Questions:

1) For auto-x is it better (more efficent & good enough) to go with the lightest rotor/pad combo and spend money highend pads (carbotech, cobalt)?


2) The difference between ITR calipers, 11.1" rotors & HF calipers/9" rotors is 28 LBS
How much does that matter on the track in terms of performance?


To keep it simple for arugment sate...lets ssuming the car:
2200-2500 lbs
under 250 whp

I know that the caliper is no considered to be "rotoating mass" but still mass non the less.



FACTS:


Weight for PAIR "Loaded Calipers" :
ITR = 28 lbs
GSR/EX = 18 lbs
DX/LX = 15 lbs
HF = 13 lbs
*note all are different in pad suraface area & piston size



Weight for PAIR of front rotors:
Prelude 11.1" rotors = 27 lbs
GSR/EX 10.3" rotors = 22 lbs
DX/LX 9.4" rotors = 20 lbs
HF 9" rotors = 14 lbs



Weight of front calipers & rotors:
ITR calipers + 11.1" = 55 lbs
GSR calipers + 10.3" = 40 lbs
DX/LX calipers + 9.4" = 35 lbs
HF calipers + 9" = 27 lbs
ITR calipers + 10.3" =50lbs *hybrid combo



..... Thoughts?

 

Keep it light for autox!!!!!! All brake are, are heat sinks and you will not build enough heat in a 60 sec run to need a larger rotor. If you can lock them up with smaller brakes.... big wont be better. Just make sure you are using a more agressive ft pad. I have a CRX that is CSP prepped and I can lock up V710's all over the place with stock brakes if I'm not carfull. And becuase weigh is important I'll be replacing my ITR brakes on my H2 car with Spoon janks as soon as I can get my hand on a set.

 

That's my thoughts exactly but just wanted to know for sure.

In that case would 9" HF rotors be optimal (granted I'm using a much more aggressive pad)

 

Yup!!

 

there is an even smaller option that we used on our autox car...the 1st gen CRX stuff is TINY.

 

Don't forget the aluminum rear drums. Not sure how much weight they save though.

Edit: For 2.) The tiny brakes will be destroyed on a big track, so performance is...finishing the session/race vs. not. The brakes are sort of enough for a stock-motor car (IT cars are doing it), but for anything else they just aren't enough.

 

1986-87 CRX HF rear drums (aluminum body with iron braking surface/liner) are 4 lbs each versus the all steel version from the other models at 7 lbs each.

 

I did the HP loss calculations a few days ago. Please understand this is only an estimate. The only way I can get a more accurate number is if someone wants to cut their rotor into three pieces and weigh them for me, I have to pretend the rotor is a uniform disc.

0-90 mph in 15.5s:
ITR Rotor 11.1" 14lbs: 38.57Watts - 0.0517HP
LS Rotor 10" 12lbs: 27.38Watts - 0.0367HP

These numbers are per rotor, so it would be double those numbers per axle.

Also, just for fun I put in the 1/4 mile time for my brother's cavalier (12.2 @ 124 mph) and for the ITR Rotors it worked out to 93 watts or 0.1245 HP and for he LS Rotors it was 66.011 Watts or 0.08849 HP.

However, the moment of inertia for the rotors are not 100% Accurate. Brake rotors have most of their mass on the outer part, but I don't have enough data about the rotors to accurately model that it. Therefore I used the moment of inertia calculation for a uniform disc.

All calculations were done with a tire size of 205/50-15 as well. With a larger tire, the hp loss due to the rotor would be less. (HP loss due to the tire would increase.)

Also, this is based on average HP over an entire 1/4 Mile run.

 

Interesting calculation d1ck. I remember one from years ago about unsprung weight, where Xlbs of unsprung weight (calipers, rotors, wheel, etc.) = Ylbs of sprung weight, and Y would be a higher number. Basically, it would be equivalent to taking out so much weight from the interior or whatever, and basing speeds/times off that. The hp angle is a new one though

 

i have seen a HF with a D16A6 not have enough brakes even in a short 60 sec course.

ymmv.

 

what do you mean "not enough" brakes?.... pad surface area too small or did the guy have on stock pads?

I couldn't image that there would be that much big difference between 9.0" & 9.4"

it's not like going from 9.4" civic to 10.3" gsr setup....

 

I'd also be surprised at that, knowing that some ~200hp SM cars have used the lesser base-model Integra brakes just fine with the right pad selection (which would be sort of equivalent to the comparison above).

 

yes, the pads were too small.

ymmv

 

great post OP! have you hardcore ax'er found brake ducting to be worth while on ax? i would imagine true even on a short course... can't hurt right?

 

some people run non-vented disks upfront, basically what is normally a rear setup on the front. they claim the unsprung weight saving is more important for autox, but where we race there is very little braking involved, so i would have to agree. this annoys the hell out of me because i run rsx-s brakes all around lol, but on the street or road course nothing compares to massive brakes on a light car

the majority of autox courses are too short and there is too much wait time between runs to really worry about heat soaking the braking system. that being said because speeds are relatively low the small hit you take to aero is mostly negligible.

 

well this is an interesting ghost bump.... one the same exact day, but 2 years later.....

 

IMO if you can't lock your tires you don't have enough braking power. But you shouldn't be able to lock your tires instantly or easily. I really don't think 15lbs is substantial in brakes because most of that is caliper weight and not rotating. Also the benefits far exceed the minimal weight increase.

 

I can tell you that running a lighter caliper does make a big difference. The steering feel is lighter and makes it feel more effortless. That was actually the first thing I noticed after installing aluminum calipers.

 

Rotating unprung weight (rotors) is by far the best place to lose weight in a car. Static unsprung weight (calipers) is the second best place to lose it.

As small as you can go whilst being able to comfortably lock the brakes and have them not fade on you is the way to go. I swapped back from 11.1" to 10.3" rotors as the bigger ones made the car worse in a variety of ways.

 

Easiest place to shave weight... I agree. It's also the most expensive place. 2 piece rotors and forged billet calipers are incredibly high in price. Take Spoon calipers for example, they use the same pads as an ITR caliper but are 5 times the price of brand new ITR calipers from Honda. Better stopping power? No, simply lighter weight and maybe better modulation. 2 piece rotors now initial cost is high because of the hat but replacement rotors are about the same. I like the Wilwood brake kits but I do think they are a waste for gaining more stopping power over a 11.1 or 11.8 OEM brake upgrade. Brembo, Stoptech, AP Racing... those will put you through the windshield if your tires can handle them.