A fat tire bobber.. ? First build.

I have to thank Jeep2003, LowandWide and Paticus for their detailed project logs for their fat tire bikes. :thumbsup: Lots of good info there... and sweet looking bikes..

The first pic is a 1/4 scale drawing I made. I wanted to be sure the seat height and general fit would work out. 50" wheelbase, 22x11-8 tires. Didn't draw any handlebars, I guess they'll be made to fit..
I kept referring to a picture of an old Scout when I drew this, I didn't drop the frame so much, though. I would like to keep some ground clearance for the trails.

I got a (the) cheap pipe bender on sale at Princess Auto for $99 Cdn. I think I'll end up packing the pipe with sand for the tighter bends... judging by my tests on some scrap. The second photo is 1" pipe that will be the backbone. Spent about half an hour this morning with the bender, thinking it would be another test, but it actually turned out nicely. It's an old piece of gas line from our house... :smile: I marked it every 2 inches and gave the jack a few pumps at each mark, then fine tuned it to look like the picture...we'll see how it fits. The rest of the frame will be 3/4" schedule 40.


Yes, if you need any pipe bent to a zero inch radius... I'm you're guy lol
I made a saddle(?) to keep the pipe from lifting out of the die. It helps, but I may use sand, too. The frame requires only 45 degree bends at a maximum, which is nice. :) Two to bring the upper wishbones in to the back bone and two for the tubes coming down off the steerer tube. I'll use a double tube at that location like the old Scouts.

Yes, if you need any pipe bent to a zero inch radius... I'm you're guy lol
I'm "your" guy... where's my grammar? :smile:

Here's the mod I made to the 3/4 pipe die. Not my idea... found on youtube..
Also was messing around with 'tubemiter' , a neat little program that prints templates for fishmouth cuts. I haven't done much welding in a lot of years, and have never worked with pipe/tube before, so I do need more practice.

I need to elongate the holes on my jackshaft plate to give a bit of chain adjustment. The temporary shaft is a piece of tube I happened to have in my scrap bucket. I have a clone engine that came from a water pump, it had a 20mm shaft that I "engineered" down to 3/4" :laugh:

Picked up my tires from the post office this morning. I was going to paint my rims, then I can mount the tires and start doing some more figuring.

I cut the jackshaft plate with my angle grinder, and used the big drill press at work for the 1-11/16 holes. Mocked it up in cardboard to make sure it would fit. The tube is 1-1/4"pipe, which has an I.D. of just under 1-3/8". A bit of work with a file and the flanged bearings fit nicely. The empty hole will need to be a countersunk bolt so it won't hit the chain. Actually , I found out the other day that I have access to a tube bender and miterer from one of the guys at work. I think I'll be okay with my bender, though.

Looking good! Are you going to make a tank to fit in between the top tubes? thatll look awesome. Youll definatly want plenty of ground clearance wide bikes hit bottom easier on turns
Looking good! Are you going to make a tank to fit in between the top tubes? thatll look awesome. Youll definatly want plenty of ground clearance wide bikes hit bottom easier on turns
Hey, thanks.
I'd love to make a tank, but I'm not sure I have the 'technology'... lol I'll have to look into that. At the very least, I was thinking I'd put in a sheet metal filler plate up there. It might look cool from a distance... :smile:

Yeah.. ground clearance..thanks for the tip. Maybe I won't drop the frame at the back. Two less bends to do.. ha ha
I've been working for the last 5 days, so not much progress, but I did manage to drill my rear sprocket... just for looks, really. Used the same holesaw as I did on my jackshaft plate, and I'm surprised that it's still sharp, but I've been using lots of cutting fluid.

Going to pick up my 3/4" pipe for the frame this afternoon.

Thanks Guys.
Hopefully this works out according to the plan in my head :smile:

Picked up a couple of 10' lengths of pipe at Home Depot, $20 a piece, I was happy with that. I need to get my axle plate measurements figured and get those cut out of 1/4" plate. Then, I think, I'll build from the plates forward..
I got my tires mounted this afternoon, now I can figure out how fat the back of this bike needs to be... the tires are 22x11-8, and are fully 22" tall, but only 9" wide on my 8x7 rims ? No worries, I guess. :smile: They're cheng shin c829 tires.

I made the upper wishbones yesterday, this morning I'll finish fitting them to the backbone. The bender makes 'okay' bends to around 45 degrees. I didn't pack the pipe with sand. I think the bends ended up being 43 or 44 degrees, not sure, but they're both the same...which was more important to me.. :smile:

This "How To" at chopperhandbook.com has been really helpful contact Many good tips. I'm not trying to make this thing perfect, but would like to do what I can to make sure it turns out straight (ish). :laugh:

I went with 13" between the insides of the tubes, for sprocket/ disc spacing and a little extra just in case. I wanted to leave space for a disc brake, I have been thinking of a band brake on the clutch, but I'm wondering if this bike will be a bit big and heavy for that..

I'm pretty happy with that...

I probably won't take a close up after I weld it together... lol . I suppose I should weld a few more practice joints. I also need to figure out something to hold the backbone straight while I weld it, or volunteer some good helpers..

I've only had a bit of spare time to fit a couple of cross pieces. The rear one is a temporary spacer. I marked the top of the pieces because pipe isn't ...quite... round... :smile: ...as I've found out, so everything fits best this way. I would guess tubing is probably nicer to work with.

Also found this 'drive plate' at Princess Auto for my front hub. It had a 1-5/8" bore so I used a sanding drum on my die grinder to carefully enlarge the hole to fit 1-1/4" pipe... which has the correct I.D. for the bearings. It's a snug fit so I can tap it in to place and (hopefully) weld it at a 90 degree angle to the pipe. :laugh: