JayG

I'm looking at picking up a set of Racing Dynamics wheels as a spare set for track/AX use at really good price.

From what I can tell, they weigh around 6-8 lbs more that the wheel I use now.

I know heaver wheels can effect performance, but in reality how much? My car is basically stock, soon to get a suspension upgrade like PSS9's. I am a relatively new track driver, about 18 track days under my belt. I am not concerned with a few 10'ths in lap time, but several seconds would be a concern

My thought is to most likely use them for practice sessions on the track and switch to my lighter wheels for timed runs. Maybe the same for AX.That way I can save my "good" tires for when it counts. Or, since the new wheels would let me use wider tires on the front (8" vs 7" wheel, use them for my timed runs

They also come with with 4 virtually new tires, but not ones I would use for the track or AX

stownsen914

As a new-ish driver, you would probably be hard-pressed to notice. Wheel weight does make a difference, though, so as you gain experience you may notice the difference. But even for a very experienced driver, I can't imagine the difference being several seconds per lap.

mark kibort

the weight of the wheel could NEVER make several seconds per lap difference.
ive posted this many times before, but the weight on the wheel, at a max can only effect brakiing and acceleration as if that weight was in the car , times about 1.4. that means your 6 lb heavier wheel , is like 9lbs sitting in the car... (or x 4 , or 36 lbs in the car) thats All ! No more! its basic physics. (transnational vs rotational inertia equivalence which is easy to calculate) so, if you have a 10:1 HP to weight ration (3000lb car and 300hp) its like you just gave up 3.6HP. you will never notice this.

the other factors are gyroscopic effects and unsprung weight effects on suspension action and recovery. the quick answer to this, is that if we are talking a smooth track, the effects will not be noticible. much harder to calculate, but on a bumpy track, the differences would be more noticeable, handling-wise.

Great idea.. i did that for many years.. one set for practice and one for qual and race.. and those rims were about 5lbs heavier per wheel and tire.... never noticed much of a difference. certainly would never be worth more than a few tenths even by the best of drivers.

JayG

Thanks Mark.
Lots of misinformation on the internet. I was hoping for a straight answer and got one

As a side note, I picked up the wheels and when I weighted them, they are only 1-2 lbs heaver not the 6-8 I thought from research on the web than my current Boxster S wheels I use for the track. As a bonus, they are wider wheels so I can go with some extra rubber especially on the front

Based on your calculation, all I need to do is take a good dump and I'll effectively shed the extra weight from the wheels
Hell, if I remove the rear speaker shelf, that will drop me around 30 lbs, but then I won't be able to hear my tunes on the track

mark kibort

Glad i could help.. also, good news that they are less than expected. often ive found that there are different tires that can be 4lbs heavier per tire too. that's the effect of near .. not exactly, 2x the weight as if it was in the car (bigger diameter)

Have fun!

Mark

TraqGear

Thanks Mark! I've always been a weight ****, especially in this area. Now, I can relax a little.

Tell us a little more about diameters and the effect they will have on the car.

gbuff

Gotta be light wheels for me....I'm a lightweight myself and with light wheels I don't break my a$$ quite as much putting 'em on/taking 'em off the car

Great info, Mark

Gary

golfnutintib

lightness matters a lot to me too, esp. on a performance car and on track - my rule of thumb for rotating inertia effects are 2.5 to 3x static weight

less rotating mass and static mass for the car to fight with as we speed up and slow down again and again has a cumulative effect...

obviously skill of driver, type of track/roads, average speeds and driving style all factor into how much tangible difference it would make

mark kibort

as important as weight is to performance, the relation you quoted is not correct. its not 2.5 to 3x. in fact , its 1.2 to 1.5x, and this is easy to prove using some basic math converting rotational to translational KE. Illl answer why in the next post

mark kibort

since inertia is based on diameter, if you think about it, if a weight was on the outer diameter, like the tire tread, it would travel 2x the speed of the linear speed of the car. but with tires, not all the weight is in the tread or at the outermost diameter, so, its less than 2x. for wheels, its more like 1.4 to 1.5 times the weight if it was siting in the car, depending if you have a 17" diameter or 18" diameter wheel.

hahaha.. I know, that was the best day when both sets were the same light wheels.... (for just moving them around , period!)
. my street (fun) car has super heavy high performance wheels. they must weigh 40lbs each! a big pain to put them on, especially with those BMW style stud lug nuts..... and I work out and its still a pain

JayG

Thanks again mark for the info

You should come down to So Cal and play with us. PCA SDR has some nice events
http://www.pcasdr.org/competition/dett-schedule/

CFOS at Autoclub Speedway and Buttonwillow are also Club Races

mark kibort

I'm planning the schedule for this season... Ill try and make a couple event, sounds fun! I want to get down to AutoClub. Certainly, doing a couple POC races this season too.
Thanks!
Mark

JayG

If you want to run CFOS, be sure to register as soon as it opens up as it sells out fast.

Its a really great event and 3 days on the roval is fun.
I can't do it this year as I have a major trade show te following week for my work and have to be in Las Vegas by Sunday.

mark kibort

thats a good idea.. im going to make a 4 day weekend of it, and see some friends down there. Ive always wanted to try the roval... i thought willow springs was a roval!

JayG

I'm one of the slower cars and I hit around 130-135 into turn 1.
I don't have the ***** to hold that speed into 2. Exit 2 full gas and then a 5-2 downshift into turn 3

Hell of a lot of fun!!!