Brake Calipers: Multi pistons? Neccesary or not?

mfereborn

Right lads and lasses,

I've been looking through various pictures on the forum of self-build bikes today and have noticed something interesting - and i feel it may be a more money than sense thing in many cases!

Coming from a world of motorcycles and going fast i understand the importance of brakes and one of the most obvious things about motorcycle brakes is that theyre heavily biased towards the front where you may have as many as 8 pots/pistons yet only 1/2 on the back.

Now this is simply because you don't need much braking force on the rear when all the weight goes forwards onto the front wheel underbraking and 2 pistons is mroe than adequate to lock the rear wheel easily.

So why is it on mountain bikes through these forums i have counted various bikes with twin-opposed pot calipers front and back?

There surely wont be any advantage of having extra pots on the rear, particularly when pushbikes are so light and the wheels so easy to lock up?

Can someone explain why some people ass such large calipers onto the rear of their bikes?

glauciaregina9

Good point. Now you mention it, it is mad and pointless. And therefore why do bike companies supply bikes with unnecessarily equally-potted front and rear calipers seeing as it's completely wasted on the rear?

Perhaps there are a lot of people don't appreciate or realise the explanation you gave.

Or it's just a symmetry thing.

It would feel odd buying two differently-potted brakes for my bike, but only because a matching pair has become 'normal'.

abarth_1200

I would prefer using the extra useless pot in the back in the front.

But I think its to do with manufacturing costs, marketing, spare parts and more importantly pads, might also come down something as little as lever feel and bite point, differences between basically 2 different brake systems might feel odd

peter413

It's because you need a lot of power for DH and your weight is quite often over the back so power can be put down well through the rear especially with a grippy tyre.

What are you going to say when you hear about Hope M6's which people still use front and rear

nicklouse

as i keep saying the front is for braking and the rear for steering.

also you dont really need more that one piston each side.

peter413

Do you mean control nick?

mfereborn

I cant see a purpose in more than 2 pistons on the rear of even a DH bike, even with a riders weight over the rear its far too easy to lock the wheel with that, nevermind having more pistons!

I admit on DH bikes more weight+ higher speeds calls for higher stopping power however a single or twin opposed piston caliper and a large diametre disc is more than adequate.

With regards to the mention of feel, well this comes down mostly to the size of the master cyclinder, a correctly formed and manufactured brake system shouldnt require extra pistons if it improves feel, it just means the internals M/C pistons diam. should be reduced so it pushes through less fluid for the same amount of lever travel.

FURTHERMORE, the rebuild expense of a caliper is vastly increased by havng multiple pots with regards to dust and fluid seals, nevermind should you wish to replace the pistons.

then theres the increased weight, and potential for damage...


Maybe I'm onto something here?

Hercule Q

lets just go back to V brakes

bikedibley

I've owned so many bikes and so many sets of disc brakes. My experience is so far, that Formula disc brakes are THE BOMB. They are awesome. And only the usual twin piston design.

Hope brakes with their four pots are no more powerful (with the exception of their 6 pot models). But remember, it's not all about power. modulation and control is key.

Rockhopper

On my Stumpy FSR I've got four pot brakes on the front and two pot on the rear - so there :-)

peter413

Rockhopper wrote:

On my Stumpy FSR I've got four pot brakes on the front and two pot on the rear - so there :-)

Same here except my stumpy has just turned into a 456 :P

Northwind

If you want to stick with the motorbike comparison, remember when they launched the SRAD 750 with the 6-pots and the 600 with the 4-pots? And everyone thought "Ooh, the 6-pots will be more powerful" but they turned out to be rotten, and all the racers on the 750 and on the TL ended up retrofitting the 4-pots off the 600

On pushbikes, 2 pistons can give all the power you need so it's not so much why the rear has the same number as the front, 2 is a good number, it's just that the front generally has no need for more. You tend to find smaller discs on the rear though.

nicklouse

peter413 wrote:

Do you mean control nick?

not really.

nicklouse

peter413 wrote:

It's because you need a lot of power for DH and your weight is quite often over the back so power can be put down well through the rear especially with a grippy tyre.

nope. the rear still does very little.

most people who ride DH have big discs as that is what came on the bike.
look at DH racers and they will use the size that is needed to do the job.

i know one who has 180 front and 140 rear or he has too much power.

peter413

nicklouse wrote:

peter413 wrote:

Do you mean control nick?

not really.

How does it help with steering?

I was always told not to use brakes in corners as well as many others :?

Anonymous

It helps with steering when you need to throw the arse end of the bike round a sharp switchback.
Like a rally car's handbrake.

peter413

yeehaamcgee wrote:

It helps with steering when you need to throw the ars* end of the bike round a sharp switchback.
Like a rally car's handbrake.

I thought so, I have always been told not to do this but it never stops me if I need to do it

Anonymous

If you need to do it, you need to do it.
Don't expect the back brake to slow you down at all though.

Northwind

OTOH sliding the rear for steering is pretty damn antisocial if you're riding on a manmade or delicate trail... Totally unacceptable many places IMO.

peter413

Northwind wrote:

OTOH sliding the rear for steering is pretty damn antisocial if you're riding on a manmade or delicate trail... Totally unacceptable many places IMO.

have you ever seen me do it on the trails?

I don't do hardly ever, only when I'm kinda racing myself or someone else and even then I try not to.

I do do it quite a bit on my local hills that hardly anyone rides on (maybe 10 others) and most of the walkers don't mind since they get a thrill out of just seeing a bike whizzing down something that they can barely walk on

Northwind

Wasn't telling you off Just a general observation.

peter413

I know, just wanted to protect my own @rse