Lotus Elan

Ride Height

PostPost by: JJDraper » Wed Sep 15, 2010 10:10 pm

I have TT shocks & springs fitted, and they ride very well - but I worry that they needed to be wound up pretty high to get the ride height right. They also make a grating noise as the springs rub in the shock tube. My previous shocks had stronger, slightly wider diameter springs fitted which didn't distort, or need so much adjustment to get the right height. The welded washer at the top of the unit also distorted (banana shape now) within a few thousand miles, but hasn't broken yet. I know my car is at the heavier end of the spectrum, but still within published spec for the car and I haven't used the car for any track work.

The side by side pic shows the old & new shocks, with the old one at the setting that gave the correct ride height.

I may have a go at fitting the springs from my old shocks on the units or possibly show them to TT for some advice (!). I suspect the springs may be a bit weak for my car.

As regards handling, they are very good and I have them set up at the 'comfortable' end of the damping settings.

For looks, they are works of art, but they do rust..

Jeremy
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Old and New shocks.jpg and
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PostPost by: jonnyconcrete » Thu Sep 16, 2010 8:41 am

Ewww! I'm not sure I could get on with a grating noise...did TT give you a choice of springs?
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PostPost by: jonnyconcrete » Sat Sep 18, 2010 9:31 am

TTR coil overs fitted (much free advise from Eddy and a free tour of the store full of very exotic 26R bits!!)...no strange noises, ride height restored and very very plush!
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PostPost by: CBUEB1771 » Sat Sep 18, 2010 6:14 pm

jonnyconcrete wrote:The inch loss is actually the length of the shock when compressed...so the tyres are not in the equation. It has to be the spring or the shock...I think!


Johnny - Are you getting your expected length dimensions from the +2 workshop manual? The +2 workshop manual has the wrong dimensions but it would make you think you have the opposite problem, that the ride height is too high. When Lotus prepared the workshop manual for the +2 they copied many of the illustrations from the Elan manual, including the dimensioned front and rear suspension drawings for the Elan. Comparing the Elan and +2 drawings, things look good with the +2 control arm lengths being significantly longer than those for the Elan. However the draftsman got lazy :shock: with the spring/damper units and did not change the dimensions for the +2. Both the Elan and +2 work shop manuals give these dimensions as 9.79" full bump, 11.84" normal ride height and 13.54" full droop. Keeping in mind that all of the increased track at the front of the +2 comes from increased suspension link lengths the spring/dampers must also be longer. I have not found a reference for the correct +2 damper dimensions but they have to be at least 1.5" longer than for the Elan. What is the length you measure at normal ride height? I can understand you getting something close to 13", looking at the workshop manual and concluding that your ride height is too great.

I discovered the workshop manual problem when I first bought my +2 in 1977. When I test drove my +2 I immediately found that one of the front damper shafts had broken where it passes through the frame turret. My deal with the seller had her replacing the front dampers. Her mechanic (Ed Loveday, rest his soul) looked at the +2 workshop manual and concluded that a set he had in stock for an Elan were also correct for the +2. His thinking could be excused because the dampers he had in hand matched the dimensions in the manual. However once installed in my +2 they were obviously wrong with the car at near full bump when down off the jacks. Old age has me rambling on too long here. Just keep in mind that not everything in the workshop manual is correct.
Russ Newton
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PostPost by: jonnyconcrete » Sat Sep 18, 2010 6:41 pm

Russ, many thanks for this insight...most useful. Simple question, what do you consider the correct ride height measured from the ground, up through the centre line of the wheel, to the bottom of the wheel arch (i.e first contact).

I've been messing around with mine today, and the best feeling when driving the car, by feeling I mean the most neutral turn in occurs at 604mm ground to wheel arch bottom. Lower than that and the car feels tail happy...higher and turn in isn't sharp.

And...I can drive over speed bumps in a straight line! :P

This measurement by the way, was 582mm on the old shocks.
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PostPost by: mikealdren » Sat Sep 18, 2010 9:17 pm

Jonny,
be careful taking body measurements. The manual give chassis ground clearance and that is the best way forwards, the fibreglass bodyshells can vary and the height at which they are mounted relative to the chassis also varies, many have spacer washers under the mounting at the front footwell and several people here can tell you about the difficulties in getting the right height for the mounting of the front undertray to the chassis on the front of the chassis crossmember.

The wheelarch height certainly affects the look of the car but the chassis ride height is more accurate for handling.

Mike
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PostPost by: CBUEB1771 » Sun Sep 19, 2010 2:32 am

jonnyconcrete wrote:This measurement by the way, was 582mm on the old shocks.


Johnny - It just dawned on me that we were assuming you meant you were measuring the front damper length dimensions. At 582 mm you are very close to what the workshop manual shows for the length of the rear damper at normal ride height for the +2 and the Elan. Which dampers are you measuring, front or rear? There may also be errors in the work shop manual for the rear suspension dimensions. However at the rear the frame is much wider between the turrets on the +2 than on the Elan and I suspect the differences in damper lengths at the rear are much less than at the front. The workshop manual shows the lower control arms at both the front and rear lying in a straight line at normal ride height. By that I mean that a string drawn taught from the centerlines of the outboard control arm pivot bolts would cross the centerlines of the inboard pivot bolts. This makes sense because in that condition any bump deflection from normal ride height would introduce negative camber, the desired result for cornering. Why don't you check that, see if the control arm pivot bolts fall on a line at normal ride height. Don't forget the weight loading as suggested earlier. I also agree that measurements to body features don't mean much, it is the suspension geometry that matters unless you need to fuss with aero forces at high speed.
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PostPost by: jonnyconcrete » Wed Sep 22, 2010 6:46 pm

We're pretty much sorted this end now...interesting perspectives though...especially the parallel bottom linkage theory, I gave it a whirl and the ground clearance was down to just under 5 inches!

I've settled for 6" and damping at 10 clicks from full soft...I have to say that the ride quality from the TTRs is absolutely first class...I'm tempted to do the rears now.
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PostPost by: jonnyconcrete » Sat Sep 25, 2010 9:32 am

Just re-read the thread...very interesting stuff about tyre profiles...mine are 175/70/13 which makes the roling diameter -1" on standard...therefore the defacto ride height is -.5"...so the current 6" is right.

That was more by luck than judgment on my part!
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PostPost by: fatboyoz » Tue Sep 28, 2010 1:01 am

Johnny,
The bottom wishbone being parallel with the ground is not just a theory. If you look in the Elan Workshop Manual (Elan S4 for me , but dimensions are the same for +2) you will find three dimensions measured from the top coil-over mount to the centre of the bolt on the lower wishbone. Droop: 343.91mm, Bump: 248.66mm, Normal Ride: 300.73mm. The difference between droop and bump is the effective travel of the coil-over unit (95.25mm). The normal ride is approximately half way between. I have my ride height set with parallel wishbones, and it measures 300mm. Not theory, but fact.
The ride height as indicated in the manual, measured from below the front crossmember to the ground, is only correct if you have the 300mm dimension correct and the original tyres fitted. If you fit different sized tyres, you must make an allowance for this in the crossmember to ground clearance.
The critical measurement therefor is not ground clearance, but your parallel/300mm wishbone measurement. This will ensure a ride as per the book.
I initially set my ride height, using the ground clearance method, by winding up the adjustable spring seats. I ended up with the wishbones pointing downwards at the wheel end and then the tyres starting to wear on the outer edges due to excessive positive camber that this configuration induced. I have readjusted back to parallel wishbones and am keeping an eye on the tyre wear. I have also set tow-in at approximately 4mm as per Rohan's suggestion.
Colin.

jonnyconcrete wrote:We're pretty much sorted this end now...interesting perspectives though...especially the parallel bottom linkage theory, I gave it a whirl and the ground clearance was down to just under 5 inches!

I've settled for 6" and damping at 10 clicks from full soft...I have to say that the ride quality from the TTRs is absolutely first class...I'm tempted to do the rears now.
'68 S4 DHC
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