Brake Bias Valve confusion

[andy bell]

I purchased a Caterham supersport and I am finding whilst it is an utterly amazing experience to drive both on track and road there are some things that leave me flummoxed. I have the valve installed on my car next to gear stick on passenger side and I asked about it and was told 'best to leave it fully forward until you know how to use it'. Which was fair enough but my inquisitive side is shouting that I need to know more...

 

In addition I have always found the brakes to be a bit gradual which I took(guessed based on 0 knowledge) was caused by following bits:

 

AP Racing brake bias valve

AP Racing uprated brake master cylinder

high effort brake pedal this video and then 17:12. I hammer along the straight at 105 at Knockhill then hard on brakes quite far back

 

I understand the concept of it (ability to say how much brake is done front/back) but where my skills are lacking is understanding when it should be used...

 

Is this something I should really try and get a track day with someone very familiar with Caterham to explain visually and from conversation? I guess the valve fully to front is balanced brakes on front/back?

 

Valve is pictured below in its usual state

 

 

Edited by - andy bell on 11 Jul 2013 14:43:33

[Roger Ford]

Furthest forward position means maximum effort to the rear. Fiddling with it will only reduce rear braking. If you've got big brakes at the front and standard brakes at the back, it's probably well underbraked at the rear, so there are no circumstances in which the adjuster will improve things.

 

Can you lock your fronts up? It ought to be easy with big brakes. If you can't, you need to sort it out. Probably soon.

[andy bell]

not lock up no - if i am doing a decent speed (say 60) and slam on brakes its very much a gradual stop. As you can see on video I do a hard brake from 105mph down to about 40mph and 0 lockup...

 

The plan tonight is to take the wheels off and check all the brake pads (all obvious stuff) and perhaps its just my lack of checking all this a few months after I bought the car rather than before I drove it. Shocking eh.

 

Edited by - andy bell on 11 Jul 2013 14:54:18

[oldbutnotslow]

Andy

A few things here

Firstly a 7 is a non servo brake system whereas your tintop has a servo which multiplies the braking effort that you put on the brake pedal so don't expect them to feel the same

The brake bias valve is used to restrict the brake pressure to either the front or more usually the rear brakes by making 'the hole' that the fluid has to pass through smaller thus restricting the amount of fluid that gets to the calipers.

I would indeed endorse what CC have said don't mess with it unless you are going to race. On anything other than an out and out racer its not necessary.

 

You dont say which brake system you have ie standard or uprated AP or how long it has been since the fluid was changed or what type of pads you have.

 

Given that you have a bias valve it may be that you have a hard race pad in there. These are designed to work at much higher temperatures than a road pad and to resist fading by the material going outside its operating window.

Again this may be an issue. It will feel very much as you have said "OMG its not going to stop!!"

 

If this is the case a more road biased pad may suit your driving requirements

The pads generally say what the make they are and may well have a number on them ie Padigd RS14.

 

There are other things that will influence brake performance but I wont go into these at this stage.

 

Learning how to drive your car is the first thing that I would recommend. A Novice track day is where to start and make sure that you buy some professional instruction. Most of us are not born great drivers and the majority of us only aspire and dream of being a 'driving God' 😬

 

You local 7 club meeting is an excellent place to start.

 

[andy bell]

thanks some great information and really helping me to understand alot more. I got the car and guess I didnt really take into account what I would need to get into the habit of doing - nieve i know. The pads are as below and I think the person I bought the car off may only have raced in graduates series and I believe was kept/maintained by McMillan Motorsports.

 

Brakepad wise its

 

- Pagid RS15 front brakes

- Mintex M1144 rear brakes

 

And brake system wise its

AP Racing brake bias valve

AP Racing uprated brake master cylinder

high effort brake pedal

 

and I havent changed the brake fluid so guess I have to do this before the days trackday.

 

And I guess from your fantastic post(s) its designed to be for racing more than gentle pootling which explains what i am finding. All just equates to me doing more track days and getting to understand the car. And looking at the website for both manufacturers they both seem to be designed for very high running temperatures.

 

Have done 2 so far 1 more to come and I come blessed with an understanding that I have no great driving skill and eager to learn. Never been a fast driver so its all a huge learning experience.

 

Edited by - andy bell on 11 Jul 2013 15:10:24

[Roger Ford]

Sorry, so not big brakes just AP additions. Who did you buy the car from? I might know it.

 

With that setup, you would have to push hard to lock it up, but it should certainly be quite possible, especially when the pads are hot.

 

You're probably better off with a standard master cylinder, and some more road-oriented pads.

[andy bell]

So I guess long term would rather it be better on track than road - I can cope with the way it drives on road :) Plus its *so* much fun.

 

I got the car from Mr Bassage and upgraded it from Tracksport to Supersport

 

 

Edited by - andy bell on 11 Jul 2013 15:36:29

[Roger Ford]

Ah, if it was Tracksport it would have been the official Caterham series, not Grads.

 

But if it's now in Supersport setup you can come and race it in SigMax class with the Grads. Bet you'd soon learn to fully utilize the brakes then!

[andy bell]

that is my cunning plan ultimately but thats dependant on a few things: me actually getting some skills driving and perhaps just as hard saving my money to do it. Living scotland means alot of trips trailering or else finding the money to get it looked after race by race.

[Z3MCJez]

Quoting Roger Ford: 

Furthest forward position means maximum effort to the rear.

 

Unless you've got the other sort of lever valve (there are two that look almost identical that operate in opposite ways, amazingly), or you've had it fitted backwards so that it makes sense to your (my) simple brain when you're trying to fiddle with it in a pack of 6 cars at 110mph.

 

I agree with Roger that fully open means that there is no restriction to the rear, so maximum braking to the rear. For me, fully open is all the way back.

 

Jez

[Roger Ford]

We went to Knockhill once

[Z3MCJez]

Having read more of the thread, the *generally* accepted position, certainly of people that I know, is that having both the AP master cylinder and the high-effort pedal is too much. You should have very little brake travel. But you will have to mash the brakes to get any real pressure into the system given the way the levers work.

 

The RS15 should have reasonable bite from cold, but they are also designed to run hot, so road use is not really ideal. To be honest, for the road, you'd probably be better going to Mintex M1144 front and standard rears. Although you'll find you need to change them rather more often than the Pagids. I doubt that the M1144 at the rear are anything like good enough to balance the Pagids though, so leaving the valve all the way open is almost certainly the right place to be. Better pad balance should be a first step.

 

I wouldn't necessarily change the master cylinder back to standard (although until yesterday I could have sold you one of those!) as I prefer the lower dead travel that you get from the AP master cylinder, but I would put a standard pedal back on (I've actually got one of those that I could sell you and I could probably chuck some part worn road pads in at the same time that would help with the balance, *ONCE BEDDED IN*). Alternatively, you can drill another hole in the brake pedal to change the leverage back towards where it would normally have been.

 

Regarding brake fluid, before doing a full change, make sure that the system is fully bled - is the pedal soft at all - with your setup it should be hard as soon as you push it.

 

Also, try *STAMPING* on the pedal as hard as you can. Really stamp (make sure there's nobody behind you). It should lock up once the pads have done a couple of stops. Then come and race in SigMax!

 

Jez

[Shaun_E]

Pagid RS15s will glaze over if used gently on the road and even a track day won't improve them much. I used to cover 6000 miles a year and also do sprint/hillclimbs and I never got decent performance with RS15s although others will disagree!

I switched to RS14s front and RS4-2s on the rear and this worked much better but I would still hesitate to recommend them. There are other choices out there which would suit you better.

[andy bell]

so went through my spares i got with it and appears I have spare's of both (for front) and some random pads. I guess the two rears at right came with car and cant read anything on third from right but it says AP racing so guess from old front brakes.

 

spares i have

 

I also liked this amusing piece of paper i found at box..

warning!

 

I have learned so much today taking wheels off - apparently front brake pads and rear brake pads are a different shape - who knew... I did say I was a novice right?

 

I actually have all the spares since it started off from Academy days and I need to think about seeing if can sell random bits e.g. - original Academy/Roadsport front springs/dampers, original narrow track upper and lower wishbones, steering rack

 

My winter plan is to take as much off the car and learn what is going on.

 

Edited by - andy bell on 11 Jul 2013 19:04:16

[andy bell]

Right so took tyres off had a good poke about and seems pads are not too bad.

 

Would it be right with the combination of the pads as they are and the brake bias valve its perhaps been setup so that at maximum braking it never locks up (or minimises)?

 

So lets just say I put the valve further back what would I expect to find - from what people have said front would be more likely to lock up.

 

Why would I want far more brake at front than rear? Any specific track scenario

[Roger Ford]

Quoting andy bell: 

Right so took tyres off had a good poke about and seems pads are not too bad.

 

Would it be right with the combination of the pads as they are and the brake bias valve its perhaps been setup so that at maximum braking it never locks up (or minimises)?

 

So lets just say I put the valve further back what would I expect to find - from what people have said front would be more likely to lock up.

 

Why would I want far more brake at front than rear? Any specific track scenario

 

It shouldn't be set up so it can never lock up. That way you can never apply maximum braking. If you can't lock it up, either you're not pressing the pedal hard enough (and, as said, that takes much more effort than a road car, even before you start adding big-bore master cylinders and high effort pedals) or there's something wrong with the setup.

 

Moving the valve back will make it more likely to lock the fronts first. You should only need to do this if you find the rears are locking before the fronts.

 

If you bought the car from McMillan, why don't you call Andy Mac for advice? He's usually very helpful. I can predict what he'll say though: Move back to the standard M/C and pedal, use his "specially made" brake pads, and don't bother with the bias adjuster at all - leave it "off" or even take it out of the circuit.

[charlie_pank]

My 7 stops faster than anything else I've ever seen on the road. I have some Pagid things in the rears and Mintex 1144s in the front. Standard calipers, no bias valve.

 

If you can't lock up the wheels, and/or you feel like an emergency stop is impossible, then there's something seriously wrong with your setup. I strongly advise you to investigate it thoroughly before you drive it again.

[andy bell]

Hmm got me worried now ;) Not sure if this helps but I have a vbox and I have a Micro input module and monitor brake (as can be seen from video) input. Now in the scene tools itself when i go into MIM and goto brake the scale is 40 and min/max is 0/100. (This was all setup so perhaps I am assuming wrongly it was setup correct)

 

I looked at my last knockhill run using circuit tools (about 1h track time) and my maximum braking effort was 37.605...

 

In reading manual I think i need to start from scratch over winter and have a look at everything - twice. Then check it, twice.

 

Edited by - andy bell on 12 Jul 2013 13:44:04

[Pezky]

It might sound daft but when you press the brake pedal are you just flexing your ankle or pressing with the whole leg 🤔

 

Seat position in the car can make a difference to the pressure on the brake pedal.

 

I use the bias valve in my car to reduce the rear braking as it would lock the rears in the wet

Running an uprated M/C, HiSpec 4-pot front brakes DS2500 pads and standard rear.

[andy bell]

hmm lots to think about and when you ask a simple question of what I am doing perhaps its just me being dumb as it just happens. Will put my concrete shoes on next time...

 

I think i will go out in the car and there is a road that is a dead end but means I can get up to decent speed. Will try to keep hammering the brakes from about 40mph to 0mp and see what happens.

 

I guess (from what people are saying) I should see car shudder to halt quite quick? I will record it and see what people think.

 

Edited by - andy bell on 12 Jul 2013 14:06:11

[charlie_pank]

In Autocar's 0-100-0 test:

 

Caterham CSR260 0-30 1.57 0-60 3.50 0-100 7.72 Reaction Time 0.37 100-0 3.86 Overall 11.95

Lamborghini Gallardo 4.20

Porsche 911 Turbo 4.25

Lotus Exige S 4.23

 

'quite quick' would be an understatement.

 

 

Edited by - charlie_pank on 12 Jul 2013 14:01:58

[CharlesElliott]

You do have to push the brakes a lot harder than in a road car, but I can certainly lock up the fronts in my equivalent race car (same as Roger's). The car certainly stops quickly if I want it to.

[CharlesElliott]

Take a look at this video from 1:55. Braking from ~105+ mph to ~35.

[CharlesElliott]

Can you see in circuit tools or whatever it is the -g you experience under hard braking? You should be ~-1g (on CR500s or A048Rs).

 

EDIT to change units away from the gravitational constant.

 

Edited by - CharlesElliott on 12 Jul 2013 14:47:59

[andy bell]

I have created a new scene in the car with huge brake/throttle and plan to do multiple brake tests from about 60mph on a safe road. Going to document a 'normal' brake and a 'use every ounce of strength in my feeble legs' brake.

 

As ever really appreciate all helps/suggestions shows how good the club can be.