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Old 11-20-2012, 01:18 PM   #1
BenjaminDG
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Dual rear brake calipers

What do you guys think of this?

http://www.mototuneusa.com/innovativ...technology.htm





In short the lower caliper is operated by the front brakel ever (via reducing valve te lower the pressure) which pulls the rear end towards the grounds.

The top caliper functions as a normal rear brake.

Advantages according to me and the website: rear end is more stable during braking, more rear tire traction during braking so possibly you can brake later then usaul?

But the front end will likely raise up a little during braking?

Other disadvantage is that it adds more unsprung (correct word?) weight which is worser for turns ans steering the bike.

The top caliper in this configuration pushes the rear end up so maybe in a corner you could possibly steer faster in or have a higher corner speed entry.

But this will put less pressure on the tire so lesser traction => more dangerous for highsider loss of traction?

You could remove the standard braking config and only use the lower calipers config to reduce the extra unsprung weight but then you would lose the abilty to resteer in a corner?

Any toughts on this?

Have never seen it in motogp?
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Old 11-20-2012, 03:01 PM   #2
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Don't see the point considering some gp racers don't touch the back brake


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Old 11-20-2012, 10:08 PM   #3
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Re: Dual rear brake calipers

Seems like a waste of time...I wouldn't bother.

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Old 11-20-2012, 10:50 PM   #4
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Re: Dual rear brake calipers

You can set up two lines to work on one caliper... And if you want all the benefits claimed, just learn to use that right foot.
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Old 11-21-2012, 08:25 AM   #5
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Re: Dual rear brake calipers

Well the advantage of this system is that its automaticlly so no need to use the right foot and activate the rear brake manally.

I have done this on the track when i accidentely apllied the rear brake during hard braking before a corner.

The bike felt a bit more stable then without using the rear brake.

I've heard that some guys use the rear brake moments before the front brake for the above reason.
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Old 11-21-2012, 02:08 PM   #6
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Re: Dual rear brake calipers

Did some more research and this caliper doenst really serve as a brake, it can rotate in relation with the disc rotor so most of the brake force is transferred towards the swingarm/frame which will be forced towards the ground.

Looks something that could work to me.

But you will lose the rear brake as 'slowing the rear wheel down', altho it will slow down it a bit but not as much compared to a normal rear brake setup.
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Old 11-23-2012, 01:47 AM   #7
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Re: Dual rear brake calipers

Stunters usually have a rear brake setup like this.
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Old 11-23-2012, 07:00 AM   #8
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Re: Dual rear brake calipers

This sytem was used by Jan Greven on his kawasaki zxr750 wsbk and he finished 5th in 1998 so i dont think its useless after all.

In fact i think of making my own system like that but will use only the lower caliper and not 2 like his to reduce unsprung weight.

I think that the normal rear brake was an obligation for competing in the wsbk.

But i wonder what happens when the rear wheel lifts of the ground?

Anyway i've send an email to Jan Greven for some more info and pics.
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Old 11-23-2012, 08:24 AM   #9
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Re: Dual rear brake calipers

Does anyone know what happened to motoman?
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Old 11-23-2012, 09:52 AM   #10
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Re: Dual rear brake calipers

A lot of what was said in the first post was false. Where the caliper is does not effect squat or anti squat of the bike.

Braking with the rear prior to application of the front can squat the rear, but wont "pull the front up". It may limit sudden chassis dive though.

Rear brake application can stead the chassis if used to a point the rear isnt locked up. When the weight is almost nothing on the rear wheel though, it is easy to lock up. NOt being able to modulate it independently since it is tied with the front means you can exactly control if it is locked or not, without letting off the front brake as well. Shit idea in that sense.

I have no idea what you mean by "lose the ability to resteer in corner"

Unsprung weight negatively effects suspension action. it wont really effect the change of direction being a caliper though, as apposed to rotational mass like a wheel or brake rotor. Rotational mass and its inertia have an exponential effect.
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Old 11-23-2012, 11:56 AM   #11
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Re: Dual rear brake calipers

You are right, i misformulated that part.

But the disadvantge of this system are more unsprung wait (perhaps) and locking up the rear wheel when it loses traction (wheel in the air).

When you brake hard and the rear wheel loses its traction then you will force the swingarm to maximum positon, then the caliper will stops the rear wheel from sprinning since it no longer force the swingarm towards the ground.

The rear wheel stops and the swingarm slightly goes in (negative springtravel).

When you no longer brake the rear wheel can spin again and the swingarm should be able to move again.

Could this be dangerous in the track, how about the forces you will force on the reaction bars,swingarm and frame?
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Old 11-23-2012, 12:04 PM   #12
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Re: Dual rear brake calipers

our bikes have rear brakes?
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Old 11-23-2012, 12:13 PM   #13
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Re: Dual rear brake calipers

Yes but the rear brake with this system isnt used in the first place the slow down the rear wheel, altho it does that do eventually.

It forces the swingarm into the pavement so that you can brake later and have more traction/stability on the rear wheel during front braking.
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Old 11-23-2012, 01:01 PM   #14
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Re: Dual rear brake calipers

Bad idea - on the track you really want to be able to control the brakes independently. You say it doesn't brake the wheel at first because the caliper moves? Even if that worked, it has what, a quarter revolution of the wheel at most? That's 1½' of riding distance or so.

Especially Honda has made bikes with linked front and rear brakes but they are for street use. Everyone who raced those few sport bikes made with that redid the system to be independent.

The few race bikes you do see with an extra caliper in the rear have a separate thumb lever complete with its own master cylinder, NOT linked to the front brakes. It's typically used by racers with limited use of their right foot (the first modern thumb brake was developed for Mick Doohan IIRC - after he destroyed his ankle) or ones that are heavy on the rear brake (the foot pedal can be hard to reach in right turns. And even then they usually just substitute the foot control all together to save weight.
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Old 11-23-2012, 01:04 PM   #15
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Re: Dual rear brake calipers

BTW, the reason you don't want them linked on the track is that when you do brake hard, you unload the rear wheel which will then lock up if the brakes are linked. If you don't unload it, you aren't braking hard. FWIW, the gyroscoping effect of the spinning rear wheel plays a large part in keeping the bike stable - if you lock it you lose that.
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Old 11-23-2012, 02:08 PM   #16
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Re: Dual rear brake calipers

Well it actually force the swingarm towards the ground when you use the front brake.

That instead of the backend of the bike that raises (like in a normale situation) you will also force the swingarm downwards.

Thus increasing rear tire stabilty (and breaking later).

I dont think that the rear caliper will lock up the tire while it still moves or has traction of the pavement (there is a pressure regulator that allows how much force is used on the rear brake).

When you do brake so hard that the rear wheel is off the ground, then it the tire will lock up.

But even then the tire can still move (back and forth alittle).

Becaus the rear calipers can rotate in comparison wiht the rear axle and it is linked with the swing arm using traction bars and a pivot point.

So i think even if it stops in the air, the moment the rear wheel touches the ground and when you stop using the front brake it can all move again.

Hopefully Jan Greven could supply me with more info and pics.

I should add that Jan Greven used this bike in wsbk and many european championships back in the 90's and/or early 2000's.
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Old 11-23-2012, 02:15 PM   #17
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Re: Dual rear brake calipers

If it were that good of an idea, and he were that successful with it, it would be used at least by a few major teams today.

Nobody that I know of does.

Not all ideas are good ones, and just because one dude made it work doesnt mean it is a good idea either.
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Old 11-23-2012, 02:18 PM   #18
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Re: Dual rear brake calipers

It won't work. And why are you so certain that something that may have worked for one racer a decade and a half ago would be the greatest thing since sliced bread when nobody else uses it? If it was so great, why isn't it used by GP, WSB, etc.?
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Old 11-23-2012, 02:32 PM   #19
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Re: Dual rear brake calipers

I wonder to?

Perhaps you do not only need the adjust the pressue between front brake and rear brake (lets say that the rear brake uses 10% incomparison with the front brake) but you need to adjust that force (10%) variable in relation with how much force you put on the front brake or how far the suspension dives.
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Old 11-23-2012, 02:36 PM   #20
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Re: Dual rear brake calipers

Id say for the AVERAGE rider on the street, a linked brake system may work ok. But not some fancy dual brake setup being needed. There are ways to preserve the rear brake pedal and link it to the front still.

but for racing, or high level track riding, linked brakes on a bike is a bad idea.
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