Adam M

Simon, you could argue that giving the wheel a bigger disk will make it heavier and therefore increase the inertia, but I think you will find, this is nothing compared to teh fact that it is the kinetic energy of a 1300kg car moving forward at speed that makes the disk hard to stop, not the spinning inertia.

The things to consider are the greater area for heat dissipation and therefore fade resistance. The size of the calipers is not s important as the size of the pad which will should remain teh same although I am not familiar with this kit. regardless of pressure, the calipers will impart a force to the pads. If the pressure between them is high due to small area calipers then distortion of the pad is possible, but little more so than on the standard setup.

SimonH

Thanks for the replies guys.

Ian, I understand the point about the leverage arm however does it not work the other way too? By making the disc bigger you will have a higher rotational velocity at the outer edge where the pad is being applied. That higher rotational velocity will give a higher inertia at the edge meaning the pads & calliper must work harder to dissipate the energy and slow the disc...

I appreciate that in the grand scheme of things a few extra mm of diameter on brake disc and a bit extra inertia aren't really going to change the price of fish on stopping a 1.3 ton car however I'm just interested in the mechanics of why this setup should be better.

At the end of the day, Ian, it's probably not going to stop buying one of your big disc conversions...

SimonH

Technical question.......

I'm getting some 17"s soon and want to upgrade the brakes at the same time. I can't justify a set of Alcons or probably even AP 4's but see that Godspeed do a big disc conversion using the standard callipers.

My question then is this:
What advantage is gained by using standard callipers on a bigger disc?
Surely the contact area from the pads is going to be the same as that on a smaller diameter disc given that the calipers are the same size?
At the same time surely as the braking force is being applied further out from the centre of rotation there must be a greater rotational force and inertia to overcome?
How can all of the above improve brake performance (other than change in disc quality and pad compound)?

Cheers

Godspeed Brakes

iTrader: (259)

Hi Simon , The reason the standard calipers work better with bigger discs is the calipers have more leverage , I can explain it better by try undoing a wheel nut with a small ratchet , then using a power bar , it's a lot easier with the power bar as you have more leverage , it work the same with the brakes , also our 335mm kit has bigger pads than the standard subaru pads , Cheers , Ian

GavinP

Simon,

Have you got 2pots or 4pots on your car at present ?

Thanks

Gavin

scoobyboy

i agree with ian it's coz of the extra leaverage the further away from the centre of the wheel the caliper is the easier it is to stop a car

Mog

I may be wrong BUT a larger disc having a larger circumferance will spin more slowly and take less effort to stop, also more surface area to dissipate heat

Just my 10bob's worth

SimonH

Sorry, been away for the weekend...

Gavin - I've got 4 pots; car's a MY00.

Mog - if you make the disc larger the <I>rotational</I> velocity at the outer edge is going to be higher than for that of a smaller disc on a car travelling at the same speed.
I would agree that there is more surface over which to dissipate the heat but surely the pads'll be generating more heat than on a smaller disc because of the increased disc inertia they're working against.

carl

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by SimonH:
<B>Mog - if you make the disc larger the <I>rotational</I> velocity at the outer edge is going to be higher than for that of a smaller disc on a car travelling at the same speed.[/quote]

Actually the rotational velocity (radians/sec) is the same -- it's the <I>linear</I> velocity tangential to the edge of the disc which gets bigger, e.g. (for those who remember vinyl) a 12" single rotates at 45rpm as does a 7" single, but the 12" one has a higher linear velocity under the stylus at its outer edge.

I think Adam has it spot on though -- the leverage is more important than the increased inertia.

Mark A

iTrader: (1)

[QUOTE]Originally posted by carl:
[B] Actually the rotational velocity (radians/sec) is the same -- it's the <I>linear</I> velocity tangential to the edge of the disc which gets bigger,

This is the exact reason I gave up physics after O level. ie v-boring.

Re-arrange this into a well known saying "a life get" You guys have too much time on your hands.

Mark A

iTrader: (1)

Train spotting anybody ?

Mark A

iTrader: (1)

Just me then, I'll get me coat.


edited because I'm pissed

[This message has been edited by Mark A (edited 13 August 2001).]