Front:Rear Brake Bias Adjustment

Hi there,

I suspect that my Beat’s brake balance is biased too far to the front, and I am wondering if it will be possible to slightly adjust the brake balance. It is just that, when compared to my similarly-aged Civic, albeit with better tyres (Goodyear F1s as opposed to Uniroyal Rallyes), the Beat locks up the front tyres before a comparable braking g-force is attained. This is a particular problem in wet conditions.

I am not much of a mechanic, so thought I’d leave the actual job to my local Honda garage, but I thought I’d first check with the experts, i.e. you guys. How do others feel about their Beat’s braking performance compared to normal cars? Do I have more than one option for increasing the rear-bias? How simple would the job be? I don’t really have a great deal to spend.

If I remember correctly, like a racing car, the Beat has pretty perfect weight distribution of 57:43 rear:front, and obviously a low centre of gravity, so when one slams on the anchors, the forward weight transfer will probably tend to spread the load about 50:50 between front and rear, which should mean that the tyres are evenly loaded and therefore working more efficiently than for a front-engined car. So you would think that the Beat would have amazing braking – Porsches, with their rear-engine layout achieve outstanding braking due to this rear weight bias.

When braking in slippery wet conditions, with a lower attainable g-force, not as much weight transfer takes place, so the fronts have too little grip, resulting in even more premature lock-up. I hear that some modern cars actively change their brake balance according to brake pedal pressure to help deal with this problem, but the Beat does not appear to.

Trying to find a full set of 4 decent tyres of the same make means that my rear tyres are not quite the standard dimensions – they are 165/65/R14 instead of 165/60/R14, so the sidewalls are taller than ideal. Theoretically, this could contribute to the problem, as the brakes apply a torque, and to find the force at the tyre contact patch, you divide this by the tyres radius. But the increase in radius is 8.25mm, which would reduce the force by 3%. I have figured out that this would only increase the front bias by about 0.75% and the rear by 0.75% - trust me on this! I feel that the problem is significantly worse than this.

Sorry if that was a bit long. Thank you for your help!

Bruce

Well I see you looked into this a little deeper then most. I agree that the brakes on the Beat are not as good as a lot of cars but there are many factors which contribute to poor stopping. Such as:

Tyres- quality, type, width.
Weather and road surface conditions.
Brake pads

I think the first improvement you need to make is to get wider wheels and appropriate tyres. I foung that in the wet the car used to skid if you applied the brakes heavily even at low speeds.

The funny thing I found is that I have gone through about 3 sets of rear pads and I have not yet had to change my front ones, pointing to the fact that the car brakes mostly with the back.

My point is if you are not happy with the braking then start with the tyres, then pads, then bleeding the system etc.

Quote:

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Originally posted by Bruce

When braking in slippery wet conditions, with a lower attainable g-force, not as much weight transfer takes place, so the fronts have too little grip, resulting in even more premature lock-up.

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I think you might be on to something there. I must admit that i find my beat overly front happy when it comes to breaking in the wet.. That’s with excellent standard tyres, however the break performance did improve quite a bit when I changed the fluid, fully bled the system and swapped the rear callipers and pads, im still not 100% happy but I think ill live with it!!

My advice would be to bleed the system and get some decent pads first. I wouldn’t be confident playing around with the break pressure distribution, its a little out of my league and im sure Honda Japan back in the day set it up as best they could with the server etc in the car.

Oh and welcome to the boards!

Michael

I have to agree with Adam and Mike, I figure that the front end of the car is so light that braking too hard too, too quickly won't allow for weight transference so the wheels have a tendancy to lock up.
It sounds like you may be suffering a bit more than most so it may be worth checking your front shocks. Weight transference is transmited from the chassis to the road wheel through the springs and shocks and the springs are not that stiff compared to a heavier car. They are going to give a bit initially because they are progressive and you need for your shocks to deal with this delay, if they are leaking internally they won't do it. It's just a thought, alternatively learn to drive the old fashoned way, Cadence braking. I don't mean to cast a slur on anyones driving ability but taking your foot OFF the brake when you wany to slow down ASAP is not natural and takes a bit of time to get used to.

might be worth stripping the front brakes and repalcing the piston seals . Mine locked up on the front and I replaced the pitted piston one side to solve the probelm.

Dust seals are a pig to refit though and best to have some to hand if case they tear upon refitting. cost prohibits caliper repalcement if you didint know ....cheers andrew

Thanks for your comments,

Tyres

Adam, I like the tiny tyres on the Beat. Narrow tyres are more consistent, and the steering system is built around them. They also allow me to slide about within the speed limit.

Having said that, it is frustrating (albeit unsurprising) to find such a poor choice of tyres in the Beat's sizes. The directional Uniroyal Rallye 680s I use look fantastic, but I feel are a bit too hard a compound - economic wear rate and noise are of no interest to me. Can anyone suggest any soft grippy tyres fitting standard front and rear wheels?

I suggest you check your handbrake is not running slightly on all the time if you are getting such heavy wear on the rear pads. (Probably makes it handle better!) If, instead, your pedal braking circuit was given too much rear bias, you would know all about it, because the rear would lock up first and overtake the front. This would tend to happen in the dry. That's why road cars are always set up with a disproportionately frontward bias.

Pads

Hmm. Michael, you suggest getting decent pads, but that pressure distribution would be tricky? What if I got decent pads on the rear and not so decent (or new) on the front?? If this is too risky and it makes the rears lock first, then I guess I'd have to get new front pads too. Aren't they Rover units?

Dampers, weight transfer

TinyTim, I think the dampers are in OK condition, may have a little bit too much stiction for me, but will do. You are right about the soft springs, but the relatively long wheelbase and low, far back Centre of Gravity will limit front weight transfer compared to most cars, and it shouldn't take too long for the transients to settle down into a steady state. Once this has all happened, and have been braking for a few seconds, the premature front lockup still happens when pedal pressure is added.

Technique

I have never believed in cadence braking. Might work reasonably in a straight line, but whilst cornering hard, it might spin it. If it locks up, just ease off, and reapply not quite as hard. This way will probably stop you quicker too.

So are we sure that pressure redistribution solution is too ambitious? Has anyone tried it?
Where are the board's stalwarts... Steve, Adrian, OzSamurai?

Thanks again,

Bruce

Quote:

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Originally posted by Bruce

Pads

Hmm. Michael, you suggest getting decent pads, but that pressure distribution would be tricky? What if I got decent pads on the rear and not so decent (or new) on the front?? If this is too risky and it makes the rears lock first, then I guess I'd have to get new front pads too. Aren't they Rover units?

Bruce [/B]

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I doubt that would have the desired effect, the pressure applied to the pad would remain fairly constant regardless of whether the pad is new or used I would imagine, thus changing the rear pads should not change the bias, however it may help breaking if there are crappy pads on it at the moment.

New pads are not expensive, I would just replace them as a matter of course, I use Apec breaking pads on my own baby and they seem quite good the parts number are PAD 610 and PAD 611 im not to sure which is the front and which is the rear.

New callipers are quite expensive; I managed to get a good used pair, and am planning to recondition my old callipers when I get a chance.

You are looking for answers but don't really want to change anything.

I had the same problem, if you can call it that and solved it by:

Getting and changing

New pads,
Really hard sports suspension,
Wider front and rear wheels- 6"x14"
Really good tires
and bleeding the system properly.

I didn't use physics to solve my problem and I don't have a clue which single thing made a difference but I don't have that problem anymore. So take a pick!

Quote:

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You are right about the soft springs, but the relatively long wheelbase and low, far back Centre of Gravity will limit front weight transfer compared to most cars, and it shouldn't take too long for the transients to settle down into a steady state. Once this has all happened, and have been braking for a few seconds, the premature front lockup still happens when pedal pressure is added

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The low weight and low CoG is why it's important with standard springs that the dampers are working correctly (as opposed to OK), unlike many cars there should be no bounce on the suspension and it should take a heafty shove to force the corner down after which it should return to ride height under damper control.

Quote:

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I have never believed in cadence braking. Might work reasonably in a straight line, but whilst cornering hard, it might spin it. If it locks up, just ease off, and reapply not quite as hard. This way will probably stop you quicker too.

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That IS cadence braking. It is specifically for getting round corners when there is no ABS a lot of guys on the rally circuit use it even if they have ABS as it gives the driver control and feel rather than rely on the system.

I get the feeling you are being sucked into the theory and forgetting the practical aspects of dynamic motion. The Beat is an exceptionally light car (1/2 the weight of a Carrera) as you know friction is dependant on force and quite simply there isn't much on the Beat, it is however capable of 120mph (I think Garys does 130). Wider tyres offer a greater surface area and whilst classroom work would suggest this will have no impact on friction in practice it does increase the chances of having good contact. Therefore is definately has an impact. If you are using good quality tyres I would suspect they will give very little deformation under the weight of the Beat which again will work against you.

Standard size tyres to have a go with:
Continental ECO Contact (definate 1st choice) £200+
Yocohama S306 (runner up) £200 ish
blackcircles.com will deliver or fit.

I think the single biggest problem is the weight or the lack of it. Its all at the back and the front is left really light. But there is nothing that we can do about that.

Good point about theory vs. practice - that's me to a tee! I am trying to understand the mechanical bits better, so am still keen to know more about any potential for brake fluid pressure distribution adjustments.

Adam,

I realise that all the weight is on the rear - that's why I want more braking going to it, and less on the front. It is currently not set up correctly. Maybe I should test this by gently easing on the handbrake as I brake, to see if it decelerates better, or just spins it. Hmm. Maybe not...

I think the bleeding and pad change may help a bit, so will consider it.

Harder suspension would only effect the first few fractions of a second of braking, and not the settled steady state braking I spoke of.

Grippier tyres will help, as it will transfer more weight forward. I see those EcoContacts EPs are now available for both front and rear sizes. I had better wear my current ones out a bit sooner.

But you mention 6"x14" wheels. So have you got the same sized tyres front and rear? That would solve the braking issue, but how does it corner? Does it tend to oversteer at high speed? The rear on mine already can feel a little light when cornering at high speed and hitting a nasty bump.

Although the friction is lower for a lower vertical force, you must also remember that if the mass is lower, then you need proportionally less force to get a given acceleration. A little known fact is that a tyre's coefficient of friction actually slightly increases with lower vertical force, so with a lightweight, evenly balanced car (a low CoG helps keep it balanced), you can get exceptional g-forces.

TinyTim,

Your comment about the low vertical force not squeezing the tyre enough to get a long enough contact patch makes me wonder about my last statement, and whether it is only true up to a point. But the Beat's standard tyres are so small, they are surely designed to flex enough for lightweight cars.

I thought cadence braking was the continually repeating cycle of stamping, easing off, stamping, easing off. That's what I think is a bad idea.

Jeez, 130 mph??? They must be huge tyre diameters to get the final drive gear ratio long enough. Unless he's changed the cogs?
It must get a bit unstable too - it is very darty at high speed I find.

Bruce

We'll all be 'heeling and toeing' next!

PW

Have you got a spare wheel? My wife tells me her Beat was noticeably different to drive when she took the spare out to have a new tyre fitted.

I have considered removing the spare to save weight, as the only puncture I ever had was when karting.

But I reckon that removing mass from the front would only worsen the problem, as the front is already lacking grip and needs more.

Ah well. Thanks anyway.

Bruce