From: rhaar@albert.cs.gmr.com (Bob Haar)
Newsgroups: rec.autos
Subject: Re: Mech ABS retrofit (ABS-TRAX)
Date: 21 Nov 92 19:33:32 GMT
Reply-To: rhaar@albert.cs.gmr.com
Organization: G.M. Research and Environmental Staff

In article 53060095@hpsgm2.sgp.hp.com, leonglaw@hpsgm2.sgp.hp.com (Lawrence LEONG) writes:
|>I've just seen a mechanical ABS retrofit.  Its called "ABS-TRAX" and is
|>supposed to be derived from aircraft systems.  Have you heard of it, and if
|>so, any data-points or anecdotes?
|>
|>The system consists of a small pressurised chamber which fastens (one per 
|>brake circuit) onto the master cylinder output, somewhat like a reserviour.
|>The chamber contains a pressurised Nitrogen chamber and diagphram; when the
|>brake fluid hits a pre-set pressure (supposed to be within 5-10% of lockup),
|>a valve will actuate to relieve the pressure and keep the wheels on the 
|>threshold of skidding (somewhat similar to threshold braking).  Under normal
|>braking, it is supposed to not activate.
|>
|>There is no speed sensor like the electronic versions.  Since this device 
|>works on a principle similar to threshold braking (I think), it appears to
|>be better than electronic ABS, no?
|>

No way can this beat an electronic ABS. It is really not an ABS system
at all. What is does (if anything) is to limit the maximum hydraulic pressure
in a braking circuit.

Now brake force corresponds roughly with hydraulic pressure, but neither
one has much to do with wheel lock up. 

Think about this: It take MUCH less brake pressure to lock-up a wheel on wet
pavement than it does on dry clean pavement. If this device was set up to
prevent lock-up in slippery conditions, it would greatly reduce you
braking ability on good traction. If it was set to prevent lock-up
on dry pavement, you would lock the wheels before it acted on wet pavement.

The problem is that there is no feedback that can cause its behaviour
to vary with the conditions. Electronic anti-lock systems do this
by moniotring the change in wheel speed. Rapid change means the tire
is slipping.

In threshhold braking, there is also feedback through the senses of the
driver and his judgment based on what that vehicle has done in
similar conditions before.

|>The sales guy could not tell me how/what was used to determine the threshold 
|>nor the method of pressure relief.
|>
|>This system is supposed to in use on aircraft, and is supposed to reduce 
|>braking distances by up to 30%.  Its also supposed to be DOT certified (for
|>what its worth).  The company claims to have sold 15000 units in US alone.
|>
|>
|>Does anyone have any experience with this?  Does this system sound viable? 
|>Is this really used in aircraft?  Should I part with good money for this?
|>
|>(price is approx US$620, incl installation).
|>

Pure snake oil.  Don't get taken in. RUN, do not walk, out of that store.


ANd don't believe any claims about insurance reductions 
without first checking with you insurance company about this
specific device.

	Robert Haar               InterNet : rhaar@gmr.com 
	Computer Science Dept., G.M. Research and Environmental Staff
DISCLAIMER: Unless indicated otherwise, everything in this note is
personal opinion, not an official statement of General Motors Corp.




Newsgroups: rec.autos