This is a peace offering from another post and an attempt to learn some meaningful information for anyone running a BBK (non-Stop Tech of course). Apart from your car noticeably locking up the fronts or rears during braking, is there any method for measuring brake bias?

Also, does anyone have, or know of a brake bias adjuster for our cars? And if so, how do you install it?

 

From the Stoptech article:
http://www.stoptech.com/tech_info/wp...formance.shtml

"Brake bias can be measured in several ways. One method – the way the auto manufacturers do it – is to actually mount wheels on the vehicle that are equipped with strain gages, so that the actual torque at each wheel can be measured throughout a stopping event. Analysis of the vehicle deceleration data combined with the measured torque values and knowledge of the vehicle parameters mentioned above (wheelbase, CG height, weight on each axle at rest) allow us to calculate brake bias for that particular event. This is the most precise method of measuring brake bias. However, there are simpler and cheaper methods that can be just as effective.

We know where most auto manufacturers tune brake bias – they like our cars to be front-biased in all conditions achievable by the tires offered on the vehicle. This helps to insure {sic} vehicle stability under braking by the mass public. If we measure stopping distance of the vehicle as delivered from the showroom floor, we have a good benchmark for a vehicle with a 5% to 10% front brake bias.

Now, if we make changes to the car that can effect {sic} brake bias and re-measure stopping distance, we can tell immediately if we have taken a step in the wrong direction. For example, it is not uncommon to install more aggressive front brake pads (which will make the car even more front biased) and see stopping distances go up 5% or more. Dedicated race pads can result in even longer stopping distances.

The most dramatic front-bias impacts are usually brought about by “big brake kits” which are not properly matched to the intended vehicle. Any time that a bigger front rotor is installed, there is a simultaneous need to decrease the effective clamping force of the caliper (installing smaller pistons is the easiest method) to offset the increased torque created by larger rotor effective radius. The objective is to maintain a constant amount of brake corner output (torque) for a given brake line pressure as Figure 6 illustrates. Unfortunately, too many upgrades do not take this factor into account, and those poor cars end up with both bigger rotors and larger pistons which serve to drastically shift the bias even more forward. While rock-solid stable under braking, stopping distances will go up dramatically."

In summary, they seem to be saying that stopping distances are the best measure for determing best brake bias, though I would think testing with an accelerometer (G-tech or other) would also tell you the answer fairly quickly (i.e. find your max decel g-rate.)

In terms of adjusting brake bias, I don't know that anyone has developed or tested a specific application for the G, but essentially a brake proportioning valve is what you are looking for. There are a number of generic ones out there, though, such as:
http://www.speedwaymotors.com/p/6494...ing-Valve.html

The only additional thing to consider here with our cars is the EBFD feature that distributes braking force differentially depending on braking force, weight transfer, slippage and traction of each situation. I beleve that our EBFD only really activates when wheel slippage is in effect, but I'm not sure exactly how it works.

 

You can only decrease the bias with brake bias adjusters, not increase bias. So if you have put some huge bbk in the front and that put your front bias out of whack, the only way to get it back into line (without a rear bbk) is to limit the bias in the fronts via bias adjusters. This will reduce the brake force that the front applies and corrects teh front/rear bias again.

Unfortunately, you just about negated any benefits you tried to give via the bbk purchase in the 1st place. Maybe the fade resistance and feel are worth it? Who really knows. Putting brake line bias adjusters in line with my front brakes isn't my idea of a proper solution.

The only decent way of measuring bias (w/o the expensive equipment to do so) would be to use math. Determine the bias with the known aspects of the oem system, calculate how the new parts affect this ratio and then come up with the estimated end bias.

 

calculations are also only a very crude estimate of bias to get you into the ballpark range

 

I suppose it depends on how much information you have and the cacluations you have to work with. If you have forumulas that can account for things like coeff of friction of the particular pad one is using, I would guess it would be a decent method. It's that or use some expensive testing equipment and hire some expensive testers. Who does that?

I'm not saying it's the best way, but even that would be world's better than what apparently some bbk makers do?

 

Anything is better than nothing at all right? When doing the calculations, you have to make a lot of assumptions regarding the "effective" force applied, and what the "effective" coefficient is. This becomes particularly difficult when the piston sizing varies for all the pistons and then extrapolate out from the radius change in the rotor over the width of the pad, and it becomes somewhat of a mess of a problem. Thats why I haven't sat down with your numbers for the 06 pads yet

 

My buddy had some formulas that worked them out. I didn't think the piston size variations had any significant effect other than their size themselves? At least not on the scope of basic bias calculations. A bunch of little pistons might even out the brake forces but the total force would still be the same. ie.. 1-2 pistons = xx area vs 6-8 pistons = xx area.

 

yes, but since they apply the pressure unevenly on the pad, this will change the amount of effective friction that is being applied across the pad, the orientation plays a role, so if you could find a way to flip the piston order around, then you would get different torque numbers.

 

I agree I guess. But in the general scope of discussion you want to use the information for, I don't think it would be too bad to make some assumptions in order to get a general idea of how off some of these bbk designs are.

 

I know the G35 has a quite a bit of rear brake bias. IMO nissan have reduced it. I would like to reduce it, but not sure what i can do...?

-Sean

 

Brake bias arguments on our cars is a bit of a moot point. We have electronic brake force distribution. So the system will try to compensate for what it detects in variances in brake bias as much as it can based on wheel spin, weight load, g forces and brake force.

Shift your brake bias up front, mechanically, it'll overwork the rears and reduce braking power in the front to even it back out. On h

 

I have never heard this before...i know the VDC will apply certain sides more than others to compensate for wheel spin or loss of control, but under normal braking it will make adjustments?

-Sean

 

EBFD is part of the ABS module and really just an enhancement of ABS functionality. It ties its best to vary brake force at all four wheels to optimize brake torque without lockup.

If I have a chance later, I'll have to see if I can dig it up from the FSM.

 

It can only do so much though, as the stoptech test clearly shows differences from shifting the bias even with ebfd

 

Which is why I stated it was a crude estimate to get you in the ballpark