jangy

Has anyone ever actually tested the difference in saving weight at the wheels / rotors? I've ordered the HRE comp wheels and am getting rotors soon. I assume I'll save almost 20 lbs at each corner but have no idea how dramatic it'll actually be.

Will I just feel more response, or is there an actual 1/4 mile difference?

chiromikey

i haven't tested cars but the measurable difference on motorcycles is huge...whether it be dyno, 1/4mile, or lap times. the measurement on cars would, no doubt, not be as significant but i'm sure it would be there with the weight differences you're talking about.

OzE55

If thats true could it explain the difference in times between the E55 and E63? The later comes with 19"s standard and bigger brakes.

tigerlam92

You should see a quarter mile difference. The response and acceleration will be slightly improve.

This is probably done since racing of any type started many years ago. This is commonly done for both drag and road race. I had done this for wheels, flywheels, driveshafts, etc. Not many people do this for rotor since braking is really important and the gain doesn't warrant the cost like the PCCB of the 911 GT2.

For acceleration it is about the moment of inertia of a rotating mass.
I = m r^2

Below is what I pulled from the net. The 1:8 ratio may be exagerated IMO.

Q: Why is the weight of wheels important?
A: Wheels are rotating mass/unsprung weight. Every 1 lb reduction in rotating mass is equivalent to an approximately 8 lb reduction in static weight. With lighter weight wheels, you will benefit from increased fuel savings, quicker braking, improved tire wear and better acceleration. Always ask about the weight of wheels. Your vehicle is not engineered for heavy wheels. Therefore, it will not perform well if you effectively put four anchors on it!

Rotational Weight
Let's start with some physics, first to discuss weight and wheels. It is often said that if you're trying to trim some weight off your bike, the most significant effects will come from lightening your wheels, because the wheels rotate. With respect to ultra events, this dictum isn't so important. It is true that rotational weight counts twice as much as non-rotational weight, it is also true that this rotational weight difference has its effect only under certain circumstances, like acceleration. While we are getting up to speed, lighter wheels will help us to accelerate more quickly, but once we reach our cruising speed, the weight difference has no added effect, as far as the spinning wheel is concerned. At a constant speed, weight on the wheels counts exactly the same as weight elsewhere on the bike, or on your body. While the ability to accelerate quickly may be an issue if you're riding a road race or a criterium, it's not going to be much of an issue for long-distance ultra events, where you are most concerned about maintaining a constant speed. So, lighter weight should certainly be a consideration, but in ultra events the real effects of lighter wheels aren't going to be felt as much as in other cycling events.

Vetluver

In the US E63 have the same size wheels and tires as E55, 18"s. CLS55 and 63 have 19's.

Dogshine

I would love to know the weight of my cls55 wheel/tire compared to one of an e55... I'm just too lazy to pull my wheel. We all know the e55 clocks better times than the cls and I wonder if its due to wheel weight.

OzE55

Bummer.
So much for that theory.

Cylinder Head

iTrader: (1)

Sport Compact Car did an in-depth report on the effects of unsprung weight a few years back (try four) and the data I remember from it was something to the effect that every pound of unsprung weight is equivalent to about 3 pounds (rather conservative a number if you ask me) of sprung weight. Reducing it as much as possible is always a great idea.

e55 baller

A 1:8 ratio seems very high. I always used the rule of thumb...can't recall the source or physics mathematics but 1lb lost in unprung weight = 1.7lb lost in the sprung weight due to inertia.

100lbs less in sprung/car weight should be 1moh faster and 0.1 sec lower.

Rock

Jangy,

I did test to see if it made a difference in my 1/4 mile (trap speed). I assume I have reduced about 15-20lbs of unsprung weight (per corner) with my LMs and Evo floating rotors.

No difference in trap speed was noted at the track. But what I have noticed with this addition is that the car seems much lighter on its feet and it feels like it accelerates quicker when at speed.

I think lighter wheels and brakes are a no brain-er for anyone modifying their E.

chris @ evosport

I remember reading something similar and I believe it was for every 100lbs shed you lose .1 on your quarter mile, permitting you're a capable driver. Reducing unsprung weight also helps the car handle better as in both acceleration and braking the car will respond quicker. I'm honestly not sure of how many members here track their car, but a difference can definitely be seen/felt by reducing weight, without question.

e55 baller

so far I have managed to take out about 100lbs between the brakes, battery, and misclleanous crap. I weighed the car at 3955 with 1/4 tank. Stock is about 4087.

jangy

E63 does have 18s in the US, but the 18 vs 19 is why I have always thought the E beats the CLS.

jangy

Did you also change your overall diameter? If so, that would affect gearing. Assuming you have a larger diameter, you would have taller gearing. If all that is so, I'd still consider it a gain if your times remained the same, even with larger setup?

jangy

Actually, we need to start taking it to the track. We have been meeting up for rides on public roads and I think it may be a better idea to pay and get in a controlled environment before something bad does happen.

tigerlam92

Absolutely. Did the public road a lot before. Then been on a couple of cruise and always hating it because the lead or organizer would have a well preped car with lots of experience in AutoX and road race, then lead the pack really fast. And each time some young kid will crash there car.

Now, I carefully select the group I go out with in public cruising who are more mature and able to handle it properly (driving and self control)

Now I just take it to the track (1 every 2 month) to the tracks like Thunderhill (love this), Infineon (fun), and Laguna (scary- maybe cause I sat in the car when my friend total his vette in the front straight). It is so much safer and more enjoyable to push yourself and your car to the limit on the track.

jangy

sound familiar?