Lotus Elan

Fast road springs

PostPost by: miked » Mon May 09, 2016 10:22 am

I am talking about modified rear struts with small springs deemed as "fast road".
Is it me or do some of these springs seem weak? You fit them and they sag, you adjust them again and again. You put some fuel in and a passenger and they really sink. I have experienced this now on three different cars. I will check the poundage with the supplier and post. Also any new recommendations from them.
Last night I was comparing (subjective I know) an S4 back end (with the fast road set up) against an unmodified Sprint with the big old springs. Considering that the the fast road are meant to be up rated against normal they do not feel it, at all. I can sink the back end of the S4 with ease. Yes, subjective and not very scientific. I know that adding weight will naturally sink a car. My Plus 2 starts quite high at the rear and goes down but in a progressive manner that gets firmer (as you would expect).

Whilst I don't want to spoil the ride I am going to look at fresh springs. The front is also questionable but not as bad. I have had to keep making adjustments to those as well. Is this just me or are there others that struggle with rear ground clearance because of this and lack of confidence in these spring. Any suggestions welcome as I don't know much about this subject.

Rohan, I read your old posting last night about your set up but assume that it was your track Elan settings.
Interesting about the 2 x 15 mm spacers for the bump stops. I have the alloy spacers for the Plus 2 ( and that does sit on them nice) but did not realise that you had done them on your Elan. I think I need to look there also. What would poundage would you say for fast road. I saw 115 F and 95 R. Would that be it?

Mike :)
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PostPost by: rgh0 » Mon May 09, 2016 11:46 am

Hi Mike

I would consider around 115F / 95R lb/inch to be the bottom end of the fast road spec for someone using modern higher profile tyres tyres who does not want to affect ride to much. The top end of the fast road spec ( and soft end of race spec) I would consider around 150F / 110R lb/inch for some one using track day tyres ( eg yoko A050R 60 profile ) and who does not worry about ride comfort to much compared to handling. How hard in suspension you go also depends on how good the roads are you drive on. At the top end of the range a significant mid corner bump will throw you more offline than with the softer setting.

In addition to spring rates you need to consider front roll bar stiffness and the rear Aeon rubber springs.
I am a fan of using a stiff front bar - I used a 22mm / 7/8th inch bar with the soft fast road spec with good results.

The rear outside of an Elan can sit down in a corner as it rolls leading to a sudden over-steer transition which can be hard to handle. Retaining the original Aeon springs and adding the Plus 2 style spacer helps prevent this. This is especially important if the car is heavily load I think. With most narrow springs you cant fit the original Aeon rubber springs and some people discard them. There is a VW / Audi rubber spring that fits and I have read it is similar in rate to the orignal though I have never see this in practice.

A very experienced suspension engineer i used to race against ( he was a very very quick and way above my class :D ) who worked for the Koni distributor in Australia once told me that most people ( even top racing drivers) cant tell a difference in spring rates of less than 50%. So you really have two steps from standard - the low end of fast road and top end as you will struggle to feel the difference in between

cheers
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PostPost by: vincereynard » Mon May 09, 2016 2:07 pm

rgh0 wrote:Hi Mike

A very experienced suspension engineer i used to race against ( he was a very very quick and way above my class :D ) who worked for the Koni distributor in Australia once told me that most people ( even top racing drivers) cant tell a difference in spring rates of less than 50%. So you really have two steps from standard - the low end of fast road and top end as you will struggle to feel the difference in between

cheers
Rohan


A good aquaintence of mine was a competition development engineer for Jaguar. He told a story concerning Graham Hill, who always wanted stiffer dampers on the front of his E type. The solution was to take a new pair, paint them red, tell him they were special experimental dampers. He was then a happy chap and expressed them a great improvement. Allegedly.
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PostPost by: holywood3645 » Mon May 09, 2016 5:26 pm

I always thought the 'Aeon rubber springs' as just bump stops that would cushion hard bottoming. Are these the same?
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PostPost by: rgh0 » Mon May 09, 2016 8:41 pm

holywood3645 wrote:I always thought the 'Aeon rubber springs' as just bump stops that would cushion hard bottoming. Are these the same?
James


They are more than just bump stops. The form part of a progressive rate spring system for the rear suspension.

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PostPost by: seniorchristo » Mon May 09, 2016 9:50 pm

Hi Miked
I am considering a "fast road " setup from TTR which I believe is 125 lb. front 100 lb. rear. TTR wouldn't be the supplier of your springs would they? Has anyone experience, good or bad, with the TTR fast road and/or maximum comfort (115 lb. front - 100 lb. rear) spring/shock set up?
Regards, :)
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PostPost by: elancoupe » Tue May 10, 2016 1:34 am

seniorchristo wrote:Hi Miked
I am considering a "fast road " setup from TTR which I believe is 125 lb. front 100 lb. rear. TTR wouldn't be the supplier of your springs would they? Has anyone experience, good or bad, with the TTR fast road and/or maximum comfort (115 lb. front - 100 lb. rear) spring/shock set up?
Regards, :)
Chris


I have the TTR fast road setup on my car, can't say enough good things, I highly recommend it.
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PostPost by: miked » Tue May 10, 2016 8:47 pm

Sorry for late reply. Granddad time.

Thanks Rohan for your detailed answer. I found out that the rears could be 80LB and front 120. They are from Tony but way back maybe 18 - 20 years. Back then they supplied 80 LB for the rear. I talked with Stuart there yesterday and he now supplies 100 Rear and 125 Front. They used to be 120 front but were difficult to fit due to there length. The new 125 are shorter. I need to pull the back end apart and look. I did not just want to jack them up again.
I will check the roll bar thickness as I don't think this was uprated but could be wrong. I will see if I can find out anything about the VW/Audi rubber springs. I think I have two spare alloy Plus 2 blocks in the garage. It would be good to sort out the bump stop issue. I understand where you are coming from re the progression. With the Plus 2 you can feel the car on them through the bends and a kind of seamless transition as you lean in which always impresses me considering it is a very standard car.

Cheers Rohan and thanks again.

Vince, good tale about Graham Hill. I had heard that he liked his car rock hard. :D
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PostPost by: jbeach » Tue May 10, 2016 9:07 pm

Mike,

I have a set of Tony Thompson adjustable shocks to install on my front suspension, but don't know the spring rate. Can anyone give me a way to tell by looking at them what the spring rates are?

Many thanks!

John
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PostPost by: miked » Wed May 11, 2016 6:41 am

Hi John, it is etched into one end of the coil generally so they have to be off in your hand to see the etching. Mike
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PostPost by: rgh0 » Wed May 11, 2016 9:42 am

From the coil diameter, wire diameter and number of coils you can calculate the spring rate. The are a number of calculators on the internet to do this if you google "spring rate calculator".

regards
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PostPost by: msd1107 » Wed May 11, 2016 2:33 pm

When our Elan's were new, tire technology would give a cornering ability of maybe .7-.8g. Modern sticky tires will go well over 1.0g. This causes the car to roll more, and requires corrective action.

So, in addition to upgrading springs to "fast road specification", the roll bars need upgrading also.

This is relatively easy for the front, since different diameter front roll bars have been available for years. Upgrading the front then normally requires adding a rear roll bar to balance the handling.

Also, more roll stiffness keeps the engine more upright during cornering, keeping at bay the sickening decrease in oil pressure at high g loads.

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PostPost by: Davidb » Wed May 11, 2016 6:27 pm

This is the VW bump rubber that I have fitted to the rear shocks of my Elan - but it is not on the road yet:
http://www.ebay.com/itm/Porsche-924-944 ... 0C&vxp=mtr

While they look like steering rack boots in the photo I can assure you they are quite stiff!

Perhaps Rohan can comment if these are what he had in mind?
p1060122.jpg and
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PostPost by: rgh0 » Wed May 11, 2016 8:33 pm

Yes that was the ones I had seen referred to.
The original Aeon rubber springs had a spring rate of about 50 lbs/ inch rising to double that after about 1 inch of travel so you want something similar

cheers
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PostPost by: jbeach » Thu May 12, 2016 4:24 pm

Thanks Mike and Rohan.

Turns out I have the TTR fast road (125 lb) front and will be going with the compatible TTR rear units. After reading this thread, I'm glad that's what I have. I will post a report on their performance as soon as I'm back on the road.

Best regards,

John
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