Torsion Bar spring rate ?

[carlt]

Have posted this on 'do you know' , but-
Anyone have the figure for the torsion bar spring rate
Am also wanting to work out the increased rate if the bar is shortened by 4"
[anyone have the math for this]
Cheers
Carl

[Alec]

Hello Carl,

I think a figure of 120Lb(inch?) was quoted here before but my feeling is that it is less than that.

As far as the increase by shortening 4" would be old length divided by new length giving an increase factor. i.e half the length would double the spring rate? The only problem with shortening is attaching the cut off end. Both ends are a larger diameter and splined so this would be lost? Uprated torsion bars are available. (Birmingham Minor Centre for one?)

Alec

[Mogwai]

I measured mine before before I fitted marina torsion bars. may not be the most scientific method but to raise the arm 1 inch from rest the scales read about 110lb . I did the same when the marina bar was on & it took about 130lb to raise it 1 inch

also tried this spring calculator it did give similar results http://www.proshocks.com/calcs/torsionrate.htm

[bmcecosse]

Excellent facts there Mogwai! Well done. I agree with Alec -how will you attach the arm to the bar after shortening ? And in any case - 4" is not going to make a huge difference. Of course that figure is taken with a standard full length lower arm - if you used a shorter arm the 'wheel rate' would rise in proportion - assuming the wheel is at the end of the arm of course!

[carlt]

Thanks for the replies
The reason for the shortening is that I want to shorten my 1956 Buckler spaceframe chassis [ it uses Moggy mechanicals ]
Two main reasons for this : I have a Falcon MK2 body wich would then fit nicely and there is a 4" section of chassis that is structurally weak , only has 4 parallel tubes in this section ,these are 1.25" diam x 1.2mm wall thickness.
The only parts that need altering to achieve this are the torsion bars and the 2 piece steering column .
Mogwai , the Marina bars you used , were they 1300 or 1800 ones , I had already considered using these if I need to stiffen it up a bit .
Cheers
Carl

[Mogwai]

Sorry im not sure what marina they came off I would assume a saloon but I have heard that the van & estate ones are stronger

[Innovator]

I remember seeing the spring rate or maybe wheel rate written in a road test or workshop manual somewhere. 120 lb /inch I seem to remember.

[rayofleamington]

You won't be able to shorten a Minor Torsion bar without opening an can of something unpleasant.
As it is possible to get new torsion bars with different rates, then there is someone manufacturing them. 'IF' you can find the actual manufacturer, you will probably be able to get a custom set made 4" shorter.
Bear in mind that a parts supplier may not want to tell you their source/s as this is often hard earned information.

[bmcecosse]

It's always possible the 'stronger' torsion bars are standard units that have simply been through a heat treatment cycle to toughen them up! Anyone care to measure the thickness of a 'stronger' bar to see if it's been increased over a standard bar ?

[jonathon]

I was under the impression that the effective spring rate of the bar is determined by its length, diameter and material. Does heat treatment really work with this type of product?
The firmer 1.8 Marina bars were a larger diameter than the 1.3's and I'd imagine that this is the route taken with the uprated Minor ones. Always ready to accept new ideas though

[bmcecosse]

Yes indeed Jonathon - but that would be quite an exercise to set up to make 'new' ones, and by re-treating it may be possible to up the rate by 20% or so by making the bar tougher, but of course more susceptible to breakage. I'm just postulating! Hence request for diameter measurement. Could be of course that all uprated bars are actually ex Marina - were there different bars across the range, or did the sportier (!) versions have stiffer springing ?

[jonathon]

All 1.3's were the same diameter as were the 1.8's only the latter being of a slightly larger.
Maybe the cost of 'setting up' is reflected in the high asking prices !

[bmcecosse]

Ok thanks J !

[carlt]

hi rayofleamington , am interested to know why you think shortening the torsion bars will 'open a can of .....'

[superchargedfool]

I am under the impression that marina lcv bars were stronger, can anyone confirm or deny this?

I have marina van ones on mine and they are definitely an improvement over moggy ones.

[Kevin]

It could be worth while contacting the Marina Owners Club.

[wanderinstar]

Apparently the saloon bars were 19mm, some estates were 20mm but the van/pickup used 21mm, 30% tougher.

[jonathon]

I thought all 1.3 cars were the same as the Minor only the 1.8's and commercials has the 30% uprated bars

[bigginger]

Same (ish) here, though I *thought* it was only the commercials

[wanderinstar]

Don't shoot the messenger. Source of info is " Owen Burton Morris Minor Modification Mnual"
Page 27 Lowering the front suspension.