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[05omegav6]

How far would the subframe need to be moved to correct the camber?

Currently: N/S is at 0, O/S is at -3.

Tracking is true, and the wheel centered.
Both struts are at the inner limit of their adjustment.
No feathering on either of the last two pairs of tyres, just rapid wear on the outer 50%.
The front arms are 20k old, pattern and poly bushed, with no evidence of play at either the rear bushes or the ball joints.
Tyres are/were all Runway Enduros, fitted new and have not been swapped around the car.

Previous set of front tyres had worn on the outer half of the tread, (5k), one side more than t'other, so tweaked the camber by corresponding amounts, ie more on the wheel that was more worn.

Just had tyres replaced and the set that came off were still worn unevenly. N/S became useless 3k ago, O/S lasted to 8k. Both worn heavily on outer half. Camber now adjusted as above.

I'm thinking that by moving the subframe towards the near side, the Camber should even out at -1.5 both sides . The question is how far would it need to be moved to acheive this?

Also would moving the subframe rearward slightly reduce the castor angle enough to move the full lock footprint of the tyres to their centreline rather than on the outside edge , assuming of course that this is why the outer edges are wearing more quickly...

[feeutfo]

What's the ride hight at the front? Floor to wheel arch?

[Andy H]

I am confused 

I thought moving the subframe from side to side changed the caster and was only necessary to even up the caster when it was wildly different between each side.

The slotted holes for the two bolts that attach the hub to the McPherson struts are used to adjust camber and allow masses of movement. I am surprised that you cannot get get the camber to -1 deg 10 sec. Have you got a bent strut?

[Abiton]

"OOF calling Tony; come in Tony"

[feeutfo]

As Tony H says, that's my understanding. Subframe only needs moving to correct caster angle.
Camber should be easily achieved via two bottom shock bolts. Possibly incorrect shocks, incorrectly drilled holes, or another cause for outside edge wear being ecxcessive toe.

Or, springs too long would cause the opposite of excessive lowering, which gives excessive camber. There for too long a spring gives less camber, although they'd need to be bloody long to run out of camber adjustment tbh.

[Andys VXR]

dont worry[/img]

[Andys VXR]

[05omegav6]

What's the ride hight at the front? Floor to wheel arch?

690mm give or take a couple of mm, same both sides. Wheels standard 16" 5 spokes.

As Tony H says, that's my understanding. Subframe only needs moving to correct caster angle.
Camber should be easily achieved via two bottom shock bolts. Possibly incorrect shocks, incorrectly drilled holes, or another cause for outside edge wear being ecxcessive toe.

Or, springs too long would cause the opposite of excessive lowering, which gives excessive camber. There for too long a spring gives less camber, although they'd need to be bloody long to run out of camber adjustment tbh.

Shocks genuine VX same p/n as original plod ones, springs original plod spec and not broken.

Front/back movement of subframe would affect both castor and toe, side to side should have less effect

Something's not right though to be wearing the outer half of the tyre, inside edges still had 3+mm tread

dont worry[/img]

helpful...not

What effect could a bent arm have? Nothing obvious wrong but problem only apparrent over the last 10-12k

Much as I love this car it seems determined to drive me mad

[Agemo]

You say "tracking is true", is it set to zero toe? It seems to me you have slight play somewhere, and the tracking is then taking up the slack and running with some toe in. This would be wearing the tyres, especially if we are talking about the outer half of the tread. (If it was just the shoulder, I would suspect Camber)

[feeutfo]

What's the ride hight at the front? Floor to wheel arch?

690mm give or take a couple of mm, same both sides. Wheels standard 16" 5 spokes.

As Tony H says, that's my understanding. Subframe only needs moving to correct caster angle.
Camber should be easily achieved via two bottom shock bolts. Possibly incorrect shocks, incorrectly drilled holes, or another cause for outside edge wear being ecxcessive toe.

Or, springs too long would cause the opposite of excessive lowering, which gives excessive camber. There for too long a spring gives less camber, although they'd need to be bloody long to run out of camber adjustment tbh.

Shocks genuine VX same p/n as original plod ones, springs original plod spec and not broken.

Front/back movement of subframe would affect both castor and toe, side to side should have less effect

Something's not right though to be wearing the outer half of the tyre, inside edges still had 3+mm tread

dont worry[/img]

helpful...not

What effect could a bent arm have? Nothing obvious wrong but problem only apparrent over the last 10-12k

Much as I love this car it seems determined to drive me mad

Oh don't get me wrong, sub frame position affects ever setting, as everything is bolted to the subframe itself. But Wim would only consider moving it to correct castor. Ones that's correct, they then go on to do camber then toe last.

Ride hight is high. Iirc stock is 670. But would need to check.
If so that would contribute to the lack of camber adjustment, if I have my simple brain working correctly.
What is the toe setting currently? Should be -10mins (+/-10) is there a melted bead or line on the outer edge?

Are we looking at a diy setup here?


Oh, and are the springs marked LA?

[Kevin Wood]

I think if the toe was far enough out to make the camber adjustment impossible it would be undrivable. However, the wear pattern doesn't match the camber and, if DIY camber changes have been made, the toe will be way off.

Not sure if the subframe mounting holes are slotted to allow side-to-side movement. Obviously, if you can move it sideways, it might transfer some of the camber to the other side but I'd be surprised if it would move enough, tbh.

I think something's up with the strut or strut mounting, or a wishbone bush has given. Possibly the pattern wishbones aren't accurately dimensioned. I know mine went miles out when I fitted pattern wishbones, but within the range of adjustment.

Shifting the subframe will throw everything out, though, so I'd just throw it at WIM and see what they say in these circumstances, I think.

[feeutfo]

Tolerance in the subframe position at the factory is vast, with no consideration given to its exact position. They just fire the bolts in and send it as is.

But I don't see any advantage to be gained in moving it given the symptoms.

Might be worth posting a pic of the tyre tread..?

[Andy H]

Front/back movement of subframe would affect both castor and toe, side to side should have less effect

I don't agree. On pushbikes and motorbikes the steering pivot axis leans backwards to give the castor. On a car the McPherson struts lean towards the centre line of the car. If you move the subframe sideways the castor will increase on one side and reduce on the other. Moving the subframe backward or forward probably won't make much difference to either castor or camber (but might affect the toe )

What effect could a bent arm have? Nothing obvious wrong but problem only apparent over the last 10-12k

A bent McPherson strut may have used up the adjustment available from the two bolts that hold the hub/stub axle to the McPherson strut

[feeutfo]

Front/back movement of subframe would affect both castor and toe, side to side should have less effect

I don't agree. On pushbikes and motorbikes the steering pivot axis leans backwards to give the castor. On a car the McPherson struts lean towards the centre line of the car. If you move the subframe sideways the castor will increase on one side and reduce on the other. Moving the subframe backward or forward probably won't make much difference to either castor or camber (but might affect the toe )

What effect could a bent arm have? Nothing obvious wrong but problem only apparent over the last 10-12k

A bent McPherson strut may have used up the adjustment available from the two bolts that hold the hub/stub axle to the McPherson strut

Wishbone will bend long before the strut will. There is no lateral tension on the strut, other than the restriction of the top mount, think wishbone replacement, or even better think shock replacement. With just the top shock nut to hold it, the shock is free to move any direction it pleases , as it must.
If a shock is bent, there will be massive surrounding damage.


When setting castor, the critical measurement is the bottom steering pivot being forward of the top shock mount. Hence moving subframe for and aft affects castor, and will affect toe. But everything, including camber, affects toe hence its set once castor and camber are correct.



Ride hight affects camber. It is riding high. A rather amusing example, hold your arms out level and bent at the elbow, chicken impression style, to imitate the wishbone. (snigger)
Now, hold your arms on a level plain. Your elbow is the steering knuckle/stub axle with the wheel and shock attached, your hand is the front wishbone bush, and your shoulder the rear wishbone bush. Now fit a longer spring, this means your elbow must sit lower relative to the body.
Take that to an extreme and fit an even longer spring , your elbows sit lower still, as they do so they MUST get nearer your body and ribs. Due to the pivot points of the wishbone(your shoulder and hand can't mover remember) your elbow must also get closer together and give a narrower track in effect, this means the McPherson strut stands more upright as the stub axle (your elbow) is pulled in board closer to the body. As the shock stands more vertically this eats up the adjustment left that's needed to achieve -1.10. I am suprised ALL the adjustment is used. But add in pattern bones and excess toe and we might arrive with your issue....  Might.

But then Chickens might fly.     BAKAAARP BUK BUK.


If there is indeed no more camber adjustment left, you could ovalise the holes in the shock clamp, fit shorter springs, use narrower bolts(not a good idea), fit camber adjutment bolts.

But I'd bet there is a toe issue as well.

[feeutfo]

Thinking further, if the top of the wheel took a blow hard enough for the wheel to hit the shock, that would bend it.

[Andy H]

Wishbone will bend long before the strut will. There is no lateral tension on the strut, other than the restriction of the top mount, think wishbone replacement, or even better think shock replacement. With just the top shock nut to hold it, the shock is free to move any direction it pleases , as it must.
If a shock is bent, there will be massive surrounding damage.

Is this the car that needed a new bonnet after a shunt on the motorway?

When setting castor, the critical measurement is the bottom steering pivot being forward of the top shock mount.

I don't think this is true. To avoid 'bump steer' the steering axis has to run through the centre of the tyre's contact patch. This implies that the top mount has to be nearer the centre of the car than the bottom mount.

[feeutfo]

Wishbone will bend long before the strut will. There is no lateral tension on the strut, other than the restriction of the top mount, think wishbone replacement, or even better think shock replacement. With just the top shock nut to hold it, the shock is free to move any direction it pleases , as it must.
If a shock is bent, there will be massive surrounding damage.

Is this the car that needed a new bonnet after a shunt on the motorway?

When setting castor, the critical measurement is the bottom steering pivot being forward of the top shock mount.

I don't think this is true. To avoid 'bump steer' the steering axis has to run through the centre of the tyre's contact patch. This implies that the top mount has to be nearer the centre of the car than the bottom mount.

Two different aspects. Castor is not directly related to bump steer.
Castor relates to steering centring and stability at speed v quickness of steering. Exactly as you described re motor cycle steering angle. Chopper has massive steering angle and turns slowly like a barge with heavy steering, sports bike has nearer upright forks and pushes the boundaries of stability in the interest of quick steering into turns.

Altering the subframe will not help in this case.

[05omegav6]

Quote from: chrisgixer on Yesterday at 21:56:24
Wishbone will bend long before the strut will. There is no lateral tension on the strut, other than the restriction of the top mount, think wishbone replacement, or even better think shock replacement. With just the top shock nut to hold it, the shock is free to move any direction it pleases , as it must.
If a shock is bent, there will be massive surrounding damage.Is this the car that needed a new bonnet after a shunt on the motorway?

No evidence of damage either on the suspension/body shell. To clarify, after damaged slam panel was cut off car, new panel dropped straight in. No damage what so ever to the inner wings.

Remeasured the ride height: 680mm. believe that stock plod is a touch higher than standard Springs are the original plod ones, not sure of the designation

Are we looking at a diy setup here?

Yup After doing the arms at the Lakes it was feathering the edges and pulling all over the place. Track was set to be equall/even side to side, IIRC trackrod lenght was set to 373mm and the camber set to be slightly -ve, 3/8"ish but even side to side. The car drove smoothly, no wandering/pulling.

Car due its next 6 monthly check at the end of next week, will see if that throws up any component issues first. No point it going in for a set up if I've to pull the arms off...

[feeutfo]

Quote from: chrisgixer on Yesterday at 21:56:24
Wishbone will bend long before the strut will. There is no lateral tension on the strut, other than the restriction of the top mount, think wishbone replacement, or even better think shock replacement. With just the top shock nut to hold it, the shock is free to move any direction it pleases , as it must.
If a shock is bent, there will be massive surrounding damage.Is this the car that needed a new bonnet after a shunt on the motorway?

No evidence of damage either on the suspension/body shell. To clarify, after damaged slam panel was cut off car, new panel dropped straight in. No damage what so ever to the inner wings.

Remeasured the ride height: 680mm. believe that stock plod is a touch higher than standard Springs are the original plod ones, not sure of the designation

Are we looking at a diy setup here?

Yup After doing the arms at the Lakes it was feathering the edges and pulling all over the place. Track was set to be equall/even side to side, IIRC trackrod lenght was set to 373mm and the camber set to be slightly -ve, 3/8"ish but even side to side. The car drove smoothly, no wandering/pulling.

Car due its next 6 monthly check at the end of next week, will see if that throws up any component issues first. No point it going in for a set up if I've to pull the arms off...

yeah no point, ESP as tyres are unevenly worn now anyway. I'd use the remaining life of those tyres to get things sorted. Find the faults if any, rectify, set up, new tyres once happy.
 Have to say though, the DIY set up is only ever going to be a "save as much tyre wear as possible before the car goes for full geo set up" type affair. It's possible to get it close via various means on the drive after work done, but it MUST be at least checked on a full geo rig. Or this situation can easily arise.

Have a look through the test zone, there's a wip in there for checking toe, see if the front wheels are pointing in a roughly similar direction.

[feeutfo]

Ps, there's mention of a "rough road package" for suspension listed. Believe plod use those as well. In fact there's various options, if you can spot the ident numbers and colours painted on the springs that might help ID them.