Lotus Elan

One Inch Front Swaybar

PostPost by: type26owner » Thu Jun 24, 2004 3:15 pm

Besides Dave Bean selling me a 1" front swaybar he had some advice to give concerning the usage. The design is poor in that it tends to bind the suspension through part of it's range of motion. That's not the problem though just the cause. What it does is to overly stress the threaded attachment point on the damper bottom to the point it's subject to rapid fatigue and eventually it will break it off. He atttributed this type of failure to the racing incident he had at Thunderhill and the result was his 26R was damaged severely. He said it did a snap oversteer maneuver while cornering which he could not recover from and the car went sideways and rolled.

Okay, that's good to know! Going to install the swaybar with new dampers and since I'm putting 10k+ miles on my car per year I guess replacing them every two years is prudent. That's about the same time interval for renewing the braking system anyhow.

Thanks Dave!

-Keith
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PostPost by: khamai » Fri Jun 25, 2004 3:22 pm

Hey Keith,

Dave's is totally correct on this. Chapman used the same design on the Europa. The sway bar is "hard" mounted to the A-arm thus forcing the arms of the bar to move in & out (like squeezing or spreading the arms) as the suspension goes thru its travel.

As you can imagine this will stress the studs welded on the bottom of the dampers and they WILL fail. And as Dave points out MUCH more rapidly with a stiffer bar.

On both my Seven (same binding problem) and a Europa, I changed to a stiffer bar with drop links. In both cases I had to go to a stiffer spring (about 15-20%) to remain at the same wheel rate because I lost the "spring rate" of the binding sway bar!

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PostPost by: type26owner » Fri Jun 25, 2004 6:54 pm

Kiyoshi,
Did a finite element analysis on the stiffness between the 11/16" stock swaybar I've got installed now and the 1" one. Turns out the 1" bar is about six times stiffer. Guessing that's way too much and it will introduce a huge amount of understeer. I've changed my mind and have a 13/16" bar on it's way instead which is only twice as stiff as the smaller one.

Geez, even Carroll Smith concedes intuition and guessing is best for dialing in this stuff. Just don't want to be at the track and totally baffled. Great, this means I've got more homework to do. :)

Would love to have my car handle like the Ferraris did in qualifying at Indy. Little wonder they dominate.
Regards,
-Keith
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PostPost by: rgh0 » Sat Jun 26, 2004 12:19 am

Keith

A very experienced suspension tuner who works with the major racing teams here once told me to try spring rate changes in increments of 50% and roll bar changes in increments of 100% as that is about the minimum change that most of us amateur drivers can even feel as significant. He says a lot of professional drivers he works with are not much better at sensing setup changes either!

So going with the 100% step to a 13/16 bar is probably a sensible step. However I feel with sticky tyres and relatively soft springs you may end up wanting to go stiffer again.

Intersting to here DB comments on the risk of breaking off the mounting studs with the stiffer bars, I must ensure I keep a closer eye on this. Incidently I have run my current 22.4 mm ( 7/8) bar for 16 years and about 20,000 racing miles with no problems and only one shock change in that time. My personal preference is that the 7/8 bar is as soft as I would want the roll bar to be with modern sticky tyres and spring rates around the standard to 50% higher levels. But I will be interested to see how your 13/16 bar goes.


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PostPost by: type26owner » Sat Jun 26, 2004 1:42 am

Rohan,
The Sumitomo's would be a real stretch to be described as 'sticky'. Stretching the truth that is. I'd be surprised if it were able to achieve 1g on a skidpad. If I don't get the car perfectly balanced on the first attempt, that's no big deal. Just don't want it to be so far off it's no fun to drive. Thanks for all the help.
-Keith
p.s. Ran the FEA on a 7/8" swaybar and it's about 4 times stiffer then an 11/16" one. I didn't know that size was an option!
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PostPost by: garyeanderson » Sun Jun 27, 2004 1:16 am

I believe the stock bar is 5/8", I have installed an Addco 7/8" bar in front with Dave Bean's recomended "stage 2" springs front and rear on two Elans. The Addco bar is about the largest you can use with the stock links and feels like a very thick wall or solid bar judging by the heft of it. The front springs were 115lb/in x 12" x 2" the rears were 95 lb/in x12" x 2.5". This setup is relatively soft and the front bar seamd OK. I put an estimated 30,000 New England street miles on the S4 and maybe 5000 street miles on the S2 in the same locality without any issues. I am not saying that it isn't a problem, more likely "the luck of the draw" of where things break. The S4 I drove for close to 10 years befor I sold it and still wish that I hadn't.
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PostPost by: type26owner » Tue Jul 06, 2004 1:57 am

The newly installed 13/16" anti-rollbar has helped reduce the total oversteer and the body roll by about half. On left-hand corners I'm fine, stable and neutral. On right-handers there still is to much oversteer and any steering wheel corrections are over exaggerated by it wiggling in yaw. Could be a weight jacking issue. Could still be sidewall flex in the LH rear since it's a LH car. Could be a soft rebound setting in the right side dampers. Could be the left rear bumpstop is to tall or to stiff. Anyone else experience this unequal behavoir before? :wacko:

Already have read all that Fred Puhn and Carroll Smith have to say about this subject. Carroll swears by the usage of properly tuned compliant bumpstops.

-Keith
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PostPost by: rgh0 » Tue Jul 06, 2004 11:27 am

Keith

The drivers weight certainly makes a difference in handling in LH versus RH corners. My Elan is less stable in left hand corners being a right hand drive car. My last 2 spins on the track have both been on high speed left handers and both happened much to quick to catch with sudden oversteer on turn in when I had braked to late and the car had not settled.

This was one of the reasons I wentto stiffer 150# front springs from the 115# ones I had been running.

I would guess your rear LH bump stop may be coming into play a little to early with the extra drivers weight. Reduce the spacers a little or go for stiffer front springs.

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PostPost by: type26owner » Tue Jul 06, 2004 1:50 pm

Rohan,
Thanks, I'm not crazy afterall! According to Fred Puhn it should be possible to cancel out the static unbalance to the wheel vertical loading caused by the driver's seating position. I read that section once and didn't catch on how it's done. It didn't make any sense to me but I'll reread it again. :blink: All my prior suspension tuning experience is on single seaters where the driver is centered and their head is located close to the polar moment.

My one outing so far with my car taught me the importance of not missing the braking point. The lack of anti-dive causes bigtime weight transfer and slow pitch response which makes staying within the traction circle exciting while you're running out of pavement on entry. It's much worse though having it prone to wagging the rear of the car from side to side by about plus or minus four to six inches while in the traction circle and cornering however.

I'm not liking the option of applying heavier springs to it. Not so sure that's the best way to maximize the diameter of the traction circle to suit me. That just seems to me it takes away more of what's left of any nimble comfy ride attributes and turns it into more like a kart.
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-Keith
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PostPost by: type26owner » Wed Jul 07, 2004 2:35 am

According to Fred Puhn it should be possible to cancel out the static unbalance to the wheel vertical loading caused by the driver's seating position

My paraphrasing of Fred's statements was wrong. What Fred says is you can balance the RATIO of front to rear weight when compared from side to side. The driver weight does upset the total balance so all four wheels will have different vertical loads. There must be some ways to apply asymmetrical tweaks to make the traction envelope more circular and larger in diameter. None of literature I've read tells how though. Oh well, time to experiment. :D
-Keith
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