Blew a tire on my 18s. Spare tire is 17in

[jok3sta]

ok I have s4 wheels with tires that are 225/40/18. I blew one of my tires out yesterday and my spare tire is the stock 235/45/17.. I understand that running different rims sizes can damage the quattro drivetrain if off by too much.. i did a tire size comparison and this is what it shows


Stock Tire - 225/40R18 >Search Tires Tire 1 - 235/45R17 >Search Tires
Section Width: 8.85 in 225 mm
Section Width: 9.25 in 235 mm
Rim Diameter: 18 in 457.2 mm
Rim Diameter: 17 in 431.8 mm
Rim Width Range: 7.5 - 9 in
Rim Width Range: 7.5 - 9 in
Overall Diameter: 25.08 in 637.03 mm
Overall Diameter: 25.32 in 643.12 mm
Sidewall Height: 3.54 in 89.916 mm
Sidewall Height: 4.16 in 105.66 mm
Radius: 12.54 in 318.51 mm
Radius: 12.66 in 321.56 mm
Circumference: 78.79 in 2001.2 mm
Circumference: 79.54 in 2020.3 mm
Revs per Mile: 829.3
Revs per Mile: 821.4
Actual Speed: 60 mph 100 km/h
Speedometer1: 59.4 mph 99.0 km/h
Speedometer Difference: - Speedometer Difference: 0.961% too slow
Diameter Difference: - Diameter Difference: 0.95%

now my question is.. since this shows that they arent too far apart can i run this for a little while until i switch to my winter tires.. I really dont want to throw my winter tires on yet because i will wear them out prematurely.. and i dont want to buy a new tire because i plan on buying 4 new tires anyway in winter time but i dont have the money to get them right now.. any advice??

[RecklessTuning]

so your saying you rather mess up your drive train then either buy 1 new tire or throw your winter tires on?

[AudiDriver1986]

just throw the winter set on... i mean you can throw the 17" on if you just need to drive the car to a place to get a new tire (that shouldnt cause mch if any dammage) but i wouldnt drive on a 17" when the others are 18" especially for long distances, i mean spend 200 bucks on a new tire, or have to replace something that costs a whole lot of money, its up to you... but i would just throw on winter set or get a new tire

[jok3sta]

so your saying you rather mess up your drive train then either buy 1 new tire or throw your winter tires on?

Noo.. what im saying is id rather get an answer to the question that i asked by someone who is knowledgeable to the topic and not a comment that not only doesnt answer my question but wastes everyones time. But thanks for showing interest :)

[jok3sta]

just throw the winter set on... i mean you can throw the 17" on if you just need to drive the car to a place to get a new tire (that shouldnt cause mch if any dammage) but i wouldnt drive on a 17" when the others are 18" especially for long distances, i mean spend 200 bucks on a new tire, or have to replace something that costs a whole lot of money, its up to you... but i would just throw on winter set or get a new tire

ok thanks.. I Kinda figured thats what i should do.. I already have teh car on jacks and everything.. but i just feel bad throwing these expensive winter tires on just to wear them out by winter.. The reason I asked is because ive read that it is ok to run different sizes if the diameter difference is within 3% of each other, these are under 1%

[widgget]

omg! the two ringers are going at it!

[Johann@Carbnlab]

Why not buy a new tire now? You're going to need it anyway after winter.

[RecklessTuning]

Ok i'll break it down for you. Wether it is the same size or not I wouldn't do it. There is no way that it is the same rotational mass and will wind up messing your tranny up on a AWD car. This is the exact reason that people tear there tranny's up with big break kits b/c no one thinks about rotational mass. It could rotate at the same speed and everything but the shear weight will cause issues. Now you might see the problems now or later but i'd rather prevent them.

I'm not trying to be a dick yet... but your asking a question that doesn't make since. You rather save a set of tires ($400) over your trans ($2000).... what?

[A4SoftWalker]

Meeehhh 9 revs per mile is nuthin - put it on and keep rollin bro believe me I run a staggered setup and the difference is more than 9 tiny revs/mile.

There is a percentage difference that the system was designed to accommodate for to allow different tire pressures and the like I think it is 3% rolling diameter difference? That is MUCH more than 9revs.

[jok3sta]

Ok i'll break it down for you. Wether it is the same size or not I wouldn't do it. There is no way that it is the same rotational mass and will wind up messing your tranny up on a AWD car. This is the exact reason that people tear there tranny's up with big break kits b/c no one thinks about rotational mass. It could rotate at the same speed and everything but the shear weight will cause issues. Now you might see the problems now or later but i'd rather prevent them.

I'm not trying to be a dick yet... but your asking a question that doesn't make since. You rather save a set of tires ($400) over your trans ($2000).... what?

Well you came across as a dick in you first post, but I respect your second post.. And it was just a question.. I was in the process of changing the wheels over and i just thought i would ask to see if it was possible or not since they were close in diameter.. But now that ive gotten a few response saying its a bad idea Now i know.. Which is why you ask quesetions.. to learn.. Thanks to everyone who responded.. and to the guy saying 2 ringers goin at it.. Ive been a member longer than you :P and i have over 17 thousand post on vwvortex so im no rookie.. just someone asking a honest question

[Rommulus]

You will be fine if you want to run the spare for a while.

[Capt. Obvious]

This is the exact reason that people tear there tranny's up with big break kits b/c no one thinks about rotational mass.

Seriously? Big brake kits cause transmissions to wear out? Are you fucking retarded or something? Anything you have said or will ever say on this website should now be completely disregarded moving forward. Let someone who knows what they're talking about handle this question.

For the OP: YES, you CAN run the mismatched wheel combo if you need to. It's not ideal, but you're not going to hurt anything. The important numbers in all that stuff you posted above are these ones:

Overall Diameter: 25.08 in 637.03 mm
Overall Diameter: 25.32 in 643.12 mm


That is approximately a 1% difference in rotating diameter. Cars that are lowered and/or have a crappy alignment and eat front tires have a larger rotational difference than that. In fact, when you replace the bad tire, the fresh tire will probably have a larger rotation difference than that when compared to the other tires you have on the car. Also, any weight differences between the different wheels is not going to be an issue either, I bet your stock wheels are within 3-5 pounds of your aftermarket wheels, with a pretty similar weight distribution. Michael Schumaker himself probably couldn't tell you what corner had the mismatched wheel in a street driving situation.

The AWD system in our cars is not the fragile glassware everyone makes it out to be. It can handle A LOT of abuse.

[RecklessTuning]

I wouldn't have said it if I haven't seen it several times. Big breaks + big wheels = tranny problems down the road.

but what do I know i'm just some jerk on a forum...

[Capt. Obvious]

Retarded big wheels on donks/Escalades/ghetto rides... I'll give you that one. That's a lot of extra unsprung weight on a large rotation radius exerting itself on the drivetrain. But, a BBK on a smaller car like an A4 running a set of 18s/19s/20s (and usually the people who plunk down the cash for a proper big brake setup are also running forged/lightweight wheels), no way.

Wow, I sounded like huge dickwad in my first post, sorry about that... [:\]

[jok3sta]

just for the record, since I hear you talking about weight, the 18in wheels are the stock 18 s4 avus wheels and the 17s are the stock 5 star sport package wheels

[Capt. Obvious]

Those are almost identical in weight with tires on them IIRC. Tire weights vary, but it's still gonna be pretty darn close.