Lotus Elan

Steering rack height?

PostPost by: steve.thomas » Fri Oct 21, 2016 4:40 pm

I recently fitted TTR adjustable front damper / springs to my Plus2 and have finally been able to get a lower ride height with the wishbones parallel to the chassis cross member as per the diagram in the manual. However, the steering feels heavier and when viewed from the front the tie rods slope upwards towards the road wheels. The diagram in the manual seems to show the rack and tie rods parallel with the wishbones which would make sense and give the maximum advantage. I suppose this is an inevitable consequence of lowering the ride height, but I don't think I've ever heard that the rack height should be altered to compensate? I believe later Plus2's had longer springs, would it therefore have been the case that the rack would have been mounted lower from new? (mine is a 72 car).
Steve
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PostPost by: Gray » Fri Oct 21, 2016 4:54 pm

If the rack is mounted at the correct height toe in should not alter as the wheels move up and down on the Elan and +2. Therefore, there should be no reason to change the rack height with lowered suspension.

I once had an interesting discussion with John Miles about introducing a little bit of bump steer as it might actually make the car more stable - he found this developing other cars after leaving Lotus. I'm intending to try on my S4 when I get it back on the road.

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PostPost by: Foxie » Fri Oct 21, 2016 10:13 pm

With double wishbone suspension as on the Lotus Elan, there will always be a variation of toe across the suspension travel range. This can be minimized by setting it on the vertical tangent of the plotted curve by adjusting the rack height.

A good way of setting this is by fixing a laser pointer to the hub, and recording the trace on a sheet of paper fixed to a board as the hub is jacked throught the suspension travel range. Rack shims are then changed to establish the curve for the next height. When all the curves are plotted, the rack height giving minimum change can be identified.

Further trial and error variations on this may give better or worse steering feel.

Useful post attached :)
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Bumpsteer.doc
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68 Elan +2, 70 Elan +2s
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PostPost by: gearbox » Sat Oct 22, 2016 3:45 pm

Steve;

Whenever you change suspension geometry, and as in your case by lowering the car, you alter all the other settings such as camber, castor, toe, etc. All these things have to be re aligned given the new ride height. If you are using the original A arms, your adjustment is limited. You can adjust toe from the tie rod ends, castor with washers spacing the A arms back or forward, but you will be out of luck with camber as the fixed A arm points cannot be changed. The rack moving up and down is for bump steer and all you are trying to do is to maintain a relatively equal toe as the wheel moves from static position to a compressed position. i.e. if the toe is set at say 1/8" "IN" you would want the toe to stay "IN" whether it be 1/16" or 1/4" when the wheel is compressed or elevated by an inch and pretty much equal for both sides as it goes through the compression range. By moving the rack up and down, you can adjust this using shims. The danger is if the new alignment shows a toe going from "IN" to "OUT" and then you become a passenger in your own car as it will steer the car on every bump. You can't really do these adjustments by eye.

I assume you are saying that the car is harder to turn while it is moving. Perhaps you now have excessive toe in. While that will give you more straight line stability, it will wear the tires a lot faster and cause a heavier steering not to mention slowing the car down. On my Formula Fords, I generally run zero toe, this gives me less rolling resistance and on some tracks, toe out for faster turn ins. But at zero toe, you are working the steering wheel even in straights and is a trade off for faster speeds. For a road car like our Lotus, I would run 1/8" toe, or 1/16" in on each side. But again based on your preference and driving style. Good luck Allan
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PostPost by: john.p.clegg » Sat Oct 22, 2016 8:24 pm

Steve
Your car will only "toe-out" if the steering geometry is wrong....both wheels should "toe-in" when deflected from the static ride height ( either up or down ).

John :wink:
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PostPost by: steve.thomas » Sun Oct 23, 2016 4:10 pm

Thanks for the replies guys. From the archives I found a useful post by Tony Vaccaro linking to an article on the http://www.Lotusowners.com website. Using his 'old man' method I made a simple jig and measured the toe-in at 12mm - probably explains the heavy steering. I've re-set to 4.5mm and will see how it feels on the road tomorrow.
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