Unequal pad wear

[Chrispy]

When I swapped my pads over on Monday I noticed that the right front had considerably more wear than the left front, rears were fairly equal. Is this expected at NHMS from trail braking into the left hand corners? The car was stopping in a perfectly straight line, no pull and the pad wear was fairly evenly dispersed front to back.

[breakaway500]

I have noticed over the years since the introduction of 4 channel ABS,pad wear on cars to be uneven,particularly on cars that are driven hard. I believe this to be the direct result of the abs system being able to control the application pressure on each caliper individually of the others..therefore the unequal wear to the pads from corner to corner.Unless you find something mechanically wrong with a caliper,as in sticking pistons or misalignment of the pad carrier,I would say not to worry.

[nateh]

If at all possible, nerf that ABS. Uneven pad wear is the least of your concerns.

Every year we have a big wreck which would either have been avoided or greatly reduced without the influence of ABS. Most recent: Cayman at NHMS.

[eastcoastbumps]

There is clearly something wrong with those AP calipers you have on your car. I'll take them and be sure they're properly disposed of.

[Chrispy]

Hmm, the ABS in this car is very good at keeping the car straight under unusual braking situations. During a spin it pretty much lets you lock them up so you stay on a straight path. What happened with the ABS in the Cayman that made things worse?

@eastcoast - if you know how much pads and rotors are for these brakes you might change your mind

[TroyV]

I wouldn't mind hearing an analysis on this specific to the incident.

[StephanAlfa]

Hmm, the ABS in this car is very good at keeping the car straight under unusual braking situations. During a spin it pretty much lets you lock them up so you stay on a straight path.

I am sure others, like me, will disagree on this... ABS during a spin will not lock up unless you take the foot off the brake once and put it back on again.
ABS in racing conditions is the kind of tool you don't want unless you plan to fight the machine. "Unusual conditions" is something you can best deal w/o ABS for more predictability as ABS quicks in under this condition you'd be fighting both the system and the car instead of controlling it.

[nateh]

This is second hand, and Troy, you were in the car, so correct me if I'm wrong.

The driver lost the tail under power coming onto the straight. He tried to correct and failed, and went both feet in as he should have. (No obvious driver error here, except getting on the power too much while starting his pass attempt.)

The tire tracks showed all 4 sliding, but traveling in a curve that ended at the inside wall.

If the wheels are locked the car will spin in a straight line. We can conclude from this that the wheels were not locked, despite the driver's best efforts to do so.

The curved track led to an angled hit into the inside wall. (Inside wall impacts are a trademark feature of a failure to lock the wheels in time.) If the wheels had been locked, the angle would have been more acute and therefore less severe. Conceivably the car would have gone straight down the track without hitting the wall - depending on whether he got the wheels locked in time. Locked too early, he would have hit the outside wall - but again, at a more acute angle and therefore with less damage.

[nateh]

Stephan, it may be that some ABS systems will behave as you describe - allowing a lockup after a second application. I don't know how to verify this except for each driver to try it in their own car.

[nateh]

Some ABS systems also have an "ice mode" which can come on after hitting some bumps under braking. In this case, the pedal goes hard and there is no braking action at all. It may be that you can recover by pumping, but this is counter-intuitive if you aren't prepared for it. An instructor totaled a student's car this way on the inside of turn 11 a few years back.

[nateh]

A theme you might notice here - I get the impression that ABS wrecks are most common with expert drivers. If true, this is because they are driving very close to the limit, and therefore when ABS bites there is less margin for recovery.

[Chrispy]

I've tested my cars spin-ability a few times now both wet and dry at about 60-70mph. The ABS system on my car feeds on the yaw sensors, so if the tail is slightly out under braking it will bring you straight and true. Once the rotational acceleration is beyond a certain point it doesn't try to correct and you are on your own.

Nate, wouldn't the car have curved down towards the pit wall anyway as that is the way the track slopes?

[nateh]

I don't think the slope is enough to change the car's direction significantly with the wheels locked.

Chris, when you say "you're on your own," do you mean that you can lock the wheels or not? This is the critical question.

[Chrispy]

The skids marks and pedal feel seem to indicate that the wheels are completely locked.

I also experienced the dreaded ice-mode briefly at turn 11. It happened when I went out in the open track session after the TT and still had the shocks set up for the wet conditions so there was a lot more front weight transfer than usual. I think I was just a little bit off line on the entry and probably ran over some marbles. Went a little bit deep into 11 but wasn't horrible. It was the only time that has ever happened to me on track, although I have had it happen under auto-x conditions quite a few times.

[paultg]

Some ABS systems also have an "ice mode" which can come on after hitting some bumps under braking. In this case, the pedal goes hard and there is no braking action at all. It may be that you can recover by pumping, but this is counter-intuitive if you aren't prepared for it.

I experienced this with my 2002 WRX when I lived in the bumpy boston roads / Everett Ma. When I replaced the all-season stock tires with a Falken Azenis tire it seemed to go away.