Is Rear Toe-in Adjustable? Options

[bilgladstone]

As per title. Caster/camber is fixed, as we know. Is the toe adjustable? Thinking about it because of tire wear - inside tread.

Bil

[Duck]

For the rear, wouldn't you want no toe-in? Adding toe would cause wear, and an extra load that our already strained engines don't really have a chance to overcome.

I guess you could change it with a shim plate like you posted in another thread to modify the camber... but at the factory I'm sure there is a jig that takes careful consideration into the parallelism between the two welded supports on the DeDion tube.

Here's a good page: http://www.ozebiz.com.au/racetech/theory/align.html

-Iain

[bilgladstone]

For the rear, wouldn't you want no toe-in?

Yes, exactly. I want to confirm that my rear toe is zero and adjust it to zero if it is not, because I suspect it might not be right on the money. My rear tires wear faster than I would like. It could be my driving :confess: but I'd like to be reassured that the suspension is set up "as per".

Thanks for the link, Iain.

B

[MightyMouseTech]

It may not be the most "polite" solutiong, but I have always thought that it you took two long pieces of pipe and slid them into the rear tubes, you could easily bend the tubes toward or away from each other to modify the toe. Although, whenever we have a smart that has been in an accident, and the rear toe is out, we just have the rear suspension replaced.

This post has been edited by MightyMouseTech: Feb 4 2010 - 06:38 PM

[Duck]

I suppose one way (along those lines) to adjust the toe in would be to install a turnbuckle-style linkage where the rear links are. Recall that the linkage is as such:



In machinery design we often use a solution like this, with a left-hand and right-hand threaded nut:



That way you can adjust the distance between the two rod eyes. Same setup is used on your steering up front. You might be able to do something like that to tweak your tow in angles.

(Actually, I think we must have discussed this online before, because I found this sketch that I'd done up as well)

-Iain

[bilgladstone]

So... there is no adjustment that can be done at a normal alignment shop?


@Duck: yeah, I think there was a couple of guys offering a pair of rods like that to replace the oem smart rods. One end was fixed and the other was adjustable. And because of the Heim ends with no flex bushings, they said they were hard like a rock and recommended for race application only.

Their installation notes emphasized measuring the C:C distance on the oem installation before removing them, and then very carefully fine-tuning the new rods to exactly the same dimension once installed and weight-loaded. I guess if you had a 3-bolt alignment plate setup, you could tweak it like that. Too much trouble for me.

@MightyMouseTech: the "snipe and bend" idea sounds very risky. Like breaking a turkey wishbone (in reverse) - the two sides never have exactly the same strength due to material variability so you are as likely to make the problem worse as not.

So... there is no adjustment that can be done at a normal alignment shop?

This post has been edited by bilgladstone: Feb 4 2010 - 07:20 PM

[MightyMouseTech]

So... there is no adjustment that can be done at a normal alignment shop?

I do a fair number of alignments on smarts that have been in an accident, and if the rear is out at all, it means a complete new DeDion tube, and only the dealer has the special tools to install one properly.

As for Duck's idea with the adjustable tension rods, I have seen something like that for our cars, I saw it on here somewhere for sale at some point....

[bilgladstone]

OK then. Thanks guys. :-/

[MightyMouseTech]

OK then. Thanks guys. :-/

Well, you showed the alignment shims in another thread...did you ever find out if they would work? On old VW's we used shims like that on the rear, and if you turn the shim 90 degrees you are adjusting the toe and not the camber, and you can vary the angle anywhere between to get a combination of toe and camber. They usually came with a chart that would tell you such and such an angle means X-camber and Y-toe change.

[Mike T]

The problem with the Watts linkage adjustment is that the tension on the tube and hence toe out will vary proportional to the amount of extension or compression the rear springs are under, the lowest toe effect being when the Watts links are perfectly horizontal......it is not by any means a fixed effect. And compared to the Watts link on the B 200 which has a toe compensator of sorts; it is a very simple affair on the smart, more likely to have undesirable side effects.

[bilgladstone]

Well, you showed the alignment shims in another thread...did you ever find out if they would work?

Yes, according to the designer they will work. They reduce negative camber and no other axis. I remain unconvinced that it is a good idea

[bilgladstone]

The problem with the Watts linkage adjustment is that the tension on the tube and hence toe out will vary proportional to the amount of extension or compression the rear springs are under, the lowest toe effect being when the Watts links are perfectly horizontal......it is not by any means a fixed effect.

Ah... so adjusting rear ride height (as with Bilstein adjustables) will affect toe-in?

[Mike T]

Well it would appear to (assuming bushing hysteresis - under compression or tension - is not all that extreme), so what you would want ideally is to have the Watts links perfectly horizontal when the car is at its normal operating weight, with you in it....that would leave the C-shaped tube in whatever its natural state is or was out of the box.

This post has been edited by Mike T: Feb 4 2010 - 09:14 PM

[bilgladstone]

Well it would appear to (assuming bushing hysteresis - under compression or tension - is not all that extreme), so what you would want ideally is to have the Watts links perfectly horizontal when the car is at its normal operating weight, with you in it....that would leave the C-shaped tube in whatever its natural state is or was out of the box.

But the rods are not normally horizontal. Look at the red line or any smart. the inside attachment points are higher than the outside points. So I'd want to lower the back end until these are actually horizontal to achieve "zero toe"?

I might be misunderstanding what you're meaning

 de_dion.jpg ( 38.44K ) Number of downloads: 8

[Duck]

Take a look at this sketch I drew earlier to illustrate:



-Iain

[Mike T]

Well my thoughts were theoretical....I would say controlling toe on the rear of this car is a lost cause!

[tolsen]

Well my thoughts were theoretical....I would say controlling toe on the rear of this car is a lost cause!

I agree, especially as the reason for uneven tyre wear is the -2 degrees camber.

[bilgladstone]

I agree, especially as the reason for uneven tyre wear is the -2 degrees camber.

Not that I 100% disagree with you but it would be interesting to nail down the question of why some peoples' rear tires show very little wear after many, many kilometers when others' similar tires appear to wear down in a fraction of the distance.

I'm thinking maybe turning? Faster:slower or maybe even the number of turns in the same km? City v. highway, in general terms.

[Duck]

Driving styles... environment, etc.

-Iain