Pinky II

[bobbrown]

It’ll be due to the proportioning valves Paul,

In simple terms ... If a standard car was always 200 front and 100 rear on the MOT and upgrading the fronts, or both front and rear, always took it to 300 front and 100 rear then in theory the valves could be changed to give 300/150 so the brake balance was back where it started.

Ray

My standard figures were ...

....................N/S.......O/S
Rear..............100.......100
Handbrake.......150.......150
Front..............275.......275

Do not think the statement "It’ll be due to the proportioning valves" is correct.
On a MOT the brakes are tested per axle and the relationship front to rear is NOT tested.
You would need a 4 wheel brake tester to see what the figures were front to rear.

As I said before the figures are dependant on a number of factors not least is the tyres you have fitted.

Bob

[RayD]

Bob,

I know how you said before the figures are dependent on a number of factors not least is the tyres you have fitted.

I wasn’t intending to disagree, but to expand on what was already said.

I've never seen a 4 wheel brake tester but I imagine the results would be the same.

I thought Paul was expecting the rear wheel figures might reflect how much better the rear callipers and discs would be over the standard set up.

If for instance he, or someone else, imagined the callipers were twice as good - they might have expected the readings to be 350/200

The callipers might be twice as good - but it won’t reflect on the MOT machine.

I was trying - and seemingly failing - to explain why it might be.

As to whether it is due to the proportioning valves ...

As you know the proportioning valves limit the pressure going to the rear brakes.

On a normal MOT test rig the standard rear brakes might give a reading of 100, as indeed mine do.

If you blanked off the hydraulic pipes to the rear the reading would be zero instead of 100.

If the proportioning valves were set to give 99.9% to the front and the remainder to the rear, the reading would be in single figures instead of 100.

In the same way if it was 95% to the front the reading would be more ... and so on.

With the valves being set as they are and providing the brakes are capable of it, and the weight remains the same, it seems they will top out at 100.

I couldn’t possibly have known this were it not for Jay. If he had said his rear figures were 120 and he didn’t have 6 bags of cement in the boot, it would have shown the ceiling was higher than mine were capable of achieving.

If on the other hand you removed the proportioning valves - in all probability the reading would be higher at the back and Jay’s would be higher than mine.

It’s remotely possible that it wouldn’t be ... but it would have to be an amazing coincidence that the weight of the back end of the car and the setting on the proportioning valves were in perfect unison.

I think what I’m trying to say is "It’ll be due to the proportioning valves"

Ray

PS ...

As I was writing the first post I was thinking people would be pleased at the prospect of being able to pursue the idea of changing the PV’s to take full advantage of the newly acquired extra braking capacity. Perhaps not.

[bobbrown]

Ray,

The proportioning valves only start to work once the pressure has reached 15bar up to this point the pressure to the rear is the same as it is to the front; from that point onwards the pressure is reduced in relation to the front pressure.
Which ever way you look at it even if you fitted very very large brakes all round (discs and calipers) the brake loads on the brake tester would remain pretty much the same as the wheels would lose grip at exactly the same point and are not brake dependant rather tyre to roller grip dependant, which is weight dependant as well as the coefficients of friction between the two. If the same car with the same tyres was tested with standard brakes and then the brakes were changed to something larger or even smaller the figures on the whole should remain the same asumming you do not go outside the bounds of what could be considered normal.
I think people read too much into the brake test as it is only there to ensure the brakes are working and you have no imbalances left to right not front to rear as this function is not tested.

Let us not forget it is the tyres that stop the car.

Bob

[Elanlover]

...........Let us not forget it is the tyres that stop the car.Bob

I sense another Bob Group Buy.......................Bob's Tire Upgrade!!!!!!

[bobbrown]

I do not think so, might be interesting to see what the figures came out like with a set of soft slicks.

[RayD]

I agree with you Bob,

The highest pressure my brake pipes ever see is on the MOT test.

I imagine the point at which the rear wheel reading is taken there is as much pressure in the front pipes and therefore as little in the back as there’s ever going to be.

Compared to a standard Élan, fitting 4 pot callipers and larger discs on the front will almost certainly increase the front brake meter figures. Jay’s are considerably higher than mine. For all I know with the right brakes and tyres it may go up to 400, but the rear figures would stay as they are.

To understand it’s being caused by the proportioning valves you need to look at the handbrake figures ... they are higher than the footbrake and all the other parameters are the same - the same pads, discs, weight, tyres, rollers and the same friction.

How else could it possibly be explained?

Please let me know if anyone understands the point I’m making.

Thanks
Ray

[Paul.P]

I understand Ray !

[Monty]

Don`t you just love Brakes


Oh BTW i may off forgot to mention that i do have Trackday tyres fitted

[dapinky]

Monty,

Do you have an LSD fitted?

[Monty]

Monty,

Do you have an LSD fitted?

Nope, but i`ve got a quaife ATB

[dapinky]

Just as a thought - you shouldn't allow the MOT tester to do the front (driven) wheels on a brake roller with an LSD fitted - It'll bugger the whole lot up!

[bobbrown]

Ray

I do understand but I suppose it has as much to do with how much effort the tester puts in to the pedal when checking the rears, There should in theory still be enough pressure available at the rear (29bar later proportioning valves) to lock the rears. but it may be that my calculations which take weight transfer into account which isn't going to happen on a set of brake rollers.

[RayD]

I understand Ray !

Thank you for that Paul.

Ray

[RayD]

Ray

I do understand...

In that case Bob ... back to where we were ... the reason the increased braking capability isn’t showing up on the MOT is due to the proportioning valves.

It will probably have a similar effect in normal road use and there might be some benefit in exploring the idea of adjusting the valve pressures so the balance is the same as Lotus intended. (Assuming they got it right)

Marie’s car in particular may benefit from having the valves changed when the Brembo’s are fitted at the back.

Ray

Out of interest ... the background in the picture above ... which was used for counting the post viewers ... is our lawn ... the bird unfortunately is quite dead ... one of the few disadvantages of having a 7 metres of glass at the back of the house ... while we have an un-interrupted view of the horizon, the birds can only see a reflection of it.


.

[Paul.P]

Very dangerous playing with the proportioning valves !, people have tried in the past & almost killed themselves, hope you boys are as clever as you think you are ?.
Looking at the evidence, this is what i suspected, & that is that this rear brake upgrade is mainly for dust seals & looks, but does not really give any significant better braking.

[RayD]

I agree with you about being extra careful with proportioning valves Paul.

It would want exploring properly, and only in an attempt to make sure the brake balance was as it should be.

Ray

[Monty]

Very dangerous playing with the proportioning valves !, people have tried in the past & almost killed themselves, hope you boys are as clever as you think you are ?.
Looking at the evidence, this is what i suspected, & that is that this rear brake upgrade is mainly for dust seals & looks, but does not really give any significant better braking.

The rears don`t have dust seals and they do improve the rear braking hence why you can`t use this set up with standard front brakes and Brians 15" kit as it would change the brake balance. My rears are bigger than the Stock front brakes

[Monty]

Just as a thought - you shouldn't allow the MOT tester to do the front (driven) wheels on a brake roller with an LSD fitted - It'll bugger the whole lot up!

Well how do you get a pass on the MOT if you don`t allow them to test the front

Since the ATB doesn`t use a clutch type system then it no probs for the pink bomb

[Paul.P]

and they do improve the rear braking hence why you can`t use this set up with standard front brakes and Brians 15" kit as it would change the brake balance. My rears are bigger than the Stock front brakes

Well your the man that should know Monty, your driving the car, i was just looking comparing last years MOT results to this years, which shows approx a 10% improvement. I don't even know how much these cost, but my question/point was, does the cost warrant the 10% improvement ?

[Nige]

My experience of the rear conversion now combined with the previously upgraded fronts is that on the track (never tried it and wouldn't want to on the road) the car is far more stable under braking than with the upgraded fronts alone. With the fronts only, under hard braking the rear would go light and "squirrely" no problem if expected and braking in a straight line, not conducive to trail braking. The braking with the rear upgrade is far more stable and at Castle Combe this year I was able to brake something like 10m later for the corners (past the cone rather than on the cose) than with the fronts on their own and with far more confidence no other variable such as tyres. This doesn't explain the figures Monty has but is a subjective view based on how the car feels.