Lotus Elan

Straight line stability

PostPost by: vincereynard » Fri Aug 28, 2015 10:44 pm

Through discussion with various chaps who have dealt with the +2 for decades the general concensus
seems to be that it is unsuitable for motorway journeys, especially in 4 speed form, because it is very twitchy in side winds. Reason being the flat underside apparently.

Now, I would be the first to admit , that they have forgotten more than i know, however, not to beat about the bush, or fiddle faddle about, to come right out plain - that makes little sense to me!

The early cars were often praised for they excellent straight line stability, it was the later ones that seemed to have the problem. The later ones also seemed higher at the front. Could this be a clue? I do seem to remember an American road test that showed quite a strong front end aerodynamic lift. Perhaps the angle of the body is quite critical. Is it more twitchy with weight in the boot?

I once owned a Rochdale Olympic that was very flat underneath. In fact the whole car was a bit wing shaped! I fitted a small bib spoiler under the nose and I cannot remember stability being an particular problem.

So what are the experiences of members?
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PostPost by: rgh0 » Fri Aug 28, 2015 11:10 pm

My Plus 2 is stable in cross winds and high speed cruising. I run it relatively low as I use 175/60 x 13 tyres so the car is low compared to photos of many cars I have seen

The only time I find some directional instability is that it responds to depressions in the roadway made by heavy trucks to some degree if they are present or to off camber situations when it wants to run down the camber. The track day style tyres I use are sensitive to these situations I find.

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PostPost by: stugilmour » Sat Aug 29, 2015 12:59 am

My experience is pretty much the same as Rohan's. I used to run similar tires, but like the car better using the stock 80 profile size.

I did have directional stability issues when the rear was not at correct toe-in. I have adjustable wishbones from Spyder, so it was just a matter of getting it st up correctly, which for some reason took a couple of tries.

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PostPost by: vincereynard » Sat Aug 29, 2015 10:53 am

That's for that.

So the consensus is that there is nothing fundamentally wrong with the shape.

When, or if ever, I manage to get my hands on a +2 I shall probably experiment a bit.

Such as, purist alert, duct the rad properly, change the air cleaner and maybe get another bonnet that I can experiment on.

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PostPost by: john.p.clegg » Sat Aug 29, 2015 1:11 pm

Vince

or fit a splitter...

spltteri08.JPG and


splitter0010.JPG and



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PostPost by: vincereynard » Sat Aug 29, 2015 10:48 pm

mrjxc09 wrote:Vince

or fit a splitter...

John :wink:


That Sir is exactly what I had in mind! A small bib spoiler or splinter just under the air intake.

Did you make it yourself or is it a bought in object?

And A PIT! I am green.

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PostPost by: john.p.clegg » Sun Aug 30, 2015 6:24 am

The "splitter" is a home made stainless item,one day when there was nothing else on the list,as for the pit,that has been a long story,not only water but methane and the local H&S wanting to evacuate the area...
The splitter fits with just 4 self tappers,two of which are the number plate fixing screws and as for it's effectiveness...no noticeable difference...well not enough to keep it on.

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PostPost by: Andy8421 » Sun Aug 30, 2015 7:53 am

mrjxc09 wrote:The "splitter" is a home made stainless item,one day when there was nothing else on the list,as for the pit,that has been a long story,not only water but methane and the local H&S wanting to evacuate the area...
The splitter fits with just 4 self tappers,two of which are the number plate fixing screws and as for it's effectiveness...no noticeable difference...well not enough to keep it on.

John :wink:

Splitter works by creating a pressure differential above and below the splitter plate. The air above the splitter stalls and creates an area of high pressure, the area beneath the splitter is usually the fast moving entry to the low pressure under floor area and at a much lower pressure to the air above the splitter. The area of high pressure air above the splitter exerts a downward force, pushing the splitter down. If it had been working, I am afraid it would have ripped off the 4 self tappers. Probably a good job that it didn't.
Searching the web you can find splitters that have rose jointed bracing bars to the front edge to transfer the downforce to the body. If you were trying to control the flow of air under the car (which is not a bad thing) you would need an airdam, not a splitter.
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PostPost by: Andy8421 » Sun Aug 30, 2015 8:17 am

vincereynard wrote:Through discussion with various chaps who have dealt with the +2 for decades the general concensus
seems to be that it is unsuitable for motorway journeys, especially in 4 speed form, because it is very twitchy in side winds. Reason being the flat underside apparently.

Now, I would be the first to admit , that they have forgotten more than i know, however, not to beat about the bush, or fiddle faddle about, to come right out plain - that makes little sense to me!

The early cars were often praised for they excellent straight line stability, it was the later ones that seemed to have the problem. The later ones also seemed higher at the front. Could this be a clue? I do seem to remember an American road test that showed quite a strong front end aerodynamic lift. Perhaps the angle of the body is quite critical. Is it more twitchy with weight in the boot?

I once owned a Rochdale Olympic that was very flat underneath. In fact the whole car was a bit wing shaped! I fitted a small bib spoiler under the nose and I cannot remember stability being an particular problem.

So what are the experiences of members?

A flat floor is generally a good thing if you can limit the air flowing under the car. The floor tray of the Elise is almost completely flat, the engine compartment is deliberately enclosed to encourage laminar flow of air under the car. Apparently (I have never seen a decent analysis), the combination of flat floor, rear wing, airdam and rear diffuser on the Elise actually creates net downforce at speed. Most cars generate lift at speed.
In comparison, my Elan generates significant lift. In profile, the shape looks like a wing, and the rounded front edge directs air under the car. Flat out on the Lavant straight at Goodwood the front gets extremely light and very unpredictable. At first sight, I would have thought that a decent air dam under the front of an Elan would make a significant difference to lift at high speed. It would need to significantly reduce the airflow under the car, so would need to reduce the gap between the front of the car and the road. It would need to run from wheel to wheel to work. As a result, it would be extremely ugly. Something like this: (not an Elan, but you get the point)

http://i.ebayimg.com/00/s/OTQ4WDE2MDA=/ ... 880000500F
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PostPost by: jimj » Sun Aug 30, 2015 8:56 am

I don`t know about +2s but, certainly, in an Elan I`ve always found the car to feel sort of nervous above around 70mph and, as Rohan says, especially if the road is uneven. German autobahns are bad for this where the tarmac is depressed into 2 ruts where the heavy lorries run, and their track is rather wider than the Elan. More than a handful of times I`ve suspected a puncture when there was none.
I`m not convinced it`s an aero problem, I think it`s because the Elan steering is so precise you`re not inclined to hold the wheel loosely, relax and let the car run. In other cars from the 60s, especially Healeys, and more so on older cars with imprecise steering you have to this. It works for me.
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PostPost by: gav » Sun Aug 30, 2015 3:48 pm

A timely debate - I noticed my sprint tends to go light between 75 and 80 which can be a little disconcerting.

I was thinking about a bib but was struggling to come up with anything that didn't destroy the elegant lines.

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PostPost by: Mazzini » Sun Aug 30, 2015 7:01 pm

jimj wrote:I don`t know about +2s but, certainly, in an Elan I`ve always found the car to feel sort of nervous above around 70mph and, as Rohan says, especially if the road is uneven. German autobahns are bad for this where the tarmac is depressed into 2 ruts where the heavy lorries run, and their track is rather wider than the Elan. More than a handful of times I`ve suspected a puncture when there was none.
I`m not convinced it`s an aero problem, I think it`s because the Elan steering is so precise you`re not inclined to hold the wheel loosely, relax and let the car run. In other cars from the 60s, especially Healeys, and more so on older cars with imprecise steering you have to this. It works for me.
Jim


Absolutely agreed!!!! I've had my cars laser aligned and corner weighed.
Last edited by Mazzini on Sun Aug 30, 2015 7:15 pm, edited 1 time in total.
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PostPost by: Spyder fan » Sun Aug 30, 2015 7:06 pm

The splitter is the way to go if you experience high speed lift or instability. The Europa spoiler can be cut down and fitted to the Elan or fitted as is with a little fettling to the +2.

My S4 is rock solid at German motorway speeds and it has the Europa spoiler suitably cut and shut. 185bhp and a high 5th gear equal a cruise speed of 100mph at less than 4500 rpm. The only problem is the wig buffeting, luckily my wig is original and anchored correctly in my scalp via the follicles.
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PostPost by: Mazzini » Sun Aug 30, 2015 7:20 pm

Spyder fan wrote:The splitter is the way to go if you experience high speed lift or instability. The Europa spoiler can be cut down and fitted to the Elan or fitted as is with a little fettling to the +2.

My S4 is rock solid at German motorway speeds and it has the Europa spoiler suitably cut and shut. 185bhp and a high 5th gear equal a cruise speed of 100mph at less than 4500 rpm. The only problem is the wig buffeting, luckily my wig is original and anchored correctly in my scalp via the follicles.


Sounds lower geared than a modern Elise S?
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PostPost by: Spyder fan » Sun Aug 30, 2015 7:35 pm

Mazzini wrote:
Spyder fan wrote:The splitter is the way to go if you experience high speed lift or instability. The Europa spoiler can be cut down and fitted to the Elan or fitted as is with a little fettling to the +2.

My S4 is rock solid at German motorway speeds and it has the Europa spoiler suitably cut and shut. 185bhp and a high 5th gear equal a cruise speed of 100mph at less than 4500 rpm. The only problem is the wig buffeting, luckily my wig is original and anchored correctly in my scalp via the follicles.


Sounds lower geared than a modern Elise S?


Probably a good thing :mrgreen: it's not built for high speed motorway work, more a point to point machine on British A roads. But it does okay on the motorways and is easy to live with.
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