Lotus Elan

Is Corner Weighting Effective on Standard S4 DHC?

PostPost by: jbeach » Thu Apr 12, 2018 3:26 pm

Dear Elan Community:

If my brake bleeding goes as planned, my '69 DHC should be back on the road this Sunday. While I still have many projects (dash replacement, window mechanism fettling, windshield gasket replacement, etc. etc.), I've now completely replaced and/or refurbished front and rear suspension and braking system, added modern, aluminum radiator, dual "puller" cooling fans, stainless exhaust, Vredestein Sprint +, Panasports, CV driveshafts, and a few other things. If I've done everything correctly, I should have an as-new driving experience. Needless to say, I'm very excited.

I'll be posting reviews on all of the components I've purchased from the various suppliers as I experience them.

So, one thing I've done is replace my standard suspension with a TTR fast road setup that is height (and damping)-adjustable front and rear. On another post one of our forum members rhetorically asked whether the standard Elan frame/body setup is torsionally-stiff enough to react to efforts at corner-weighting. I'm not an engineer, but it does make intuitive sense to me that a more torsionally-stiff frame/body structure would be more sensitive to changes in corner-weight caused by adjustments to each corner's suspension height than a less torsionally stiff structure. On the other hand, the Elan is so ultra-sensitive to driver input, it seems to me corner weighting, if effective, would be a very worthwhile method of fine-tuning its handling.

So the question I'm posing is this: Is the standard Elan DHC body/frame structure torsionally stiff enough for corner height-adjustments to effectively equalize corner weights? Do such efforts make a material difference in the Elan's handling?

I will value everyone's input on this, but am particularly interesting in hearing from members who have actually utilized (or attempted to utilize) corner height adjustments toward equalizing corner weights, preferably on a DHC with a standard frame.

Many thanks!

-John
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PostPost by: nmauduit » Thu Apr 12, 2018 4:19 pm

In my eye the first order goal for corner weight adjustment is exactly what it says: make sure the weight is adequately distributed on each wheel, statically - esp. with adjustable perches and stiffer springs, it is very well possible to have a setup that would be worse than a non adjustable setup (e.g. to illustrate the point, if a spring is somehow set such that the corresponding wheel is barely liftting the car, and as a result holding a lot less than it should).

That while cornering the frame may twist and alter the geometry of a previously well balanced car is an other matter, which takes pushing the car to its limits to fully grasp I believe, and the total effect would be less (the frame is not bubble gum after all) and symetrical.
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PostPost by: elancoupe » Fri Apr 13, 2018 1:07 am

I would highly recommend corner weighting for an Elan with adjustable shocks. I have such a setup on my car, and tried to be fastidious about getting it set right. I was still unhappy with how the car sat, and knew it wasn't quite right. I had the car alined and corner weighted by someone who is a professional Elan race mechanic, and he allowed me to assist.

The weighting was pretty far off to start, but the alinement was good outside of a caster adjustment on one side. The fact that my car is RHD, which means the driver and the gas tank are on the same side, made a perfect result not attainable. However, the improvement was significant, the car sits, drives and handle fantastically. It was worth every penny.

This on a car with TTR chassis, cv joints, TTR fast road shocks and all adjustable arms.
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PostPost by: rgh0 » Fri Apr 13, 2018 12:34 pm

The softness of a standard Elan suspension is such that provided the ride height is reasonably even and no sag in an individual spring then the cars corner weights will be OK. It also means that the chassis is stiff compared to the suspension so chassis stiffness is good and not an issue

When you go to a competition Elan running 400 lb/in front springs and 200 lbs/in rear springs and big front bar and maybe rear bar also then the question changes. A small difference in suspension setting on one corner makes a big difference in load on all the wheels so corner weighting is more critical. The chassis is also much more flexible compared to the much stiffer suspension so chassis flex starts to play a much bigger picture in the overall handling setup.

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PostPost by: prezoom » Fri Apr 13, 2018 3:50 pm

Corner weighting a street car to get it close is a good idea, if you have fully adjustable suspension. However, from that point, any little change in weight will make a significant change from the original setup. As an example, on a race car, it must be done with the driver onboard, they must be wearing the exact gear that they are going to use in competition. That includes the helmet. Just moving ones arms from the driving position to shift gears, not having the helmut on the head, or just tilting one's head, will change the measurements. Of course fuel and other liquids, including drinking water, will also make a change. On the race cars, we used to set up with half the amount of fuel we would normally use in a session. Our goal was to try to get within 3 pounds of cross weight on a car with a minimum weight of 1680 pounds including driver. I corner weighted my S2 when I first finished the car. Have not checked it in the past 12 years and I am still happy with the way the car handles. Have yet to corner weight the Plus2, as I have sold my scales and platform, but still have access to them. One of these days I will get a roundtoit.
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PostPost by: jbeach » Fri Apr 13, 2018 4:15 pm

This is very helpful, everyone!

So I?ll borrow some scales and use my adjustments to get it close, understanding that changes like passenger weight, fuel load, luggage in the trunk, etc., will make it impossible to get things perfect in all circumstances.

REALLY looking forward to the experience of driving a well-sorted Elan!

-John
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PostPost by: 69S4 » Fri Apr 13, 2018 4:32 pm

If your focus is on the track I can see how setting the corners up might make easy horsepower but for cars just used on the road I wonder if getting it right to the nearest few (or 20) kg is going to make much difference. Getting the simpler stuff right first - tyre pressures, wheel balance, front and rear toe, ride heights, bump steer, spring rates, damper settings etc would get a road car pretty close. I would have thought you'd have to be "making progress" considerably in excess of the speed limits before slight errors in corner weights would be noticeable.
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PostPost by: ceejay » Thu Apr 19, 2018 8:03 am

Corner weighting the elan is something that you may do once or twice, a race car maybe a a little more.
This is something that always intrigued me, so I decided to build my own, which I show in the photos below.
With corner weighting, you don't have to weigh in an actual measurable load weight.


The corner weight tool is something to check (Compare) spring load from the rear to the diagonal oppisite front wheel. The gauge on this C/W tool reads in PSI and Kpa.... notes were made of each corner reading, adjustments were made via the adjustable spring platforms mainly on the rear until corner weight readings were within 10%, for a road car you wont get it much closer than that... and there's no need to, a race car, may be you will get it closer.

Anyway, this is not a lesson on the how to of corner weighting, Fred Puhn does a great job explaining the science, as does Carroll Smith in "Prepare To Win".

Is it worth all the trouble - Yes - As long as you have adjustable spring perches both front and rear.
(Don't forget to disconnect the ARB front and rear if fitted)

So this was my little DIY Corner weight project.
See a couple of photos below. This tool is ultra quick, and very easy to use while checking corner weights on the elan or any other light car.

Oh, you might be wondering what the slider plate is under the wheel? That tool is used to feel when the tyre just loses contact with the plate, at that point you note the reading on the pressure gauge, that's how it works.
But always do a bench mark reading so that you know what it was before you "started to fiddle".

This design of C/W gauge is what a friend of mine employed when checking the corner weights on his open wheeler formula car... and well, at the time, I kind of sketched out and took the dims of all of the parts, thinking I might build a corner weight gauge one day...Thirty years down the road that's what happened.
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2-cw-gauge.jpg and
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