Lotus Elan

Oversteer on corners

PostPost by: gus » Fri Feb 09, 2018 11:04 pm

JonB wrote:
I have ordered the turnbuckles and will get a local firm to machine the sleeves and do the welding. For the front suspension, I have ordered a full set of bushes from Sue Miller. I'll be dismantling everything this weekend. What joy.



Stooooooooooooooooop

your alignment results show an issue that cannot be resolved by 'adjusting' anything

The rear camber did not change due to a dimensional issue

figure that out before cutting things up
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PostPost by: pauljones » Sat Feb 10, 2018 8:25 am

Are your wheels loose at all? Properly seated and tightened?
Kick the tyres and light them fires...!!!!!!!
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PostPost by: JonB » Sat Feb 10, 2018 8:44 am

@gus: One adjustment at a time. There isn't a way to adjust the rear - I will do the front bushes and see how things stand then.

@paul: Of course they are.

Actually I am thinking that the slight play in the O/S rear bearing might have something to do with it.
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PostPost by: pauljones » Sat Feb 10, 2018 9:56 am

Jon

A strange point to make but mine worked loose untill i swapped from eared spinners to the big bolt.
Nice n tight and not worked loose since.

I was reading your post in the other section, having never stripped the rear bearings out before all i say say is perhaps they need to be done and replaced or re packed with grease.

Im trying to work through the easy things to do first, my point being if the bottom arms are correct dimension and bushed then surely thats a solid structure.? Next is the wheels and bearings. If they look good id want to be checking the new driveshafts to ensure they're fitted correctly.
After that i think look at the top mounts of the struts.
Ill be honest, im at my limits of advice then, bar a complete strip down and re assembly im stuck to offer any further advice.
Kick the tyres and light them fires...!!!!!!!
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PostPost by: nmauduit » Sat Feb 10, 2018 10:52 am

mark030358 wrote:
possibly not in this thread, but my comment was mostly discussing to the other thread cited in reference just before my reply and from which I have taken an excerpt that clearly pushes that hypothesis, which I refute


Errmmmm are you alluding to my link and the results obtained?

And nowhere does it mention rear bump steer in my post.
thanks
Mark


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
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PostPost by: JonB » Sat Feb 10, 2018 11:20 am

OK playmates, a full set of front bushes just arrived by post.

Guess what I'm doing next? :roll:

Oh, and the turnbuckles arrived too, but I'll put those to one side for the time being.
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PostPost by: MarkDa » Sat Feb 10, 2018 11:28 am

We've got to be careful when considering camber angles, because of suspension geometry they do change significantly with load hence the specifed ride height for measurement.
A loose wheel bearing will add negative camber to some degree - more at front than rear because of bearing centres but how much? It's easily checked and remedied (at front anyway)
On standard cars there's nothing to adjust -
so does major variance from spec indicate chassis distortion?
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PostPost by: pauljones » Sat Feb 10, 2018 11:34 am

Well as your not that far from me i dont this weather doesnt effect your progress.
Its hammering it here in South Hampshire.
I hope you get to the cause.
Kick the tyres and light them fires...!!!!!!!
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PostPost by: JonB » Sat Feb 10, 2018 11:48 am

@paul - well come over and drive it, see what you think then!

Yes, the weather is bad for getting in an unheated garage, right enough!

I found some info on the rear shockers.

2 x Koni rear strut inserts.

Converting the Koni piston rods from split pin slot to split pin hole. Testing the dampers, resetting and installing them in the rear strut housings. Filling both housings with antifreeze.

2 x rear springs.
2 x Lotocone inserts machined.


Not sure what it all means. For example, machining Lotocone inserts? Why? And why fill the housings with antifreeze? Is this instead of damper oil? The work was carried out some time in '91 and the info comes from an undated itemised printout. I know the rough time this work was carried out as it has the owner's name on it and I can correlate it to the purchase history.
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PostPost by: nmauduit » Sat Feb 10, 2018 12:33 pm

JonB wrote:For example, machining Lotocone inserts? Why?

could be for altering (increasing) the camber (as done on some race cars), that would be around the attaching holes to the rear turrets...

JonB wrote:And why fill the housings with antifreeze? Is this instead of damper oil?

anti-freeze or engine (no damping required actually) would be to assist heat transfer from the shock to the tube to help dissipation, and avoid internal corrosion
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PostPost by: JonB » Sat Feb 10, 2018 12:46 pm

I read up on the Lotocones. The voids in the rubber are supposed to go fore - aft. As seen in this picture of the rear of a Lotus chassis:

http://images.lotuselan.net/lel/22817/0 ... 0above.JPG

In the picture, we see that the tabs of the Lotocones both point to the upper right / lower left and the voids in the rubber are fore / aft.

The Spyder chassis has four mounting holes which means you have two different ways to mount the Lotocones. In other words, it is possible to get the voids left - right. I have examined my Lotocone tabs from under the car and they are fitted symmetrically, which I think means that one of them is the wrong way round. I think it is the driver's side one (this should have the tab inboard when viewed from under the car but it is outboard). Which is odd, because the right rear wheel has the best camber in the second set of readings.

The discussion is here: lotus-suspension-f42/lotocone-mounts-spyder-chassis-t26504.html

Maybe it's a red herring?

I also worked out what the Lotocone "inserts" are and why they are machined (just to take up play between the cone and a non Lotus damper, which has a smaller diameter).
Last edited by JonB on Sat Feb 10, 2018 12:53 pm, edited 1 time in total.
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PostPost by: oldelanman » Sat Feb 10, 2018 12:49 pm

JonB wrote:For example, machining Lotocone inserts? Why?


It could be because the original rear dampers used a special stepped, castellated top nut which centralised the damper rod in the lotocone. Modern replacement dampers use a standard nyloc top nut so a top hat spacer is required to do the job. Some are supplied with the spacer, others not and they need to be made up.
rear-damper-top-nut-001.jpg and
ttr-rear-shock-top-mount-spacers-005.jpg and
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PostPost by: JonB » Mon Feb 12, 2018 8:51 am

JonB wrote:Just had a chat with someone @ Spyder. Front caster can be adjusted, minutely, by fitting washers / shims to the top wishbone pin and ball joint bolts. Seems a bit marginal.


So, I decided to try and calculate the effect of adding a 1mm shim to the top ball joint / rear wish bone arm, which would have the effect of moving the top joint back by 1mm. For this calculation I start with an assumed castor of zero as a baseline, then add the 1mm to form a right angled triangle:

castor-illustration.jpg and


On the left we have a castor of zero degrees as the line between the axle and top ball joint is vertical. On the right, the top joint is moved back by 1mm creating a right angled triangle with points a, b and c. Measurement ac is 140mm, ab is 1mm and using Pythagoras' theorum we can calculate bc as 140.003mm.

In order to calculate the angle at c we need to use the formula acos (ac / bc) which gives about .375 degrees per mm of spacer.

My math is terrible of course, so the formula came from http://www.bbc.co.uk/schools/gcsebitesi ... rev4.shtml Anyone care to comment?
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PostPost by: john.p.clegg » Mon Feb 12, 2018 9:04 am

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 :wink:
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PostPost by: rgh0 » Mon Feb 12, 2018 9:45 am

You lost some accuracy with your calculation method. Better to use Artan or Arsin as the actual length of the link does not change as you displace it This gives around 0.41 degrees.

Adding caster can help straight line stability but also helps turn in by increasing camber on the front outside wheel as you turn.

Increased front toe in to the maximum end of the spec and rear toe in to the middle to maximum end of spec helps also and off course bump steer adjustment.

I have always found my Plus 2 more sensitive in a straight line to varying road surfaces and throttle application than my Elan. i have put this down to more movement of the longer suspension arm on the bushes. One day I will try poly bushes in the Plus 2 to see if that helps.

The tyre world has moved a long way since ACBC first setup the Elan and Plus 2 and I am sure he would now be doing something different. If Lotus had any commercial and historical sense they would develop and sell a non adjustable suspension upgrade / rebuild package developed to suit modern tyres for the Elan and Plus 2. But I guess not enough money in it from their perception.

But if they factor in what this would be worth for their current car sales advertising
i.e
"Handling is in our DNA and we support the handling of our cars for 50 plus years as our 50 year old cars are better than most modern cars in terms of handling"

I think they would be sensible to do it. The did an upgrade/ rebuild package for the later Esprits a few years ago but unfortunately did not do one for my S1 so I am stuck doing it myself when I have time :lol:

cheers
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