Brake calipers/mastercylinder/ratios...

So... I've got a K100 that I've fitted leading links to(since it's a
sidecar tug.) The leading links came on another K100 with a different
master cylinder and also different calipers.

The calipers are 4 pot and probably from a GSX600F; I've stripped them
and the pistons are 27mm. If possible I'd like to use the standard BMW
master cylinder since this makes things easier with the switchgear.

The GSX600F calipers have four 27mm pistons per caliper which gives a
'piston surface area' of 8 * (pi*(27/2)^2) = 4580mm^2.

The standard BMW K100 8v has 2 pot brembos with 38mm pistons which gives
a 'piston surface area' of 4 * (pi*(38/2)^2) = 4536mm^2

Looking at these figures, surely this means the standard K100 master
cylinder should be able to handle the GSX600F calipers, doesn't it? To
apply the brakes in either case there's a similar surface area of
pistons to move and surely that's all that matters?

Am I about to do something else stupid? (apart from riding a sidecar
across Germany in the winter because 'Bonwick thinks it'll be a laugh')

 

I'm not an expert on brakes and I always go for the 'if it works then
it's right' approach so just get it on the road and see if they work
well enough for a spot of motorway cruising.

It's not as if we're going to be going for stupid outbraking stunts
once we get to the twisty bits near the rally site and there's no
chance of it getting at all competitive with three BMW K100 outfits
competing for the same piece of road is there?

It could be a lot worse. There's another big challenge waiting out
there and all we need to do is find it..

 

I'm going on a solo if that makes it better.

 

Pause at 1:58...

 

How long did it take you to find that?

 

Why? I can't see a smart car.

 

Slightly less than 2 minutes.

 

OK, who are you and what have you done with the real Bonwick?

ah, ok - normal service is resumed, I see.

 

I did. And?

 

So'm I.

It occurs to me that the last time I rode an XT600 in the snow, I fell
off. Twice.

 

Probably still en route, or not allowed on site, or something equally
humiliating.

 

Did the Smart Car get the Elefantentreffen sticker?

 

(The Older Gentleman) wrote in

a suspiciously familiar selection of old tat

 

I'm sure you'll beat that record this time.

 

Hold your nose and cross your eyes.

 

No... of course not.

Now, remind me... what radius is your rear wheel with the tyre on and
are you running the standard K100RS gearing?

Krystaltreffen would be 'interesting' but since it's in a hotel I'm not
so sure.

 

What - smashing the headlights of motorbikes belonging to jews ?

 

I'm packing spare brake and clutch levers. For the rest, the XT seems
pretty crash-proof.

 

This reminded me of the exit...




But less crowded and with fewer people falling over.

 

An unscientific test (apart from taking a run down the road and giving
it some) is to get a small graduated beaker, or even a syringe tube, and
find out what each master cylinder delivers for a given movement of the
handlebar lever. Then take 'em apart and compare master cylinder piston
areas.

Do you know the piston area of a Suzi master cylinder compared to a BM
one? That gives the ratio of pressure increase.

Pumped volume comes into it as well. What is the volume of fluid needed
to move the Suzi pistons a given distance compared to the BM ones?

If you move one caliper piston 1mm then for 8 pistons you need
effectively 8 mm of movement and the volume of fluid to achieve that.

A bit late at night for hydraulics but I reckon (assuming 0.5 mm of
movement max but possibly half that) the Suzuki needs 4 times as much
fluid to move it's pistons compared to the BM.

In theory, you have more brake area on the Suzi calipers and so friction
for a given force, so the Suzi would need less pressure from the master
cylinder to achieve the same braking effect for a given mass. If the
master cylinder produced 50 bar of pressure (I've no idea what they
actually produce), that 50 bar is spread over the whole area of the
friction material (pressure = force / area). So, for less pressure the
Suzi master cylinder piston could have a smaller pressure ratio compared
to the BM i.e. the master cylinder piston is larger in relation to the
size of the caliper piston compared to the BM.

Then there is the leverage ratio on the handlebar lever....