Radial Disc Brakes

Kev

I mentioned Telelever above. It's interesting that the latest telelevers in the spy shots look exactly like upside down forks. Is that a fashion thing, driven by the need to keep sales from the steadily rising competition (with regards to GS models). Or is it the way evolution works regardless of fashion. In other words, we want the benefits of radial calipers, so we design the bottom of the fork leg to accommodate them. That means beefing that bit up. As a consequence we find that the loadings on the fork leg proper have changed, so we can reduce them down. The result. They look like telescopic upside down forks! May as well colour them accordingly.

Or a combo of the two?

Hi BIKenG

It's great to have some input and thoughts on this. I'm looking forward to hearing Kev's response. In the meantime I've been pondering a bit more on this anyway and here's how I see things to date.

Engineering is a bit like politics, there is rarely just one answer, usually a compound effect. For my money, there's a little bit of everything that has been said so far involved here.

1) With the move to upside down forks and the desire to keep fork overlap as good as possible, balanced against the need for decent fork travel, the cast end of the fork is quite short. You'd be hard pushed to attach a long caliper to it without ending up with a shape very similar to what we now commonly see. I agree, I see no firm reason for the casting to be precisely in the form of 2 perfectly "radial arms. In fact I've seen quite a few designs that have nothing radial about them, except for the fact that the caliper, if moved in or out on spacers, will move in a perfectly "radial" manner or direction.

2) If the need to mount the caliper so as to enable it's movement on spacers arose first, then you would still end up with a shape similar to what we now see. How else would you anchor the far end of the caliper? In conjunction with the ever shortening fork leg end, you have your first compound effect.

3) If we look at the forces involved in severe braking and think how the fork leg would try to bend, I think the bottom cast "radial arm" anchors the bending force quite well. I may be wrong, so I welcome input and correction if that be the case. 

4) Calipers have got longer and they are now attached at the extreme ends for the very reason you have given. Discs are now getting smaller in outside diameter as Kevin says, to keep gyro forces down. But this is only made possible because braking pressure is able to keep going up. It has to. Overall braking performance is getting better, even though discs are tending to get smaller. Ever more pressing need to anchor the caliper better and protect the fork leg from bending than ever before.

5) Consider how upside down forks are put together at the bottom end. You have the steel tube pressed into the cast end. It's not one homogenous piece like it used to be. If I'm right with my analysis in 3) then without the cast radial lower arm maybe there would be more tendency for the two parts to separate.

6) Bling! As you've already said. A strong identity. But for my money, that's last on the list. The political bonus. The engineering has been done by that stage. I think the "radial" moniker is a misnomer, but hey, that's marketing. What else would you call the breed?