Front brakes

[Kozy]

If anyone needs help designing a braking system, give me shout.

I created a setup app for the MX5 which takes into account pretty much every parameter you can imagine and accurately calculates how each individual change will affect things like brake balance, stopping distances, disc temperatures and pedal effort.

https://www.blackartgraphics.com/pages/mx5-brake-b...

I can’t make one for every car (it requires knowing the CG height and prop valve properties) but having worked out the calculus that powers that app, I should be able to help you pick a decent set of discs and calipers for almost any car.

[Ste372]

Hi kozy can I give you a message and we can discuss what I'm trying to do?
Thanks Ste

[InitialDave]

Kozy said:

D2 strike me as one of those companies that make a part, and then make a bracket to fit it to almost every car on the market. Wouldn’t trust them to have done any vehicle specific R&D beyond the caliper bracket...

Seems like a distinct possibility, yes, it was just the first thing Google threw up.

[GreenV8S]

Kozy said:

(it requires knowing the CG height and prop valve properties)

I'm surprised you're taking the proportioning valve characteristics as an input - I would expect that to be an output (i.e. calculated to give the correct dynamic pressure distribution based on the CoG height/wheelbase/static line pressure of the selected setup).

[AW111]

Kozy said:

If anyone needs help designing a braking system, give me shout.

I created a setup app for the MX5 which takes into account pretty much every parameter you can imagine and accurately calculates how each individual change will affect things like brake balance, stopping distances, disc temperatures and pedal effort.

https://www.blackartgraphics.com/pages/mx5-brake-b...

I can’t make one for every car (it requires knowing the CG height and prop valve properties) but having worked out the calculus that powers that app, I should be able to help you pick a decent set of discs and calipers for almost any car.

Nice program : I had a play, trying to input my MR2, but got stuck at the brake size drop-down, because none of the options matched the MR2 sizes.
A version where rotor sizes (and bias) could be typed in would be great.

Data for you :
1986 MR2 (aka AW11 mk1a).

Weight 970 kg + driver
45% / 55% f/r
COG 432 mm (without driver)
Wheelbase 2319 mm

Tyres :
185/60/14 f & r (stock),
195/50/15 f & r (currently fitted)

Brakes (85-86)
Front 243 x 18 mm (vented)
Rear 240 x 10 mm (solid)

Brakes (86-90)
Front 258 x 18
Rear 263 x 10

I can't find my bias valve data, will update when I do.

Note : Mk1 MR2's are known for locking front brakes : one option is to keep the 243 mm fronts, and fit '97 263 mm rears.

[Kozy]

GreenV8S said:

I'm surprised you're taking the proportioning valve characteristics as an input - I would expect that to be an output (i.e. calculated to give the correct dynamic pressure distribution based on the CoG height/wheelbase/static line pressure of the selected setup).

Other brake bias calculators do that sort of thing, they are open loop calculations which take a target level of acceleration and give you the parameters required to achieve it.

This is a closed loop calculation which will tell you what the car does as standard, and how each individual change will alter the performance. It's a subtle difference, but it is what makes this quite a powerful tool. The former is only really of use to people building cars from scratch, whereas the latter will tell you how to optimise what you already have. The only issue is, you need a lot of info for it to be accurate!

[Kozy]

Ste372 said:

Hi kozy can I give you a message and we can discuss what I'm trying to do?
Thanks Ste

You haven't set yourself up to receive emails. I think I have, so feel free to shoot me an email over.

AW111 said:

Nice program : I had a play, trying to input my MR2, but got stuck at the brake size drop-down, because none of the options matched the MR2 sizes.
A version where rotor sizes (and bias) could be typed in would be great.

Data for you :
1986 MR2 (aka AW11 mk1a).

Weight 970 kg + driver
45% / 55% f/r
COG 432 mm (without driver)
Wheelbase 2319 mm

Tyres :
185/60/14 f & r (stock),
195/50/15 f & r (currently fitted)

Brakes (85-86)
Front 243 x 18 mm (vented)
Rear 240 x 10 mm (solid)

Brakes (86-90)
Front 258 x 18
Rear 263 x 10

I can't find my bias valve data, will update when I do.

Note : Mk1 MR2's are known for locking front brakes : one option is to keep the 243 mm fronts, and fit '97 263 mm rears.

I'll try and find some time to set one up. If you can find the prop valve data that would be good, otherwise I'll just drop the adjustable Wilwood valve in.

[GreenV8S]

Kozy said:

GreenV8S said:

I'm surprised you're taking the proportioning valve characteristics as an input - I would expect that to be an output (i.e. calculated to give the correct dynamic pressure distribution based on the CoG height/wheelbase/static line pressure of the selected setup).

Other brake bias calculators do that sort of thing, they are open loop calculations which take a target level of acceleration and give you the parameters required to achieve it.

This is a closed loop calculation which will tell you what the car does as standard, and how each individual change will alter the performance. It's a subtle difference, but it is what makes this quite a powerful tool. The former is only really of use to people building cars from scratch, whereas the latter will tell you how to optimise what you already have. The only issue is, you need a lot of info for it to be accurate!

I don't really follow what you mean by 'closed loop' and 'open loop' calculations and the difference between them. I guess you're trying to say you assume the brake balance is currently right and must not be allowed to change, and you assume the pedal force (line pressure) is also perfect and so the bias valve does not need to change. That might be the case in specific situations but will not always be the case.

[Kozy]

GreenV8S said:

I don't really follow what you mean by 'closed loop' and 'open loop' calculations and the difference between them. I guess you're trying to say you assume the brake balance is currently right and must not be allowed to change, and you assume the pedal force (line pressure) is also perfect and so the bias valve does not need to change. That might be the case in specific situations but will not always be the case.

Far from it. The brake balance is rarely 'right', that's the point.

No, it is closed loop because it always solves the following equation:

Front Grip - Front Brake Force = 0

That is to say that it always finds the point of front tyre lockup, no matter what changes you do.

It does this by making tiny iterations to the pedal input force until the front brake force is equal to the available grip, and takes this point as the threshold braking limit. From this the current line pressure is used to work out the rear brake force, which is added to the front to give the total brake force, which gives you your rate of acceleration and load transfer. The load transfer of course feeds back to the available grip at the front axle, and so it goes in a cycle, it's a constant feedback loop which continues until the equation is satisfied.

It's complicated to explain, but essentially making changes on this model will give you an accurate simulation of the real world effects. By knowing exactly what point the front tyres lock up, things like dynamic load transfer, rate of acceleration and stopping distances can be calculated. It can tell you how changes to the braking system will affect the amount of pedal force required to achieve threshold braking, and even brake disc temperatures can be simulated by knowing the amount of energy flowing though them.

Using a simple open loop calculation, the only result you would get is that your brake force distribution changed from '75/25' to '78/22'.

Not terribly useful in comparison...

Edited by Kozy on Thursday 2nd November 21:29

[GreenV8S]

Kozy said:

Using a simple open loop calculation, the only result you would get is that your brake force distribution changed from '75/25' to '78/22'.

Not terribly useful in comparison...

I've got exactly the opposite opinion, but perhaps that's because we're trying to solve different problems.

I'm envisioning this being used by somebody trying to design a braking system upgrade. The goal is to achieve the best performance, handling and safety by designing a setup that has the correct thermal, static and dynamic balance. The arithmetic involved is not especially difficult and no harder than what you've already done. A tool similar to the one you have created could be quite useful to somebody trying to do that.

On the other hand, knowing how many seconds per lap (or whatever) are being lost due to a badly designed braking system seems to be focusing on the wrong thing and I don't understand why somebody would find that useful.

[Kozy]

GreenV8S said:

On the other hand, knowing how many seconds per lap (or whatever) are being lost due to a badly designed braking system seems to be focusing on the wrong thing and I don't understand why somebody would find that useful.

Those are ‘interesting byproducts’ of the calculation, stuff that can be worked out if you know the stopping distance.

You cannot easily calculate the stopping distances for a given set of parameters using an open loop calculation, it is a balance equation which needs to be solved.

[GreenV8S]

Kozy said:

Those are ‘interesting byproducts’ of the calculation, stuff that can be worked out if you know the stopping distance.

You cannot easily calculate the stopping distances for a given set of parameters using an open loop calculation, it is a balance equation which needs to be solved.

What you're calling 'closed loop' is just successive approximation. It's a way to solve the equation. It's not the only way, and with a bit of maths it would be possible to calculate it directly if you wanted. Not that I would bother - the iterative approach trades CPU cycles for thinking time which is IMO a good tradeoff when you only want a rough approximation.

I still don't get the intended use of the calculator. Is it trying to show people how much their poorly balanced setup is impacting performance to convince them to correct it? I'm surprised any convincing is necessary. I'd expect anyone sufficiently interested in the stopping distance to want this type of estimate, to be dissatisfied with a poorly balanced brake system and want to know how to correct that. That addresses the handling and safety issues as well as improving performance. The maths is no harder, the parts are no more expensive, and I can't see any good reason not to correct the balance.

If the braking system is balanced correctly we can get a reasonably good estimate of stopping distance from speed and mu and don't need all that successive approximation.

[Kozy]

Plenty of people in the MX5 community find it a useful tool to optimise their brake setups, that was what it was designed for.

I’m not really sure what your issue is with it, but you’ve clearly convinced yourself that it serves no real purpose, and I have far better things to do than to try and convince you otherwise.

Edited by Kozy on Tuesday 7th November 19:34