Lotus Elan

Tire Brand And Size?

PostPost by: type26owner » Mon May 16, 2005 6:21 pm

Hey Robb,
I'm wondering if the SLA (short/long a-arm) suspension is setup correctly. Are you using the original springs? Is there 6 inches of ground clearance to the chassis with you in the car?

The car can be greatly improved upon in handling with some simple, inexpensive modifications.

Now I think about it maybe the MX4s rubbed on the fiberglass too on my car. The memory is fading.....
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PostPost by: rgh0 » Tue May 17, 2005 9:36 am

Keith

The XAS FF stood for "Formula France" which if I recall correctly was a one make racing formula using Renault 12 Gordinis. A great tyre in its day based on putting a soft racing compound on the standard XAS road tyre design. The equivalent of something like some of the soft compound japanese road tyres today.

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PostPost by: steveww » Tue May 17, 2005 11:41 am

Got it in one Rohan. They are making them again in 155 x 13 :D

As it is an older design of tyre the round shoulders suit the Elan. The tyre is also semi-slick on the outside just like the modern Yokohama. Hmm... nothing new in automotive engineering.

More details here:
<a href='http://www.michelin-passion.com/passion/front/templates/affich.jsp?codeRubrique=39&lang=EN' target='_blank'>http://www.michelin-passion.com/passion/fr...ique=39&lang=EN</a>
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PostPost by: robb4100 » Tue May 17, 2005 1:54 pm

Hi Keith,

The clearance without me in the car from the ground to chassis was less than 4.5 inches- I had to buy a low clearance jack! just to get it off the ground. I presume this means that the SLA suspension is not set up correctly.

I do not know if the springs are original, but might be able to find out from the PO's notes. I suspect not since the chassis was a race car in its earlier life.

I would appreciate any advice on how to best check this out, and set up the SLA suspension correctly.

Thanks!

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PostPost by: type26owner » Tue May 17, 2005 2:02 pm

As it is an older design of tyre the round shoulders suit the Elan.

Hey Steve, why are rounded shoulders so desirable? On my car which is tweaked somewhat to improve the handling by reducing the rate and amount of body roll. I get distinctly different wear patterns from the front and rear tires. The rears wear out the center of the tread leaving the shoulders intact. The fronts have a lower wear rate in the center and wear off the shoulders first. The tires that I tried that had rounded shoulders usually also had paper-thin sidewalls. The only way to get them to perform was to inflate them well beyond what's recommended. What pressure do you run XASs at on the track? How much does one of these tires weigh? Are the sidewalls stiffened?

Have you tried the RE92s yet?
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PostPost by: type26owner » Tue May 17, 2005 3:10 pm

Robb,
The upper a-arm is the shorter one so it's range of motion dictates the amount of camber. The car is designed to have a slight amount of positive camber when loaded but traveling straight ahead. That means the upper a-arm must be positoned to be horizontal at that load condition. The ride height via the spring controls this effect. Lowering the car makes the a-arm incline upwards towards the wheel and cranks in negative camber and <span style='color:red'>shortens the suspension travel</span>. This is okay if you've got the springs and swaybar to compensate to slow and reduce the body roll rate. If you don't what happens is the body will roll and violently impact the travel stops which instantly overloads the tires and the car will spin out of control. A total loss of control at high cornering speeds is a real seat nipper. The RE92s will definitely cause the body to roll so be careful if you've never pushed your car to the limits before. It can be terrifying if your car is not setup correctly.
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PostPost by: steveww » Tue May 17, 2005 4:11 pm

Keith,

No idea on the weight of the tyre. Appeared to weigh a similar ammount to the Uniroyals that I took off but this is only from lugging them about, nothing scientific here.

The Lotus suspension design is now well over 30 years old and way back then wide flat low profile tyres did not exist. Unlike modern designs the Elan suspension is not good at keeping the tyre's tread flat to the road surface.

I am currently running the XAS tyres at the pressures in the manual for high speed motoring. I have not been out on the tack yet with these tyres but these pressure appear to be working for the road. Ah-em I don't hang about on the road either B)

Compared to the previous tyres they appear more stable. Previously when turning in you could feel the tyres roll on the rim and settle in to a slip angle. Now turn in is crisp and the slip angle considerably less. Grip levels are much improved. Previously a dab of right foot midway round a tight bend would get the car well sideways :D Now it just bites in a goes until the inside rear spins away the power. Hmmm LSD anyone.


BTW: On the ground clearence thing. Measuring from the bottom of the sill to the floor is aprox 6.25" all round on my S4.
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PostPost by: type26owner » Tue May 17, 2005 7:07 pm

Steve,
Suggest you do the this quick test to find out how well those tires perform. On a long straightaway without any other vehicles around take it up to 120mph and then stand on the brakes while steering straight ahead. I almost rolled my car when I had the MX4s set to only 32psi. Scared the holy crap out of me and I definitely nipped a piece of my driver's seat loose that time. I didn't have a rollbar at the time but it was installed soon thereafter.

Trust me having the sidewall stiffeners helps.
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PostPost by: robb4100 » Tue May 17, 2005 7:58 pm

Keith,

I think I understand most of that I and I will check my paperwork to see if there is any spring infromation there.

I presume that the clearance for a standard set up should be around 6 ". Is that correct? You said that"simple and inexpensive modifications" can help. I presume that one would start with the springs which may be too short or too soft. Is that correct?

One other oddity that I have noticed is that the top of the shocks protrude about 3/8 inch throught the fibreglass into the engine compartment. That cannot be correct.

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PostPost by: type26owner » Tue May 17, 2005 8:14 pm

Robb,
I'll help you later on tonight.

You've probably had a failure of the rubber bumper washer at the top of the damper that takes the jounce loading. The one on the underside of the chassis top mount. Mine broke in the exact same way. I made up 1/8" thick washers to assure that never happens again.

While you've got the damper out remember to clean out gravel and dirt from the chassis pocket behind the damper otherwise the chassis will rust through there eventually.
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PostPost by: steveww » Tue May 17, 2005 9:56 pm

<!--QuoteBegin-type26owner+May 17 2005, 07:07 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (type26owner @ May 17 2005, 07:07 PM)</td></tr><tr><td id='QUOTE'><!--QuoteEBegin--> On a long straightaway without any other vehicles around take it up to 120mph and then stand on the brakes while steering straight ahead. [/quote]
While I have not tried this from 120mph..... There is a favourite bend of mine which requires a big stop, from aprox 100mph down to 20mph, I usually press the brakes at aprox 150yds back. My S4 has always managed this even on the old tyres. However before I did the brake mods it did tend to lock up the rears which can be a bit exciting.

I would say that with the XAS it is more stable under braking that before. However any car on an 80 profile tyre is going to move about a bit, that is the fun of driving old cars on high profile skinny tyres. You just have to learn how to drive round it. Its the same as my old Porsche 911, some idiot put all that weight in the back, just alter your driving to allow for it.

To corner quickly in an old sports car on high profile tyres you are going to have to drift it. Turn in allow the slide to start, take off some lock, play the throtle and round you go :D Totally different to a modern sports car where you will loose time when sliding. Just look at any old pictures of sports car racing. There are some great pictures of Stirling Moss in the 722 Merc in this months Motor Sport. Now if I only had on tenth of his talent.
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PostPost by: type26owner » Tue May 17, 2005 10:12 pm

Steve,
Okay I'm dazzled. I'll have to buy a set and try them out.

I'm kinda in shock right now, my wife saw another Elise yesterday and now she wants to trade in her Corvette and get one. If it doesn't come with GPS she'll drive off and she'll never find her way home again. :(
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PostPost by: type26owner » Wed May 18, 2005 2:33 am

Robb,
Check out your suspension first before I spend a bunch of time explaining stuff. Look for the front and rear bottom spring perches to see if they are adjustable in height. Next be aware there are two different types of adjustable springs. The Dave Bean ones have a spring ID of 2.5" while all the others are 2.25". This makes a difference as far as your upgrade options go. BTW, I have not studied this stuff in ten years so I might not be current anymore.

If you have the full blown racing springs and sway bar then 4.5" of ground clearance is about right. Anything lesser sprung as stiffly requires more ground clearance at 6". The swaybar that the racers use is 1" diameter. I have the halfway one installed which is 7/8" and the original one is 13/16" if memory serves me correctly. Or is that 11/16"? Help!

Actually I'd say the original suspension is okay for the ladies to motor around town but not for pushing the performance envelope. The halfway setup makes the car a reasonable car for road usage and for occasional ventures on the race track to do trackdays only. To be competive to do vintage racing you'll need the full blown racing setup. The racing setup is about 10 seconds faster a lap then the halfway setup. The original setup should not be tried on the track cause it's really quite unsafe.
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PostPost by: rgh0 » Wed May 18, 2005 9:47 am

Robb

6 inch clearance was orignal with standard suspension and tyres. If you are not running original tyre diameters you need to adjust target ride height for suspension at original geometry. My race car runs at about 4.5 inchs ground clearance about half the reduction is due to lowering the suspension and half due to smaller diameter tyres.

Lowering the front and rear suspension about 3/4 of an inch puts a little negative camber on the wheels in normal straight ahead travel which improves turn in and stability on the track. Running stiffer springs and roll bar is needed to ensure you dont run out of suspension travel in a sudden way with a lowered suspesnion as Keith observed.

Keith
Dont know what toe in you use, but for heavy high speed braking like you describe I find running front toe in slightly above the book specification range helps, especially if the braking area bumpy. The other thing to be careful about is is trail braking into a high speed corner the tail is lightly loaded and easily lost very quickly and unexpectledly with no warning in an Elan.

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PostPost by: robb4100 » Wed May 18, 2005 10:54 am

Keith and Rohan,

I should have some time this evening to look at this and will get back to you. If not tonight then it will be Saturday. Thanks for the info, advice and help.

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