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Brake balance adjustment
matt_gsxr - 26/5/13 at 09:58 AM

Hi there,

So I have a balance bar and a couple of cylinders. I set it biased heavily to the front for SVA and it passed.
Basically as we all know the fronts need to lock before the rears.
It has also gone through an MOT more recently so in general terms it is adequate.

But, I am fairly sure that the rears are doing quite little. Slow to clear rust from rear disks, lock-up from front on track.

So I know how to make the adjustment but I don't know how to gauge quantitatively whether it is better. I am sure I can kid myself that it improves when I make an adjustment, but I have cleaned the car before and felt that it drives better, so I know how fallible my senses/brain is.

Any recommendations?

Matt

matt_claydon - 26/5/13 at 11:53 AM

You want the most effort from the rear you can get whilst still locking fronts first.

Next track day, move the bias progressively towards the rear until you experience rear lock-up, then bring it back towards the front a few turns to bring back stability and with a bit of a safety margin. Ideally do this in wet and dry to ensure the car's safe in all conditions.

You want to do it from a decent speed to ensure full weight transfer to the front, so best not done on the road.

phelpsa - 26/5/13 at 12:39 PM

quote:
Originally posted by matt_gsxr
Hi there,

So I have a balance bar and a couple of cylinders. I set it biased heavily to the front for SVA and it passed.
Basically as we all know the fronts need to lock before the rears.
It has also gone through an MOT more recently so in general terms it is adequate.

But, I am fairly sure that the rears are doing quite little. Slow to clear rust from rear disks, lock-up from front on track.

So I know how to make the adjustment but I don't know how to gauge quantitatively whether it is better. I am sure I can kid myself that it improves when I make an adjustment, but I have cleaned the car before and felt that it drives better, so I know how fallible my senses/brain is.

Any recommendations?

Matt


Matt,

The annoying this about these cars is the diagonal weight imbalance. I've found that if I run the brake bias that should be appropriate it locks the passenger side rear, so I always end up winding it forward to the point where they are doing very little again!

Adam

britishtrident - 26/5/13 at 12:46 PM

To road test you need a good smooth clean dry tarmac surface.

At slow speed apply the brakes until you feel a wheel lock, if front adjust the balance one turn at a time then road test repeat until you feel either front and rear locking together or slight locking at the rear alone. For road use back the adjustment off 1.5 turns from this point and retest, for track use back off 1 turn from the rear locking point and re-test if it feels OK carefully test again at progressively higher speeds.

For track use in the wet you can use more bias towards the rear --- try 1 turn difference between wet and dry settings.

[Edited on 26/5/13 by britishtrident]

britishtrident - 26/5/13 at 01:12 PM

quote:
Originally posted by phelpsa
[The annoying this about these cars is the diagonal weight imbalance. I've found that if I run the brake bias that should be appropriate it locks the passenger side rear, so I always end up winding it forward to the point where they are doing very little again!

Adam



In the old days with drum brakes there was the option of fitting a smaller bore wheel cylinder on the left rear.

A lot depends on by what the car is corner weighted if the car is set to have equal front weights it will make premature locking on a single rear wheel inevitable, this one of the reasons I prefer weighting based on the theoretical share of the load.

matt_gsxr - 26/5/13 at 02:59 PM

Thanks guys. Very good tips.

I will put it into practice the next time I have some track time.
Not sure I know how a rear lock-up feels compared to a front lock-up, but I guess I will learn!

Regarding corner weights, mine are all fairly equal (rear passenger side is probably a bit lighter but not much).

Thanks again,

Matt

adithorp - 26/5/13 at 06:41 PM

quote:
Originally posted by matt_gsxr
Thanks guys. Very good tips.

I will put it into practice the next time I have some track time.
Not sure I know how a rear lock-up feels compared to a front lock-up, but I guess I will learn!

Regarding corner weights, mine are all fairly equal (rear passenger side is probably a bit lighter but not much).

Thanks again,

Matt


You'll know it when it happens.

Feels the same as locking the rear wheel on your bike. Rear end dances around and tries to overtake the front.

I'd go 2 turns to the rear then test. If it locks the rears come back 1 turn, if not try another 2 turns... repeat 'till it's right. You do need to do it at max braking or you won't get max weight transfer of the rear. Mine was fine braking hard from 50 but lethal/fun (delete as appropriate) from 100.

matt_gsxr - 26/5/13 at 09:53 PM

Thanks Adi,

So, its a case of "you will know!".

I can see why this might be inadvisable on the local bypass.

britishtrident - 26/5/13 at 10:08 PM

Be cautious when adjusting more bias on to the rear, one turn of adjustment will make a bigger difference when the bar is centred than it will towards the extreme ends of adjustment.

Premature front locking is a nuisance but premature locking of both rears on can put you into the ditch in the blink of an eye.

unijacko67 - 26/5/13 at 11:05 PM

Once you have it set to max rear without lockup or as you like also be careful when changing tyre type mid event or so as this has given me scary moments in the past. I’m considering a couple of bias gauges as clicks either way on the adjuster are hard to keep track of, but if you have set results with set tyres at set pressures it should speed up the fine tuning.

Has anyone used bias gauges, as I would think it would be the most useful gauge in the car?

matt_gsxr - 27/5/13 at 07:35 AM

I've no experience of bias gauges, but I am surprised that the balance adjusters don't have a counter on them so you know how many turns. You would have thought this would be a standard, I guess you can count threads in the footwell.

britishtrident - 27/5/13 at 09:58 AM

The traditional way is to measure how much the adjuster sticks out at one end.