Lotus Elan

Oversteer on corners

PostPost by: JonB » Mon Feb 05, 2018 11:44 am

Having finished the back end, I have been testing the car and discovered some unpleasant behaviour in corners. It seems the car wants to turn in more aggressively than I ask it to. This happens as the suspension is loading up into the bend. What it feels like is an amount of oversteer that is not caused by the rear end coming loose, and it requires minor correction every time. This makes the car difficult to steer smoothly, especially when driving in a spirited fashion.

A few points about the car:
  • Has Kumho tyres all round - 165x13 with good tread, inflated to the correct pressure (23 PSI all round, I think).
  • Front suspension joints all replaced (ball joints, track rod ends and trunnions / uprights), but not the wishbone bushes.
  • Rear suspension bushes all replaced and CV jointed halfshafts fitted.
  • No evidence of bump steer, so I think this isn't the root cause.
  • I have attempted to set the tracking at the front, but it may be out.
  • There is no free play in the steering column, or very little, but the column bushes definitely need to be replaced.

What might be the cause of this oversteer?
1973 Elan Plus 2S 130/5 - UK - Chassis 50/1115L
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PostPost by: jono » Mon Feb 05, 2018 11:50 am

Do you have the standard Aeon bump stops and standard springs fitted?

Have you checked the rear toe?
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PostPost by: rgh0 » Mon Feb 05, 2018 12:00 pm

Your car should also have aluminium spacers that fit on top of the Chapman struts to bring the Aeon rubber springs into play earlier, do you have those?

What is the front and rear toe- in?

Do you have any other non standard front or rear components in the suspension?

A properly setup Plus 2 should be nice and neutral unless a corner is really stuffed up and then it hsould be gentle under steer.

Can you describe more the situation when you experience over-steer e.g. speed, type of corner, load in car throttle or braking situation etc

cheers
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PostPost by: Craven » Mon Feb 05, 2018 12:08 pm

As you have changed the track rod ends, check you don’t have bump oversteer.
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PostPost by: john.p.clegg » Mon Feb 05, 2018 12:21 pm

Front Tracking
Rear Tracking
Front to rear alignment
Bump steer

John :wink:

lotus-suspension-f42/tracking-t19506.html
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PostPost by: Chancer » Mon Feb 05, 2018 12:29 pm

Toe out on one or both rear wheels.
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PostPost by: JonB » Mon Feb 05, 2018 12:35 pm

Hi John

I think there is no bump steer. Was wondering if worn bushes at the front might be the culprit. Anyway, I read that thread on tracking a while ago and tried to make my own gauge using the "old man's method", but I suspect I got it completely wrong.

Regarding the diagram on the first post, do I take it that I could set the front tracking by the simple expedient of making them in line with the toe in at the rear using a straight line?
1973 Elan Plus 2S 130/5 - UK - Chassis 50/1115L
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PostPost by: john.p.clegg » Mon Feb 05, 2018 2:54 pm

Jon
Yes,providing the rears are in the right place.....

John :wink:
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PostPost by: JimE » Mon Feb 05, 2018 5:16 pm

Tyre pressures are higher that recommended by Lotus. I run with 20 psi front; 24 rear. Jim
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PostPost by: pauljones » Mon Feb 05, 2018 5:36 pm

Thankfully its only over steering on corners and not on straights, or you would have a serious problem.
Kick the tyres and light them fires...!!!!!!!
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PostPost by: Billmack » Mon Feb 05, 2018 7:25 pm

Assuming nothing is falling off you have rear wheels toed out or you are turning in early.
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PostPost by: JonB » Mon Feb 05, 2018 7:33 pm

How can they be toed out when there is no adjustment?

It's a Spyder chassis that has no visible damage and the wishbones have new bushes.
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PostPost by: Billmack » Mon Feb 05, 2018 7:49 pm

I have set toe on many cars with string. Set up 4 jackstands or paint cans or w hatver you canattach a string to ahead and behind the car. Give yourself some space to measure distance between strings.make them parallel to each other and the car centerline. On the c/l. I just make sure they are all the same distance from the tires a nd parallel to each other taking into consideration that front and rear track width may not be same. Then just measure at front and rear of each tire. Relatively easy. Forty years of s uccess speaking here.
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PostPost by: Billmack » Mon Feb 05, 2018 8:14 pm

Adverse stackup of tolerances. That would be the engineering term. And looki g around I would not be surprised to see even spyder themselves offer adjustable control arns. Possibly if you have upper control arms back there you could have rear bump steer but unlikely. Front bumpsteer i do not consider all that important as one wheel is unloaded and the other you have control if by the steering wheel...as long as its not huge. Bad handling is produced by the rear wheel toing out under compression because you have no control over that.Even toeing in back there is not that bad. Out, well, the back of the car just winds its way up toward the fence.
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PostPost by: MarkDa » Mon Feb 05, 2018 10:55 pm

Jon
Get back to the 4 wheel alignment centre to get a full geometry check.
I suspect poor rear toe in being the probable issue.
Mark]
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