Double disc on the back?

[Yoyo]

Seeing double discs on the front of bikes is nothing new these days. But one thing i've been thinking is, why don't they put it on the back too? The disc is already there with the sprocket.

Has it ever been done?
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Joe: I don't wish to floccinaucinihilipilificate your choices, but the best word in the world is gaylord.

[Timmeh]

I suspect that it may down to be clearance issues. Any horizontal movement of the chain and rear spindle would cause it to strike the disc with disastrous results.

A shaftie, on the other hand, is a different story.
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[bikertomm]

facepalm.jpg




I guess in a lot of cases it's not necessary, you don't want to be locking up the back with ease, also.. the sprockets are usually in the way..


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[Pol Anorl]

Just stick your face in the back wheel. Job done.
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[pdg]

If I read it correctly he was implying that it would be possible to use the sprocket as a brake disc....

Obviously it would work perfectly, and the chain oil would stop any brake squealing.

[fatpies]

before putting in a whole extra disc and calliper.

They could just improve the calliper which is on there already, more pots, opposing pots, larger surface area and even bigger disc.
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[fatpies]

[DrDonnyBrago]

You can lock the rear wheel on a high performance motorcycle at pretty much any speed with a single small disc and a single pot floating caliper, why would you want/need to make it more powerful?

That said, some stunters will have a second brake caliper on the rear disc and some faggy Yank chopper things do use the sprocket as a brake disc, I can only assume they don't oil their chains.

https://www.hoheydesigns.com/store/images/honda/F4i%202%20big-rotor-brembo.jpg

https://static.ddmcdn.com/gif/suicide-softail-chopper-profile-6.jpg

[-Matt-]

Never seen a caliper on a sprocket like that before looks like a recipe for disaster

[RhynoCZ]

Can you block the wheel with single disc brake? - Yes, you can.

Look at 70's and 80's bikes, there were way bigger discs on the rear wheel. Today, when most of your weight is above your front wheel, it'd be quite stupid to keep that ''powerful'' brake on the back.

Case closed
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[Timmeh]

[RhynoCZ]

[DrDonnyBrago]

[RhynoCZ]

Have you seen this: https://www.youtube.com/watch?v=4ED8BfPtaTw ?
I think that'd be the source of OP's idea
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[Timmeh]

[DrSnoosnoo]

How do these Mercans survive on a "sports" bike if they don't use their front brakes? I mean, damn!

Do they get their licence from collecting tokens from their corn flakes?
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[Im-a-Ridah]

The best way to slow down quicker is bigger tyres. It's the grip between the tyre contact patch and the road that is going to let go soonest. Obviously Mark doesn't need brakes, he just crashes into the nearest wall at max speed, then walks off uninjured.

[MarJay]

Err... Because the geometry of a motorcycle means that the rear brake is much more likely to lock up than the front?

Jeez Warped, you get dumber by the day.
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[Yoyo]

Saying about locking up is pretty much the same as saying why put 2 on the front. You can flip a bike that only has one disc on the front. So not really that stupid.
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Joe: I don't wish to floccinaucinihilipilificate your choices, but the best word in the world is gaylord.

[bikertomm]

[MarJay]

[Teflon-Mike]

Why have a disc on the back wheel at all?

It's just extra unsprung mass.

Why not, put the brake on the gear-box out-put shaft?

Where, spinning about 3x as fast, it has 3x the mechanical advantage over the rear wheel; & is therefore more powerful and less 'grabby' providing much more 'feel'....

There is an answer to this one....

Any-one know what it is?

Can any-one else site examples of machines fitted with out-put shaft brakes?

And following on from that idea; what about epicyclic front brakes?

The floating disc, running on an epicyclic gear, at potentially 3, 5 or even 10X wheel speed. Even greater mechanical advantage over the wheel, means that the brake can be made smaller, hence lighter to do the same job, while at the same time offering greater braking feel.

There is also another pottential influence of geared front rotors; rotating at much higher speed, the gyroscopic effect of the brake rotor is amplified.

This opens up myriad possibilities over the dynamics of the machine. A high speed rotor, at lower speeds would not amplify the gyroscopic inertia so profoundly, so the machine could use quite 'unstable' geometry for low speed handling, the rotors effect increasing with speed, providing a much higher degree of stability at high speeds.

But conversely... the rotor could contra-rotate.... turn backwards compared to the wheel.... NOW the rotor's gyroscopic effect would be countering that of the wheel; this would mean that the geometry could be made 'naturally' more stable for slow speeds, but as speeds increase, the rotor would more effectively counteract the wheel's gyroscopic tendancies, such that the steering would not become so heavy and the bike would be much more eager to lean and turn....

Why don't bikes use these kind of technologies?
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[MarJay]

[DrDonnyBrago]

[karoshi]