smart51
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| posted on 24/11/15 at 08:39 PM |
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does a rear disc conversion make sense?
For a low budget tin top track car, is it worth the bother of replacing rear drums with discs? What are the benefits of each? I've been told
by some that the stopping force of a drum brake can be the same as a disc and that the main benefit is bling / pub talk. Is there some truth in that?
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DW100
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| posted on 24/11/15 at 08:56 PM |
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If it is FWD and you remove all the inside trim then the front will be doing 80% of the work.
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Wadders
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| posted on 24/11/15 at 08:56 PM |
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does a rear disc conversion make sense?
Only if it weighs less.
[Edited on 24/11/15 by Wadders]
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britishtrident
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| posted on 24/11/15 at 09:28 PM |
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It really depends on weight especially the weight on the rear wheels ---- Some ultra light Minis racing in the Special Saloon used to run with only
one brake shoe on the rear but massive vented discs at the front. On the other hand to notch Special Saloon racing Imps needed identical
10.25" discs all round.
Drum brakes have differently shaped friction characteristic from disc brakes at low hydraulic pressures they self servo and give more braking
friction than disks but the friction falls off more sharply as the force applied increases.
This can be quite advantageous for front/rear brake balance in changing weather conditions.
One disadvantage with drums especially in smaller drum sizes due to mechanical distortion of the drum and shoe the friction characteristic falls off
so much that no matter how much extra force you put on the pedal the barking effort at the wheel won't noticeably increase.
.
Discs give better pedal feel they are self-adjusting and they cool faster and suffer less from pad friction fade and are immune from long pedal due
to thermal expansion and suffer less from long pedal due to fluid boiling.
i
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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smart51
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| posted on 24/11/15 at 09:38 PM |
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quote:
Originally posted by britishtrident
It really depends on weight especially the weight on the rear wheels ---- Some ultra light Minis racing in the Special Saloon used to run with only
one brake shoe on the rear but massive vented discs at the front. On the other hand to notch Special Saloon racing Imps needed identical
10.25" discs all round.
Drum brakes have differently shaped friction characteristic from disc brakes at low hydraulic pressures they self servo and give more braking
friction than disks but the friction falls off more sharply as the force applied increases.
This can be quite advantageous for front/rear brake balance in changing weather conditions.
One disadvantage with drums especially in smaller drum sizes due to mechanical distortion of the drum and shoe the friction characteristic falls off
so much that no matter how much extra force you put on the pedal the barking effort at the wheel won't noticeably increase.
Discs give better pedal feel they are self-adjusting and they cool faster and suffer less from pad friction fade and are immune from long pedal due
to thermal expansion and suffer less from long pedal due to fluid boiling.
So drums are probably better for road use but if you're fond of repetitive heavy breaking, discs could be better.
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mcerd1
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| posted on 25/11/15 at 01:01 PM |
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overall if you don't feel the car is under braked at the rear then its probably only worth it if your going to make a significant weight
saving
also to add to BT's list:
Handbrakes
the self servo effect that the drums have also applies to the handbrake.
even though the drum brake 'self adjusters' normally mean you need to adjust them yourself - the adjusters for the handbrake on discs can
be even more of a PITA, if they are really seized up then you'll need to rebuild the calipers 
also if you've managed to get the brakes nice and warm before parking, the drum will cool down and contract - effectively tightening around the
shoes and increasing the effectiveness of the handbrake as it does so...
but as discs cool down they contract they shrink away from the pads and reduce the effectiveness of the handbrake...
(I remember a few years ago several tin-top models that were rolling away 30min after being parked...)
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smart51
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| posted on 25/11/15 at 01:26 PM |
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The standard brakes are fine for road use but can fade with track use. I want to keep 13" rims so I can have decent track day tyres so I
can't make the front brakes bigger, though fast road pads can be fitted to reduce fade a bit.
Basically, I'm costing a list of mods and picking the ones that give the best return for a limited budget. I'm guessing that rear discs
might not make the cut.
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alfas
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| posted on 29/11/15 at 09:48 PM |
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the problem with kitcars is that they mostly use the identical brakes as the donor, but with less weight on the back.
therefore the rear brake cannot work as efficant as in the donor.
improving the rear you can fit bigger rear wheel cylinders.
quality rear shoes and drums in good nick would also improve things.
with bigger rear wheel cylinders your master-cylinder might come to its limit and needs to be changed too.
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britishtrident
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| posted on 30/11/15 at 06:48 AM |
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quote:
Originally posted by alfas
the problem with kitcars is that they mostly use the identical brakes as the donor, but with less weight on the back.
therefore the rear brake cannot work as efficant as in the donor.
improving the rear you can fit bigger rear wheel cylinders.
quality rear shoes and drums in good nick would also improve things.
with bigger rear wheel cylinders your master-cylinder might come to its limit and needs to be changed too.
???????
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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alfas
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| posted on 30/11/15 at 09:12 AM |
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oops....did not read the original posting correctly.....sorry.
now i see its not about a kitcar.
anyway: the mentioned improvements could be also done on a tin-top car for improving the rear brake efficiancy.
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