

[Rob98GST]

I ran 205/55/16 up front and 225/50/16 in the rear of my 91 talon awd for over two years/around 30k.

I sold the car two months ago. I never had any problems.

 

[ECLIPSE4x4]

I will agree on that, you should not have a difference between 1/8th of the tread. Although I have changed a lot of tires 2 fronts, 2 backs. there was not that much difference in the tread. I have done that on my GSX for about 3 years.

Just because I have done it does not make it right. I have heard the same story that you need to change all 4. This is coming from techs that are good friends.

So take it for what you will, but I don't want to be the casue of someone blowing out their transfercase.

Has anyone seen anything in either an owners manual or the shop manuals?

 

[Eagle 5]

Would there be any benefit to having wider tires in the rear than up front on an AWD? This assumes that the overall diameter of the front and rear tires is the exact same, only the rears are wider than the front? I know some of the exotic AWD cars have wider tires out back then up front, jsut wondering if it helps with anything like handling or something.

Now the overall diameter would be the same so that all the wheels spin at the same rate... other than when turning and such.

 

[jtmcinder]

I doubt it. In fact, it would probably make the understeer worse.

Now, if you were to suggest wider tires up front....

-J "I think Lisa Kubos Honda just plain looks silly" toby

 

[14.5 drift]

Mc-G is right. The exotics are ussually mid engine cars and more weight is placed on the rear, hence the wider rear tires.

 

[Eagle 5]

ok, i understand the mid engine and more weight to the back, just was not sure if it would help any, maybe on launching the car since the weight shifts to the rear, youd have more tire...not that its needed with AWD unless making a lot of power, or if it would help turning in anyway.

 

[jtmcinder]

Originally posted by 14.5 drift
Mc-G is right. The exotics are ussually mid engine cars and more weight is placed on the rear, hence the wider rear tires.

Please name an AWD car that is not either front- or rear-engine. I'm just trying to figure out how you get power to both the front and rear if the engine is in the middle. I know how they do it on a pick-up truck (although this is front-engine, the system would still work if it were mid-engine, because of the height); but I have no idea how they would do it on a car. Thanks.

- Jtoby

 

[Eagle 5]

Bugatti Veyron is the first one that comes to mind. Also the AWD lamborghinis are mid engine. one shaft goes forward and one goes to the back. which could mean they may have diff ratios so that may make it easier to have wider in the rear

 

[14.5 drift]

Originally posted by jtmcinder
Please name an AWD car that is not either front- or rear-engine. I'm just trying to figure out how you get power to both the front and rear if the engine is in the middle. I know how they do it on a pick-up truck (although this is front-engine, the system would still work if it were mid-engine, because of the height); but I have no idea how they would do it on a car. Thanks.

- Jtoby

porche makes an all wheel drive mid engine vehicle. I'm not sure what your asking but I dont think it would be a 50/50 split. Would probly favor the rear wheels in order to prevent over steer unlike my car, .

 

[monotalonawd]

I always loved the way a rwd v8 look when fitted with larger tires in the back. I also thought about doing it on my Talon but mostly for looks.

In the March issue of SCC, there is an AWD 3000GT owned by GT Pro rolling on 245/35R-19 in the front and 275/30R-19 in the back.

Seeing that they would do that on their car, maybe I would do it also

 

[jtmcinder]

Originally posted by 14.5 drift
porche makes an all wheel drive mid engine vehicle.

Really? I was under the impression that the AWD Porsches were all rear-engine. Unless you mean that silly SUV; who cares about that! I know that the AWD 911 is rear-engine, not mid-.

The two exotics cited by Eagle 5 are real, AWD mid-engines. I had never heard of either one and say thanks for the pointer. Normally I avoid thinking about things that I'll never be able to drive, but in this case it was interesting.

- Jtoby

 

[ACM]

Missed the Group B rally cars as well - most of those were mid-engined AWD. One of the Ford variants had front engine with rear transmission (a la 944) and shafts running all over the place...

Charles