Scarey no brakes story

[Chrissso]

I've just put on some second hand tyres on my 16" rims on the front. They have a profile of 55 where as I usually get brand new ones with 45. (Consequently, the car looks like a trailbike now, heh).
Anyway, I was cruising rapidly towards an intersection that was turning orange so I gassed it, knowing that I could stop in time with the awesome braking power of the SSS.
The ABS kicked in about half as early as it should of, and scared that absolute shit out of me, as I could not stop anywhere as quickly as I used to. I put it down to shit tyres, but they are yokohama, which are not exaclty shit.
Later on, I found a long stretch and tried it again, same result. The tyres where not squealing. The only thing I can put it down to is that the ABS measures the RPM of the rear tyres & then the RPM of the front. If then may conclued that if the front tyres are not spinning as fast as the rear, they must be skidding.
Does anyone know anything about ABS? Would this be the case? Just bear this in mind, as My stopping distance has now more than doubled.

[cargle]

abs measures the rate of deceleration.

if the rate is high is assumes you are trying to stop very quickly and it kicks into gear.

have you checked your brakes? make sure you have heaps of pad left and that there is nothing loose etc..

[Chrissso]

Pads are low, might be that.
I noticed an imidiate difference on the new tyres. - might be just shite?
The rate of deceleration used to be twice as much as now! Big difference.
Thanks for the input!!!

[Longrod von Hugendong]

I always thought ABS worked with sensors on each wheel......if the ECU sees you are travelling at speed and senses a wheel has stopped spinning (i.e. Lock up) it releases the brake on that wheel for a fraction of a second repeatedly until the brakes are disengaged.......so effectivly they will work at any speed.
Am I right??

Ryan

[Chrissso]

I thought thats how it works.
My front tyres have a bigger diameter than the back, and would roll at a lower RPM. I dunno tho, I know nothing about ABS.

[GroundZer0]

Early ABS braking systems and cheaper ones used Acceleration sensors until they started giving troble from sensors giving incorrect readings

They use sensors on each wheel and if they detect wheel slipage the wheel is released so traction is regained then switched back on until it loosed traction again.

had to do a project of car safety a couple of months ago :mad:
Very boring shit but still useful:Flipa:

[Chrissso]

That must be it then. Thanks.

I think I'lll get tyres all the same size ASAP, of rotatae the tyres in the mean time.
It's friggin dangerous!!!

[cargle]

ABS does not wait until a wheel has stopped or slipped otherwise it has already failed.

ABS senses the rate of deceleration via sense on the wheels

If there are any decelerations that are unusual, (rapid deceleration) it will disengage the brake until it sees acceleration and engage to see deceleration again.

So basically it will predict wheel spin/slippage and prevent it.

[Chrissso]

Yeah, but my problem is that the ABS kicks in at 1/2 the decelleration rate that it used to. This means that the decelration rate has changed, so if tis is the case, then my sensor is ****ed. Problem is that the difference was immidiate with the bigger tyre change. If ABS uses bothj technique, which it verywell may do, then it's not the delceleration sensor that's ******. The Difference in rotation theroy makes more sense.
Thanks fdor you rinput dude, but I don't recon that's it.:thumbsup:

[salv]

when i was driving my my 17s ont eh front and my stocko 14`s on the back and carrying a heavy load in the back...my ABS light came on and ABS was not functioning at all...I think this system may have a problem working with dissimilar sized wheel/tyre combos-as the rolling diameter differed...

[Spectrix]

Mnnn yeah
Best to get new tyres I think.. gonna need the brakes sooner or later and you don't wanna have a smash.. specially if your insurance company refuses the claim because of defective tyres sizes.

:bawlink:

[Chrissso]

Very True!!!
I'm going to get mine all the same size. That's the important thing. As long as there all the same size.