Should brake pads cover the entire surface area of the rotor?

[drtruong]

Hello primer

Should the rotor be covered the entire surface with brake pads, or is it normal to have some gap in the inner side of the rotor? Or are the brake pads are small for the rotors

The brake pad is applied and as you can see the pad does not cover the whole surface of the rotor, maybe several mm off?




This is the old one that has rusty line on inner ring

 

[Old Guy]

Personally, I would not sweat it. From the disc wear pattern on my OEM rotors and pads I am pretty sure that there is a gap from the bottom of the pad to the small radius of the braking surface. The force applied closer to the center of the hub is less important than the force at the outside radius. That is why larger diameter disks generate more retarding torque even with the same caliper and pad size.

What you definitely do not want is the pad overhanging the outside radius of the brake rotor. That would create some potential problems after a little pad wear sets in.

 

[esqu1re]

I think most, if not all, of the cars I own have that small gap.

 

[drtruong]

Thank you and you have made me feel better. Still don't understand why would not they cover the entire surface of the rotor and would not it brake better since it would have a larger surface area?

 

[Old Guy]

More pad surface area may have some benefit once you get into heat management problems (repeated heavy braking on the race track). However, the usual path to greater pad surface area is the mungo 6 or 8 puck calipers, although on most cars that is more show than actual function. In terms of the retarding torque that the caliper can generate that is more a function of the effective radius of the pad / caliper, the pressure generated by the hydraulics and pad-disk coefficient of friction. Fractionally increasing the pad area would have little to no effect on maximum retarding torque.

When Prime still had the Wiki there was an extended discussion of brake system performance and options for the NSX. The Wiki and the info is gone from the current version of Prime; but, if you use the Wayback machine (internet archive) you might be able to find an Archived version of NSX Prime from more than 5 years ago which still had the Wiki with the discussion of brake system performance.

 

[drtruong]

More pad surface area may have some benefit once you get into heat management problems (repeated heavy braking on the race track). However, the usual path to greater pad surface area is the mungo 6 or 8 puck calipers, although on most cars that is more show than actual function. In terms of the retarding torque that the caliper can generate that is more a function of the effective radius of the pad / caliper, the pressure generated by the hydraulics and pad-disk coefficient of friction. Fractionally increasing the pad area would have little to no effect on maximum retarding torque.

When Prime still had the Wiki there was an extended discussion of brake system performance and options for the NSX. The Wiki and the info is gone from the current version of Prime; but, if you use the Wayback machine (internet archive) you might be able to find an Archived version of NSX Prime from more than 5 years ago which still had the Wiki with the discussion of brake system performance.

Many thanks