Hi guys, it seems that I need your help once again...


Today I went for a "fun" drive on a fantastic mountain road...Even if I was not driving at the limit (I like driving fast but not dangerously on public roads, even if they are desertic),the car had a strange handling behaviour in certain conditions: when braking firmly (not extremely hard), every time a wheel came over a little bump (very very very little bumps, the tarmac is nearly flawless), the tire lost grip and ABS came in a little....just for a moment and barely perceptible.

Now I can't think that ABS was over-reacting, because I could hear the tire squeal for a moment.

Is it the car that has some suspension issues or is it me that over-estimate the braking capability of the car?

I was not able to pass 5000rpm in 3rd on that twisty road, so the braking speeds were not high.

 

Hard to say without feeling it because the car does have random ABS issues, but on the other hand, the brakes are very strong and you can easily get the abs to come on with not a lot of pedal pressure on cold tires on the street.

And yes braking over bumps can also engage the abs because you'll be on the brakes and momentarily while the tire isn't on the ground, it won't spin and the abs will chop in real quick.

I'm leaning towards the last one if it doesn't exhibit this problem any other time. Usually when the ABS is acting up you KNOW for sure. The pedal modulation and braking over bumps is something that is learned over time.

Might want to have it checked just in case though. If you are bold though you can try disconnecting the PSM precharge pump and going over those same bumps with the same brake pressure and see if it still happens.

 

i think it's normal. mine does the same thing not worried about it, at least i know the abs works

 

tire pressure?

 

Just to add a little to Heavychevy's post, which I agree with...

The tire doesn't have to come off the ground completely. The acceleration load a tire can transmit to the road is an increasing function of load on the tire. So if you are near threshold braking, and then unweight the wheel even a little bit, by going over a bump, the tire can go over its friction limit and the abs will kick in.

 

i have the same experience once in a while, i think its normal.

 

Thanks guys.

I have to say that, even if ABS kicks in a bit, the car remains very composed and in control. I have to add that this is happening especially when I am at the end of the braking, at the very beginning of the corner, trying to load the front a bit to get a better corner entry.
Maybe some more rubber on the front should help...or simply I really need a good set of adjustable coilovers...

I'll have the ABS checked anyway...

 

am thinking this is a case of you getting scared way before your cargets scared have had the front end of my car get washed out a few times and felt the same on of feeling not to worrie imo

 

gotta proof read thats on/off feeling

 

Normal ABS function for the conditions you described. IF your brakes and suspension are within spec. Frankly, I'd personally wait for a repeat of the effect before looking for a problem. You are now attuned to what your brakes are doing, so you won't miss any major problems.

 

Thank you guys for your opinions, I appreciate.

Next wednesday will be public holiday, and it seems that I'll be on that road again to do some more testing..


BTW my tire pressures are 36.25psi on all four tires...my mechanic said that the pressures Porsche recommends are too high.

 

You will see a lot of rear tire wear at those pressures.

One of the reasons for differential pressures front/rear is the 38%F/62%R weight distribution as well. While you are out playing with your car, try it with both your current and stock settings for tire pressure. I expect that you will be able to feel a significant difference. You can decide which you like better.

Bouna fortuna!

 

Now I tell you something: I'm at the second tire swap in less than 7.000miles....my rear tires got completely worn out twice!!!!!!!!!!
I thought that it was an alignment issue both times, but now I see....


I cannot thank you enough for this advice!!!

I hope I will be able to reciprocate.

Grazie!

 

tutto e a posto, non ti fare paura