tire upgrade

**dyel1500** · 09-20-2016 12:41 PM

First time poster here,

currently have 235/45R17 on my 05 a4 b6 3.0 quattro
according to my research the rims are 7.5Jx17 ET38 if im correct.
Friend of mine has a set of 245/40R17 he wants to sell me for cheap.
Would this fit on the rim or would they give me any problems with rubbing?

Thanks in advance

**Charles.waite** · 09-20-2016 12:49 PM

7.5" wheels likely had 225 width tires. an 8" wheel will have 235 width. Given that you're running 235, I would presume you have 8" width wheels and 245s should fit fine.

Post up a pi of the wheels and we can tell you for sure what the width is. Or you can just remove one and the specs should be moulded into the inside of spokes.

**eljay** · 09-20-2016 01:07 PM

I wouldn't put 245 tires on 7.5". The sidewall will concave out and compromise handling. As Charles said, check the actual wheel width to be sure.
Depending on the wheel, the specs might be on the face under the center cap including the part number.

Regarding 245/40 tire vs 235/45:

You will be ~1/4" lower to the ground as well. Click on the above pic for full list of differences.

**dyel1500** · 09-20-2016 03:27 PM

http://postimg.org/image/ajf556q4b/

forgive the dirtiness of my rims, tires are completely bald so i went out drifting the other night to get my moneys worth out of them.

**texasboy21** · 09-20-2016 03:28 PM

Ive ran 255s on the stock 5 spokes, and yes there was too much sidewall flex. I since went down to 245s and all is well.

**noldevin** · 09-21-2016 05:52 AM

Despite what an unfortunately large amount of car enthusiasts think, it is not beneficial to oversize tires on a small wheel.
Your tire's measured tread width (check tirerack) should be within about 0.5" of the wheel width (ideally the same). Much more than that and you are going to create a trapezoid shape that pulls the outer edges of the tire in towards the wheel and sacrifces most of the extra grip you're trying to achieve. Too much less and you stretch the tires, some of you might like the look of stretched tires but these are pretty heavy cars and should really have tires appropriate for the wheels.

If your OE size was 235/45R17 then the 245/40R17's should fit okay. I wouldn't go any bigger than that though, and your ride quality and gas mileage will suffer slightly due to the shorter tire. You also run a slightly higher risk of bending a wheel or bubbling a sidewall.

**Charles.waite** · 09-21-2016 08:32 AM

^this. Also make sure the tires are 93 load rating or above. Otherwise the handling and treadwear will be awful.

**texasboy21** · 09-21-2016 08:40 AM

7.5" is 190mm, and 8" is 205mm.

I agree that going too wide on a wheel is detrimental, but sticking with the same width seems a bit narrow.

**noldevin** · 09-21-2016 12:05 PM

Originally Posted by texasboy21

7.5" is 190mm, and 8" is 205mm.

I agree that going too wide on a wheel is detrimental, but sticking with the same width seems a bit narrow.

The "ideal" tire setup is a bit narrower than most would go with, usually one or two sizes lower. A very slight stretch, but nowhere near to the extent that you would see on a stance car. It helps a lot with sidewall stiffness and steering response. Though typically if you get tires where your wheel width falls near the middle of the tire's recommended wheel width range, you'll be golden.

The taller your sidewall is, the more you can get away with going wider. However, you're also going to introduce a lot of slop and lazy handling feel.
I think an ideal setup for the weight of these cars would be something like an 17x9 with 255/40r17 tires. That way you can fit wide enough tires to handle the weight and improve handling, keep a similar amount of sidewall for comfort. Of course, these aren't really sports cars so audi went smaller in the name of cost and fuel economy.