GTD brakes? - Page 2

Dave Bilyk · 11-20-04, 04:37 AM

Howard, heres a picture which gives a better idea of location. The support rails are pieces of angle slotted to allow fore and aft adjustment, you can just see one of the slots near the bottom left.

Howard Jones · 11-20-04, 04:57 PM

Your GTD is a lot different than my GTD. I think I could use a drop down peddle box though. Thanks for the pictures.

Dave Bilyk · 11-20-04, 06:32 PM

Sorry Howard, I should keep saying, it's a DAX, but I think it uses the GTD suspension and other bits and pieces.

Scott · 11-22-04, 06:07 PM

Be advised that using a hanging mount pedal assembly may be harder with LHD than RHD due to the relative placement of the pedals and the steering column. I am having to go with a floor mount setup because the column interferes with a hanging clutch pedal.

Scott

Hemipanter · 11-23-04, 06:06 AM

Michael
I usually calculate with a factor of 0,25 to get an idea of the ratio needed for a manual brake system. If the car weights 1000 kg which shold be close to your car, then 1000 *0,25=250. The total ratio from the pedal to disc pad should then be 250:1.
If the pedal arm is 300mm long and the master rod is located 60 mm from the bearing end the pedal ratio become 5:1. Then the total ratio should be devided by this, so 250/5=50. The hydraulic ratio should then be 50:1 between the master cylinder and caliper piston area.

If the maste cylinder happen to be two 3/4" then the area become 570mm2. 570*50=makes for a total caliper area of 28500mm2.
This math is to calculate for a reasonable pedal effort, and a real race car may go a lot heavier. But even this "softer" ratio may feel a little hard for an "regular" sunday driver.
Then we must calculate for the brake balance front to rear of the car. If you want me to show this math, let me know.
Goran Malmberg

linder · 11-24-04, 02:23 AM

Goran
Thanks for the calculations.I would be nice also to know how to do the ratio front rear calculations.All I know at the moment is that I am using the gtd setup with granda front(vented) and scorpio rear(solid).gtd mastercylinder without boosters.I dont have the measurement for my pedal setup with me.
brgds
Michael [img]/ubbthreads/images/graemlins/grin.gif[/img]

Hemipanter · 11-24-04, 09:17 AM

Brake bias is a bit tricky to calculate properly as we have to make estimations like where the CGH is located, in order to predict braking weight transfer.
Lets say that the car has a static 60-40% distribution rear to front. But under full brake of 1g, there is a 45-55%. If racing tires is used there might be 40-60% situation. The caliper piston should have about the same distribution as this dynamic wheight placed on the tires under braking. But even tire size has an influence as the more heavely loaded front tires is loosing friction of coefficient. And moost of us probaly has bigger rear tires. But as we want the front tires to lock up first theis is sort of even things out.
The masses of the disc should also match the dynamic condition which means that the front discs should have say 55-60% of the iron.
Even the pad area should match this size of load, nothing said here WHAT pad area should be used, just the size distribution.

Goran Malmberg

Hemipanter · 11-24-04, 12:34 PM

If we have 28500mm2 in total piston area, 55%from it makes 15650mm2 up front and 45% 12850mm2 at the rear.If we presume 2 x 4 piston calipers we have 8 pistons at 1956mm2 each front and 1606mm2 rears. This makes 1,78 pistons rear and 1,96 front. Lets make it 1,3/4 and 2 inch. But we may use 5/8 master and size down in caliper pistons accordingly.

We should not use more iron in the disc than nessesary as the unsprung weight is getting high then. It is better to fabricate a proper disc cooling system. Pad size is very much given by the selected piston area. Therfore a suitable pad material should be selected for proper pad temperature.
Exept for temperature there is no difference in braking power with different pad area.

If a stiffer rollbar is mounted on the front axle, this axle is transfering a larger amount of the total weight transfer. Making a big difference between the left and right tire. This makes the car to understeer, or getting less grip. The same goes for the whole car when it comes to braking. The weight is just moving along the car in place of sideways.But here BOTH sides transfer the same amount of weght over to the front axle. Making a big difference between the front and rear axle, making the whole car to loose grip. We can NEVER brake harder than the grip of the tires. Therfor we should pay great attentione to brake bias, car balancne and proper tire size and wheel alingment.

The last lines was maybe a little of topic, hope you dont mind.
Regards
Goran Malmberg

Gary Gibbs · 11-24-04, 08:52 PM

I have mentioned this before. For those of you who have access to Matlab or want to port my code over to Octave I can let you have a program that calculates all you want to know relative to braking. You just need to have all of the input dimensions, etc. and can play around with brake force and piston size, etc.