Hi everyone---

I have an 04 A4 3.0 Ultra Sport. This car comes with the RS4 18' wheels...they're 235/40ZR18. I'm looking to put on winter tires and the recommended size that I've researched is 205/55R16, if I get 16's. By my calculations, the tire circumference for my tire is 19.6'. The circumference for the winter tire is 18.2'. This is a difference of 1.4 inches. Now...the ultra-sport has the RS4 suspension, including a lowering of 1.5 inches. So the lower circumference of the winter tire will allow more room for putting snow chains on, but would the difference cause too many extra miles to the odometer, and how much for every 1k miles?

Please let me know as soon as possible because there's a good deal for some tires/16' wheels that I'm wanting to get but the deal ends very soon. I basically just need advice on weighing out the options. Thanks

Mark

 

I did not do the ciphering, but the circumference has to be more than the 19 some inches you quote... you sure this isn't diameter?

I have often purchased tires from TireRack and the spec sheets they have for each tire will give you an accurate circumference. From this you can determine impact to speedo / odo accuracy, and investigate any clearance issues.

 

you're right..I had already checked and the circumference of the 18' wheel on the outside is 19.6, 18 inside..the overall circumference is about 23'...what is the circumference of the 205/55R16 tire? I can find that out on tirerack?

 

I'm sorry....diameter...on everything..duh its not the circumference. But yeah its more than 19'. It's 23 in diameter

 

You're confusing circumference with diameter. A 235/40 18 tire has a circumference of 79.8" and will turn 794 revolutions per mile. Your substitute 205/55 16 has a circumference of 78.2" and will turn 811 revolutions per mile. Your speedometer reading with the non-standard tire would be 2.1% too fast. If it reads 60mph you would be traveling at 58.8mph.

 

hey thanks a lot for your help..shows me there's very very little difference between the two tires..only problem is I don't think I can even get cable chains on either tires cause there's very little clearance.

 

Why do you need cables or chains? Snow tires and AWD is good enough for pretty much anything.... you must be into some craaaaaaaazy stuff in the winter.

 

If you really need that exta safety, get some socks for your car:



It has been tested and approved by most european car manufacturers, including Audi.

A colleague has them. He says they're excellent, and far easier to use than chains.

They may look like some "wonderproduct" out of TV-shop, but several serious tests has been made (by car manufacturers, car magazines and universities and other researchers). They work very well on ice and snow, providing far better traction than snow tyres. Downside is, they shouldn't be used on paved surface, only snow/ice.

See Autosock website for more information. There's also a very technical explanation on how they work.