It is currently Fri Mar 29, 2024 6:46 am




Post new topic Reply to topic  [ 14 posts ] 
Chassis Strength 
Author Message
Site Admin

Joined: Fri Apr 13, 2007 5:42 am
Posts: 37
Location: Devon
Post Chassis Strength
I remember someone posted up a wonderful stress analysis of the Coupe chassis on the old forum. (Brian was it?)

Does anyone still have these images? It would be nice to get them back online!

Cheers,
Henry


Fri Jan 04, 2008 10:02 pm
Profile
Admin, and Coupe Nutter
User avatar

Joined: Fri Sep 14, 2007 10:34 pm
Posts: 1762
Location: In the workshop
GTM: Cox/Coupe
Post Re: Chassis Strength
Dada

hope Bryn doesnt mind

Image

Image

Image

Did that work?

if not i have another cunning plan

WEST

_________________
IF wile e coyote had a GTM he would have one with Nitrous too! watch out road runner! The First GTM into the 11s then the 10s, PB 10.87 @ 125.5 Mph on A048 tyres, and fully road legal at Santa Pod


Fri Jan 04, 2008 11:01 pm
Profile
The Terrible Tims

Joined: Fri Sep 28, 2007 7:56 pm
Posts: 747
Location: In the garage,Sileby, LEICS
GTM: Cox/Coupe
Post Re: Chassis Strength
Seems to me like the the rear frame accounts for half of the movement in the chassis. So I'm hoping that the improvements I've made to the rear of mine would result in less twist. I think the other thing to note is to try and make the tunnel as stiff as possible. I've added some box section to the area around the gear selector, to try and add some stiffness.

_________________
Tim Rowe

"Is est totus perfectus per fumi quod speculum"


Sun Jan 06, 2008 9:43 pm
Profile E-mail
On the Road
User avatar

Joined: Fri Oct 12, 2007 9:38 am
Posts: 740
Location: Stoke
Post Re: Chassis Strength
Note that movement in the chassis is not the prime aim of a finite element analysis - the twist shown is usually amplified to give an idea of the movements involved - otherwise you would hardly see them. The primary use of the diagrams are in the colours - as in the grading to the side. Red is bad, blue is good. There are a few places on the chassis giving large point loads - These are the areas that need beefing up or redesigning to spread the load - to avoid failure in these areas - not to stop the twist. If you stiffen the chassis to lessen twist you may induce point loads and cause failure.
The thing to do if possible here is to get hold of the original analysis and try a few mods to lessen the point loads and possibly stiffen it up at the same time.

Note the red bits around the aperture in the tunnel, and how evenly stressed the sills are!

Phil (Still looking for a Coupe)

_________________
GTM Libra, GTM Coupe, Siva Moonbug, GMC Safari And DeTomaso Pantera.


Mon Jan 07, 2008 6:56 pm
Profile
GTM delivered
User avatar

Joined: Tue Sep 18, 2007 7:53 pm
Posts: 44
Location: North Wales
Post Re: Chassis Strength
The bit that interests me are the stress points at the bottom of the access hole to the engine in the rear bulkhead. It doesn't look massive, but I notice that my chassis is splitting slightly at these points due to the seperate metal sheets coming apart.

There are some large stress points in the foot wells I notice, did West not have a problem there on his car (his must be a good test chassis due to the large mileage he has clocked up).

Anybody done FEA with the body on? While all the literature in the sales said it was an unstressed fiberglass body, that is not strictly true, more semi-stressed as the chassis is an open monocoque. I've noticed with my bare chassis that it does flex a reasonable amount and was looking at putting a simple cage in to reduce this (just continuing the rear roll hoop forwards over the doors, down the A pillars to the front jacking point, plus a joining member across the top of the screen).


Mon Jan 07, 2008 10:05 pm
Profile
Admin, and Coupe Nutter
User avatar

Joined: Fri Sep 14, 2007 10:34 pm
Posts: 1762
Location: In the workshop
GTM: Cox/Coupe
Post Re: Chassis Strength
Durbs wrote:
........there are some large stress points in the foot wells I notice, did West not have a problem there on his car (his must be a good test chassis due to the large mileage he has clocked up).

Anybody done FEA with the body on? While all the literature in the sales said it was an unstressed fiberglass body, that is not strictly true, more semi-stressed as the chassis is an open monocoque. I've noticed with my bare chassis that it does flex a reasonable amount and was looking at putting a simple cage in to reduce this (just continuing the rear roll hoop forwards over the doors, down the A pillars to the front jacking point, plus a joining member across the top of the screen).



Someone remembers well :!:
After a couple of track days I had noticed the areas in the foot wells, had been flexing, one advantage of painting your chassis in a colour other than black is you can see the cracks form in the paint if there is any flexing., This evenings top tip..

I also found the box section between the diagonal cross brace and rear shock mount on the space frame had been flexing massively, hence why my car now has a piece of 2x1 welded ontop from the shock mount foward a few inches [and Tim has built this part of his frame in 2x1 after talking to me], not the prettiest way but when you find the problem and your amoungst a weekend engine out grear ratio change, and back in time is short. Was found between track days and two days before the next which was paid for :!:


Will hopefully get around to doing a chassis model myself and adding a cage etc to see the difference, but probaly end up actually fitting the cage first at this rate.

The Body does add torsional strength and this is why i strongly recomend you glass in your windscreen surport tubes and atleast PU your tub to the chassis at the rear when you fit it as this will stiffen up the chassis i have seen the difference when i did a simple lifting one corner test on my chassis when i had it sat on a jig during some work, nothing techincal just a visual test and it made a difference glassing in the window tubes..

Also may i add the diagonal plating under the dash between bulkhead and A panel, these are spot welded inplace, at least stitch weld these, three stiches extending the exsiting spots will do, as this panel did a surprising amount


Enough of my dribble this evening

I have done well over 40K miles with honda power now, plus the mileage I did before I even started this Honda Power fun.

WEST

[excuse any mistakes have had a couple of drinks this evening]

_________________
IF wile e coyote had a GTM he would have one with Nitrous too! watch out road runner! The First GTM into the 11s then the 10s, PB 10.87 @ 125.5 Mph on A048 tyres, and fully road legal at Santa Pod


Tue Jan 08, 2008 10:21 pm
Profile
The Terrible Tims

Joined: Fri Sep 28, 2007 7:56 pm
Posts: 747
Location: In the garage,Sileby, LEICS
GTM: Cox/Coupe
Post Re: Chassis Strength
WEST wrote:
After a couple of track days I had noticed the areas in the foot wells, had been flexing, one advantage of painting your chassis in a colour other than black is you can see the cracks form in the paint if there is any flexing., This evenings top tip..



That is good news, as I've bought the paint for the tub and it definitely isn't black.

WEST wrote:
I also found the box section between the diagonal cross brace and rear shock mount on the space frame had been flexing massively, hence why my car now has a piece of 2x1 welded ontop from the shock mount foward a few inches [and Tim has built this part of his frame in 2x1 after talking to me], not the prettiest way but when you find the problem and your amoungst a weekend engine out grear ratio change, and back in time is short. Was found between track days and two days before the next which was paid for :!:


Can't beat taking an idea and building on it. Just ask Mclaren.

WEST wrote:
Also may i add the diagonal plating under the dash between bulkhead and A panel, these are spot welded inplace, at least stitch weld these, three stiches extending the exsiting spots will do, as this panel did a surprising amount


I should have all the welding done on the tub this weekend, so I will have to put that little tweak on the list of things to get sorted.

A good collection of drunken knowledge there Neil :lol: :wink:

_________________
Tim Rowe

"Is est totus perfectus per fumi quod speculum"


Wed Jan 09, 2008 11:35 am
Profile E-mail
The Terrible Tims
User avatar

Joined: Sat Sep 29, 2007 12:23 pm
Posts: 487
Location: suffolk
GTM: Cox/Coupe
Post Re: Chassis Strength
I've been cutting around the box at the rear and although it looks rust free its surprising how much internal corrosion there is, the box is pretty thin to start with :!:

_________________
I'm not a complete idiot, parts of me are missing!!!!!


Wed Jan 09, 2008 12:55 pm
Profile
Admin, and Coupe Nutter
User avatar

Joined: Fri Sep 14, 2007 10:34 pm
Posts: 1762
Location: In the workshop
GTM: Cox/Coupe
Post Re: Chassis Strength
the other Tim wrote:
I've been cutting around the box at the rear and although it looks rust free its surprising how much internal corrosion there is, the box is pretty thin to start with :!:



Yep most coupes seem to have 18swg tubing which is 1.2mm thick to start with, was shocked my self when i first found this as always assumed it was 16 swg 1.6mm.

Quote:
A good collection of drunken knowledge there Neil :lol: :wink:


JD and Dr pepper went down well last night :P

WEST

_________________
IF wile e coyote had a GTM he would have one with Nitrous too! watch out road runner! The First GTM into the 11s then the 10s, PB 10.87 @ 125.5 Mph on A048 tyres, and fully road legal at Santa Pod


Wed Jan 09, 2008 2:04 pm
Profile
GTM delivered
User avatar

Joined: Tue Sep 18, 2007 7:53 pm
Posts: 44
Location: North Wales
Post Re: Chassis Strength
WEST wrote:
Also may i add the diagonal plating under the dash between bulkhead and A panel, these are spot welded inplace, at least stitch weld these, three stiches extending the exsiting spots will do, as this panel did a surprising amount


Noticed my chassis has gone in this place as well, so will definitely be stich welding down there as well as round the rear access panel.

West, how did you strengthen the chassis round the footwell, if I remember rightly you changed the shape slightly as well? Was this to reduce the stress or just to give you more room round the pedals?


Wed Jan 09, 2008 3:31 pm
Profile
The Terrible Tims
User avatar

Joined: Sat Sep 29, 2007 12:23 pm
Posts: 487
Location: suffolk
GTM: Cox/Coupe
Post Re: Chassis Strength
I'm hoping my cage will negate most of the above problem areas apart from near the rear shock mounts. :!: :)

_________________
I'm not a complete idiot, parts of me are missing!!!!!


Wed Jan 09, 2008 7:12 pm
Profile
Part built GTM

Joined: Fri Aug 15, 2014 4:49 pm
Posts: 141
GTM: Cox/Coupe
Post Re: Chassis Strength
Does any still have the pictures from the thread saved that they could re-upload?

Also, West, what do you mean by the below? pictures would be a great help

thanks


WEST wrote:
I also found the box section between the diagonal cross brace and rear shock mount on the space frame had been flexing massively, hence why my car now has a piece of 2x1 welded ontop from the shock mount foward a few inches [and Tim has built this part of his frame in 2x1 after talking to me], not the prettiest way but when you find the problem and your amoungst a weekend engine out grear ratio change, and back in time is short. Was found between track days and two days before the next which was paid for :!:


Sun Dec 21, 2014 1:14 am
Profile E-mail
Admin, and Coupe Nutter
User avatar

Joined: Fri Sep 14, 2007 10:34 pm
Posts: 1762
Location: In the workshop
GTM: Cox/Coupe
Post Re: Chassis Strength
As if by magic

a picture speaks a thousand words

Attachment:
spaceframe.jpg
spaceframe.jpg [ 38.38 KiB | Viewed 22454 times ]


The bits in red are what I am talking about, and the black line is where I experienced the signs of flexing. On some chassis the diagonal going down to the bulkhead is in a slightly different position I have noted on a couple of cars. If you think about it the whole weight of the rear of the car is on the tower mounts. The little bit of box section between the diagonal and the tower mounts is quite stressed hence the additional brace.

Neil

_________________
IF wile e coyote had a GTM he would have one with Nitrous too! watch out road runner! The First GTM into the 11s then the 10s, PB 10.87 @ 125.5 Mph on A048 tyres, and fully road legal at Santa Pod


Sun Dec 21, 2014 11:04 pm
Profile
Part built GTM

Joined: Fri Aug 15, 2014 4:49 pm
Posts: 141
GTM: Cox/Coupe
Post Re: Chassis Strength
That's perfect, and a great explanation! Thank you Neil.

Whilst we are on the subject, is there anywhere else which would benefit from strengthening, apart from that what is in this thread?

James


Wed Dec 24, 2014 8:04 pm
Profile E-mail
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 14 posts ] 


Who is online

Users browsing this forum: No registered users and 4 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © phpBB Group.
Designed by Vjacheslav Trushkin for Free Forums/DivisionCore.

phpBB SEO