ZombiePorsche44

Yes

forklift

I did a bunch of searches on this last year and on other forums. The general consensus here on rennlist agreed w/ Greg’s findings of about a second and I don’t dispute those.

However, the consensus on some of the other forums (Corvette and Bimmer) were that it didn’t make too much difference, if at all time wise. I also emailed Dave Empringham (Rolex driver) and he said a few tenths at best. As mentioned the taller wheels will change effectively change the gearing to the high side, which is detrimental right?...even though the 18s have less roll. Weight appears to not change much as the taller 17” tire offsets most of the wheel savings (from a thread on the DE forum last month (or two). I never thought about what Zombie said about the different tracks, but that makes perfect sense.

All of the big pro teams AFAIK run 18s (if not 19s) for some reason, although one of them is that it allows them to run bigger calipers. I hear 17” slicks are more difficult to find also.

I stayed w/ 17s for one reason, cost. Besides the cost of the new wheels, 18” tires are much more expensive and I go through a lot. 275/18s are roughly $100 more per tire.

I have been thinking about posting a thread about how much time different “mods” save after my disappointment (so far) with the JRZs and monoballs. Here is what I keep reading though and they were all true, I could drop up to 16 seconds! Speed just cost money, right?

This is for someone who is advanced, not in a beginner or intermediate group, where seconds come easier. Right now I am fighting for 10ths:

18s vs. 17s = 1 to 1.5 seconds?
Double adjustable suspension = 2 to 4 seconds? (not what I found)
Hoosiers over RA-1s = 1 to 2 seconds? (this I believe)
Guard LSD over stock LSD = 1 second?
LWF = ½ second?
R&P = ½ to 1 second?
Data Acquisition: 1 to 2 seconds
Driver Coach for the weekend: 1 to 4 seconds

I might start a thread on this in the racing/de section at some point (maybe now), but thought it applied here somewhat.

mbb993

Thank you all the above responses and great info, as always! This place is great!

Although clearly debatable, from what I can gather there may be a small performance advantage to the 18" wheels. The main issue is cost, especially frequently replacing the tires for track use. I may just be looking in the wrong place but after some shopping around I have more questions.

1. Is availability more limited for brands and styles of 17" rims or are most style and brands offered in both sizes. (styles like Fiske FM/10 and BBS-RSGT)

2. Browsing around it seems there are many more 18" tires to choose from?

3. Will a "big red" brake upgrade fit in the 17" wheel or does this require 18"?

4. What kind of "weight difference" are we talking about from a 17" cup to an 18" wheel? I have no idea what my current wheels weight. (I will have to sneak out the BR scale when my wife is asleep and check!)

Thanks

mbb993

Off topic , but do you have any info comparing lap times of an LSD car to NON-LSD?

forklift

I should have been more clear, but those are all estimated based on posts I have read (and I don't agree with all of them). My guess is about a half second, but really have no idea. Also, all of those depend the length and layout of the track.

CWay27

17 inch wheels are as much available as 18 inch wheels. Tires choices are better in 18" because alot more cars are running these sizes (225 - 235 and 265 - 285 for rears). 17 inch will clear big reds so no problem for that. Depending on quality of your wheels, 18 inch could be lighter than 17 inch. Personally I would of loved to run my Kinesis K58 in 18 inch on the track but tires were too much for me. With the deal I got on my Z211 at barely 900$ for 2 sets, it was a no brainer to go with 17 inch. If you compare looks well........



or

Bill Verburg

1)Generally, not but it does depend on the brand

2) It depend more on what brand and model of tire than the size, Some brands are better in 17 some in 18

3) Big reds fit in 17s radially and usually axially but the axial room does need to be checked before wheel purchase.

4) again weight is all over the chart, best to check on specifics

Bill Verburg

Besides aspect ratio, actually as a result of lower aspect ratio, 18s will be wider for the same width w/o being taller. This helps acceleration in most speed regimes and gives more cormering power.

Martin S.

probably won't be able to tell the difference on a narrow body car, IMHO. Here is what I looked at:

If I went 18" wheels, I could put down 10mm more rubber front and rear, 235 front to 245, 275 rear to 285...that's nice, but I don't think it is that big of a deal, 10mm, please. How wide is 10mm? Picture it with your fingers.

And, the aspect ratio could go down from 40 to as low as 30% on the rear, maybe down to 35% on the front, less side wall flex....I suppose I could feel this were I driving on the edge at 10/10th.

The down side for the cafe race/DE Driver/occasional racer like me, the 18" tires weigh more and they cost more too. In addition, I would have to go out and buy 18" wheels, at least $1,800 if I went to MY 2002 996 wheels, about the same for hollow turbo style wheels...on the other hand I can but a set of Cup wheels, 7" and 9" for about $600. I have done just this and have three (3) sets of Cup wheels.

For me...I am too cheap and I am on a racing budget (My wife says I am). I really don't expect to sit on the pole anytime soon....I'll stick to the 17" wheels and use the Hankook (Hoosier) knock off tires. If the 18" are faster, I wonder if I have enough talent to appreciate the advantage.

If money were no object, I have a set of 18" BBS 3 piece wheels, nice and light, and the best tires money could buy...maybe even the Hankooks. They work for me! Why 18"? They look cool!

mbb993

OK, last question....maybe.

I could use some suggestions for 18" rims that would meet or beat the weight of factory 17" cups?

Are 18" tire weights close to a 17" tire of the same brand?

Sorry, that was two questions...

TargaTango

I have tried to attach a great chart very helpfully compiled and previously posted by AVoyvoda in 8 March 2006.

And here is a contrary view about the benefits of decreasing profiles which I have previously posted. Barry Lake, writing for the Australian magazine Motor some years back (I am not exactly sure but I am guessing circa December 1998) discussed the trend to increasing wheel diameters and lower tire profiles with Yoshihiko Ichikawa the then technical manager for Bridgestone Motorsport UK and the design team leader of Bridgestone tires for the Honda NS-X, and Kazuo Shimizu a Japanese rally and touring car champion with 2000 plus laps around the Nurburgring testing tyres. Here are some of their opinions:

* Ichikawa and Shimizu believed that the trend to lower tire profiles in expensive performance cars was driven by fashion.

* Ichikawa was of the view that if F1 regulations allowed freedom of size that the desire would be for tires that were wide and tall to gain maximum footprint and therefore grip, but that a compromise would have to be found as this would create problems with aerodynamic drag. The only reason he saw for having a larger diameter wheel and hence lower tire profiles was to fit larger brakes inside the wheel.

* Ichikawa believed that the ideal tire profile for road cars was 50 to 60 series, and that once you get to 40, 35 and 30 series you have to “throw away all the sidewall stiffness to get reasonable ride”. Shimizu agreed saying that the then latest ultra-low profile tires had so little sidewall stiffness that cars moved all over the place at high cornering speed.

Now maybe tire technology has advanced to such an extent since the article was written 7 or so years ago that the above no longer holds true; or maybe not.

All the best,

Greg Fishman

Factory 996 02 wheels would work for a narrow body car. Or anyone of the 3 piece forged wheels from companies like Forgeline, BBS, Fikse, HRE, etc.

Jack of Hearts

I find this all very interesting. I have exxperienced that "double set" that Greg describes on my street car, which has the M030, 17s and Michelins. And I don't like it either.

Greg Fishman

I can help you solve that. How much money you got?

Jack of Hearts

hah. not nearly enough.