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IRS chassis - cad, 3d ..and moving on to discuss chassis stiffness


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4 minutes ago, JohnC said:

Hi Stuart,

That looks like mine. Including the mountings for tubular shocks concentric with the springs. Just being picky, but I believe "box section" refers to the original method of (cold) folding a flat plate and then welding an external flange (i.e., the original TR6 chassis section). RHS is a continuously seam-welded hot rolled section. That's what my chassis is made from. I can't see any flanges, so I suspect that's what the one in your photo uses.

Cheers,
John

Yes theres no flanges anywhere on that chassis it is very strong and I like the diff bracing too.

Stuart.

 

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6 hours ago, JohnC said:

Hi Stuart,

That looks like mine. Including the mountings for tubular shocks concentric with the springs. Just being picky, but I believe "box section" refers to the original method of (cold) folding a flat plate and then welding an external flange (i.e., the original TR6 chassis section). RHS is a continuously seam-welded hot rolled section. That's what my chassis is made from. I can't see any flanges, so I suspect that's what the one in your photo uses.

Cheers,
John

Ratco in US make replacement frames. Seems to be cold rolled box section steel.

See here for information if interested. Not cheap and then have add freight costs for overseas. 

https://sites.google.com/view/ratco-test-site/tr-4a-5-250-6-products/construction-details

Their home page

https://www.rat-co.com/tr-4a-5-250-6-products

 

Simon

 

 

 

 

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8 hours ago, stuart said:

When Rubery Owen stopped manufacturing chassis one of the guys who used to work there made his own from box section, they were very good unfortunately he only made about a dozen. Picture below is one of them.

Stuart.

200866123_jeffstr5155.thumb.jpg.7261a7742edb4a36bd5ca210b1d2cec6.jpg

Hi Stuart,

I take it the Rubery Owen man made his before the DVLA restrictions upon new chassis ? and the chassis counting towards identity when rebuilding a car? That does restrict us in the UK to using either the original chassis repaired or (cough) another used chassis to replace a rotten damaged one. 

I remember that you'd said that CTM were the only DVLA approved new chassis manufacturer (now moved to France but still making them) and the same problem no doubt would befall a Ratco chassis, notwithstanding being in the US and the costs it presents, it presumably wouldn't meet DVLA requirements without inspection and their approval  ?

The UK is very tight for non original new parts that trip the 6 tests of originality to allow registration without it becoming a Q plate kit car, damn it must be lots easier in the various previous colonies.

Mick Richards

Edited by Motorsport Mickey
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So a slightly off topic question, how much does a chassis degrade over time from use and being exposed to the elements during normal use, assuming no real exposure to harsh environments such as salted roads etc? I know it will be impossible to answer as all cases differ but I imagine there is some fatigue due to use, and some degradation from being exposed to moisture in the air etc.

For my car, it was new in New Zealand in 1972 and spent 19 years there so was driven in rain (occasionally) and would have been exposed to some salt from driving near the ocean. From 1992 through to 1998 it was in Vancouver BC so similar weather and was not driven during the winter, just laid up in the garage. From mid 1998 it has been in the US desert southwest so only really exposed to heat (but it is a dry heat they say).

I guess a thorough inspection and some measurements of wall thickness would be needed to quantify this. It is not something I worry about but I do wonder about it from time to time.

Simon

 

 

 

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3 hours ago, Motorsport Mickey said:

Hi Stuart,

I take it the Rubery Owen man made his before the DVLA restrictions upon new chassis ? and the chassis counting towards identity when rebuilding a car? That does restrict us in the UK to using either the original chassis repaired or (cough) another used chassis to replace a rotten damaged one. 

I remember that you'd said that CTM were the only DVLA approved new chassis manufacturer (now moved to France but still making them) and the same problem no doubt would befall a Ratco chassis, notwithstanding being in the US and the costs it presents, it presumably wouldn't meet DVLA requirements without inspection and their approval  ?

The UK is very tight for non original new parts that trip the 6 tests of originality to allow registration without it becoming a Q plate kit car, damn it must be lots easier in the various previous colonies.

Mick Richards

Not sure when those restrictions came in, but my car was rebuilt on that chassis in 1989 in the UK. I brought it with me when I moved here soon after that. The chassis was made by Chassis Craft in Birmingham (prop E&J Neale). I'd be curious to know if this is the Rubery Owen spin-off. I doubt it, as I think CC was started by a repair/ resto company called Dee & Gee. Stuart - do you know?

John

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On 7/26/2020 at 9:22 PM, Paul Wike said:

Hi All,  TR-Register Newbie here ,   i was wondering if anyone had an accurate CAD drawing or 3D model of the standard TR6 chassis ?   I am wanting to make some brackets for a Celette Jig that i can use to measure and do basic repairs.

Any help is greatly appreciated.

Paul W.

Sorry Paul - I cannot see that the ACAD drawing I made for the TR4A would be of any use to you.  It was handy for me to appraising its design, but I wouldn't have thought it any use for bracketry on a TR6 jig. 

Because my drawing is for the TR4A ..it was derived from the drawing and a mean of the dimensions  given in that particular workshop manual. And even then the provided data only gives measurements to check for distortion, and no dimensions for the sections themselves.,  so it is unsuitable for either manufacture or repair.

Pete.

 

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On 7/24/2019 at 10:01 AM, Bfg said:

B)

That ought to keep you busy and out of trouble for a few hours.  Might I ask what you hope to use the model for ..aside from just the enjoyment of modelling it in 3d ? 

ie., are you exploring design changes ?

.

If I remember correctly GKN Telford manufactured the TR Chassis? They would certainly have Detailed Drawings of our Chassis. Has anyone ever approached them or know someone who works for them? They also have made Armored vehicles for the MOD. I would have thought that they would have had an input into the Design of the TR Chassis and knowing how BL worked, BL would have chosen the cheapest design that they could get away with!

Bruce.

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12 hours ago, kiwican said:

So a slightly off topic question, how much does a chassis degrade over time from use and being exposed to the elements during normal use, assuming no real exposure to harsh environments such as salted roads etc? I know it will be impossible to answer as all cases differ but I imagine there is some fatigue due to use, and some degradation from being exposed to moisture in the air etc.

For my car, it was new in New Zealand in 1972 and spent 19 years there so was driven in rain (occasionally) and would have been exposed to some salt from driving near the ocean. From 1992 through to 1998 it was in Vancouver BC so similar weather and was not driven during the winter, just laid up in the garage. From mid 1998 it has been in the US desert southwest so only really exposed to heat (but it is a dry heat they say).

I guess a thorough inspection and some measurements of wall thickness would be needed to quantify this. It is not something I worry about but I do wonder about it from time to time.

Simon

Simon, there are way too many variables to even suggest an answer.  It starts off from the specification and batch of steel used to make your chassis and even how that was stored before use, and goes right the way through to how well it was protected (particularly inside the sections), and then how the car was used over the years (think of the chassis and body tub torsion experienced in a rally car). And even though your car may have enjoyed (or been bored by !) a gentle life, you will really never know whether a previous owner, his wife or son, was a pretty awful driver.  As a design engineer I'm generally sympathetic to the cars I drive and the motorcycles I ride - but even then I can cite quite a few occasions when the vehicle flew and/or span, slid sideways or whatever.  I know I did bend the chassis of one car (..actually a three wheeler) in landing after a hump-back bridge.  Admittedly for some time, appraising a car's chassis design was part of my job, but still sports cars in particular ought to be enjoyed. 

Chassis wall thickness most often tends to lessen in places where you cannot see, ie., inside the chassis rails and under brackets or doubling plates. Without dissembling or cutting into a chassis - you cannot see nor measure them.  Even then, the weakness of a chassis is often in the welds and rolled seams ..they having been sheared and twisted. Again it's impossible to see inside a folded or rolled and spot-welded seam. External welds and the metal around them can be assessed, but only fully when the chassis (..or a suspect area) is chemically stripped of paint and surface rust.

Possibly a fairly accurate non-destructive test would be to jig the bare chassis and deliberately twist and bend it. Then compare those results with a brand new chassis likewise tested. That would give you a fair indication of it's current structural state. 

But as that's generally not economical, a private owner might compare a known-to-be-good car with your own.  Rest each car's chassis (wheels off the ground) on hard blocks and jack up one corner. Measure chassis distortion from a datum floor, and otherwise compare how well the door shuts, the bonnet and boot lid fit / open / close.   

Alternatively, a really experienced restorer ..of your particular model of car, will have gotten 'a feel' for structurally good cars, and those which are let's say 'a bit ropey'.  They may be able to drive your car and give you their opinion as to whether yours feels 'tight' or otherwise.

Hope that helps,

Pete.

 

Edited by Bfg
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9 hours ago, JohnC said:

Not sure when those restrictions came in, but my car was rebuilt on that chassis in 1989 in the UK.

I had designed and was making / supplying replacement chassis (for Citroen 2CV + Falcon & Lomax Kit cars) in the early to mid-1990's  ..that was before the DVLA's points system.  I don't recall when it was introduced but I suspect it was introduced when or soon after classic vehicles became road-tax exempt.

Pete.

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6 hours ago, Bfg said:

Sorry Paul - I cannot see that the ACAD drawing I made for the TR4A would be of any use to you.  It was handy for me to appraising its design, but I wouldn't have thought it any use for bracketry on a TR6 jig. 

Because my drawing is for the TR4A ..it was derived from the drawing and a mean of the dimensions  given in that particular workshop manual. And even then the provided data only gives measurements to check for distortion, and no dimensions for the sections themselves.,  so it is unsuitable for either manufacture or repair.

Pete.

 

No worries Pete ,  i think i can manage with the workshop drawings - just sometimes hard to understand where the actual point is referenced - for instance checking for twist - jacking up to a certain height for points A and F - doesn't really suggest if the underside of the bracket etc Point F in the manual could refer to the top , bottom or any of the two holes in the bracket just a bit ambiguous ;-).  all part of the fun !

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7 hours ago, Bfg said:

Simon, there are way too many variables to even suggest an answer.  It starts off from the specification and batch of steel used to make your chassis and even how that was stored before use, and goes right the way through to how well it was protected (particularly inside the sections), and then how the car was used over the years (think of the chassis and body tub torsion experienced in a rally car). And even though your car may have enjoyed (or been bored by !) a gentle life, you will really never know whether a previous owner, his wife or son, was a pretty awful driver.  As a design engineer I'm generally sympathetic to the cars I drive and the motorcycles I ride - but even then I can cite quite a few occasions when the vehicle flew and/or span, slid sideways or whatever.  I know I did bend the chassis of one car (..actually a three wheeler) in landing after a hump-back bridge.  Admittedly for some time, appraising a car's chassis design was part of my job, but still sports cars in particular ought to be enjoyed. 

Chassis wall thickness most often tends to lessen in places where you cannot see, ie., inside the chassis rails and under brackets or doubling plates. Without dissembling or cutting into a chassis - you cannot see nor measure them.  Even then, the weakness of a chassis is often in the welds and rolled seams ..they having been sheared and twisted. Again it's impossible to see inside a folded or rolled and spot-welded seam. External welds and the metal around them can be assessed, but only fully when the chassis (..or a suspect area) is chemically stripped of paint and surface rust.

Possibly a fairly accurate non-destructive test would be to jig the bare chassis and deliberately twist and bend it. Then compare those results with a brand new chassis likewise tested. That would give you a fair indication of it's current structural state. 

But as that's generally not economical, a private owner might compare a known-to-be-good car with your own.  Rest each car's chassis (wheels off the ground) on hard blocks and jack up one corner. Measure chassis distortion from a datum floor, and otherwise compare how well the door shuts, the bonnet and boot lid fit / open / close.   

Alternatively, a really experienced restorer ..of your particular model of car, will have gotten 'a feel' for structurally good cars, and those which are let's say 'a bit ropey'.  They may be able to drive your car and give you their opinion as to whether yours feels 'tight' or otherwise.

Hope that helps,

Pete.

 

Thanks for the reply Pete.

I did not think there would be an easy answer and you noted a few things I did not think of. I guess you just have to monitor the condition of your vehicle and make decisions based on what you see.

 

Cheers

Simon

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  • 11 months later...
On 7/28/2020 at 1:02 AM, kiwican said:

Ratco in US make replacement frames. Seems to be cold rolled box section steel.

See here for information if interested. Not cheap and then have add freight costs for overseas. 

https://sites.google.com/view/ratco-test-site/tr-4a-5-250-6-products/construction-details

Their home page

https://www.rat-co.com/tr-4a-5-250-6-products

 

Simon

 

 

 

 

Hello All, 

I've just come across this site while doing some study on enhancements for my sad old TR5. Thanks for the interesting material here, is the discussion still active?

I followed the link in the post to the Ratco site, moving on from their chassis page I was deeply alarmed to see their fabricated replacement semi-trailing arm for TR4A/5/6. It violates basic principles of stress management, it could come with a "fail here" sticker pre-attached. I don't believe the item pictured will be durable. I'm writing this as a caution from my background of 45 years in automotive design and development, including time in design analysis at Triumph, Canley.

Clive

 

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5 hours ago, Clive R said:

Hello All, 

I've just come across this site while doing some study on enhancements for my sad old TR5. Thanks for the interesting material here, is the discussion still active?

I followed the link in the post to the Ratco site, moving on from their chassis page I was deeply alarmed to see their fabricated replacement semi-trailing arm for TR4A/5/6. It violates basic principles of stress management, it could come with a "fail here" sticker pre-attached. I don't believe the item pictured will be durable. I'm writing this as a caution from my background of 45 years in automotive design and development, including time in design analysis at Triumph, Canley.

Clive

 

Clive, Welcome to the forum. Can you elaborate on your concerns:  https://sites.google.com/view/ratco-test-site/tr-4a-5-250-6-products/rear-trailing-arm-project

always keen to learn,  Peter

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Best explained by the attached file, I hope. Having just one suspension link per side, all the loads must go through it - driving, braking, cornering and supporting the mass of the car. That gives some complex loading conditions, the original casting has careful shaping to manage the loads and avoid stress concentrations at any point. the fabricated part, however, passes all the loads through junctions where the very substantial hub / bearing holder reduces to much smaller sections of tube. in addition, the loads are applied in the middle of a tube, forcing it to bend. Considering the multiple loadings applied to the region shown with the jagged red outline, and the fluctuating direction of the cornering forces, I would not be surprised to see failures in that region.

My sketch assumes standard dampers, attached behind the wheel centre. In this case the damper loads will tend to balance the spring load (to a varying and completely unpredictable degree depending on the road surface). This means the resulting loads passing through the trailing arm to the chassis, due to springs / dampers, will be relatively low and occasionally zero. If, however, an owner fits telescopic dampers concentric with the spring, the spring and damper loads will always add to each other and will always create a reaction force at the chassis attachment (because there's no longer a counter force behind the wheel centre). This will further add to the loads passing through the highly stressed section of the trailing arm.

I hope the sketch will make this more clear than my words!

C

 

IRS rear arm loads.pdf

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It looks nice though, doesn't it? 
Brave attempt by the supplier.

Another weak spot may be the sharp cut-outs. Sharp non-radiussed corners can be starting point for fatigue. I would add a radius, like R25 in those windows.

A test period as done by the supplier will help identify short-use related issues, but a component like this requires long exposure to the actual loads (ie many miles) to show those defects.

The challenge is weight versus strength and stiffness.
A welded component (fabricated we call it in our industry)  can hardly beat a cast item where the design can be optimized for all aspects/loads.

Cheers,

Waldi

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Why bother, plenty of TR trailing arms on ebay.co.uk and ebay.com (UK and USA). Fixing a problem that doesn't exist. If you're not going original you might as well design something better not a basic copy out of some old steel box section you have lying around the back of the workshop

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18 hours ago, Clive R said:

Best explained by the attached file, I hope. Having just one suspension link per side, all the loads must go through it - driving, braking, cornering and supporting the mass of the car. That gives some complex loading conditions, the original casting has careful shaping to manage the loads and avoid stress concentrations at any point. the fabricated part, however, passes all the loads through junctions where the very substantial hub / bearing holder reduces to much smaller sections of tube. in addition, the loads are applied in the middle of a tube, forcing it to bend. Considering the multiple loadings applied to the region shown with the jagged red outline, and the fluctuating direction of the cornering forces, I would not be surprised to see failures in that region.

My sketch assumes standard dampers, attached behind the wheel centre. In this case the damper loads will tend to balance the spring load (to a varying and completely unpredictable degree depending on the road surface). This means the resulting loads passing through the trailing arm to the chassis, due to springs / dampers, will be relatively low and occasionally zero. If, however, an owner fits telescopic dampers concentric with the spring, the spring and damper loads will always add to each other and will always create a reaction force at the chassis attachment (because there's no longer a counter force behind the wheel centre). This will further add to the loads passing through the highly stressed section of the trailing arm.

I hope the sketch will make this more clear than my words!

C

 

IRS rear arm loads.pdf 261.65 kB · 33 downloads

Thanks Clive, I have long puzzled over the  use of cast alloy for the trailing arms, but now see in the region of max stress you emphasis that it forms a box section. Alloy castings must have been more expensive than the forged steel wishbones of the front suspension so unsprung weight in a steel t/a must have been unacceptable to Triumph engineers.  Peter

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On 7/25/2021 at 6:24 PM, Peter Cobbold said:

Thanks Clive, I have long puzzled over the  use of cast alloy for the trailing arms, but now see in the region of max stress you emphasis that it forms a box section. Alloy castings must have been more expensive than the forged steel wishbones of the front suspension so unsprung weight in a steel t/a must have been unacceptable to Triumph engineers.  Peter

To be frank I doubt unsprung mass per se was the main consideration in the original part, remembering the trailing arm was attached to a floppy set of girders so no dynamic boundaries were being pushed. More likely a pragmatic decision that a casting was the best way to get the requisite shapes, sections and blends to avoid stress concentrations at corners and joints, and a cast iron part would have been ridiculously heavy. The horizontal web joining the main arm to the bottom of the hub housing shows the force directions were considered, it doesn't look like an intuitive feature. As to the fabricated part, personally I think it's hideous. (Sorry Waldi!) In particular, I was brought up to believe triangles are sacred, loads should only be applied to their corners. By contrast, the chunk of tube that applies most of the driving load to the centre of the transverse tube will not only cause high stress, it will also tend to cause fluctuating toe angles at the wheel as drive and cornering loads are applied. I haven't calculated how significant that might be but it's clearly undesirable to add to an existing weakness in the car's dynamics. I've almost finished...but the square tube running back from the inner bush appears to form the end of a stiff assembly terminating at a flat sheet (the spring pan). Vertical loads bending the part, such as in braking, will cause a stress concentration as the end of the tube digs in to the sheet. This would be aggravated if an owner fits a telescopic damper concentric with the spring as it increases the load at this point (by removing the load from the original point at the rear of the arm, where it tends to counter the spring load and reduce the bending force on the arm overall.

My summary - it's just wrong!

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