Radial mount calipers ???

[Huzo]

Today I was meandering through a large dealership and wondering why I haven't had the "I wants" for about 8 years and while staring at nothing in particular I began to look at the radial mounted calipers on the Dukes, Triumphs and just about everything else worth taking home. Thing is, I can't think of why radially mounting the calipers would be of any benefit, yet it clearly is, these guys don't change things for fun,(but sometimes fashion). I can perceive that the power of a disc brake/caliper combination is a function of the friction of the pad on the disc x the distance of the pad centre of pressure from the axle centre. All that's ok, but where is the benefit of radially mounting the calipers ? Anyone know or a good educated guess ??? An engineer's opinion would be good.

[beetle]

I'm sure someone will come along with all kinds of pseudo scientific reasons why radial mounted calipers are better. Truth is they are not. Zero, zip, zilch difference in performance of the caliper itself.

[Huzo]

I'm sure someone will come along with all kinds of pseudo scientific reasons why radial mounted calipers are better. Truth is they are not. Zero, zip, zilch difference in performance of the caliper itself.

Good to here the debate open Beetle with that as the first shot. (BTW, I reckon I'll just book the bike into Pete at Bungendore and get him to do it. BANG !!!)

[pete roper]

Race bikes have them because it allows quick changes of rotor diameter. We have them because we're wankers.

[tris]

As always,thanks for the clear and succinct explanation Pete 

While we're on a roll - what about rim brakes like the Buells

[pete roper]

Less rotating mass but it's carried further out from the center of ratation. You'd need to calculate which has more or less gyroscopic effect. I can't be arsed.

[nbags]

less flex,i think also an advantage caliper is parallel to the rotor,no need to shim caliper to fork legs and maybe just easier to assemble at factory.time is money.

[Dukedesmo]

The main reason why radial calipers are going to be better is; given most, if not all high-end and bikes and particularly race bikes use them, all the development is done on them rather than the 'old-fashioned' axial mount calipers. Therefore they will tend to be better whilst axial calipers remain as they are.

Other than that there are a few claims as to why the design is better, less flex etc. but apart from ease of changing disc size I can't imagine any difference is actually measurable/noticeable.

That said both my Ducatis have them and the braking is excellent, requiring only two fingers for any amount of braking power, I have to recalibrate my brain when I ride the Lemans.

[bad Chad]

Here is an explanation
http://www.motorcyclistonline.com/videos/mc-garage?video=x4oeurx

[pauldaytona]

Anyway, since there are radial, there has been no development on axial calipers at all. For radial there are cast monobloc calipers, mounted on ducatis/ aprilias and the like. And not expensive

[rocker59]

Race bikes have them because it allows quick changes of rotor diameter. We have them because we're wankers.

 :1:

[rocker59]

Less rotating mass but it's carried further out from the center of ratation. You'd need to calculate which has more or less gyroscopic effect. I can't be arsed.

A magazine did the Rotational Inertia test on several wheels ten or twelve years ago.

Despite being the lightest wheel/rotor package, the Buel rims had the highest rotational intertia.

So, less unsprung weight, which is good for suspension.  More rotational inertia, which is bad for turning.

Buell made up for it with radically steep (for the time) steering geometry.

[oldbike54]

 Rim brakes also (or I've read) place less stress on the wheel under hard braking .

 As for the radial caliper question , under racing conditions they do place less stress on the forks under really hard braking , allowing the suspension to continue working . Of course this is with a gummy slick and on clean pavement , probably not an issue on the street .

 Dusty

[Huzo]

Thanks everyone for that. It made sense when explained especially the tutorial posted by bad chad.

[Rusnak_322]

Rim brakes also (or I've read) place less stress on the wheel under hard braking .

 As for the radial caliper question , under racing conditions they do place less stress on the forks under really hard braking , allowing the suspension to continue working . Of course this is with a gummy slick and on clean pavement , probably not an issue on the street .

 Dusty

actually the stress levels don't change, they are just moved. The buell allowed a smaller wheel center "hub" because the stress was transferred to tge rim.

[Huzo]

actually the stress levels don't change, they are just moved. The buell allowed a smaller wheel center "hub" because the stress was transferred to tge rim.

Yeah but as Dusty says, the spokes won't feel it.

[oldbike54]

Yeah but as Dusty says, the spokes won't feel it.

 Correct , the load is moved almost completely to the rim allowing for a lighter hub and spokes .

 Dusty

[Rusnak_322]

Correct , the load is moved almost completely to the rim allowing for a lighter hub and spokes .

 Dusty

The spokes have to deal with the braking force with the rim mount rotor, when they didn't when the force was transferred to the hub. So the spokes don't get smaller.

[oldbike54]

The spokes have to deal with the braking force with the rim mount rotor, when they didn't when the force was transferred to the hub. So the spokes don't get smaller.

 Actually this isn't correct . A rim mounted brake eliminates the twisting forces involved thereby reducing the torque applied to the spokes . Also , the force needed at the rotor will be reduced due to the increased leverage . Like opening a door by pushing on the point farthest from the hinges as opposed to using a lever to open the door at the hinge point .

 Dusty

[Rusnak_322]

Actually this isn't correct . A rim mounted brake eliminates the twisting forces involved thereby reducing the torque applied to the spokes . Also , the force needed at the rotor will be reduced due to the increased leverage . Like opening a door by pushing on the point farthest from the hinges as opposed to using a lever to open the door at the hinge point .

 Dusty

I think you are correct, I didn't think about the fact that the braking force is transferred fro. The rotor to the caliper and fork leg, bypassing the spokes and hub.

[oldbike54]

I think you are correct, I didn't think about the fact that the braking force is transferred fro. The rotor to the caliper and fork leg, bypassing the spokes and hub.

 We are here to serve and learn 

 Dusty

[Dukedesmo]

I think you are correct, I didn't think about the fact that the braking force is transferred fro. The rotor to the caliper and fork leg, bypassing the spokes and hub.

Bikes with rim mounted discs only require the one disc, and/or smaller or less piston calipers to achieve the same braking force due to the huge mechanical advantage of braking a larger circumference.

[Huzo]

Good stuff lads, everyone's on the same page. You are a gentleman Rusnak...

[Old Jock]

Even the bicycle has them

[mtiberio]

I believe radial calipers are stiffer. that is all...