450Z brake bias tuning

[marcg]

I have spent most of the summer dialing in the suspension and brakes of my 450Z with, for the most part, great success. The only short coming so far was that I cannot seem to get the brake bias to my liking. Don't get me wrong, the car stops VERY well, but I still feel that the rears could carry more of the work load then they are presently.

I designed my own front system with 12.90" x 1.25" Wilwood GT directional rotors (RH #160-4564) and Wilwood Forged Billet Superlite calipers (#120-8466-R/L), loaded with the mild Wilwood "Smartpad" (150-8854K) to give me trouble free (aka "confident inspiring") braking.

For the rears, I was running out of time to do my own conversion so I simply used Modern Motorsports 240SX/300ZX rear conversion with an 11.0" dia rotor loaded with their KVR carbon fiber pads.

I changed the master to suite (ZX) and added a Wilwood proportioning valve as well.

I realize that such proportional valves are limited in their ability to adjust the pressure, but even with it totally "off" I still feel that the fronts brakes are doing too much of the braking. After doing some temp reading on the rear I concluded the rears were not working hard enough due to the hard pads. So I tried a softer street pad and got better temps but still not able to to get the rears to bite enough.

It looks like my problem is that I have too much effective front braking torque for a given pressure in the system VS the rear. Should I try to go to a larger dia rotor on the rear to get things back in balance? Or should I try to get a dual master cylinder system and hope I can get enough of a pressure bias to make things work.

Anybody had this problem before? opinions?

[mark]

I would try this. It allows for dual masters and not much fab work. My current project has dual masters but John was not offering this product at the time I put mine together. I wish this had been available.

 

http://www.betamotorsports.com/products/index.html

[JMortensen]

I would try this. It allows for dual masters and not much fab work. My current project has dual masters but John was not offering this product at the time I put mine together. I wish this had been available.

 

http://www.betamotorsports.com/products/index.html

Agreed. Either go dual masters, or get a bigger rear brake setup. It will be really hard to get those rears doing much at all when you have the same size master for both front and rear systems.

[EMWHYR0HEN]

I have spent most of the summer dialing in the suspension and brakes of my 450Z with, for the most part, great success. The only short coming so far was that I cannot seem to get the brake bias to my liking. Don't get me wrong, the car stops VERY well, but I still feel that the rears could carry more of the work load then they are presently.

I designed my own front system with 12.90" x 1.25" Wilwood GT directional rotors (RH #160-4564) and Wilwood Forged Billet Superlite calipers (#120-8466-R/L), loaded with the mild Wilwood "Smartpad" (150-8854K) to give me trouble free (aka "confident inspiring") braking.

For the rears, I was running out of time to do my own conversion so I simply used Modern Motorsports 240SX/300ZX rear conversion with an 11.0" dia rotor loaded with their KVR carbon fiber pads.

I changed the master to suite (ZX) and added a Wilwood proportioning valve as well.

I realize that such proportional valves are limited in their ability to adjust the pressure, but even with it totally "off" I still feel that the fronts brakes are doing too much of the braking. After doing some temp reading on the rear I concluded the rears were not working hard enough due to the hard pads. So I tried a softer street pad and got better temps but still not able to to get the rears to bite enough.

It looks like my problem is that I have too much effective front braking torque for a given pressure in the system VS the rear. Should I try to go to a larger dia rotor on the rear to get things back in balance? Or should I try to get a dual master cylinder system and hope I can get enough of a pressure bias to make things work.

Anybody had this problem before? opinions?

 

 

 

I have the same calipers up front and I WAS considering MM 240sx/300zx rear setup. I just wasn't sure about the F/R bias. Thanks for the info!

 

The dual master cylinder mod seems kinda pricey. A cheaper way would be to keep the 300ZX Rotor (Z31) and swap the 240sx caliper for a larger one.

 

I was considering the rear calipers of the Z32 300ZX which are dual piston and much larger than the 240sx, but it uses a vented rotor.

 

What other larger rear calipers could we possibly use with the solid Z31 rotor? Donor car? Sorry for the thread jack.

[mark]

If you use a rear caliper with a larger piston area you will have less rear brake bias. To increase rear brake bias (increase the travel of the pistons in the rear calipers) you need to either use a bigger master for the rear or a smaller piston area in the rear calipers.

 

The converse of this would be to leave the rears alone and reduce front brake bias.

[marcg]

I have the same calipers up front and I WAS considering MM 240sx/300zx rear setup. I just wasn't sure about the F/R bias. Thanks for the info!

 

The dual master cylinder mod seems kinda pricey. A cheaper way would be to keep the 300ZX Rotor (Z31) and swap the 240sx caliper for a larger one.

 

I was considering the rear calipers of the Z32 300ZX which are dual piston and much larger than the 240sx, but it uses a vented rotor.

 

What other larger rear calipers could we possibly use with the solid Z31 rotor? Donor car? Sorry for the thread jack.

 

The problem I have is not with the caliper size but rather the rotor dia relative to the rear rotor. What dia rotor are you using?

As Mark indicated if you go to a bigger caliper on the rear you will make things worse because your master cylinder won't be able to put out enough volume to make the pistons move out enough to apply pressure to the rotor. It's simple math to calculate the volumes and travels to check.

I'm looking for a larger dia rotor for the rear. Which will also dictate using a vented rotor as a larger dia solid rotor is unlikely. I also have some Z32 rears floating around in the basement. I may do the math to see if my ZX master will work with it.

[blueovalz]

If you use a rear caliper with a larger piston area you will have less rear brake bias. To increase rear brake bias (increase the travel of the pistons in the rear calipers) you need to either use a bigger master for the rear or a smaller piston area in the rear calipers.

 

Mark, I must respectfully disagree with this in part. The smaller piston will indeed increase the clamping speed as you say, but will REDUCE the clamping force. With less piston area, more pressure (pedal pressure) will be required to clamp the rotor. This line of thinking would mean a piston of 1/2" in diameter would outperform a 3" diameter piston in a caliper. Yes, the smaller piston would move quickly toward the rotor, but wouldn't have any clamping force. It's all about ratios; Increasing the slave cylinder size in relationship to the master cylinder size will provide less movement at the slave, but more pressure, and visa-versa. Doing this also increases the required stroke at the pedal will reducing the amount of pressure required on the pedal. It's just like a cheater bar; A long bar requires a lot of movement on the end of the bar, but for the same pressure on the end of that bar, more torque is provided.

 

In regards to the original post, I've run into the same issue that Marcg posted with my first conversion (which was very similar to this one). I found that without the proportioning valve, the balance was almost neutral, but when I started using wider rear tires, I found I needed larger calipers (read piston diameter) in the rear. Eventually I went to 1 3/4" front, and 1 1/4' rear (same size tires on all four corners at this time). Weight bias, suspension geometry, and other things will alter the ideal setup, but it sounds to me like you've assessed you problem correctly. Reducing the front piston diameter would provide the improved balance, but would require a little more pedal pressure overall. This wouldn't really be a problem using the OEM booster though, and if it did, you could regain some of that pressure by returning back to the 7/8" MC (which would lengthen the pedal stroke slightly, but provide good modulation).

[bjhines]

You might just try a different set of pads on the rear.

 

I have several 240Zs. One of them has worked well with the ZX/Toyota fronts and the 240SX rears. I originally used Hawk Blue pads on the front and Hawk Black pads on the rears. The Bias was perfect with this pad combination. I switched to Ferodo 2500 pads for the front and my Bias went all to crap. The rears now overpower the fronts with those pads. BTW the Ferodo 2500 pads ARE NOT SUITABLE for track use, no matter what they say. I am going back to the Hawk Blues.

[mark]

Mark, I must respectfully disagree with this in part. The smaller piston will indeed increase the clamping speed as you say, but will REDUCE the clamping force. With less piston area, more pressure (pedal pressure) will be required to clamp the rotor. This line of thinking would mean a piston of 1/2" in diameter would outperform a 3" diameter piston in a caliper. Yes, the smaller piston would move quickly toward the rotor, but wouldn't have any clamping force. It's all about ratios; Increasing the slave cylinder size in relationship to the master cylinder size will provide less movement at the slave, but more pressure, and visa-versa. Doing this also increases the required stroke at the pedal will reducing the amount of pressure required on the pedal. It's just like a cheater bar; A long bar requires a lot of movement on the end of the bar, but for the same pressure on the end of that bar, more torque is provided.

 

In regards to the original post, I've run into the same issue that Marcg posted with my first conversion (which was very similar to this one). I found that without the proportioning valve, the balance was almost neutral, but when I started using wider rear tires, I found I needed larger calipers (read piston diameter) in the rear. Eventually I went to 1 3/4" front, and 1 1/4' rear (same size tires on all four corners at this time). Weight bias, suspension geometry, and other things will alter the ideal setup, but it sounds to me like you've assessed you problem correctly. Reducing the front piston diameter would provide the improved balance, but would require a little more pedal pressure overall. This wouldn't really be a problem using the OEM booster though, and if it did, you could regain some of that pressure by returning back to the 7/8" MC (which would lengthen the pedal stroke slightly, but provide good modulation).

 

 

Terry you are correct as usual. My post was not as detailed as it should have been. Thanks for your indepth answer.

 

I still think John's piece is a very good way address the issue of dialiing in brake bias with different caliper combinations. You havet the ability to pick the master size as need for front and rear and a balance bar to fine tune.

[mark]

However, if we are talking about the ZX master cyclinder. it has limitations. If rear calipers with a larger diameter piston are used, the ZX master may not have enough volume to move the pistons enough to provide any reasonable clamping force.

 

I'm sure there is a range of piston sizes that would work to increase or decrease rear bias with the ZX master but above a specific piston area the ZX master would run out of fluid. Any one know the stroke of the ZX master?

 

Yes it's a slow day at work.

[marcg]

I found that without the proportioning valve, the balance was almost neutral, but when I started using wider rear tires, I found I needed larger calipers (read piston diameter) in the rear.

 

Do you not think that if I kept the hydraulic system "as is" but, increased the dia of the rear rotors, I would then be getting more braking power due to the increased surface area combined with more effective brake torque for the same pressure. Would this not get the braking power back in check so that I could then be able to adjust the rear pressure using the bias valve.

[JMortensen]

Do you not think that if I kept the hydraulic system "as is" but, increased the dia of the rear rotors, I would then be getting more braking power due to the increased surface area combined with more effective brake torque for the same pressure. Would this not get the braking power back in check so that I could then be able to adjust the rear pressure using the bias valve.

Yes, increasing the diameter of the rotor effectively increases the length of the lever that the caliper grabs onto, so it does increase the rear bias, in effect similar to installing a bigger caliper in the rear. The problem is that the front rotors in this case are so big that you'd probably need to play around with the rear rotors and calipers a bit to get the right ratio.

 

That's why I like the dual master setup. If it's wrong, you buy another $50 master cylinder and try again. If you're changing brake parts you're making caliper brackets just about every time you change something.

 

Something that hasn't come up yet is the idea of putting an adjustable proportioning valve in the front. It's a bad idea. Don't do it: http://www.stoptech.com/tech_info/wp_proportioning_valves.shtml

[marcg]

That's why I like the dual master setup. If it's wrong, you buy another $50 master cylinder and try again. If you're changing brake parts you're making caliper brackets just about every time you change something.

 

Something that hasn't come up yet is the idea of putting an adjustable proportioning valve in the front. It's a bad idea. Don't do it: http://www.stoptech.com/tech_info/wp_proportioning_valves.shtml

 

Thanks for confirming that I am going in the right direction. I may still consider the dual master if it clears the left valve cover. On the other hand making brackets isn't a problem as I have a fully equipped machine shop available to make such items.

Thanks for the link to the proportioning valve section. I agree that on a Z no one should ever put a proportioning valve on the front system. Although, I have a few friends running some very prepped (lowered and stiffened) MR2s and Fiero's that have severe bias problems getting the fronts to not lock up prematurely due to the lack of weight transfer. A couple of them are going to try putting proportioning valves on the front to try to regain some brake control.

Thanks for the info.

[blueovalz]

I'm sure there is a range of piston sizes that would work to increase or decrease rear bias with the ZX master but above a specific piston area the ZX master would run out of fluid. Any one know the stroke of the ZX master?

It's very close to 1". I've got this MC on mine and have at least a 3/8" of leftover travel with a fully functioning brake system on the caliper pistons listed previously. So... (check my math)...

 

A 15/16" MC has a piston area of .690^2", which gives it a swept volume of .690^3" at a 1" stroke.

My Front 1.75", 4 piston calipers have a total (left and right side - 8 pistons total) area of 19.24^2", and the rear 1.25" 4 piston calipers have a total area (left and right side - 8 pistons total) of 9.80^2". The sum of these two areas are 29.04^2" for the entire brake system. Multiply this total by .010" (an assumed value that represents the piston movement to move the brake pad from the at-rest state to contact with the rotor) to get the total volume needed to close the gap between the pad and the rotor at all wheels, which equals .29^3" of fluid volume. This means that the ZX MC moves roughly 1/3 of its full stroke to effect a full piston movement at the caliper of each wheel. Add a little more for a binding pressure (the brake fluid is non-compressable), and I would guess you're only using 1/2 of the capacity of the ZX MC.

 

So yes, the ZX MC has plenty of volume to handle the big brakes.

[mark]

I've got the ZX master on one of my cars so this really does interest me. If (a BIG IF) I understand Terry's post then it takes 1/3 of the stroke of the master to make the pads contact the rotors assuming .010 inch of travel and the volumes stated above.

 

Is that correct?

[tube80z]

You may want to take a look at http://www.jakelatham.com/radical/info/brake_calculators.shtml and see what your current system looks like before making changes.

 

C

[1 tuff z]

marc, i've been working on my bias for years now [no exageration]. here's my current setup that works very well. mml front 13" rotors with the cobra 2 piston calipers, kvr pads, 240sx rears 11" rotors hawk hp+ pads. i called a few brake pad places to inquire about coefficient of friction [ranges] for pads and simply went with a slightly higher cf for the rear pads.

my z is a 73, no factory prop valve, no factory safety valve [the one on the left front strut tower], no aftermarket prop valve [found that by removing it i gained a bit of rear bias].

 

it doesn't have the initial bite that my daily driver honda accord does but hot lapping at watkins glen, it truly works great.

 

i also checked my brake line pressures [small gauge at the bleeder screw]. initial moderate pedal application is approximately 500 psi rear, 700 front, mashing pedal as hard as i can gives me approx. 1300 rear, 1800 front.

 

i couldn't find anything anywhere online to give me an idea of what the pressures mean [relative to each other], so i called a friend at classic tube [classictube.com]. he felt that i have plenty of brake line pressure, the master cyl is doing it's job and perhaps the system is fine.

 

i'd really like to run the same pads front & rear [really don't like the lack of initial bite of the kvr's and the dust they coat my wheels with are really starting to kill my nice wheels].

 

marc, if you come up with a way to mount the 240sx calipers further out and source a rotor to match them, i'd want the same. with "more" rear brakes, i could reinstall my prop valve and gain some adjustability-but at a minimum run same pads f/r.

 

i looked into what the 240sxr's use to upgrade their rear brakes and it's the z32 calipers. not too expensive, but the rotors are 5 lug [i'm 4 lug] and the parking brake is a drum within the rotor, again not what i'm looking for....

 

david

[EMWHYR0HEN]

Thanks for confirming that I am going in the right direction. I may still consider the dual master if it clears the left valve cover. On the other hand making brackets isn't a problem as I have a fully equipped machine shop available to make such items.

Thanks for the link to the proportioning valve section. I agree that on a Z no one should ever put a proportioning valve on the front system. Although, I have a few friends running some very prepped (lowered and stiffened) MR2s and Fiero's that have severe bias problems getting the fronts to not lock up prematurely due to the lack of weight transfer. A couple of them are going to try putting proportioning valves on the front to try to regain some brake control.

Thanks for the info.

 

If your willing to make brackets for a larger calper, or a bracket for a larger rotor w/ 240sx caliper, I'd be interested in buying oa pair from you and i'm sure many here would be also.

 

Now I guess the problem is which rotor or caliper to use.

It's going to be hard to find a soilid rotor bigger than 11'' as it will also be hard to find a bigger caliper that uses non vented rotors.

 

I guess a vented rotor would provide what were looking for here, besides any machine shop can drill holes to make a 5-lug rotor to a 4.

 

Just throwing this out there, would a toy 4x4 caliper be suitable for the rear?

[bjhines]

I keep thinking.... The bias is not very far off. There are several different compounds within each available series of brake compounds from a variety of manufacturers. It only costs $100 for most of the small rear brake pad sets. I could probably nail it in one try. If I had more money/or time I could probably find WORKING cross-combinations from half a dozen manufacturers that would work well under varying conditions.

 

If you brake to within an inch of your life regularly from 120MPH to 60MPH or less the differences become obvious to any engineering minded enthusiast.

 

I like the Hawk Blue/Black compounds because they are cheap and they will work consistently under varying conditions. Sure.. they eat rotors for breakfast. Sure they make a mess out of wheels(and paint). But they throw cool sparks at night.

 

I have some $20, organic, El'cheapos that I slap on for street driving. They work great on the street. I can't imagine why I would need a race pad for street. I can't imagine using ANY streetable pad on track. I have a set of Ferodo 2500s for S12W calipers I will never use again. I don't think there is any such thing as a crossover pad. The Ferodos are not the first time I have purchased a "streetable" pad and been sorely dissapointed on track.

 

The DS2500s have a lot of friction, good initial bite. But they fade fast. The Coeff. of friction is not the whole story. You need a lot more information or a few good laps.

[1 tuff z]

bj, i had been told that there is a 'transfer' of pad [something] to the rotor during the bedding in process and that if i changed pads from track to street i'd either need a set of rotors for my street pads or have to 'cut' the rotors prior to swapping pads. not being an engineer myself [or much skill in that area] i tend to listen to those who are experienced. one of the reasons that i do much reading and little posting here-to learn and benefit.

 

as far as same pads on my car, no real good reason except trying to keep similar performance at all four corners.

 

i'm very open to suggestions/ideas from those who know.

 

i would really prefer to not run track pads on the street. seems that street pads have a nice initial bit and work great unless you're running repeated and higher speed/high effort stops.

 

so, can i switch pads and keep a set that i use only for track and street-without separate rotors and/or turning my rotors to clean the pad material from the rotors?