Lotus Elan

14 inch tyres and gearing.

PostPost by: bill griffiths » Mon Nov 23, 2020 11:06 pm

I agonised about getting a 5 speed box during a lengthy rebuild of my Plus 2, but decided against it.
Since the car came with 14 inch minilites fitted with 185/60 tyres as well as a set of original wheels I reasoned that I could adjust RPM per MPH to some extent with tyre sizes.
I am attracted to a set of 14 inch 185/70 CN 36 which with a 3,55 diff will give a little over 60 MPH at 3,000 and make for slightly less frenetic longer journeys.
Your thoughts would be kind.
My previous early Plus 2 was not too quick off the mark, although the new one has a bit more power.
I do not know the fitted first gear ratio, but since the box is a little noisy, longer legs might be better with a lower first gear ratio if available. Problem is to ascertain the ratio I have!
At 3000 RPM first gear presently gives 18 MPH.
Again, help would be most welcomed
Regards,
Bill
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PostPost by: TBG » Mon Nov 23, 2020 11:09 pm

Have you looked at my posts? Fitting a 3:1 CWP with a tourqey engine? Brilliant and a lot less faff..... :shock:
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PostPost by: bill griffiths » Tue Nov 24, 2020 7:37 pm

Thanks, TPG.
The answer is NO!!
Thanks for bringing the thread to my attention. More food fot thought.
Regards,
Bill
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PostPost by: 1owner69Elan » Tue Nov 24, 2020 8:44 pm

Problem is to ascertain the ratio I have!
At 3000 RPM first gear presently gives 18 MPH.


It would appear that you have the standard, semi-close 4-speed. Paired with a 3.55 diff.
First ratio is 2.97
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PostPost by: bill griffiths » Wed Nov 25, 2020 2:04 am

Thanks, Napa. (Beautiful place!) Most obliged.
I found today that my early Plus 2 will not take a 185/70 14 tyre because there is insufficient room in the wheel arch.
The biggest I could fit was 185/65 which did improve things a bit and also gives a better ride compared with the 185/60 tyres fitted to the 14 inch minilites.
I now get a true 20 MPH per 1000 RPM and thus under 3000 RPM at 60 MPH. I find that over 3000 the noise of the engine quickly increases.
Any improvement short of a 5th gear will now have to be by way of a diff, perhaps with a compromise of about 3.5:1, or indeed whatever becomes available for road use of about that order.
3:1 apparently works but may take a lively engine to get the best results.
Now to address engine noise. I think my new car has a larger diameter pipe!
Regards
Bill
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PostPost by: alanr » Wed Nov 25, 2020 9:29 am

This is interesting because I too have deliberated over the 5speed versus diff ratio /wheel size swap and have also concluded a 5speed gearbox conversion for me is a no go.

Just plucking numbers out of the air but wouldn't something like a 3.2:1 or 3.3:1 ratio be a good compromise?
I think TBG got his 3:1 CW&P specially made so obviously not impossible to obtain.

Alan.
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PostPost by: TBG » Wed Nov 25, 2020 10:27 am

Yes I got it made by Northern Tool and Gear in Arbroath Scotland. Gordon made a batch of I think 12 when he made mine so probably still some left. Simply brilliant..................... :D

https://www.ntgear.co.uk/
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PostPost by: elans3 » Wed Nov 25, 2020 11:12 am

Been in touch with Gordon at Northern Tool this morning. He has some left and they are £462 inc VAT and overnight shipping. If I didn't already have a 3.55, it would be a no-brainer. Still contemplating changing it even so.
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PostPost by: elans3 » Wed Nov 25, 2020 12:48 pm

Gordon at NTG has been in touch again.
If three people wanted to order, the price would come down to £415 each.
More than that, the price would come down even further.
Current :- Elan S3 DHC SE S/S 1968,
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PostPost by: alanr » Wed Nov 25, 2020 1:51 pm

The problem for me that TBG is the only one so far who has done the 3:1 ratio conversion and it is great that the outcome has really worked well for him and his car. Good one!
However until a few more have done it and have discovered that it is ok with say just an ordinary torque engine and can additionally confirm in another car that the end result is worth the cost and effort involved then I think I maybe want to sit on the sidelines and watch for while.
In other words I personally don't think I am brave enough to do it ....Yet!

Alan.
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PostPost by: elans3 » Wed Nov 25, 2020 2:30 pm

I know what you mean Alan, however, I can confirm that my S3 with a standard engine copes easily with it's 3.55 AND the close ratio (2.5 : 1 first gear), and I'm confident that it could cope with a 3.1 CWP.
I don't think there would be any problem whatsoever with a semi-close ratio box and standard engine.
Steve
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Elan S3 FHC Pre-Airflow 1966
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PostPost by: alanr » Wed Nov 25, 2020 2:52 pm

Thanks for the reassurances and thoughts Steve.
I will give it some thought....

Alan.
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PostPost by: TBG » Wed Nov 25, 2020 4:58 pm

I get 22mph per 1000 rpm in top. The only slight downside is that in towns with a 20mph limit I am in third. Also in towns with a 30mph limit on a slope I am also in third. Pulling away on hills and so on not a problem. The joy of cruising at 70 - what ever that is! - at under 3500 rpm is a joy. Yes I do have a bit of a tor :shock: :shock: quey engine - 1700 with QED 420 cams and Keith Franks NF tubes.
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PostPost by: billmoore42 » Sun Nov 29, 2020 12:43 am

I have a 67 FHC with donuts, a 3.77 rear, and I believe a standard gearbox. It has a tall block 1700 CC motor with original head and dual Webers, that seems to be quite torquey, and certainly more peppy than my MGB which has a shaved head higher compression engine and headers.

As this is the only Elan I have ever driven, one thing that bugs me is the way I have to feather the clutch when starting out from first at traffic lights, etc. Is this caused by the donuts? Reading the abundant literature online seems to point in this direction, and old Lotus employee Mike Kimberley has been quoted way back as he wanted to get rid of the 'dreadful surge' presumably caused by the rotoflex donuts. Do you recommend this conversion to a 3.1 Diff only be undertaken if the car already has its drivetrain converted from the rotoflex donuts to the flexible axles?

I have contacted Gordon and he has said he will ship the 3.1 gearset to the USA, and have a local shop that is willing to do the conversion. My only hesitation is how my car will perform around town getting away from traffic lights. It would be wonderful if this conversion was driveable around town, as the 5 speed route sounds like a nightmare.
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PostPost by: TBG » Sun Nov 29, 2020 9:04 am

Billmore , I find driving anywhere a breeze with the 3:1. I had to convince a chum that it worked by reversing up and then going up forwards on a VERY steep hill. No problem but a bit of clutch slip like I had to use before conversion.
I do have solid drive shafts with four CV joints. :D
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