Oversteer on corners

[Chancer]

The tangent of the angle ABC is the opposite/hypotenuse

1/140 = arctan angle ABC

Angle ABC = 0.41?

But you are just completely overthinking this, many people myself included have suggested or even said forcefully that you have toe out on one of the rear wheels, mine was one of my rare concise postings with the minimum of words, all you needed to do was get a piece of string and the evidence would have been staring you in the face.

Instead you have wasted your money on a superdooperwhizzyshiny 4 Wheel alignment check carried out by someone that cannot even see that he should be embarrassed and ashamed about the figures he has given you.

Just use it as toilet paper which is all it is worth and you will can concentrate on the real problem, before cutting and altering anything try to see what is causing the toe out and possibly the other changing suspension angles although I would not give any credence to anything on the toilet paper, check all the wheel rims for buckling, you can discount Wheel bearings unless the Wheel feels like it could fall off in your hands, check carefully all the suspension bushes especially the Lotocones, check the chassis suspension pick up points and rear wishbones for damage.

The only thing that i might take from the print-out is affirmation that you have toe out on the RH rear Wheel as it seems to be the only figure that remains constant as it should.

Get a piece of string and see what is staring you in the face, I bet the oversteer is far worse on LH corners isnt it?

[MarkDa]

Jon
I'm afraid that your calculation isn't quite right, as the upright is of fixed length you create an isoscles triangle rather than right angle.
An approximation to calculate the angle in radians 1/140 and multiply by 2pi.
Or if you could have used Tan with 1&140 without Pythagoras.
You get very much the same answer of course because the displacement is so small - but we're nothing if not pedantic here!
Being even more pedantic or is it helpful? - you did measure upright effective length to centre of upper ball joint didn't you? And presumably made some assumption about the trunnion being flexible?

Mark

[rgh0]

The tangent of the angle ABC is the opposite/hypotenuse

1/140 = arctan angle ABC

Angle ABC = 0.41?

Chancer
Beat you to it with the calculation
But agree with the rest of what you say

cheers
Rohan

[vincereynard]

This all seems like doing it the hard way.

You do not have a hypotenuse as the length does not change.

Just draw it on a bit graph paper.
Vertical of 140 mm. Mark horizontal to that and measure off 3.5 degrees. (A)
Measure along that line another 140mm and measure the length opposite the A

It comes to approx 9mm. Way more than can be tweaked from packing out the top joint.
Of course shifting the bottom 'bone in the opposite direction would also help.

Either is a bit pointless until you get the ride heights at both ends correct.

[john.p.clegg]

+1 for Chancer / Rohan here , apart from "Angle CABC = get a piece of string."

John

[JonB]

Anthony Colin Bruce Chapman (9 May, 1928 - 16 December, 1982) was the founder of the British sports car company Lotus and principal of Team Lotus, which won the Formula 1 World Championship seven times.

"Make the suspension adjustable and they will adjust it wrong -- look what they can do to a Weber carburetor in just a few moments of stupidity with a screwdriver. "

John

The calculation was a bit of a thought experiment and I don't really care what Chapman said in this regard. Besides, that's been quoted so many times on these forums that I think it's becoming a bit of a cliche. As to all the F1 success, those cars had fully adjustable suspension.

Anyway, the thing I am after is correct handling (as opposed to building an adjustable suspension). Adjusting the suspension, whether Colin would have liked it or not, is a means to that end and not something I would do lightly.

I have done some forum searches and one thing I did not consider was the possibility of additional stress on the kingpin if the top joint is moved back. However, before attempting this I do have the front wishbone bushes to change, as I believe mine are rather more flexible than they ought to be.

Instead you have wasted your money on a superdooperwhizzyshiny 4 Wheel alignment check carried out by someone that cannot even see that he should be embarrassed and ashamed about the figures he has given you.

It is information. That machine is more accurate than a piece of string and while I do have a means of measuring total toe in, roughly, I don't have the time or patience to try and measure rear toe in relative to the car's centre line. Naturally, I regret the cost, but the figures are telling me something of value so I do not consider it a waste of money. As to why there is variance in non adjustable parameters between the two sets of measurements is anyone's guess. I wish I'd spotted it at the time so I could ask the fellow.

Just draw it on a bit graph paper.

My thoughts exactly, until I discovered I cannot find a protractor here to measure the angle with.

I also realised that the length of the hypotenuse wouldn't change in reality when shims are added, but the relative distance is very small so not likely to introduce unacceptable error margins (IMHO).

Regarding getting the ride height correct, that is what the guy at Spider said but my car does not have the facility to adjust it. However, measuring it would perhaps help diagnosis (not tried it yet, but we're looking for 13.5" from the front lower shock absorber bolt to the bottom of the upper suspension mount plate, apparently) despite the fact that I cannot alter it.

All very frustrating as the car is pretty standard apart from the Spyder chassis. One would think it would work as Lotus intended. I will repeat what I said before - that there's no evidence of accident damage - and as far as I am aware the Spyder chassis is manufactured to accurate tolerances. Anyway - I do need to check the Lotocones as I think one of them is not mounted properly (bush voids left / right vs front / back) and I commented on this on the rear suspension thread. It's not inconceivable that the rubber is all perished.

As a reminder, the thread has split in two now as I am trying to address different problems with the steering. One is the roll steer, the other is the vagueness when going in a straight line and lack of self centring. I do not know if castor improvements will address the former, but they certainly should help with the latter.

[Donels]

I have followed this thread since it started and it surprises and entertains in equal measure. I think you have too much advice and too many rabbit holes to fall down to be helpful. If I could give one further piece of advice it would be....take the car to someone who knows how to set it up and get them to check it out and do it for you. It will probably be much cheaper!

The alignment measurements you have all assume the chassis was manufactured perfectly.......

[jimj]

Mr. Donels offers the best advice of all, it does seem as if there are too many variables for an amateur to check. I know you`ve remarked before that your location isn`t too convenient for Lotus specialists but if you add up all the time you`re expending, you could use that time to take the car quite a distance.
You could take the long-suffering Mrs. B. have a nice drive and a nice lunch.

One more thing: how old are your tyres?
Jim

[JonB]

The tyres were new in July 2014, so they are only 3.5 years old. They look new, too. The history shows they have done less than 1500 miles.

As to nearby specialists, I'd be OK if only I could get Miles to pick up his phone..

[Donels]

It's probably too far for you from the South Coast but Paul Shipley at PJS Sportscars could sort it for you. He is a noted Elan, and all things Lotus, restorer and race preparer. He has a new facility in Tatenhill, Staffordshire and has all the laser alignment kit. I was there a few weeks ago.

[JohnP]

Mr Donels is right. A specialist will know what feels right, in particular with unevenly loaded rear seats per your original description.
Miles has retired I believe.
Try Club Lotus magazine. Lots of specialists advertise therein.

[jimj]

I was actually thinking of PJS when I suggested you travel awhile to get things right. OK it`s a bit far from the South Coast, wherever that is, somewhere between 3 and 4 hours probably. It could well be worthwhile and I doubt you`d regret it.
Jim

[john.p.clegg]

Is the ride height equal on both front corners? Springs , as we all know , should be changed in pairs , but if one is short of cash or about to move it on ?

John

[JonB]

Miles has retired I believe.

Part retired. He's still got a stock of parts to sell, but I think "part" is turning into "fully" retired as you said.

@Cleggy: They look to be contemporary with each other. Certainly the car is level left to right.

[MarkDa]

When you measure the angles again after rebushing it might be worth persuading the operator to allow the wheels to be rotated to see if the measurements are affected by rim imperfections.
I have to agree that the laser machines just measure what they see and good technicians who understand suspension geometry are probably thinner on the ground than they ought to be.
It will be important to ensure that ride height is at least the same even if you cant acheive the specification if the measurements are to mean anything.
As mentioned by others there were differences last time you went that shouldn't have occurred.
So watch for those and if they happen again query with the technician.