Hi everyone!
I have an old SAE drawing from 1976 of the Toronado front suspension
geometry. Looking at it, the steering axis inclination intersects the road
surface about 1/4" OUTBOARD of the tread centerline. This means the forces
from torque steer and braking have only a 1/4" lever to pull with in severe
circumstances. Moving the wheel out farther changes this relationship for
the worse, and I wouldnt recommend it. Looking at the tread centerline to
bearings relationship, the weight is borne between the bearings which is
good enough I think. Much of the bearing loading for driving is effected by
the positive camber on the front wheels, which moves the tread beneath the
spindle slightly.
All the front end stuff is designed with motion in mind, a single wheel
bump or blowout etc moves the suspension in directions to minimize the
unbalanced forces. This is good practice, and all cars do it. On FWD
designs its especially critical. If the front tires were to be moved in
line with the rears you would be giving the tire a tremendous lever to
influence and control steering in severe situations like blowouts etc.
I would imagine the GMC already locates the tread centerline slightly
outboard of the Toronado (in relation to the balljoints) to keep this 1/4"
offset at the road surface on slightly taller tires. Looking at this image,
which is unfortunately not 'scaled' I'd estimate the steering axis
inclination at about seven degrees. This basic arrangement is common to
pretty much all FWD cars, and I wouldn't think spacing the tires farther
outboard is a good idea, personally. Theres other better ways to tame rut
running. If a perfectionist just HAD to see all his wheels in line, moving
the complete controlarm/spindle etc assembly outboard from the frame would
be the only properly engineered solution in my view. I doubt this sort of
'suspension widening' would be a practical solution, and if nothing else,
it still wont eliminate rut running completely.
The Toronado in 1966 used a 8.85-15 tire which rolls 739 revs per mile.
with a 3.21 axle, this is 2372 rpm @60 mph, which would be slightly higher
in practice allowing for slippage, say maybe 2600 on the road.
Later models used L78-15 tires which in thier tallest incarnation roll 697
revs/mile, and with a 2.73 ratio (lets say a 1975 Toro) would give 1902 RPM
@ 60 MPH at the other end of the scale, perhaps 2000 rpm in actual driving.
Just some quick thoughts;-)
Last, thanks to everyone who replied regarding my 9.50-16.5 E tires info
request, I'm off to the tire stores this morning to follow up!
Brent Covey
Vancouver
I have an old SAE drawing from 1976 of the Toronado front suspension
geometry. Looking at it, the steering axis inclination intersects the road
surface about 1/4" OUTBOARD of the tread centerline. This means the forces
from torque steer and braking have only a 1/4" lever to pull with in severe
circumstances. Moving the wheel out farther changes this relationship for
the worse, and I wouldnt recommend it. Looking at the tread centerline to
bearings relationship, the weight is borne between the bearings which is
good enough I think. Much of the bearing loading for driving is effected by
the positive camber on the front wheels, which moves the tread beneath the
spindle slightly.
All the front end stuff is designed with motion in mind, a single wheel
bump or blowout etc moves the suspension in directions to minimize the
unbalanced forces. This is good practice, and all cars do it. On FWD
designs its especially critical. If the front tires were to be moved in
line with the rears you would be giving the tire a tremendous lever to
influence and control steering in severe situations like blowouts etc.
I would imagine the GMC already locates the tread centerline slightly
outboard of the Toronado (in relation to the balljoints) to keep this 1/4"
offset at the road surface on slightly taller tires. Looking at this image,
which is unfortunately not 'scaled' I'd estimate the steering axis
inclination at about seven degrees. This basic arrangement is common to
pretty much all FWD cars, and I wouldn't think spacing the tires farther
outboard is a good idea, personally. Theres other better ways to tame rut
running. If a perfectionist just HAD to see all his wheels in line, moving
the complete controlarm/spindle etc assembly outboard from the frame would
be the only properly engineered solution in my view. I doubt this sort of
'suspension widening' would be a practical solution, and if nothing else,
it still wont eliminate rut running completely.
The Toronado in 1966 used a 8.85-15 tire which rolls 739 revs per mile.
with a 3.21 axle, this is 2372 rpm @60 mph, which would be slightly higher
in practice allowing for slippage, say maybe 2600 on the road.
Later models used L78-15 tires which in thier tallest incarnation roll 697
revs/mile, and with a 2.73 ratio (lets say a 1975 Toro) would give 1902 RPM
@ 60 MPH at the other end of the scale, perhaps 2000 rpm in actual driving.
Just some quick thoughts;-)
Last, thanks to everyone who replied regarding my 9.50-16.5 E tires info
request, I'm off to the tire stores this morning to follow up!
Brent Covey
Vancouver
