I figured I would post this question in here because the appearance section would have the largest number of posts from people with 18" or larger rims. I have an A4 with 2.73's and would like to upgrade to 3.73's. I am also going to 18" rims. I have heard that the extra diameter of the wheel has an effect on the final drive ratio but I don't know how much. Have any of you guys noticed a degradation of performance with 3.73's and 18" wheels together. If so, would it be better to use 4.10 on an A4 with 18's to get similar results to a 3.73 with 16" wheels. I'm not looking to drag race the car, it's a convertible it's supposed to look good first and formost

 

It would depend on the actual outside diameter of the new tire/wheel combination. I went from 16x8 rims with 245/50-16s to 17x9 w/275/40-17s front and 17x11 w/315/35-17s on the rear. The tire diameter is very close to the stock tire so I noticed no difference.

A different tire diameter will give you problems with your speedometer accuracy, too. Compare the specs of your current tires to the ones of what you plan to get to see how much different they will be. A math whiz should be able to help you figure the effect on gear ratio. I used to know but too much overtime, not enough brain cells.

 

If you get an 18" wheel that will use a 275/35/18 tire your speedometer will still be exactly right. That's because it's the same diameter as your stock tires are.

An 18x9.5 to 18x10.5 will work great with a 275/35/18 tire, with the 18x9.5 being the preferred wheel size for that size tire.

-Shawn

 

Thanks for the info! I guess it wouldn't have that much of an effect if I stay in the correct tire size. I do want to put some meat in the back, partly because of traction and partly because I think it really sets off the look of the car. What's the best size to put on a 18x10.5 wheel in the back with minimal modifications to the speedo and to the body?

 

The perfect size for an 18x10.5 would be a 315/30/18. If you don't want that big of a tire, a 295/35/18 works great for an 18x10.5" rim as well.

Michelin makes a Michelin Pilot Sport in the 315/30/18 size, and Pirelli makes the Pirelli Pzero Rosso in that same size. There are quite a few people that make 295/35/18's

-Shawn

 

You're an immediate answer machine aren't you, hehe? Thanks for the help.

 

You are welcome.... Shawnbot at your service

-Shawn

 

larger diameter wheels will decrease the performacne of a 1/4 mile race, but it will increase your slolom abilities. the weight of the larger wheels will affect braking and 60' times. just something to think about. if you plan on getting larger rotors to fit the wheels, that will solve your braking problem, and some light weight wheels will solve the take-off and 60' times.

my neighbor has a ta with 18's on it, and they weigh a ton. my 17's are billett and only weigh like 25 pounds with tires.