Author Topic: brake calipers - does it matter where the disc is grabbed?  (Read 99 times)

Tinworm

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I have a very tight space inside the back of my kart, so I wondered if the caliper has to be in a particular position, relative to the disc? I mean, for instance, could I mount it behind the disc instead of in front of it or on top of it?

Are they directional, or is it irrelevant where the disc is grabbed and whether the wheel is going up-hill or down?
I don't want to bore you all with the details, here. But if you are interested, have a look at my blog https://peteskart.blogspot.com/

-Peter

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Jimr1999

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As I understand it...
Provided the mounting points can take the strain, your constraints will be that the pads are fully within the area of the disc and not overhanging (this can lead to the pads touching each other when worn in and not braking the disc), the caliper body or retaining pins are not rubbing the rim of the disc and that you can bleed the caliper somehow with the bleed nipple at the highest point.

I got around the bleeding bit by bleeding the caliper off the CK on a spare disc (it is mounted on flexible hose) and then underslinging mine. Not the easiest thing to bleed but do able with a bit of patience and time.

Hope this helps
« Last Edit: 10 May 22, 06:29 am by Jimr1999 »
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Tinworm

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Thanks Jim, I think that answers it.

I thought that I might have my caliper at the back of the car, behind the axle.

How large will your disc be?
I don't want to bore you all with the details, here. But if you are interested, have a look at my blog https://peteskart.blogspot.com/

-Peter

Jimr1999

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Mine is 220mm but my wheel is a smaller radius than yours I would think,
... You can lead a horse to water, but a pencil must be lead.

Tinworm

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when you are braking, is the size of wheels relevant? We all have the same horsepower
I don't want to bore you all with the details, here. But if you are interested, have a look at my blog https://peteskart.blogspot.com/

-Peter

Jimr1999

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Probably more relevant is the contact patch and the CoF of the tyre as when that slips your brake has done its job, but the force transferred down the bigger lever of a large radius wheel to the fulcrum/axle has to be counteracted by a larger radius of the disc or greater pressure on the pads to make that happen.
Stefan helped me with the maths on mine <hat tip, yet again Stefan>, he has some great graphics he shared and I think he has written much about braking on this site. Well worth tapping his brains on this subject.
... You can lead a horse to water, but a pencil must be lead.

synthpunk

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Ive been working on this very conundrum. It’s a saga worthy of a thread on its own, but since you’ve already started one, I’ll join in..

The long and short of it is that I’ve made a very curvy, strong and attractive unibody cyclekart from wood. I did the wood bits first because that’s my happy place, and I sort of assumed by the time brakes became relevant I’d be far enough along the metalwork and mechanics learning curves to work it out, and simply weld a suitable bracket on somewhere, somewhen, somehow.

That time it appears is now. The problem I have is that everything’s made of wood, so it’s really hard to weld things on to. And there are no parallels or right angles to take a datum off, so it’s difficult to think of a way to get the calliper parallel to the disc anyways…

This led me to the thought that I needed to weld up some sort of subchassis that holds the engine, transmission, axle and brakes together in a hopefully square, not too heavy, easily removable unit…

Which in turn has led me to several conclusions, via cutting up lots of metal, various major backtracking moments and a few moments of clarity to several more refined conclusions-

1- build a sort of subchassis that bolts in the back and holds everything in place

2- get slightly sidetracked, and think of a way to equip said subchassis that so it has the ability to add rear suspension, in some way.. preferably that doesn’t weigh much. Probably using rubber…. Because I like it.

3- get completely sidetracked, end up coming up with a way of making a ‘floating calliper mount’ sort of affair that holds the calliper in perfect alignment at all times, is totally adjustable, and in effect even would allow me to use it in my original, ‘no weld’ scheme of lightweight bolted aluminium engine mounting, thus negating the need to even bother with the inevitable extra weight penalty of either options 1 or 2….. although suspension to make up for the total lack of twist and flex in my chassis does sound good…

So the caddy for options 1 and 2 was already halfway built as it goes, before I came up with option 3 whilst thinking in the shower on Sunday morning, so I think I’m going to end up trying all 3.

Tomorrow or Thursday after the postie has been I’ll post some pics of the brake calliper arrangement. It’s mostly made of Righettit parts, so not the cheapest option but still a fraction of the price of a Kelgate floating brake system for Pro karts.

Pics to come… cheers!
Rich