Wilwood Brakes
Discussion
I ask why!?!?!
We have a setup already tested with old parts and parameters but works.
We have a hydraulic system on limit level bit works (pedal is hard to push but travel is acceptable).
Why try to change hydraulic system? Isn't better idea change mechanical action???
Our discs is 320mm diameter and in a 18'rims you can fit 360mm without change hydraulic balance and braking force and with same braking friction you have 12% braking power, without change pedal force, with increased warm dissipation.
We have a setup already tested with old parts and parameters but works.
We have a hydraulic system on limit level bit works (pedal is hard to push but travel is acceptable).
Why try to change hydraulic system? Isn't better idea change mechanical action???
Our discs is 320mm diameter and in a 18'rims you can fit 360mm without change hydraulic balance and braking force and with same braking friction you have 12% braking power, without change pedal force, with increased warm dissipation.
I suggest the 6 pot upgrade from my experience both racing and road. I have raced 256 Rotax Superkarts and Radicals. The Radical Prosport I raced, funnily enough had Wilwood brakes with 4 pot calipers all round but the car only weighed around 650kgs so the 4 pots were well up to the job. During my Ultima GTR ownership I always felt the brakes were not sharp enough. As Alberto says you have to push the pedal really hard but the bite wasn't sharp enough for me. I experimented with different pads having spoken to number of people in the trade but still wasn't happy.
Having spoken to AP Racing Technical I changed both the brake master cylinders. The front from 0.75 to 0.625 and the rear from 0.625 to 0.7. The brake pedal travel went from 46mm to 60mm and was slightly softer with better feel and more bite. AP said that the 0.625 master cylinder with 50lbs of pedal pressure gives 814psi whilst the 0.75 master cylinder gives 649psi. I still felt this still wasn't enough and having spoken to number well known people who have fitted the 6 pot calipers I felt this was the next step. I never got around to this upgrade as I have since sold the car. I have replaced it with a similar car weighing the same as the Ultima and it came with 6 pot calipers and 360mm vented discs as standard and guess what, job sorted. I don't even have to think about the brakes now they are spot on.
Hope this explains better why I think this upgrade is worth a look at.
Having spoken to AP Racing Technical I changed both the brake master cylinders. The front from 0.75 to 0.625 and the rear from 0.625 to 0.7. The brake pedal travel went from 46mm to 60mm and was slightly softer with better feel and more bite. AP said that the 0.625 master cylinder with 50lbs of pedal pressure gives 814psi whilst the 0.75 master cylinder gives 649psi. I still felt this still wasn't enough and having spoken to number well known people who have fitted the 6 pot calipers I felt this was the next step. I never got around to this upgrade as I have since sold the car. I have replaced it with a similar car weighing the same as the Ultima and it came with 6 pot calipers and 360mm vented discs as standard and guess what, job sorted. I don't even have to think about the brakes now they are spot on.
Hope this explains better why I think this upgrade is worth a look at.
This is a topic very close to me at the moment, I have Hi-Spec monster 4's with 365mm discs, they are awesome at stopping but I have the urge to reduce the un-sprung weight by going down size to factory spec discs and AP 6 pots up front, the question is with the added weight of the bigger calipers is it worth the gain let alone the money?
Racingroj: Interesting that you changed the size of the master cylinders.
Can I ask, did you measure individual wheel braking performance and/or combined front - rear axle brake performance before and after your conversion and did you measure the front and rear axle weights?
If so, did you work out brake bias requirements based on front and rear axle weights to determine front - rear brake performance split? If so, what was the new percentage split when compared to the standard setup and could you get this on the standard bias bar setup?
Can I ask, did you measure individual wheel braking performance and/or combined front - rear axle brake performance before and after your conversion and did you measure the front and rear axle weights?
If so, did you work out brake bias requirements based on front and rear axle weights to determine front - rear brake performance split? If so, what was the new percentage split when compared to the standard setup and could you get this on the standard bias bar setup?
Good questions. Didn't measure the performance via pressure sensors or the like just feel.
Regarding the brake bias set up I had a 60/40 front/rear (dry conditions) on both sizes of cylinder. Checked this with a clamp from the pedal to the chassis bar under the dashboard and kept checking with a torque wrench on one of the wheel nuts. You can pick your own torque until you achieve the 60/40 split. The only down side with this method is keep having to take the clamp off to change the brake bias.
I guess it depends what your experience is and what your individual requirements are for the brake performance and other aspects of the car. The brake performance of the Ultima stood out to me when actually comparing it against my every day car which is an Audi A6. I know this has power assistance but it does so for a reason. Some builders have added power assisted brakes to the Ultima but I came to the conclusion from my research i.e.. specialist professional builders, AP Racing technical and my own racing experience that the car is better served by adding 6 pot callipers on the front.
Regarding the brake bias set up I had a 60/40 front/rear (dry conditions) on both sizes of cylinder. Checked this with a clamp from the pedal to the chassis bar under the dashboard and kept checking with a torque wrench on one of the wheel nuts. You can pick your own torque until you achieve the 60/40 split. The only down side with this method is keep having to take the clamp off to change the brake bias.
I guess it depends what your experience is and what your individual requirements are for the brake performance and other aspects of the car. The brake performance of the Ultima stood out to me when actually comparing it against my every day car which is an Audi A6. I know this has power assistance but it does so for a reason. Some builders have added power assisted brakes to the Ultima but I came to the conclusion from my research i.e.. specialist professional builders, AP Racing technical and my own racing experience that the car is better served by adding 6 pot callipers on the front.
OK thank you for sharing.
Stopping distance is the marker of brake performance, regardless of rotor diameter, pedal ratio, pad material, number of pistons in your calipers or the feel of the pedal. I can understand the hard, dead feeling on the pedal and the need for more feedback but changes to the system need to be calculated and measured based on data captured. Changes that make things feel better may not always reap betterment.
Fundamentally your maximum deceleration is limited by the tyre to road interface and this is effected by CG of the car, front/rear bias and more importantly the dynamic weight transfer during braking, plus other parameters. If you intend to fit 6 pots, do the hard maths to determine system performance first as you may find after they have been fitted they actually reduce the key metric of stopping distance. They will for sure, and more importantly, change the front to rear bias unless other components of the stock system are changed or adjusted along with them.
Stopping distance is the marker of brake performance, regardless of rotor diameter, pedal ratio, pad material, number of pistons in your calipers or the feel of the pedal. I can understand the hard, dead feeling on the pedal and the need for more feedback but changes to the system need to be calculated and measured based on data captured. Changes that make things feel better may not always reap betterment.
Fundamentally your maximum deceleration is limited by the tyre to road interface and this is effected by CG of the car, front/rear bias and more importantly the dynamic weight transfer during braking, plus other parameters. If you intend to fit 6 pots, do the hard maths to determine system performance first as you may find after they have been fitted they actually reduce the key metric of stopping distance. They will for sure, and more importantly, change the front to rear bias unless other components of the stock system are changed or adjusted along with them.
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