Rorty
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 posted on 4/7/03 at 04:18 AM |
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Caliper Position.
After the query about rear castor, I thought I'd initiate an old chestnut, which I don't think has appeared here before.
Does it matter whether a caliper is mounted fore or aft of a hub?
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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Alan B
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| posted on 4/7/03 at 12:23 PM |
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I don't think it does....it generates the same torque reaction wherever it is mounted...
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ned
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| posted on 4/7/03 at 12:26 PM |
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this was discussed elsewhere on the forum IIRC the general concencus was that it doesn't matter, but it'd be easiest if the bleed nipples
were at the top, stops you havinbg to take the calipers off to bleed the brakes.
An interesting comment was that formula one sling them on the bottom/underside to reduce the centre of gravity.
Ned.
beware, I've got yellow skin
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sgraber
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| posted on 4/7/03 at 02:52 PM |
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I debated putting them on the bottom to reduce the cg, but the location of the E-Brake bracket made that all but impossible. In addition, I think that
pebbles and dirt would probably get caught in the caliper easier if it were upside down.
graber
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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ceebmoj
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| posted on 4/7/03 at 02:58 PM |
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Hi
I was looking at a TVR diff (cant remember the model sorry) the other day that had in board disks has anybody else used such a diff on hear or built a
car with inboard disks?
All though I assume that by moving the mass round in the suspension system would require different spring rates to be used. All though I know very
little about this so I may well be wrong.
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ProjectLMP
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| posted on 4/7/03 at 03:03 PM |
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I think that the F1 cars that have the calipers on the underside have a hard time bleeding them. I think I read in RaceTech that that is the reason
all teams haven't adopted this approach.
Inboard brakes don't appear as good as outboard to me for two reasons. Firstly, there is the issue of cooling them. More importantly all the
braking torque goes through the drive shafts. The stress reversals can play havock with the shafts and joints.
Home of the Astronomicalcost Mid engined LMP project
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ned
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| posted on 4/7/03 at 03:07 PM |
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the danger with inboard disks is breaking a drive shaft and having no brakes ARGHH!
Ned.
beware, I've got yellow skin
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Spyderman
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| posted on 4/7/03 at 11:38 PM |
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I don't think that the race teams would put the calipers on the bottom for CG reasons. Possibly for cooling reasons?
Anything on the wheels or hubs is unsprung weight and as such does not contribute to the CG height.
Terry
Spyderman
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Rorty
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| posted on 5/7/03 at 04:04 AM |
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An interesting selection of replies. I initally posed the question with regard to a calipers relative position around the wheel hub, but the thread
grew to include inboard mounting also.
Of course, the positioning of a caliper has absolutely no effect on the functioning of the brakes or suspension. I have in the past, had, and have
seen the same discussion several times, with some people adamant the position of a caliper would affect a car's handling.
The point about the bleed nipple's orientation is probably the only valid one in general terms.
It's also funny how inboard brakes go in and out of fashion. Again, there were valid comments made here about the effects of constant direction
reversal of the driveline components.
I run inboard brakes on my off-road cars, with no detriment. However, I can only run my drive shafts on one side, and have to mark them to prevent
them being inadvertently swapped over. Previously, when I have swapped them over, they have failed before the first lap was complete, yet they
don't suffer from being contra-loaded. This would point to the forces in forward driving, being far greater than when braking or landing off a
jump.
There are two reasons I keep the brakes inboard; one is to reduce the weight at the ends of the wishbones, which can alter the flight of the buggy
when jumping, and the other is, that by mounting the disc on the "engine side" of the "diff", it multiplies the amount of
braking by just over 4:1.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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kb58
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| posted on 5/7/03 at 04:55 AM |
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quote:
Originally posted by Rorty
... that by mounting the disc on the "engine side" of the "diff", it multiplies the amount of braking by just over 4:1.
About the brakes, I'm not sure how to read that. If you look at it from an energy-in vs. energy-out point of view, it doesn't matter
where the brakes are. You have a certain amount of weight (the car) to slow down from one speed to another, so it doesn't matter how fast the
brake disks spin, or where they're located in the chain of things.
Back to your original question. I vote for locating them upright because of the bleeder, but toward the center of the car as viewed from the side.
That is, behind the axle at the front and ahead of the axle at the rear. It'll make a small contribution to decreasing the moment of inertia
(allows an improvement in turn-in.)
[Edited on 5/7/03 by kb58]
[Edited on 5/7/03 by kb58]
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Jumpy Guy
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| posted on 6/7/03 at 12:59 PM |
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tuppence worth on calliper position
I have worked with a couple of F1 teams, designing test rigs for braking... all of the teams have tried moving the callipers, and all have encountered
heat related problems, being quite tricky to move the air away in a efficient way
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Rorty
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| posted on 7/7/03 at 04:58 AM |
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kb58, by mounting the brake on the engine side of the diff, you're multiplying the brake effort by the diff ratio.
With regard to your comment about the moment of inertia, you know, I hadn't even thought about it's effect on the front wheels, with
relevance to caliper postitioning. It's a very valid point though. Do any of you with good reading, have any references to this area?
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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kb58
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| posted on 8/7/03 at 01:10 AM |
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Could be, but I can't see it. I keep going back to my "energy in, energy out" theory. It doesn't matter where the brake
rotor is or how fast it spins, it all comes down to the energy removed from the system. If you have it placed where it spins faster, then it has less
torque resistance. If placed where it spins slower, it'll be harder to slow down. It's all the same.
[Edited on 8/7/03 by kb58]
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Rorty
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| posted on 8/7/03 at 04:03 AM |
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I hear what you're saying, and on reflection, you're perfectly correct. I do however put great store in practical experience, and testing
has shown me that placing the rear brake between the engine and diff works better. Maybe there are other elements at work that I've overlooked.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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giel
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| posted on 15/7/03 at 07:06 PM |
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I've been reading through this thread and I think I help out on a few things:
1. Yes it does matter (in theory) where the callipers are positioned, for the CG height as well as the moment of inertia. I just wonder if the
difference would be significant for a non F1 car.
2. Yes the brake performance does increase by putting the brake on the drive shaft before the diff. Surely you cannot get out energy that you
haven't put in, but the point is that you DO put in more energy, because the shaft spins faster than the wheels. If you want I can explain why.
The disadvantage I see, especially off road, is the loss of brake torque on both of the axle's wheels if one of the wheels is on slippery
surface. Have you noticed this in your experience?
Giel
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Spyderman
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| posted on 15/7/03 at 11:28 PM |
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quote:
Originally posted by giel
I've been reading through this thread and I think I help out on a few things:
1. Yes it does matter (in theory) where the callipers are positioned, for the CG height as well as the moment of inertia. I just wonder if the
difference would be significant for a non F1 car.
2. Yes the brake performance does increase by putting the brake on the drive shaft before the diff. Surely you cannot get out energy that you
haven't put in, but the point is that you DO put in more energy, because the shaft spins faster than the wheels. If you want I can explain why.
The disadvantage I see, especially off road, is the loss of brake torque on both of the axle's wheels if one of the wheels is on slippery
surface. Have you noticed this in your experience?
Giel
The only way any possible effect on the CG could be achieved is if the suspension is virtually solid as on F1.
As soon as there is movement in the suspension it's value is negated.
And a very valid point about not mounting brake on propshaft. It is only effective if good grip is available to both tyres.
Terry
Spyderman
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kb58
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| posted on 16/7/03 at 01:25 AM |
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quote:
Originally posted by giel
...
2. Yes the brake performance does increase by putting the brake on the drive shaft before the diff. Surely you cannot get out energy that you
haven't put in, but the point is that you DO put in more energy, because the shaft spins faster than the wheels. If you want I can explain why.
Giel
Actually, I can explain why.
Yes it is spinning faster, and of course has less torque resistance. You can't get around the "big picture" of energy in and energy
out. Heat is heat, no matter how it's generated. Spin it fast, but with little torque, or spin it slow with lots of torque, what's the
difference. None.
Here's another way to look at it. Say you have a brake right at the flywheel (on the input to the tranny,) and a second brake at the output of
the tranny. You drive at 60mph and stope using the first brake, then measure the temperature. Now repeat using the second brake, in any gear you
want. Measure the temperature again and compare.
They will be the same, unless you have found a way to get around F = MA.
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Rorty
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| posted on 16/7/03 at 03:10 AM |
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giel:
quote:
The disadvantage I see, especially off road, is the loss of brake torque on both of the axle's wheels if one of the wheels is on slippery
surface. Have you noticed this in your experience?
Yes, you're quite correct. Point of braking is an art off-road, but when you hit the spot, it really does make a difference.
kb58:
quote:
They will be the same, unless you have found a way to get around F = MA.
Yes, that's true also.
I'm not smart enough to work out the differences, but I've been off-roading in enough different cars over the years, and I know a pre-diff
brake is more effective.
Any theories?
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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TheGecko
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| posted on 16/7/03 at 04:11 AM |
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I agree with what Kurt is saying about the energy at both points being the same but I suspect that the braking system does not convert that energy
into heat evenly with relation to speed. Maybe something in the pad/caliper/disc combination makes it more effective at higher RPM's.
Rorty's practical experience would appear to support this.
Or is there some other factor about the diff mounted disc that makes it perform better. Cooling? Torque reaction direct to chassis instead of
through suspension?(assuming IRS). Who knows? 
Anyone on the list work for a brake manufacturer and can let us in on the performance characteristics for different disc speeds?
Dominic
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ceebmoj
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| posted on 16/7/03 at 07:53 AM |
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Hi
I had assumed that when breaking was done inboard in the manor that is being described above with the break disk on the drive shaft that some form of
LSD would be used so that even if grip was lost on one weal you would still maintain some breaking ability is this is not true I would have thourt
that this method would be slightly risky.
However when I menachoned inboard mounting of disks I had ment in the form of the being two disks and both of them being mounted on the diff end of
the drive shaft
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Spyderman
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| posted on 17/7/03 at 12:06 AM |
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I am making a few assumptions here, but would imagine in Rorty's case that balanced left/right braking is not an important part of off-roading.
Slowing being done mainly by front brakes and rear brake being used to slew vehicle sideways?
Also I should imagine that his vehicles are very light and have minimalist bodywork and comforts!
If a diff brake was so successful then I'm sure it would have been implemented by a mainstream producer.
The propshaft brake used on Range Rovers is only a secondary braking system and such only needs to be approx 10% of main braking efficiency.
Terry
Spyderman
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Rorty
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| posted on 17/7/03 at 02:31 AM |
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ceebmoj:
quote:
I had assumed that when breaking was done inboard in the manor that is being described above with the break disk on the drive shaft that some form of
LSD would be used
The rear axles in our buggies are effectively locked (hence a single brake disc), that is, there isn't a convential dif. See pic
below.
Spyderman:
quote:
I am making a few assumptions here, but would imagine in Rorty's case that balanced left/right braking is not an important part of off-roading.
Slowing being done mainly by front brakes and rear brake being used to slew vehicle sideways?
Also I should imagine that his vehicles are very light and have minimalist bodywork and comforts!
Funnily, braking is fairly even to take
advantage of available grip, but can be altered on-the-fly.
The throttle is used for slewing and also for about 60% of steering!
The buggy is extremely comfortable (have a look on my site for a view of the "office", far moreso than my family sedan! The shocks give a
hovercraft-like ride and even the jumps are a pleasant experience. Hitting a kerbsized object at 120kph is barely detectable.
 
Rescued attachment LT_RH_rear.jpg
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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Spyderman
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| posted on 17/7/03 at 04:11 PM |
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Rorty,
The point is there is very little in common between your offroaders and road cars.
I don't doubt you have made it very comfortable, but it is a completely different thing to a seveneasque!
You wouldn't use a locked diff on a road vehicle, so therefore you need to brake each wheel seperately.
Hitting a curbsized object in a sevenesque could be very painful, especially the cost!
Terry
Spyderman
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suparuss
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| posted on 17/7/03 at 09:22 PM |
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may have an answer to the thing about haveing more braking force with pre diff braking. in theory the energy in - energy out would suggest that it
would be the same, but think about it- as an unrelated example, if you have say an electric drill with a 2 speed mechanical gear box, put it in low
speed and its harder to stop the the chuck from moving, in high speed its a lot easier because the power source needs more torque to move the chuck-
in the drills case the motor, and in the cars case the momentum of the car moving foreward, the torque is constant at the wheels but is changed by the
gear ratio of the diff t9o move faster but with less torque, so regardless of speed it will be easier to stop?
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Rorty
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| posted on 18/7/03 at 02:14 AM |
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Spyderman:
quote:
The point is there is very little in common between your offroaders and road cars.
Oh I don't know, I think the similarities are many.
quote:
You wouldn't use a locked diff on a road vehicle
Why not? Many do. There must be dozens of companies making after market components to convert diffs to "lockers". I know a lot of
circuit racers run lockers, but they can be used on the road too. Obviously one's driving style would need modifying slightly to eliminate
understeer!
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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