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I looked on the internet and couldn't find a direct answer. I have a car and i was told i new new rotors because the rear-driver side couldn't be turn down enough to remove the pits/lands to make it smooth without going below minimum specification of thickness.

Without going into details, the rear rotors (both have been turned) but the one with the most damage was turned down more reducing the thickness. Can the car brake evenly with different thickness rotors?? Wouldn't it cause unequal balance in braking pressure?

My thought is (mine you hypothetical numbers) if the braking hydrualtics is equal on both sides say 35psi. And the rotors are different thicknesses, wouldn't the brake pads/caliber have different travel times? That being the case, I would think 35psi on both sides would be inadequate, because, the amount of force needed to stop (push the brake pads against the rotor) would be different. One may need 45psi vs 35psi to exert the same amount of force against the rotor?

I'm sure something is flaw in my [b]concept[/b] thinking here but would this be true? I'm not a mechanic or a auto technician. But can someone give me their thoughts on why concept of thinking here. Please ignore the idea of braking with below minimum specs. I'm only asking about a certain question.

Thanks y'all!

  • Welcome to Motor Vehicle Maintenance & Repair! I'm going to let someone answer this mathematically, but there are three forces at play here: the diameter of the caliper piston; amount of hydraulic force; contact area of the friction material on the rotor. The thickness of the rotor should not affect the braking force. Nothing about the thickness of the rotor affects any of the factors involved. There is going to be slightly less mass, which affects cooling, but there should theoretically be no difference in the amount of stopping power. – Pᴀᴜʟsᴛᴇʀ2 Jul 10 '18 at 23:36
  • PS: This is a great question! – Pᴀᴜʟsᴛᴇʀ2 Jul 10 '18 at 23:36
  • Thanks. I can get the other forces and thinking about it, and i admit, i might have a flaw in my logic. I would think the reduce thickness would affect response time which would affect the amount force needed. But i think am wrong about force needed. It would be the same Reckon question more about the quickness, how it affects braking. I hear that rotors should be done in pairs so reckon that where i err? Why would they need to be the same if thickness doesn't matter?? – deskmonkey Jul 10 '18 at 23:59
  • Because of caliper design, the brake pads will sit off the rotors the same amount no matter the thickness of the rotor itself. – Pᴀᴜʟsᴛᴇʀ2 Jul 11 '18 at 0:13
  • They are? Then thickness doesn't matter, but it does for the caliber piston. Like i did read, it could cause hydraulic problems -- piston pushes too far out. I will mark this as solve. That answer is satisfactory for me.Thank you very much. – deskmonkey Jul 11 '18 at 0:51
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Yes, rotors can be different thicknesses, as long as the active friction area is the same And they are above the minimum thickness.

It is customary to fit new rotors in pairs when both are worn significantly and one is below the limit - new rotors and pads tend not to have brake balance problems after...

One way you give yourself brake imbalance issues is to fit new pads to one side or a new rotor with old pads etc etc

We did have a car (that was sold new) that when it came in for some brake work it was noticed that the driver’s side had a vented front disc and caliper and the passenger side a solid disc - same diameter so no brake imbalance... At the time, vented discs were for “sport versions...” It was a factory build mistake : a “Friday” car...

Edit: as for pressure in the brake system you should take a ball-park figure of some 1200psi... but this does vary as to the system...

  • OT: a “Friday” car... - Funny, here in Germany it´s call Mondays car. Where is this phrase from? – Daniel Jul 11 '18 at 10:12
  • @Daniel not sure - one of those colloquialisms that colour the language we use everyday, but there may be some statistics which show a higher error rate for products built on certain days... That could be an interesting research topic... – Solar Mike Jul 11 '18 at 10:37
  • OH I´m sorry, I mean in which cultural pretext is this used/ are you from? American? UK? – Daniel Jul 11 '18 at 10:47
  • @Daniel oh English as in Man of Kent, but you won't have heard that one either... :) – Solar Mike Jul 11 '18 at 10:54
  • No, I haven´t - but Wikipedia suggests "born east of the Medway" :) Sounds like the English are so eager to get wasted they can´t be bothered with good work on Fridays, whereas the Germans start a little bit later but then still have a hangover on Mondays ... ;) – Daniel Jul 11 '18 at 11:01

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