Planning to start a trip on Friday I put a new tyre on a front wheel (same casting reference as the one I took off) I had acquired as my rotors were down to 3.5 mm.

The pads are now binding against the rotor. On inspection I saw that the pads are resting against the outer of the two concentric rings on the rotor.



The ring outside the ones that house the rivets.

The bottom edge of the pads are just caught by the ring, creating a shallow crescent of contact.



This outer ring is c. 10mm wide where it is proud of the rotor. My old rotors show a trace of this ring and the outer circumference is burnished and worn down so that only about 5mm width remains proud.

The contact area of the rotor is just a touch under 5mm thick. This is obviously only a slightly used pair of rotors (possibly even from the K1100 - which I understand is thicker). All the rotor measurements seem otherwise the same as the ones I swapped out (Outer diameter, circumference to rain slot start, rain slot bottom to centre.

Is this ring that is making contact with the pads normal for a newish rotor and expected to just wear in during use. 

Haven’t tested yet as still flushing the brake lines.

Small bit confused.


You put on a tyre, but seem to be also saying its a different wheel and different rotors.

Assuming you only put a tyre on then check the spacers are correctly located. Also on a regular K front end you do axle bolt up hand tight, then bounce the front end to settle everything, then torque of the axle and then the pinch bolts in that order. Calipers need off to get the wheel in and out.

Those rotors are K100 rotors too, not K1100.

Did you change the pads too? If the rotors are off another bike then you should replace the pads too.

Yup Olaf, New tyre on a different wheel and rotors (both used). Even tho its on leading links, I’ve bounced the whole setup before tightening the pinch bolts. What seems to be at issue is the pad length (from its fixed position in the fixed position calipers) allows it to traverse that raised ring above the rivet circle by a couple of mm.

I’ve also looked at the pics of the oem rotors at motorworks, and they don’t seem to have that outer band (although it should be clear in my pics and exists on the ones I have just swapped out albeit worn) change of spec maybe.

15 mile test - rotors warm to the touch after 3 - hot after 8. Calipers off again tomorrow to seek anymore clearance.

Measure the old discs Stu. As someone said (above?), they're probably slightly different diameters. If that's the case and you have no adjustment in the caliper positions, you're going to have to join my club. In the past, when fitting new pads to almost dead discs, I've had similar problems so I just took a long trip out and kept applying the brakes gently until they took up the shape of the disc. Yes... reduced pad life, I know, because you have one area slightly thinner than the rest.

The other thought is that latewr (post '86) pads are a different size to their predecessors, but I think that only applies to length, not height. Maybe.

Dai wrote:Measure the old discs Stu. As someone said (above?), they're probably slightly different diameters. If that's the case and you have no adjustment in the caliper positions, you're going to have to join my club. In the past, when fitting new pads to almost dead discs, I've had similar problems so I just took a long trip out and kept applying the brakes gently until they took up the shape of the disc. Yes... reduced pad life, I know, because you have one area slightly thinner than the rest.

The other thought is that latewr (post '86) pads are a different size to their predecessors, but I think that only applies to length, not height. Maybe.

Post 86 are 2mm bigger to not fit the earlier calipers. I think that's due to sintered pads.

I have Ks that use both earlier and later pads and have both types of pads but not near my shed at the moment to measure them. But I can say the bigger ones do NOT fit the earlier calipers, having tried it.

If you have later discs they may differ as to ABS/non ABS and that may be the cause of your problem, if that wheel came off a K100LT ABS. Shoulder on your replacement rim is the later one from I think some time 89/91, its flat, early is concave. Just possible there's a slightly different configuration as the forks changed.

I don't entirely trust the casting references already having cast K parts that are so clearly different stamped using the same numbers.

Maybe put your replacement discs on the old wheel to see if it solves the problem? Just try it without the the tyre.

Cheers Dai, took the pads out after yesterday’s run and the the elipse worn by the ridge  was already apparent (about 2mm at its widest point from the bottom of the pad). Took a dremel to the pad edge this a.m. to simulate your technique.   I guess Clymer just forgot to document it.

PS you are right on the pad size changes.

And thanks too Olaf, only just seen your post. That’s interesting. 
Can’t believe I didn’t spot the different rim profile! Which reinforces your point about the casting number.

tinyspuds wrote:And thanks too Olaf, only just seen your post. That’s interesting. 
Can’t believe I didn’t spot the different rim profile! Which reinforces your point about the casting number.

I am not sure if it makes a difference.

I have both types and have put the later rims on the older K but only on the rear. I haven't done a front change but all my front 'concave rim' ones are in non bridge forks, the K100LT has the later flat shoulder rims AND the fork bridge so there is potential for a slight difference.

You probably should check your the bearings are correct/correctly seated because they determine the spacing from caliper to caliper and if incorrect force the calipers off centre on the disc. I did a heel change on my RS but the replacements are also concave and I moved the discs over.