lowered rear axle alignment out!!!

[dandywarhol]

What we haven't mentioned is the effect on the latitute of the axle trailing arms when the springs are shortened. With standard springs the trailing arm chassis point is 40mm HIGHER than the axle mounting point. So when you corner into, say, a lefthand bend the body tilts and the offside arm becomes nearly parallel with the ground (thereby pushing the rear axle back a bit). The converse happens on the nearside. This is like TGP's drawing above. This in effect makes the vehice oversteer slightly.

Hope you're still with me here - if you now fit 50mm lower springs the chassis pivot is now lower than the axle pivot and the left hand bend will "shorten" the arm, thereby tending to make the vehicle understeer.

As for the panhard rod - the standard springs setup has the chassis pivot around 20mm higher than the axle pivot point. Lowering the body 50mm will have the axle point 30mm higher than the chassis which could try to make the body roll more

Bongo type of rear axle setup

[The Great Pretender]

Very intresting Dandy, it would be nice to know the measurements with the Bongo loaded.

[dandywarhol]

I don't find the trim height changes all that much when loaded up but then again I've got airbags on mine. I don't think there's enough reduction in height to "reverse" the geometry that 50mm lowered springs would do.............................

[cheffy34]

Well it beyond me guys but you have made me look into the actual role of a panhard bar


interesting


mmmmmmmmmmmmmmm food for thought

[dandywarhol]

As TGP says - think of all of the suspension arms/bars working through an arc - the arcs longest dimension will be parallel to the ground and shortest at 90 degrees to the ground. anywhere in between has an effect on the axle movement and causes rear wheel steer. Engineers only recently got fly for it on mass production cars and used it to their advantage.
You can make the rear wheels turn slightly to the right if a car is turning left and the rear will be pushed around to the left making a front wheel drive car become more neutral steer rather than understeer through a corner.

One of the first mass production cars I saw it on was the Citroen ZX where the whole rear subframe was designed to flex on its mountings to rear steer the car - its called "compliance steer" (the suspension rubbers comply with a force and are allowed to flex accordingly)

I'm reallly only a theorist on this sort of stuff - TGP is the man who's used it in practice on race cars I believe.

[bigdaddycain]

As an owner of a lowered bongo, i have read this thread with much interest... (twice in some cases to fully understand)

However... When on original wheels and suspension, i noticed a tendency of excessive tyre wear on the insides of the rear tyres.. Before i had the vehicle tracked, i fitted 18" alloy wheels, and shortly after some 50mm lowering springs, not only did this make the steering much more direct,understeer seemed decidedly reduced! The handling imprioved also, and the tyre wear evened out, i haven't yet felt the need to have the vehicle properly tracked up (in fact, i've never had the tracking done on the bongo) As there appears to be no pulling to either side, except a slight tendency to follow the camber of the road to the gutter, but that happens on every car should the camber be great enough. The only downside to the lowering of the vehicle appears to be a compromised ride (but i prefer it firm anyway) reduced ground clearance (it's a good job i'm really careful) The bongo eats through front CV boots, (because of the acute angle of driveshaft to CV joint, especially when the wheels are on full lock). Otherwise, no probs!

(though now i'm REALLY reluctant to ever get the tracking done in case it buggers it all up!)

[francophile1947]

Join the confused clan Ste
I just wonder what happens with my pneumatic suspension I've never noticed any problems with handling, either with the suspension fully raised or lowered

[bigdaddycain]

Join the confused clan Ste
I just wonder what happens with my pneumatic suspension I've never noticed any problems with handling, either with the suspension fully raised or lowered

And that's yet another story! But i guess if you haven't had any probs, or suffer from any undue, uneven tyre wear, then i guess it's ok!

Have you fitted the new wheels yet? Has that made any differences in the handling?

[francophile1947]

Have you fitted the new wheels yet? Has that made any differences in the handling?

Yes and No

And that's yet another story! But i guess if you haven't had any probs, or suffer from any undue, uneven tyre wear, then i guess it's ok!

No uneven tyre wear at all Got the old wheels in the garage at the moment - keeping them for the winter, cos' even you couldn't restore them

[bigdaddycain]

Yes, i remember em' john... They needed a bit more than a quick once over!