Popo928

I went to S4 brakes on my S2 as you might remember. Also, the rear tires are up to 285's with 225's in front. Some woman pulled in front of me which made me realize my fronts lock up way too fast. I know I need more braking from the rear. Given S4 brakes, no ABS, 285's on the rear with 225's on front, would you all recommend the 33 bar or the 55 bar rear bias valve?

THX

worf928

Go 33 first and try it. I have a 33 BAR on my '91 and its fine. I have a 55 BAR on my '89 and I think it's a bit too much for the street. With the 55 BAR regulator you can easily lock up the rears if you are not braking in a straight line.

Peter F

Does this have any impact on the ABS brake function or will the system just adopt to the changed bias?
Where do you best buy a new regulator?
I noticed there is only 18 bar on my GT and I'm thinking upgrading to 33 bar.
I have also 225 tyres front and 285 rear.

/Peter

Vlocity

Is the 44 bar not available any more ?

I did the same brake upgrade and I'm running 275 on the rear for street and 315 on the rear with 275 on the front for track. The 44 is perfect with a very aggressive Pagid Black pad. No lockup and I am seeing almost even front to rear pad wear. Where in the past I was going through at least 2 sets of fronts to the rear. I also don't have ABS so the balance was critical.

I'd go with a 44 if it is available.

Ken

fabric

I have the 33's on for street driving. Seems to give just that bit of extra bias to the rear, so there's a little less dive under hard braking, and I"ve never felt the rear feel like it's going to snap around. I felt it was an easy and worthwhile change, even for the street.

marton

Putting bigger brakes on the front will always increase stopping distances because it changes the front/rear bias.

Fixes can be one or more of the following;
change brake bias
stickier tyres on the back
move weight from back to front

Marton

the flyin' scotsman

Went to the 33 bias valve last fall to reduce front wheel lock up. It really helped 'flatten' the car under heavy braking reducing nose dive and smokin' the fronts. Now that I also went to ss lines with PBR ceramics I'm quite happy with the system for the street.

deutschmick

I have GTS front brakes on my '91GT with a 33 bar valve and it's about perfect for hard street use.

dr bob

The "fun" starts when you stab hard at the brakes in the rain with no ABS and "extra" rear bias. You'll have a 911 moment, the moment just before you back into a guard rail (or worse..). Be VERY careful if you do drive in the rain at all. There are some pretty good reasons why the factory used the smaller rear bias pressure limits. Many of those reasons came from back-motor car development. Under hard braking, oversteer is oversteer even in the 928. Having the polar moments out at the ends of the 928 makes handling and ride excellent, but with the nose planted under hard braking and the rear slipping, it feels just like an older 911 on the loose.

928Myles

Dr Bob, would the 33 bar be ok for a '90 S4 with abs in the rain given that the abs should kick in before you lose rear traction? IFIRC the abs works independantly on the front and as a pair on the rear. Under hard braking in the dry my abs kicks in but I feel that it is the front that is causing this. Increasing the rear bias, I feel, would help solve this? No?
Cheers, Myles

Gary Knox

I have had the OE 18 bar, and the 33 bar, the 45 bar, and the 55 bar on my '88 and '89 street/track cars (with ABS). I'd DEFINITELY not go any higher than the 33 bar on a street car without ABS. I found that the 55 bar locked up the rear a bit on the ABS cars when braking hard, and the rear was going over a rise in the track - unloading the rear. I like the 45 bar, but for long term safety reasons have gone back to the 33 bar - don't want no squirrely 911 type action when I'm approaching a narrow corner at high speed, a concrete wall on one side, and something that is making the track traction less than ideal!!!
Gary Knox
West Chester, PA

dr bob

The 33 bar would be a good next step to try, but... As much as I love ABS, I don't really want to regularly drive at the limit and beyond, depending solely on the ABS to save me from disaster. The 33 will no doubt help a lot with the dry braking balance. I'd hate to have you do some damage in a wet corner, when the ABS may not be fast or accurate enough. In a corner, especially a wet one, the ABS will limit rear wheel slip in one axis only -- the center axis of the car. If the car starts to rotate (oversteer induced by weight transfer), ABS reducing the braking on the rears will have only a marginal effect. When the rotation angle exceeds the available steering lock, the car will continue to rotate completely out of control. You MUST release the pedal before that point, even with the ABS hammering away.

No matter what combination you try, spend a bit of time in a safe spot (large empty parking lot...) in the rain, and learn the limits of your brakes. Everybody should do this even with the stock bias valve. Do straight-line stops, then some hard braking while turning. If the car snaps around under full braking as you turn, you know what the limit is, and can then decide if this combo is appropriate for the pads, tires, road surface and driving conditions you face.


------

One of the first performance driving courses I took included a slow-speed slalom, around little cones, on a polished concrete pad wetted with soapy water. (Staging area at the old Orange County Raceway drag strip). The cars were rear-engined Corvairs, on bald 13" tires. 15-20 MPH in these conditions simulated 100 MPH speeds in a patrol car, they said. The course was designed to teach local LEOs high-speed pursuit techniques without risking their lives during training. It was a great exercise in demonstrating how the physics apply to the real world of car dynamics.

Popo928

Turns out ABS cars have 18 bar valves and the later non ABS like the 85 and 86 (not 86.5) had 33 bar valves. Vlocity - PM sent for part number. I think yours is a 45 bar from a 944?

Shane

My early 86 had abs and the 33bar valve. Porken stopped by while I was there on vacation and picked it up for his '86.5 monster...

I put a 55 in my '86.5 and love it, but as worf said don't do any heavy braking in the middle of the corners.