Hey Steve...was thinking about what you said a while back...

[plug1]

Ryan your car looks sweet with those rims........but now you will never keep up j/k!!!

That was in regards to me tossing 18's on my car...i figured you were commenting on the weight rather than the size...so i thought you would be interested in reading this, i sure was.

<a href=http://www.audiworld.com/tech/wheel13.shtml>Click HERE</a>

[Tsunami]

I can't read that...it's in a different language! :eek:

[gjcivic]

so... uhhhh... is that good or bad????

[Brian]

I read most of it. Any way you look at it unsprung weight expecially when it is far from the center axis, decreases acceleration. It's not going to be a huge difference, but definetly a couple of .10's in the 1/4 at least.

[Tsunami]

so then what is better? Smaller rims? or bigger?

[2000SiVTEC]

a smaller rim will be better as there is less unsprung weight like Brian said, it is just simple physics. Bigger wheels don't make you faster, they will only make you slower.......

[YDRSBTR]

Handling is, however, often improved with a larger and wider wheel.

[SC-MECHAM-WS6]

just get more horse power to compensate for the loss of the bigger wheels... ;)

[plug1]

Originally posted by 99SIVTEC
I read most of it. Any way you look at it unsprung weight expecially when it is far from the center axis, decreases acceleration. It's not going to be a huge difference, but definetly a couple of .10's in the 1/4 at least.

No way it will be a couple of .10's...you gotta read the whole article to see the point. The article is a proof with a formula...you kinda have to take everything as a whole.

I'm not saying a heavier wheel won't affect acceleration, i'm just saying it affects it so little, that unless you're upgrading to a wheel that is over 10lbs a piece in weight from the previous wheel you ran, its not even worth worrying about.

If i ran a set of Volk 14lbs wheels...right after i ran with my BBS 17lbs wheels...the change in time would be in the .100's if not the .1000's. Saying all condition are the same...and the wheel width's are the same.

If you run a set of 18", 18lbs wheels...compared to a set of 17" 17lbs wheels...the difference wouldnt even be noticeable...given the wheel widths are the same.

A mag a while back (scc i think) did a dyno test using wheels with a 10lbs difference. The loss was less than 2hp. i can understand if you're running 17lbs wheels...and upgrade to 30lbs+ wheels. But since i was running 17lbs wheels and upgraded to 23lbs wheels...i'm not worried.

Wheels width is a whole different story....aka more surface space = more friction.

[newt2]

Weight isn't the biggest factor, wheel diameter is. With a larger wheel, more of the weight is located father away from the center of the wheel.

You can actually test this effect yourself. Put a weight on the end of a string and swing it in circles. Start with a smaller diameter circle then switch to a wider arc. You should be able to feel in your arm the difference in effort it takes to get the larger diameter arc spinning.

You can have a 15" wheel and an 18" wheel both the same exact weight. Put them on identical cars and the car with the smaller wheel will out accelerate the car with the big wheels.

Bigger wheels don't mean better handling either. Go to an autocross and see how many people are running big wheels. I can tell you now that the fast guys are all running stock sized wheels, maybe a +1 size. The newbs are the ones running big old wheels with rubber band tires. British touring cars use big wheels for one reason, they run 15" brake rotors and need a rim that can clear the brakes.

Edit: I's just like to add that a +1 size wheel package will have virtually no effect on a cars performance as long as weights are close. It's when you start doing +2, +3 or even +4 sizings that you're really going to start to notice a difference.

[Brian]

Originally posted by newt2
Weight isn't the biggest factor, wheel diameter is. With a larger wheel, more of the weight is located father away from the center of the wheel.

You can actually test this effect yourself. Put a weight on the end of a string and swing it in circles. Start with a smaller diameter circle then switch to a wider arc. You should be able to feel in your arm the difference in effort it takes to get the larger diameter arc spinning.

You can have a 15" wheel and an 18" wheel both the same exact weight. Put them on identical cars and the car with the smaller wheel will out accelerate the car with the big wheels.

Bigger wheels don't mean better handling either. Go to an autocross and see how many people are running big wheels. I can tell you now that the fast guys are all running stock sized wheels, maybe a +1 size. The newbs are the ones running big old wheels with rubber band tires. British touring cars use big wheels for one reason, they run 15" brake rotors and need a rim that can clear the brakes.

Ahhh exactly what I was trying to get across. That guys physics formula's did not take into consideration unsprung weight increases. Unsprung weight increases as you move farther from a center axis. As pat said, you can have two wheels that weight exactly the same, but if one is a 13 and one is an 18 then the 18 will definetly slow down the vehicle's acceleration. This was a huge deal when I used to race mountain bikes. We would spend huge ammounts of money on carbon fiber wheels, lighter tires, and light weight tubes just to get an edge over others. You definetly noticed the difference while trying to sprint up a hill.

I can GUARANTEE that a set of 18's that weight a few lbs more than 16's or 17's will lose you at least a couple .10's in the 1/4 mile. Why do you think Steve and I swap our wheels for the stockers every weekend when we race?

[Brian]

I can give a first hand example. One night before Steve was boosted he raced a stock SI on the street. Steve had his 17's on his car. The guy edged him out. We were pretty shocked because Steve runs about a half to a full second in the 1/4 than a stock SI. After a night at bandimere we came home and he ran into the same car only this time steve had his stock wheels on. Steve walked the guy big time.

[plug1]

Originally posted by newt2
Weight isn't the biggest factor, wheel diameter is. With a larger wheel, more of the weight is located father away from the center of the wheel.

You can actually test this effect yourself. Put a weight on the end of a string and swing it in circles. Start with a smaller diameter circle then switch to a wider arc. You should be able to feel in your arm the difference in effort it takes to get the larger diameter arc spinning.

You can have a 15" wheel and an 18" wheel both the same exact weight. Put them on identical cars and the car with the smaller wheel will out accelerate the car with the big wheels.

Bigger wheels don't mean better handling either. Go to an autocross and see how many people are running big wheels. I can tell you now that the fast guys are all running stock sized wheels, maybe a +1 size. The newbs are the ones running big old wheels with rubber band tires. British touring cars use big wheels for one reason, they run 15" brake rotors and need a rim that can clear the brakes.

Edit: I's just like to add that a +1 size wheel package will have virtually no effect on a cars performance as long as weights are close. It's when you start doing +2, +3 or even +4 sizings that you're really going to start to notice a difference.

Yup, good points.

I never really said that running a 22" 17lbs wheel compared to a 16" 17lbs wheel wouldn't slow you down. I was making the reference strictly to weight above. Diameter is a whole different story just like width is.

Good point about people who track...half the guys you see out there are running lighter, wider 17's (i like volks in this example) as opposed to running street 18's or 19's. The other half of people who know what they're doing are running stock sizes. This is from what i've seen and heard anyway...and that makes sense.

But all in all, like you said...a +1 diameter with close to the same weight is not going to have as big of an affect. I asked one guy up in Denver who i know is running the same old BBS RK's that i had...he said they were closer to 19.8-.9lbs on some fine tuned scale at his work. Kinda dissapointing considering BBS lists them at 17lbs. The 18" RX's i am tossing on my car weigh 23-24lbs on a bathroom scale...not the most accurate, but whatever.

With what i've learned...i don't see my car losing a couple .10's with a wheel that is 1" greater in diameter and only a few pounds heavier.

Oh and Brian, with that example there are too many variables...just because they raced twice doesn't mean the drivers launched the same way/shifted at the same speed etc...

If you want my example similar to that...i raced another friend of mine with a silver A4 here in town...similar mods to mine. He had his 18" 24lbs wheels on...i had my 16" 26lbs stock wheels...i beat him by a good 2-3 car lengths. The main difference between our cars is that his exhaust is not cat back...so half of his exhaust is still pushing through the stock piping...which you know is a huge bottleneck. The next time we raced eachother...he had his stock 16's on...and we came out with the same results. But again, there are too many variables to go by a couple of races...especially when you're racing me in my AWD...i launch differently every single time i race that thing, its tough :)

[newt2]

I didn't know A4's came with 17"s. Cool...

[Brian]

Originally posted by plug1



Oh and Brian, with that example there are too many variables...just because they raced twice doesn't mean the drivers launched the same way/shifted at the same speed etc...



These two races were both from a roll..........

It's not going to kill your car or anything. My main point was compared to a lightweight set of 16's or similar your car would be noticeably slower. The wheels look sweet on your car either way and I probably would have made the same choice in getting them.

[plug1]

Originally posted by newt2
I didn't know A4's came with 17"s. Cool...

<b>'i had my 16" 26lbs stock wheels'</b>

;)

Every A4 listed as a 2001.5 or newer has 17's in the "sport" package...even the new body 2002's.

These two races were both from a roll..........

It's not going to kill your car or anything. My main point was compared to a lightweight set of 16's or similar your car would be noticeably slower. The wheels look sweet on your car either way and I probably would have made the same choice in getting them.

Thats whats funny, is me and the other A4 raced from stand stills and in gear...oh well, no big deal.

Thanks for the compliment...i'm not really not all that concerned or as concerned as others when it comes to 1/4 mile times anyway.
I just didn't know about the whole wheel weight deal...figured i'd share for others who didn't know either. I hope someone learned something from this thread...cause that was my point :)

[exciv2000]

So if my stock tires are 14" and my summer tires are 17" and only 4.5 lbs heavier per wheel/tire combo than the 14" wheel/tire combo, how much am I suffering? To be honest, I can't really tell the difference between the two, other then the fact that the snow tires on the 14" rims are easier to spin and don't "hop" so much during launches.

Also, would it be advisable or not to run 14" stock tires or drag radials up front and still keep my 17" tires on the rear when at the track?