Alright guys, I've been searching high and low and have found some good info on brakes and the various systems and custom brackets that people are making all of which looks and sounds awesome. In my case, however, I'm curious when a proportioning valve is actually needed/required and if there are other calipers that fit to avoid the need of plumbing one in.
Here is my scenario:
I've got a Empi disc kit out back and assuming an Empi kit up front (car came with the front disc setup, so not 100% but sure looks like Empi). I've replaced the front discs with a set of drilled rotors, other than this its a pretty basic setup.
I had always planned to run a proportioning valve and actually have a Wilwood one mounted in the car right now, just not plumbed. My car is dual purpose drag/auto x so things get complicated as I plan to run a line lock + staging brake. Factor in the proportioning valve and it makes for adding quite a bit of brake line and complicating the setup.
This leads to the questions. Those of you doing road racing/auto X did you feel the proportioning valve was required with doing disc brake conversions? And secondly, are there calipers out there that are bolt on (I've been seeing more and more Wilwood calipers out there) that would benefit enough to alleviate the need of the valve?
I've currently got the rear of the car torn apart and now is the time to address the brakes. Still working out other kinks in the car and haven't had a full chance to run it yet (I've done about 3 auto x events but something has broke each time) which is why I'm asking the question here. I have no issues plumbing it in, but if there are easier ways (i.e. different calipers) I'd much rather take that route.
Help! - Proportioning valve or new Calipers?
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type1.racer
- Posts: 21
- Joined: Tue Aug 11, 2020 9:54 pm
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Ian Godfrey
- Posts: 208
- Joined: Thu May 27, 2010 2:52 am
Re: Help! - Proportioning valve or new Calipers?
a good but tricky question. There are a number of variables in every setup but broadly I like to have a bit more brakes in the rear than I need (locking up first and very dangerous) and then tone them down with a proportioning valve so the front always locks first under gentle brakes and particularly under panic braking. The aim though is to have the brake balance close so you are just 'fine tuning' the set up with the prop valve. Because of the way they work they cannot 'balance' a system that is way out of wack. On a race car you might tweak your valve as your fuel load drops (the car balance changes), or your tyre grip goes off with wear etc.
So Tyre width and stickyness: eg: a typical drag bug with 205's on the rear and say 145's on the front needs lots more back brakes, many put T3 wheel cylinders in the back drums to achieve the effect. Big brakes on the front with 145's lock way too easily.
My KG had 205's on the back and 195's on the front with a rear disk kit with a 32mm single piston caliper. I thought with the disks on the back I would need more brakes on the front so I got 42mm T3 calipers (40mm are stock) but the fronts locked way to early so I went back to stock size front caliper and just used a touch of the prop valve to get a nice balance. I was surprised by the BIG difference 2 mm in piston size makes, but the surface area of the piston changes a lot % wise.
So assuming a master cylinder with the same bore front and back (typical VW) these things all have an effect:
Weight distribution: vw's are roughly 60/40, rear/front, but remember when you brake, weight transfers to the front, and the front brakes will do more than 50% of the work, thats why we still have more brakes on the front than the back
Tyre width front to rear: where you have more contact patch usually needs more brakes
Tyre stickyness: what G's are you going to develop on braking? more G's is more weight transfer, so more front brakes needed.
Disk diameter: bigger disk, more leverage by whatever caliper is on there
Piston size: The most common way to roughly tune the brake balance,
Pad composition: a harder/softer pad in the back can a good way to balance the setup if there is no prop valve.
So sadly you need to do some experiments or find someone with a similar set up to you as a starting point
If you are changing wheels and tyres for drag and autocross your set up will only be correct for one of them.
let us know what way you end up going
So Tyre width and stickyness: eg: a typical drag bug with 205's on the rear and say 145's on the front needs lots more back brakes, many put T3 wheel cylinders in the back drums to achieve the effect. Big brakes on the front with 145's lock way too easily.
My KG had 205's on the back and 195's on the front with a rear disk kit with a 32mm single piston caliper. I thought with the disks on the back I would need more brakes on the front so I got 42mm T3 calipers (40mm are stock) but the fronts locked way to early so I went back to stock size front caliper and just used a touch of the prop valve to get a nice balance. I was surprised by the BIG difference 2 mm in piston size makes, but the surface area of the piston changes a lot % wise.
So assuming a master cylinder with the same bore front and back (typical VW) these things all have an effect:
Weight distribution: vw's are roughly 60/40, rear/front, but remember when you brake, weight transfers to the front, and the front brakes will do more than 50% of the work, thats why we still have more brakes on the front than the back
Tyre width front to rear: where you have more contact patch usually needs more brakes
Tyre stickyness: what G's are you going to develop on braking? more G's is more weight transfer, so more front brakes needed.
Disk diameter: bigger disk, more leverage by whatever caliper is on there
Piston size: The most common way to roughly tune the brake balance,
Pad composition: a harder/softer pad in the back can a good way to balance the setup if there is no prop valve.
So sadly you need to do some experiments or find someone with a similar set up to you as a starting point
If you are changing wheels and tyres for drag and autocross your set up will only be correct for one of them.
let us know what way you end up going
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type1.racer
- Posts: 21
- Joined: Tue Aug 11, 2020 9:54 pm
Re: Help! - Proportioning valve or new Calipers?
Despite you not directly answering the question, I think you answered the question. Sounds like (what I suspected) I am better off plumbing in the proportioning valve. Worst case scenario, I can't get enough balance and I end up swapping calipers.
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Ol'fogasaurus
- Posts: 17760
- Joined: Mon Nov 13, 2006 10:17 pm
Re: Help! - Proportioning valve or new Calipers?
I think Ian did a pretty good job as each of the things you are doing with your rig are so very different so the need, front to rear, is going to be different to each use.
Not sure if you are using a line-lock or not when drag racing (I just checked and they are still being used on the front brakes) but the need for loading front to rear is most likely going to be different than what is needed in Autocrossing (which there are several types of autocrosses and sizes of the courses requiring different needs).
The 60/40 thing is pretty much true but when you have a rear engined' vehicle as compared to a front engined' vehicle the loading on hard braking is going to be very different when the weight of the rear engine and trans is thrown forward. Those of us on the sand can speak to that for sure (ever had the steering wheel ripped out of your hands with just a touch of the brakes so the front brakes lock up in the soft sand and dig in then face to any direction they want to. One reason we usually don't use front brakes.
Tires, their sidewalls, tread, material, etc. plus the rim specs all have to be considered to the game also. You also have to throw in the shocks, spring rates and other unmentionables also
.
I'm not sure how much change you can get with a proportioning valve but it has to help some when the needed ratio is finally hit.
I played with drag racing but it got too $$$. A couple of the clubs I belonged to were into Autocrossing so I got a bit of that dialogue and sports car track racing I heard about too. Often what is good for one seemingly should be good for something else but that, all too often, wasn't/isn't necessarily true. All-in-all all of them were too $$$ for me to play with (setting up got the sand isn't much better either
).
Lee
Not sure if you are using a line-lock or not when drag racing (I just checked and they are still being used on the front brakes) but the need for loading front to rear is most likely going to be different than what is needed in Autocrossing (which there are several types of autocrosses and sizes of the courses requiring different needs).
The 60/40 thing is pretty much true but when you have a rear engined' vehicle as compared to a front engined' vehicle the loading on hard braking is going to be very different when the weight of the rear engine and trans is thrown forward. Those of us on the sand can speak to that for sure (ever had the steering wheel ripped out of your hands with just a touch of the brakes so the front brakes lock up in the soft sand and dig in then face to any direction they want to. One reason we usually don't use front brakes.
Tires, their sidewalls, tread, material, etc. plus the rim specs all have to be considered to the game also. You also have to throw in the shocks, spring rates and other unmentionables also
.I'm not sure how much change you can get with a proportioning valve but it has to help some when the needed ratio is finally hit.
I played with drag racing but it got too $$$. A couple of the clubs I belonged to were into Autocrossing so I got a bit of that dialogue and sports car track racing I heard about too. Often what is good for one seemingly should be good for something else but that, all too often, wasn't/isn't necessarily true. All-in-all all of them were too $$$ for me to play with (setting up got the sand isn't much better either
).Lee
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Ian Godfrey
- Posts: 208
- Joined: Thu May 27, 2010 2:52 am
Re: Help! - Proportioning valve or new Calipers?
Type1.racer, yes I should have been a bit more straight forward, definitely add the the prop valve as you will use it to balance your system.
I prefer the dial type rather than the knee or lever type.
good luck
I prefer the dial type rather than the knee or lever type.
good luck
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H2OSB
Re: Help! - Proportioning valve or new Calipers?
I autoXed a '73 Super Beetle with CB Performance disc brakes, F/R with a factory drum brake master cylinder. The car stopped on a dime. Not a single thing fancy about those brakes...no cross drilling, and the rears weren't even the kit that uses a hub and 914 rotors, just the typical, inexpensive rotohub.
Until about 4 months ago I had that car and my 1974 Super Beetle which is not currently a running car, but is going to have a much higher level of performance when done. I have a more exotic (in relative terms) and expensive set up on the '74 with Boxster rear calipers and rotors over custom hubs on the front and 944 rear brakes on the back all with the slightly larger "disc brake" master cylinder.
If I had autoXd the '73 BEFORE I spent the money for the brakes on the '74, I would not have bothered with the more expensive set up. In other words, those disc brake conversion kits, with a factory MC are very well balanced and effective, right out of the box. No need for a proportioning valve. In fact, I once autoXd in monsoon like rain and couldn't break the back end loose...course I had other suspension mods on the car, but the point is, the brakes were excellent. The CB kits are no different than anyone else sells, so I would imagine the brakes on your car are, at least, 95% identical to the brakes I had on that car.
Before plumbing in the valve, try the car, as is, to see if you think it's even necessary. If you're just trying to make sure you can dial the brakes in perfectly, why not, you already own the valve.
I've never "officially" drag raced, so I don't know how the braking set up would differ, but Ian made good points about the adjustability of brake bias, particularly if you're tracking the car for longer events and the f/r bias changes as the fuel load is reduced.
I will say, I planned my Boxster/944 set up based on anecdotal evidence from a couple guys who use their cars on the more extreme side and report a very balanced feel. I didn't want to use a proportioning valve if I didn't absolutely need it.
H2OSB
Until about 4 months ago I had that car and my 1974 Super Beetle which is not currently a running car, but is going to have a much higher level of performance when done. I have a more exotic (in relative terms) and expensive set up on the '74 with Boxster rear calipers and rotors over custom hubs on the front and 944 rear brakes on the back all with the slightly larger "disc brake" master cylinder.
If I had autoXd the '73 BEFORE I spent the money for the brakes on the '74, I would not have bothered with the more expensive set up. In other words, those disc brake conversion kits, with a factory MC are very well balanced and effective, right out of the box. No need for a proportioning valve. In fact, I once autoXd in monsoon like rain and couldn't break the back end loose...course I had other suspension mods on the car, but the point is, the brakes were excellent. The CB kits are no different than anyone else sells, so I would imagine the brakes on your car are, at least, 95% identical to the brakes I had on that car.
Before plumbing in the valve, try the car, as is, to see if you think it's even necessary. If you're just trying to make sure you can dial the brakes in perfectly, why not, you already own the valve.
I've never "officially" drag raced, so I don't know how the braking set up would differ, but Ian made good points about the adjustability of brake bias, particularly if you're tracking the car for longer events and the f/r bias changes as the fuel load is reduced.
I will say, I planned my Boxster/944 set up based on anecdotal evidence from a couple guys who use their cars on the more extreme side and report a very balanced feel. I didn't want to use a proportioning valve if I didn't absolutely need it.
H2OSB
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Ol'fogasaurus
- Posts: 17760
- Joined: Mon Nov 13, 2006 10:17 pm
Re: Help! - Proportioning valve or new Calipers?
One thing I kind of alluded to but did not talk about it is the size of the autocross area being used. More speed more brake and maybe balancing of the system needs to be done.
I don't know if it is still being done but around here (once-in-a-while) they had drag races where you launched hard but then you have to weave through the cones (they started close to the start then ended partway down the strip) where you finished with your foot stomped on the loud pedal.
The other autocross that I liked the idea of was where you had to parallel park in one area of the track then back-in park in another area of the track. Measurements to closeness of the line in the parallel parking were added if not within the 1/2" to 1" distance and the same for centering in the back-in parking area plus time got you a score. Complicated but shows more car skills of the person.
Lee
I don't know if it is still being done but around here (once-in-a-while) they had drag races where you launched hard but then you have to weave through the cones (they started close to the start then ended partway down the strip) where you finished with your foot stomped on the loud pedal.
The other autocross that I liked the idea of was where you had to parallel park in one area of the track then back-in park in another area of the track. Measurements to closeness of the line in the parallel parking were added if not within the 1/2" to 1" distance and the same for centering in the back-in parking area plus time got you a score. Complicated but shows more car skills of the person.
Lee