4 replies to this topic

[Tail slide]

I'm determined to correct the hopelessly imbalanced brakes for track and road use, without resort to 4-channel ABS which Duncan and others have said doesn't give good initial bite for track use anyway.
I'd be interested in anyone else's experiments that may have already got there!

I'm competing in a few hillclimbs this year in the Midland Speed Championship, where braking set-up is tested more severely than on most circuits due to the number of 90-degree corners to slow with ideally all 4 tyres on brink of lock-up, over bumpy approaches from 80mph down to 30mph, which is the max you'll go through at even on soft tyres.

The brakes on my road-track TVR were easy to improve and set up for perfect balance in wet or dry, with a bias valve on the rear circuit, but the hopelessly overbraked fronts together with the VX's interfering ABS system. I put a bias valve in the front circuit a few weeks ago and the 'fail-safe' system compensated by locking up the rears first even with ABS off, so it had to come off again.

For info, the VX already has Nitrons and correct geo, set to maximise grip and traction about 6 clicks back from the 'full hard' that works on smooth circuits, running 205-section front tyres (medium-soft Kumho's) at 25psi, and DS2500 pads. At Loton Park hillclimb yesterday - my local - the fronts were locking up way early as expected for every sharp corner, but it still got 2nd in roadgoing class on a cold day when the tyres were nowhere near sticky, just beaten by a few tenths by a 350bhp impreza.

I need an improvement before Harewood hillclimb next Sunday, so after a night looking at all types of pad compound graphs and availability, have ordered two different compounds that have the most similar profile as temp increases (most vary widely as temp increases) not too different friction from the DS2500 so pedal effort isn't much greater or less, and available in VX pad sizes. These are Carbone Lorraine RC5+ for fronts with 0.4 mu friction, and RC6E for rears with 0.47 mu... but unfortunately this 17% higher ratio for the rears can only be a guess on my part, taking account of the weight distribution and alleged 60:40 bias to the front.

Hopefully 17% is slightly on the conservative side, as I tried rears locking first and didn't like it!

Anyone else done this, or can calculate it any more scientifically before it's too late to change my pads order?

Edited by Tail slide, 09 April 2012 - 09:58 AM.

[Winstar]

Anyone else done this, or can calculate it any more scientifically before it's too late to change my pads order?

http://i902.photobuc...otonPark001.jpg

plenty of people used to run with Pagid RS14 front (~0.5 mu*) and RS15 rear (~0.6 mu*) in the old days, but CL stuff seems to be the poulaar choice these days.

*friction graphs here http://www.motorspor...ictionChart.pdf

[JG]

I think i slightly wider front tyre would go a long way to help your balance. the car feels very different under braking on 16s than it does on oem 17s

[MrSimba]

Cl5 fronts & CL6 rears is what Chris @ Hofmanns recommends

What leading Elise Trophy driver Chris Randall has to say:
“Having been a staunch supporter of Pagid for many years I was reticent to try this new pad from Carbon Lorraine but the very first time I tested the pad I was blown away by the performance and feel through the pedal. In the LOTRDC series we run on Yokohama A048 tyres, these tyres combined with conventional pads make the feel through the pedal very poor. This makes it hard for the driver to find an accurate and consistent braking point.
With the Carbon Lorraine pad, feel is transformed due to the way the metal compound of the pad is constructed. Unlike a resin based pad these pads completely resist fade and their performance remains consistent up to 1000 degrees. The other big advantage is the performance of the pad from cold, completely removing the need to work the brake pedal on your warm up lap in order to have brake temperature when the green light goes on.
On the Lotus Elise chassis I race the piston sizes of the front and rear calipers are miss-matched, causing too much brake force applied to the front tyres and not enough to the rear. Using the excellent variety of compounds produced by Carbon Lorraine we have been able to increase friction between the rear disc and pad to rectify the brake imbalance problem. The beauty of the sintered technology means that we can have pads at opposite ends of the car with different friction levels but near identical characteristics which is something we have never been able to achieve with resin based pads.”

Edited by MrSimba, 09 April 2012 - 10:12 AM.

[Tail slide]

Thanks for quick replies. Very encouraging to hear that 0.5 - 0.6 ratio has been professionally tested, and specifically this CL5 with CL6 combination by Chris. Sound like problem may be solved. JG - I'm now running 205 fronts (on wider rear rims) with 235 rears, which seems sweetly neutrally balanced in the corners, which I'd quite like to leave undisturbed. I did try running the fronts at a lower pressure, but as expected it just upset the contact patch leaving black lines each side of contact patch under lock-up.

Edited by Tail slide, 09 April 2012 - 10:24 AM.