Aps frame material size

[Greaseballracing]

Hey guys I'm in the process of building an aps-bf 650. It's rear engined with a 100" wheelbase, I'm looking for advice on the frame material. My local speed shop is drag racing based and they have in stock 1 1/4 x .0.82 cromoly or I can go to 1 1/2 x 0.155 mild tube not really sure and I can't seem to find a definitive answer as there seems to be no requirements in the rulebook. Any advice would be much appreciated. Thanks guys. Owen.

[Peter Jack]

The wall thickness you show for 1 1/2 doesn't look correct.

Pete

[Greaseballracing]

Yeah it's been converted (roughly) from metric. As listed from the website is 25.4 mm x 3.96mm

[manta22]

Decimal point is missing.

Regards, Neil  Tucson, AZ

[Greaseballracing]

Sorry guys from Australia, I'm not used to working in inches I'll edit it

[Stainless1]

25.4 is one inch not 1 1/2 although 1 inch .155 wall should be sufficient for bike frame with the proper triangulation and design.

[Vinsky]

1-1/2" sounds like streamliner material. I'd say 1" od x .095 is more than enough for a 650.

[tauruck]

Sorry guys from Australia, I'm not used to working in inches I'll edit it

You could use a combination of 38mm and 25mm tubing.

[Greaseballracing]

Thanks for that stainless, vinsky & tauruck. The next deciding factor is chromoly or mild steel, does anyone have any ideas, I believe my headstock is chromoly so that is the way I'm thinking but if there is safety or legal issues with that I will machine a stock from mild steel.

[tauruck]

I build bike frames but I'm no expert knowledge wise on welding 4130 to mild steel.

I'm sure it could be done by the right welder.

My info over here in South Africa and from what I read is that Chromoly needs to be stress relieved in a furnace after welding to prevent it getting brittle.
Harley frames pre rubber mount get a pounding from the motor and they don't break so maybe there's an answer in that for you.

[WCJonesJr]

Check this link for info from Lincoln Electric on welding 4130 Chrome Moly.

http://www.lincolnelectric.com/en-us/support/welding-how-to/pages/chrome-moly-detail.aspx

[tauruck]

Thanks for the link.

I learned a lot.

[manta22]

Chrome moly tubing that is usually used in building aircraft & race car chassis is 4130N. This is in a "normalized" condition. Welding normalized 4130 does not require stress relieving. Several FAA handbooks cover this.

Regards, Neil  Tucson, AZ

[bak189]

Mild steel......085........Bronze welding (Brazing)   

[Greaseballracing]

Thanks everyone that's the info I've been chasing. Looks like chromoly is the go, the shop stocks 1" x .120 or the next heaviest is 1"x .188 so I reckon the .120 will be my frame. It's planned with a double backbone and lots of triangulation so should be very strong. Thanks again for all the help.