Brake rotors experiment

[planedick]

I finally got my setup for grinding brake rotors done and have done a couple of rotors I had laying around. One of them was badly gouged and took lots of grinding to make both sides smooth. The rotors start out at .260" thick and this one was only .215" when I finished. The other one finished out around
.240" I put them on the Pathfinder front wheel and rode for about 500 miles using the front brake heavily. Although the factory says not to grind the rotors as the thickness cannot be smaller than .260", I found no detrimental effect to braking performance or any problems whatsoever. I'm confident that I can do brakes for others. A smooth brake rotor makes the pads last much longer than a rough one.

[GARTHXS]

sounds good

Any luck with drilling or slotting them ?

[DGXSER]

I think the issue with getting them thinner is that they will tend to warp from the heat. I takes a minimum thickness of metal to absorb the heat of the brakes being applied at highway speeds and such with out reaching a temp high enough to cause permanent distortion/warping of the metal.

Will be interesting to see how it holds up over time. I am certain the factory number has a safety factor applied to what the minimum thickness is, just never calculated out what that factor is, since I don't know the composition of the metal in the disc.

[planedick]

Rest assured

I did many high speed hard stops, dragged the brake while going down the freeway to heat 'em up real good then did hard stop too. No different from the like new discs I have that are full thickness.

[MaximPhil]

Hi Planedick,
Like you I expect there is a huge safety margin built in to the factory spec. I would however caution against charging people for something that is "not approved" by the factory.
the 0.215 raises the question of at what point the piston would pop out of the caliper? Hate for you to be "coming down the mountain" when it all blew apart. Having experienced the poping out of a piston on a pick em up truck it really can happen with 3 more working we made it home

[Larrym]

PlaneDick,

Rotors had to meet OEM standards on a bike that showed 160 mph on the speedo. You can bet that the guys in lab coats did a braking test from that speed. Wouldn't you? As the rotors are also a heat sink you can see why they wanted as much metal as they could to absorb then radiate the heat in a controlled manner.

No way that I am ever going to push the envelope that far or fast. For my style of riding I'd be comfortable with what you've done. I am concerned about the extra travel of the pistons. Does the math work out so that if your pads are worn to the point of almost being metal to metal... the pistons stay put?

[dbwill]

rotors

A good experiment but carries a big liability when you go below the factory specs, If I did my math right the one is 17% below the min .260 the other one is 7%. I would also be concerned the they might crack . Does any one know what a new rotor spec are? Den

[81xsproject]

Good job, Dick. I think it is awesome. As far as safety vs thickness goes, has anyone ever seen rotors from other late 70's/early 80's bikes? My buddies KZ rotors are probably half the thickness of the mighty XS's. As far as heat goes, the XS has such immense engine compression, I don't know how the hell you get the brakes hot.

[randy]

I contacted Mikes XS to inquire a bout the thickness of his part# 30-3065 rotors, 'cause I think I recall that someone here used those rotors on an XS11. His reply:

Rotor 30-3065 is 4mm thick where the pads touch the disc. Hope that was what you're looking for.
Mikesxs

4mm works out to .157 in. Anyone used these rotors, and how are they performing?

[DGXSER]

Holy Crapoly

That is amazingly thin by comparison Randy. I knew there was safety involved, but never dreamed it would be that much. I am certain the new .157 won't give the same life as the originals, but they would have to be safe (at least one would hope) for them to sell them.

Now I REALLY wonder why I can't find anyone to turn my rotors!

[randy]

Keep in mind, those rotors are sold for use on the 650. But I do recall that someone used them on an 11. Now, my memory isn't what it used to be, so let's see who replies here!

[TopCatGr58]

Hey Randy,

Check out this recent thread by Erollig: MikesXS Rotor thread.

In that thread, I had done some research, and the early XS11's and 650's used the same Yamaha part #, so they were the same thickness!

Erollig posted some photos, and you can visibly see that the rotors are THINNER than the ones that Ken Talbot posted of his XS11!!

Remember, the newer rotors are also extensively drilled and so perhaps they either dissapate the heat better/faster, or just dont' heat up as much??? But also don't know if they are made up of different types of alloys than the old OEMs???

So, I think the grinding the OEM XS11's a little narrower wouldn't be much to worry about afterall, but perhaps it would be prudent to drill them IF they are not slotted/drilled already!?
T.C.

[GNEPIG]

Hey Dick, I have a set of rotors that needs resurfaced, how much to grind two?

[foreda]

Rotor turning and drilling

Greetings all.. Does anyone know what the minimum thickness of the 78 e rotors? I would like to turn mine but Auto shop says they won't touch em. Also, does anyone have a pattern for drilling the rotors?