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Which other sports cars had spaceframes made with square tubing?
bigtime - 14/3/14 at 10:52 AM

As far as I know most sports cars from Ferrari, Lamborghini have used round tube in their spaceframes.
Which other sports cars have used square tubing?

Are square tubing and its welds THAT weak compared to round tube?
Would gusseting make joints at least as strong as those in round tubing?

v8kid - 14/3/14 at 12:10 PM

the reason that for the weight round tubing has a higher torsional stiffness - its a weight saving thing principally

scootz - 14/3/14 at 12:13 PM

Square tubing also makes it easier for us to rivet on panels without having to form the ali over round rails first.

Ivan - 14/3/14 at 12:26 PM

Strength doesn't really come into it - round tubes of the same "strength" are lighter than square ones, but square tubes are much easier to join at angles than round ones as the round ones need "fish-mouthing" making it tricky for amateurs to construct. The fabrication issues don't really matter in a factory environment but weight does hence their use of round tubes.

Not Anumber - 14/3/14 at 12:48 PM

Remeber that guy who popped up and said we were all doing it wrong with 1" tubing and we should all be building chassis with 4" diameter round. Oddly he doesnt appear to have built anything as yet.

chrism - 14/3/14 at 03:03 PM

quote:
Originally posted by Not Anumber
Remeber that guy who popped up and said we were all doing it wrong with 1" tubing and we should all be building chassis with 4" diameter round. Oddly he doesnt appear to have built anything as yet.


Didn't/Doesn't one of the cobra replicas use a tube chassis with 2 x 4" diameter tubes forming the backbone, I seem to remember reading about it years ago.

Thinking about it doesnt the MNR chassis use round tubing instead of square.

[Edited on 14/3/14 by chrism]

v8kid - 14/3/14 at 03:10 PM

I know we are digressing but I'm sure I saw posts on this site with calculations that showed a ladder chassis (i.e. 4" round tubes) if properly designed was as stiff as the locost chassis.

As said above not so easy to hang stuff off though

Cheers!

[Edited on 14-3-14 by v8kid]

theduck - 14/3/14 at 03:53 PM

quote:
Originally posted by chrism
quote:
Originally posted by Not Anumber
Remeber that guy who popped up and said we were all doing it wrong with 1" tubing and we should all be building chassis with 4" diameter round. Oddly he doesnt appear to have built anything as yet.


Didn't/Doesn't one of the cobra replicas use a tube chassis with 2 x 4" diameter tubes forming the backbone, I seem to remember reading about it years ago.

Thinking about it doesnt the MNR chassis use round tubing instead of square.

[Edited on 14/3/14 by chrism]


Yes MNR does, but not 4inch diameter n

ceebmoj - 14/3/14 at 04:49 PM

quote:
Originally posted by v8kid
I know we are digressing but I'm sure I saw posts on this site with calculations that showed a ladder chassis (i.e. 4" round tubes) if properly designed was as stiff as the locost chassis.

As said above not so easy to hang stuff off though

Cheers!

[Edited on 14-3-14 by v8kid]


Cymtriks seems to have a number of posts along thous lines. I think his caveats where along the lines that its much harder to design a proper space frame that a ladder chassis and most kitcars are a long way from a proper space frame and also there are benefits to mounting and protection that come from space frames. maybe he is about to make the point.

redturner - 14/3/14 at 05:45 PM

My single seater racing car is constructed from square tubing, my mates, same year, different manufacturer, round tubing. both about the same weight. My Turner sports car has 2 x 3" round tubes running front to back in the form of a ladder chassis...So did A.C and lots of others.....

TheGiantTribble - 14/3/14 at 05:53 PM

IIRC when Marcos stopped using the wooden chassis, they used square steel tube.

Sam_68 - 18/3/14 at 07:19 AM

quote:
Originally posted by ceebmoj
Cymtriks seems to have a number of posts along those lines. I think his caveats where along the lines that its much harder to design a proper space frame that a ladder chassis and most kitcars are a long way from a proper space frame and also there are benefits to mounting and protection that come from space frames.


He is also relying on substantial 3D scuttle bracing for the 'ladder frames', for which he claims competitive stiffness, so they're not true ladder frames. In fact, they are effectively ladder frames with significant (if crude) hybrid spaceframe/unitary bracing. True ladder frames are sh1te... end of.

Also, his 'advantages' focus on ease of fabrication and cost for equivalent stiffness, not stiffness:weight.

A properly designed spaceframe will always offer a substantially better stiffness:weight than a ladder frame.

quote:
Originally posted by ceebmojmaybe he is about to make the point.


Shhhh... I think they've got his levels of medication just about right recently - don't wreck the good work by provoking him !

v8kid - 18/3/14 at 08:51 AM

Karts are ladder frames aren't they? They don't seem to be sh1te and are quite quick

oops forgot to mention the whole unrelated point - they are made from round tube!

[Edited on 18-3-14 by v8kid]

coyoteboy - 18/3/14 at 09:37 AM

Karts are not really ladder frames, no.

Ivan - 18/3/14 at 11:40 AM

quote:
Originally posted by chrism

Didn't/Doesn't one of the cobra replicas use a tube chassis with 2 x 4" diameter tubes forming the backbone, I seem to remember reading about it years ago.

Thinking about it doesnt the MNR chassis use round tubing instead of square.

[Edited on 14/3/14 by chrism]


Nearly all Cobra chassis including the original are ladder frame consisting of some variation of two large diameter tubes and they work pretty well.

If I recall my one's chassis weighs about 90 lbs so they aren't ridiculously heavy either considering they cope pretty well with nearly 600 hp of Detroit heavy metal

[Edited on 18/3/14 by Ivan]

redturner - 18/3/14 at 12:00 PM

Not only Cobra replicas but the original A.C Ace cars from which they derived had a ladder chassis with 2 large tubes.....

v8kid - 18/3/14 at 12:48 PM

quote:
Originally posted by coyoteboy
Karts are not really ladder frames, no.


How would you describe them? I can't think of anything else offhand.

Mr Whippy - 18/3/14 at 01:15 PM

quote:
Originally posted by v8kid
quote:
Originally posted by coyoteboy
Karts are not really ladder frames, no.


How would you describe them? I can't think of anything else offhand.


karts are ladder frames but flex a lot. Most ladder chassis flex but are more geared to overall strength and it takes a lot of extra bracing to reduce it. I could probably pull at least 5 tons with my landy but it twists so much off road sometimes the doors pop open but it's not built for cornering so not issue

Sam_68 - 18/3/14 at 08:05 PM

quote:
Originally posted by v8kid
Karts are ladder frames aren't they? They don't seem to be sh1te and are quite quick


Karts are a very special case and actually rely on frame flex for their handling. In fact, you tune the handling of a kart partly by adding or removing stiffness from the frame.

In very basic terms, you use the caster angle and the very large scrub radius that karts have in their front steering geometry to physically lift the inside rear corner almost completely off the ground at turn-in, in order to kill the massive understeer that you'd otherwise get with a solid (no differential) rear axle. You then use the frame flex to progressively re-establish and manage the loading on the inside rear as cornering forces build up, to allow you to accelerate out of the apex whilst avoiding a snap transition to oversteer on the short wheelbase.

It's a black art, and one which bears little relationship to conventional chassis tuning on a sprung car with its very different steering geometry and wheelbase:track ratio.

Sam_68 - 18/3/14 at 09:28 PM

quote:
Originally posted by Ivan
Nearly all Cobra chassis...

If I recall my one's chassis weighs about 90 lbs so they aren't ridiculously heavy either ...


Really?!

That's 41 kilos?

Bearing in mind that a typical Westfield spaceframe weighs about 68 kilos and even the featherweight carbon fibre monocoque tub of the Westfield FW400 was quoted as 45 kilos, I find that figure surprising, to say the least!

41 kilos is into pick-it-up-with-one-hand territory?

Ivan - 19/3/14 at 08:28 AM

quote:
Originally posted by Sam_68
quote:
Originally posted by Ivan
Nearly all Cobra chassis...

If I recall my one's chassis weighs about 90 lbs so they aren't ridiculously heavy either ...


Really?!

That's 41 kilos?

Bearing in mind that a typical Westfield spaceframe weighs about 68 kilos and even the featherweight carbon fibre monocoque tub of the Westfield FW400 was quoted as 45 kilos, I find that figure surprising, to say the least!

41 kilos is into pick-it-up-with-one-hand territory?


I won't argue because it was 24 years ago when I last picked it up and wife and I lifted it onto building stand with no real problem, so I guessed at 90 lbs. It certainly seems lighter by memory than my locost chassis but then we are both 25 years older now