smart51
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| posted on 22/6/14 at 07:57 PM |
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What effect would lack of camber gain give to steering?
Imagine a car where the front suspension was designed so that the wheels stayed exactly perpendicular to the road regardless of body roll. Now
imagine the rear suspension is pure trailing arms such that if the car rolls 5 degrees, so does the wheel camber. Let's say the front has a
stiff anti roll bar and firm damping so that the car rolls fairly slowly. And you made a sudden turn of the steering wheel then held it in the turned
position, what affect would you expect to see from the rear suspension?
[Edited on 22-6-2014 by smart51]
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daniel mason
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| posted on 22/6/14 at 08:09 PM |
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Are you saying that the front is so stiff there is zero suspension travel, and on very stiff springs with a stiff front arb?
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smart51
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| posted on 22/6/14 at 08:13 PM |
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No, not at all. I'm saying that the front wishbones are designed to have equal camber gain to roll so that the wheels remain perpendicular to
the road, regardless of suspension stiffness. I'm suggesting that the damping is fairly stiff so that the body roll is slow. With slow body
roll, the effect of roll can be felt as a change in the car's attitude to the road as the car rolls.
[Edited on 22-6-2014 by smart51]
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daniel mason
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| posted on 22/6/14 at 08:17 PM |
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The outside wheel is always going to be loaded up more than the inside but if you stiffen the front too much then I'd say there would be
terminal under steer. Especially in the slower corners!
I think the monoshock cars like the force etc are designed so that roll and damping are separate so you can adjust one without the other. They tend to
be set up very stiff with. Very little or zero droop
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ashg
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| posted on 22/6/14 at 08:18 PM |
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i think the thing you would notice would be increased understeer
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
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daniel mason
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| posted on 22/6/14 at 08:25 PM |
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I'm a bit out of touch with F1 suspension design,and not sure if they still run a pull rod front set up for neater packaging. But I saw some
thermal imaging of the current cars going through the tunnel an Monaco GP and they were getting more heat on the inside front right tyre going round
the Right handed. And they run servers neg camber.
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smart51
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| posted on 22/6/14 at 09:26 PM |
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I'm thinking of the effect of the rear wheel camber as the car rolls. When the initial turn in is made, all the wheels are close to vertical.
Slowly, the car rolls so slowly the rear camber rolls with it. What will you see happen as it rolls?
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daniel mason
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| posted on 22/6/14 at 09:48 PM |
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It's difficult to understand exactly what you want to know but when the car is sat stationary then the wheels are not close to vertical. The
camber is built in to give the best results when loaded up!
The only way to get the wheels to be vertical when cornering is to have massive tyre pressures,rock hard sprints and mega stiff damping. With the
front set like thisthr rear is irrelavent as like said you will have terminal under steer.
I set my radical at exactly the same damping front/rear with rebound damping 1 click Stiffer at front. But I run a front arb and leave the rear one
off.
Some circuits I run 7-9 clicks all round. Shorter tighter places 4-5 clicks. It makes a massive difference when your chasing hundredths of seconds!
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daniel mason
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| posted on 22/6/14 at 09:49 PM |
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Rear camber is also less than front and so is tow. I run my rears at 0deg toe (parallel)
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FazerBob
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| posted on 22/6/14 at 10:46 PM |
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quote:
Originally posted by daniel mason
It's difficult to understand exactly what you want to know but when the car is sat stationary then the wheels are not close to vertical. The
camber is built in to give the best results when loaded up!
The only way to get the wheels to be vertical when cornering is to have massive tyre pressures,rock hard sprints and mega stiff damping. With the
front set like thisthr rear is irrelavent as like said you will have terminal under steer.
I set my radical at exactly the same damping front/rear with rebound damping 1 click Stiffer at front. But I run a front arb and leave the rear one
off.
Some circuits I run 7-9 clicks all round. Shorter tighter places 4-5 clicks. It makes a massive difference when your chasing hundredths of seconds!
I agree with Daniel, to maintain 0 camber at the front is virtually impossible. Tyres, dampers, springs etc would have to be so stiff that you would
have bounced off the road long before you reach the point of massive under-steer, which by the way you would probably achieve with only the outer
wheel on the road, as the mass of the car would be trying to pivot on the outer front wheel contact patch thereby lifting the inside wheel.
Bob
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daniel mason
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| posted on 22/6/14 at 10:55 PM |
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Because the radical is so low (40mm) and there is very little roll anyway. Setting the front too stiff just makes it an Under steering pig!
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Ugg10
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| posted on 22/6/14 at 10:56 PM |
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Have a look at the dax camber compensation system, that may give you some clues.
---------------------------------------------------------------
1968 Ford Anglia 105e, 1.7 Zetec SE, Mk2 Escort Workd Cup front end, 5 link rear
Build Blog - http://Anglia1968.weebly.com
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daniel mason
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| posted on 22/6/14 at 11:00 PM |
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It's quite fun to play around with the suspension to actually see what's happening. Jack up the front an play around with it!
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drt
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| posted on 23/6/14 at 02:52 AM |
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I think 100% camber compensation is meant here...
So your role pole (not point) is on the other upright.
This will lead to great jacking forces and with the front sole responsable for the roll stiffness
+ has stiff dampers...
understeer city will be the result.
And this is on a biljart track...
Any bump will give a lot of camber gain (you can compensate a bit with very log wishbones)
And thus will upset the car.
Same for the dax system, things get really weird really fast 
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smart51
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| posted on 23/6/14 at 06:54 AM |
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OK, you all seem to be missing the point here. The difficulty of achieving the hypothetical situation I described is not what I'm looking for.
Let me put the question another way.
If a car has trailing arm rear suspension, then as a car leans in a corner, the rear wheels will lean by the same amount. This camber gain will
affect the steering of the car. What effect will this have? With the steering wheel held steady, Will the car turn in more as it rolls, turn in less
as it rolls? Will it have no effect or will it do something else?
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Sam_68
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| posted on 23/6/14 at 07:21 AM |
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quote:
Originally posted by smart51
OK, you all seem to be missing the point here. The difficulty of achieving the hypothetical situation I described is not what I'm looking for.
Let me put the question another way.
If a car has trailing arm rear suspension, then as a car leans in a corner, the rear wheels will lean by the same amount. This camber gain will
affect the steering of the car. What effect will this have? With the steering wheel held steady, Will the car turn in more as it rolls, turn in less
as it rolls? Will it have no effect or will it do something else?
OK. Your entirely hypothetical situation assumes that the front suspension maintains perfect camber control as the car rolls (easy enough with a beam
axle), whilst the rear develops camber angle equivalent to roll angle, with no consideration of relative roll stiffnesses/damping front:rear?
The answer is straightforward enough: the grip at the rear would be progressively degraded relative to the front. leading to progressive oversteer.
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MikeRJ
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| posted on 23/6/14 at 11:24 AM |
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quote:
Originally posted by FazerBob
I agree with Daniel, to maintain 0 camber at the front is virtually impossible.
No it's not. A live axle manages this very simply. The Dax independant front suspension system also maintains constant camber under many but
not all conditions.
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smart51
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| posted on 23/6/14 at 11:28 AM |
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Yeah, OK, rear end grip would reduce if you were on the limit. I'm thinking more about the effect of the camber.
I'm told that a wheel that leans over wants to run round in a circle about the point where the axis points to the ground. If your car is
turning left, it leans to the right. Becase your rear wheels are leaning to the right, they want to turn to the right. This would make the car turn
quicker, which would increase body roll, with would make the rear wheels want to turn round a tigher circle, which would make the car turn even
faster... I was hoping to tease out whether you think this would be a noticable effect or not.
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coyoteboy
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| posted on 23/6/14 at 12:34 PM |
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As mentioned above, biggest effect IMO would be the reduction in rear contact efficiency vs the front, which would lead to oversteer pretty
quickly.
Sounds similar in a sense to a peugeot rear trailing arm bearing failing - even slight cornering leads to ass-clenching as the rear takes the
commanded input and adds positive feedback. Horrible to drive.
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britishtrident
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| posted on 23/6/14 at 02:20 PM |
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It all depends on the weight distribution and roll couple distribution. On a lot of small fwd cars such as the real Mini anhd Metro or Golf were
designed with either plain trailing arms or a torsion beam to give a ground level roll centre and zero camber gain this is used to counter understeer
without having excessively stiffen the rear springs or resort to a rear anti-roll bar.
Interesting Rootes did the exactly the opposite on the front of the Hillman Imp which used a front swing axle with a relative high roll centre (at
least on the Mk1) to do induce terminal under steer. The rc was higher than intended by the desiggners because of interference at a late stage by Lord
Rootes, but is was put right on the Mk2 and the rcs were lowered even more on the coupe and sport models to give near perfect balance.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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britishtrident
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| posted on 23/6/14 at 02:25 PM |
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quote:
Originally posted by smart51
OK, you all seem to be missing the point here. The difficulty of achieving the hypothetical situation I described is not what I'm looking for.
Let me put the question another way.
If a car has trailing arm rear suspension, then as a car leans in a corner, the rear wheels will lean by the same amount. This camber gain will
affect the steering of the car. What effect will this have? With the steering wheel held steady, Will the car turn in more as it rolls, turn in less
as it rolls? Will it have no effect or will it do something else?
Not camber gain ? I think you mean camber loss as on the rear of a BL Mini or Rover 100 or a 2CV?
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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smart51
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| posted on 23/6/14 at 02:30 PM |
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quote:
Originally posted by britishtrident
quote:
Originally posted by smart51
OK, you all seem to be missing the point here. The difficulty of achieving the hypothetical situation I described is not what I'm looking for.
Let me put the question another way.
If a car has trailing arm rear suspension, then as a car leans in a corner, the rear wheels will lean by the same amount. This camber gain will
affect the steering of the car. What effect will this have? With the steering wheel held steady, Will the car turn in more as it rolls, turn in less
as it rolls? Will it have no effect or will it do something else?
Not camber gain ? I think you mean camber loss as on the rear of a BL Mini or Rover 100 or a 2CV?
Probably. In the scenario mentioned, if the car was leaning at 5 degrees so would the rear wheels, whereas the front wheels would still be
perpendicular to the road.
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Sam_68
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| posted on 23/6/14 at 02:36 PM |
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I sense a PistonHeads 'plane on a conveyor belt' scenario developing here... 
quote:
Originally posted by smart51
Yeah, OK, rear end grip would reduce if you were on the limit. I'm thinking more about the effect of the camber.
No; rear end grip would reduce (relative to the 'perfect' front), progressively and roughly in proportion to the camber, not just
'on the limit'.
That is the effect of the camber, in terms of tyre behaviour.
quote:
Originally posted by smart51I'm told that a wheel that leans over wants to run round in a circle about the point where the axis
points to the ground.
It might want to, but you've got a bunch of rigid steel suspension links stopping it.
What you're describing (I think) is simply the fact that you're moving the CoG of the mass of the wheel inboard from the centre of the
tyre contact patch, so that the wheel is continually trying to 'fall' into the direction of lean as it rolls.
For this reason, if you take the wheel off your car and roll it along the ground, unless it's completely vertical it will describe a graceful
arc as it rolls along (right up until it slows down to the point where it falls over, anyway). But the forces involved are pretty trivial (a wheel
doesn't weigh that much, and the CoG isn't moved inboard of the contact patch centre by very much for the sort of camber angles
we're talking about).
Note also that for any given angle of lean, a wheel rolled in this way will run straighter, the faster you roll it (or, to look at it another way, the
curve will tighten as is slows down). That's because the faster it's rolling, the greater the 'straight on' part of the force
vector (caused by the momentum of the wheel) is compared to the 'falling over' part of the force vector (caused by the mass of the wheel x
the distance its CoG is offset to the inside of the contact patch).
At the sort of forward speeds we're interested in with a car, I would suggest that you can safely disregard the 'falling over' part
of the force vector: it's trivial. Compared to the self-aligning torque of the tyre, and the moment caused by the scrub radius (which are again
reacted by the suspension links at the rear), it won't have any measurable effect at all.
But for what it's worth, when restrained by suspension links, the wheel is 'falling over' against the resistance of the mass of the
car and so would offer a tiny, miniscule and irrelevant force that would tend to counter (to an un-detectable degree) the basic oversteer
effect of the camber degradation of the rear tyre's grip.
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Sam_68
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| posted on 23/6/14 at 03:10 PM |
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quote:
Originally posted by britishtridentThe rc was higher than intended by the designers because of interference at a late stage by Lord
Rootes, but is was put right on the Mk2 and the rcs were lowered even more on the coupe and sport models to give near perfect balance.
Since drifting off-topic would probably be merciful for this thread and the sanity of all involved...
As an ex-Imp fanatic, my understanding is that it wasn't interference by Lord Rootes, but rather that they realised that they had to raise the
ride height of the car slightly to comply with headlamp height regulations. The very early Mk1 Imps had front springs of 10.07" free length
(manufacturer's spec., not mine... I think it's safe to assume that they didn't measure the springs to a production tolerance of a
hundredth of an inch!), but it was found that when they settled in service, the headlamp height fell below the legal minimum. As a stop-gap solution,
they changed early in the Mk.1 production run to 10.35" free length springs, which raised the ride height (and hence roll centre height) by
about 3/8".
This was addressed by a revised wishbone mounting bracket design on the Mk.2, however, to drop the pivot position back down to where it should have
been.
The coupe and sport models in standard form weren't any different to the standard Mk. 2 saloon brackets and springs, but a common aftermarket
modification was to fit 'Monte Carlo' springs of 9.57" free length that lowered both the ride height and RC still further (and
increased negative camber), or to fit aftermarket brackets that lowered the pickup positions without much affecting the ride height (but which
required you to adjust the rack height, too, to avoid bump steer).
I went the 'Monte Carlo' route with my Imps/Stiletto and it transformed the handling.
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britishtrident
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| posted on 23/6/14 at 03:42 PM |
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quote:
Originally posted by Sam_68
quote:
Originally posted by britishtridentThe rc was higher than intended by the designers because of interference at a late stage by Lord
Rootes, but is was put right on the Mk2 and the rcs were lowered even more on the coupe and sport models to give near perfect balance.
Since drifting off-topic would probably be merciful for this thread and the sanity of all involved...
As an ex-Imp fanatic, my understanding is that it wasn't interference by Lord Rootes, but rather that they realised that they had to raise the
ride height of the car slightly to comply with headlamp height regulations. The very early Mk1 Imps had front springs of 10.07" free length
(manufacturer's spec., not mine... I think it's safe to assume that they didn't measure the springs to a production tolerance of a
hundredth of an inch!), but it was found that when they settled in service, the headlamp height fell below the legal minimum. As a stop-gap solution,
they changed early in the Mk.1 production run to 10.35" free length springs, which raised the ride height (and hence roll centre height) by
about 3/8".
This was addressed by a revised wishbone mounting bracket design on the Mk.2, however, to drop the pivot position back down to where it should have
been.
The coupe and sport models in standard form weren't any different to the standard Mk. 2 saloon brackets and springs, but a common aftermarket
modification was to fit 'Monte Carlo' springs of 9.57" free length that lowered both the ride height and RC still further (and
increased negative camber), or to fit aftermarket brackets that lowered the pickup positions without much affecting the ride height (but which
required you to adjust the rack height, too, to avoid bump steer).
I went the 'Monte Carlo' route with my Imps/Stiletto and it transformed the handling.
The floor pan on the late. Mk 1 and Mk2 was also different from the original Mk1 as well as the steering column passed through the floor 1"
lower, top bracket for the column was also longer.
Sport and Coupe defo had shorter springs than the saloon, Husky and Van were longer. Interestingly all the production springs sets were the same rate
and only differed in length.
Van spring sets were exactly the same as Chrysler Comps RAC springs.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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