[Mk2] [Generic] I really need some help from brake experts or alike! project.

[RyanRs]

I really want to have a go at making a rear brake upgrade for the mr2 so i can use my 4-pot fronts to there full potential and not have to reduce there effectiveness with a bias valve!

My maths skills are not good enough confidently work out the size rear caliper required to return the bias back to stock. Perhaps if i was walked through an example of what i need to calculate and how, i would stand more of a chance.

What i can say is..
I am running an Ally 4-pot nissan caliper (50% lighter than stock with pads!) on a 324mm disc. The pad only reaches the top 2/3 of the disc.
On the rear i have the stock 1 pot on a 324mm disc.

he problem i have is far too much front bias as i can lock the front wheels up far too easily, even at speeds over 100mph! They bite really good but emergancy braking is hard as your leg litterally has to become a human ABS system!

MC wise im using a 1" hilux unit.

I want to upgrade the rear caliper to a 2-pot or even a 4-pot, whichever gives the best bias. Handbrake wise im not worried as i have a plan.

Can someone either calculate for me, or help me calculate my current bias and what size rear caliper i require to restore 'close to' facory bias? and that way i can look for the perfect rear caliper to do the job!

Thanks for all the help.

[Nic]

Couple of links that may help

http://www.imoc.co.uk/forums/viewtopic. ... hlight=wms

http://www.imoc.co.uk/forums/viewtopic. ... hlight=wms

[toxo]

I'm no expert on hydraulics, but my understanding is that if your front brakes use many smaller pistons as opposed to fewer larger pistons then they need LESS brake fluid pressure to apply the pads to the discs. So your 1" M/C might not actually be helping you - it would reduce the movement required on the pedal to fully apply the front brakes resulting in you having less granular control and locking up more easily.

I think...

[Nic]

You could have a look at the larger Supra 2pot rear calipers, info here:

http://www.mkivsupra.net/vbb/showthread.php?249089s

[toxo]

Not and keep a legal handbrake...

[raptor95GTS]

I have porsche calipers up front and dont get the ABS coming on that often even when I'm really standing on the pedal (and trying to get it out of kilts). What tyres do you have front and rear?

A bigger master cylinder means more (foot) pressure to achieve the same line pressure but shorter pedal travel.... I think or I could be talking rollicks!

The MRS has a bigger rear piston and still the handbrake levers but you'd need to shave the pads to fit over the RX8 disc

[RyanRs]

Well that is one problem i do have, my rear tyres are 245/45/17 Continental SP3000's and on the front are a pair of dirty cheap crap that go shiny when you lock them up! I know some of my problem lies there. I can left foot brake, right foot throttle and drive as far as i want up the road without the front wheels turning!

I have got a pair of second hand toyo's coming -235/45/17 to try , see if that makes a difference.

Handbrake wise on the rear, being as i will have to design an adapter bracket to fit a different caliper, i intend to have a spur off the bracket with a mount for an independent handbrake caliper.

[smartdj]

Hey I also have the 4pot nissand calipers upfront.

I'm also running the 324mm rear discs upgrade which gaz does



I don't get any front lock atall. Never!

My tyres are
F 205 toyo
R 235 Yokohama

[RyanRs]

Hmm, what suspension do you have tho? and are you running the stock MC?

[raptor95GTS]

change the front tyres for something that actually grips..

[Al-sw20]

change the front tyres for something that actually grips..

This.

It is simple physics. If you can lock the wheels (or cycle the ABS), you cannot stop any quicker. You only have two contact points in the braking system. The pad and the rotor and the tyre and the road.

Since you are able to easily lock the pad and rotor, you need a better tyre to grip the road.

[RyanRs]

Yes but its not simple physics! Say i fit a pair of R888 soft up front, and it still skids! then obviously increasing front end contact grip is not going to solve the problem! and if it does prevent skidding, does that mean the cars weight distribution under braking is back to normal? no of course not! Next thing your sliding off a corner backwards! I do agree however that i need better rubber up front but iirc it was nathan that even said it will not be the solution to the problem! Suspension geo, weight shift, down force, CofG point etc all come into the physics equation! This is why many people who 'Upgrade' brakes on an mr2 end up increasing there stopping distance as opposed to reducing it as by moving the bias aft of where it is most balanced, will unsettle the weight distribution through each wheel.

[raptor95GTS]

We don't need a load of !!! in your replies.

I can left foot brake, right foot throttle and drive as far as i want up the road without the front wheels turning!

^^ that's what you said previous. Cheap xxxx tyres on an MR2 is just asking for trouble and no amount of dodging the point will make a difference or change that fact.

Also, bigger front caliper pistons move the bias forward meaning you will lock the fronts easier (like you are doing) and you will slide off in a straight line looking directly at what you are about to hit not backwards which would be the rears locking. Balance left to right should be the same providing you have the same hardware on that axle.

No one said fitting better rubber up front would resolve the bias shift that YOU put in but by allowing the fronts to generate more grip (= more braking at that end of the car) you will allow the line pressure to build up in the rear pipes thus allowing the rear calipers to work harder. You could of course look into gutting the brake proportioning valve to allow more pressure to the rears thus moving the bias further back.

Your CofG wont have changed much in fact it's likely heavier at the rear now but by such a small percent it's not worth thinking about. With my 996 calipers and same discs as you I added just under 1kg to the fronts and 5kgs to the rear but in a 1300kg car....

However, since you only want to spend your money on upgrading the rear I believe the MRS caliper is a step up in terms of size but you'd need to shave the pads in order to fit over the wider RX8 discs. I'm not sure who else has the same lock up issues as you with the exact same kit.

I have the same braking setup at the rear as you but with the 996 calipers up front (and ABS) 215x40x17 F1 Goodyears and the stock m/c and I really really have to stomp on the brakes to get the ABS to come in (which is where yours would lock) It's not something I can do with a casual dab on the pedal and I'd certainly be expecting something to happen if I hit the pedal that hard. I've done plenty of hard stops and the car has pulled up smoothly and in a straight line

[Nic]

I've just refurbished my stock front and rear calipers, fitted new OEM discs, OEM pads, braided lines, Motul RBF600 fluid and brake master cylinder brace. The brakes are now easily up to the job of stopping the car from silly speeds, they give good progressive braking, are very balanced under heavy braking and if I wanted to will easily lock up all four wheels (non ABS).

On the road I don't really see the point in fitting bigger calipers, bigger discs and fancy pads, they wouldn't stop the car any quicker and it'd be all to easy to screw up the front/rear brake balance.

[raptor95GTS]

nic, no point in having 400brake or fancy exhausts but when folks ask about it they get loads of advice. The second someone mentions bigger brakes everyone poo poo's the idea. The man has fitted his kit, lets help him get it working eh?

[Harold]

I don't quite understand why you'd spend thousands on engine mods and big brakes and yet have cheap crappy tyres.

[raptor95GTS]

I don't quite understand why you'd spend thousands on engine mods and big brakes and yet have cheap crappy tyres.

ryan try keri-wms for a walk through on the calculation and have a gander at his posts here http://www.imoc.co.uk/forums/viewtopic. ... c&start=20

but seriously, put something grippy on the front otherwise any brake kit including stock will be pants not to mention you'll understeer off the road

[RyanRs]

I don't quite understand why you'd spend thousands on engine mods and big brakes and yet have cheap crappy tyres.

because i do about 1000 miles a year in the car and i have never had to change the tyres. the front tyres are 6 years old and still have about 6.5mm tread left on them so it has never crossed my mind to replace them. However I will get some stickier rubber on the front and see if it helps although some of the reasons i want to upgrade the rear calipers is to get better bias, better stopping distances and to hopefully sort the issue of crap handbrake!

Allan, i have spoke to Keri before however theres only so much info they will give me as it competes with there own products.

[raptor95GTS]

dude, tyres that are six years old?? No wonder they lock up when you hit the brakes lol. Seriously, stop fart arsing about and get some decent rubber on there I found out my handbrake was crap cause I had the wrong cables fitted. Thanks for Peter at Sbits for fixing that for me

I can understand Keri keeping some things to himself.

edit: make sure you match grip levels / compounds front to rear other wise a grippy front end and tail happy back end will have you on your ear!

[RyanRs]

I guess the rubber will go hard over time, didn't think of that. Ill get some R888's on the back and prob some T1r on the front. see how that goes.