Date: Mon, 21 Jun 2004 15:27:09 -0400
Reply-To: vw4x4@FYI.NET
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Eric Zeno <vw4x4@FYI.NET>
Subject: Re: Brakes (upgraded and standard)
In-Reply-To: <2388.63.103.227.2.1087838883.squirrel@63.103.227.2>
Content-Type: text/plain; charset=us-ascii; format=flowed
Try semi-metalic brakes. These are made to running hot.
Eric
Ryan Press wrote:
>Kim Brennan said:
>
>
>>I was giving some thought on a drive home late Saturday to the issue of
>>brakes. The few folks that have actually upgraded to the "big brake"
>>kits haven't had really definitive comments on whether they allow you
>>to brake "better. This is not what this posting is about however.
>>
>>Braking is, in essence, a way to transfer motion energy into heat
>>energy. it does this by the mechanical application of calipers (and
>>brake shoes) to the front discs (primarly, but also to the rear brake
>>drums). The resulting friction of the brake pads/shoes against the
>>discs/drums results in the generation of heat. In time it also slows
>>the vehicle down. However, now you have hot discs/drums.
>>
>>In order to improve your braking capability, then, you need to do at
>>least one of the following, increase the clamping force, increase the
>>friction factor, increase the transfer of energy (heat) to the
>>destination (discs, shoes).
>>
>>The Big Brake kits, primarily attack the last two items. The friction
>>factor is increased (marginally, in my opinion) by having a larger wear
>>area (larger diameter disc). The transfer of energy is increased by
>>adding more mass to the discs and adding ventilation to the discs
>>(meaning they can accept more heat in, as they in turn can transfer it
>>to the air faster. )
>>
>>Note that cross drilled discs (frequently available in high end sports
>>and sporty cars) add increased ventilation with the cross drilling,
>>with a slight loss of mass of the disc. I presume that they have done
>>sufficient testing to notice a gain in the heat transfer with the
>>added ventilation despite the loss of mass. Since there is also,
>>however the added benefit of removing unsprung mass (increasing
>>acceleration performance) there may be a separate compromise decision
>>impinging on cross drilling.
>>
>>Of course, this is all just 2am rambling. The type of discussions that
>>geeks have way too late at night...
>>
>>
>>
>
>
>I've been giving thought to my 2wd Vanagon Westy's braking capabilities as
>well. Just this last weekend, towing my dirt bike down the Hopland Grade,
>my brakes were overheating.
>
>It takes a pretty substantial pedal force to lock the wheels up, and
>obviously the brakes are becoming too hot for the friction material.
>
>With the big brake conversion it seems like a lot of money for a marginal
>increase in braking capability.
>
>I am not convinced cross-drilled rotors are the best solution either. If
>the holes are truly drilled and not cast-in then they can become the
>starting point for stress cracking. I much prefer slotted rotors, with a
>cast-in slot. I have these on my MkIV GTI.
>
>Also, I believe the benefit to cross-drilled rotors is to allow hot gases
>to escape the brake pad surface, and that cross-drilled rotors do not
>substantially cool the rotors down vs standard vented rotors.
>
>I have in my possession a set of shoes and pads from Porterfield Brakes.
>They have the R4-S Carbon-Kevlar compound. They have an average
>coefficient of friction of 0.4 mu, and advertise low dust and long
>rotor/drum life.
>
>I have not yet installed these pads and shoes and I'll post an update when
>I've had a chance to give them a good test.
>
>Ryan
>
>
>
>
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