Yes, I’m sure it will, especially if we consider bias ply tyres. I need to do some study as I’ve never worked with them.
I also want to check the effect of tyre width, including a recent suggestion that (if I understood correctly) tyre width doesn’t change ground contact area. I think that would require the tyre to be equally flexible in all directions, like a balloon. Any thoughts?
I pulled some books out of a storage bin this morning. Top of the pile: British Standard 1726, Design and Specification of Coil Springs. Part 1, 1964. Where have you been old friend?
Did I miss something, where does it show thw spring rate?
Hi Randall…The spring rate for the SC parts spring is shown in the link to SC parts i posted above…however this is for the SC parts spring…they show another spring just below with a higher rate…note this is for their spring and not nessecarily the same a Factory spring that i havent seen rates for…Steve
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Got it, thanks +20 charachters.
It wasn’t that aero, in a straight line, was an issue, and it was a non-issue in corners, but it just helps the self-centering effect.
How did I know that this would move into a realm where it became right over my head …….I’ve never had engineering or racing background ….so now I’m finding this hard to keep up ……. However I will be pleased when the investigations and discussions conclude that “ all is good ….keep driving it the way it was designed”
That we can have these discussions and the clever people on here can provide the answers is AMAZING ……. Thank you all
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Don’t feel bad, Danny: there’s still a fair amount of this high order suspension physics that’s a bit beyond me too! I am learning as we go along here, too.
One of the best, most-accessible books that you can get on this subject–and I cannot highly recommend it enough – – is by Fred Puhn, “[How To Make Your Car Handle.”](https://How To Make Your Car Handle.")
Concerning tire width, section with, and contact patch dynamics, read Ryan’s input in this link.
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At least you have a mechanical and racing background ….start early with your dad …. my dads idea of racing was running to the outside toilet!
I’m from a very different profession that had less rules about physics and more about interpretation of rules of tax laws ….there were obviously some laws like evasion of tax that you applied the unbending physics and couldn’t change …… but many others were about interpretation.
What the difference in the two professions is about is that one is working with natural laws of physics and one with legislated unnatural laws that contrived and confected to suit government demands on the populace
Oops I’ve digressed
Danny, I’ve seen your work, and I’ve seen your posts: there’s nothing about this stuff that you cannot grok!
Just stick with Clive, and he’ll get us through!
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Let’s keep expectations under control here! I was lucky to work with, and stand on the shoulders of, some giants in the field - if I can pass along a little of that, and learn something in return, we’ll all be doing well.
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Love a good Quora debate, there’s always a couple of people ready to argue anything with equal and opposite ferocity.
Seriously though, I hadn’t seen the Haney work, it sounds completely reasonable. I had reservations about the freedom of tyre structure to change its shape but I’m happy to be set straight on that. I don’t think it is critical for this discussion as those square inches of ground contact area will affect ultimate grip, while the lower (g) level handling we discuss is more related to tyre cornering stiffness - I don’t think there’s any dispute that a wider tyre will deliver more of that. We might debate how much of a good thing is enough, of course, and what side effects emerge.
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I’ve taken some time following up on this as I wanted to check my data and not add confusion to what’s already out there. My purpose was to establish or confirm a value for the original E-type spring rate… I ran spring rate calculations through a couple of online sites, then an old spreadsheet I made years ago, then finally did it longhand. With a pen. In a notebook. Weird scenes indeed. Springs are not complex in themselves but I’ve put detail in the steps I used because they lead to ride frequencies, and that looks like an interesting discussion.
I’ve generally used metric data because I’m more comfortable with strings of zeros, the formula also works in pounds and inches for the brave and careful.
The base formula for rate K of a spring is:
K= G(d^4)/8nD^3 where :
G is shear modulus, I used a standard value for spring steel 81,000 N/mm^2
Following data come from the Jaguar sheet supplied by Steve:
d is wire diameter, 11mm
D is mean coil diameter, to centre line of wire (=inside coil dia + d, or outside coil dia - d, of course), 74.5mm
n is the interesting one, and the reason I’m labouring this detail. It’s the number of working coils, which is less than the total physical coils (N) because end coils which are wound and ground to give a flat mounting surface don’t behave like full working coils. Different sites and experts give various ways to account for this. British Standard 1726 (surely you didn’t think you’d heard the last of that?) suggests n=N-2 for springs like ours, that is counting one coil at each end as non-working. I’ve found that 1.5 can give a figure closer to actual test data, but every spring is different and finally we rely on the spring supplier to make what we’re asking.
All that is a long way to say I don’t know what the rate of the spring listed in the Jaguar sheet posted by Steve actually should be!
Taking the coil number in the Jaguar sheet (9.38) as working coils gives a rate of 217 lbf/in (38N/mm). I think it’s more likely they quote the actual coil number for identification purposes, in which case the working coils could be as low as 7.38, for a rate of 276 lbf/in (48N/mm). Deducting my preferred figure of 1.5 coils instead of the standard 2, the rate is 259 lbf/in (45N/mm).
Until I can get a measured value I plan to use 262 lbf/in, because it’s convenient as 46N/mm. Would be very interested in alternative values or conclusions.
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With all this theory …… why wouldn’t we grab one and measure the forces in a spring rating machine
Excellent idea. Straight to the heart of the matter, none of that Pom screwing around.
Well it will depend on what spring you actually test…in the service manual there is shown data for early and later springs…also any original spring will be over 50 years old…someone must have Jaguar data for their spring rate…possibly in service bulletins…Steve…PS…250-270lbft/in are typical figures mentioned by many when discussing original spring rates but only speculation so your figues are bang in middle
The new ones from barrats work well on the car …so presumably are correct ….of course we also ask them
Yes, this isn’t an original discussion, there must be a mountain of actual test data out there.
Then we can talk about the front…
I was just about to say that 
wait until we get to the torsion bars!
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Just back on the springs …… the weighted load would naturally compress them a bit….however the weight of fuel 56 litres approx at 56 kg vs the spare tyre of say 30 kg plus tools and jack don’t add up to anywhere near the fuel weight …… so this needs consideration as well ….then there is the compensation required for the driver as well
Yes, your homework assignment is coming right up