New bike project - what steel tubing should I use for rear forks?

Joined
Sep 9, 2016
Messages
47
I'm looking to build another bike, a full suspension swb this time. Similar in design to an Optima Lynx, 20" front and 26" back but the main design problem for me is the back forks. I'm calling them forks because it isn't a rear triangle, just a fork.

My question is what steel should I use for the forks? My last bike I built with 1.5" square 1/10" thick tubing, it was all I could find locally and I forget how much it was but ordering in something thinner was crazy expensive. I don't want to use that tubing again because it's heavy. The frame of the bike will be 1.5" conduit, it's only the forks I'm asking about.

Here are my options:

-1" round tube with 3/32" thickness
-1.5" round tube with 1/16" thickness
-1.5" square tube with 1/10" thickness
-1" square tube with 1/10" thickness
-1.25" square tube with 1/8" thickness
-1.25" square tube with 1/10" thickness
-1"X2" rectangular tube with 1/10"thickness

That's what I can either buy locally or already have some scrap of. I can also get all the regular sizes of conduit. I'd love to use the 1" 3/32" round or 1" 1/10" square for weight reasons but I'm unsure if it would be strong enough.

Opinions?
 
Joined
Oct 19, 2012
Messages
1,018
Location
Wakefield, UK
Tubes get most of their strength from their diameter rather than their thickness. Personally I'd use the 1.5" 16swg. There's no appreciable difference in weight per foot between 1.5" 16SWG and 1" 10SWG but the wider 1.5" tube will flex less than half of what the 1" tube will.

Conduit is often galvanized so take care when welding if that's the case. I've also heard some stories about it's brittleness but never seen any actual evidence. Something to scout the 'net for before committing yourself.
 
Last edited:
Joined
Sep 9, 2016
Messages
47
I think I'm going to try the 1" 3/32. It's actually thicker than 1", I only eyeballed it before but next to a piece of 1" conduit it's about 5mm bigger. I cut off a length 2' long and jumped up and down on it, it hasn't bent at all. Besides, even if it does bend I can just rebuild the back end with something larger. I feel that 1.5" will be really bulky back there so I'd rather not go that large if I don't have to. Thanks!
 
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