How thin is too thin?

[ALdad]

by ALdad 06 » Sun Mar 21, 2010 7:38 pm

 

The pads on my 2000 sport need replacing. Rotors are about 3.4-3.5mm. What risks or issues am I taking in running one more set of pads maybe about 15k miles? I commute daily the bike stops just fine. But the pads are really thin. Will one more set of pads 15kmi. I am guessing will shave another .2 or .3 mm off rotors. Tell me if I am stupid in pushing it .

[docc]

The wear limit on the rotors is 3.9mm.

 

I'm thinking you've already "pushed it."

[raz]

For minimum thickness, trust the stamped figures on the rotors above anything else. I got brand new OEM rotors that was thinner than the WHB minimum! Their stamped figure was way lower too of course, so no problem.

[docc]

I looked for the stamping on my old rotors, but didn't find any. The 3.9mm figure is from the shop manual.

 

The full thickness is apparently only 4.1mm!

[ALdad]

How many of you have actually measured your rotors? The manual says replace at 3.9, that’s .2 mm wear from new. .2mm is 2 sheets of paper. Could someone tell me how this small amount could make a difference in performance or safety? I am sure there is a reason. I would sure like to know. The bike has 34k mi. this is the second set of pads. The first were stock and the last ones were the Kevlar organic. I commute stop and go traffic and I hardly use any rear brake so I would assume the wear is normal. I don’t have a problem replacing the rotors, other than I am a cheap bastard. But I would like to know what the issues are with thinning discs from one who really knows brakes. I am guessing thin rotors are more susceptible to warping and eventually the calipers won’t grab, but .2mm, please. I have the same thoughts with our car when I am told I need new rotors every time it goes in for brakes

[docc]

My worn front rotors were 0.138" (3.5mm) after 45, 608 miles and the replacements (take-offs from an 1100 Sport) are 0.153" (3.9mm) after 24,373 miles.

 

Jeez, I need brakes again?

[Greg Field]

There are two issues:

 

1) Rotors that are two thin can break. I doubt this would happen at the thicknesses you describe.

 

2) The thinner the rotors, the farther extended the caliper pucks are. If they extend too far, too little puck shoulder is left inside the caliper, so the pucks can start to cock and then wear the caliper bores unevenly or even jam. As your rotors wear thin, it's a good idea to replace the pads often, to maximize the amount of puck left in the bore. You could also make shims for the back side of the pads to do the same thing.

[Dan M]

I wouldn't worry too much. <.5mm is not going to be of much consequence. if they are true i don think you will have any issue with strength warping or caliper pistons too far out their bores.>

[ALdad]

Thanx, I am going to replace rotors and pads. Any recomendation on better than stock?

[gstallons]

Clean the rotor mounting surfaces prior to installation. When you install these rotors be SURE to tighten them in a criss-cross pattern and torque them to the proper value while doing this.

[guzzimeister]

Hi

 

I worked in the brake industry for a few years (Continental Teves) and for waht it's worth:

1) my rotors are stamped min thickness of 3.2mm

2) major issue in taking rotors MUCH below this is warping, and in EXTREME cases cracking. In 30 years I have only seen one cracked rotor and that was on a hat type rotor on a car which had done 90k miles. I wouldn't worry about taking rotors to 0.1 - 0.2 below min thickness, but after that the risks go up sharply

3) if you are unlucky enough to pop one of your caliper pistons out, you will notice it is about 3/4 as high as its diameter. I used to test disc brakes to destruction and because of this area of spport I never had one cock and jam. They used to jam because of overheating damaging the hard chrome finish, dust build up, and because the pad itself would work a groove into the caliper body. This is with the rotor glowing orange........

 

My view is that if you are an aggressive rider, expect to change your rotors at 40k, much as you would a car. If you don't ride on the brakes you might get to 60k. If at any time you notice brake performance deteriorating, the common sense thing to do is check rotor and caliper. If either look iffy, repair/replace. Biggest issue with worn rotors is that getting the caliper off over the lip at the edge can be difficult - all brake system components are designed with massive safety margins as product liability legislation can kill even the biggest, ask Brembo US Inc.

 

Sorry to preach, hope it's useful.

 

Cheers

 

Guzzimeister

[ALdad]

Hi

 

I worked in the brake industry for a few years (Continental Teves) and for waht it's worth:

1) my rotors are stamped min thickness of 3.2mm

2) major issue in taking rotors MUCH below this is warping, and in EXTREME cases cracking. In 30 years I have only seen one cracked rotor and that was on a hat type rotor on a car which had done 90k miles. I wouldn't worry about taking rotors to 0.1 - 0.2 below min thickness, but after that the risks go up sharply

3) if you are unlucky enough to pop one of your caliper pistons out, you will notice it is about 3/4 as high as its diameter. I used to test disc brakes to destruction and because of this area of spport I never had one cock and jam. They used to jam because of overheating damaging the hard chrome finish, dust build up, and because the pad itself would work a groove into the caliper body. This is with the rotor glowing orange........

 

My view is that if you are an aggressive rider, expect to change your rotors at 40k, much as you would a car. If you don't ride on the brakes you might get to 60k. If at any time you notice brake performance deteriorating, the common sense thing to do is check rotor and caliper. If either look iffy, repair/replace. Biggest issue with worn rotors is that getting the caliper off over the lip at the edge can be difficult - all brake system components are designed with massive safety margins as product liability legislation can kill even the biggest, ask Brembo US Inc.

 

Sorry to preach, hope it's useful.

 

Cheers

 

Guzzimeister

Thank you, I love common sense answers!

[docc]

I looked much, much more closely and found the stamping on my 2000 Sport front rotors:

 

" MIN. TH. 3.6MM "

 

I still can find no stamping on the 1100 Sport take-offs that are on the bike now. Surely, it must be there somewhere . . .