Lotus Elan

Anti Roll Bar Diameter

PostPost by: ivan.wood » Fri Apr 24, 2020 9:45 pm

I am restoring a 1965 Elan S2 and I bought new superflex Anti Roll Bar bushings from the UK some time ago and I got around to fitting them today but the drop links are loose on the ARB, where as I expected them to be tight. I checked Brian Buckland's restoration manual and he said the ARB is 11/16" dia but mine is only 5/8" so was there a change made to the design at some point? I know people have used thicker ARB for racing etc but mine is a stock car that was in storage for many years.

Can anyone enlighten me as to why this has occurred and can I get bushings to fit the smaller diameter ARB?

Thanks

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PostPost by: benymazz » Sat Apr 25, 2020 11:29 pm

My S2 has a 5/8” bar as well and this is the stock diameter, I think. I also think that the 5/8 and 11/16 ARB bushings are interchangeable - perhaps you got a bushing for a 3/4” diameter bar (which was standard on the Plus 2 I believe)? Could be wrong on all of this.

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PostPost by: ivan.wood » Sun Apr 26, 2020 1:47 am

It appears that there were both 5/8” dia and 11/16” ARB in use as well as 3/4” on later models.
RD Enterprise have 3 sizes listed and it appears the 5/8 and 11/16 have the same OD and profile but different ID. May be some earlier models had the smaller diameter but mine is a 65 S2?

Good old Colin just cause more confusion.

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PostPost by: rgh0 » Sun Apr 26, 2020 3:53 am

I think all Elans came with 5/8 inch roll bars ( my S4 did) and all Plus 2 came with 11/16 inch roll bars ( my 73 Plus 2S 130/5 did). People may stock 3/4 inch bushings to suit larger diameter bars but i don't these were standard on either the Elan or Plus 2, maybe on the 26R ?

The Elan parts manual only lists one bar and bushes for the Elan for all models. I would guess you have bushes for a Plus 2.

But with all things Lotus when it comes down to what was fitted to what models when there is lots of variation and debate so I could be wrong :D

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PostPost by: 661 » Sun Apr 26, 2020 9:33 am

For the record, TTR 's 26R ARBs are 22mm and 25mm.
Raceworks run a car on 32mm!
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PostPost by: rgh0 » Sun Apr 26, 2020 10:57 am

661 wrote:For the record, TTR 's 26R ARBs are 22mm and 25mm.
Raceworks run a car on 32mm!


I use a 22 mm bar on my Elan. if you go above this you can break the studs off the bottom of the shocks and you would probably crack the chassis mounts. You need to think about a different roll bar connection system but I dont know what TTR and others do for their and 25mm bigger bars for their roller skate racers as never been tempted to go that hard on the suspension.

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PostPost by: 661 » Sun Apr 26, 2020 12:20 pm

Rohan, marginally off topic, but once you've corner weighted the car, how do you allow for the slight differences in the front heights side to side if the ARB doesn't have at least one adjustable drop link? Or do you just get on with it :)
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PostPost by: alanr » Sun Apr 26, 2020 12:31 pm

My +2 has been fitted by a previous owner with a 1inch bar that Kelvedon sell. This is a tubular anti roll bar, not solid. I assume the thinner bars being talked 11/16ths etc are solid and not tube?
On the road my car doesn't feel unduly stiff at alll but then again I don't know what it would feel like when it left the factory with the standard bar.
Link to the Kelvedon uprated bar:-
https://kelvedonlotus.co.uk/product/fro ... ar-1-inch/

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PostPost by: ivan.wood » Sun Apr 26, 2020 4:59 pm

May be a larger diameter tubular ARB has the same torsional rigidity as a solid one for less weight? Just a thought no scientific evidence to back it up.

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PostPost by: benymazz » Sun Apr 26, 2020 5:32 pm

ivan.wood wrote:May be a larger diameter tubular ARB has the same torsional rigidity as a solid one for less weight? Just a thought no scientific evidence to back it up.

Ivan


Ivan,

You’re correct. Has to do with polar moment of inertia (the resistance of something to deformation due to torsion). The polar moment of inertia of a shaft is I believe proportional to the 4th power of the radial location of the shaft material. In laymans terms, the farther away the metal is from the axis of rotation/torsion, the more work it does to prevent twisting.

This is the same reason that driveshafts (propshafts in the UK) are hollow and not solid. For a given mass, a hollow shaft will be able to transmit more torque, but will take up more space. Axle shafts are more likely to be solid because for a given diameter, a solid shaft will be stronger (but heavier).

If one knew the wall thickness of the 1-inch tubular ARB they could calculate the torsional stiffness of it and compare it to the original solid bar.

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PostPost by: ecamiel » Sun Apr 26, 2020 5:51 pm

On all thick roll bars, you must enlarge and seriously radius and relieve the stud holes or you will break the studs off. I have run a 1-inch solid bar in front with Bean full race stiff springs and an adjustable rear bar with no issues. The reliefs are a necessity. If you test with no springs and only one attached, the need for chamfering the holes becomes apparent.

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PostPost by: 1owner69Elan » Sun Apr 26, 2020 5:53 pm

Previous discussion on tubular ARB’s:


viewtopic.php?f=42&t=42472&p=301185&hilit=+Tubular#p301185
A8814CD2-606C-41DA-801A-2334C66B1E29.jpeg and
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PostPost by: 661 » Tue Apr 28, 2020 6:59 am

ecamiel wrote:On all thick roll bars, you must enlarge and seriously radius and relieve the stud holes or you will break the studs off. I have run a 1-inch solid bar in front with Bean full race stiff springs and an adjustable rear bar with no issues. The reliefs are a necessity. If you test with no springs and only one attached, the need for chamfering the holes becomes apparent.

Eric
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Forgive me Eric, are you talking about the hole on the arb that goes over the lower shock stud?
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PostPost by: 2cams70 » Tue Apr 28, 2020 8:59 am

Car manufacturers sometimes adjust the suspension settings to tailor the handling characteristics to what is preferred in different countries. Perhaps they specified the Elan with a bigger antiroll bar at the front for the American market to give the car more understeer!
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PostPost by: ivan.wood » Tue Apr 28, 2020 10:41 am

It might be the other way around since my car was originally sold in Virginia and has a 5/8” bar. Brian Buckland in his manual (he presumably is referring to the UK) said it is 11/16”.

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