Car is 'crabbing' down the road...
Greg Zelna
the road, where from behind you can see all four tires, as
if they all arent following the same track... Well lo and behold,
I was following my wife and her '86 Volvo 240 does it ! The car
only has 45k mi, is in great shape (no wrecks as far as I can tell)
original paint, but we did buy it used a few months ago.... It drives
just fine, no pulling in either direction, brakes nice and straight,
no shimmying or vibration at any speed- so you'd never notice the
'crabbing' effect from inside the car, but it definitely is noticeable
from behind while driving... Don't have enough miles on the tires to
notice any uneven wear...
My question(s) is, is this simply a 4-wheel alignment problem, is it a
sign that the car was at one time wrecked and repaired (what I always
thought caused this...), are there any other reasons for this ? The last
thing I want to do is go into a shop or the dealer completely ignorant and
take thier word for everything... If there are no other symptoms other than
the fact that visually the car drives down the road skewed, should I leave
well enough alone ?
Thanks,
Greg
Scott D. Berry
Greg Zelna <gze...@osprey.mlb.semi.harris.com> wrote:
>I suppose you've all seen the cars which seem to 'crab' down
>the road, where from behind you can see all four tires, as
>if they all arent following the same track... Well lo and behold,
>My question(s) is, is this simply a 4-wheel alignment problem, is it a
>sign that the car was at one time wrecked and repaired (what I always
>thought caused this...), are there any other reasons for this ?
There can be other causes: back in the '70s, when I was a summer student
working for Buick, we had cars coming off the assembly line that did
that occasionally. We referred to it as 'dogtracking' instead of crabbing,
but your term is better IMHO. It turned out that the problem was that
a particular frame supplier was sending frames where the attachments for
the rear control arms were out of spec. We had several frames specially
built with a controlled set of positions, built the cars and spent a
Saturday driving the cars down a chalk line in the administration building
parking lot to measure the crabbing amount. Sure enough, there was
a direct correlation between the frame error and the crabbing offset.
Solution was to provide rear control arms which were made long or short
to fix the problem.
Scott D. Berry, Physics/Florida State Univ., be...@redbeard.physics.fsu.edu
pad...@141.240.2.145
>I suppose you've all seen the cars which seem to 'crab' down
>the road, where from behind you can see all four tires, as
>if they all arent following the same track... Well lo and behold,
>I was following my wife and her '86 Volvo 240 does it !
Anything which changes the alignment of the rear wheel to the centerline
of the vehicle can cause this even something as simple as a worn-out
bushing in a control arm, it does not necessarily indicate a poor repair.
It can indicate more serious problems (broken link, bent trailing arm) so I
would have it checked out by someone who understands suspensions.
A. Padgett Peterson, P.E.
Cybernetic Psychophysicist
(po on)Socialize Lawyers Not Doctors(po off)
PGP 2.4 Public Key Available
Dennis J. Ciplickas
In article <1994Jun2.1...@brtph560.bnr.ca> sca...@brtph275.bnr.ca (Chris Lastinger P090) writes:
>...Well, apparently the rear axle on some Volvos is smaller in
>length than the front...
>...I don't think this is true of all Volvos...
I was under the impression that most cars on the road today had a
wider "track" in front than in back, maybe by about an inch or so.
You're right about it looking funny though, when you catch it at the
right angle.
-Dennis
Lee Hetherington
| Well, apparently the rear axle on some Volvos is smaller in
| just to one side, it looks like the alignment is off. Try looking at
| the rear of the car on the passenger's side, and see if it doesn't
| look like the car is "crabbing" the opposite way.
|
| I don't think this is true of all Volvos, and may just be true
| of my friend's only because he rebuilt it himself and may have put a
| non standard sized rear axle on it. Hope this helps
The rear track is definitely smaller than the front track on Volvo 240s.
I think the difference may be on the order of 3in, but I don't have the
numbers with me. So, you might not be really be seeing crabbing as
suggested above.
--
Lee Hetherington
i...@lcs.mit.edu
pad...@141.240.2.145
>Beware the old optical illusion whereby you look down one side of the car
>and see what appears to be a 'crab' when, in fact, you see the result of
>rear wheels that are closer together than the front wheels. This seems to
>be a pretty common trait in autos and I never liked the way it looks from
>behind. I wonder why they do this anyway???
Co$t. The front track is defined by the width of the frame rails plus
suspension geometry. The rear track (on a live axle car) is defined by the
axle tubes and axle length.
If you can use the same suspension components across a range of cars with
different frames, costs go down but the front and rear tracks will not
necessarily match. And then there was the Isetta.
A. Padgett Peterson, P.E.
Cybernetic Psychophysicist
(po on) Socialize Lawyers (po off)
Tim Mortensen
>I suppose you've all seen the cars which seem to 'crab' down
>the road, where from behind you can see all four tires, as
>if they all arent following the same track... Well lo and behold,
>I was following my wife and her '86 Volvo 240 does it !
Beware the old optical illusion whereby you look down one side of the car
and see what appears to be a 'crab' when, in fact, you see the result of
rear wheels that are closer together than the front wheels. This seems to
be a pretty common trait in autos and I never liked the way it looks from
behind. I wonder why they do this anyway???
--
\ _
0 0 Tim Mortensen
(
\__ t...@xtmorte.dwp.la.ca.us
Chris Lastinger P090
|> I suppose you've all seen the cars which seem to 'crab' down
|> the road, where from behind you can see all four tires, as
|> if they all arent following the same track... Well lo and behold,
|> I was following my wife and her '86 Volvo 240 does it ! The car
|> only has 45k mi, is in great shape (no wrecks as far as I can tell)
|> take thier word for everything... If there are no other symptoms other than
|> the fact that visually the car drives down the road skewed, should I leave
|> well enough alone ?
|>
|> Thanks,
|>
|> Greg
A friend of mine has a Volvo wagon, and I was driving behind
him a while ago. He rebuilt this car from the ground up, and when I
noticed that he was "crabbing" big time, I let him know.
Well, apparently the rear axle on some Volvos is smaller in
length than the front. So when you look at the car from the rear and
just to one side, it looks like the alignment is off. Try looking at
the rear of the car on the passenger's side, and see if it doesn't
look like the car is "crabbing" the opposite way.
I don't think this is true of all Volvos, and may just be true
of my friend's only because he rebuilt it himself and may have put a
non standard sized rear axle on it. Hope this helps
--
www
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the States.
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Paul W. Schwartzkopf
psc...@luc.edu
Einar Sjaavik
> I suppose you've all seen the cars which seem to 'crab' down
> the road, where from behind you can see all four tires, as
> if they all arent following the same track... Well lo and behold,
Park the car on an empty lot. Go behind it at some distance,
make sure you're *exactly* at the extension of the car's centerline.
Then have a look. My guess is you'll find that you got fooled by the
fact that you were not straight behind it, sitting on the left side
of your car. It's especially easy to get fooled by cars having
considerable smaller track width at the rear than in the front. The
old Citroen DS21 models always looked like they went sideways.