I believe standard Minor torsion bars at 3/4 diameter. So 19mm. Your 21mm sounds reasonable.
I'm aware that 'uprated' torsion bars are available, but their uprated-ness is given as a percentage. It wouldn't be impossible to get a supplier to measure them. Something I'm considering for Bluey to reduce the bottoming out of being lowered.
If the standard torsion bars are 3/4", then the increase in stiffness with the van bars is around 22% (assuming heat treatment spec is more or less the same). Good dampers will help a lot to prevent excessive suspension travel. Standard ones with SAE40 oil is a good start.
Is that 22% just the increase in CSA? Because surely the addition of material to the outside is more effective that the neutral material in the centre?
I've fitted SPAX dampers all round, but raised the front slightly at the same time. Not had a problems bottoming since, but wouldn't mind going back down a little some time.
You are correct of course Chris - thinking that extra metal on the 'outside' will do more. It's way beyond me to work out what the improvement will be - a load test on a rig would be interesting! But I wouldn't expect much more than the suggested 22% -maybe 25% at best..... If you have drained the oil (or removed the valves) from the lever dampers - I suggest you put them back in service WITH the teledampers. I'm sure you will find a very worthwhile improvement - start with 20W50 and perhaps move up from there. I used to run levers + tele dampers and it was very effective on my rally Minor.
Yes, that was wrong, the stiffness in torsion is not proportional to the difference in cross-sectional area. If all else fails, get out the text books!
As the bar length is the same, and we have to assume that the metallurgical characteristics are the same as there is no other information, then the difference in torsional stiffness is proportional to the difference in polar moment of inertia, which for a solid circular shaft is:
πd4/32
As both PI and 32 are both constants, this means that the difference is stiffness is proportional to the difference in shaft diameter to the power 4, i.e. d4
Taking the Marina van and Minor bars:
Marina van bar is 0.811” (measured on the car)
Minor bar is 0.75” (I don’t have a standard torsion bar to hand, does anyone have one they can measure accurately please?)
0.811” to the power 4 is 0.4326in4
0.75” to the power 4 is 0.3164in4
Increase in stiffness = 0.4326 / 0.3164 = 36.7%
Hope that is a clear explanation? I have put a note on the earlier post to refer to this later one.
Spring steel is generally in the 'high' carbon range and is designed to be 'through' hardened, which is achieved by means of hardening and tempering. The whole heat treatment cycle is constructed to ensure that the required metallurgical properties are consistent throughout the material cross-section and length.
With large cross-sections (not small diameters like the torsion bars), you can exceed the 'limiting ruling section' for through hardening and much work goes into the initial design to make sure that this does not happen. Although there are alternative quenching fluids, such as water, that extend the section, they also result in brittleness through very rapid quenching, and that is rarely desirable.
To achieve predictable spring rates in a mass production environment, the principles involved are a bit more than a 'guide'!
Yes Richard - I am an engineer.....but the quenching/tempering etc will not reach equally in to the centre at the same rate as it quenches/tempers the outer layers..... They obviously had a process that worked - and worked well, since snapped T bars are pretty well unknown - but I'm not convinced you can apply the Math to it as exactly as you have.....
Didn't they shot blast the originals for extra toughening?
I recall from one of the Minor books that a lot of effort went into the engineering of the torsion bars.
"Once you break something you will see how it was put together"
So how do new cars get away with space saver wheels .
And there are very few people on this forum that have even the slightest inclination of what is cool is ,even the young members seem to struggle with concept of cool .
Space saver wheels must be clearly marked as such (usually in some Hi Viz way) - and in use have a strict speed limit. If Plod sees you belting along with a saver wheel - you are likely to be pulled. And of course - if you have an accident attributable to using a saver wheel at too high a speed - you will likely not be covered by Insurance.
Our 5.5" x 13" wheel will not fit under the boot floor, so my 'space saver' spare is an A40 3.5" x 13", fitted with a 155/80x13 tyre, which has a very slightly smaller o/d than the 185/70x13 fitted to the other wheels.
The spare should be fitted to the front, as I have an LSD, and they don't like differing sized tyres on each side! In recent years I have had to use it twice and it worked fine.
Talking of wheels and pcd. I have just bought a spacesaver tyre for a Fiat Punto (Never been used) the latest puntos don't come with spares wheels, so the one bought is for the previous model. I now find there is 2mm difference in the pcd! from one model to the next. I should have suspected the unexpected. It's been 98mm for years now it's 100mm------Anyone for a brand new punto spacesaver!
