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Huge brake upgrade for S197 chassis

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Fabman

Dances with Racecars
6,518
8,154
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
I know that "rule of thumb" has been around for a long time. But as with many rules of thumb, the applicability of that "rule" never seems to show up. In this case, it's about rotating weight - more correctly rotational inertia - and I'm about 99% sure that it came out of the hotrodding side of the automotive hobby because 1:10 can't be justified through the physics and math involved. A 1 to 10 ratio might well apply to flywheel weight loss as an overall average up through the gears, due to the fact that they are being accelerated rotationally several times faster than the wheels.

I found at least a couple places that back my own rough 1:2 rule of thumb, which I've been able to verify via comparing acceleration simulations.


Norm
Then all the chassis books I read as a pup growing up in this sport were wrong.
Silly me for believing it.
 

TMSBOSS

Spending my pension on car parts and track fees.
7,529
5,242
Exp. Type
HPDE
Exp. Level
10-20 Years
Illinois
I believe one of you are discussing the rotating mass while the other is concerned with the effect of weight as applies to suspension rebound, grip etc.. Or the positive effects on forward acceleration as opposed to corner grip.
Or it could just be me.
 

Fabman

Dances with Racecars
6,518
8,154
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
I believe one of you are discussing the rotating mass while the other is concerned with the effect of weight as applies to suspension rebound, grip etc.. Or the positive effects on forward acceleration as opposed to corner grip.
Or it could just be me.
You are correct, which is why I specified "Unsprung weight" and noted "Rational weight" as being something different. Norm gets that. He just isn't buying the 10-1 ratio we all read in books, and he may very well be correct. The only reference I have is all the books I read, and at one time I had read a lot...like everything I could get my hands on. While my retention of the information is spot on, I didn't personally crunch the numbers and simply have to rely on the info given. Perhaps it was wrong.
 

Norm Peterson

Corner Barstool Sitter
939
712
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
Then all the chassis books I read as a pup growing up in this sport were wrong.
Silly me for believing it.
I'm honestly curious which books you might have seen it in. I've got a fair collection myself (not all softcover). Most of mine don't address this relationship at all (I just looked at several).

But Paul Van Valkenburgh's book (Race Car Engineering & Mechanics) does, and he comes up with each lb of tire weight effectively incurring an additional 3/4 lb for its rotational effect. Or 1 to 1.75, 10 lbs rotating = 17.5 lbs sprung. I'm willing to go 1:2 even though I've found 1:1.5 to be frequently possible with realistic wheels and tires.

FWIW, in actual testing
http://www.hotrod.com/articles/light-vs-heavy-wheels-comparison/
finds 82 lbs lost from the wheels and tires (combined) to be worth 0.111 seconds in the 1/4. That corresponds to a 1:1.35 ratio based on the 100 lbs = 0.1 second rule of thumb if you scale the 82 lbs actually "lost" up to 100 (really not much of a stretch).


Norm
 

Fabman

Dances with Racecars
6,518
8,154
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
I'm honestly curious which books you might have seen it in. I've got a fair collection myself (not all softcover). Most of mine don't address this relationship at all (I just looked at several).

But Paul Van Valkenburgh's book (Race Car Engineering & Mechanics) does, and he comes up with each lb of tire weight effectively incurring an additional 3/4 lb for its rotational effect. Or 1 to 1.75, 10 lbs rotating = 17.5 lbs sprung. I'm willing to go 1:2 even though I've found 1:1.5 to be frequently possible with realistic wheels and tires.

FWIW, in actual testing
http://www.hotrod.com/articles/light-vs-heavy-wheels-comparison/
finds 82 lbs lost from the wheels and tires (combined) to be worth 0.111 seconds in the 1/4. That corresponds to a 1:1.35 ratio based on the 100 lbs = 0.1 second rule of thumb if you scale the 82 lbs actually "lost" up to 100 (really not much of a stretch).


Norm

Im not talking about rotational weight, I’m talking about vertical movement. A wheel goes over a bump- a heavy wheel is more resistant to that change of direction-then the wheel has to rebound- a heavy wheel doesn’t want to quickly change direction.
Try this: fill your tires with water and drive it down a bumpy road, tell me if your car doesn’t feel like it’s much much heavier than it actually is. That’s the point. Rotational inertia is a different although related dynamic. I’m not talking about that as I pointed out more than once....
 

Norm Peterson

Corner Barstool Sitter
939
712
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
Let me think on that a bit (damped vibrations, and I probably have a spreadsheet I can use for that, too) . . . but in the meantime a 1:10 ratio doesn't make much sense for this either if you were to take 10 lbs away from a wheel and tire assembly that only weighs 55 lbs in the first place.

I was an engineer for far too long to forget about subjecting any "rule of thumb" to at least a quick and dirty sanity check.


Norm
 

Fabman

Dances with Racecars
6,518
8,154
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
Let me think on that a bit (damped vibrations, and I probably have a spreadsheet I can use for that, too) . . . but in the meantime a 1:10 ratio doesn't make much sense when you take 10 lbs away from a wheel and tire assembly that only weighs 55 lbs in the first place.

I was an engineer for far too long to forget about subjecting any "rule of thumb" to at least a quick and dirty sanity check.


Norm

1 pound of unsprung weight= 10 pounds of sprung weight. So a wheel that is 1 pound lighter x 4 wheels would make the car react as though it was 40 pounds lighter.


Sent from my iPad using Tapatalk
 

Mad Hatter

Gotta go Faster
5,237
4,227
Santiago, Chile
I am talking to Tim right now to get a set. Wondering is it worth it getting anodized or just painted? Is the extra $200 better spent towards more brake pads?? That and whether or not to go Girodiscs or just the GT500 clunker that last for ever..... Both together would pay for at least two pair of G-loc R18's
 

Mad Hatter

Gotta go Faster
5,237
4,227
Santiago, Chile
Normally I would not even ask, but Tim gave me the choice of painted black and anodized. More a speed first kind of person! But did not want any problems in the future either.......


upload_2018-2-23_20-47-54.png

This was the painted one. If it holds up to track abuse, thats fine by me.
 
Normally I would not even ask, but Tim gave me the choice of painted black and anodized. More a speed first kind of person! But did not want any problems in the future either.......


View attachment 3470

This was the painted one. If it holds up to track abuse, thats fine by me.

They will look good for a little while, depends how hot they get LOL. @PeteInCT is going to be running the Black units. We keep the anodized ones on the shelf but one of our other suppliers is trying to get some of our business so... gloss black less costly by a large margin for now. I have personally gotten the anodized ones very warm, as @captdistraction has. The anodize obviously holds up better. G-LOC's dust will not damage the finish of either.
 
https://www.opmustang.com/store/p16...on_Caliper_Brake_Upgrade_Package_-_FRONT.htmlrG1ZrCt.jpg
Website Updated! Re-ran some numbers and the Calipers are a $95 Option. Basically to keep it simple we just give you a coupon code if you opt for the Gloss Black Calipers and it saves you $95 from the prices on our site. Our Kits are now how everyone wanted them. We know the factory brake shields clear in most cases, you should be running brake cooling ducts anyway. They come with Calipers, Goodridge Hoses, Hardware, Pads (Compound Choices) and Rotors. Additionally you can upgrade to the Girodisc Two Piece Rotor. Lots of parts and it meets our free shipping limits so there's that.
 
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Mad Hatter

Gotta go Faster
5,237
4,227
Santiago, Chile
Steve, that was a great tip, Ordered 4 kits so far from Tim and hope to begin installing them next week. Since the S550's sold in Chile only came with 14" brakes and the S197 only have the stock brakes (if you can call them that...), We now have lots of cars lining up for the upgrade..... One is a V6 so.. hope the master cylinder can take it!?
 

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