crazy plans 4 wheel abs

[JGood]

Interesting info on the stock bias valve. If I get back on track next season I'll play around with pad combo's and post my results.

Experiment with your HT10 idea. Some months ago I posted at BF.c and SpecE30 a chart that shows the action of our brake bias valve. Hydraulic pressure is linear for a while and then there is a ~35% reduction in rear pressure. That is to say that the curve had a "knee" in it. You also have to factor in the fact that the rear piston is smaller so that reduced braking action too.

The bottom line is that our rear brakes don't do much. If you go to the same pad all around, your rear pads will do more then your current set up. Not much more tho. The bias action of the valve and rear piston size will overwhelm any pad choice you make.

I've experimented with what I think are the most aggressive rear pads available for us, and front ABS still kicks in first.

Keep in mind that the brake bias valve doesn't kick in under light to moderate braking. Therefore putting highly aggressive pads in the rear may create a rear biased braking condition under light to med braking. I say "may" because the smaller size of the rear piston still creates bias. This rear biased brake scenario isn't necessarily bad, but does have to be understood.

The perfect solution would be to pull the OEM bias valve and install an adjustable one. That would create balanced braking curves with all corners doing their best. But note that our rear rotors aren't cooled for shit so as you start getting the rear brakes to do more, you may create a rear rotor cooling problem.

[RangerGress]

Do you think a relatively stock e30 could benefit from more rear bias? I run HT10 front and HPS rear, and was considering going HT10 rear for more rear bite in straight line braking, as I feel like it is tail happy in those situations.

The issue preventing me from that setup is my trail brake abilities. I can modulate so well with my current setup, I feel like I'd be jeopardizing that balance with more rear bite.

Experiment with your HT10 idea. Some months ago I posted at BF.c and SpecE30 a chart that shows the action of our brake bias valve. Hydraulic pressure is linear for a while and then there is a ~35% reduction in rear pressure. That is to say that the curve had a "knee" in it. You also have to factor in the fact that the rear piston is smaller so that reduced braking action too.

The bottom line is that our rear brakes don't do much. If you go to the same pad all around, your rear pads will do more then your current set up. Not much more tho. The bias action of the valve and rear piston size will overwhelm any pad choice you make.

I've experimented with what I think are the most aggressive rear pads available for us, and front ABS still kicks in first.

Keep in mind that the brake bias valve doesn't kick in under light to moderate braking. Therefore putting highly aggressive pads in the rear may create a rear biased braking condition under light to med braking. I say "may" because the smaller size of the rear piston still creates bias. This rear biased brake scenario isn't necessarily bad, but does have to be understood.

The perfect solution would be to pull the OEM bias valve and install an adjustable one. That would create balanced braking curves with all corners doing their best. But note that our rear rotors aren't cooled for shit so as you start getting the rear brakes to do more, you may create a rear rotor cooling problem.

[SpecM]

Factory ABS in an e30 is a three channel system. Left front, Right front, and rear.

Bingo. BMW already has a system that is 95% as effective as a four-channel settup

[jlevie]

Do you think a relatively stock e30 could benefit from more rear bias? I run HT10 front and HPS rear, and was considering going HT10 rear for more rear bite in straight line braking, as I feel like it is tail happy in those situations.

The issue preventing me from that setup is my trail brake abilities. I can modulate so well with my current setup, I feel like I'd be jeopardizing that balance with more rear bite.

Yes I think it could benefit from more rear wheel braking. I use the same pads front and back (HT-10's initially, PFC-01's until Bimmerworld ran out of stock, and now PFC-06's) and judging by the fact that I go through at least 2 sets of front pads for each set or rear pads it would appear that rears aren't doing much. Just about every time I use the brakes I go all the way into ABS activation. It always feels like it is only the fronts that lock up on a dry track and the only time I've felt the rears lock up has been on a wet track. That also suggests to me that more rear braking would be helpful

Granted, vehicle dynamics works against the rear brakes (weight shifts forward), reducing the effectiveness of the rear brakes and making the car feel somewhat tail happy in straight-line braking. But it seems to me that if the brake bias was more neutral there'd be close to equivalent wear front to back when running the same pads front to back. With respect to using trail-braking to induce rotation, I suspect that vehicle dynamics would over power any increase in rear brake effectiveness. It certainly did in the Skip Barber formula cars that have perfect weight and brake balance. I had no trouble inducing rotation when I wanted to (or on occasion when I didn't intend to). But I did find that those cars were much more amenable to trail-braking deep into a corner w/o rotation as a means of reducing the braking zone.

While there are corners where using trail-braking to induce rotation is of benefit, I'm not convinced that is in general the fast way around the track. But that does depend somewhat on the tires. The Toyo R888's that we run in Spec E30 don't seem to like large slip angles as compared to the RA-1's we used to use. Do a lot of sliding on R888's and they go away pretty quickly.

[JGood]

It would if you do something to make the rear brakes more effective, like fiddling with the brake bias valve or switching to a dual master cylinder setup. In the stock configuration the rear brakes don't make a large contribution.

Do you think a relatively stock e30 could benefit from more rear bias? I run HT10 front and HPS rear, and was considering going HT10 rear for more rear bite in straight line braking, as I feel like it is tail happy in those situations.

The issue preventing me from that setup is my trail brake abilities. I can modulate so well with my current setup, I feel like I'd be jeopardizing that balance with more rear bite.

[SpecRaceM5]

I'd sooner invest my money in driving schools and track days than crutches for my driving skill. Just my 2 cents. I don't feel that deleting ABS is necessary to "prove" you are a good driver, however I don't see a point in upgrading it either. Just my 2 cents.

Cheers,

Brian

[JGood]

My pump was fucked so it was $1600 for a new one or $80 for a proportioning valve.

Or probably $30 for a used ABS pump that works great ;)

[jlevie]

wouldn't a 4 channel do a better job of keeping the rear wheel deacceling at the same rate that just a single line for both sides

It would if you do something to make the rear brakes more effective, like fiddling with the brake bias valve or switching to a dual master cylinder setup. In the stock configuration the rear brakes don't make a large contribution.

[Fidhle007]

I doubt there's very many people on this forum who are able to outperform the ABS system (consistently). Even if so, the risk of flat spotting a tire vs. the tiny bit of time saved by you outperforming the system and saving a tiny bit of weight is hardly worth it to *most* people.

If I ever touch the ABS system, it's going to be to upgrade to the Bosch Motorsport ABS M4

The only time I can think of where it may be an issue is autox'ing with 275+ v710's or A6's. With 225 V710's, at low speeds and full threshold braking, I had an issue once with the ABS engaging and not releasing even though the tire wasn't slipping. The deceleration rate was above what the computer allowed. It only happened on one course, one day, though.

My pump was fucked so it was $1600 for a new one or $80 for a proportioning valve.

[a_thomasmr23]

i didn't know about the 3 channel system that was what i was trying to get to so BMW beat me to the punch by about 20 years

wouldn't a 4 channel do a better job of keeping the rear wheel deacceling at the same rate that just a single line for both sides

[JGood]

Those of us who care... :-D

I doubt there's very many people on this forum who are able to outperform the ABS system (consistently). Even if so, the risk of flat spotting a tire vs. the tiny bit of time saved by you outperforming the system and saving a tiny bit of weight is hardly worth it to *most* people.

If I ever touch the ABS system, it's going to be to upgrade to the Bosch Motorsport ABS M4

The only time I can think of where it may be an issue is autox'ing with 275+ v710's or A6's. With 225 V710's, at low speeds and full threshold braking, I had an issue once with the ABS engaging and not releasing even though the tire wasn't slipping. The deceleration rate was above what the computer allowed. It only happened on one course, one day, though.

[Fidhle007]

Those of us who care... :-D

[erik325i]

Most of us here have deleted the ABS already so UPGRADING the system isn't even in the picture.

Some people have deleted the ABS (including me), but I wouldn't say most...

Erik

[jlevie]

and why would anyone want more than that?

Good point! In a racing environment a 4-channel system would be helpful, if the class rules allow that mod and you've done something to get more use out of the rear brakes. On the street there's always the option on dialing back to the point that you don't need a 4-channel system.

[StereoInstaller1]

Factory ABS in an e30 is a three channel system. Left front, Right front, and rear.

and why would anyone want more than that?