Technical Information - Brakes

[alansupra94]

I am looking for possibly technical information regarding the brake setup in the VR4 (or 1G). I am mainly looking for # of pistons, piston size, rotor size/thickness and any more technical information regarding brake bias.

Reason is I might be fabricating some Wilwood calipers for the front and back and I need some comparison specs to do some calculations.

Of course as always, all my finding will be public so you guys can replicate what I am doing including brackets and what not.

 

[iceman69510]

here you go:

Front:
2 pistons, diameter 41.3 mm

Rotor thickness 24 mm

Diameter 276 mm

Rear:
single piston, 34.9 mm

Thickness 10 mm

Diameter 265 m

 

[alansupra94]

Excellent. Now I will be calculating braking power and brake bias. What is an ideal number? Time to go take out some books on brakes!

 

[jepherz]

Ideal number for what? Aren't there just way too many variables? For instance, if ALL you change was put wider tires on your car, it inherently has way more bias up front, no?

 

[donkeylips]

I think if you put stickier tires on your car you will end up with more rear bias. You will be able to decelerate faster and transfer more weight up front than you were before.

I've been researching this a lot trying to figure out the right proportioning valve to use for my abs delete. I'm not sure I want to just slap any AWD DSM one on there just yet. I found that the galant gsx ABS cars used the same prop valve as our cars despite the smaller brakes up front. I just wish the non-abs valve was still available from Mitsu.

 

[alansupra94]

Quoting jepherz:
Ideal number for what? Aren't there just way too many variables? For instance, if ALL you change was put wider tires on your car, it inherently has way more bias up front, no?



Well I guess you can say there is alot of variables but I guess I would go with "ideal" conditions. I was thinking more along the lines of moving from a approximate 80/20 to a 60/40. There is a fine line where you won't see an improvement in braking and more of an decrease in stability.

 

[CutlassJim]

Quoting donkeylips:
I think if you put stickier tires on your car you will end up with more rear bias. You will be able to decelerate faster and transfer more weight up front than you were before.

I've been researching this a lot trying to figure out the right proportioning valve to use for my abs delete. I'm not sure I want to just slap any AWD DSM one on there just yet. I found that the galant gsx ABS cars used the same prop valve as our cars despite the smaller brakes up front. I just wish the non-abs valve was still available from Mitsu.



Stop overthinking it and just use a 1G AWD one. I've done it to two cars and they both stop mint. If your worried about something not being "ideal" on a car then you're never going to want to drive any car that's on the road, they are all one big compromise.

 

[donkeylips]

First of all, which is better - 1GA or 1GB?
I live near Watkins Glen and hope to someday get into road racing. I want to do the ABS delete for obvious reasons. But I'm worried that the prop valve I choose will decrease my braking performance. Or if I really choose the wrong one, would I ever run into rear lock-up on the icy roads I drive on all the time?
I'm looking at this chart now:

It looks like the AWD Galant prop valve has the highest split point. If I am interpreting this correctly, it will take more brake pressure to decrease pressure at the rear brakes. So by comparing all of these valves in the same vehicle, our stock valves will stay 50/50 with a little bit harder braking than the others. So anywhere that the blue line is above all of the others, this valve is more rear-biased than the others. I'm not sure what pressures are normal for road racing, but I think where the lines start to cross, we're getting out of typical range, even for racing(I could be very wrong, I guess this is an important thing to know). So if this valve was used in another chassis that normally uses a more front-biased valve, you could potentially experience rear-lock under hard braking. If we use a valve from another car, it will be even more front-biased than our forgiving(safest, lowest-common denominator) stock valve and stopping distances will go up because our rear brakes aren't doing anything. I'm just trying to get the most performance out of the system that I can.

All of that analysis was basically for braking pressures below 1100. So...if they do get higher than that, everything changes. So like I said before, in order to use this chart effectively I need to know what kind of pressures are normal for various operating conditions. I don't know that much about brakes, I'm trying to learn before I get the 1g AWD valve just because everyone else does it and it "works".

 

[RedTwo]

The rear brakes do bugger all though. Have you ever managed to locked up the rear brakes?

 

[cheekychimp]

^^^ Yeah I used to yank that handle behind the gear stick just before going into turns! /ubbthreads/images/graemlins/grin.gif

 

[donkeylips]

Quoting RedTwo:
The rear brakes do bugger all though. Have you ever managed to locked up the rear brakes?



No because I have the proper proportioning valve. Just because they're smaller than the front doesn't mean you can't...when you're decelerating at a very fast rate you're transferring tons of weight from the rear to the front. With no prop valve you definitely would lock them up, even though they provide less frictional stopping force than the fronts. Now, with any of these other prop valves would you cause a condition where the rear brakes would lock up? Maybe not, I really don't know. Maybe it could if brake pressure exceeded 1200psi. If not I'm worried about the opposite effect - the rear brakes doing nothing like you say. If the system is working properly they should work together to cut down stopping distances and lap times.

 

[GreenGSX]

You know you have a VR4 in Rochester that road races at the Glen right?...you can certainly just dupe my set-up if you like. Heck, you can come down in May to the PCA event and the Glen and I'll take you out for a ride.

There are a ton of variables that go into picking brake stuff. Tires, springs, pad choice..blah blah. The bottom line is that none of the valves you listed are going to be much different on a daily driver and I bet you couldn't tell the difference on a road race car either. The fact is the rear brakes do very little work. I'll give you an example. I use Hawk DTC-60 pads on the front and the CHEAPEST semi-metallic rear pads I can find. I go through a set of front pads every 3-4 days at the Glen. I go through a set of rear pads every 5-6 days. I've never replaced the rear rotors...ever.

Don't over think it. Get rid of the abs and get out and drive. Hell, you should be worrying less about proportioning valves and more about getting those evil POS rear calipers to work right.

Kidding aside...I have a lot of experience prepping DSM's and VR4's for road racing so don't be afraid to drop me a note if you need a hand.

 

[alansupra94]

See I plan on giving the brakes a bit more work. I do want to keep my ABS because I daily drive the car in the winter.