Best Answer tiger99 , 26 November 2016 - 12:19 PM
One modern European car was a downright disgrace. BMW E36 Z3, 5,600 Nm/deg on a good day with no rust. About as stiff as a tea tray. That set the alleged high quality manufacturers off on a ridiculous quest to achieve needlessly high numbers, to outdo one another. But the real measure of a successful design is the torsional resonant frequency, because it takes into account the vehicle mass. A lightweight car like the Mini does not require a stupidly high torsional stiffness, but should achieve as high a resonant frequency as a heavyweight. It is likely that the Mini is much better in that respect than certain ladder-chassis SUVs.
This site http://blogs.youwhee...rehensive-list/
is largely confined to cars available in the USA but gives some interesting numbers. Not many classic cars, and those ladder chassised abominations with "torsion boxes" (which were a frequent source of structural cracking) would have scored very low indeed.
This link http://www.minimania...Body_Dimensions (please bookmark that site for future reference)
gives the numbers you are all waiting for, and as expected the saloon is ahead of the van due to the opening rear doors and lack of rear bulkhead. I have converted them for a direct comparison with modern stuff. That is 11,460 Nm/deg for the saloon and "only" 9,320 Nm/deg for the van. Very adequate for a lightweight car!
I don't have access to the torsional resonant frequencies and can't calculate them as they depend on mass distribution. But what i can say is that Alec knew exactly what he was doing!
If making a convertible, you will not get back to the original stiffness by adding box sections in the sills only, and you will have to be careful not to get problems where thick metal joins thin, which is not to sat that you should not do it to improve bean (bending) strength. A bit too low to add useful side impact protection.
The late LJK Setright, possibly the only truly competent motoring journalist of last century (and we seemingly don't have any now!), used to consider that for a road car 5000 to 10000 lb ft/deg was ample. So the Mini's 8,450 in real units was well within the upper range of what he considered to be adequate.
I can't find the figure for the old A35 right now, but it was up in silly supercar numbers, designed by ex-aircraft people, as was the 1800 Land Crab, designed by Alec.
But please be aware that torsional stiffness degrades quite badly when parts of a monocoque which are only carrying secondary loads are corroded, because they allow the primary structure to flex more, and bulge under compressive loads. And I don't doubt that oversills will send it way down. After a proper restoration, with welds located in the correct places, it will be as original, or maybe even better if you have seam welded where only spots were used originally.
I am very interested in stiffness figures for classic cars, so if you have any, this might be a good place to post them, so we can all be enlightened, and see just how good our Minis really are.
But to return to the original question, you certainly do not need to connect the front and rear subframes other than via the standard monocoque. You would be hard pressed to make much difference anyway unless you used a cruciform box section like old Rolls Royces, etc, or a true triangulated space frame. It is hard to improve good things.
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Mini Mad
Posted 25 November 2016 - 01:23 PM
I've seen a lot on older US muscle cars like the Camaro SS etc that they'll add in extra support beams connecting the front and rear subframes to gain better rigidity.
Did a quick google around and didn't find anything specific to the mini for this. Is it worth it? Is it possible? Has anyone done it?
Mini Mad
Posted 25 November 2016 - 01:42 PM
possible, but doubt any difference would be measureable, better investing in a good roll cage and anti roll bar...
Up Into Fourth
Posted 25 November 2016 - 01:45 PM
I've seen a lot on older US muscle cars like the Camaro SS etc that they'll add in extra support beams connecting the front and rear subframes to gain better rigidity.
Did a quick google around and didn't find anything specific to the mini for this. Is it worth it? Is it possible? Has anyone done it?
You are misunderstanding the design of the US cars. US cars of old (and some not so old to be honest) do not have subframes. They use ladder chassis design. Ie, beams placed longitudinally with cross braces between, making it appear like a ladder. The engine and shell then bolt onto this.
European cars use subframes front and back attached to a monocoque shell. This was pretty much pioneered by the classic Mini actually. This is recognised as being a more advanced and stronger setup than the ladder chassis for many many reasons I wont go into. As far as I'm aware, the only place you will find ladder chassis these days are in buses, articulated trucks and trailers.
Hope that clears it up for you.
Edited by Mini 360, 25 November 2016 - 01:48 PM.
Mini Mad
Posted 25 November 2016 - 01:58 PM
I've seen a lot on older US muscle cars like the Camaro SS etc that they'll add in extra support beams connecting the front and rear subframes to gain better rigidity.
Did a quick google around and didn't find anything specific to the mini for this. Is it worth it? Is it possible? Has anyone done it?
You are misunderstanding the design of the US cars. US cars of old (and some not so old to be honest) do not have subframes. They use ladder chassis design. Ie, beams placed longitudinally with cross braces between, making it appear like a ladder. The engine and shell then bolt onto this.
European cars use subframes front and back attached to a monocoque shell. This was pretty much pioneered by the classic Mini actually. This is recognised as being a more advanced and stronger setup than the ladder chassis for many many reasons I wont go into. As far as I'm aware, the only place you will find ladder chassis these days are in buses, articulated trucks and trailers.
Hope that clears it up for you.
Thank you for the information! This does clear things up.
possible, but doubt any difference would be measureable, better investing in a good roll cage and anti roll bar...
Yes, that was what I was wondering. E.g. even if you can do it. Is there a point?
Well I'll be buggered if I can find it
Posted 25 November 2016 - 02:35 PM
I've seen a lot on older US muscle cars like the Camaro SS etc that they'll add in extra support beams connecting the front and rear subframes to gain better rigidity.
Did a quick google around and didn't find anything specific to the mini for this. Is it worth it? Is it possible? Has anyone done it?
You are misunderstanding the design of the US cars. US cars of old (and some not so old to be honest) do not have subframes. They use ladder chassis design. Ie, beams placed longitudinally with cross braces between, making it appear like a ladder. The engine and shell then bolt onto this.
European cars use subframes front and back attached to a monocoque shell. This was pretty much pioneered by the classic Mini actually. This is recognised as being a more advanced and stronger setup than the ladder chassis for many many reasons I wont go into. As far as I'm aware, the only place you will find ladder chassis these days are in buses, articulated trucks and trailers.
Hope that clears it up for you.
Thank you for the information! This does clear things up.
possible, but doubt any difference would be measureable, better investing in a good roll cage and anti roll bar...
Yes, that was what I was wondering. E.g. even if you can do it. Is there a point?
Seeing as the mini is superb car to drive I'd say absolutely not.
One Carb Or Two?
Posted 25 November 2016 - 02:46 PM
It might make it safer in a head on !
Crazy About Mini's
Posted 25 November 2016 - 02:53 PM
Don't some racers tie in the subframe mounts to the roll cage?, sort of the same principle
Moved Into The Garage
Posted 25 November 2016 - 03:01 PM
Don't some racers tie in the subframe mounts to the roll cage?, sort of the same principle
yes the cages can be tied into the subframes but require some serious cutting out of the body.
Stage One Kit Fitted
Posted 25 November 2016 - 03:14 PM
Project Binky has tubing running through the voids in the sills connecting the front-back and adding rigidity.
Moved Into The Garage
Posted 25 November 2016 - 03:17 PM
Project Binky has tubing running through the voids in the sills connecting the front-back and adding rigidity.
new episode tonight.
Twisted Paint Polisher!!!
Posted 25 November 2016 - 03:21 PM
Project Binky has tubing running through the voids in the sills connecting the front-back and adding rigidity.
But Binky is not what we would call a run of the mill mini.
As nick has said when you think of how the subframes attach to the standard shell of a mini and then you want to tie those together front an back will take a lot of metal work.
Unless you are building a shell like Binky or something of that ilk then it will be a serious amount of work.
One Carb Or Two?
Posted 25 November 2016 - 03:50 PM
I've seen a lot on older US muscle cars like the Camaro SS etc that they'll add in extra support beams connecting the front and rear subframes to gain better rigidity.
Did a quick google around and didn't find anything specific to the mini for this. Is it worth it? Is it possible? Has anyone done it?
You are misunderstanding the design of the US cars. US cars of old (and some not so old to be honest) do not have subframes. They use ladder chassis design. Ie, beams placed longitudinally with cross braces between, making it appear like a ladder. The engine and shell then bolt onto this.
European cars use subframes front and back attached to a monocoque shell. This was pretty much pioneered by the classic Mini actually. This is recognised as being a more advanced and stronger setup than the ladder chassis for many many reasons I wont go into. As far as I'm aware, the only place you will find ladder chassis these days are in buses, articulated trucks and trailers.
Hope that clears it up for you.
Well, maybe you should do some research before stating something like that, because the Mustang has always been unibody, since 1964. And yes braces exist to connect the front and rear subframes, popular with the fox body style cause they are quite twisty.
Can't speak for the Camaro, don't know
Up Into Fourth
Posted 25 November 2016 - 04:38 PM
when I build a convertible , I tie in the front & rear sub frames with a 40x80 box tube , seam welded to inner sills
plus bracing & gussets to the tower bolts on the front sub frame , & 2 extra cross member tubes
one way to solve scuttle shake
a little bit heavier than a normal saloon , but stronger in a frontal impact & better in a side impact - in some collisions
lots of vehicles still use ladder frame chassis , certainly not rare
Moved Into The Garage
Posted 25 November 2016 - 05:37 PM
The torsional rigidity and strength of a Mini Body Shell is pretty high, off hand and from memory around 2500 lb / in. Given the length and weight of the cars, nothing further is needed.
Up Into Fourth
Posted 25 November 2016 - 09:08 PM
I've seen a lot on older US muscle cars like the Camaro SS etc that they'll add in extra support beams connecting the front and rear subframes to gain better rigidity.
Did a quick google around and didn't find anything specific to the mini for this. Is it worth it? Is it possible? Has anyone done it?
You are misunderstanding the design of the US cars. US cars of old (and some not so old to be honest) do not have subframes. They use ladder chassis design.
Hope that clears it up for you.
Well, maybe you should do some research before stating something like that
You should realise that I didn't say every American car, just the vast majority. 
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