Lotus Elan

Plus 2 tire pressure

PostPost by: Lotus 50 » Wed Apr 15, 2020 9:05 pm

What tire pressure is appropriate? Street use? Track day? ( unlikely but I would like to try it again)

185/70-13 Sprint Classics from Vredestein
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PostPost by: JJ66 » Wed Apr 15, 2020 10:06 pm

Great question, as a new +2 owner I was about to ask the same thing! My car has been laid up for two years and so needs some subtle re-commissioning, however, the tyres were 25 years old (!!!!) and so for sure needed changing. I have bought Dunlop SP Aquajets in order to maintain the classic look of the car. I have set the pressures as 26 psi rear and 22 psi front. The car seems to handle well, but I note that the original workshop manual states 24 psi for the rear and 20 psi for the front, so I may try dropping the pressures a little and see what the difference is. Looking forward to hearing other comments and experience.
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PostPost by: JonB » Thu Apr 16, 2020 12:12 pm

My experience on a late +2 with modern tyres was that steering became vague if the fronts were over inflated. Try 20/24 and see how it feels.
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PostPost by: JJ66 » Thu Apr 16, 2020 1:58 pm

Thanks Jon, my steering is a little on the vague side so I will definitely be dropping pressures to see how that affects the car. Its a little vague on the rear as well, it tries to oversteer very early when turning in, so I'm planning a thorough geometry check. Thank, Jonathan
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PostPost by: JonB » Thu Apr 16, 2020 6:56 pm

I have a strong sense of deja vu.... :lol:

You’ll get a 4 wheel alignment check and discover all sorts of out of boundary measurements. Then you will realise you can only adjust front toe in. Then you will start changing bushes. Finally something you do will make it feel OK but you won’t be sure what that was..

Been there, done that, got the tee shirt. :roll:
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PostPost by: JJ66 » Thu Apr 16, 2020 7:31 pm

Haha, I'm sure you're right. After having a few TVR's I was considering modifying the suspension arms to have left/right hand thread adjusters on the leading edge as TVR's do, I would be able to tune it a bit then, but I'll go through bushes and shocks first, these seem quite old.... I've dropped the tyre pressures tonight so will see how it feels on my journey to the office tomorrow (2 miles....).
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PostPost by: Lotus 50 » Fri Apr 17, 2020 1:17 pm

20/24 is very low by modern standards. I have been running 28 front and rear, but had been considering going higher.

I did a quick Google search and found sites that recommend increasing tire pressure to improve response, but not the reverse.
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PostPost by: vincereynard » Fri Apr 17, 2020 1:24 pm

JJ66 wrote:modifying the suspension arms to have left/right hand thread adjusters on the leading edge as TVR's do,


Most (far as I know) are modified by having the adjusters on the trailing edge.

RACERWB1.jpg and


Toad's tyres pressures are 22 / 25 (ish) if it is any help. 175 / 70 Uniroyal Raintyres.
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PostPost by: JJ66 » Fri Apr 17, 2020 1:34 pm

Hi Vince, Thanks for the post, that's interesting. I believe that the reason for adding the adjusters to the leading is so that they are always in tension. Interrupting the trailing side of the arm with an adjuster or similar part may give rise to uneven forces distributed along the length and when under compression this may promote buckling or bending. On the leading edge any force taken when the wheel hits a vertical edge (and tries to knock the wheel backwards) will only result in tension which may be more predictable for the interrupted side of the arm.

That said, the Elan lower arms, relative to the mass of the car, look quite robust and the triangulated section, of which the adjuster shown below is part of, will be pretty strong. I am new to Elan's and so had not seen what was out there, but the lower arms on other cars (like Cerbera/Chimaera) have them on the leading edge. Either way, it would be nice to have some adjustment so I'll continue to study and see whats out there - Thanks a lot for highlighting the below parts from KelSport, I'll take a look! Regards, Jonathan
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PostPost by: alan.barker » Fri Apr 17, 2020 2:28 pm

JonB wrote:My experience on a late +2 with modern tyres was that steering became vague if the fronts were over inflated. Try 20/24 and see how it feels.

Are you saying 20 at the back and 24 front :?
That's the opposite to Lotus which is higher figure at the back :?
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PostPost by: Quart Meg Miles » Fri Apr 17, 2020 3:02 pm

alan.barker wrote:
JonB wrote:My experience on a late +2 with modern tyres was that steering became vague if the fronts were over inflated. Try 20/24 and see how it feels.

Are you saying 20 at the back and 24 front :?
That's the opposite to Lotus which is higher figure at the back :?
Alan

Alan, one conventionally quotes front/back for tyre pressures.
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PostPost by: vincereynard » Fri Apr 17, 2020 3:08 pm

JJ66 wrote:Hi Vince, Thanks for the post, that's interesting. I believe that the reason for adding the adjusters to the leading is so that they are always in tension. Interrupting the trailing side of the arm with an adjuster or similar part may give rise to uneven forces distributed along the length and when under compression this may promote buckling or bending. On the leading edge any force taken when the wheel hits a vertical edge (and tries to knock the wheel backwards) will only result in tension which may be more predictable for the interrupted side of the arm.
Jonathan


How about braking and acceleration? Surely the front must be under compression as some point? I had a pair from Spyder that I have taken off my car as I also think its a poor design effectively bending the wishbone. Having said that many are used in competition without a problem.

Ironically, mentioning TVR, I was intending to make something very similare for Toad.
I take it the adjustment is with 1 and it is locked with 2?
1155 Apr. 17 15.58.jpg and
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PostPost by: JonB » Fri Apr 17, 2020 3:12 pm

Thanks, Meg. Thus, no need for me to protest that I am not as thick as Alan thinks.

Oops, just did... :lol:

Vince, that adjuster will stress both bushes won't it? And would put the two bolts out of line. Face it, there is no way to win here without rose joints. Fortunately the amount of adjustment needed is generally tiny so the Spyder or KelSport designs ought to be enough.

And what about that slot in the upper arm? Are we relying on clamping force to maintain adjustment?
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PostPost by: alan.barker » Fri Apr 17, 2020 3:23 pm

Hi Jon,
no problem. I was just following "JJ66" in above post and his order :wink: :wink:
Talking about Tyre pressures i usually pump in an extra 2 psi and like the Steering not too heavy.
I must admit i'm running my 1976 TVR 3000M on 2 Bar :shock: with 205/70 Tyres.
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PostPost by: JJ66 » Fri Apr 17, 2020 3:31 pm

Hi Vince, If you think about it the front, or leading edge, of the lower arm will only see heavy compression when you hit a bump/kerb going back wards. Yes, the leading edge will be under compression during acceleration but these forces are much less (factor of 8-10?) than those given by braking or by hitting a pot hole (of which we have many!) in the road.

Is the exploded view from a 3000M/Taimar? I haven't seen that kind of adjuster before, the ones on the later TVR's were a RH/LH thread close to the pivot point. I can;t quite work out what item 1 is in the view attached. Cheers, Jonathan
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