[The Hitman]

Are bigger disc rotors more subsceptible to getting bent or damaged?, do they put more stress on the hubs, bolts, dropouts etc?

Hows about in terms of those 10'' Galfers? Easily bent?

Opinions please.....

 

[BadFastard]

they do put more stress on the bolts.
It's the cantilever principle, the one that makes a door easier to push shut at the edge of it when compared with pushing it right at the hinge.
when the caliper grips your 8 inch rotor it's 4 inches away from the centre, whereas the bolt that keep it on the hub are only half an inch away. The forces that these bolts transfer to the hub (and via the spokes to the wheel and tire so that you actually slow down) is therefore 4 divided by a half. Being 8 times the force applied at the pads.
On a 10 inch disk, the caliper sits 5" from the axle, and the bolts remain where they are. So you'll get five divided by a half. Which makes 10. So the forces are 20 percent greater.

Bending: more likely as well.

I don't see why you'd need a 10" disk anyway

 

[Kornphlake]

So are the forces of a 26" disc greater as well? (think vee brakes, I should have broken about a thousand vee brake mounting posts) This is one that I've been boggled by, I just don't know how to calculate the leverages because they are working both ways. The caliper has more leverage on the hub so the forces at the caliper are lower but the adaptor is longer so the caliper has more force on the mounting bolts, so is a lower force at the caliper times a longer lever equal to a higher force times a shorter lever?

 

[dhtahoe]

So are the forces of a 26" disc greater as well? (think vee brakes, I should have broken about a thousand vee brake mounting posts) This is one that I've been boggled by, I just don't know how to calculate the leverages because they are working both ways. The caliper has more leverage on the hub so the forces at the caliper are lower but the adaptor is longer so the caliper has more force on the mounting bolts, so is a lower force at the caliper times a longer lever equal to a higher force times a shorter lever?

Because that is being stopped at the rim the same forces do not apply. A 10 " rotor will put more stress on hub,nipple,rim. Will it fail who can say... The rotor is lower to the ground and yes you will bend is easier. It all depends on you. IMO just get the 8".

 

[Sir_Crackien]

the only bolts that a 10" rotor will stress more is the rotor bolt and the nipples. the mounting bolts will not be stresses more because teh caliper is not supplying any more force it just has more leverage. a 10" rotor will bent easier ans more often than a 8" because it is 1" close to gettnig hit and there is 1" more leverage for whatever is hitting it.

btw that 10" rotor is only designed to touring tandem(2 people and all of their supplies for a week), which are stuck on the road.

 

[The Hitman]

Has Galfer got some new floating, wavy rotors coming out?

 

[James | Go-Ride]

The forces on a wheel with rim brakes are different. You're pulling directly on the rim, so you have different forces affecting the spokes and hub. However you're not transferring force through the spokes; the friction is coming from the outside diameter of the wheel, not going through a rotor, then through the spokes and rim to the tire. Also, there's not much leverage on the brake bosses with a rim brake, as the pads only sit about a half-inch above the mounting post. I don't know how to better explain this, I don't have a degree in physics or anything. If you need to know anything about Montaigne or Nietzsche though . . .

 

[Kornphlake]

So if I understand correctly the force on the adaptor bolts would be equal to the force on the wheel times the distance from the outer circumference of the tire to the rotor divided by the length of the adaptor. Let's assume a tire is 2" tall so the effective radius of the wheel is 15" and we'll pick some arbitrary force on the wheel in a skidding condition ,500#. Now for a 6 inch rotor you've got the 500lbs, times the distance from the outer circumfrance of the tire to the rotor, 15-3=12", divided by the length of the caliper adaptor, 3". You get (500*12)/3=2000#. Okay that's great,now do the same thing for an 8" rotor and you get (500*11)/4=1375, or for a 10" rotor (500*10)/5=1000. Assuming the force to skid is constant and the caliper adaptor is mounted directly to the hub (which it isn't) an 8" rotor puts less stress on the frame than a 6" rotor and a 10" rotor even less. This means that the opposing force tryng to push the wheel out of the dropouts is less with a larger rotor right? What am I missing, everybody seems to accept that large rotors break dropouts.

 

[ChrisRobin]

I can see the rear rotor getting banged up a bit more on a DH bike since hub spacing is wider.