Front wheels locking up under braking

[xcarguy]

I'm sorry - I thought you posted that in a straight line brake test that you got pretty even lock up.

 

Ideally one would start with too much front bias and front lock up and then adjust to the rear until you get too much in the rear and then move back toward the front some so that you get all 4 wheels doing the most work they can. I think it's a bit easier to have a small amount of lock up in the front than having any in the rear as it's easier to deal with.

 

Dave

 

Dave and Don,

 

My apologies for my last post; sounds like you guys already worked that out.

[degoetz]

what type of brake pads are you running on the front and rear? And tire pressures?

22lbs frt, 20lbs rear. As by Scott's suggestion, I have tried more and less in the frt and 22lbs works the best. The rears stick so well that I don't think anything between 24 - 16lbs would make much difference.

i wanted Hawk HP+'s for brake pads but Scott said they were too aggressive and unpredictable so i am using what he uses but i don't know what they are. But they are the same frt to rear.

The bottom line is that what Scott, the designer, builder and racer ( finished as high as 3rd in the SCCA Nationals) has built is basically all the same as what he builds now except for tubbing the frame and using much wider tires.

So if I use his proven specs for a base line the only real difference are the rear wheels. I can install a front adjustable proportioning valve and I think as long as I leave the rear full open and maybe move more bias to the rear I can gain some more braking. Even 10 or 15% more to the rear without locking them up should help with the braking.

Next year he should be driving the basic same car and that will really help.

No wider tire is available in the 13'x 20" dia for the front but i could move up to a 22" dia and get a wider tire but that is not what I am planning to do that this point.

I started this thread in order to find someone that has installed more than one proportioning valve in a system.

Thanks for all the current and continued input

Don

[Davemk1]

Hey Don -

 

I know of Lotus guys who have installed prop valves on each circuit and had no trouble with it..........I'll bet you'd be fine. I installed one on the Elise i used to run in the front as the bias was too heavy that way and it worked well. I didn't have one in the rear but I can't see how having one there too would have been an issue.

 

dave

[xcarguy]

22lbs frt, 20lbs rear . . . . in the frt . . . 22lbs works the best. The rears stick so well that I don't think anything between 24 - 16lbs would make much difference.

i wanted Hawk HP+'s for brake pads but Scott said they were too aggressive and unpredictable so i am using what he uses but i don't know what they are. But they are the same frt to rear.

The bottom line is that what Scott, the designer, builder and racer ( finished as high as 3rd in the SCCA Nationals) has built is basically all the same as what he builds now except for tubbing the frame and using much wider tires.

So if I use his proven specs for a base line the only real difference are the rear wheels. I can install a front adjustable proportioning valve and I think as long as I leave the rear full open and maybe move more bias to the rear I can gain some more braking. Even 10 or 15% more to the rear without locking them up should help with the braking.

Next year he should be driving the basic same car and that will really help.

No wider tire is available in the 13'x 20" dia for the front but i could move up to a 22" dia and get a wider tire . . . .

I started this thread in order to find someone that has installed more than one proportioning valve in a system.

Thanks for all the current and continued input

Don

 

Don,

 

You're basically breaking new ground (in the Stalker realm) with your car by introducing a combination that’s yet to be tried. At the very least, install the pro valve on the front (I'm with Dave on this). If it doesn’t produce the desired results, then you’ve discovered what doesn’t work and you take a different approach. If it does work, then great! Either way, you’ve got valuable information to share with others who may be considering one of these cars.

 

Although we're talking different venues, FWIW, I’m dialed in to 22psi on the front of my car also. Even though I’m running a 16x10 combo on the front, 22 psi illuminated the graining I was getting on the inside edge of the tread at 19 psi, produced an even wear pattern and resulted in the best overall grip. I run a 16x12 combo on the rear and 20 psi; 19 psi was also producing graining in the inside edge of the tread, so 1 single psi in the rear and 3 psi in the front made a huge difference in tire wear and grip. I say this because 16-24 psi is a large psi margin and I feel pretty confident that you’ll find a psi within that range which works well for your application. If you try the front pro valve, I’d experiment with tire pressures and see what it yields.

 

As for pads, I run Wilwood BP-20 pads on front and stock 95’ Grand Am GT pads on the rear. The BP-20’s are Wilwood’s middle-of-the-road pad; better stopping power than the BP-10’s, but not as frictionally aggressive as the BP-30’s which also tend to eat rotors . . . or so I’ve been told. Several owners on this forum run Hawk pads and have had good results with them, however they very well may be better suited for the occasional track day rather than E Mod. Don’t write off trying various combinations of brake pads down the road. Again, you’re breaking new ground with your car.

 

You also mentioned possibly using a 22” tire in place of the 20”. Last year, I was running a 15x10 square setup and getting around 1.2G’s sustained. I moved to the staggered pattern I’m now running and am now gettting 1.5G’s sustained per my data logger. The reason I say this is that by going to a larger tire with a larger contact patch, grip increased significantly. A larger tire on front (this is just a thought for consideration) with a larger contact patch may provide you with additional grip during hard braking.

 

Anyway, the best of luck with getting your car setup. This time next year I’ve no doubt that you’ll have lots to good advice and valuable information to share with others. :cheers:

Edited September 4, 2014 by xcarguy

[degoetz]

From my experience I seriously doubt you would ever be able to feel a 25 or even 50 lbs lighter spring. The difference is the amount the front end will sink is VERY small (is they are 500 lbs now and they move 2" under hard braking then moving to 450lbs springs would allow the car to about 1/4" more). You'll get much more change by playing with the damping than you will the spring rate for gross adjustments like this. It would be great if you have 2 way adjustable shocks so that you could decrease the rebound damping in the rear (allowing it to rise more) while at the same time decreasing the compression damping in the front to allow it to sink more. This would allow more weight shift.

dave

I just noticed this, I am told the front springs are 200lbs and 25 & 50lbs would be a significant change. The only way to know if this would improve the handling & maybe braking would be to try them at some time.

[Davemk1]

I just noticed this, I am told the front springs are 200lbs and 25 & 50lbs would be a significant change. The only way to know if this would improve the handling & maybe braking would be to try them at some time.

 

Interesting - I would think that maybe they would be 200 in the rear but would expect twice that at least in the front. I think I ran the Birkin I ran years ago on 325's in from and I think my current Westfield has 350's I think.

 

Fun stuff.

 

dave

[degoetz]

The frt and rear suspension uses inboard shocks via push rods and rockers with adjustable motion ratios.

I have all ready stiffened the rear and the frt is as soft as it can be. Hopefully with softer frt springs I can put the rear suspension back where it was.

[Davemk1]

Ahhh. That makes more sense as the rockers change the leverage ratio.

 

Cool.

[ecarte56]

Degoetz, you probably already considered this, but for a given caliper model,

Wilwood offers different piston area choices. ex. if you have a Dynapro with 5" total piston area, you can go to the 4" or 3" version for less front bias - in case your issue is outside the range that a front proportioning valve can cure.

 

Given your tandem master cylinder installation, different front/rear master cylinder piston diameters would be another solution - I did not see one like that on the Wilwood website but they might be out there.

 

Brake setup is one of the simpler things to model on a car. There are spreadsheets on the internet. I made my own, just so I could understand the problem better. You will never get better than a rough estimate because tire and pad coefficients are a moving target - but if you can come up with a theoretical ball park estimate you can evaluate different set ups - could save time and money.

 

A separate comment about heavy cars braking better than lighter cars: a well set up heavy car with lots of rubber can have certainly have good braking - but apples-to -apples, less weight will yield better grip, better braking and faster cornering (why we like sevens.) Yes, more weight or normal force increases grip, but that benefit is netted out by the increase in the inertia of the heavier car. Meanwhile, more weight pushes the tire deeper into the aggregate, which decreases the friction coefficient. See The Tire Handbook, Paul Haney, and The Chassis Newsletter, Mark Ortiz.

[subtlez28]

I had my first track outing with M-spec #007 yesterday and could not wait to get back to this thread.

 

I am using a different tire combo (23x9.5 15" Hoosiers), but am having the same issue. My brakes may also be different as my kit was produced in late 2012 (long home build time). My kit uses Miata uprights and Miata power master. I have the upgraded Wilwood 4 pots in the front with Brunton's recommended pads (I will try to get which model and compount) and stock Miata brakes in the back w EBC yellows (again per recommendation).

 

As for the ABS vs no ABS, I don't think that is the issue. I am gradually initiating braking, the lock up comes near the end, so the panic, weight transfer is not the issue.

 

I had asked Glen about the brake proportioning valve provided with the kit. He said to keep it all the way open (no resistance to the rears) as the Wilwoods would out stop the miata brakes in back already. He was right about that...

 

I have the shocks set very soft, again per recommendation.

 

Anyway, in the fastest corner at Blackhawk Farms (1.95 mile road course), at the end of the front straight is where my lock up occurred. Entry speed was over 130. The first time you enter is more like 90-100 as it is from a stop (but on cold tires).

 

I had pretty good braking initially into that corner, but would experience lock up in front toward the end of the braking. By the end of the day, I had flat spotted the Hoosiers (I think I had 65 miles on track that day).

 

Now, this was my first experience with the car, and with slicks. So, there is some getting used to needed. I'm told slicks are much more sensitive to lock up then high performance street compounds.

 

That said, I have a lot of laps (and 3 season Championships) from this track in heavier street cars with street tires. So, I'm not all that inexperienced. I think there is a problem with the set up.

 

My thinking at the moment is:

I would like to convert to manual brakes, with a balance bar. I think this miata master is just not idea.

 

Some more aggressive pads for the back might help.

 

I would like to run a larger slick (taller at least, wider is a maybe).

 

I may try to get larger slicks yet this year (only one event left in my season), but different brake set up will have to wait for the off season.

 

My particular form of racing is different from Scott's. He does parking lot SCCA autocross. I do what is called High Speed Autocross. Here we run full tracks (all about 2 miles), from a stop, with no cones. Timing and competition is otherwise like traditional autocross.

 

BTW, for any other 7 owners in the midwest, this form of racing is kind of ideal for a 7. Check out:

http://www.mcscc.org/autocross.php

 

I'd love to see more 7s out there!

Edited September 7, 2014 by subtlez28

[xcarguy]

I had my first track outing with M-spec #007 yesterday and could not wait to get back to this thread.

 

I am using a different tire combo (23x9.5 15" Hoosiers), but am having the same issue. My brakes may also be different as my kit was produced in late 2012 (long home build time). My kit uses Miata uprights and Miata power master. I have the upgraded Wilwood 4 pots in the front with Brunton's recommended pads (I will try to get which model and compount) and stock Miata brakes in the back w EBC yellows (again per recommendation).

 

As for the ABS vs no ABS, I don't think that is the issue. I am gradually initiating braking, the lock up comes near the end, so the panic, weight transfer is not the issue.

 

I had asked Glen about the brake proportioning valve provided with the kit. He said to keep it all the way open (no resistance to the rears) as the Wilwoods would out stop the miata brakes in back already. He was right about that...

 

I have the shocks set very soft, again per recommendation.

 

Anyway, in the fastest corner at Blackhawk Farms (1.95 mile road course), at the end of the front straight is where my lock up occurred. Entry speed was over 130. The first time you enter is more like 90-100 as it is from a stop (but on cold tires).

 

I had pretty good braking initially into that corner, but would experience lock up in front toward the end of the braking. By the end of the day, I had flat spotted the Hoosiers (I think I had 65 miles on track that day).

 

Now, this was my first experience with the car, and with slicks. So, there is some getting used to needed. I'm told slicks are much more sensitive to lock up then high performance street compounds.

 

That said, I have a lot of laps (and 3 season Championships) from this track in heavier street cars with street tires. So, I'm not all that inexperienced. I think there is a problem with the set up.

 

My thinking at the moment is:

I would like to convert to manual brakes, with a balance bar. I think this miata master is just not idea.

 

Some more aggressive pads for the back might help.

 

I would like to run a larger slick (taller at least, wider is a maybe).

 

I may try to get larger slicks yet this year (only one event left in my season), but different brake set up will have to wait for the off season.

 

My particular form of racing is different from Scott's. He does parking lot SCCA autocross. I do what is called High Speed Autocross. Here we run full tracks (all about 2 miles), from a stop, with no cones. Timing and competition is otherwise like traditional autocross.

 

BTW, for any other 7 owners in the midwest, this form of racing is kind of ideal for a 7. Check out:

http://www.mcscc.org/autocross.php

 

I'd love to see more 7s out there!

 

subtle,

 

Great to here you got the car out to the track . . . fantastic! As for the front brakes, I have an idea that might be worth a look. The Wilwood BP-20’s are the ticket for guys like me who are running manual, dual MC brakes with a bias bar. Do you happen to know is you are running BP-20 pads with the power assist? Here’s where my idea comes in; if you are running BP-20 pads, you might try dropping down to the less aggressive BP-10 pad. This might make the rears works a bit harder and possibly prevent the lockup on front. At least worth a shot before changing out your brake setup.

[toedrag]

I may have missed it in the thread, but I think the MC is from the NB generation Miatas, which has built-in proportioning within the MC. This is why the middle port is used on the rear brakes. In the Miata application, the two adjacent ports on the end of the MC are used for Front Left & Front Right calipers. In the Stalker application, one of the two ports is used for front brakes, and the other is plugged.

 

One alternative approach might be to move the Rear brake line to the other "Front Caliper" port on the MC, and then plug the middle port on the MC. This would allow full breaking force to both front & rear, which would also mean the proportioning valve would likely need to be used and not left wide open.

[subtlez28]

You make an interesting suggestion toedrag. However, I am sort of locked (that was for you X) on moving to manual brakes.

 

I wanted to go manual initially, but was talked out of it. I understand why Brunton likes power brakes (and power steering) for low speed autocross, but I think manual would be the better choice for me personally. I'll contact Wilwood and get something properly sized for my application. This will also open up some shelf space!

[toedrag]

Here's an interesting read on Brake Bias:

[/url]http://www.stoptech.com/technical-support/technical-white-papers/white-paper---brake-bias-and-performance-why-brake-balance-matters

 

What surprised me is how switching to a more aggressive compound on the fronts, or having a BBK could actually negatively impact stopping distance because it puts too much front bias in the system.

 

What this car currently has is likely:

-6 piston front calipers, and 4-piston rears => front bias

-Using the middle port of the MC => more front bias

-Proportioning Valve wide open, and no one seems to be complaining of rears locking up

 

My conclusion: It seems like there is too much front bias in this system, and I'm more convinced now that the rear brake line should simply be moved to the now-plugged MC port, and the middle port of the MC should be plugged. I'll probably do mine this way, and I'll let you know how it turns out when it's completed in 6+ months

[xcarguy]

. . . . However, I am sort of locked (that was for you X) on moving to manual brakes . . . .

 

Thanks. :jester:

[degoetz]

Did some testing before I installed front proportioning valve.

All tests were done at 20mph to lock up.

With clutch disengaged - good braking with all wheels locking up at hard brake pedal force, not much control when that happens.

1st gear - better braking with only fronts locking at very hard brake pedal force.

2nd gear - not as good braking with fronts locking up at med hard brake pedal force.

It seems like the engine breaking (1st) or pushing (2nd) along with the big rear wheels have an affect on the total braking.

I have not tested the car with the installed front proportioning valve yet but I hope to increase braking closer to the 1st gear results, since I run in 2nd gear most the time i will adjust the valve until it locks up rears and back it off. That should give me maximum braking with my set up and allow me to adjust frt to rear to conditions and if I change wheels.

http://i644.photobucket.com/albums/uu163/degoetz/001_zpsb6664fb0.jpg

Edited September 13, 2014 by degoetz

[xcarguy]

Looking forward to your results. :cheers:

[subtlez28]

Degoetz, I wish you luck with your set up. I am also interested to hear your results.

 

 

I have a low speed autocross I can run this weekend. I would like to switch to a more aggressive rear pad for that (ultimately switch master cylinders over the off season).

 

Does anyone have a suggestion on a level or two more aggressive pad than the current rear EBC Yellows? I have miata rear brakes.

[toedrag]

Not sure if EBC has their Orangestuff yet for Miata brakes, but you could look into it. They are a pretty aggressive track pad.

Edited September 15, 2014 by toedrag

[toedrag]

degoetz, here's another thought:

 

Have you tried measuring the brake fluid pressure at each corner? Speedway makes a pressure gauge with 1/8 NPT female fitting, which means it'll thread into the braided lines since they have a 1/8 NPT male fitting on the caliper end. The gauge also has a bleeder valve for removing air after installation:

$29, http://www.speedwaymotors.com/Speedway-Single-Brake-Pressure-Gauge,592.html

 

http://static.speedwaymotors.com/RS/SR/Product/54544025_L.jpg