Lotus Elan

What degree of caster is best?

PostPost by: jon1986eac » Thu Jul 30, 2009 6:41 am

Not sure if I am barking up the right tree but it has been suggested that changing the caster to about 6 deg will help the handling on my S3. The car is very quick at about 180bhp and weighs 620kg. It seems to get a bit wandery at about 80mph under hard acceleration! I'm not quite sure what it is at the moment but it does use Spyder wishbones.

Any advice would be great.

Thanks
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PostPost by: twincamman » Thu Jul 30, 2009 11:48 am

if you are looking for 'turn in' yes but if your looking for stability under acceleration that is controlled by the right foot - Front toe in causes the wheels to bump straight under braking and go to zero for stability in turns that require braking ----under hard acceleration the car squats to the rear and transfers the weight rearwards and the front wheels unload reducing the tire patch contact to the track making the car feel loose in the front -- [I'm assuming you don't have a toe out setting on the front wheels 1\8 th in is good ]---so enter the turn as smoothly as you can and exit as smoothly and quickly you can and be gentle on application of the accelerator on the exit. 'To be fast be smooth" by that I mean control all movements of everything you do in and to the car --no sudden or violent moves of the steering braking or throttle avoiding sudden weight transfers ----and remember the elements of the cornering mantra ---BRAKE SHIFT TURN APEX BALANCE ACCELERATE ON LINE -you must also be able to analyze the track so you can see what corners are sacrifice corners for car set up and position e.g. [ the middle of an s bend ] and which are important to enter and exit correctly --180 hp in a 1400 pound car can cause torque steer -weight transfer and generally screw up the laws of physics AND AREODYNAMICS so you may want to consider a front spoiler ED
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PostPost by: Davidb » Thu Jul 30, 2009 6:44 pm

What Ed said plus check the toe in on the rear wheels-try a little more....
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PostPost by: elandoc » Mon Aug 03, 2009 6:27 am

Hi Jon,
My S3 DHC has the same problem of being a bit twitchy at high speed. I know S1s and S2s had a lot more castor than the 3s and 4s, as did the 26Rs.
You have similar amounts of bhp to mine, but a lot lighter - how the hell did you get an S3 down to 620Kg?
Anyway, like mine, yours is probably very stiffly sprung - this exacerbates any other suspension geometry or set up problems you may not otherwise have noticed, so go through your measurements very carefully. I had by far the best improvement when I checked and corrected bump steer - these things are very sensitive to it.
I also agree with David - the back end set up has a profound effect on straight line stability.
See how you go - and tell me how you got it so light! Is there anyone with a lighter (road going) Elan?
Cheers
Patrick
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PostPost by: jon1986eac » Mon Aug 03, 2009 1:55 pm

Thanks for the advice. I does feel like the car is lifting a little. The navy Elan behind mine in the picture is the most unbelievable Lotus I have ever seen. It is road legal and weighs just 550 kg!! The guy who owns the workshop is a fantastic engineer and works on some amazing cars. He built the blue car to an incredible standard. I am very lucky to have him preparing my car but as I am sure you know, once you start with one thing you find a whole host of things that need attention. My ?500 spare cash after I purchased the car has not gone very far but it may well weigh sligthtly less though!
elandoc wrote:Hi Jon,
My S3 DHC has the same problem of being a bit twitchy at high speed. I know S1s and S2s had a lot more castor than the 3s and 4s, as did the 26Rs.
You have similar amounts of bhp to mine, but a lot lighter - how the hell did you get an S3 down to 620Kg?
Anyway, like mine, yours is probably very stiffly sprung - this exacerbates any other suspension geometry or set up problems you may not otherwise have noticed, so go through your measurements very carefully. I had by far the best improvement when I checked and corrected bump steer - these things are very sensitive to it.
I also agree with David - the back end set up has a profound effect on straight line stability.
See how you go - and tell me how you got it so light! Is there anyone with a lighter (road going) Elan?
Cheers
Patrick
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PostPost by: twincamman » Mon Aug 03, 2009 3:22 pm

welll Jon ---if you are going to pay someone to do a basic prep on the car you had better buy some dental floss some jack stands [to hold the floss ]and a measure tape and learn how to 'string' a car ---Its not rocket science and the simplest of tools [wrenches -vice grips and screw drivers ] will pay for themselves many times over and you will have few bob left over to put some Guinness in the gas tank --that's what we all do --NOW -----not to be insulting BUT it sounds like there is a whole BUNCH more time to be had in the driver than in chassis set up at this time ---- so concentrate on your driving and when the lap times are consistent to 1 \ 10 th of a second or so THEN spend your time on demon chassis tweeks because right now you just want everything pointing in one direction so you can learn the fast way around ----ed
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PostPost by: jon1986eac » Tue Aug 04, 2009 8:16 am

Thats a bit Harsh! I'm sure I could learn how to string a car but that is not the work I am having done. My main concern as a novice driver was the unsettling feeling when everything went light. Thought it best to try and sort that out as it felt unsafe. I agree the driver needs loads of work but I have not felt this in any Elan I have had before.

twincamman wrote:welll Jon ---if you are going to pay someone to do a basic prep on the car you had better buy some dental floss some jack stands [to hold the floss ]and a measure tape and learn how to 'string' a car ---Its not rocket science and the simplest of tools [wrenches -vice grips and screw drivers ] will pay for themselves many times over and you will have few bob left over to put some Guinness in the gas tank --that's what we all do --NOW -----not to be insulting BUT it sounds like there is a whole BUNCH more time to be had in the driver than in chassis set up at this time ---- so concentrate on your driving and when the lap times are consistent to 1 \ 10 th of a second or so THEN spend your time on demon chassis tweeks because right now you just want everything pointing in one direction so you can learn the fast way around ----ed
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PostPost by: twincamman » Tue Aug 04, 2009 12:19 pm

welll not everyone is a natural Nuvolari [although they all think they are]--but if your ego wont allow you to accept some well proven advice from 37 years of race experience that's up to you ---as I said 'not to be insulting but going fast in cars is a serious pastime and if you cant figure when the back of the car is steering you then you may get hurt and there just isn't any other way to guild that Lilly -----ed
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PostPost by: miked » Tue Aug 04, 2009 9:12 pm

I had rear track out of alignment on my standard S4 and found it with the string line. My car was twitchy at 70 plus. I had a lot of toe out on the left and a little on the right. I fitted the those Spyder rear adjustable "A" frames with the turn buckle affair (in the rear leg, like the Pat Thomas ones). I wanted to retain bushes being a road car. I was then able to set the correct toe in each side. One of the best things I ever did. Lot more stable after.

Do you perhaps have rod end adjustable type rear A frames? Has rear track been checked. No matter who built the "A" frame and what their name is, they could be giving toe out.

When you say you have Spyder bones, do you mean rear double type? I am not as experienced as a Ed and a lot of the others but is it also possible to get a form of bumpsteer over the travel. I am told that race guys check rear bump.

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PostPost by: toomspj » Tue Aug 04, 2009 10:20 pm

I think the guys are being a bit harsh. If your chassis set up is bad then it's hard to learn to be consistent especially if you are correcting slides on the straights!
It sounds like you're not sure if problem is at the front or the back - often you need to change the oppposite end to where you see the problem, but it does sound like it's at the back in this case. My experience suggests the following:
At the back, make sure that there is no play in the wishbone and uprights - if you can feel any, it will have an amazing effect on the steering. Many of the uprights being used are now around 40 years old and won't take the strain - i've sleeved mine. Once that's checked out, I would set the rears to toe in around an 1/8 each side, like the others say .

At the front , once you've set the castor, camber and approximate ride height you need to get the bump steer spot on. These Elans are amazingly sensitive to it, but generally the problem is under braking. I think 5 or 6 deg castor is a good place to start, camber will depend on the rubber you're using but neither of those is likely to be giving the problem you're describing. Toe in is essential - if you have toe out it could be quite unstable.

One other thing - the suspension bush sets that are commonly used have a skinny ferrule which if overtightened will lead to the suspension locking up. And if you leave them loose at the back it can cause all sorts of rear wheel steering. I let someone tighten my bones then couldn't understand why the car kept wanting to swap ends - I now use my own design which are far more robust.

Of course all this assumes you've got good shock abs too....

Good luck - what series are you planning to race in? Just so I know when to watch out for a luridly weaving Elan!

Paul
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PostPost by: Davidb » Wed Aug 05, 2009 1:31 am

I would recommend a book that came out many years ago but is still the best I have seen on this subject: "How to Make Your Car Handle" by Fred Puhn, published by HP books I think. It first came out in the seventies and nothing has changed much since.
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PostPost by: batfish » Wed Aug 05, 2009 8:55 am

The book mentioned in the previous post is still available from Demon Tweaks,

regards

Andy
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PostPost by: rgh0 » Wed Aug 05, 2009 1:05 pm

What springs are you running ?

Elans get very twitchy as you stiffen up the suspension and very sensitive to alignment and corner weight accuracy.

cheers
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PostPost by: andyelan » Wed Aug 05, 2009 6:11 pm

Hi there

Does anyone have a picture showing showing what these Spyder adjustable rear wishbones look like

Andy
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PostPost by: Davidb » Wed Aug 05, 2009 7:51 pm

Jon1986: What style driveshafts are you using? Presumably CV style but if they are sliding spline you could have a problem with the splines locking up-that can be very unsettling-ask me how I know!
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