Carrera Mike

I have been wanting to replace my 17" cups with 18" 5 spoke carrera wheels. I looked up the weight differential with the wheels and tires, it would be 30 lbs of unsprung weight. Is this a big deal?

TrackJunke

Yes, 30 lb of unsprung weight is significant. It will allow your tires to remain in better contact with the road, which will result in better cornering.

Carrera Mike

Mark of Baltimore, as I was searching all the postings about weight savings on seats and wheels, I read this reply you posted "I was slower than Harvey through oak tree and rollercoaster but was able to keep up with him on the straights. 205 and 255 17" tires on cup wheels vs. his much wider but heavier 245/285(?) tires cost him power on the straights."

Should I keep the 17s? I get my kicks in the freeway out-accelerating other fast cars, would the 18's slow me down considerably? I really(2x) like the looks of the 5 spoke carrera wheels.



VS.

Viken

Thirty pounds less? Whoever told you that? Consumer Reports?

Cups:
7" x 17" - 19.07 lbs
9" x 17" - 22.26 lbs

18" Carrera:
8" x 18" - 20.50 lbs
10" x 18" - 22.70 lbs

Don't forget that the 18" tires will be heavier than the 17's. So much for 30 lbs savings.

Mark in Baltimore

Hi, Mike,

From what I've read here, the 17" cups are light wheels. If you go to 18" wheels and tires, I think it's important to stick with a light wheel to reduce the unsprung weight and, for acceleration issues, rotating mass. That's part of why I chose the Fikse FM-10's and part of the reason the Hoosier race tires without steel belts are so successful.

Some on this board are diehard 17" fans and say that, for the track, 17" wheels are the way to go due to the lighter weight and greater accelerative ability. Other people say that the 18" wheels and tires allow greater cornering control. Greg Fishman did a test between the two and, if memory serves me, found the 18" combo to be faster, perhaps partly due to the greater confidence he felt with the shorter, more secure sidewall.

I liked the look of the 18" FM-10's. Regardless of size, I knew I wanted to go wider, thus, slightly hurting acceleration. I felt that whatever I was giving up in weight due to a wider tire, I would make up in cornering ability. I guess the theory is that if you can corner faster, you can carry more exit speed down the straight. Also, 17" tires have a taller sidewall but have smaller diameter wheels, while 18" tires have shorter sidewalls and, theoretically, less weight for a given, equal width. But, then there's the issue of the larger wheel.

I'm no certainly no expert in this subject, but I hope that helps. Try doing some searches since this is asked quite a bit. I think the search function is having some trouble because I couldn't pull up the oil cooler thread Anir started several months ago.

Good luck!

Carrera Mike

Viken, I redid my computation and I'm just coming up with 8.8lbs more for the 18's wheels and tires. How the heck did I come up with 30lbs initially???

Here's the the data I have:

17"cups:
7x17" 19 lbs. 2 oz.
9x17" 22 lbs. 5 oz.

18" 5 spoke 2002 carrera wheels:
8x18" 19 lbs. 5 oz.
10x18" 23 lbs. 6 oz.

Tire weights(S-03s):
17s"
F 205/50-17(24lbs)
R 255/40-17(27lbs)

18"
F 225/40-18(25lbs)
R 265/35-18(29lbs)

Tire weights source links:
S-03:
http://www.bridgestonetire.com/dpp/s...sproductid=227

S-02:
http://www.bridgestonetire.com/dpp/s...productid=1024

graham_mitchell

Mike, those links don't work. I suspect you copied and pasted them from another thread? Long URLs printed to these pages are truncated and the missing characters replaced with "..." as you can see above. You need to copy and paste the actual shortcut.

Edward

Carrera Mike,

I'm "assuming" (only because you didn't say so explicitly) that you're concerned for track purposes. I bring this up because in terms of weight differences, I doubt that there's any discernable difference in handling on the street. Any differences in "feel" or grip are attributable to contact patch and profile, not to weight (within reason, of course).

Now for the track, I think only the finest drivers, and I DO mean the truly top in their class, really are the ones to eek out the most performance from any subtle differences in unsprung weight and rotational mass. If I recall correctly, many moons this was was hashed out and it was ViperBob, I believe, that pointed out that a good driver can go equally fast on 17 or 18s so long as the suspension is set up to accomodate the differences between the two. Just my two bits worth...

Edward

Carrera Mike

Thanks Graham. links are fixed now and I added the sizes of the factory specs for the tires on my post above.

chris walrod

you may want to keep the 17" cups around in case you decide to do some track events where rules dictate original size wheels for a certain class etc. I too am casually looking for a set of the Carrera 5 spokers for the street, and I will keep my cups for track days.

Mark in Baltimore

Yeah, Chris is right. A year ago I protested that I had no need for a trailer or a second set of wheels. Now, I have a Trailex and kept my 17" cups for rain tires.

Carrera Mike

Okay guys, I really hozed up my computations. I'm only coming up with 8.8lbs difference (with both the wheels and tires) between the 17s and the 18's. Sorry. (How the heck did I initialy come up with 30lbs?????)
So what do you guys think of 8.8lbs unsprung?

Mark & Edward, thanks for the comprehensive analogy.

Chris, Good point in keeping the cups.

Mark, I did see your trailer at VIR full of wheels & tires. I should have just helped myself while you were having fun at the track (Kidding). Whats the weight on those Fiske??

thanks..

Mark in Baltimore

So, is that 8.8 lbs total or per corner for the wheel/tire package you're looking at?

Sorry, I don't have a clue what the Fikses weigh.

Phil

Should I keep the 17s? I get my kicks in the freeway out-accelerating other fast cars, would the 18's slow me down considerably?

I'm no expert, But I don't think 8.8 lbs (carrera mike's numbers, I did not do the math) of unsprung weight will have any significant impact on " out-accelerating other fast cars"

Carrera Mike

Mark & Phil,

It's 8.8lbs more total for the 18s.

To be exact:

1.3 lbs on EACH front and

8.1 lbs on EACH rear