Oversteer on corners

[MarkDa]

An interesting discussion on ride height with link to post on loading to acheive standard.

lotus-suspension-f42/plus-ride-height-t28885.html

[JonB]

Didn't know it is 37.5" high. That's why it looks so low.

Remember my tyres are not the right profile. They are about 1.5" smaller than originals (so the wheel arches are not what you'd call full). However, this has no bearing on the front castor as they are the same size all round (i.e., equally low to the ground). Does make it difficult to set the loading up when the book says 6.5" from the ground at the front cross member and mine is already 5.5" unloaded. Plus, is a Spyder chassis so different cross member, potentially. Fortunately they told me what the effective damper length should be (13.25") so I will go by that.

[john.p.clegg]

Unladen height 3' 11"

Otherwise it would outdo the GT40...


John

[prezoom]

All this chasing one's tail is quite entertaining. All measurements that are listed, in reality are out the door in this day and age, what with the modern tires and the availability of sizes. What one is looking for is, keeping the front lower control arms parallel with the ground when the car is loaded under normal operating conditions. With front steer, the steering rack and tie rods should be parallel with the lower control arms. This will bring bump steer to a reasonable number. Then play with the amount of toe in that you are comfortable with. With front steer, any bump or rebound will result in toe in when following these guidelines. More toe in, more straight line stability, more tire scrub, more rolling resistance. Toe out only works under racing conditions when one is looking to improve turn in under certain conditions. But, makes braking in a straight line, and keeping the car from darting around a challenge. Camber can also be made adjustable, and should be equal at both front wheels. Increasing caster can be about as much as you can stand. More that the original listed amount will help straight line stability. The width of the attachment points of the rear lower control arm at the chassis helps control the amount of rear steer under bump and rebound. Camber control is another issue, as with the lower control arm parallel to the ground, it will increase the negative camber. Of course, this is only adjustable if you have spring mounts on the struts that are adjustable. The only accurate way to achieve desired rear toe is with adjustable lower control arms. Pick your number and take your chances. Adjustability makes changes quite easy. All of the above is only applicable if the suspension attachment at the chassis are as exactly designed. Of course, under the manufacturing conditions present at the time these chassis were constructed, you can expect some variance from the original specifications. All this nonsense about Chapman knowing best, is only applicable to the time he was constructing these cars, and the limitations he was under to make them cost effective. If the standard configuration of the road cars was optimum, then there would have never been a 26R.

[john.p.clegg]

Fancy using 26R and road cars in the same sentence....

John

[prezoom]

Zachery.

[mark030358]

yes, I'm referring above to the thread you linked (not your post, note, but at least one within this thread : I quoted verbatim it for reference, assuming that the whole thread would be read as suggested).

I'm glad the readjusted geometry settings are fine with you and restored your car to a performing driving as it should... that was not the point discussed here but rather the effect of rear geometry on an other car, and what can cause "bump steer" (i.e. nothing at the rear under normal operating conditions).

Nic

My post and the reason I linked it relate to topic of the thread "Oversteer on Corners" and in particulary the geometry settings which fixed similar issues on my car. And yes, its super stable and very predictable.

thanks
Mark

[JonB]

Unladen height 3' 11"

Otherwise it would outdo the GT40...


John

Yes, sorry - I misread the diagram.

[JonB]

All this chasing one's tail is quite entertaining.

A little harsh, if you're referring to my efforts to date - and if so, I disagree. Everything I have done to the car (including the four wheel alignment) has resulted in an improvement. If you mean the discussion on this thread, I might agree with you, because we all have different points of view.

All measurements that are listed, in reality are out the door in this day and age, what with the modern tires and the availability of sizes.

I would use the factory measurements as a baseline, but what I am trying to do is fix a steering problem (well, two actually, as I said before). I won't quote the rest of your post but it does look like good advice to me. However, at present, my suspension is distinctly non-adjustable and I would like to try and get it near to optimum without the huge expense of making it adjustable. So far, I have committed to fitting adjusters for rear toe-in only, on the grounds that it's not too expensive and I understand the car is very sensitive to this parameter.

So like I said, my plan is to fit the new front bushes (should have done them when I replaced the uprights) and see what effect they have. That leaves the anti-roll bar and drop link bushes left to do at the front. At the rear, it is just the Lotocones that are left to do. I think the shock absorbers and springs are OK.

Does that sound reasonable?

[Orsom Weels]

Hi Jon,

I think if I were in your position, the first thing I would do would be get another alignment check done by someone else. I would have to worry about any technician who said he was ?happy? with those results. Instead of trying to work out how to rectify things, what you should be asking your self is can you believe what you have been told.
For instance, how do you loose virtually a whole degree of camber on the n/s/r wheel & change a ? degree of positive camber into a ? degree of negative camber on the o/s/r wheel ? And why have the front camber figures changed so much between the before & after tests ? These figures shouldn't change significantly if at all unless the ride height was significantly different between the checks, which, of course, it shouldn't have been.
The only figures that have remained unchanged are the caster measurements, & quite frankly, if they are correct, the car is never going to feel stable in a straight line, this is where you should be concentrating your efforts. Lotus spec for caster angles are 2 ? ? 3 ? degrees, you apparently have just under ? a degree o/s & essentially no caster at all n/s. Why ? Bodging spacers between ball joints & wishbones should not be necessary, if the measurements are accurate, find the real cause.
The other measurement that has remained reasonably static is the rear toe. Ideally the o/s would match the n/s, but whilst much has been made of the n/s/r wheel toeing out, 0 degrees 02 minutes is close to nothing at all, 1 minute on a 13 inch wheel equates to 0.1mm, you're looking at about 0.02mm or about 0.001?. I really don't believe this is your biggest problem.

Regards, Tim

[JonB]

Sage advice Tim, thanks.

He said he was happy with them in the context of many modern cars he'd tested that were worse. I took it with a pinch of salt, especially after test driving it and finding only a small improvement.

If I make the assumption that the chassis is undamaged and within tolerances (I may as well, because it's not possible to correct it), then logically the only things that might cause this are the front bushes (including anti roll bar and drop links) and / or Lotocones. Everything else that might affect geometry has been renewed.

I figured on another visit to an alignment shop, but only after doing the front wishbone bushes and making the rear arms adjustable for toe-in. At least then I'd get some value from it (in that the toe-in could be set at the rear as well).

I do have a concern. The Hunter machine's settings say "Elan 67-73" or some such; not "Elan Plus 2". They do not have the same suspension parameters, do they?

[rgh0]

Didn't know it is 37.5" high. That's why it looks so low.

Remember my tyres are not the right profile. They are about 1.5" smaller than originals (so the wheel arches are not what you'd call full). However, this has no bearing on the front castor as they are the same size all round (i.e., equally low to the ground). ...........

The smaller wheels don't affect the caster angle but they do affect the caster amount i.e. the wheel contact patch is behind the steering pivot by less, so the caster self centering affect is reduced and thus stability in a straight line reduced.

[MarkDa]

Jon
Geometry specs are the same for later Elan and Plus2
Mark

[Chancer]

Well said Tim, even at 250% magnification my eyes struggle to read the figures, I was sure it was the RH rear that was toeing out but now it looks to be the left, isnt it 34 minutes of toe out and not 2 minutes?

These whizzbang machines are only as good as the guy using them and he has to be competent and aware enough to question the figures that it spits out.

Given that in 45 years of motoring I have yet to see a single mechanic or tyre fitter put a pair of tracking guages together to checak (and adjust if necessary) that they read zero before measuring the vehicles tracking, given how the delicate measuring instruments are thrown and dragged around I have little faith in them suing somethinh even more accurate.

A great tool in the right hands, nothing more than a money spinner in others.

[Chancer]

Just been squinting at the figures again, if they are to be believed and I am not so sure of that, but the rear toe ones have not changed so maybe they are correct, then both rear wheels are toeing out (the RH one being near as dammit to parallel) total toe out being 32 minutes and the thrust angle of 18 minutes (surely that should be 16 minutes?) means the car will be crabbing does it not?

I certainly predict that it wont like turning into LH corners and will snap into oversteer on RH ones which is the opposite of what I said earlier from my flawed memory.