Silly question about "big" brakes

[Peter Carmichael]

 

 

Edited by - Peter Carmichael on 23 Jul 2007 11:41:59

[Setok]

Peter, as I said, I'm not quite sure what the terms are in English (and I only vaguely remember them in Finnish). Your equation is fine, but surely you are going to need more stopping power to stop dead something with more kinetic energy/force/whatever (locking wheels), in other words to counter the forward moving vector. Like, a wooden fence would probably stop a car rolling along at 5 km/h while it won't do it if you're going along at 100km/h.

 

We're talking about locking the wheels here and optimal braking. After they are locked then additional braking power isn't going to help, but my claim is that bigger brakes are needed to reach that point at higher speeds.

 

Braking feel and everything else is obviously important as well, but that's not really what I'm talking about.

 

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Kristoffer Lawson

[Ron_F]

Not sure if I want to re-open this debate but I do have another "silly question" about my big brakes

 

During a recent MOT, both myself and the tester noticed that the off-side front brake locked up much earlier that the near side front, i.e the osf brake gave less braking than the nsf brake. The car was well within the permitted limits (so it passed) but neither of us could understand why one side gave significantly less braking than the other.

When the brake balance was tested, both rollers going, the dials progressed at an equal pace, but it was always the osf that locked first.

When tested individually, the nsf gave about 1.5 times the braking force of the osf.

The car is an SV140 with the uprated Caterham big brakes, 7800 miles since new, still plenty of pads

 

I had previously noted that the osf tyre was always the first to lock when pressing on, I put this down to uneven weight distribution.

 

On the Brake test rollers, both wheels would have the same mechanical grip, so what would cause the osf to lock first?

[6speedmanual]

Ron

 

Weight distribution also at work on MOT brake rollers.

 

If you had previously noticed osf locking up before nsf, the MOT measuring equipment is confirming this. As it happens in a static condition on the rollers, I suspect a mechanical issue, rather than driving style eg: braking into turns.

 

More likely to be uneven braking effort rather than chassis set-up (because weight will be more on osf due to driver).

 

Possible causes include:

 

One or more lazy/seized pistons in one of the calipers

Glazed pads/discs on one side

Blocked hydraulic pipe

etc

 

Peter

 

 

6SpeedManual

*tongue*There's no such thing as too much BHP per Ton 😬

[iguana]

As above, need to investigate that, would expect nsf to lock up 1st, always did when solo in my old track car & on road rubber, balance was fine & calipers were new.

 

Just had similar on my old bmw tintop, but worse so MOT fail on balance, so yesterday took caliper off & apart, piston had rust on it, seal was caught & not allowing full movement, popped piston out carefully cleaned it & de rusted, the seals were fine popped it back in & all seems good, hurrah.

 

 

[Alex Wong1697456877]

No science.

 

Subjectively, the big brakes are much better at stopping the first time and repeatedly.

 

Subjectively, it feels like the control up to the point of locking up is much better with the big brakes.

 

Again no science, but if you turn in hard and just yank the wheel to one side, the tyres will loose grip well before you generate 1 g lateral force. If you gently feed the wheel, you'll generate up to about 1g before the tyres give. It feels like the same thing. The way the braking force is applied allows you to get much higher slowing forces, and in a much more controllable manner with the bigger brakes.

 

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[Ron_F]

Guys,

Thanks for your feedback, maybe I'm a bit thick 😳 but how/why would reduced braking effort cause the osf to lock up earlier?

 

Surely, if the braking effort was reduced as a result of a mechanical problem (sticking piston etc), then the osf brake would not be able to lock the wheel at all. Currently it locks it than sooner than the nsf.

 

Is this a case where the application of common sense doesn't work

 

Ron

 

[6speedmanual]

Hi Ron

 

"Uneven" braking effort, not necessarily excessive effort on osf. The nsf could be suffering one of the aforementioned issues.

 

When one of the front wheels is giving less, the tendency is to press pedal harder to try to acheive the expected vehicle retardation and lock up point of the working brake/wheel is arrived at very quickly.

 

Peter

 

 

6SpeedManual

*tongue*There's no such thing as too much BHP per Ton 😬