Lotus Elan

Steering geometry - can someone put my mind at rest........

PostPost by: George4th » Sat Sep 01, 2012 7:39 am

Having been reading the archives I have become paranoid about reconditioned racks and toe out.
I am building up a new chassis from scratch and I am concerned about the amount of toe out which can be visably seen on full droop.
Via another post (with help from Gary) I have checked the overall dimension of the rack and it seems about right.
The track rod ends are either the same or give a better (reduced) dimension than the originals

So would it be normal to have 25mm toe out measured on the discs when the suspension is in full droop held on TTR shocks. (The chassis being supported on axle stands)

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PostPost by: nebogipfel » Sat Sep 01, 2012 8:15 am

George

I suspect you have no need to worry.

You can't sensibly check the toe in/out properly until you have a complete car, engine in, sitting on it's wheels and the suspension has settled into position.

If the rack is correct all should be well :wink:
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PostPost by: simonknee » Sat Sep 01, 2012 9:06 am

Remove the shocks and then prop up the wishbones so that the lower ones are horizontal.
If you have enough range of movement in the track rod ends to get toe-in then I reckon you'll be alright.
This isn't going to be exactly where your car will sit but it's much nearer than full droop.

Or you could make the rack as short as possible and then move the suspension through full travel.
If there are no positions when it goes toe-in then perhaps you do have an issue.
There should be a range of positions (both side same height of course) where you get toe-in.
Save this info for when you have the car fully assembled and it may come in useful if you are struggling.
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PostPost by: Elanman99 » Sat Sep 01, 2012 9:55 am

George4th wrote:Having been reading the archives I have become paranoid about reconditioned racks and toe out.
I am building up a new chassis from scratch and I am concerned about the amount of toe out which can be visably seen on full droop.
So would it be normal to have 25mm toe out measured on the discs when the suspension is in full droop held on TTR shocks. (The chassis being supported on axle stands)

Thanks
George 4th


Something very wrong here (25mm Toe out at the disk!)

Basically toe in (or out) should not change with suspension travel. In the real world however is does vary slightly.

On the Elan the rack is adjusted in height using shims to reduce 'bump steer'. Search the forum for that and you will get lots of of info.


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PostPost by: AHM » Sat Sep 01, 2012 10:33 am

Is the toe correct to the settings given in the manual at the correct ride height?

Does the rack measure up to the dimensions given in the manual - if it does there isn't too much wrong with it!

Is the rack shimmed correctly?

If you haven't set it up to these settings then you are guessing!

What is the correct setting (between discs) at full droop? I'm not sure what you are trying to achieve or why you are trying to measure at full droop? What is it at full bump? In cornering the inner wheel will be in droop and the outer bump... what hapens then?

Read the stuff on here about bump steer and more generally about roll steer.

Worry when you can't achieve the settings given in the manual.

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PostPost by: terryp » Sat Sep 01, 2012 11:14 am

a few differences in opinion :shock:
Last edited by terryp on Sat Sep 01, 2012 6:47 pm, edited 2 times in total.
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PostPost by: ricarbo » Sat Sep 01, 2012 6:40 pm

25mm toe out at the discs - That's far too much. You need to get it down to 0mm and a bit of adjustment either way, in my opinion. it sounds like you have the Triumph track rods, as distinct from the track rod ends, but you say you haven't. If you have the Triumph rods, you can't shorten them and cut a longer thread because the original threads are rolled, not cut. In other words there is not enough thickness on the track rod, so you must get the original length track rods.
If it's a Triumph rack, you also need to add the right spacers to reduce the travel so the tyres don't touch the anti roll bar.
I think you need to firstly get the bottom wishbones parallel to to bottom of the front cross member of the frame, then take the measurements, (should be zero with a bit either way for final tuning) then secondly check for variation as they move up and down, that's where the steering rack shims make a difference.
regards
richard
Last edited by ricarbo on Sat Sep 01, 2012 6:58 pm, edited 1 time in total.
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PostPost by: George4th » Sat Sep 01, 2012 6:50 pm

Checked this evening and its more like 15mm.
I think all I can do is address it when the body is back on and the suspension is in the correct position
Thanks for all the replys

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PostPost by: Elanman99 » Sat Sep 01, 2012 7:15 pm

George

It will be much easier to get the suspension sorted whilst you have the body off. As Simon suggested do a trial assembly of the front suspension but don't fit the springs and dampers (and the anti roll bar).

That way (and its the best way) you can move the suspension over its full travel and shim the rack for minimum bump steer.

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PostPost by: TimMullen » Sun Sep 02, 2012 1:00 am

Elanman99 wrote:Basically toe in (or out) should not change with suspension travel. In the real world however is does vary slightly.
Actually, on most cars the toe changes considerably and intentionally with suspension travel. When you hit a bump, that tire goes up, and toes in tending to turn the car away from the bump. If it didn't toe in, then the car would want to turn to whichever side the bump was on. A carefully designed suspension takes that and more into consideration when it created.

Full droop to normal ride height can be considerable, and it probably goes through a lot of toe change.

By the way, untill the car is at it's finally ride height, you can't set things like toe-in/out, etc. And make sure that you DO NOT tighten the suspension bushings until the car is at normal ride height (and rolled back and forth several feet if it has been off the ground) before you tighten the bushings to the proper torque.
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PostPost by: George4th » Sun Sep 02, 2012 8:37 am

Thanks to all.
PS - I wasn't trying to adjust or set the toe in, merely to put my mind at rest from anyone who has built up their suspension recently and have seen the same thing.
The wishbones and the steering tie rods are at different angles so its bound to alter the toe in / toe out with suspension travel but I wanted to check if anyone knew by how much and whether my 15mm looked wrong.
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PostPost by: elansprint71 » Sun Sep 02, 2012 9:54 am

Some rather dangerous opinions being stated here; 25mm toe-out at the disc equates to much more when the wheels are on. As stated by the engineers already, assuming that the rack height is approximately OK, it should be around the zero mark and will not vary too much throughout the entire suspension travel.

If you cannot set the discs to parallel, there is something very wrong with your components. When I trial-fitted a Triumph rack (just to see what happen) I could not get any EDIT:toe-in out at all, there was about 4mm EDIT:toe-out (measured at the wheel rim) even with the track-rods screwed in tight. I fitted the spacers and still had to shorten the track-rods to bring it into Elan spec.

Please guys, if you do not know what you are talking about with safety-related items do not post.

If we had a moderator here, suggestions which are likely to kill somebody would be deleted immediately.
Last edited by elansprint71 on Mon Sep 03, 2012 7:55 am, edited 1 time in total.
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PostPost by: Elanman99 » Sun Sep 02, 2012 9:57 am

Tim.Mullen wrote:
Elanman99 wrote:Basically toe in (or out) should not change with suspension travel. In the real world however is does vary slightly.
Actually, on most cars the toe changes considerably and intentionally with suspension travel. .


I probably should have said does not change 'much'.

I know sometimes a small amount of bump steer is deliberately incorporated into car suspension design to alter the feel of the car handling (oversteer/understeer), but I doubt a 'considerable' change is ever made. With your analysis since the wheel being raised does not know whether the bump is on the inside or the outside of the tyre so the steering change might be in the reverse direction.

The other reason I think it might not work is that it would increase tyre wear because changing the toe of one wheel make the tyres 'fight' against each other.

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PostPost by: George4th » Sun Sep 02, 2012 10:40 am

elansprint71 wrote:Some rather dangerous opinions being stated here; 25mm toe-out at the disc equates to much more when the wheels are on. As stated by the engineers already, assuming that the rack height is approximately OK, it should be around the zero mark and will not vary too much throughout the entire suspension travel.

If you cannot set the discs to parallel, there is something very wrong with your components. When I trial-fitted a Triumph rack (just to see what happen) I could not get any toe out at all, there was about 4mm toe-in even with the track-rods screwed in tight. I fitted the spacers and still had to shorten the track-rods to bring it into Elan spec.

Please guys, if you do not know what you are talking about with safety-related items do not post.

If we had a moderator here, suggestions which are likely to kill somebody would be deleted immediately.


Pete
Just to put your mind at rest , I would not drive the car unless I could get the specified toe in at the correct ride height.
My components .........
New Galvanised Lotus Chassis
Refurbished Lotus Wishbones from Spyder
Track Rod ends from Susan Miller
Reconditioned rack (new rack bar and one tie rod) from SJS Sportscars - Overall length checked with Gary (Pissant)

I don't think there sounds to be anything wrong with the components?
Other items - vertical links etc do not appear to be bent in any way

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PostPost by: George4th » Sun Sep 02, 2012 11:25 am

Pictures...... can anybody see anything wrong?
P1010168.JPG and

P1010169.JPG and

Both track rods are screwed on as far as they can go. The extra thread on the RH side as you look at it is because the tie rod is new.

Cheers

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