Personally I didn’t know the answer …but I wanted to see if there was anything that I was missing out on……. It seems that I’m missing quite a bit …… but it is very interesting ( at least to some of us) ……and an opportunity to extend the life of my grey matter by exercising it .
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Hi Danny…as most who actually drive these old 60s cars have said in the posts above stick with the standard set up as per the factory spec…you will then be driving a car as designed…you wont be dissapointed…after that you can then start to “tweek” things based on your driving style…Steve
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I’m going to hide behind my total lack of E-type driving experience here. My approach is to look at the system behaviour - depicted by numbers, charts or whatever is available - and comment on anything that looks unusual by current practice. I’ll describe the possible effect of that, and what we might do to change it. Over to you from there!
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Then, comes the acid test: that’s when those four little patches of rubber hit the road!
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I stand ready to be judged by a jury of my peers 
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Following up on Tom’s comment, this is a chart of load vs deflection for some different material jounce bumpers. Contact would start on the left side, load rising to the right as the damper is compressed.
The black line is a generic rubber bumper (not an actual Jaguar one). It has little deflection and would push high forces into the structure (and occupant).
The blue line is a ring of urethane cut from a 4-section Mercedes bumper. It’s clearly more progressive but also too short, it would allow metal-to-metal contact at full damper compression, indicated by the red dashed line.
The green dashed line is a composite of two urethane rings, it’s more progressive and controls travel to a reasonable distance. I think it would be a good starting point for trials.
As Tom says, urethane gives good damping so would offer a good quality feel of “cushion” and control. Rubber, by contrast, tends to give a feeling of “rattling” or bouncing on and off the bumper. I think the urethane would give a particular advantage with the E-type front structure.
Unless anyone has actually tried it and found otherwise, in which case I’ll slink way and try harder…
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By rake do you mean dropping the nose of the car to counter aero lift? According to my data it would also give a slight increase in caster angle, which is one of the main contributors to steering return torque. The other is self-aligning torque (SAT), which is a tyre property and tends to reduce with vehicle speed - so if you start with the typically low E-type castor and lose SAT you could quite possibly notice a reduction in steering feel at high speed.
Increased caster should help this situation and would also give a slight gain in negative camber in a turn.
SAT results from the nett lateral force in a corner acting behind the wheel centre line due to a thing called pneumatic trail shifting the forces rearward in the tyre. Hence a torque is created, in plan view.
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Clive, excellent points. The devil is in the details.
There are some Jag lovers, if I recall, that are running as much caster as they can adjust in. I have not tried this yet but it is on my list.
Another experiment that interests me would be to measure the lift at higher speeds.
Yes: it, and the spoiler, make a noticeable decrease in lift at high speed. @soothsayer1 can confirm that.
Dad, being the studious mechanic that he was, made that modification to the car when it first became a race car early in its life: when he noticed that fact, he increased the Caster at least as far as the limited E-type adjustment would allow, and didn’t notice an increase in return torque.
The car is ultimate undoing, as we all know, is its lack of really really good racing brakes: they may be fine for the street but they are utterly and totally inadequate for competition, and Dad and its then-current owner realized it was gonna cost way more green lubricant to make it a viable track car than the owner wanted to spend, so it came back to a street car!
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In my old 2+2 at about 90 the front became noticeably lighter to the point I backed right off …… I never had anything adjusted on that car ….I bought it , drove it, and eventually sold it as other cars arrived in my garage …… I guess the PO may not have adjusted the ride height and caster etc correctly ……. I rely on a local Jag guy who races to do the final front end adjustments …. And he adjusts ride height and caster to suit
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Interesting. I can believe castor would be a minor factor relative to aero but anything is worth a thought. I’d rather be wrong than ignorant.
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That was a bit of a long shot. Can I try another way - does anyone know the original rear spring rates? One step from there to ride frequency, which is a good way to sidestep the subjective verbiage around ride quality and get a number to ponder.
No? You know what’s coming next…
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…if no one knows the original rear spring rate, does anyone have one at hand, and would be kind enough to measure?
Just need to know:
- wire diameter (preferably with a caliper or micrometer)
- coil diameter (inside or outside)
- number of coils
Ideally also a photo to allow a judgment of how many coils are “active”
Well that called my bluff…
thanks, I’m on it.
Can I take the inside diameter as the standard / typical 1.875 inch from that era?
Inner diameter 2.5in…as far as im aware…but iv never measured it and dont have one to hand but its mentioned here as 2.5in Coil spring - Jaguar - British Cars - SC Parts Group Ltd
You’re right thanks, and that page actually shows the spring rate so that’s a step saved. I’m making some dimension and unsprung mass estimates which can be easily updated later with better info.
Clive…dont assume that the spring rate in the SC parts link above is correct as per original E type springs…thats just the rate of their spring…it dosnt give wire diameter etc…there is a lot of discussion on springs…typically many who replace their originals find that their ride height is too high…this can be down to the replacement spring or shock perches…or if a spacer is used or not under the spring…this did change with models/year etc…many have calculated spring rates previously…a search on the forum will give lots of conflicting figures…Steve …PS you have joined in the spring rate/shock discussion previously Identifying shocks and ride height - Page 4 - The 'E' Type Forum
As much caster as they can actually achieve? Or as much as they can achieve within published alignment specs?
FWIW, when getting an alignment I routinely ask the guy to dial-in as much caster and (neg) camber as he can manage, within spec. I’ve always been happy with the steering feel and driving behavior afterwards.
IMO, if discussing getting the best out of standard suspension, I’d put this at the top of the list as a no-brainer…until or unless someone comes along and says that XKEs respond poorly to it, in which case I’d deny, deny, deny that I ever made such a suggestion ! 
If I understand Clive correctly, return torque can be influenced by SAT…which is itself the result of pneumatic trail shifting…and is something that will vary with tire design?
In this thread I’m discovering new things to learn about! Lateral tension profiles. Trail shifting. I’m not sure I’ll be able to fully wrap my head around all of it
Cheers
DD
Yes, I remember it well, I tried to give a simple graphical way to check and set spring length and ride height. It brought the discussion to an abrupt halt, sorry about that.
The spring rate calculation is simple in itself but it requires an estimate of the number of active coils, typically taken as the number of coils which don’t touch each other when the spring is compressed. I suppose it’s more likely the Jaguar data gives total coils, for identification purposes? If I use their value of 9.375 coils I get a rate of 217 lbf/in, if I guess 1/2 inactive coil each end and use 8.375 active I get 243 lbf/in, not far from the SC value of 233.
As you say, it’s possible to get many answers for the same spring. In my past life I would use the calculation for a first-pass design to check travel and stress, then leave the supplier to adjust the detail to get the desired result.
I wasn’t planning to get into spring lengths and ride heights, it’s very easy to get knotted up in terminology. This website does a good job of taking that on, and has a lot of good detail including spring stability and stress.
I’ll have a look at ride frequencies after I’ve converted the spring data to metric numbers. Sorry chaps, I respect heritage but inches, pounds and fractions are too difficult these days.