My Brake Bias.

[Beagler]

Have 4 pot Caterham calipers with vented discs on the front, uprated M/Cyl and standard Sierra calipers on the rear. I get the feeling the rears are working harder than the fronts judging by the brake dust coming of and initial wear marks on discs. Thinking about a bias thingy. Anyone fit one and where. A diagram or photo would be good.

[aerobod - near CYYC]

The standard rear brakes just have to work harder than the fronts when you have the 4-pots. I get about 5 track days (about 1300km / 800 miles) to a set of the standard LP507 pads and 8 from a set of Ferodo DS2500s, but I'm so far up to about 30 track days and 30,000km of road use and only just over half worn on the front AP pads. The short rear pad life is quite linked to the stickiness of the tyres, though, as with road tyres I was getting much better pad life, the wheels (and hence pads) being a lot cooler than when I went to slicks and R-compound track tyres.

The rears are already biased towards less braking than optimal for the best stopping distance, so I don't think a bias bar will reduce wear without making the braking distances longer. With the DS2500 pads that are a higher friction coefficent than standard pads, the rear wheels still won't lock before the fronts do, which is generally a good thing from a car stability perspective.

[Beagler]

Please delete.

[Beagler]

Looking on line I may be better fitting softer pads to the front any recommends.

[Wrightpayne]

Online 'the internet' or online the caterham forum?

Setting aside the dust issue, does the car brake safely and pull up quickly without locking the rears?

I'd go with James's advice - it has been discussed previously on the forum that the OEM fit rear pads are not the most suited material.

[timb2117]

Ahh Aerobod I hear your pain, essentially I had the same issue did a bit of trial and error including changing pads but always found the rears to be overcooking, also just did not on track get the most of the big brake front set up - does look pretty though :)...

My eventual solution was a brake in line bias adjuster mounted on firewall - BEWARE this may not be road legal dependent on your regs!

I then trialled repeatedly - long deserted flat road stopping hard until I could just get the fronts to lock up first. Then forget it.

Most road cars are set to around 60-70% bias to front but for some reason the Cat seems to do more rear....I have come across some manufacturer systems that alter this.

Totally get Wrightpaynes contention that if she pulls up straight and true then that = safety and is good. 

If you'd like photos of my set up just post me and I'll drag the bonnet off.

[Beagler]

Agree with your findings.  Like to fit softer front pads first but would appreciate your photo.

[aerobod - near CYYC]

Hi Tim, when I use the car in the right way, I get incredible braking with the current setup, but at the expense of rear pad life. Some of the things that detract from optimum braking (which is good enough to out brake C5 Corvettes on R-Comp tyres with track pads and any other road car I know of on track):

- will always get front wheel lock up until front tyres are warm, which requires aggressive cornering to heat them up, whereas the rears warm up much faster.

- need to be aware of adverse track camber approaching a corner and change line appropriately, this is especially apparent on right hand corners (my car is LHD) due to weight transfer form the extra weight on the left side, leading to right front tyre lockup.

- be aware on long straights that front tyre lockup will be more prominent due to some tyre cooling down the straight.

- front tyre lockup will happen in the rain due to not being able to maintain an adequate temperature with an R-comp tyre in the front tyres only, as the rain will keep cooling them fairly rapidly.

It really all comes down to being able to get brilliant braking from any speed when the front tyres are warm enough, but the challenge is to avoid circumstances where they cool down. The acid test is whether the car is handling neutrally in the corners, if it is giving any understeer then the front tyres are going to lock before optimum braking is possible when the brakes are next used.

I would look at putting in an adjustable brake bias valve, but as the car is road legal, it looks as though I would fall foul of the law here in Alberta, although it doesn't mention adjustable brake bias valves explicitly, it does refer to type approval of components being required, which I'm sure the bias valve wouldn't be, for road use.

[Beagler]

Is it the case that a brake bias valve decreases pressure from one circuit eg rears and allows increased pressure to the other circuit eg front. I believe a bias valve needs some sort of anti tamper whilst driving to be legal. Is this so. The pads that came with my 4 pot Caterham calipers by AP racing are the softest they provide so a bias valve looks more attractive. Any photos of a setup would be appreciated.

[timb2117]

Ok yes Beagler you have gone into it way more with temps etc than I have, I just noted that the reaars carry a lot more heat than front and originally I could not even get ANY heat into front calipers. I agree the general braking is superb, I just wanted more work out of the fronts, I have road pads at cooler running on front and comp ferodo on rear. Photos:

I ended up with an AERO brand one that was not cheap but fits well up against the scuttle - all it does is reduce in varying amounts the amount of fluid getting to rear.

the two small nuts above it are the mounting bracket I made as it was only made for 90 degree mount.

Please ignore my hideaous wiring and do you know how hard it is to apply sikaflex neatly in this spot? :)

Hope this helps, BTW I'm running toyo proxxes r888r tyres in 16' 

[Beagler]

Thanks timb thats kind of you.

[Ivaan]

This is the set up on my car.

with twin master cylinders and a balance bar.

With my set up ( Bike Engine ) it's lighter on the front, so a lot of the brake effort is done at the rear. With the balance bar I can easily move the braking effort front - back, so that the fronts just lock first. The downside of twin master cylinders is a heavy solid brake peddle.

Clive

[Beagler]

Thanks guys. What I am trying to do is transfer pressure from rear brakes to front. As they are separated hydraulically on my M/Cyl, I dont see achieving this with a bias valve hence Ivaan's setup.

[paul richards]

Brake bias valve achieves balance front to rear by limiting pressure in rear system.

Balance bar simply alters the pressure that the pedal puts on separate front and rear master cylinders. 

You cannot increase pressure into the front system unless you change the diameter of the front master cylinder. 

Im sure you can achieve balance by selecting different brake pads.
 

[Beagler]

I need to bed the pads in and then try locking wheels whilst heavy braking. If the fronts lock first all is ok.

[timb2117]

I understand your points and Paul yes totally get what you're saying.

In effect (I hope:)) by limiting the pressure going to rear then I stand harder on pedal thus transferring more to front than the rear is getting.

I certainly dont think the pedal pressure i use is untoward even for a non - assisted system, and certainly on track heel and toeing is a breeze.

I'm happy but then I can also see the mechanical beauty of Ivaans set up.

I did try pad compounds but it was not successful (again though I think I took the advantage differential of front to rear way too far by fitting the twin pot fronts) - did I mention they look pretty though? Ha ha.

[Beagler]

This extract from the build assy. confirms the front and rear brake systems are separate so no pressure can be transferred from rear to front. A bias valve can only reduce pressure not transfer it.

 

The braking system is of the dual circuit hydraulic type. The front and rear circuits are operated independently from a tandem master cylinder, so that in the event of a hydraulic failure in one circuit, full braking force will still be available to two wheels through the remaining circuit.
 

[SLR No.77]

Not entirely correct because the two circuits are not entirely separate, they are linked by a common pedal and master cylinder piston.

If you imagine the rear circuit closed off completely, the full pressure of the pedal will be applied to the front circuit only, but at an increased level to having both circuits functioning. This is how a bias valve works.

[Beagler]

Think I'll stick with Caterhams perception. If there is a connection front and rear then any fluid loss would result in total brake failure hence the tandem M/Cyl.

[SLR No.77]

Maybe read my first paragraph again ....

[Beagler]

Have read it. Still #19.

[John Vine]

I like these discussions!

I think CC's description in #18 depends on what meaning you attach to the word "independently". 

With a tandem cylinder, "independently" doesn't mean that you could pressurize one circuit without the other -- rather, that the hydraulic circuits are separated so that a leak in one circuit doesn't compromise the other.   It's worth noting that there are actually two pistons, both operated together (that is, in tandem) by a single pedal and single pushrod.

There's a very good write-up here (for rear-wheel drive).

JV

[Beagler]

This is interesting

https://www.tceperformanceproducts.com/bias-calculator/

 Copied this,

Proportioning valves are typically installed on the rear circuit where they can only retard the rear brakes, which might be counterproductive. After installing a Mustang / 8.8 axle, I needed to increase the rear's contribution to overall braking so I played around with different wheel cylinders and brake shoes. Now I think I'm pretty well set for dry roads, but a proportioning valve might be nice for damp road driving. 

[timb2117]

I feel like Switzerland inbetween Beagler and SLR, totally hear what both are stating, both are correct.

I am also fascinated by people like race drivers who have sufficient feel MID RACE to alter and adjust their brake bias to allow for fuel load, tyre wear, weather etc

I have really just fitted it to achieve one simple aim and left it there, and am satisfied that limiting the rears power (per equal pedal stroke to pre fitting) has evened out some of the rears over exuberance and the front does more, relative to the rear.

Thanks all though for the information and nice links.

[Beagler]

I think, though a brake bias valve in the rear circuit reduces pressure there is no link or automatic increase in front brake pressure, there is when the pedal is pressed harder to compensate. Therefore the balance is improved but at the expense of more exertion on the brake pedal.