Dolly (suspension) disease

[slant4]

Your point is valid re the rack wear. Mine appear to be ok, but I know heralds and dervivred suffer. Could be the lock ? FWD's are limited using a stop which should take the load off the rack on hard corenring

[2F45T4U]

there unequal length wish bones arent they? Hence the lower the suspension goes the more camber you get. Hence saggy 29 year old springs affect the geometry

[slant4]

The unequal wishbone lengh means that when the wheel travels up, it travels inward (I'd love to sketch it for you but just don't know how on here!) If the ride height is low, ie the springs are not pushing down enough, the wheel will be part way up the travel, hence the camber will be changing for the top of the wheel to start to point in. So looking at the facts, the track would not change as such, as the track rods on the rack will move in an arc and as they are bolted to the bottom ball joint, will travel near there. The top will be moving in!

I'm intending to do a comprehensive article on suspension and geometry for the mag, along with sketches to show this and things like offset and the impact!

[Dollyboy]

tracking does change as suspension height changes, lower ride height goes, more toe out you get...

rack is fixed length, lower ride height goes the longer the rack would need be to maintain same toe angle, hence more toe out the lower you go

makes sense really...

[2F45T4U]

unless the pivot point of the rack is in the right place

[Dollyboy]

makes no difference where the rack is, its overall length isnt going to vary...

wheels go up, rack wants to stretch, cant really stretch very much because is made out of metal ?!

[Mr.Speedy]

The only way to reduce bump steer effects is to make the track rods from steering rack as close to the same length of the wishbones as possible. Also the joint from track rod to rack would need to be as close as poss to the wishbone pivot on chassis.

[Dollyboy]

who's on about bump steer?

hows my manifold???

[2F45T4U]

Yer that's what I was on about. If the arc of movement is the same for the track rod end as it is for where the track rod end connects to the hub then when the wheel goes up the wheel points in the same direction.

[slant4]

The toe change is mininal within the usual movement of the suspension. One of the benefits of the Triumph uneven wishbone design is that the pivot point for the track rod is almost in line with the pivot of the tca, hence little bump steer.

Anyway we are talking about CAMBER of the wheel.

"A major importance of camber is tontrol tyre wear. If excessive camber tilt is adjusted to the wheel assembly, shoulder wear will develop in the outer edge (possitive) or the inner edge(negative) fo the tyre.

Excessive possitive camber tends to cause excessive squeel driving around turns and increase driver effort, neg the opposite!"

The comments / benefits of camber, along with combined king pin inclination refers to what is nown as possitive and negative offset! Some modern vehicles have some of this built in

[george]

and some modern (chrysler) have crash bolts available which enable you to adjust the camber albeit marginal to ofset problems on vehicles which require adjustment
this is also of benefit to people who wish to lower the car with lowering
springs and fit larger rims to bring it it within manufactures tolerances

[slant4]

Yep toyota and bmw do something similar (as do merc I think) Triumph did it with shims on the subframe.

[Jon Tilson]

while the comments above are mostly true and scientiific what you are all talking about really is excessive tyre wear. This is caused by tyre scuffing or slipping....ie the tyre is running at an angle to the direction of travel.
While camber has some effect on tyre wear it isnt that great compared with scuff/scrub caused by being OUT OF TRACK! You only have to look at a Spit rear wheels to know that. They all have camber of varying degrees depending on how decrepit the rear sping is. Ive got 2 spits and one sags and has for a while. It exhibits no perceptible inner tyre wall wear and the camber is far in excess of anything you'll ever see on the front of a dolomite, lowered or not. This is because the wheels are parallel to the direction of travel unless I'm looning round a roundabout, and no tyre scrub is occurring.
So please all stop talking this utter tosh, thinking on the hoof etc and trying to sound knowlegeable and get some proper engineering realism in hear. Talking all this crap about secondary effects just brings the collective knowledge of the board into disrepute and runs the risk of new dolly owners wasting a fortune solving problems they just dont have. I'm sorry to be on my high horse about this but we want advice of quality on hear dont we?
I'll say it for the last time....
Its the tracking....(quietly this time so maybe you all listen).

Jonners

[tinweevil]

Scientific, oh...kay...

As the camber increases the mass of the vehicle is not supported evenly across the tyre width. What does that do to the forces exerted on the tyre? It concentrates them into a smaller area at one edge. This increases the frictional loading and heating in those areas and so increases wear. At the same time the opposite is true in the area of reduced load exacerbating the uneven wear effect. Frictional loading is much much lower at the back because toe is generally zero.

Just a hypothesis of course.

I'm quite happy to bring Blue to a tracking station of your choice once it's back on the road (unlikely to be this year).

Tinweevil

[george]

but you are talking about rear wheels which dont turn do have two bugs
which must rate as extreme on camber (not lowered yet!)
dont forget the angles on a front axle turning corners do agree some might have a tracking problem but toe is usally has signs on the tyre such as feathering on the edges i suspect some dont exibit this type of wear so are presumeably having other types of wear as these angles would be much further out of tolerance