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I'm running a NA6 with DBA brakes, Ferrodo pads and a biasing valve (fully open). I am consistently locking the front left under heavy braking especially on hill climbs where the tyres and brakes are cold.

Is this just because I'm sitting on the right of the car so there is less downwards weight on the passenger side so less friction? I have bled the brakes a few times so it shouldn't be an air pocket. What can you do to fix the issue other than not braking so hard?

Does upgrading to a larger brake (NA8b) help with brake control? Other than this lock up issue, I find when I'm tracking the car, the brakes are excellent and I think I'd rather keep to the lighter brakes rather than have extra weight on each corner.

A fully open bias valve would be allowing the same pressure on the rear as the fronts. You should be getting rear lock up first if anything.

What pads? What brake pressures? When were the calipers serviced/rebuilt? Are the slider pins greased?

I assume that your braking is being done in a straight line?

You could install ABS?

The NB8B could fix the problems only because they could be in better conditions than yours.

Magpie wrote:A fully open bias valve would be allowing the same pressure on the rear as the fronts. You should be getting rear lock up first if anything.

What pads? What brake pressures? When were the calipers serviced/rebuilt? Are the slider pins greased?

I assume that your braking is being done in a straight line?

You could install ABS?

The NB8B could fix the problems only because they could be in better conditions than yours.

Thanks for your help Magpie, I'm fairly new to racing the mx5 so I'm not sure what is right or wrong with the handling of my car.

The rears don't seam to lock up on the track even when braking hard while turning. They did in a motorcross slalom I found the back breaking out a bit under brakes when the fronts were loaded right up and the back light. On the track the car is very stable, other than the front left locking before the others when at the limit.

Pads are the Ferodo DS3000 which are excellent when hot, but I think they might be partly causing the issues when cold as they bite, which is making it hard to judge the lockup point.

Brake pressures, I'm not sure of... standard NA6. (other than proportioning valve)

Calipers may be the issue, which is really why I posted. Is it common for the driver side to lock up first due to the weight difference on that side, or do I have a mechanical issue? I'll grease the sliders for next event though they slide well by hand last time I checked. Maybe the caliper pots need machining.

Those of you who race NA6's, are you using the standard size rotors / calipers or have you upgraded to the larger NB or 270mm rotors and calipers?

When did you last strip/rebuild your callipers? A new seal kit, clean the piston bore, and regrease the slider pins? If you haven't done it, give it a go and come back if the problem persists. And yes, do the rears too, sounds like they are not pulling their weight.

It could be the bias valve needs to be on the fronts ... what pads are you using on the rear? If using 3000s, maybe try a different pad in the rear. I will let someone who has that brake setup make the suggestion, but I always used a different pad in the rear of the GM when tracking it. Took some experimentation to identify the best combination, but when it was sorted ... .

greenMachine wrote: ... what pads are you using on the rear?

Actually thats a good point! they are standard pads in the rear which is probably why I can have the full bias. I was saving money at the time and figured the front pads made the biggest impact anyway. Upgrading the rear pads might help stop a bit quicker but I don't think it will stop the left front locking up over the right.

A rebuild sounds like the best option as they probably have never been done (120km). Should I spend the money on a size upgrade on the front instead?

Don't get me wrong, the car stops great at the moment, in fact it's a bit scary how late I can brake into some corners. I'm just finding it's hard to commit into some corners when the left locks up on cold tyres. I'm focusing on improving the handling of the car at the moment whilst the speed is down before I move up to a more powerful engine.

Does anyone run lower pressures on the left side of the car to counter driver weight?

I think it is normal for front left to lock first. Has happened on my cars too. Might have something to do with pressure difference. Buy an NB8B. Problem solved.

A lock up like this? This was from the tyres being at their limit (possibly braking a little late) and a slight move of the steering to the right caused the left front to loose grip and hence the spin. I'll get the data files out of the car soon and see what the front pressure was, but I think that it will confirm lockup pressure and in excess of 1g on the front tyres.

A quick calculation on weight transfer shows that I had 760kg of weight on the front or 27% more than normal! The rear was 29.5% lighter due to the 1g + braking. This would appear to be about the limit for the FZ201's (based on my setup). Using this information I could go through all my data and see how often I had the tyres on the limit of letting go. Now I just need a high speed corner spin to establish a bench mark...

Data analysis time. This is a log on the spin (solid lines) and a 'normal' run through the same corner. Hopefully the OP will get some help from this post...

Green =brake pressure, blue = rear wheel weight, grey = speed

1.15 sec decided to brake, there is still weight being transferred to the rear as car is still accelerating.
1.31 sec braking commenced, weight coming off rear wheels. However the spin (solid lines) track for the brake pressure has a much steeper curve. Therefore more weight is loaded to the front.
1.8 sec max weight transfer to the front has been achieved in the spin track, but in the non spin weight and brake pressure is still building
2.95 sec this is the start of the spin. Surprisingly this is where I started to trail brake and commenced turning in for the 'normal' lap. Further the braking duration was about the same.

It looks like the brakes were applied too hard in the initial instance, this caused too much weight to go to the front. A very slight movement of the car caused the oversteer as the rear had no grip. The slight movement more than likely was a result of the heavy braking.
Spin Breakdown on Flickr

[quote="madjak"] I am consistently locking the front left under heavy braking especially on hill climbs where the tyres and brakes are cold.quote]
Are you only having these problems on the same courners???? only when all is cold. Sounds like you might be unloading the left, causing the light wheel (left) to lock.
Just athought, but I would be adjusting your bias to give more rear brake and then try that. Set up is just trial and error and maybe small flatspots.

Talk to some of the other local mx5 runners about what they run.

Remember set up for track (time to warm everthing up and time for qualifing etc) is completely different to hill climbs, no qualy no warmup.

Terry

Great info Magpie. I like the telemetry data you are capturing! What system is that? It looks like that you would have picked up a lot of time as you had reduced your speed to the same speed as the previous a whole 0.4 seconds earlier.

In my case, the lockup definitely starts on the front left, and will move to both fronts if I don't get off the peddle. Its happening on the first few corners into the hill climb when the tyres are cold so I think I'm just overbraking on cold tyres. It hasn't yet caused me any spins or anything but it makes it hard to commit under brakes.

I'm running the same event as last weekend again in a few weeks. The road surface is a bit loose and is very bumpy. I'm braking from 4th gear down to 2nd gear into a 90 degree sweeping right hander. The road is wide enough that I can go out wide if I can't get the speed down due to the lockup but then I miss the line into the following left.

Next run, I'll try running slightly lower pressures on the left to see if I can balance the car a bit better. I'll also hook up my goPro so it's easier to see the issue. My post was mostly to do with the NA6 brake setup and if others were running the smaller disc size on their race cars. Should I be looking at upgrading a larger size to help with brake modulation and pedal feel?

Your biggest problem is as tbro said, a hillclimb gives you no time to warm anything up.

Because of this, most of the info given isn't relavent to your situation because it mainly relates to track work where you have time to warm everything up.

An example, my old 240Z was set up for track work with Hawk DT70 pads in the front and hard road pads in the rear with the front rotors being consumable items, 2 sets of pads to a set of rotors.

On the track, you had time to warm the brakes up and they worked very well, I knew that they had gotten to temperature when they were squealing on cool down laps. They took a bit to warm up, and if I didn't get them warm enough, they were very sketchy into the first corner. Once they were hot all was good for the race.

Come hill climb time, they were the worst brakes you could imagine, no heat in them meant no stopping until you locked up, and then no stopping with control. I have agreat picture from the Cootha Classic where I am understeering through the bollards forming a chicane because of cold slicks and cold brakes. That gave me a clean sweep and a horrendous time penalty that put me out of class contention.
This made some hillclimbs a very arse puckering experience, down the hill into the second loop at Mt Cotton for one, and when the Cootha Classic was run, the down hill section after the chicane that had a right hander with a short sharp up hill section over the line and then a small bit of road to slow down in before heading off to the pit area, on a couple of runs I very nearly ran out of road after the line as the brakes were still cold.

At one stage I was contemplating using two brake set ups, one for circuit and one for hillclimbs, but as I was only doing a couple of hill climbs a year, for me it wasn't the extra cost and time. I lived with the compromised brakes. It cost me a lot of time, but I was there for the fun and with the cold tyres was able to put on a show most runs, especially at Noosa......

To fix your problem of locking up on the hillclimb you basically have two choices:
1. Live with it, start braking a little earlier, but with less pressure and try to keep the speed through the corner up and onto the throttle a little earlier at the exit.

2. If you have upgraded the front pads, go back to a very soft standard road pad, same for the rear. A hillclimb doesn't use much brakes compared to a couple of track laps so you won't cook them.

Some advice I received when I first started racing, from a very smart sports 1300 driver/engineer/constructor regarding brakes was to use the softest pad possible for the car.

The data is capture using Innovate stuff.

You could run a few PSI less to get some heat into the tyres quicker.

the easiest way to get heat into the tyres for a hill climb is to use very very soft tyres. That's why you will see the serious open wheelers using wets or super super soft slicks wrapped in plastic to keep them clean until they are ready to run.

Hillclimbs are probably the best place to learn how to drive fast on cold tyres and brakes, as for every run you will have cold tyres and brakes. The only time you get heat into anything is if you are allowed to do a burnout before the start to get heat into the drive tyres. Some venues allow this and some don't.

For production type cars where tyres are limited, basically use the softest tyres you can get. A hillclimb is one place that a brand new road tyre may give slightly better performance than a worn one will as the tread can squirm and get hotter quicker, but this would be very marginal, remember most hillclimbs are under 1000m long so not much time to heat anything up when runs are only 40-60 seconds from start to finish.