Brakes and Brake Bias

[adma23]

Hi all,

I have a 2012 Radical SR4 with the 280mm floating brakes kit as used on the SR3.

I have this issue with Brake Bias. Unless it is set full front I keep locking the rears and sometimes spinning violently as a result

Having called Radical Technical they never offered advice on the issue and just said that it is not 'normal' to have them set full front.

Funny thing is that when i checked the brake pressures (I have the sensors) the percentages make sense when the clicks are set as they should be.

Anyone has any advice in this regard?

Also - I know the pads are performance friction but anyone knows if the size is from another car? As well as the discs? Would be great to be able to source them at lower prices than Radical charges. Same goes for drive-shafts.

Thanks!

[LCM]

They're right at Big R, full front bias isn't normal. But, Radicals are race cars not road cars and there is an expectation that they will be maintained by someone with skills in race car preparation and operation so they're not really in a position at Peterborough to tell you what's wrong with yours.

Did you get the car new or used?

Have you checked the system out (no air in the hydraulics, correct master cylinder sizes, neither master or slave cylinders seized/binding, fresh fluid [it's heavily hygroscopic so is only really good for a year])?

Anyway, for brake stuff Big R's prices aren't bad but the go-to guy for us hillbillys is the late great Roy Lane's son Antony at Techcraft (I've not met anybody who knows more about stopping a car): http://www.techcraft.co.uk/. The brakes for modern Radicals are the same as those made by HiSpec so you can find the equivalent HiSpec caliper here: http://www.hispecbrake.co.uk/ and then order PF01s from Techcraft.

For drive shafts:
Brand Mechanical Engineering Co
25 Wainwright St
Aston
Birmingham
B6 5TH
0121-327 6622
[e-mail]

I've used them in hillclimb cars with a range of pretty potent engines for 10 years or so and haven't broken one yet!

[adma23]

I bought the car from Radical and it had been used for a year. They checked the car before I took delivery and the master cylinders are correct sizes. Haven't checked if anything is ceased. Thing is the car stops. And the pedal feels great. Just has to be on full front bias and the car loses stability on braking sometimes. I know radicals are meant to brake super late into corners but mine doesnt inspire that kind of confidence. I've been told i might have to lower front ride height too but i'm sure this doesn't result in brake bias beig ten clicks further front than they should be!

As to all the other info - super thanks! Very very helpful!

LCM said:

They're right at Big R, full front bias isn't normal. But, Radicals are race cars not road cars and there is an expectation that they will be maintained by someone with skills in race car preparation and operation so they're not really in a position at Peterborough to tell you what's wrong with yours.

Did you get the car new or used?

Have you checked the system out (no air in the hydraulics, correct master cylinder sizes, neither master or slave cylinders seized/binding, fresh fluid [it's heavily hygroscopic so is only really good for a year])?

Anyway, for brake stuff Big R's prices aren't bad but the go-to guy for us hillbillys is the late great Roy Lane's son Antony at Techcraft (I've not met anybody who knows more about stopping a car): http://www.techcraft.co.uk/. The brakes for modern Radicals are the same as those made by HiSpec so you can find the equivalent HiSpec caliper here: http://www.hispecbrake.co.uk/ and then order PF01s from Techcraft.

For drive shafts:
Brand Mechanical Engineering Co
25 Wainwright St
Aston
Birmingham
B6 5TH
0121-327 6622
[e-mail]

I've used them in hillclimb cars with a range of pretty potent engines for 10 years or so and haven't broken one yet!

[BertBert]

I think that full front is "right". Stopping the rears from locking seems to be quite an interesting exercise.

[adma23]

BertBert said:

I think that full front is "right". Stopping the rears from locking seems to be quite an interesting exercise.

not sure i understand. can you explain please?

[BertBert]

My experience (albeit in an SR3) is the same as yours! With all things equal when you are doing some big braking, it's pretty hard to get the bias forward enough in practice to stop the rears locking and the rear end going away. I think this has also been reporting as worse in the SR1s.
Bert

[Josh Smith]

It may not be the case but worth checking.......when the bar is wound to one extreme, the threaded bar can catch on the pedal box. I cut mine down on the pr6.

[splitpin]

Hi Adrian

Subject of course to the bias adjuster working correctly, my gut reaction is to think that as you have to run real soft all round and especially the front because of the Maltese bumps, the front must be pitching down too much and unloading the rear. I suspect you might need better quality perhaps more bespoke dampers (are you still on single Intrax?) and/or springing and/or that perhaps the rear brakes are simply too big/grabby for how you need them to work from cold. Whether that could be overcome with different spec pads I don't know.

Obviously it'd be bonkers to be changing dampers and/or brakes on the off-chance, so I think you really do need have another go at getting some further input from/via The Big R eg advice from the Italian Hill Climbing Chaps with their big-engined SR4s who are sometimes in action on some pretty bumpy roads?

[LCM]

Josh Smith said:

It may not be the case but worth checking.......when the bar is wound to one extreme, the threaded bar can catch on the pedal box. I cut mine down on the pr6.

...........and of course Smith the Elder nearly totalled himself at Redgate at the end of last season with just the same phenomenon (design issue?).

[adma23]

You;re all right it turns out. Had the pedal box checked out and the thread does protrude and in fact hit the right side of the box so much so that the black paint on the pedal box is scratched off where the adjustor hits it.

Also - the track (I race in Sicily not Malta but it is super bumpy anyway) is quite particular in that it requires hard braking in some very tricky corners. Tricky due to two main reasons - very bumpy on the braking area - and in two of the turns there is quite a downhill too which inevitably exacerbates the issue.

So while solving the adjustor issue I still believe that two way adjustable dampers will do a lot to improve the ride on this track. I'm on one of the softest spring rates all round - 80 - and still the front jitters when turning into the straight and I can only press on to the accelerator when the car has settled down which is costing me precious time. On the same track I use my Exige S280 (Time Attack) with double adjustable Nitrons and it is so much more compliant on braking and turning in.

Problem is Intrax I believe make single and triple adjustable and I'm not exactly a pro so i've learnt that the less there is to adjust at the end of the day probably the better off i am meaning my preference would definitely be for double rather than triple adjustable suspension. But independent rebound adjustability on a bumpy track is so valuable to have as i've learnt from the exige so eventually I either find out if there is another suspension that offers two way adjustable - or - funds permitting i eventually get KW to make a set to my specifications.

Ultimately - another point raised - yes i do believe the brakes on the rear are over kill. I'm not sure whether PF make less aggressive pads for the rear. or any other pads manufacturer in that matter. But I have been given a contact for brakes further up on this thread and I'm sure that giving them a call will prove to be very helpful in this regard.

Thanks so much to all of you for the first hand advice - In so far as Radicals go - info on the web and google searches are more often than not quite futile. But this post has provided me with so much more than I could have expected!

[DarcySmith]

LCM said:

...........and of course Smith the Elder nearly totalled himself at Redgate at the end of last season with just the same phenomenon (design issue?).

Indeed!