Your thoughts on 17s for track use
 

I considering biting the bullet and getting some light weight, forged 17 (or 18) inch track wheels for my Carrera. I've got 993 TT brakes on it which is the reason for 17 or 18s. Otherwiser I'd just keep the Fuchs. I currently have the Mille Miglia Cup IIs which everyone knows weigh a ton.

I was thinking of Fikses, Forgelines, HREs, Kinesis, something along those lines.

Any opinions will be most appreciated.

Thanks,

17's are the way to go, but I have no real data.... just that the fastest cars in class are running them. I've never run anything else. Probably due to the fact that you can squeeze 245s and 275s under the carrera fenders on your new 17s! ... and less of a sidewall. You could run 18s, but they're a good bit more expensive for the wheels, as well as the tires. I have fikses, love them, but some guys say they are prone to cracking though. Search rennlist on the topic.

Good Luck!

I am curently running Fiske 17's with 225 45 front and 255 40 rear, when I had 235 in fornt I had a bit of rub. Are you trelling me I can run 275 in the rear without rubbing the insides? I do have some room on the outside of the wheel to the fender, but inside is marginal. I am getting ready to get tires for next season and can't afford to buy another mistake. What do you reccommend? Thanks for the help.
I'm in an 88 911 BTW...

Thanks Mitch! Now to convince the CFO that some nice, light 17s are much needed.

Hey Mark,

If you're looking for faster lap times (aren't we all) Caren/CFO approves it, 18s are supposed to be worth a few seconds per lap.

Here's the source. I am also looking for wheels for my 951. I contacted Wheel Source in Dayton, Ohio since they are retailers of Forgelines (and I purchased tires from them when living in Ohio). I know they run a couple 951s in PCA racing. I was told that on their cars (well set up E-class cars) that moving from 17" to 18" was worth 2-3 seconds per lap at Mid-Ohio.

Since it will be many years until I'm competitive enough for 2-3 seconds to make a difference and 18" rims are significantly more expensive, I've decided to go with the cheaper 17" wheels (Fikse's).

If you're looking for Fikse's, call Paul at Radial Tire in Silver Spring. He's got the best price I found.

Jerome:
I didn't know Radial Tire sold Fikse's. I think 17s will work, since you confirmed what I also have heard (18s are a lot more $$$$).

I have started looking for some stronger, lighter wheels since I was told how much the extra unsprung weight of my current wheels affects my car.

Mark, I have been told that 18 actually take away your torque and 17's are optimum. I thnk it may have been Bill Verburg that told me that. I can't be certain it was him though.

sleder,
As long as the rolling radius of the tire is the same between 17" & 18", you shouldn't notice a difference.

For example, from Toyo's website for their RA1s:
275/40-17 tire has diameter of 25.67 inches
a 275/35-18 tire has a diameter of 25.55 inches.

I doubt you'd notice the difference in radius between these 2. Tire mfgrs have made the sidewalls shorter for larger wheel sizes to keep the rolling radius about the same.

Mark and Jerome,
You guys are gonna need a lot more than lightweight wheels to keep in front of me next year! I've been very busy this fall/winter

:cheers:


What you've heard about the weight making a difference is true. My car feels much quicker with FM10's vs. stock/cast wheels. My BBS are lighter still, and I hope to see the same improvement when I finally try them on track.

Hey Mike,

Hopefully you've been busy this fall learning how to drive. ;)

But remember, DEs are non-competitive. We'll have to save it for a club race...
-------------------------------------
I use aftermarket Borbet C2s for the track which are HEAVY!!! Acceleration is much reduced (feels like my turbo isn't working) compared to using my factory rims with slightly undersized tires. Feels like I'm losing 50 hp whenever I switch wheels.

Jerome:
I think the Borbets weigh about the same as my Mille Migilia Cup IIs. (a ton).

Mike, Mike, Mike.... E-F (Group 3 at the SP race) at alot of races, has the most cars and is extremely competitive. Your first practice session will be a lot to digest, but wait until your first practice start. You have no idea. ;)

:cheers:

a few seconds a lap???? common folks, dont get sucked into this non-science! Let me explain:

the difference is immeasureable, especially by DE and even good club guys.(this should discredit your sourse completely on this subject matter)
On a dyno, expect even a 10lbs per wheel difference, to be less than 1hp!!!!!!! (thats with either a 17 or 18" rim as there is really no difference) This also for a car on the dyno in 4th gear. Obviously, if you understand the physics, this dyno example would be 4-5hp in 3rd gear and 10-15hp in 2nd and up to 30hp in first. The point here is that , on a road course, the main differences will be in the sidewall thickness and how the tire reacts, not in the weigth distribution of the wheel effecting inertia, as wheels generally are close to lighter than tire weight anyway, right? (ie hoosiers weight 25lbs and kinessis rims weigh 19lbs. as far as weight goes, the unsprung weight is what we are talking about here. If it changes, it really effects suspension reaction on a tight turney course. on longer, slower transition courses, it probably is unnoticable, even by the best of pros. (ie Road America, Laguna seca vs Lime Rock or Sears Point)

so, since the overall diameter, rarely changes when going from 17 to 18" diameter rims, the overall weight generally doesnt change, so I would like to better understand how going from 17-18 " rims shaves 2-3 seconds. (actually, that is a rhetorical question !!) I can say that the 18" is more critical for tire pressures. (high pressures make 18" tires more "skatey" than the 17s due to the shorter sidewall)
Ive actually posted the fastest times on the hoosier 17s, vs my toyo 18s that I run in SpeedGT World Challenge. However, that is is mostly due to the tire compound, not diameters! heck we barely see 4 seconds going from a street tire to a DOT racing slick. so, the 2-3 seconds you saw on different rims are due to many other factors!

MK

a more direct point here, is that we used a Toyo RA1 this SpeedGT season . my time at Laguna (and I race there over 7 times a year), was almost the same time as with my Hoosier. 1:40.8 vs 1:40.2. Now, the compound was more sticky, so I would imagine that is the reason for the difference in times . Keep in mind that the Hoosiers are 5lbs lighter per tire!! so, the 20lbs of rolling weight is like 40lbs if it were stationary in the car as far as only accleration because the weight change is on the outer diameter (compared to an overall diff in weight , like a rim change, where that 20lbs would act more like 30lbs instead)

Now, since I only saw .6 seconds for a 5lb heavier tire, and a tire with noticably more grip, I would say that the fact that I had lighter wheel was almost unoticable. If you did notice this, you were imagining it, especially if you are not a track at least as much as I visit mine in the area.

this is just the reality of the lighter wheel hype.. buy the lighter wheels because it saves you overall weight!!! (and that all adds up)

Mk

Mark,

Very good points. I am also an advocate of the 17s vs. the 18s. The only point that can be made for 18s that I have seen is that you have a 1/2" less tire flexing on turns (assuming the same diameter tires, and then only the lower half of the tire is an issue on a turn). Hoosier has been building 17s for quite a while with very strong sidewalls. They are also more forgiving to tire pressures.

So people point out that 18s have faster turn ins. Can this be good for seconds a lap? Are they some other cheaper solutions to achieve a faster turn in (removing other rubber elements in the suspension)? Do these make that kind of time difference?

My personal feeling is that I am not a Pro driver, and there are always thing I can improve on every lap. The tiny amount of faster turn in contributed to the tire sidewall with todays technologies I feel has no impact on my lap times at all. Guess I will find out next year as I am going to larger brakes which UNFORTUNATELY requires me to now drive 18s...

the side wall differences have very little effect on turn in speed (time, etc) all the many compliance issues are what determines a turn in rate. sidewall will probably not even make the top 10 factors. shocks, damping , spring weight, driving style, balance of the car, over all weight , tire compound, air pressure, etc, all will FAR out weigh any diff between a 17 and 18 " tire.
as I said, ive been doing this a while,and i can feel very little diff between my 17s and 18s. the main difference I feel is the type of compound the tire is, and how old it is. a new 18 and new 17" tire will be almost identical in performance.

shaving 2-3 seconds let a long 1/10s of seconds is unlikely, if not impossible. However, I would love to think that going to a 18 from a 17 or vise a versa could buy me a 1:37.xx at laguna seca, from my 1:40.2 now. see how silly that sounds!! aint going to happen!! (not for tire size reasons!)

Mk