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?

I don't think it does....it generates the same torque reaction wherever it is mounted...

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.

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

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.

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.

the danger with inboard disks is breaking a drive shaft and having no brakes ARGHH!

Ned.

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

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.

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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.

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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

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?

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]

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.

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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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

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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

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giel:

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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?

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They will be the same, unless you have found a way to get around F = MA.

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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

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

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

ceebmoj:

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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

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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!

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Rescued attachment LT_RH_rear.jpg

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

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?

Spyderman:

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The point is there is very little in common between your offroaders and road cars.

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You wouldn't use a locked diff on a road vehicle

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Originally posted by suparuss
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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im not convinced the speed has anything to do with it, just the torque at the calipers . sure heat is created, but that is constantly variable on a car any way depending on cooling efficiency and the speed you are going at the time which effects airflow over the disks. more heat is probably made by moving the disk faster but the brake components are designed to take really high temperatures.
formula 1 cars cant stay standing for too long because with no air flow the heat from the brakes startd to boil the fluid in the pipes.

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Originally posted by suparuss
im not convinced the speed has anything to do with it, just the torque at the calipers . sure heat is created, but that is constantly variable on a car any way depending on cooling efficiency and the speed you are going at the time which effects airflow over the disks. more heat is probably made by moving the disk faster but the brake components are designed to take really high temperatures.
formula 1 cars cant stay standing for too long because with no air flow the heat from the brakes startd to boil the fluid in the pipes.

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youre kidding right?? after a few full speed laps there is enough heat in the disks and pads so that if the car stands still, since there is no air flow to cool the caliper, the heat just transmits through the caliper to the pipes. anyone who even watches f1 should know that.

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Originally posted by suparuss
youre kidding right??

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re underslung calipers catching stones etc, and being difficult to bleed.
On my bikes (bimota) has a rear underslung caliper and I believe a few kawasakis do too, it doesnt seem to suffer from seizure from dirt or stones etc into it though the torque arm anchoring the caliper does cover the intake area of the caliper.
They got round the tough bleeding problem by.... putting the bleed nipples on the top (bottom?) of the caliper...
Again I havent had a problem getting it to bleed up, but if it ever gave me problems or the nipples were in the wrong place id use the cunning highly tech solution of undoing the mounting bolts and holding the caliper up with a tyre lever where the disc would be.
As for why a underslung caliper, not going there..