i'm currently running 195/60 azenis on the 14" alloys that the previous owner of my integra had on the car when i purchased it. i'm now starting to look at 15x7 wheels to mount 205/50 azenis (there don't seem to be any 15x7.5 in 4x100 and a proper offset, but if you can prove me wrong on that...)

it seems that for around $125 i have a few options in the 13-13.5 pound range (leaning towards team dynamics racing pro race 1)

for $200 there is the 11 lb oz superleggera

and for $300 i can get the ssr competition that weighs in at a scant 9.2 lbs

(since the volks, racing harts, buddy clubs, advans, etc. all cost more than the SSRs and don't weigh much, if any, less, i'm not really considering them)

so while i know lighter is better, has anyone switched wheels (not diameter, just weight) and noticed a significant time difference on an autocross course? how much time savings can i attribute to each pound of wheel weight i reduce? is this a matter of hundredths? tenths? a whole second?

thanks for any insights on this issue,
-phil

 

Unfortunately, you'll probably only fight yourself to a draw going with bigger wheels. The wheels will weight less, but their mass will be located farther from the axis of rotation, negating any advantage.

If you want to get quicker you need to go with smaller, wider wheels, not bigger.

Look at any car at Nationals - if their class rules allow it they run 13x8's....for a reason!

This violates the first rule of the "Ricer's Code" which says bigger is always better, but it's the first rule of the "Racer's Code" - faster is always better....

 

I think Rockfish66 is correct only for Street Prepared. He doesn't seem to understand that nothing is made to fit 13x8" rims for STS. 15" - 16" rims are ideal for STS, for you can get the best gearing with the widest street tire available. As far as how much a pound is worth on an autocross course, probably only .1 sec on a 60 second course. It's all a function of your budget and autocross level. If you're running the National schedule and are off the leaders by .4 second or so, the SSR's might be worth it. If you're only running locally, I'd consider the 13# $125 wheels. Either way, you should try to maximize the width of the rim to meet the high end of the rules. Unless you plan on running 205's for the rest of the car's career, I'd put 7.5" rims on, and run 215's-225's if possible.

 

if i was running in DSP, i'd be buying 225 hoosiers on 13x8.5 panasports, but i'm in sts, and there really aren't any good street tires (no azenis, no bfg t/a kd) that come in 13" sizes. the 205/50 15 is THE tire for sts nationally (or the same size bfg for some). since i know that's what tire i need, i'm trying to determine how much time a few pounds of wheel weight is worth.

 

Yeah, of course you're right. I could have been more clear about that statement being class dependent...

If you are limited to 15's for other reasons (tire choice is good one!) then lighter is of course better.

GRM has good article on weight in the new issue - the most interesting thing being that reducing weight folows the law of INCREASING returns, so every pound you take off helps more than the pound before.

Back to the original question, I've heard varying estimates that each pound of unsprung weight is equivalent to 2 to 10 lbs of sprung weight, depending who you ask. So taking 20 lbs out of your wheel/tire package could be the same as taking 200lbs out of your car! That sounds like an improvement to me....

 

http://www.unf.edu/~jgarner/rkemomi.html

http://physics.bu.edu/py105/notes/Torque.html

http://hyperion.advanced.org/16600/a...linertia.shtml

 

from the second link:

The moment of inertia of an object depends on where the axis of rotation is. The moment of inertia can be found by breaking up the object into little pieces, multiplying the mass of each little piece by the square of the distance it is from the axis of rotation, and adding all these products up.

this makes it seem that the 22 lb tire (which i'd think has more mass at the outer edge (tread) than on the sidewall) will have much more effect on the overall moment of inertia than the difference between 9 and 13 pound wheels. though given the tire as constant, obviously it will still have some effect.

edited to note that the 3rd link doesn't seem to work.



[Modified by Philbert, 12:25 PM 4/7/2003]

 

is this the april issue?

i've heard the 10 pound thing before too, but wasn't sure if that was a commonly accepted number or just someone's wishful thinking. i think most are agreed unsprung weight is much more important than sprung.

 

it's hard to find a light, 15x7.5 wheel that is 4x100 bolt pattern. most of what i've found doesn't come in 4x100. i think the kosei k1 used to be available, but tirerack only currently shows the 15x7 now.

 

I think it might be the May issue. It's got the dyno article on the cover.
It's out at newsstands, that's where I got mine.