Brake upgrade

[PW@Woodsport]

Indeed lol, I was just trying to say that more piston area ie bigger calipers will *not* shorten your stopping distances, purely because you have more brake force. But a bias change will.

Not necessarily - in the standard setup the rears aren't providing as much braking as they could thanks to the bias valve. With ST165 front calipers and the bias valve gutted the bias is approximately the same as standard, but overall braking is improved whilst still having the safety of the fronts locking before the rears.

And don't forget that in most cases cars with upgraded brakes will usually also have more overall grip than standard as they'll probably be running bigger modern tyres with more grip than the OEM ones back in 1985 so are less likely to lockup with the higher braking forces IYSWIM

100% agree with that, it's also reinforced by real world experience which confirms exactly that.

[MrLuke]

Same size disks, but larger pad area and higher clamping force as the two cylinders are greater area than the standard single one

A better distribution of the braking force is the main benefit from increasing numbers of pistons i.e. squeezing the disc in 2 places works better than just 1.

[BarronMR]

Not necessarily - in the standard setup the rears aren't providing as much braking as they could thanks to the bias valve. With ST165 front calipers and the bias valve gutted the bias is approximately the same as standard, but overall braking is *improved* whilst still having the safety of the fronts locking before the rears.

you may need to clear up the term *improved* for me, can you give me a measurable aspect to this? Repeated stopping capability, single stop distance or such like?

Anyways back to point at hand, so assuming the same tyre frictional restraints as the previous set-up, bias is the same. The fronts lock first in both instances, I still say that by altering the bias alone its possible to achieve the same stopping performance. This being measured by distance over a single stop as a system with the ST165 setup without adding the associated mass.

Its the only reasonable explanation that all your achieving by fitting the ST165's is using more of the rear end frictional capability.

I'd happily wager the stock mk1 setup even with modern tyres, with a perfect bias could likely still lock all 4 wheels. Thus exceeding the clamping load required to achieve a maximum effort stop.

And don't forget that in most cases cars with upgraded brakes will usually also have more overall grip than standard as they'll probably be running bigger modern tyres with more grip than the OEM ones back in 1985 so are less likely to lockup with the higher braking forces IYSWIM

Agree, but it is also the case that the braking system will of been designed to cope with the worst possible case scenario. This being full laden t-bar supercharger with all the trimmings. Leaving a great deal of excess braking capacity for the average sunroof n/a.

Going back to bias, I really wouldn't want to mess with it too much. The more grip you have the more the weight transfers to the front leaving the rear with less and less dynamic load with which to apply a brake force. Locking a rear in 99% of driving situations is a much more serious event than a front lock.

[BarronMR]

100% agree with that, it's also reinforced by real world experience which confirms exactly that.

Hey Paul,

I agree that fitting the calipers can reduce the stopping distance, but what I disagree with is that its in any relation to the size or configuration of the stoppers.

My theory is the shorter stopping is purely down to bias change.

[BarronMR]

Same size disks, but larger pad area and higher clamping force as the two cylinders are greater area than the standard single one

A better distribution of the braking force is the main benefit from increasing numbers of pistons i.e. squeezing the disc in 2 places works better than just 1.

The distribution only effects how the same force is applied, in reality this mainly effects wear and temperature distribution. My point still stands the stock system can in any event lock the darn wheels, being able to apply anymore force is just wasted effort.

And to be honest you would be better using a differential bore, ie 2 different sized pistons

[PW@Woodsport]

100% agree with that, it's also reinforced by real world experience which confirms exactly that.

Hey Paul,

I agree that fitting the calipers can reduce the stopping distance, but what I disagree with is that its in any relation to the size or configuration of the stoppers.

My theory is the shorter stopping is purely down to bias change.

Hi mate, the problem with that theory is that if you only gut the bias valve on a stock Mk1 with stock calipers it won't stop as quickly as an St165 caliper'd car with no gutted valve.

So there has to be more going on than just bias.

Toyota switched up to twin piston calipers on the Rev1 Mk2 but retained the same size master cylinder as a Mk1.

All i know is the St165 upgrade is significantly better than stock at stopping the Mk1, but i do see what you mean about it affecting bias, there is no doubt it has to.

[BarronMR]

Hi mate, the problem with that theory is that if you only gut the bias valve on a stock Mk1 with stock calipers it won't stop as quickly as an St165 caliper'd car with no gutted valve.

So there has to be more going on than just bias.

Toyota switched up to twin piston calipers on the Rev1 Mk2 but retained the same size master cylinder as a Mk1.

All i know is the St165 upgrade is significantly better than stock at *stopping the Mk1*, but i do see what you mean about it affecting bias, there is no doubt it has to.

*I assume you have meant a straight-lined test here*

But perhaps by fitting a variable bias valve, you could dial the optimum straight line brake bias in (ie locks all four wheels as close to simultaneously as possible) and in theory the standard setup will be able to apply the maximum brake force that the vehicle is frictionally capable of. This is assuming that the calipers can apply a powerful enough clamping load to overcome the brake torque.

[PW@Woodsport]

Both to be honest, we've just found it stops better under all conditions than stock.

There has always been quite a lot of resistance to accept the St165 caliper mod by some, i have no idea why, it's an excellent upgrade, still a Toyota caliper and plugs straight on, gets rid of the front lock up tendancy and reduces stopping distances, fits under stock wheels and it also doesn't suffer fade.

Win all round really, too many people have tried it for themselves and found them great, so don't listen to me banging on about them, i'm only the guy that discovered the mod.