Plus 2 Braking No Servo
Posted: Thu Feb 04, 2010 9:13 pm
I see that there was a thread running in the racing section about braking etc, some of which includes a reference to using a split circuit tandem cylinder, without servo.
This has me thinking: split braking (front/rear), handbrake efficiency requirement reduces to 16% from 25%, got to be a good thing for MOT passes. Servo sticking on problems eliminated (more reliable braking). No chance of sucking the brake fluid into the intake manifold via failed servo seals (more reliable braking). Easier bleeding (thats good). Better braking modulation and feel, especially in the wet.
But downside, higher stress on bulkhead due to higher brake pedal force - so I will have to reinforce the bodyshell further - but that can be done on the inside of the body.
First some calcs. See Racetech spreadsheets. Target deceleration of around 0.87g. This gives me a target pedal force of 40 kgf (simple test rig with bathroom scales tested by me and my small wife shows this can be achieved). Need to measure or guess the COG height so used US SAE paper comparing sportscars, sedans and SUVs with their measured data (very few cars significantly below 0.5m)
Need some street suitable brake pad compound with reliable coldish friction coefficient: seems Ferodo DS2500 are quoting 0.5 across all temperatures (actually they have a whole lot of test data to show slight ratcheting with repeated brake applications.
Next measure all the vehicle brake system parameters such as caliper piston sizes, wheelbase, tyre sizes, brake pedal mechanical ratio etc and input into spreadsheet.
Results are that using a master tandem cylinder of 0.813" diameter, target of front wheel with non-race rubber lockup with less than 45kgf seems entirely possible. (Note Nokia publish a whole series of data on tyre effective friction against various slip ratios).
What tandem cylinders are available? Well the nice guys at AP racing manufacture a special for Caterham with the above 0.813" diameter. They OK'd publishing on this site. Same vertical bolt pattern and spacing so should mount direct to existing Plus 2 pedal box (but Plus 2 pushrod would need to be correctly spaced to give correct clearance/backlash or replaced with a new item).
So, obvious question, anyone been down this route before. Anyone not running a Servo in a Spyder Zetec and if so/ whose master cylinder?
Regards
Note BG Developments are the distributor retail) for this AP Racing Product.
Gerry
This has me thinking: split braking (front/rear), handbrake efficiency requirement reduces to 16% from 25%, got to be a good thing for MOT passes. Servo sticking on problems eliminated (more reliable braking). No chance of sucking the brake fluid into the intake manifold via failed servo seals (more reliable braking). Easier bleeding (thats good). Better braking modulation and feel, especially in the wet.
But downside, higher stress on bulkhead due to higher brake pedal force - so I will have to reinforce the bodyshell further - but that can be done on the inside of the body.
First some calcs. See Racetech spreadsheets. Target deceleration of around 0.87g. This gives me a target pedal force of 40 kgf (simple test rig with bathroom scales tested by me and my small wife shows this can be achieved). Need to measure or guess the COG height so used US SAE paper comparing sportscars, sedans and SUVs with their measured data (very few cars significantly below 0.5m)
Need some street suitable brake pad compound with reliable coldish friction coefficient: seems Ferodo DS2500 are quoting 0.5 across all temperatures (actually they have a whole lot of test data to show slight ratcheting with repeated brake applications.
Next measure all the vehicle brake system parameters such as caliper piston sizes, wheelbase, tyre sizes, brake pedal mechanical ratio etc and input into spreadsheet.
Results are that using a master tandem cylinder of 0.813" diameter, target of front wheel with non-race rubber lockup with less than 45kgf seems entirely possible. (Note Nokia publish a whole series of data on tyre effective friction against various slip ratios).
What tandem cylinders are available? Well the nice guys at AP racing manufacture a special for Caterham with the above 0.813" diameter. They OK'd publishing on this site. Same vertical bolt pattern and spacing so should mount direct to existing Plus 2 pedal box (but Plus 2 pushrod would need to be correctly spaced to give correct clearance/backlash or replaced with a new item).
So, obvious question, anyone been down this route before. Anyone not running a Servo in a Spyder Zetec and if so/ whose master cylinder?
Regards
Note BG Developments are the distributor retail) for this AP Racing Product.
Gerry