Chrysler Magazine

I thought torque steer was due to different front end right and left
axle lengths, and that this was a serious problem with early FWD cars,
but now, not so much.

 

NowItsWhatever wrote:

"Torque steer" is simply the coupling of engine torque to the need for a
corrective input with the steering wheel. Its got many, many, many
different causes. Even RWD cars can exhibit torque steer, especially
solid rear axle cars with big torque-monster engines (muscle cars are a
prime example).

I've never really understood the claim that unequal-length halfshafts
contribute greatly to torque steer on FWD cars. The only possible reason
for that would be if the CV joints are forced into binding on the
short-shaft side, and that shouldn't ever happen if the design is any
good at all. Not many FWD cars have truly equal-length halfshafts.

 

If FWD is so superior why do BMW and Mercedes retain RWD in the larger cars?

DAS

For direct contact replace nospam with schmetterling
---

 

Could it be that a compact FWD car doesn't convey the high end image
those two cars project?
Of course space efficiency isn't as big a problem in a larger car.

So why did Volvo finally switch to FWD.
My Volvo loving brother in law was very upset when Volvo switched to FWD.
I suggested he look at the RWD Lincoln.
Finally he bought a FWD 2001 Volvo and loves it.
He lives in snowy Toronto, snow like Sweden gets!

 

-I did notice the slight torque steer on our early '80 Horizon with VW
drive train, but only when pulling out into traffic with high power and
hard over steering. They just didn't have enough power to give trouble.
-My '81 TC3 with the 2.2L engine had bags of power, but torque steer was
hardly noticeable.
-Torque steering isn't a factor with my '95 LH's longitudinal engine
mounting.
-Torque steer on my Wife's quite powerful '01 Sebring is very slight
under high power; hardly noticeable.

Those cars are a joke in snow, which exaggerates poor slippery road
handling.
On packed damp snow (the worst for traction) I've seen them having
great difficulty moving ahead on level roads. A car only recommended
for dry roads.

 

That's garbage in so far as normally powered cars are concerned.
I don't drive a race car and FWD is the last thing I would use for a
race car, only RWD for that application. Of course I wouldn't drive a
high power RWD race car on snowy roads; that would be STUPID!

My '81 TC3 with 2.2L engine had bags of power and all it did was hold
into the turn, requiring my to pull it back to the line I wanted.
Neither of it's front wheels would spin on normal road conditions.

My 3.3L LH Concord has no torque steer. With it's engine mounting it
can't have.
You are talking applying excess power for the road conditions, causing
plowing due to loss of traction on the front wheels. That isn't torque
steer! With slippery roads that can happen and most drivers have enough
sense to back off the power, so steering traction can return.
I have many years of experience with both RWD and FWD on very slippery
roads and I prefer the control on being to go on and off the power of a
FWD car to bring it around a slippery corner. Of course traction
control, which I don't have, makes this very easy for any driver.
With RWD the rear swings out under excess power and it can be very
difficult to stop the swing, spin outs being very common.

 

You are right on, plus LH cars don't have torque steer
due to the length wise engine mounting.
Actually Steve doesn't know what torque steer is.
He's talking excess power causing a loss of steering traction.
See my other post on that.

 

Longitudinal or tranverse engine mounting does not affect torque steer.
That becomes clear when you study a free-body diagram. There will
be some spin-up rotational inertia torque (counteracting what it takes
to accelerate the crankshaft and flywheel) transfered to the frame from
the engine block, but engine torque going onto turning the wheels gets
counteracted by the transmission and does not transfer into the frame -
that component is the same regardless of engine orientation.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Except for the counteraction of acceleration of the crank and flywheel,
there is no torque transferred into the frame by the engine - other than
crank/flywheel acceleration, torque gen'ed by the engine is exactly
counteracted by the transmission housing.

Just so people aren't getting the idea that *all* engine torque
contibutes to torque steer - only the part that goes into accelerating
the crank and flywheel against their rotational mass.

I just realized something: I would expect an intuitive but incorrect
assessment of torque steer from engine torque to say that a longitudinal
engine, but not a transverse mounted engine, would give torque steer.
What is the thinking behind a transverse mounted engine causing torque
steer but not a longitudinaly mounted one?

Or does this go back to the different axle lengths due to transaxle
offfset? Ahh - that must be it.

OK - the light just went on. Longitudinal is less likely to cause
torque steer because the transaxle willl tend to be centered -
equal-length axles. Transverse mount wants to offset the transaxle to
one side, taking power off the rear of the engine - different length
axles. Got it.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Never mind - see my other post - Longitudinal inherently gives equal
length axles, transverse inherently offsets the transaxle to one side =>
different axle lengths. Nothing to do with orientation of crankshaft
rotation pers se.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Some O wrote:

I understand you like FWD, and can understand why if you drive half the
year in snow. But as a person who's put 240,000 miles on a LH car with
the same longitudinal engine, I can tell you that the above is DEAD
WRONG. Any time either front wheel breaks loose, the steering wheel
jerks like it has a mind of its own. That's a form of torque steer.

 

I consider a 214 horsepower 3.5L "normally powered" and thats EXACTLY
what it does. A 300 horsepower Cadillac is also quite "normally powered"
and its worse.

FALSE. Engine mounting has nothing to do with torque steer. Torque steer
is *any* phenomenon that causes the driver to have to apply steering
input in response to application of engine power. Rear wheel drives can
exhibit torque steer under certain conditions- that's exactly why 440
and 426-powered Chrysler B-bodies from the late 60s had a different
number of spring leaves on each side in back- to prevent it from jumping
a lane sideways under hard acceleration.

 

In RWD, the engine torque does get transferred into the chassis because
the torque element it reacts against is not rigidly tied to the engine -
it reacts against the chassis instead.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Bill Putney wrote:

The only drive configuration that I am aware of where engine torque does
NOT get transferred to the chassis is the old "Torque Tube" drive like
some GMs had in the 50s where the driveshaft is enclosed in a hollow
tube rigidly connecting the engine and rear axle (and AWD Chrysler
Minivans use it today for the rear wheels, but that only absorbs part of
the engine torque). But it isn't about ENGINE torque anyway, its about
wheel torque and more importantly the forces on the steering system that
result from wheel torque. A Torque Tube will 100% eliminate torque steer
(and preferential right-rear wheelspin) on rear-drive cars... at the
penalty of frickin' ENORMOUS unsprung weight

The whole claim of unequal halfshaft length being related to torque
steer in FWD cars is a red herring IMO for several reasons. First off,
even longitudinal engine FWD cars have very unequal length half-shafts
(a good 4"-6" difference in the case of a Chrysler LH series). And in
the second case, that shouldn't matter at all unless the shaft is so
short that it makes a CV joint start to bind.

What really minimizes torque steer is setting the front suspension up
with a near-zero scrub radius so that the front wheel's thrust doesn't
get turned into a force on the steering linkage at all, but that has
some other implications. That is why the old FWD full-size GM cars from
the 60s (Olds Toronado, Cad Eldorado) had wheels with such a huge
negative offset from the hub to the rim, and had to have astrodome
shaped hubcaps as a result- to get the scrub radius close to zero.

 

I think the biggest issue with unequal-length halfshafts is that the longer
halfshaft tends to twist or flex a bit more than the short halfshaft under
hard acceleration or other transient inputs (such as unequal traction under
either tire).

 

Unequal length halfshafts are a primary cause of torque steer in FWD cars.
Google "define torque steer" for some good write-ups on it. Unequal-length
shafts are always mentioned as a significant factor, and the reason that
most manufacturers today use equal-length shafts as a direct result.

If the halfshafts are unequal length and are otherwise identical, the longer
halfshaft will tend to twist or flex a bit more under acceleration and other
transient inputs. With both equal and unequal length shafts, there can be
some torque steer under some transient inputs such as if one tire has less
traction than another under acceleration, but the torque steer will be
amplified with unequal length shafts due to the uneven shaft twist/flex.

In the past, some manufacturers used an intermediate shaft that was fixed in
place, so that both of the regular halfshafts could still be equal-length.
That helped a little. Other manufacturers made sure the longer shaft was
thicker or stronger to resist flex and twist, but if the longer shaft weighs
significantly more then you might still have torque-steer. Some
manufacturers then add a weight to the shorter shaft to compensate.

I like the longitudinal layout Chrysler adopted with the LH cars, with a
centered differential and equal-length shafts. Seemed much more elegant to
me.

 

Will this myth NEVER die?

Torque steer is primarily caused by non-zero scrub radius in the
steering geometry. When one wheel loses traction, the other wheel with
traction exerts forward thrust on the steering knuckle. And when the
scrub radius is non-zero, that forward thrust (no longer countered by an
equal and opposite thrust on the other side of the car) causes a torque
on the steering knuckle which tries to rotate the steering wheel.

It has NOTHING to do with transverse vs. longitudinal engine mounting.

It has NOTHING to do with half-shaft length.

Similar phenomena even occur with REAR-drive cas, although many people
don't call the resulting effect "torque steer" because it doesn't
manifest immediately as a force on the steering wheel.

 

Only in people's imaginations.

Yeah, its on the web so it must be true. :-/

Name me ONE common FWD car that has equal-length half-shafts. I can't
think of a single one, though there may be a few out there in fact. 99%
of FWD cars don't have equal-length shafts, though. Yes, many are a lot
more nearly equal today than in the past, but none are truly equal. Not
even the Chrysler LH cars with a longitudinal engine have equal-length
halfshafts. The driver's side shaft is significantly longer than the
passenger's side shaft.

 

Having a differential between the shafts by definition guarantees the
exact same torque on both shafts even if one is twisting and the other
is not (dropped torque on one side due to twisting gets exactly
reflected on the othrer side (differential action). Think about it: If
a CJ joint on one side breaks under acceleration, the troque on the
other side immediately drops to zero (differential action). A twisting
shaft on one side is just a less severe case of that.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

You mean you didn't know? We've only been talking about this phenomenon in
the USA since 1980. That's just dumber'n a coal bucket. But hey, don't let
me stop you. Make fun of the truth and see if you can get it to go away.