That Torsion Bar Question Again?

[DamianH]

OK, maybe not *that* torsion bar question.

I'm trying to understand the library of available torsion bars.

I have as a datum point that Series 3 torsion bars as standard settled on 0.75" / 19 mm. After that it all becomes a bit hazy. I understand that S1/S2 cars had larger diameter bars, but I see a variety of sizes quoted, up to 0.865"/22 mm. As someone else has accurately pointed out, this results in a large rate range for a given length.

Is there a definitive list of which diameters can be fitted on which cars?

Also, I'm trying to understand the whether the length of the torsion bars changes between the different cars. At first glance it's not obvious to me why a 5.3 litre V12 would be longer than a 4.2 litre I6 engine, and casually draping a tape measure from bulkhead to picture frame tells me the structure there is "about the same length" (within the precision of my tape measuring skills and the patience of various E-Type guardians). Are the torsion bars all the same length between all the cars? Are the splines interchangeable?

I don't want to engineer new torsion bars if there is one on the shelf I can use!

Thanks for any input.

[mgcjag]

Have a look here...Steve https://forums.jag-lovers.com/t/series- ... ars/436037

[DamianH]

That thread confirms 0.75" / 19 mm for an S3 car and confirms other bars are available, but not really any new information.

This post suggests they are different lengths, with the S3 bars being longer:

Just for the record, S3 torsion bars are over 4.5" longer than those fitted to S1/S2 although I believe the splines are identical (ignore the fact that the images show opposite ends of the bars and therefore different splines, they were just images I had to hand).

S3


S1+S2

There seems to be a lot of folklore about the V12 having "stronger" torsion bars but they are longer, so even at the same diameter they have a lower rate (GJ/l, where l is the length).

Wherever I look I can't find mention of smaller diameter bars than 0.75" on S1/S2, but that doesn't prove anything. I seem to be able to find plenty of mention of higher diameter bars on the earlier cars, though.

[MarekH]

It isn't really possible to easily interchange information from s3 with s1/s2 cars because their front suspensions are not interchangeable with each other.

The s1/s2 has the torsion bars terminating into a chunky horseshoe shaped plate (called "the reaction plate") to then take the load into the tub whilst the s3 dispenses with this and transfers the weight of the car onto two pieces of angle iron directly bolted to the underside of the car much further back roughly below where your knees are. That's why the bars are a different length. If you now want the same "spring" characteristics, given the cars are different weights, you'll have to play with the bar diameter as that is your only variable left.

kind regards
Marek

[DamianH]

Thanks for confirming the length difference.

What were the standard diameters of bar on the earlier cars?

I've already spotted the difference in motion ratio between the narrower and wider track cars, but it's really just the diameters I am trying to home in on. I can calculate motion ratio with the data I already have, but I can't be sure which diameters to plug in for the different cars to orient myself.

With both longer arms and a longer torsion bar, both effects soften the S3 wheel rate compared to the earlier cars *unless* the diameter was also less.

[mgcjag]

From memory early S1 cars had 0.77in diam bars...this was later increased to 0.780-0.784 as per service manual info....Steve

[dlgis]

SNGB sell 3 different ratings of torsion bar for the S1. 0.765, 0.860 and 0.835. Presumably 0.765 is standard and the other 2 are uprated

[DamianH]

SNGB sell 3 different ratings of torsion bar for the S1. 0.765, 0.860 and 0.835. Presumably 0.765 is standard and the other 2 are uprated

I've seen these. It wasn't completely clear to me which were standard and which were uprated, but I will go with the 0.765 as standard since it's usefully close to the previous assertion of 0.77 as standard.

I appreciate the input!

[mgcjag]

All the SNGB bars are aftermarket what do you mean when you say "standard"....I mentioned original dimension above depending on chassis number

[abowie]

Here's a couple of pictures.

[Bob.]

Hi Damian,
Prior to introduction of the larger diameter (0.780-0.784") torsion bars referred to above, production bars were rated at 100lb/in. The wishbone rubbers contributing a further 16lb/in.
(info from Jaguar documents dated 1962).
Bob
PS Have you seen CliveR's posts on jag-lovers? Sounds like you and he have similar backgrounds. He has been using RACE software to model S1/2 suspension.

[DamianH]

Prior to introduction of the larger diameter (0.780-0.784") torsion bars referred to above, production bars were rated at 100lb/in. The wishbone rubbers contributing a further 16lb/in.
(info from Jaguar documents dated 1962).

Bob, thanks for that information. My estimates got me to 117 lb/inch as an overall rate, which is shockingly close! There is a mixture of luck and good judgement there! I don't suppose you have a screengrab of the documents, do you?

PS Have you seen CliveR's posts on jag-lovers? Sounds like you and he have similar backgrounds. He has been using RACE software to model S1/2 suspension.

I am just discovering that, I've seen some of his very lucid discussions I think I need to connect with him!

[Bob.]

Facsimiles of the documents are in Peter Wilson's book "Strictly No Admittance". Probably be breaking some rules to post copies here.

[DamianH]

Facsimiles of the documents are in Peter Wilson's book "Strictly No Admittance". Probably be breaking some rules to post copies here.

It should arrive some time next week for me. Thanks for the pointer.