Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Help with wheel sizes and affect on differential and drivetrain


Please help with tire size question.
Hey guys so i have been searching the forums and the internet but can’t seem to find a clear answer to this question. I have a 2013 audi a5 with 19 inch summer tires. I am in colorado so very soon i need to get some winter tires. I did buy some 17 inch wheels but cant figure out what size tire i should be looking at. i have looked at 225/50/17 or 225/55/17. I like the idea of the bigger side wall on the 225/55/17 but this changes the overall diameter of the wheel by about 3/4 inch I am worried about this messing with the differential. is there a recommendation to stick to when upsizing or down sizing wheels. i found a lot of info on people wanting to stagger their tires but not much on just changing the overall diameter from stock. please help thank you so much.

1/2" difference going make one bit of difference what-so-ever.

What size tires do you have on them now?

While you were looking at tires did you happen to think to ask the tire people what they thought ?

Also most major tire sellers have online tire and wheel guides.

I tried They have snow tire and wheel packages in 16", 17, 18" and 19" sizes for a 2013 Audi A5.

Ed B.

Tire size won’t affect the differential if the tires are all the same size.

Tire Rack recommends 245/45 x 17 or 225/50 x 17 winter tires for the A5.

It does not appear that bigger brakes are an option on the A5. That should mean that wheels are interchangeable. The 19" tires are 225/35. If you buy 17" rims, just make sure that the total wheel plus tire height is the same as your 19" tires and rims.

Currently the tires on the car are 255/35/19. I have asked the tire shops and I get different answers every time.

You can trust tire rack’s #s, they’ve been selling winter tires+wheels for decades.

1 Like

+1 to texases’ recommendation.
And, if the OP is not comfortable with just taking info from Tire Rack’s website, a phone call will enable you to speak with one of their sales reps who are VERY knowledgeable.

If you have specific questions, the 'phone staff at TR can give you an accurate answer to virtually any tire/wheel-related question that you might throw at them.


1 Like

You can try the wheel and tire size calculator here.
If this car is AWD you need to get the same actual circumference on all 4 corners, and probably should have stuck with the stock size.

Let me clarify @PvtPublic’s post. If you have AWD, then at any given time, all four wheels must have a circumference within 1/4" of each other. Your summer and winter tires can be different as long as all the tires in each set match. See your owners manual for more specific information.

For speedometer and odometer accuracy, both sets should be pretty close on the outside circumferences. Using smaller wheels and taller tires in the winter is a good choice. Potholes are tough on low profile tires and wheels.

Hey Keith thank you for the info actually thank you all for the info. My main concern was changing the diameter of the wheel tire combo from stock. So as long as all 4 corners are the same no matter what diamter/circumference the stock set up was it shouldn’t matter to the differential or drive train. That is what i am hearing from these comments.

All kinds of other issues come into play, of course: rubbing, speedo, brake clearance, handling. That’s why you should use the sizes recommended for the A5, which you can find on tire rack, among other places.

I already test fitted the wheel it clears the brakes etc. I’m assuming with the tire that I’m looking at it’s actually going to be thinner and with the offset of the wheel it’s gonna pull the tire away from the suspension so I don’t think I’ll have an issue with rubbing other than maybe the three quarters of an inch taller tire but it looks like I have about 2 inches of space above the stock set up currently

Everything sounded OK with me right up until the word “offset”. The offset is the distance the plane of the wheel/hub mating surface to the vertical center of the wheel (centerline).

You have two wheel bearings on each wheel, an inner and an outer. Ideally, you want the vertical center of the wheel centered between these bearings so each bearing carries the same load. If the offset of the wheel doesn’t match the offset of the hub, then you are putting more weight on one bearing than the other.

As long as the centerline of the wheel falls somewhere in between the bearings, it will be OK. It is when it falls outside of one of the bearings that it becomes an issue.

Since the spacing of the bearings is usually around 40mm, that gives you a margin of +/- 20mm from the OEM wheels. As long as your winter rims are not made for RWD only, you should be in the ball park.

I find it hard to believe that any decent tire store in Colorado can’t handle this problem in less time than this thread has existed .

The 225/50 17s have an outer diameter of 25.85 inches. The 225/55 17s diameter is 26.74 inches. Your summer tires have a diameter of 26 inches. The 50s are closest in diameter to the OEM tires, and I’d go with that tire.