A fat tire bobber.. ? First build.

H

Havasu Dave

Moderator
#21
#21
Nice project. I know the website you linked too. Great first frame build for a guy (like me) who hasn't done an entire bike as an entry project for future chopper (Big Bike) build.

Have you considered where your steering neck rake is going to be? The website talks about heavy rakes, but with prefabricated front ends set with specific rake in mind, for trail setting.

I've been looking at some bikes, and comparing with what is common in the bike world. I see a lot around the 60 degree mark, with perpendicular triple trees that establish at least 1.5" of trail on small frames. You'll get more with your larger frame.

Sorry so long, but I do appreciate what you're doing here. I hope to get where you're at, at some point. :thumbsup:
 
jeffe

jeffe

Member
#23
#23
Thanks for the encouragement, everyone.

And, Havasu Dave, I've been thinking of just copying the Scout 101 front end geometry, which wasn't easy to find , but eventually found it here... in the specs.. 2005 Briggs Bobber in Indian Scout Style by Bob Decker Have you seen this bike, btw? Sweet. Has a TAV, too. :smile: I like the bobber look with equal size tires.

So, around 25-26 degrees of rake and 3 (or slightly more) inches of trail. I'll offset the triple trees to get the trail right. When you say 60 degrees, I assume you mean from horizontal? So, 30 degrees from vertical? Now, I don't 'know' bikes, that's why I thought I'd copy the Scout, but 25 degrees does seem a bit steep compared to a lot of other bikes? This stuff is maybe less critical when you have big mushy tires and are only going 25 mph :laugh:

Chopperhandbook.com really is a great site, tons of good reading. There's a detailed rake and trail calculator here https://www.rbracing-rsr.com/rakeandtrail.html
 
H

Havasu Dave

Moderator
#24
#24
LOL, yeah, I was watching my digital protractor and not thinking. 30 degrees. Going with a bobber, or a springer-type of setup in a solo bike, 25 would be preferable with regard to fabrication/strength and degree of spring deflection. With a 3 inch set of rocker arms sticking out, it might look great. For me, I'd need to see it mocked up on the garage floor.

You're right, big mushy tires at 25 kinda makes a lot of it moot. That Briggs bobber probably goes a lot faster than that. :)
Great link to rake and trail calculator. In another post here, there was a guy with a 20 MPH front shimmy under acceleration. Engine vibration and a near zero trail seem to be the causes, as he'd installed a pit bike front end on a vintage Cat frame and stock rake. With all of the front end modifications going on, it seems very few are interested in this very important aspect of handling.

He shored up his engine mount and flipped the lower legs around and got a better ride.

Thanks for the reply. You know more about this than I do, and I can appreciate your research and hands-on attempt here. Good stuff!
 
jeffe

jeffe

Member
#25
#25
I'll just have a rigid fork, for now, but a girder or springer fork would be cool someday. I have been looking around a bit for plans. The fork would be easy to swap out in the future.

I didn't know much about rake and trail until Google educated me... :laugh: That's a good example you gave, I read somewhere that it can be like a wobbly wheel on a shopping cart.. Your handlebars trying their hardest to spin around backwards lol

Have you tried tubemiter.exe ? Wondering about getting tubing (or pipe) to fit together properly was one of my hang-ups when I was thinking about attempting a build like this or not. It works really nicely, and I'm getting quicker at it now.. less work with a file, and more with the flap disc. I've thought of taking a few pics and doing a little 'how to' , if it might help someone out.

Anyway, what I was thinking was that it's not hard to "get where I'm at" as you said before... I have fairly minimal (and cheap) tools.
 
jeffe

jeffe

Member
#27
#27
Hey, thanks. I'm just taking my time and trying to do a nice job... :smile:

I have a Millermatic 130 with gas that was loaned to me (indefinitely)... my friend bought a new Miller and asked if I wanted his old one. I have a few welds to do on heavier stuff that I'll need help with, but mine will do a good job on the pipe.

As I said I need to practice a bit more. I don't want to blow it when I go to weld this thing together...
 
yalipito

yalipito

Member
#28
#28
jeffe said:
Hey, thanks. I'm just taking my time and trying to do a nice job... :smile:

I have a Millermatic 130 with gas that was loaned to me (indefinitely)... my friend bought a new Miller and asked if I wanted his old one. I have a few welds to do on heavier stuff that I'll need help with, but mine will do a good job on the pipe.

As I said I need to practice a bit more. I don't want to blow it when I go to weld this thing together...
Click to expand...
Check out this link, he is the best instructor you can have and it's free. He teaches Delta airlines welders.
Mig Welding Tips
 
jeffe

jeffe

Member
#31
#31
Well, I got it tacked up... looks like a huge fly swatter. :smile: I found a level spot on the floor and used the vice and a plumb bob to make sure the curved tube was over the center line. It seems pretty straight to me, but the back end tightened up a bit, the spacer is a tight fit now. I'm glad I added another half inch to the width between the tubes.

Next I need to figure out the lower tubes.



 
jeffe

jeffe

Member
#34
#34
Bah ! Do over... :doah:

I was thinking about this yesterday.. and I didn't like the 45(ish) bends. There was a huge amount of tire clearance and it didn't need to be that wide. So I bent some new wishbones this morning. 6" or so to the center of the bend, which is almost the least I can do on the bender. Still leaves good clearance for the tire and sprocket. These will come into the backbone at 25 degrees.

I think it will look better. I figured it will probably be a while until I build another bike, so I might as well get it the way I like it.. :smile:

 
jeffe

jeffe

Member
#36
#36
deejaaa said:
X2 on the great job. looks like it's going to be a great ride. will be watching this one. love fat tires.
Click to expand...
Thanks!

I got the new wishbones fitting nicely this afternoon, I'll tack it together in the morning, then I'll be back to where I was a couple of days ago...
 
jeffe

jeffe

Member
#38
#38
Thanks Guys.

...Okay, got it tacked.. Used a strap to hold it tight this time, instead of my knees. :smile: I had cut the backbone off originally, but wasn't sure where the seat post would end up being, so I figured I should add a few inches just in case.

The last pic is how I'd like to do the lower tubes, but it looks like it would hit the chain, so I'll have to keep it wide a bit farther forward. Maybe a single bend and have them angle in to where they'll meet the down tubes..? I would kind of like to get it down to 9 or 10 inches between the tubes under the engine. It's 13" at at the back.





 
jeffe

jeffe

Member
#40
#40
Shawnster said:
Cool project. I'm subscribed.
Click to expand...
Hey, thanks.

I bent some lower tubes this morning. 13" wide at the back and going down to about 7" at the front. The rear cross piece is just a spacer for welding and the seat post will come down to the center cross piece. So, I went for simple and did this with one bend and rotated the pipe to get the frame drop and angle in towards the front. I think it turned out alright.. The frame drop is the height of the orange level, about 2-1/4". The center cross piece is pretty close to where it was on my drawing .. about 13-1/2" from the back end of the tube.

I'll weld the down tubes on at the front. It would be nice to have one length going up to the neck, but I don't think I could make those bends without wasting a bunch of pipe first... :smile: Hopefully, it will be strong enough.. maybe some gussets...


 
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