Lotus Elan

Suspension Settings?

PostPost by: Lotus14S2 » Mon May 29, 2017 8:34 pm

I am asking this question as I am curious, not as any sort of criticism.

I see questions on ride height, caster, camber and toe-in.

What exactly are people doing that requires settings beyond what the factory has set the car originally.

Now, I do understand different wheels, and tires will alter some settings, but if you use the settings as given with the original wheels and tires, the adjustments should be more or less the same (i.e. a smaller diameter tire will give you a lower ride height, but the suspension geometry should be the same.).
I know that excessively wider tires, particularly if the offset is exaggerated will amplify any flaw of the geometry, but I'm assuming with most cars that the tires and wheels fall within a more normal range.
Back in the '60s thru the '80s I owned and drove a series of race cars, and setting up the suspension was a common procedure; mostly as you changed suspension joints regularly, and tuned the car dynamically on a skid pad, and track. I owned a series of small formula cars and sports racers. and had every book on the subject.
But generally if you talked to the factory they had pretty well figured out the settings and you could not go too far wrong if you followed their suggestions. If you varied from their settings it usually was not by very much, and usually had to do with a particular track, roll bar changes, or tires.
I know that many cars used in competition had to be altered to make them successful racers, this was because the cars handling was a compromise to begin with; being for the street and driven by average drivers. But, i don't think that was the case with the older Lotus cars. i think Chapman wanted the suspension set up at an optimum from the beginning. I think a good example of this, was the original Lotus Elite. I friend of mine had an Elite that he raced for many years. He had an engineering business and had his race car collection attached to his business and had full time mechanic/fabricators take care of his cars.
They decided to optimize the Elite suspension, so they fabricated all new suspension bits and had all the pickup points adjustable. With the help of a very good driver they spent weeks at a skid pad and track adjusting the suspension. When the car was fully set up they went racing and beat everyone, including some cars that you would think to be much better. They had an excellent processional driver which contributed to the success, but the car handled superbly and won many races.
Well, the organizers found out about this highly modified suspension and banned the car until the suspension was brought back to normal, as the fully adjustable suspension had not been a factory option in the homolagation papers. So they very carefully took the suspension apart and recreated the settings in non-adjustable parts. This required making a full set of new suspension pieces that looked stock, but had the optimized settings. After all this work, one of the mechanics took the old stock parts to compare them to the new. What he found was they were exactly the same, so second guessing Colin Chapman had led to nothing except a lot of money being spent.
Regards,
Tim
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PostPost by: Certified Lotus » Mon May 29, 2017 9:20 pm

Great story. I had heard many times that Chapman didn't want his suspension geometry messed with which is why it's non-adjustable. Just gotta have faith in his Lotus works engineering capabilities.
Glen
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PostPost by: rgh0 » Tue May 30, 2017 10:14 am

The fundamental difference that needs to be accommodated in a modern competition Elan is the increased grip of modern tyres compared to the tyres used when an Elan or 26R was originally being setup by Lotus

e.g.
Increased grip leads to increased tyre roll on the rim so additional negative camber helps compensate. The Elan needs less negative than many cars due to its lighter weight but some additional helps. My class limits maximum negative camber to two degrees to maintain original looks otherwise some cars would be run 5 degrees or more of neggy.

Increased front toe in to around the maximum specifications helps compensate for suspension deflection under heavy braking loads which are much greater with sticky tyres.

Increased roll stiffness compared to a 26R on the track and other changes are needed to stop excessive roll and weight transfer to the rear outside.

Most of these changes are subtle and within the original tolerances that Lotus had, thus I use suspension links within the original Lotus specification and achieve the small adjustments needed with a few shims and suspension lowering

cheers
Rohan
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