Any problem mating the C5 rotors to C3 hubs?

 

The C5 rotors will not bolt right up to the hubs. The hubs have to be machined down to accept them.

check this out.
http://temp.corvetteforum.net/c3/70lt1/brakes.shtml

 

That'll overheat really easily unless you have a very open wheel design.

Also, to the mention above of aluminum calipers saving 4 lb/wheel: Nobody here could feel a difference from that. Unsprung weight is overrated. Aluminum has different thermal properties than iron, though. That would be the more appropriate advertisement. Aluminum calipers should take longer to heat up, and the fins should help them cool down more quickly too (probably).

 

"Also, to the mention above of aluminum calipers saving 4 lb/wheel: Nobody here could feel a difference from that. Unsprung weight is overrated."

I would have to disagree with this statement. In terms of acceleration, you are probably right. But in terms of handling and suspension response and ride, 4 pounds is significant. I have a couple of suspension books and they all say the regarding handling, reducing unsprung weight by 4 pounds is like taking 16 pounds off the sprung weight. So if you want to improve your handling you can either take 4 pounds off the wheel or 16 pounds from the rest of the car. And since you are talking 4 wheels, you are taking an equivelant of 64 pounds out of the car. I know for one that there is a definite difference in handling when I have a passenger.

Also, those Wilwoods will save a LOT more than 4 pounds a wheel. More like 8 to 10. The only thing about the wilwoods is that the piston area is no larger than that of the factory calipers, so I wouldn't expect initial stopping distances to improve, unless you use a larger rotor. I have them and mine didn't. You can however expect a great reduction in fading. Mine hold up a ot better to hard continuous use than the stockers.

It will be real interesting to see how the C5 brakes work out. The pistons on those things would have to be huge to total the piston are on the stock calipers. But the C5 has some pretty good braking so it might work well. Let us know.

Chris


[Modified by 71roadster, 6:43 PM 7/27/2003]

 

How much does the stock stuff weigh?? The integra 4 weighs 5.3lbs and the Integra 6 weighs 5.9lbs. The piston area of the Wilwood Integra 4 is larger than stock.

 

Twin Turbo:
Stock calipers are 13 1/4 lbs each.

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I would have to disagree with this statement. In terms of acceleration, you are probably right. But in terms of handling and suspension response and ride, 4 pounds is significant. I have a couple of suspension books and they all say the regarding handling, reducing unsprung weight by 4 pounds is like taking 16 pounds off the sprung weight. So if you want to improve your handling you can either take 4 pounds off the wheel or 16 pounds from the rest of the car. And since you are talking 4 wheels, you are taking an equivelant of 64 pounds out of the car. I know for one that there is a definite difference in handling when I have a passenger
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:iagree: also. Aluminum calpiers have a 40% better stopping power

 

What is that supposed to mean? That the pistons have 40% larger area? That doesn't equate to 40% better stopping power.

I'll state again that weight is not a significant issue on a street car. Rotational inertia at the wheels does not add much to the effective weight of the car (things closer to the engine like the flywheel are MUCH more sensitive to little changes). If you increase the wheel assembly's moment of inertia by I, and the outer radius of the tire is r, the increase in effective mass of the car is I/r^2, which is usually less than 30% of the rotors' weight savings. The increased diameter of new rotors reduces the 30% factor even further.

Unsprung weight is more important, but there's no simple rule of thumb like 1 lb unsprung=4 lb sprung. Your books are either wrong, or are saying that in most races, finish times are similar with that conversion factor. The second possibility sounds like pure legend to me.

I say there is no direct conversion factor because sprung and unsprung weight have different effects on handling. Random changes in the road reduce traction, and the sprung and unsprung masses both affect that, but in different ways. Basically, if the imperfections are going by really quickly, the traction loss is directly proportional to the unsprung weight. Its nearly independent of sprung weight. At very low speeds, the opposite is true. What determines "fast" and "slow" is related to the spring rate and the sprung mass of the car.

Anyways, what is the total unsprung weight at one corner? My (possibly very wrong) guess is about 100 lb. All of that doesn't have a very large effect if your spring/shock combo is good, 5/100=1/20 of that surely can't be felt.

I think redvetracer has made similar statements on this forum before. I'd say he has more practical experience with brakes on C3's than any of us.

 

I too wonder how aluminum calipers have %40 better stopping power. Aluminum tends to flex more so if that was the only difference, there would be a slight reduction.

As far as weight not being a significant factor in a street car, you are wrong. My car is quite a bit faster without the weight of a passenger. Isn't yours? And I am pushing over 400 horsepower so it is not as if I am lacking the power to push the extra 180 lbs. Nor are many people on this board satisfied with "street car" performance. Most of us are looking beyond that. And nobody at all was talking about rotational inertia. I took all those physics classes myself, but I also have 15 years of experience to back up my observations. Observe this...why do indy cars still run small wheels with large sidewall tire? Couldn't be to keep rotational inertia down for better braking and acceleration.

As far as my books being wrong, you may be right. After all they were written by nitwits like Herb Adams and Dick Guldstrand who only have a lifetime of experience building and racing vettes. Go hang out in the pits sometime at a road race. Look at the unsprung components on a modern medium budget racecar. Hollow axles. Boxed sheetmetal uprights. Billet hubs. Titanium wheel bolts and studs, ceramic rotors. Nowhere else in the car is so much invested in weight reduction. And I recall redvetracr's comments. He said the average driver would not notice a difference. I would say any guy who takes his car onto a road course is not an average driver, and whether he can 'feel' the difference or not, the benefit of reduced unpsrung weight is still there.

And I would put the unsprung weight at closer to 60 lbs. Get rid of the steel wheel and go with a 10 lb lighter caliper and you may be closer to 50. A significant reduction.

Chris

 

You misinterpreted some of the things I said.

I agree that weight is important for a street car. I said that the savings from just a brake upgrade are minimal.

I actually never noticed the car being slower with a passenger. Maybe I'd notice a difference in acceleration with back to back tests with and without a passenger. I doubt I'd feel a handling difference though. Maybe you're a lot more sensitive to it than I am.

By "street car performance," I meant feel. If you regularly push the car to its absolute limit, and get extremely consistent lap times (maybe you do this?), then I agree that you will see a improved times from this kind of unsprung weight savings. I don't think you would feel a difference though.

Unsprung weight and rotational inertia are important for race cars, but old street vettes are not race cars. They're not spending considerable time taking hard turns at 120 mph (or whatever), and are much heavier overall. They're also not being modified with thousands of dollars invested to save each hundredth of a second in lap time. Most of us just want the car to feel better. Again, if you're not in that group, sorry. I think most people in this thread are though.

For the 1 lb->4 lb thing, tell me why I'm wrong without saying that other people say so. Or point me to something which does explain it either theoretically or by actual measurements.

 

the 1:4 guideline is just a rule of thumb, probably derived from experiences from testing and racing. Not everything can be explained by math and physics (stuff tends to get very complicated with something as dynamic:as vehicle suspsension). There are several books that give the 1:4 figure for unsprung/sprung weight.

If you can lower the unsprung weight, I see nbo reason why not to do it, if you are set on getting neweer brakes then get the lightest you can. It certainly won't hurt anything.

 

Of course. I was aiming my post more at people spending a bunch of money just to reduce the weight.

 

So far the only cost effective solution I've seen is 70LS1's C5 approach (assuming the bracket issue doesn't get out of hand)'

Other systems seem to be running around $900 front axle and a bit less for rear axle.

Am I missing something?