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.

 

[a73_4g67]

ok. Ive changed my rear tires to the same tire size in front. 195x60x15. The rear are of different brand but almost have the same treadwear, same rating, same tread pattern. It should be better and it feels better already.

 

[wret]

Can I use different sized, brand, age tires on my AWD DSM?
http://www.dsmtuners.com/forums/showthread.php?t=54620&highlight=merged

 

[hubz91talontsi]

So i have a 94 parts car with 2 similiar tires on the front and 2 on the back. My question is can i run them on an awd. The ones on the back have more tread then the ones on the front.

 

[Black95awd]

as long as they are the same size you will be fine.

 

[hdoerr]

But make sure that even if they are the same size, lets say 255/45/R18 that they are within 2MM tread wear. Otherwise they will affect your VC and or Center Diff.

 

[Black95awd]

But make sure that even if they are the same size, lets say 255/45/R18 that they are within 2MM tread wear. Otherwise they will affect your VC and or Center Diff.

WTF 2mm?? are you kidding me?! I have more than that difference with no adverse effects to my center diff or viscous. and how would you measure 2mm of the overall outside diameter?

 

[1992awdlaser]

It should be fine as long as they are close. If two are like brand new and the other two are bald I wouldn't do it.

and how would you measure 2mm of the overall outside diameter?

I think he means 2/32nd difference which I am sure you know you would check with a tread depth gauge.

 

[xveganxcowboyx]

I've done it and gotten away with it, but I don't recommend it. Different tread wear and different manufacturers/models can effect the diameter of the tires. Go with 4 matching tires if possible.

 

[hubz91talontsi]

Ok well ill try to get a pic up tomorrow and ill show you guys what i mean. But i guess i could just spend a few extra $ and put my other wheels on but they are winter wheels.

 

[SUPER fly TSI]

I searched but couldnt find any thing about this. I have 225/50/16 in the front and 215/65/16 in the back, my friend said that will mess up my diff. The way me explained it made sence so I was wonder if this is true? My car is AWD.

 

[webconnect]

Yes it will destroy it.

Your back will be spinning slower than your front. When you deal with AWD, buy the same brand of tires w/ same size, same size rims, and replace them all at once.

 

[TunaTalon]

If you have already been driving with those tires there's probably no need to worry because your car is no longer AWD.

225/50/16 = 835 Revs/mile, 25" diameter.
215/65/16 = 776 Revs/mile, 27" diameter.

About eight percent difference.

 

[romeen]

SUPERfly, hopefully your diff survived. I am curious if it still functions. If you don't mind post back with what you find out. I'm not being facetious, just curious.

 

[SUPER fly TSI]

alright well thanks for all the help and ill replace the tires tomorrow

 

[napkinthief]

Does 225/45/17 and 225/50/18 equal the same size tire?

My recent purchase vr4, came with 2 bald front tires and 2 60% rears. You think the damage has been done already?

 

[tunethis]

Does 225/45/17 and 225/50/18 equal the same size tire?

My recent purchase vr4, came with 2 bald front tires and 2 60% rears. You think the damage has been done already?

No. The 18" is almost 2" taller. A 225/40/18 is very close to that 17" size.

 

[napkinthief]

No. The 18" is almost 2" taller. A 225/40/18 is very close to that 17" size.

Im sorry thats what I meant 225/40/18 with 225/45/17. Will it work or bad things?

and also for a spare can I use any rim thats 45/17 or it has to be 225 aswell??

 

[ACM]

AWD vehicles need to have tires almost exactly the same tread depth, or the transfer case will be screwed.

That's not actually the case - in the case of the DSM AWD system, what gets screwed is the centre diff and to a degree, the VC, the transfer case is quite happy in this operational mode. A stock centre diff internals are not designed to be spinning constantly, there are no actual bearings inside, just thrust bearings - little more than coated washers; when the internals get spun for extended periods the result is the thrust bearings get ground away and the hard parts contact the casing and weld themselves in place. If the diff lasts long enough the VC will overheat and the plates can buckle or the fluid will shear itself to death.

This is why TRE and others offer the Torrington bearing upgrade, replacing the thrust bearings with 'real' bearings, so now the internals can spin up until the VC seizes !

Cusco offers a 35:65 centre diff which is engineered for this purpose, one could run any wheel/tyre combination as the diff is specifically designed to operate in this manner.

 

[endeffect0]

I know you guys get a lot of BS tire size questions so ill make this short and sweet.

I have a set of wheels that are using 235/40/18 tires. 2 of those tires wont pass inspection and i dont have the cash for a new set of 4 yet. But i do have a set of 225/40/18s sitting in the corner. can i mount these up without blowing up the t-case or center dif.

I know first reaction is no you cant.. but the tire size calculator put out some interesting numbers..
235/40/18

side wall 3.7 in
Radius 12.7 in
Diam 25.4 in
Circumference 79.8 in
revs/mile 794

side wall 3.5
radius 12.5
diam 25.1
circ 78.8
revs/mile 804

all that making up to just a 1.2% difference front to back
but add into that the complications that i would be stretching the 225 some and that the 235's are just barely passing.

what kinda tolerances are we dealing with here.

that's my conundrum.. thoughts?