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Do I need bigger rotors?


turbogrill
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Hi,

 

All big brake kits for my car uses a larger rotor than stock. Curious if this is really necessary.

 

The stock vented front rotor is 252mm (close to 10") and 20mm thick.  Car is a 280zx and weighs about 2700 lbs with driver, gas and everything.

 

The kits uses everything from 7% to 30% larger diameter rotors. I am very tempted to buy a wilwood Dynapro/Dynalite and fab a bracket for our 9.9" rotor.

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28 minutes ago, theamsoilguy said:

Take temps of the rotors immediately when coming off the track. Get some data and it will help. Do you use brake ducts? I run 13 inch rotors on my 3000lb car. And we still warped them twice ( one of our drivers causes it ). The pad you use changes things a lot also....

 

We have had very little issues with the rotors. They seem to hold up fine. But we are mid pack team with a low hp car.

However we are getting better and have a more hp engine now, maybe this will put more stress on the rotors.

 

How does the pad relate to this? Do I need to make sure the pad can cope with the high temps? We use good race pads, I assume they can take the heat :)

 

 

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Pad/disc temps and wear rates, along with brake balance/feel, are mostly what dictates what to change/upgrade in your brake system.  If you're wear rates/temps are not excessive and the brake balance is good, then going to a larger disc is just adding unnecessary [unsprung] weight.  I'd see how they hold up with the new power and better drivers before making changes.

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3 minutes ago, Bremsen said:

Pad/disc temps and wear rates, along with brake balance/feel, are mostly what dictates what to change/upgrade in your brake system.  If you're wear rates/temps are not excessive and the brake balance is good, then going to a larger disc is just adding unnecessary [unsprung] weight.  I'd see how they hold up with the new power and better drivers before making changes.

 

Biggest reason I want to change to wilwood is to get something better quality and maybe a little better brake feeling.

Stopping power is ok I think.

 

I think I will try and fab a bracket with stock rotor sizes.

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6 hours ago, turbogrill said:

 

Biggest reason I want to change to wilwood is to get something better quality and maybe a little better brake feeling.

Stopping power is ok I think.

 

I think I will try and fab a bracket with stock rotor sizes.

 

Brake effort or feeling is a function of pedal pivot ratio, master cylinder diameter, caliper piston diameter, pad compound, pad area, and rotor diameter.  What part of the feeling are you looking to improve?

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48 minutes ago, Ron_e said:

 

Brake effort or feeling is a function of pedal pivot ratio, master cylinder diameter, caliper piston diameter, pad compound, pad area, and rotor diameter.  What part of the feeling are you looking to improve?

 

The braking so not even, it gets a bit unstable during braking and pulls to the left. (My DE brakes much better more balanced on stock pads)

 

Another canidate could be the cut progressive springs, so maybe once side has stiffer springs

 

 

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1 minute ago, turbogrill said:

 

The braking so not even, it gets a bit unstable during braking and pulls to the left. (My DE brakes much better more balanced on stock pads)

 

Another canidate could be the cut progressive springs, so maybe once side has stiffer springs

 

 

 

Absolutely, put on some proper springs then corner balance.  Before we knew about corner balancing we would fight the steering wheel under hard braking, once balanced it was like we didn't even need to have a hand on the steering wheel when braking anymore.  The confidence factor went up dramatically and so did the ability to run it right on the track edge.

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16 minutes ago, Ron_e said:

 

  The confidence factor went up dramatically and so did the ability to run it right on the track edge.

 

This is spot on. Our car is very easy to drive fast for beginners, if we can get the braking stable it's going to be fast!

Will investigate! Thanks

 

(The car is very forgiving, when the car is perpendicular to the track you lift your right foot and turn the steering wheel. However braking is more of an adventure)

 

 

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11 hours ago, turbogrill said:

 

The braking so not even, it gets a bit unstable during braking and pulls to the left. (My DE brakes much better more balanced on stock pads)

 

Another canidate could be the cut progressive springs, so maybe once side has stiffer springs

 

 

 

Might check the alignment and make sure nothing on the suspension is out of whack, too.

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At that weight, I'd be worried that the small rotor doesn't have the mass to handle the heat of a brake heavy track like Road America.

 

We have 280 mm rotors, and consistently see 800* F rotor temps, and full of fuel, fatest driver the car maybe hits 2650 lbs.. I would not want to go smaller, and may be going larger, even though the car is getting lighter.

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We ran 11" on our 2650 lb Mustang, add 300 lb driver on to that.  It worked fine but when we went to 13" we saw significantly longer rotor and pad life.  An 11" would go one weekend only while the 13" goes close to or does two weekends.

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3 hours ago, Ron_e said:

We ran 11" on our 2650 lb Mustang, add 300 lb driver on to that.  It worked fine but when we went to 13" we saw significantly longer rotor and pad life.  An 11" would go one weekend only while the 13" goes close to or does two weekends.

 

Exactly.  Generally As brake temps go up, pad life goes down.

 

sure race pads "can" work at 1800*, but they're usually a lot happier at 600-800.  For the pads most of us are using anyway.

 

larger rotors don't just allow more brake torque, they also have more heat mass, and greater cooling abilities due to increased surface area, and increased air speed.

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 For brake darting issues; Make sure that the mounts for the drag struts are sound. 

The wheel bearings are tight and the same both sides.   Put the car on the lift and take a rachet strap to each front wheel and pull it rearward . Watching stuff move. 

 Repeat with the rear wheels. Those cars are really soft  and the mounts move a lot. 

 If you cant find anything chassis wise.  Push all of the caliper  pistons back and look for stuck pistons and hoses.  If all good add some "noise  reducing shims" behind the pad that locks up the most. The shims will reduce the initial pressure a wee bit ,reducing the lock up.  Last  runs a medium torque pad.  if you  have Hawk Blue, try HPS.  

 FWIW, on my Z  I took the 13s off and ran the 12 to reduce the front lockup.  Now ,on the truck I run 12 X4 .

Edited by flyinglizard
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Depending on the rims you are running too....I would certainly suggest you should entertain larger rotors or much thicker rotors.  Exactly correct as previously stated about rotor mass. A 15" rim can fit a 11.75" and a wilwood/like caliper , and depending on the rim you may be able to stuff in up to a 12.19" diameter rotor.  These rotors are typically offered in 0.81" (20.6mm) thickness.

 

I ran 11.75" x 1.25" front rotors on my other car (sprint races).  But I could run 2-3 seasons on a set of rotors and pads (typically Carbotech xp20).  The extra mass and improved ability to absorb the energy (heat) and dispense of it made the brakes the best part of that car.  Too bad it had a live axle...

 

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