Trying to figure out what I am going to use tire wise on my new project, and at the same time trying to understand wheel dynamics. Obviously a larger rim would be "harder" to turn and therefore would be theoretically slower, and a shorter rim would turn quicker. Now if the 17" rim was lighter than the 16" it would counteract that but to what degree. The more important question comes with tire choice. It looks like I will be limited to RA-1's. with a max section width of 8.5 on a 8" rim.

in 16" I would be able to use 205/55R16 with an OD of 24.7 and Section width of 8.3
in 17" I would run 205/50R17 OD 25.2 SEC 8.3 or
17" 205/40R17 **reinforced OD 23.4 SEC 8.5

the 205/40/17 has the shortest sidewall but what would be the advantages to running each outside of tire costs?

 

24.7 and above is pointless to run unless the tire is really wide imo. Your gearing will suffer and the weight as well.

Are you doing autocrosses or HPDE's or both?
Is there any reason you don't want to run a 15" wheel?

The advantage to the 205 40 17 is less sidewall flex (depending on the tire of choice) and crisper steering. But a smaller sidewall is not always the fastest tire depending o the driver.
I was using 215 50 13's in the 710's and was doing ok. I sold those and now run the 205 50 15 Yoko A032R's and do much better with them tire for tire. Even though they are sloppier.

 

I am running in the Canadian Touring Car Championship. I am running AP Brakes which allows me only to run a 16" rim at the smallest. I already have a set of 16" rims and looking for a second set, so maby move up to 17" depending on tire selection. The rules allow us only to run Toyo RA1's with a tire sectionwidth of no more than 8.5" in my class.

 

You're comparing tires with the same treadwidth but different outer diameters. The smaller the outer diameter, the faster your car will accelerate in each gear (like getting shorter gears), which will usually help you on the track, although it may depend on the particular track and your gearing setup. You also may avoid rubbing problems by not getting tires larger in diameter than stock. However, I don't like to get tires that are smaller in diameter than stock, either, even for track use (just my personal preference).

 

Yes but my main concern is sidewall size and performance. Stepping up to too large of a side wall.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ^AnDre^ &raquo;</TD></TR><TR><TD CLASS="quote">Yes but my main concern is sidewall size and performance. Stepping up to too large of a side wall. </TD></TR></TABLE>

Then get the 205/40-17.

What kind of car is this for?

 

1991 Civic Si

 

Then stick with 205/40-17. The other sizes are too big in diameter, and that doesn't help you at all. (Even 205/40-17 is bigger in diameter than your stock tire size, but that's the smallest size commonly available for 17" wheels.)