To C or not to BC

Here is a quick primer on the frame difference between c models and bc or some straight down tube motorbike models.
First up is a cmod frame. Take notice to the rear stay geometry along with the difference in where the straight bar attached to the down tube and mast tube. Notice on the c mod the bar has more of a gap between the top tube and where it meets the mast tube top tube juncture also the the straight bar attached higher up the straight down tube. The top tube also has a different bend to it. Sometime in 1940 but probably 41 c mods had ears attached to the frame for a drop stand from what I've researched. Tank aperture is smaller.
1939
1941 with ears


Next up is a BC frame or motorbike depending on year. Notice the rear stay geometry. Notice where the straight bar tube attached higher up the mast tube being closer to the top bar. The bar also attached further down the down tube like a b model. Tank aperture is bigger then c model. Notice top tubes gentle curve as compared to a c model.


This is a late Louisville cycle supply motorbike courtesy of Mr zebb


Next up is a double diamond frame notice rear stays are straight forming a diamond


Rule o thumb... if your fist is a super tight fit in between the top bar and lower bar it's a cmod... if you have wiggle room depending on your fist size it's a bc or equivalent. Please feel free to add differences between the years of both models.. ie tank fender lights fenders ect. Sometime in the late 40 I want to say the bc frame started having a curved down tube from what I've seen.

Here is a 1940 b and bc pictured side by side.
Notice the bc sits lower and has a curved down tube. I believe the rear stay on the Autocycle is perhaps longer? Notice how the bottom stays curve up a bit going into the drop outs on both of these as opposed to being straight like on c mods and bc mods. Maybe someone can shed some light on that. If you see your bike let me know and I'll add photo credits. Also thsnks to everyone who I've been able to gather this info from.

Like I said feel free to correct me on anything that is wrong via pm as to not cloud up the info and I will change and give credit

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As you wish.

Thanks you big lug

Obi-Wan Schwinnobi said:

Thanks you big lug

Click to expand...

Agree with mike...lol.

In all seriousness, this is great info and should be a sticky thread.

Thank you for taking the time to put this information together.

Thank you Obi-Wan. I look at these and still get confused but I'm learning and wanted to add a couple pics.

1936 electric C mod above.

1936 Moto bike above.

1939 Mead crusader C mod with curved downtube above.

Same bike a little different angle.

Nice tall frame c model

C-mods

Trying not to add more confusion...the Crusader is a Tall frame, 20 " center of BB to top of seat mast; black Electric is 19"

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