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BGTV8 · 03-09-2013, 01:36 AM

At the risk of teaching my grandmother to suck eggs .....

When tracking your car and you return to the pits/marhalling area, it is imperative that you do not leave the car parked in one place for more that a few minutes. I carry a piece of 4x2" timber and put it behind a tyre so the car cannot roll away and every 2 minutes, I allow the car to roll so the wheel rotates ~90 degrees, and repeat the process every couple of minutes until the rotor has stabilised and cooled (hopefully more uniformly that simply walking away from the car having parked it).

The reason is to make sure that one spot on the rotor does not stay under the (red)-hot pad for longer than 2-3 minutes max, as this causes the rotor to cool disproportionaltely around its diameter and you will get hot spots which are being "heat-treated" (actually, to be specific, these spots are being annealed) and these spots will lose hardness and you get differences in friction capability around the swept annulus of the rotor which will feel like a pulse under your foot which is a bit disconcerting - but if you feel a shake in the steering - then you have warped rotors - and they need machining or replacing.

You may also have brake pad material deposited on the rotor as noted in this thread.

Slotted rotors will help avoid pad deposits, but even with a brake cooling kit (unless the air is supplied via a 4"/100mm tube) will not avoid the need to "rock" the car in the pits - it is a really good habit to get into (and one you can delegate to your GF - or BF - we are not gender specific on the forum I think - so make your partner feel included and important)

RB

03-09-2013, 01:36 AM	#6 (permalink)
BGTV8 A True Z Fanatic Join Date: Dec 2009 Location: 03350 Australia Posts: 1,514 Drives: 09 Nissan 370Z M6 Rep Power: 39973	At the risk of teaching my grandmother to suck eggs ..... When tracking your car and you return to the pits/marhalling area, it is imperative that you do not leave the car parked in one place for more that a few minutes. I carry a piece of 4x2" timber and put it behind a tyre so the car cannot roll away and every 2 minutes, I allow the car to roll so the wheel rotates ~90 degrees, and repeat the process every couple of minutes until the rotor has stabilised and cooled (hopefully more uniformly that simply walking away from the car having parked it). The reason is to make sure that one spot on the rotor does not stay under the (red)-hot pad for longer than 2-3 minutes max, as this causes the rotor to cool disproportionaltely around its diameter and you will get hot spots which are being "heat-treated" (actually, to be specific, these spots are being annealed) and these spots will lose hardness and you get differences in friction capability around the swept annulus of the rotor which will feel like a pulse under your foot which is a bit disconcerting - but if you feel a shake in the steering - then you have warped rotors - and they need machining or replacing. You may also have brake pad material deposited on the rotor as noted in this thread. Slotted rotors will help avoid pad deposits, but even with a brake cooling kit (unless the air is supplied via a 4"/100mm tube) will not avoid the need to "rock" the car in the pits - it is a really good habit to get into (and one you can delegate to your GF - or BF - we are not gender specific on the forum I think - so make your partner feel included and important) RB Last edited by BGTV8; 03-09-2013 at 01:39 AM.