Rear Suspension, ride height

[Jeremy]

Mark, I bought a new set of springs from CMC. They told me they started having them made specially after being unable to source acceptable ones anywhere. I haven't measured the ride height on my car but visually I think it's perfect. (I don't go for the low-slung look favoured by some, partly because of the speed bump risk)

[mgcjag]

Hi Jeremy....get your tape measure out lowest lip of irs plate to ground...just to give us something to compare against...Steve

[Series1 Stu]

I remember that Derek Watson similarly researched this subject for the same reasons and had springs specially made.

Derek is now sadly no longer with us but I'm sure Ken Jenkins will be able to recall the details.

Regards

[PeterCrespin]

Didn't realise Derek had died? First vendor I ever visited when I got my E ‘basket case’. Nice drive from Buxton to Gt Longstone and they have a fun Fell Race there.

This thread bas convinced me even more never to discard an old spring and just pack it for ride height slightly if needed.

[Gfhug]

I’d say my car sits the same as Jeremy’s with the standard springs from Barratts. And no I haven’t measured the IRS height for you Steve. Correction, I’ve now got my clothes grubby and have 20cm or 8 inches to the IRS.

Of more concern, Jeremy, what is that mark on the front wheel arch? I do hope it’s only a reflection of light or something else and not what it looks like in the photo.

Geoff

[MarkS]

Mark, I bought a new set of springs from CMC. They told me they started having them made specially after being unable to source acceptable ones anywhere.

Jeremy,
That's interesting to hear that CMC couldn't find 'acceptable ones' anywhere.... When you got them, did it specify the poundage/rate or the dimensions.? No problem if not, I'll be on the phone to CMC tuesday.

[mgcjag]

From SC parts website...details of their springs....rear - spring rate: 233 lb/ins, free length: 10.7/8" (standard height), inner diameter: 2.1/2". Use with coil over shock absorber (part no.: 306541) https://www.scparts.co.uk/sc_en/british ... 18935.html
They also have what they call a lowered spring....rear - spring rate: 233 lb/ins, free length: 9" (lowered height), inner diameter: 2.1/2"
Jaguar E-Type Series 1 and 2 (1961-70)
Some of this info on their site is very contradictory....ensure the springs you use are suitable for an adjustable platform shock.....AFAIK standard springs are not suitable for Gaz adjustable shocks

[Jeremy]

I got just under 8" (7 15/16) to bottom of tie plate. No lip as it's the Rob Beere alloy plate with a tow hole (for towing other less-reliable makes of car when they break down you understand).



Geoff, that mark on the front wing is merely a scratch sustained while running a police car off the road during a high-speed chase.....(just kidding, it's a reflection, rest easy

[Jeremy]

And Mark, no I didn't get any specs with the springs, just the statement (delivered with some considerable conviction) that they would do the job. Which they do.

[Gfhug]

Geoff, that mark on the front wing is merely a scratch sustained while running a police car off the road during a high-speed chase

Phew, that had me worried it might have been serious

Though notice you spend ten times as much as me to get the same springs

[Jeremy]

Geoff, I have found that the best way to deal with the matter of parts prices is to forget what I paid as quickly as possible, and above all not to keep any kind of running total of the cost of the restoration....

[mgcjag]

Just to add some moe info...iv been in touch with SNG to see what they use on their demo ots EE50... I had this reply
.......Our car runs with C25951GAZADJ adjustable platform dampers on the rear together with C25939GAZ springs.
They are set to give a ride height at the rear of 7 ¼” (185 mm) from the floor to the lip of the bottom plate on the diff cage.
This gives about 1 ¼ “ (33 mm) of tyre showing between the rim and the wheel arch flange at the twelve o’clock position.
I just looked up the springs on SNG site....GAZ Rear Road Spring
Product Code:
C25939GAZ
Part Type:
Standard
Spring specifically for C25951GAZADJ. 325lbs load rate, 8 inches long.

[mgcjag]

So just to add more info from SNG......Standard springs with the adjustable platform dampers make the ride height too high, even at full extension.

[Jeremy]

And to add yet another wrinkle, what about tyre diameter? Mine are SP Sports which I believe are slightly bigger than Michelins or Pirellis...and isn't EE50 currently running on low profile 205s?

[mgcjag]

Hi Jeremy...yes...tyres and tyre pressure and car model will all make a difference.....although not the 2in that the original poster has......Its hard enough getting members to measure let alone quoting what tyres and pressure they have

[PeterCrespin]

I agree that the relation between length and ride height is not a linear one, (mainly because of the angle from the vertical, (pythagoras)), but also because the angle must effect the loading on the spring.

I was actually thinking of the relative lever lengths (Archimedes).

As with the front wishbones, a given change in setting link or damper extension gives a magnified movement of the wheel because it is further from the pivot point. Someone here plotted the front wheel position/ride height delta per unit change in setting link length. It would be the same exercise to calculate the magnified effect of moving the spring platform up or down the threaded Gaz damper body.

[Series1 Stu]

This thread is fascinating me and I would love to do as Peter suggests and do some layout but I'm nowhere near my car and won't be for some time.

Looking at the rear suspension design I would suggest (although I have no hard evidence to confirm this) that the Jaguar designers intended for the half shafts to be horizontal at the mid-laden position. This would minimise the wear on the journals by having equal angles of deflection for bump and rebound. Jaguar data shows that we have 3.125" of travel either side of mid-laden position. By the same logic, I would also suggest that the mid-laden position is also where the damper will be at mid-extension/compression.

In other words, a lower or higher than standard ride height would result in a reduction or increase in bump and rebound. As Peter suggests, for a standard set up of damper lengths and spring platforms, it is purely the fitted length of the rear springs that generate any variation in ride height.

If your car is sitting 2" higher than standard and all the components such as wishbones and drive shafts etc are standard then it's likely you have saloon car springs fitted. When I got my 420 it had a lean to one side at the rear because someone had fitted E Type springs and dampers on the right hand side.

Peter, if you can supply length between pivots of half shaft and/or wishbone then I can scheme something up while I'm out and about to help us understand the effects a little better.

Regards

[rfs1957]

Mark, what is the eye-to-eye relaxed length of your shocks ?

And is that different to what you had on it before ?

And is it different to standard ones ?

I couldn't see this mentioned anywhere in the discussion.

This would potentially have a much bigger effect than spring rates.

An inch on shock-length is worth roughly two inches at the wheel, all things remaining equal.

[Series1 Stu]

I'm not sure I agree with that, Rory.

The only real way that the dampers can affect ride height is via the positions of the spring seats, which will determine the preload on the springs as a function of spring length and rate. So it's really the combination of spring and damper that sets the ride height.

Regards

[PeterCrespin]

Inboard fulcrum to shock mount is 270 mm and fulcrum to hub carrier pivot is 410 mm (measured with a tape measure only).

At 2:1 and dampers at about six inches travel there would be a foot of wheel travel, which is obviously a bit much, even allowing for bump stops that prevent 100% of travel in normal driving. Using the half shaft as the top suspension member gives a neat, light, assembly but compromises ultimate suspension geometry & versatility compared to twin wishbones.

I’m not convinced mid-laden gives horizontal wishbones though. Time for some drawings, someone? :-)