wieght questions

[longjeeper]

ok so i wasnt sure where to put this but since i am n/a this looked good, i was wondering how much weight really mattered when racing with an elantra i mean 1/4 times and that stuff? and also how about rotational weight i could save like 8-11 lbs per wheel and tire with i went back to my stock wheels and size tires, just wondering couldnt really understand the answers i read when i searched

[joph09]

think of it like this:
it takes alot more work to accelerate a larger diameter wheel because of the added rotational inertia ( how difficult an object is to start or stop spinning) is affected by mass and radius. In the case of rims the radius has a much larger effect on the rotational inertia than weight alone. The one inch difference b/w a 17inch and an 18inch rim has the same effect on the wheel's roational inertia as increasing it's weight by 10% at the outer radius and the effect gets larger from 18 to 19, 19 to 20 etc... Plus the unsprung weight will be much more of a significance at the track taking off more weight will be more important. I took this part from Sport Compact Car Mag. every pound of unsprung weight is = to adding 1.4 more pounds to the chassis or sprung weight

hope that made sense or helped

[evan938]

and from what ive heard/learned, if you remove 100lbs, it will save 1/10 sec on your 1/4 time.

and i thought 1lb off the wheel = 10lb of dead weight? i cant believe its 1.4lbs, because when i got my 12lb wheels, the difference (14-16lbs overall) was ridiculous. i could see it seeming like the difference between a passenger or not (140-160lbs) over a 21-25lb difference. thats like pulling the spare or not

[joph09]

ya i thought that was off too but it's clear in Sport Compct Car "The truth Tuning Myths Busted Wide Open" June 2006 Vol. 18 No.6

[longjeeper]

ok that is better to understand than what i was reading all the other stuff was as confusing as hell

[joph09]

and from what ive heard/learned, if you remove 100lbs, it will save 1/10 sec on your 1/4 time.

and i thought 1lb off the wheel = 10lb of dead weight? i cant believe its 1.4lbs, because when i got my 12lb wheels, the difference (14-16lbs overall) was ridiculous. i could see it seeming like the difference between a passenger or not (140-160lbs) over a 21-25lb difference. thats like pulling the spare or not

is that 14-16lbs overall per wheel or on all 4 wheels? because when you think about it for every pound of unsprung weight equaling 10 pounds of sprung weight is hellof alot of a difference plus if you moved from a larger rim to a smaller one the rotational inertia has a much bigger effect on size than on mass alone

try riding a 18" bicycle then right after try riding a 24" or full size bicycle it'll be much more harder to stat pedalling, it's all about acceleration

[evan938]

i went from a 15" 19lb wheel (stock alloy) to a 12lb 15" wheel. its a 14-16lb difference just between the 2 front wheels...i didnt count the back since theyre not drive wheels

[SWortham]

and from what ive heard/learned, if you remove 100lbs, it will save 1/10 sec on your 1/4 time.

and i thought 1lb off the wheel = 10lb of dead weight? i cant believe its 1.4lbs, because when i got my 12lb wheels, the difference (14-16lbs overall) was ridiculous. i could see it seeming like the difference between a passenger or not (140-160lbs) over a 21-25lb difference. thats like pulling the spare or not
Assuming the same wheel and tire sizes, then going to a 1 pound lighter tire is like removing 2 pounds of dead weight per corner and going to a 1 pound lighter wheel is like removing 1.5 pounds of dead weight per corner. Those are rough estimations, and those rules basically go out the window when plus sizing enters the mix.

[evan938]

well, heres what i'll try to do.

later this month is end of the year track day...if i can remember, i will try to run w/ my GT wheels (even though they'll have snow tires) a couple times, then run w/ my 12lb nippons, and see what the difference is.

[SWortham]

Plus the unsprung weight will be much more of a significance at the track taking off more weight will be more important. I took this part from Sport Compact Car Mag. every pound of unsprung weight is = to adding 1.4 more pounds to the chassis or sprung weight
Where did they pull that number from and what do they base it on -- lap times? Do you have a link to the article?