Lotus Elan

TT adjustable shocks on elan S4 (how to set up)

PostPost by: holywood3645 » Mon Sep 26, 2016 5:52 am

I need to adjust ride height on the front of my Elan. I thought a set of TT front adjustable shocks complete with springs would give me the adjustment(s) I need. So I fitted and started playing with the platform height. The platform adjustment appears only to allow spring preload.

I have a couple of questions based on my experience and www research. The TT shock/spring setup allows adjustment of the spring preload and shocker damping. But how does this adjust ride height?
When I looked on you-tube I see the platform to adjust spring tension is already set, then ride height is set by screwing the assembly into or out of the shock/strut housing, then locked in place.\

https://www.youtube.com/watch?v=wcq7Xm-PssI

How does this translate to the ride height on the front of an Elan. Is it the intent that the spring preload adjusts ride height? I would have thought preload and damping should be set for optimum handling for consistency in RH and LH bends. With the ride height set to the correct height. How is that ride height achieved.
I think the shocks height would need adjusted (shimmed?) to get the height required. I’m probably off on my though process here, so please excuse my ignorance as there is probably a pretty fundamental concept I’m missing..
Thoughts?
James
User avatar
holywood3645
Fourth Gear
Fourth Gear
 
Posts: 936
Joined: 07 Oct 2003

PostPost by: nmauduit » Mon Sep 26, 2016 7:36 am

holywood3645 wrote:How does this translate to the ride height on the front of an Elan. Is it the intent that the spring preload adjusts ride height? I would have thought preload and damping should be set for optimum handling for consistency in RH and LH bends. With the ride height set to the correct height. How is that ride height achieved.
I think the shocks height would need adjusted (shimmed?) to get the height required. I’m probably off on my though process here, so please excuse my ignorance as there is probably a pretty fundamental concept I’m missing..


adjustable perches allow to do just that: height alteration a corner at a time, as the body is suspended by the 4 corners on the springs. If you raise all 4 springs base by 1/2" the body will go up by about 1/2". You can also adjust corner weight to balance the weight on each corner to your liking for a given track, and to do so at constant body height and attitude some spring bases will need to go down while others go up (4 degrees of freedom to adjust typically to 4 constraints: front height, rear height, 2 diagonal weight balances). Then you may want to work on shocks (damping up and down, with or without gaz which adds some springiness...) and springs themselves (rate , linear or progressive ...)
Last edited by nmauduit on Mon Sep 26, 2016 11:53 am, edited 3 times in total.
S4SE 36/8198
User avatar
nmauduit
Third Gear
Third Gear
 
Posts: 267
Joined: 02 Sep 2013
Location: France

PostPost by: rgh0 » Mon Sep 26, 2016 10:01 am

The preload on the springs when the shock is fully extended needs to be less than the normal weight on the wheel so the shock has some droop movement when its installed and does not remain at full extension. With no droop movement and the shock at full extension, adjusting the spring seat will make no difference to ride height as the suspension will always be at full droop.

cheers
Rohan
User avatar
rgh0
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 5760
Joined: 22 Sep 2003
Location: Melbourne, Australia

PostPost by: holywood3645 » Mon Sep 26, 2016 5:00 pm

So, Unlike the posting on the you tube link, we are adjusting the spring pre load to alter height.

https://www.youtube.com/watch?v=wcq7Xm-PssI

Would this not give different feeling on LH and RH turns? Assuming the preload is different. and shocks are not fully extended when sitting on the ground.


James
User avatar
holywood3645
Fourth Gear
Fourth Gear
 
Posts: 936
Joined: 07 Oct 2003

PostPost by: collins_dan » Mon Sep 26, 2016 6:05 pm

Unlike the video, TTR's setup does not allow for movement of the threaded section up or down the strut assembly, that is welded in place. Ride height is adjusted by raising or lowering the spring. I supposed that it is adjusting the pre-load, but hadn't really thought about it and didn't notice a different driving experience. On my S4, I measure ride height just behind the front wheel (6") and just in front of the rear wheel (6.5"). I keep the dampers adjusted for road driving with a semi-firm front and semi-soft rear. I used to use a full soft rear, but the car felt jittery on high speed turns. Hope that helps. Dan
User avatar
collins_dan
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1053
Joined: 09 Jan 2006
Location: Baltimore, MD

PostPost by: holywood3645 » Mon Sep 26, 2016 7:50 pm

Thanks Dan, perfectly clear.
After watching a couple of you-tube on the topic, I had been thinking of setting the preload same on both, then shimming for ride height. Maybe I will give that a go someday when I get caught up on other projects. In the meantime I will adjust the spring to achieve correct height.

James
User avatar
holywood3645
Fourth Gear
Fourth Gear
 
Posts: 936
Joined: 07 Oct 2003

PostPost by: Grizzly » Mon Sep 26, 2016 8:19 pm

James your right, if it was a proper platform adjustable strut you would have a gap between the spring and Strut (usually taken up by weak helper spring) that allows the spring to keep its length without preload (so the preload side to side is the same without altering the ride height to achieve it or vise versa)
download.jpg
download.jpg (34.81 KiB) Viewed 563 times


With weight on the suspension the weak helper spring binds like this........ So it's purpose is not to add anything to the main spring performance but to keep it located when load is removed from the road wheel.
image_983ebd8b-44bd-46fe-9c03-e619c08c3b5b.jpg and


If you wanted to do it properly ideally you need a shorter spring (say 1 1/2" shorter than the throw of the Strut) and a helper spring so the main spring doesn't dislocate every time you raise the car. I have no idea why TTR do it their way but i can only assume it's for easy of assembly, that said i bet it's very difficult to set the corner weights/Pre-load correctly and keep the hide height the same all the way round.

High quality (Road) coil overs look like this.
c41027f4-cc21-4110-9470-e646da7acf1f-800.jpg and
Chris
User avatar
Grizzly
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1267
Joined: 13 Jun 2010
Location: Cheshire/UK

PostPost by: rgh0 » Mon Sep 26, 2016 8:42 pm

All springs have preload when the cars resting on them. All springs also have preload when at full droop other wise they come loose and move off their seats and rattle.

The issue is not to have so much preload that the weight of the car does not move the suspension on full droop. With adjustable platforms you should be able to get the ride height you want without shims. if you cant then there is something else wrong with your suspension design or installation

The short light helper springs are only needed in racing setups with very stiff springs that have less travel than the full droop on the suspension. If you use them on a road setup you have something wrong with your design.

regards
Rohan
User avatar
rgh0
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 5760
Joined: 22 Sep 2003
Location: Melbourne, Australia

PostPost by: Grizzly » Mon Sep 26, 2016 9:42 pm

I think the problem here is knowing the difference between a height adjustable strut https://www.youtube.com/watch?v=B4GI2QbZ8fI and a preload only adjustable strut. https://www.youtube.com/watch?v=zK5MUK-N6yk

TTR struts are Preload adjustable only, means you have to get your springs spot on to get the correct ride height.
Last edited by Grizzly on Mon Sep 26, 2016 11:51 pm, edited 6 times in total.
Chris
User avatar
Grizzly
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1267
Joined: 13 Jun 2010
Location: Cheshire/UK

PostPost by: collins_dan » Mon Sep 26, 2016 10:08 pm

My son's miata has a helper spring set up similar to the picture. I do think the spring is much stiffer, but a miata is much heavier than an elan. Neither set up was particularly difficult to adjust ride height. Neither drooped to the point of spring moving on the perch. Both also offered good rebound in fully lowered position, so pre-load seemed OK. I'm not an expert or racer, just a fast road user, which is how the suspension is marketed. Dan
User avatar
collins_dan
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1053
Joined: 09 Jan 2006
Location: Baltimore, MD

PostPost by: Grizzly » Mon Sep 26, 2016 10:25 pm

You can buy 2.5" Springs in almost any rating or length, the trick is to get the right ones for the car your working on (more importantly the correct springs for the Struts jetting etc).
Chris
User avatar
Grizzly
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1267
Joined: 13 Jun 2010
Location: Cheshire/UK

PostPost by: nomad » Mon Sep 26, 2016 11:48 pm

I think you guys are complicating this. Stacked springs used to be quite common on racing motorcycles as were progressive wound springs. The theory being that under light normal loading the light spring would be doing the work but under heavier loading the light spring or close together coils on the progressive wound spring would coil bind and that would effectively increase the spring rate with heavier loading on the bike. Lets not forget that coil springs are rated at the weight required to deflect the spring a certain distance. Adjusting the platform a certain distance can only adjust the height. Nothing else unless the limit of the shock rod is reached. The spring rate stays the same regardless.

Ooorrr, am I completely misunderstanding the question? :lol:

Kurt.
nomad
Fourth Gear
Fourth Gear
 
Posts: 782
Joined: 05 May 2012
Location: South Dakota, USA

PostPost by: nmauduit » Tue Sep 27, 2016 7:03 am

Grizzly wrote:I think the problem here is knowing the difference between a height adjustable strut https://www.youtube.com/watch?v=B4GI2QbZ8fI and a preload only adjustable strut. https://www.youtube.com/watch?v=zK5MUK-N6yk

TTR struts are Preload adjustable only, means you have to get your springs spot on to get the correct ride height.


functionally I don't see a difference between load and preload, preload being only the specific case of load at full droop. As Rohan pointed out, some setup problems may lead to dysfunction (e.g. spring too stiff sitting on a platform too high resulting in car resting on or constantly hitting the top travel limit / or spring too short leading to zero preload and risking spring moving off their location at full droop - this is where people use helper springs...)

regular springs are about linear (Force = k * displacement, k being the stiffness coefficient) that is k is constant which makes height calculation rather straightforward : e.g. front springs k=150 lb/in loaded by 450 pound each side would be compressed by 3" each side, so if they are say 11" free length they would be 8" while holding the car (from that you set your perches 8" below the top spring seat). To be accurate one need obviously to take in account weight distribution specifics of the given car (and driver/passenger).
Last edited by nmauduit on Tue Sep 27, 2016 9:47 pm, edited 1 time in total.
S4SE 36/8198
User avatar
nmauduit
Third Gear
Third Gear
 
Posts: 267
Joined: 02 Sep 2013
Location: France

PostPost by: Grizzly » Tue Sep 27, 2016 9:25 am

Sorry my bad i didn't read the posts properly (2am and all) collins_dan has already explained the TTR's aren't height adjustable.
Chris
User avatar
Grizzly
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1267
Joined: 13 Jun 2010
Location: Cheshire/UK

PostPost by: nomad » Tue Sep 27, 2016 1:03 pm

nomad wrote:Ooorrr, am I completely misunderstanding the question? :lol:

.


After a nights sleep....I completely didn't understand the question! :?

Kurt
nomad
Fourth Gear
Fourth Gear
 
Posts: 782
Joined: 05 May 2012
Location: South Dakota, USA

Total Online:

Users browsing this forum: No registered users and 2 guests