xtyper

Since I've got most of the major power bolt-ons, I've been considering lightweight parts as my next step, specifically rims and rotors. I know all the top East Coast drag cars are running them, but my research suggests they have minimal impact beyond the simple weight reduction itself. In other words, no real extra benefit comes from the fact that it is unsprung rotating mass, on the dyno nor at the strip.

Here is a link to a popular test referenced in many of the car enthusiast forums when this question comes up.

http://www.carcraft.com/projectbuild...son/index.html

The test shows that even after removing over 80 lbs from the wheels (between rims and tires), only about .1 sec and 1 mph were picked up in the quarter on a 12 second car. That's the same differential one would expect from removing that amount of sprung, non-rotating mass. This suggests there are minimal, if any, extra benefits coming from the fact the weight reduction here was to unsprung, rotating mass.

Bottom line, why should I spend $4K+ on lighter rims and rotors to shed about 50lbs if the real-world impact of such modifications is only 0.05 sec & 0.5 mph improvement at the drag strip?

Please discuss.

James@ACG

Eric keep in mind that you will be reducing rotational Mass not just simply dead weight. Typically when you lose 1# of un-sprung rotational weight such as wheels or rotors you lose ~ 10#'s of chassis weight.

So our rotors will save you roughly 12# of un-sprung weight which would roughly equal saving a 120#'s of weight from your C63.

So if you take the complete weight savings from our rotors of 36# that would equal 360# of chassis weight.

jacob502

I dont know about that website you posted bro. 80lbs of reduced unsprung mass is like removing 250lbs off a car's overall weight. I'm pretty sure you will get more than 0.111 seconds off of your best ET. I installed some Evosprt rotors on my SL63 (you can see the photos on my profile). The car accelerates quicker on all RPM ranges. installing light rotors, tires and wheels for your C63 will defenitley improve your ET.. Do it man

Get yourself a CF trunk, hood and a lightweight battery and you will be running like a bullet

jacob502

That is correct james, but i belive for every 1lb of unsprung mass it equals 4lbs of chasis mass

it also differs for tires, wheels and rotors. The further you are from the spring the ratio increase.

for example:

Rotors~ ratio 2
wheels ~ ratio 3
tires~ ratio 4

xtyper

Thanks for responding James. However, that's exactly my confusion. My research and the real-world tests that have been done seem to suggest that unsprung, rotational weight reduction has the same effect as chassis weight reduction. I'm looking for some proof that shows otherwise and can't seem to find it.

Dads C63

Eric,
My first set of skinnies weighed about 36# which is about 20# less than the stock wheels/tires. Thats a loss of 40# rotational mass along with the lower rolling resistance with the narrower tires. I gained a consistent .15 off the 1/4 mile. Howard and Mike and numerous others have proved that to be correct. When you are running the times you are running .15 is no slouch to gain. When you run low 11's you will REALLY be wanting that .15 second. Get a set of skinnies and let it rip!!!

dodger63

Lowering rotational mass is useless, don't listen to dads your first post is right don't waist the money

xtyper

I sense a bit of sarcasm here.

xtyper

Well, you and Dodger are definitely the authority on issues like this. So if you say it works as advertised, then I am a believer. Just surprising that I can't find any independent tests out there backing it up.

James@ACG

Lets do it Eric! We can do it at the next track rental, i'll do the rotor swap in the parking lot But i will tell you that i have dyno the same car but with a different set of wheels and we made power, so there is improvements to be made with weight loss.

xtyper

Sounds like a great idea James, I'm totally down! Now we just need a Famoso private rental event.

Even Money

Reducing weight furthest from the center will have the greatest positive effect. Get some Hoosiers with custom drag rims and skinnies will be your best bet. In fact if you look at some drag rim makers, like bogart, you shouldn't drive their rims on the street as the barrels are not really designed to survive a pothole, I.e., they've minimized weight furthest from the center to maximize acceleration of the wheel.

mthis

Do it all you won't regret it.

hhughes1

Rotational weight reduction absolutely makes an impact, ask anyone who bicycles at a serious level. I bought a set of carbon fiber Easton wheels that are 1400 grams compared to the original Fulcrums at 1800 grams. The difference in just 400 grams is incredible, climbing and accelerating is night and day. This is not just a butt dyno feeling but backed up with garmin GPS data. You may think this is not relevent but I can assure you that it is.

DuaneC63

For drag racing were you're trying to shave a few 1/100 of a second off your ET, there may be more cost effective ways to achieve lower ET's (unless you done everything already like drag radials, very skinny fronts, and 90/10 shocks). On a road course the unsprung mass weight saving is much more pronounced. Unsprung weight in the twisties is greatly magnified by G forces, causing your tires and suspension to work harder. Even more important is the rotational mass for acceleration and deceleration. Each lap of a few miles may contain over 20 acceleration and deceleration cycles. Brakes get a massive workout on a road track. Since you're doing multiple laps, 1/10 of a second per lap is a major gain over a half hour race.

CampioniShop

+1

Rotational inertia and the moment of inertia have dramatic effects on performance. The farther from the hub - the less weight you ideally want.

Tire selection is highly important as well, many tires are extremely heavy (the Michelin PSS comes to mind) and these could outweigh any benefits your lighter wheels would bring.

gthal

The PSS is actually a decent tire weight wise. The RE-11 and AD-08 are much heavier tires. The PSS is, IMO, relative light... or at least comparable to tires with much softer (i.e. lighter) sidewall construction.

AMG3.2

+1 It is one of the lighter tires out there.

The Continental DW is another light tire that has great reviews.

dre5373

Sport Rider did a comparison years ago that was pretty informative...
http://www.sportrider.com/gear/146_0...n/viewall.html

Sheep

It's just physics and Dad's right on this issue. However, I would advice anyone to save up and at least go to racing/defensive/offensive driving school at least once. That way you will able to drive ANY car fast .

Sheep

sighting

i will put money on the line that a socket wrench at the strip to remove the front seat and the spare tire will yield a better decrease in times that 4k rotor kit

BAD430BENZ

4k rotor kit

which one are you looking at ?

sighting

The Evosport ones, with shims, pads and install.
But you right its probably closer to 3900

BAD430BENZ

not sure why i keep responding to this old thread.......but i just looked it all up and if you buy it all brand new :

rotors - 2450.00
shims - 120.00
front pads - 220.00
rear pads - 125.00

grand total = $2915.00

if you pay $1000 for labor on that , you are crazy

i paid $250 for install for my stuff

Jons95c36amg

Caught my attention-Bicycles at a serious level. Well the lightness on the wheels only apply when your climbing alot. Which will give you a slight advantage when comparing riders with equal fitness. Most of the guys I ride with have 15lbs bikes. Unlike my 16.5lbs bike. Most of them can't even match me on the hills.