Motorcycle tubing size

OK, I'm a dumb***, but I've only worked with cars and bicycles as far as scratch building frames. What is the baseline diameter and wall thickness for a motorcycle frame. What I'm thinking of is a medium sized V-twin motor with a "light as possible" frame probably of 4130 Cromoly since that's what I'm most familar with. I'm guessing that .090" would be a good 4130 tubing thickness, but I'd like to hear from folks who have actually put their balls on the line with a home-built frame.

Thanks,
John

 

I've only used mild steel. One inch .120 wall for most of the frame seems good and is pretty standard. For a single downtube or backbone something around 1.25" to 1.5" works well. I think the smaller dia. tube you can use the better it looks, but it seems the popular thing today is to use the largest dia. possible.
As far as chromoly goes I really don't know what you can get away with, .090 sounds like a safe bet.

 

i'll just add: the skinny stuff on most frames is 1.125" OD DOM tubing- i'm guessing .120 wall in mild steel?

 

.120

 

And make sure it's DOM tubing. I here that there are some folks out there who are trying to get away with using 'schedule' ala Home Depot. Bad idea.

Also, from what I am told, in frame building there is no real advantage of going to the expense of chromoly.

 

I think the reason for going chromoly would be the thinner wall you can get away with for weight savings (which I like), and If you have expeirience with it, I'd go that route.
I don't think DOM is necessary, theres a big difference between hardware store "pipe" and actual welded steel tubing. I have never used DOM for any frame components, and I doubt that very many factory built bikes do either.

 

Chopper builders handbook has all the answers.
http://64.172.168.34/neatstuff/index.html

 

Thanks everyone for the info! Bumpstick, that link is great. The section on rake and trail should be required reading for anyone that's thinking about building a frame.

John

 

Great site isn't it? I read just about anything I can get my grubby hands on about bike building and this site has more info than anything I've ever bought. Post pics on your frame build please. -stick

 

I think the weight savings on a motorcycle frame would be fairly minimal, and I'm sure it would be quite a bit more expensive. As far as I know, all factory frame (except some of the sportbikes that use aluminum) are mild steel.