I've been looking at a lot of photos for ideas for a semi-monocoque scratch build chassis. I have seen many claims of "full spaceframe" and "fully triangulated spaceframe" but have yet to see either.
Now I'm aware that it's next to impossible to produce a full conventional spaceframe that will fit under a GT40 bodyshell and still allow humans to enter and exit. However, of the many partial spaceframes out there, there seems to be a lot where triangulation is missed in key areas.
Here are a few of my observations:
1. Untriangulated sills - no structure to stabilise top edges of the open "hole" where you sit. Maybe other areas are worse so this is the least of the problems on some chassis'.
2. No or incomplete triangulation in the engine bay/rear suspension frame structure.
3. No or incomplete triangulation of the front suspension frame structure.
4. Little attempt to stabilise the centre tub to front frame bulkhead.
5. No triangulation in the centre tube to engine bay bulkhead.
6. Omission of load path structure from suspension points, even when such an omission is unnecessary.
On top of these observations, it doesn't seem like these points are consistent from one manufacturer to another. It seems that some have good triangulation on the front end but neglect the rear and vice versa.
I would be curious to know what the torsional stiffness of the various chassis are and wondered if anyone had any real life experience with the front/rear end stiffness, or lack thereof, in these spaceframes. The one's I've been looking at and the weaknesses I can see are:
1. MDA - Good rear end but not sure about front. Centre to front/rear bulkheads?
2. Tornado - Rear looks OK but front may be overly complicated for good load path control.
3. GTD (newest) - front and rear lacks trianguation. Centre to front/rear bulkheads?
4. Southern GT - better than GTD but engine bay/rear suspension load paths could be better transferred to tub. Front OK but still some suspension pick up issues. Centre to front/rear rear bulkheads?
5. Roaring Forties - little triangulation in the front end, looks very weak in torsion. Rear needs closer look but ??? Bulkheads as the rest.
Obviously panelling will stiffen many areas, but out of the 5, MDAs looks most promising out of the box with Southern GTs rear end being fairly simple to stiffen. Both have fairly nice pattern rear gearbox/suspension frame with MDAs being pretty close to the original pattern.
RFs front end could be stiffened fairly easily as the basic shape is simple enough but the rear could be more difficult, especially around the area that the lower trailing arm conflicts with the frame. The Tornado frame is more complex at the front, but probably better out of the box for stiffness.
I looked at the GTD for reference and it's got plenty of weak points, but some cars have done good service on the street for years. Probably a bit difficult to predict on a rough track though and suspension tuning could be challenging as the frame would be fighting you the whole time.
Anyone got and modified any of the above and why? Anyone racing them and found a particular weakness?
I know this has been covered in previous posts but they are often overly emotive and not particularly technically profficient. Too many IMHO and not enough "under X load, Y suspension point deflects Z amount."
I'm an aeronautical engineer and would appreciate people's technical input or actual test/race experience.
Better yet, would anyone with money to burn like to build an adjustable suspension rig and test them? I didn't win the lottery last night so I'm stuck.
Stew
Now I'm aware that it's next to impossible to produce a full conventional spaceframe that will fit under a GT40 bodyshell and still allow humans to enter and exit. However, of the many partial spaceframes out there, there seems to be a lot where triangulation is missed in key areas.
Here are a few of my observations:
1. Untriangulated sills - no structure to stabilise top edges of the open "hole" where you sit. Maybe other areas are worse so this is the least of the problems on some chassis'.
2. No or incomplete triangulation in the engine bay/rear suspension frame structure.
3. No or incomplete triangulation of the front suspension frame structure.
4. Little attempt to stabilise the centre tub to front frame bulkhead.
5. No triangulation in the centre tube to engine bay bulkhead.
6. Omission of load path structure from suspension points, even when such an omission is unnecessary.
On top of these observations, it doesn't seem like these points are consistent from one manufacturer to another. It seems that some have good triangulation on the front end but neglect the rear and vice versa.
I would be curious to know what the torsional stiffness of the various chassis are and wondered if anyone had any real life experience with the front/rear end stiffness, or lack thereof, in these spaceframes. The one's I've been looking at and the weaknesses I can see are:
1. MDA - Good rear end but not sure about front. Centre to front/rear bulkheads?
2. Tornado - Rear looks OK but front may be overly complicated for good load path control.
3. GTD (newest) - front and rear lacks trianguation. Centre to front/rear bulkheads?
4. Southern GT - better than GTD but engine bay/rear suspension load paths could be better transferred to tub. Front OK but still some suspension pick up issues. Centre to front/rear rear bulkheads?
5. Roaring Forties - little triangulation in the front end, looks very weak in torsion. Rear needs closer look but ??? Bulkheads as the rest.
Obviously panelling will stiffen many areas, but out of the 5, MDAs looks most promising out of the box with Southern GTs rear end being fairly simple to stiffen. Both have fairly nice pattern rear gearbox/suspension frame with MDAs being pretty close to the original pattern.
RFs front end could be stiffened fairly easily as the basic shape is simple enough but the rear could be more difficult, especially around the area that the lower trailing arm conflicts with the frame. The Tornado frame is more complex at the front, but probably better out of the box for stiffness.
I looked at the GTD for reference and it's got plenty of weak points, but some cars have done good service on the street for years. Probably a bit difficult to predict on a rough track though and suspension tuning could be challenging as the frame would be fighting you the whole time.
Anyone got and modified any of the above and why? Anyone racing them and found a particular weakness?
I know this has been covered in previous posts but they are often overly emotive and not particularly technically profficient. Too many IMHO and not enough "under X load, Y suspension point deflects Z amount."
I'm an aeronautical engineer and would appreciate people's technical input or actual test/race experience.
Better yet, would anyone with money to burn like to build an adjustable suspension rig and test them? I didn't win the lottery last night so I'm stuck.
Stew
Last edited: