Its only 1mm off when you mount it due to the weight, but when you use the two set screws it will be right on. those holes are a snap to drill.

 

It is. the radius is 1mm off, and thats why it can only be 1mm off, but if you use the centering screws, (2) of them, you will be perfectly aligned.
the hub centric discussion was really about the wheels on the wheel bearing hub area. that is not that closely used by most aftermarket wheels, and the wheels are truely centered and supported by the wheel studs as they center with tapered wheel nuts

 

I was responding to James, not sure what he meant.

 

the rotor centers on the OD of the hub flange the screws are there to hold the rotor onto the hub, , sometimes a rotor can stick to a wheel if its badly corroded

 

I know, but you can use the screws to center the rotor too, and once the wheel is torqued, its not going to go anywhere. the forces are not up and down or side to side, they are rotational and the force has a single direction.

worst case, i could weld on the hub, 4 little 1mm lips on the edge of the hub. for that matter, a little 1mm jbweld would do it too. Its not taking any force , like the wheel hubcentric design in theory does (as I mentioned, most wheels , with their hub chamfer, and over 1mm gap, and cetnerting via lug studs, does the centering)

we are talking the rotor here and 1mm off center. not a biggie by any streatch. two set screws will align and hold the rotor fine.

 

MArk, I guarantee you that a 20lb rotor spinning 1mm off center is going to be a balance problem...the closer you can get it to center, the better. You can kind of force it by putting a wheel on with the nuts finger tight, then have someone drag the brake a bit while you rotate the wheel- this will force the rotor to back up against the studs and center on the studs...fwiw...

 

little revision, I'm making them 7.00mm thick, 84.95mm O.D, and 71.60mm I.D.

 

I know it will be non-optimal if it was off that much. meaning, no set screw centering, and you bolt on the wheel. i agree to be able to center it by what you suggest, but as you say and if you think about it. as you jam on the brakes, if those rotors move at all they will move against the studs and self center.

I will probably drill the set screw holes so that the rotor is preloaded against the studs in that same respect. that way, no issue. Ill put a dial indicator to make sure on the rotor, and it will be fine.

remember even though it is 1mm off, the wheel only spins at 1500rpm and only 6.5" raduis, i dont think it would be a major issue, but I could be wrong there. however, im not going to test it to find out. it will be centered by the studs and the centering screws, so it will be fine.

thanks

Mk

 

Just thought I'd put a few numbers to the balance argument.

Centripetal Force:
F = m*r*(ω^2)
m = mass (kg)
r = radius (m)
ω = angular velocity (rad/s)

m = 20 lbs = 9.07 kg
r = 1 mm = 0.001 m
ω = 1500 RPM = 157 rad/s

Solve for F:

F = 9.07 * 0.001 * (157^2) = 223.6 kg*m/(s^2) = 223.6 N = 50.27 lbs

Now to put a little perspective in:
How much wheel weight would it take to create this imbalance?
Assuming a 18” rim (necessary for the larger disk?) with a stick on weight, r1 = radial position for the weight would be roughly 8” (just a guess)
r1 = 8” = 0.2032 m
m1 = mass of wheel weight.
ω1 = RPM of wheel
Setting the two equations equal.
m1 *r1 * ω1^2 = 223.6 N = m * r * ω^2
We know the RPM of the wheel and disk are the same so we can cancel those out of each side of the equation leaving us with.
m1 *r1 = m * r
In putting knowns:
m1 * 0.203 = 9.07 * 0.001
m1 = .0446 kg = 1.57 oz
So it is effectively like missing a 1.57 oz balance weight on your wheel.

So is a 1.57 oz wheel weight noticeable?

 

Great work from a fellow Okie. In layman's terms, the faster you go, the more you feel the vibes.

 

I'll be mocking up the Early 928 spindle/hubs next....944 prototype is done. The 928 may not need a rotated bracket at 104mm spreadwidth (I hope)
The 7mm thick centering rings are perfect.....0.000" runout

 

nice

 

As far as the rotor is concerned if it doesn't get centred by the ID of the hat onto the hub (the wheel lug stud holes are too big) then the centring screws will do it and it won't move once the wheel lug buts are tightened.

IIRC the stock rotors are hub centred, so the rotor is centred when you screw down the screws. As they are countersunk there is no play in the screws. If the lug nuts didn't clamp the rotor hat tightly enough the centring screws would bend/distort in normal use as the rotor rotates relative to the hub. Haven't seen a bent screw yet (plenty with no Phillips socket left though LOL) so the lug nuts must prevent the rotor moving relative to the hub.

 

I think the main point was that as the rotor with the set screws will be centered and the forces are rotational, and as such, they will force the rotor to be centered against the studs. (if it was to move and bend the set screws).
If I drill the screws to preload the position, then there will be no chance of bending and they will be in the proper position with no chance of bending them)

 

Unless you go really fast backwards and hit the brakes hard...