Lotus Elan

Front spring recommendations

PostPost by: paddy » Tue May 05, 2009 10:18 pm

Having sorted the problems at the back I'm now looking at the front.

There are spax adjustables here (rock hard, again, but that's now resolved).

The issue I have is that the spring perch is adjusted to the maximum extent (minimum ride height) but still it's a bit higher (say an inch) than I want. From reading previous threads it looks like it's not unusual, where springs are used that were originally intended for dampers with non-adjustable perches.

I will know more if I take it all apart and measure it, but while the weather is good I want to keep driving. So I'm after any "off the shelf" advice/suggestions as to suggested spring rate, free length and suppliers.

The following sums are based on some measurements and guesswork with everything still assembled.

- at the current ride height, the compressed spring length is 9"
- the weight at each front corner is estimated to be 360 lbs
- the mechanical advantage of the suspension action on the spring is 1.8 (read on other thread)
- this gives a load on the spring at rest of 650 lbs
- assume the spring rate is 100 lbs (guess)
- this gives a spring free length of ~15.5" which correlates with the length you'd expect for a spring appropriate for fixed perches.

I'm not racing, the antiroll bar and rear springs are standard. Any thoughts from those who've solved this problem already?

Paddy
1963 Elan S1
User avatar
paddy
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1190
Joined: 27 Oct 2008
Location: Woking, Surrey

PostPost by: hatman » Wed May 06, 2009 10:23 am

Hi Paddy - talk to Tony Thompson. What he doesn't know about spring lengths, compression rates, ride heights etc etc ain't worth knowing. :mrgreen:
hatman
Third Gear
Third Gear
 
Posts: 407
Joined: 05 Oct 2004

PostPost by: Bruce Crowthorne » Wed May 06, 2009 6:51 pm

Standard front springs I measured as 75 pound/foot stiffness, 16 inch free length and 1.9 inch id
I use Gaz shocks (highly reccomended) and use 120 pound/foot stiffness and 10 inch free length.

You will get springs from many sources but look in the Demon Tweeks catalogue or web site and they will probably have what you need.

I guess your issue will be working out what free length you need to suit your damper and ride height requirements.

But given ypur guess of 100 lb/in and 15.5 inch, then I guess you have the original springs.
So depending on how much adjustment you have on your damper body and how much you want to drop the car then maybe 3 or 4 inches shorter might do the trick?

Hope this helps
Bruce
User avatar
Bruce Crowthorne
Third Gear
Third Gear
 
Posts: 262
Joined: 30 Aug 2005
Location: Emsworth, Hants

PostPost by: TomR » Thu May 07, 2009 11:25 am

Tony sold me 120# front, 100# rear, both 12" with asjuatable perches. FWIW, I also have a set of titanium springs for the front. Renton coil springs in the US sells snowmobile racing springs that happen to be 1.9" ID, 10" FL, and several strengths from 95 - 125#. Incredibly light for $300.

Tom
TomR
Second Gear
Second Gear
 
Posts: 105
Joined: 19 Sep 2003
Location: Vernon, CT US

PostPost by: gerrym » Thu May 07, 2009 3:16 pm

Just a note of caution, check for coil binding when changing spring type and installation (adjustable spring seat etc)

Regards
gerrym
Fourth Gear
Fourth Gear
 
Posts: 894
Joined: 25 Jun 2006
Location: Aberdeen Scotland

PostPost by: dlbarnes1 » Fri May 08, 2009 4:32 am

I've recently been thru a situation similar to what you have described.

The shocks are Spax adjustable. The spring perch was set at the bottom with springs that were 16 in. free length - 75 lbs per in. The installed length of the spring was 10 in. ( 6 in. preload ). The ride height was about 1 in. above normal.

I replaced the springs with 12 in. free length - 115 lbs per in. I set the spring perch for an installed length of 9.5 in. ( 2.5 in. preload). The ride height is now normal.

I can't remember exactly what I set the damping rate at, but I think it's slightly above minimum.

Removing and installing the springs on the shocks is another story.

Dave 72 Sprint DHC
dlbarnes1
Second Gear
Second Gear
 
Posts: 140
Joined: 22 Sep 2003
Location: Redding, Calif. USA

PostPost by: paddy » Fri May 08, 2009 12:27 pm

Thanks for the replies.

I did speak to TTR and despite being determined to keep my credit card in my pocket he persuaded me that the Spax I have will not perform well so I'm getting new dampers as well as springs. The discussion on the other thread at least gives me some comfort that he's probably right. I will let you know how it goes.

At least I won't kill myself trying to take the springs/shocks apart.

Paddy
1963 Elan S1
User avatar
paddy
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1190
Joined: 27 Oct 2008
Location: Woking, Surrey

PostPost by: Bruce Crowthorne » Fri May 08, 2009 7:44 pm

I think TTR supply Gaz shocks so I guess you will end up with a set up like mine.
Seems to work well to me!
Bruce
User avatar
Bruce Crowthorne
Third Gear
Third Gear
 
Posts: 262
Joined: 30 Aug 2005
Location: Emsworth, Hants

PostPost by: paddy » Fri May 15, 2009 7:15 am

Finally got the TTR units fitted, ride height adjusted, dampers adjusted to 4 clicks above softest as per TTR recommendation, and drove to work on damp roads this morning.

Overall, much improved, totally undramatic, quiet (it previously rattled over every bump), really quite different to drive.

I didn't want to do anything too stupid in the damp but I can confirm it's not understeering any more :)

Paddy
1963 Elan S1
User avatar
paddy
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1190
Joined: 27 Oct 2008
Location: Woking, Surrey

Total Online:

Users browsing this forum: AshleyPark and 12 guests