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Cracking rotors at Trackdays


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So, for the second consecutive trackday ive managed to crack a rotor. They were new about a year ago, OEM type ones from Subtech. Original pads were bendix ultimates, just swapped to pagid RS-29 ones. I was braking pretty heavily, sometimes activating abs i guess which probably didnt help things either.

Anything I can do to help stop this happening in future? Less aggressive on brakes is an option I guess, but a bit hard to do when trackday adrenaline kicks in. Ill look at removing the ABS fuse as well.

Ducting?

Proper aftermarket rotors?

???

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whats the car, its weight, the track, weather conditions, your overall treatment of braking application, power, current brakres installed..

What do you define as less aggressive? often its the opposite, more aggressive cracks less... think about it and let me know what you think.

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Hampton downs: maybe high teen degrees air temp, dry, main straight braking from 200kph

Taupo: similar conditions/braking I guess.

Cars stock, 1300kg version 6 sti? Brakes are stock 4 pots with pagid rs-29 pads. RE11 road tyres. Taupo only really has the 3 main braking zones I guess which are in a straight line, so braking heavily for 50-75m then turn into corners.

This time as well i made sure to rotate the wheels a bit when parked up every so often to rotate the heat. Did a cool down lap after each stint barely using brakes.

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on road tires i dont see you getting to the cracking point, even at factory weight.

do you have an unrestricted front air dam area?

some times people think that being softer on brakes = better.. the nana them but sit on them for longer .. this often cooks them more.

get on them hard, slow down, and get off them. = better technique imo.

potentially your 294mm rotors might have heat soaked to much and could do with larger ones but thats working around the problem.

maybe those pads are causing it too. could also be bad luck - ive never cracked one yet, pushing more power, but on brembos, but we\'ve never run ducting yet #touchwood.

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Yeah im on the brakes as hard as I can be tbh, to the point of the abs sometimes coming on a bit. The front end of the car is all stock, so i dont know how good that is for airflow. Cracked a rotor with both the pagids and bendix ultimates.

Sigh, maybe its time to do a bembros upgrade....

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 AdamOst said:

Yeah im on the brakes as hard as I can be tbh, to the point of the abs sometimes coming on a bit. The front end of the car is all stock, so i dont know how good that is for airflow. Cracked a rotor with both the pagids and bendix ultimates.

Sigh, maybe its time to do a bembros upgrade....

i dont think you should need to honestly. are you rotors going a gross blue color before cracking? are you getting pad material left on the rotors?

also what fluid are you running.?

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i\'ve been through this exercise with a fairly stock sti.

i don\'t think there is a one-size-fits-all remedy. this is what i\'ve tried anyway, i still ruin the 4pot/1pot setup with bendix ultimates over a trackday but no major failures recently.

-pay extra attention to warming them up on the outlap, and cooling them on the inlap. ie. not using the brakes AT ALL to allow an airgap between pads and rotors in the pits. some pit entries are interesting to coast into, but i just nudge the handbrake if needed

-whilst in pits, i push the car to help cool the rotors evenly

-made sure front wheel bearings are good. ruined many many rotors until i sorted this. 2nd hand hubs are asking for failure, i pressed in genuine new bearings

-adjusted my braking style. i tend to brake about 80% of the available brake... this doesn\'t mean i don\'t brake hard, but as the car slows into corner entry i just dont brake harder while everything is red hot. (at that point there is more braking available just dont use it) i brake a little earlier to compensate. its a bit weird as people say i do brake late?

-loose all the extra car weight possible

-bring extra rotors :)

have managed a dozen spirited laps of manfield at good pace. ran out of fuel and stamina before the brakes gave up

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 kamineko said:

i\'ve been through this exercise with a fairly stock sti.

i don\'t think there is a one-size-fits-all remedy. this is what i\'ve tried anyway, i still ruin the 4pot/1pot setup with bendix ultimates over a trackday but no major failures recently.

-pay extra attention to warming them up on the outlap, and cooling them on the inlap. ie. not using the brakes AT ALL to allow an airgap between pads and rotors in the pits. some pit entries are interesting to coast into, but i just nudge the handbrake if needed

-whilst in pits, i push the car to help cool the rotors evenly

-made sure front wheel bearings are good. ruined many many rotors until i sorted this. 2nd hand hubs are asking for failure, i pressed in genuine new bearings

-adjusted my braking style. i tend to brake about 80% of the available brake... this doesn\'t mean i don\'t brake hard, but as the car slows into corner entry i just dont brake harder while everything is red hot. (at that point there is more braking available just dont use it) i brake a little earlier to compensate. its a bit weird as people say i do brake late?

-loose all the extra car weight possible

-bring extra rotors :)

have managed a dozen spirited laps of manfield at good pace. ran out of fuel and stamina before the brakes gave up

Did most of that really :( Might have gone a bit rough on the outlap on one of my stints. I now have a spare for future issues, was only 75$ each fomr partmaster. Thankfully Taupo had some in stock so I flicked the old one off, put the new one on, did a few shakedown laps to bed it in and off i went again.

My final session at taupo was 13 laps, with a big off but had no real problems with fade or anything. Same the first time i went to hampton downs

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"This time as well i made sure to rotate the wheels a bit when parked up every so often to rotate the heat. Did a cool down lap after each stint barely using brakes."

What does rotate the wheel a bit mean?..how often? how many turns? and for how long?..IMHO this is probably where they are cracking from.

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noticed the first one on the drive home, it was a bit wobbly in the steering wheel under braking but i thought ti was just the pads being low. Went to drive ot work the next day and it felt like a wheel was loose so checked them all and saw the crack. This time i noticed it when i went to swap the marshalls around the track. So both times its been after hot laps, not during.

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Have you looked into the sloted discs on t.m?

No info on how those would crack tho,iv seem discs red hot and no cracking

Almost as if the breaks were that hot and got cold water on them id say somthing like that could be possible?interesting to see the outcome

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  • General Member

Being after laps not during would make me think it might be a problem with our warm down process. I know its mentioned above but in the pits no handbrake and pushing the car forward and back seems fairly effective.

Do some reading into slotted, dotted etc. but seems to be a strong school of that that they arent much help and crack easier. I\'m considering a slotted set to replace my cracked one I have on the front currently.

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I wonder if it\'s just because you\'re doing 10+ laps at a time and your rotors aren\'t handling the strain of this. Becoming weakened and brittle so they crack once cooled/while cooling down. There\'s a lot of difference between doing spirited road driving and doing 200km->60km hard braking over and over again

I\'ve done ~6 trackdays, 1 with two pots, two with 4-pots and three with brembos and have never cracked a rotor, but I only do 5 laps per session generally.

Ducting as previously suggested is probably your best bet

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What Rob said is pretty much the cause 90% of the time when people take their road cars to track days. They stay out there for a whole session beating on the car. Generally this is more laps than an actual sprint race!

While having good pads and fluid certainly helps, there just isnt enough capacity in those rotors to take the prolonged heat generated lap after lap.

Add some brake ducting to help, or just dont do as many laps per session.

If you want to build some really effective ducts, you need to seal the back of the rotor off so that all the air you are forcing in goes to the centre of the hat, so it can be forced out the vanes and provide even cooling. I dont know if you want to go this far or not, but it is the best way to keep the discs cool... here is how I did mine:

Bumpsteer1.jpg

Its a lot easier to do this on Subarus as their front caliper is in the trailing position rather than leading. Just have to be careful when running the duct hose, as on the drivers side, it will be very close to the headers and can get burnt/damaged easily.

Fixed :)

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Might be the long stint, though i did a 13 lap stint at the end of the first trackday I went to at HD, then did an entire trackday with no issues at taupo, then did another TD at HD and did 3 normal stints, and felt the crack driving home again, then 8 months later did this trackday at taupo and felt it after my first session. These sessions are usually 1 warmup, 5 flying, 1 cooldown.

I never leave the handbrake on and always do a warm down lap at least not really using brakes. Generally my warmup lap is mostly tame, though once or twice I did go a bit hard I guess, dude to there only being a 20min gap since the last session. Ill try make more use of the warmup lap then, and for any long distance stints at the end of the day maybe take a slow lap or two in the middle.

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