Chassis.... Tube or Square?

[Fewski]

I'm not making a FSAE car, but rather a Formula 500/A-Mod car... which is similar.

I've noticed that a lot of those types of cars have square tubing for the bottom half of the chassis and round tubing for the upper or roll cage half. Why is this? And is there a benefit of one over the other?

Thanks

[Fewski]

I'm not making a FSAE car, but rather a Formula 500/A-Mod car... which is similar.

I've noticed that a lot of those types of cars have square tubing for the bottom half of the chassis and round tubing for the upper or roll cage half. Why is this? And is there a benefit of one over the other?

Thanks

[exFSAE]

I wouldn't say "a lot." SOME have a mix of square and round tube.

Easy to weld mounts to square tube. Easy to fit it together, particularly at the bottom if you're jigging things up on a flat jig. May also offer benefits for tubes in bending.

That said, I wouldn't pay much attention to what most or some cars do. Most people are idiots.

[Bobby Doyle]

Much insight can be gained from simple area moment of inertia calcs.

[Hector]

Round tubes are superior to square tubes in almost every aspect. The main benefit of square tubes is that (as exFSAE mentioned) they are easy to jig, cope, and weld.

Round tubes are generally stiffer per unit weight and have fewer stress concentrations.

If you can, use round tubes everywhere you can.

[ben]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Hector:
Round tubes are superior to square tubes in almost every aspect. The main benefit of square tubes is that (as exFSAE mentioned) they are easy to jig, cope, and weld.

Round tubes are generally stiffer per unit weight and have fewer stress concentrations.

If you can, use round tubes everywhere you can. </div></BLOCKQUOTE>

If you have some localised bending due to packaging issues and things like the cockpit that inevitably you can't fully triangulate, could a square tube with a greater EI in one direction be beneficial?

Ben

[L B0MB]

Round tube is more efficient but if your team mates are anything like mine they will whine and whine until the lower rails are square so it is easy to mount the floor to...

[Marlin]

Since F500 and A-mod both have minimum weights, having square tube at the bottom of the chassis is fine.

[vandit]

Kindly avoid these stupid design mistakes. dont put loads diagonally in square tube.

http://i296.photobucket.com/albums/mm190/vanditgoyal/IMG_0017.jpg
http://i296.photobucket.com/albums/mm190/vanditgoyal/IMG_0020.jpg
http://i296.photobucket.com/albums/mm190/vanditgoyal/IMG_0019.jpg
http://i296.photobucket.com/albums/mm190/vanditgoyal/IMG_0018.jpg

btw, our other mistake was less thickness of tubes