Lotus Elan

bump stop lenght - Sprint

PostPost by: mariodschy » Tue Aug 25, 2015 6:23 am

Hello,
i changed to adjustable suspension with 2 1/4" narrow springs 125lbft for normal road use which i ordered from Kelvedon, i also bought the suitable bumpstop but this must be shortened to the correct lenght (its has a lenght of about 6").
From Kelvedeon i got the answere that i should:
"As for the Progressive Bump Stops, if you initially cut them in half, it is really a custom fit to the car".

Has anyone experience with this and know the lenght which is ok for normal road use on a 72er Sprint, i try to avoid spending hourse in dismantling, cuting and reasamble again and again....
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- 1972 Lotus Elan Sprint LHD/DHC
- 1962 Austin Healey Sprite MK II - Sold 09.05.2016

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PostPost by: rgh0 » Tue Aug 25, 2015 8:59 am

Assuming these bump stops are similar spring rate when cut to the original Aeon rubber springs then I personally would cut them to be about 20 mm longer than the original rubber springs so they come into play a little earlier in a corner

I presume you mean you have ordered 125 lb/in rear springs not 125 lbft?. At 125 lb/in these are certainly stiff for normal road use and are at the very hard end for road use or the soft end for racing use.

If you do have these stiff rear springs then you also need to upgrade your front springs to match the stiffer rears - maybe 150 to 180 lb/in fronts and a bigger diameter roll bar around 7/8 inch / 22 mm.

This total combination will give you great balanced handling that works well with modern sticky tyres ( and will keep you up with a modern Elise in most corners) but you will loose much of the original supple ride and you will want smooth roads to drive on.

cheers
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PostPost by: mariodschy » Tue Aug 25, 2015 9:56 am

On the bill the springs are named as RACESP22510125 (Spring 2 1/4 ID 10 125) i hope these are the right ones, we allways speak about "normal road use" not lbs or ft ...
Due the reason that i don't have the original rubber i need the lenght of the original one, can anyone messure it?
Thanks.
Mario
- 1972 Lotus Elan Sprint LHD/DHC
- 1962 Austin Healey Sprite MK II - Sold 09.05.2016

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PostPost by: 7skypilot » Tue Aug 25, 2015 11:02 am

I went down a very similar route a couple of years ago in the search for better ground clearance and handling. This Forum was, and is, magnificent! One of the Members suggested using this as a rear bump-stop:

VW B3 B4 VR6 Passat Front Strut Rubber Bump Stop 1993-1997 Suspension 1H0412303

I bought two, from eBay IIRC and they have worked superbly. As Rohan suggests, a slightly longer bump stop is useful, which these Passat stops provide.

An alternative, but this suggestion is perhaps too late, is to fit 2.5" springs which will allow the original Aeon bump stops to fit inside.

Have fun!
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PostPost by: mariodschy » Tue Aug 25, 2015 12:36 pm

thanks 7skypilot that helps, they are still available on ebay:

http://www.ebay.at/itm/2x-Anschlagpuffe ... 2a11230f2d

They have a lenght of 63mm an look similar to the bumstop from kelvedon.
I'll cut it to have the upper 3 beads left this is a lenght of about 63mm.
Hope that the bumstop has the same stiffness
Attachments
IMG_7863.JPG and
- 1972 Lotus Elan Sprint LHD/DHC
- 1962 Austin Healey Sprite MK II - Sold 09.05.2016

Sorry for my bad survival English ;-)
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PostPost by: rgh0 » Tue Aug 25, 2015 12:55 pm

Hi Mario

You need to understand the specific spring rate of these springs as a 125 lb/in rear spring is not really normal road use in my opinion and requires modifications to front springs and roll bar to work effectively in the car and will be a much harder ride.

The normal original rear springs are around 67 lb/in if i recall correctly ( I don't have my manuals as i am travelling for work currently) so if these springs are 125 lb/in they are twice as stiff.

regards
Rohan
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PostPost by: mariodschy » Tue Aug 25, 2015 1:14 pm

I reconized the different spring rate so bevor i've ordered the suspension parts i've asked about the much higher spring rate and this was the answere i got (suprised that i've found the email) :D

Email from kelvedon:
"The spring rate is heavier but the narrow springs (2 1/4) are much shorter and do not require pre-loading under pressure - as a result they come with higher rates. Once the standard large spring is loaded up it achieves a spring rate of about 125 lbft. In the way the shorter narrower springs perform the same way as the much longer wider springs........

regards paul"

This was the answere, hope this is true und ok.
I allways was very satisfied with kelvedon (except the answere for the bump stop lenght :wink: )
- 1972 Lotus Elan Sprint LHD/DHC
- 1962 Austin Healey Sprite MK II - Sold 09.05.2016

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PostPost by: rgh0 » Tue Aug 25, 2015 1:22 pm

I am sorry but you have been given a misleading answer.

The shorter stiffer spring will perform in the same way as to ride height only

However it will not perform in the same way as to ride comfort and handling. The original larger diameter, longer free length and lower rate springs load to the same installed length and total lbs load, but the spring rate does not change and is always 67 lb/in and is always around half of the 125 lb/in springs

Unless you want a car that rides and handles more like a race car and you are also modifying the front suspension to match you have the wrong rear springs based on incorrect advice by someone who does not understand how springs really work

cheers
Rohan
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PostPost by: elanman999 » Tue Aug 25, 2015 1:55 pm

The standard Lotus bump stops (Aeon springs) are 78 mm long.
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John
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PostPost by: patrics » Tue Aug 25, 2015 7:58 pm

Hi
When I brought up rated rear road springs years a go they were something like 80 Ib/in so 125 sounds a lot

Regards
Steve
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PostPost by: mariodschy » Wed Aug 26, 2015 5:05 am

Thanks for this information, i am really confused because i thougt they are specialists :(
I'll check it and write kelvedeon, when i have news i'll let you know...
- 1972 Lotus Elan Sprint LHD/DHC
- 1962 Austin Healey Sprite MK II - Sold 09.05.2016

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PostPost by: UAB807F » Wed Aug 26, 2015 5:46 am

mariodschy wrote:Thanks for this information, i am really confused because i thougt they are specialists :(
I'll check it and write kelvedeon, when i have news i'll let you know...


Don't lose your faith in Kelevdon just yet, but I agree with Rohan that the answer you got didn't match the question you asked. The springs are shorter & don't need compressing to fit, but a 125lbs spring is a 125 lbs spring !

I bought springs & dampers from them in 2013 and talked with Pat Thomas about the options at the time. I ended up with a similar set-up but the spring rates were 140lbs R & 175lbs Fr. Initially I was skeptical but talking with Pat convinced me so I did the sums on wheel frequencies and decided to try it.

Pat was right, the car was transformed. It really is a pleasure to drive and while it's obviously not as soft as it used to be it's no harsher than modern sports cars.

But you will have to change the front springs, if you just do the rears you'll end up with a very strange combination of wheel frequencies. My OEM rates were 1.18/1.34 F/R, new are 1.8/1.93 F/R, so in similar ratios. Figures won't be exact because I made some assumptions on weights but the comparisons are valid. On the same basis with OEM fronts you'd have 1.18/1.82 (125lb R) and I've no idea how that would work.

Brian
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PostPost by: toomspj » Wed Aug 26, 2015 8:23 am

I have fitted 100 lb springs front and rear to my Elan Sprint. It's quite a bit firmer than the original car but is more fun to drive. I wouldn't want to go any harder. I used 12" springs which are preloaded - gives a nicer feel to a road car. I also used TTR dampers which are set to be at the very soft end of their range.

You must change the front suspension to match the rear. Elans with a hard back end will bite you especially under hard braking or in the wet!

Paul
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PostPost by: mariodschy » Wed Aug 26, 2015 2:02 pm

I got the answere from paul and he recommended to install 140lb/inch springs in front to complement the rears.
summarized:

Front: 140 lb
Rear: 125 lb

What says the guys with huge experience?
Does it be ok for normal (fast) road use, for me it sounds comprehensible.
- 1972 Lotus Elan Sprint LHD/DHC
- 1962 Austin Healey Sprite MK II - Sold 09.05.2016

Sorry for my bad survival English ;-)
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PostPost by: UAB807F » Wed Aug 26, 2015 4:27 pm

I don't have very much experience in terms of Elan spring rates but I am definitely one of those nerdy guys who turns every decision into maths whenever he can. My excuse is that if I know what the starting points are like to drive, the maths will give me an idea of where I'm going to.

Anyway, as a very rough comparison you'll end up with wheel rates between standard and what I'm using , so from a personal view, it will be fine on the road. Yes, it will be stiffer than standard but not unduly so. As a broad comparison, my elan feels less "crashy" than the wife's TT which as usual follows the fashion of low profile tyres on stiff springs. In fact I often think that despite the stiffer springs, the elan still has a softer ride than a lot of modern sporting cars.

Incidentally, Pat also advised me then to consider going to a thicker A/R bar. If you're about to order more parts, it might be worthwhile asking if they think you need the same for that set-up.
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