So I understand the basic logic behind it. Reducing rotating weight makes the car accelerate faster, handle better, and stop faster.

How much of a difference does it really make? What about rotating mass (wheel diameter, smaller tire)?

I guess my main question: Is it worth the effort to replace stock parts for smaller/lighter wheels, lightest rotors, etc?

Does anyone have real-world numbers or experience they can share?

 

Yes it's worth it. Less unsprung weight is like 4X more effective than sprung weight (depends on which side of the spring it's on). The doors, for instance, are sprung and the wheels, tires, brakes, etc are unsprung. I like to look for the lightest tires in the size I need (usually they are Toyos T1S/R). I look for the lightest rim I can afford in the size I need. I don't recommend a light rotor because you will lose it's ability to heat sink.

Further, if you drag race, wheels might make a couple tenths difference. Not worth it to me. If you like to make turns, unsprung weight differences (and sprung weight differences) will make much more difference.

For the street, who cares?

 

There has been a few studies, not easy to put into a short thread.

But for drag racing it really makes little differnce, the distance is too short. However, if your going to choose DR with 16" wheels or 19" wheels, the 16" would be noticible quicker. Not sure if it is the diamerter of the rim or the grip of the DR?

For road racing and speeds above 125 mph to 160 mph the lighter wheels makes a big differnce in acceleartion are more importantly stopping from those speeds.

The challange with equipment that is too light is that it breaks quicker and is not as reliable.

Good Luck

 

Thanks. I eventually want to get into road racing and such.

Trying to justify the price of $850 rotors vs $300 rotors.

 

Without a doubt lower weight improves performance. How much is really hard to quantify. That is why competitive racers do everything they can to reduce weight.

If you are just running your car in HPDEs and the like I would not go overboard on the weight reduction thing. The improvement in performance will not be justified by the higher cost. Just MHO.

Carroll Smith's Tune to Win has a good discussion on this topic.

 

If you want to get into road racing the the $27 Rabestos rotors from NAPA are the only way to go.

an $850 or $300 rotor will crack and need to be replaced just as fast as a $27 rotor. SO what would you rather spend? $850, $300 or $27 for something that makes no difference??

 

$27.00 for a rotor at NAPA ?, boy that sounds cheap !!! I wonder where they are made.

 

Canada & McHenery ILL USA.

actully the other rotors are over priced.

 

http://forums.corvetteforum.com/show....php?t=1763652


ref NAPA rotors

 

The expensive rotors will only crack if you buy them drilled. If you buy the slotted rotors they won't crack. The expensive rotors also have seperate hats made of aluminum, which will help in rotor cupping as the rotor heats up. I bought some Stop Tech rotors for my magnum which was always developing a brake pulse with the stock rotors. The Stop Techs are awsome. There is nothing worse than not being confident in your brakes and nothing better than the feeling of good solid brakes when you need them. The Z06 of course has very good stock brakes and I always feel confident in them but I will be getting the Stop Techs for it soon too.

 

Yes a two piece brake rotor and hat is different.

 

I ordered the RacingBrake 2pc rotors (open slot).

Thanks for the replies.

 

16" wheels give you an advantage by effectively changing the rear axle gear ratio. you can do the math if you want, but it may take the 3.42 to 3.75 or something like that. it's directly proportional to the differance in circumfrence of the two different tires. lighter wieght also reduces rotating inertia.

lighter weight wheels and tires affect acceleration more from zero to 60 than at high speeds. the wheel rotation is accelerating fastest in the beginning of a run, so that's where the lower inertia has the most affect. your wheels accelerate from zero to 60 in about 4 seconds. the same change in speed from 110 to 170 say, takes much longer, so the weight has less affect.

how the difference in rotating inertia affects acceleration time is difficult to calculate. to do the calculation correctly you need to consider the weight of the clutch, flywheel and drive shaft, then consider the inertia of the transmission and the affect of the selected gear, then the inertia of the axles, brakes, etc, and then the affect of the rear end ratio. too many assumptions and estimates to get a worthwhile number.

the best place to save weight for accelation is in the flywheel and clutch. the reduction there has all of the multipliers of the transmission gearing and rear end gearing. 10 pounds in the flywheel is the equivilent of something like 70 pounds of wheels and tires - from a strictly rotating inertia standpoint.

 

Actually it all matters, all the time. It's roughly 7x for each rotating mass in weight off the vehicle. It affects every form of movement of the vehicle. Weight from the wheel area - assuming it's a part that has to be moved such as a brake rotor - will not only help during acceleration and braking regardless of speed, but will also make the suspension functions more true to the surface it's tracking, as the system is transmitted more "data" the lighter the tire/wheel/brake/rotor and every other part strapped to it that moves up and down with it is made. Which leads you - obviously - to suspension tuning, which is going to be VERY pricey.

 

Just curious if anyone has a ballpark idea - I've got the replica C6 ZO6 (chrome) wheels and had the car dyno-tuned with them on. How much hp would I pick up with the lighter stock wheels?

 

I have the same question. I have Z06 Motorsports on my Z06 and am contemplating selling them and going back to stock Speedlines for the weight reduction. My car doesn't feel as quick or nimble with the Motorsports on. Is it just my imagination?

 

It's definately got a different feel and I would really like to know what it does to the HP.

But the chrome looks soooooooo good.

 

From my 51 lbs rear street wheel to my 39 lb rear race wheels, the car picked up 7 hp. But two different dynos on two differnt days. Both Dynojets and both SAE corrected.

 

Thanks for all of the excellent and informative replies.

 

Also remember that where the weight is, can be as important (or more) than how much.

A 10 lb heavier axle is going to have much less effect on MOI than a 10 lb heavier tire.

The tires are the largest dia object that rotate, followed by the wheels, the flywheel/rotors, etc. Reducing weight from the items that are further away from the crank/axle centerline will help the most with MOI (accel.)

Usprung weight as mentioned has to do with how fast your suspension is going to react in it's normal motion. The less the better.

You could spend awhile talking about such, but bottom line, the worst place to add weight to a car is wheels/tires. It's sheer dead weight, AND unsprung and rotational/driveline rotational.