Discussion in 'BUILT FROM SCRATCH' started by tjwilson, Oct 15, 2019.
In-Process Frame with Tires
Finally got images with tires mounted ready to post.
That big ol' rear tire reminds of the Surly Bicycle frame sticker they came out with right after they introduced the first production fat bike:
"Does This Tire Make My ... Look Fat?"
You're going to need one big 'naner to compliment that tire!
I'm looking at it thinking "Something 's missing..."
So I go back to the beginning and yep, seat stays.
Come on bro. Tick Tock (you got this )
Not only that tire but the width of the rear hub! I'm going to try putting a bend into the seat support / sissy bar to narrow it up. Otherwise the seat might end up so wide the bike will topple over because of the weight.
Tick Tock, Tick Tock... I know . Might be another one that's not going to make it across the finish line in time. Plan to keep trying though.
Funny you should mention the missing seat stays...
Seat Stays / Cantilever Tubes
Some more tube end capping, sand filling, bending and welding. I initially convinced myself that I could do these as one continuous tube per side. One practice piece confirmed that was wishful thinking! Ended up sleeving together two pieces to get what I wanted.
I fought back and forth over how to finish off the front of the cantilever tubes. I thought the rounded ends looked a little too "Schwinny". Of everything I tried and mocked up though I thought they looked and, matched the frame, best. So, "Schwinny" ends it is.
Rear Disc Brake Caliper Mounting Question
I've kind of designed and built my way into a corner on this. Between the downhill tilted chain-stays and the seat support attachments it doesn't look like I'm going to be able to mount the caliper where I've typically seen it. I'm considering a couple possible options. One basically mounts the caliper upside down, below the rear axle. The second is below and flipped so the mounting posts are inboard of the disc (I think there will be enough clearance). The second options really cleans up the run of the brake line. I'll be creating the bracket so bracket availability isn't an issue. Anyone see any potential trouble I'd be getting into? Any suggestions?
Flipped and Posts Inboard
Typically, the disc brake caliper is mounted behind the seat stay / or fork leg so that when the braking action ensues, the forward thrust of the pad grabbing the rotor is stopped by the piece of metal stay / fork ahead of it. **I'm just thinking out loud here, I know you know this**
Could you weld an extension on the 'top back' (1 o'clock - 2 o'clock position) of the drop out to mount your brake caliper onto?
I might not be following your predicament here, but even my fat bike has the same mounting locale as my Desert Sky klunker bolt and clamp on caliper mount and my mtb factory caliper mount.
I see nothing wrong with the 'Flipped and Posts Inboard' placement other than access to the mounting bolts might be an issue if they are on the backside. (Not sure if I'm seeing how it mounts correctly).
The position looks good and offers an opportunity to route the cable inside the frame!
Seat stays / cantilevers only two pieced what a novel idea.
I think mine are like five or six pieces each after all the modifications lol. As far as your brake... It's mechanical not hydraulic, correct? I don't know if a hydro caliper can operate "upside down" but a mechanical one shouldn't have any problems as long as you have the clearance for the bolts, as Ren Man noted. Good luck and skip paint to the finish line (paint it later brother)
On a bike that would be ridden hard, I might be concernedabout the forces applied to the welds if brake force pulled away from the stay rather than pushing towards. However, I doubt this one will be "shredding the gnar", so it should hold up.
It's when I think I know something that I get into trouble
Every example I could find show similar mounting to what you have. I'm just not sure if there is a big difference between pushing against, verse pulling away from, a stay or fork. What leads me to think that is the way most calipers are attached to a bracket with an adapter. I'd think the shear force on the horizontal bolts of an adapter would be more of a concern than a push or pull force... I think.
The problem with a 1 or 2 o'clock location is interference with the seat support ends for the banana seat. I'm trying to keep those as narrow as possible so the seat doesn't get so wide that it looks like an oversized hat plopped on top of a skinny old man's head! With that caliper location I'd have to move the supports outboard a bit. At least it appears that way with the 140mm disc I planned to use. Hmmmmm maybe a larger disc?
I know, that's the real attraction for me to that mount. It would clean the routing up real nice.
I have no idea why I thought they *needed* to be one piece. The flexibility to stick as many pieces together to get what you want is what makes having a welder fun!
I'm going hydraulic. If everything is sealed up the caliper shouldn't care if its upside down or not? Need to research that.
Thanks. *If* I get close it will be a bare metal finish finish for sure.
Nope, won't be "shredding the gnar"! Looks like it will be a wheelie machine though.
You might be alright with the hydro disc if you don't open up the system. Put something in the caliper, hold it upside down, pump the lever and see what happens.
If you have to remove the hose for any reason you'll have to make sure you have the proper bleed fitting, new ferrules etc. All brands have different parts. It's not universal like car brakes.
I know when I put hydro discs on my bike when I tilted it up to move it around the crowded garage the back brake would go completely slack. They need bled again though.
Hydraulic brakes are a pain in the neck for a Rat build.
A 160 rotor is more common for rear brakes. Might give you more flexibility. There are 180's available too, might compliment that big wheel / tire combo better.
You don't need to - Hydraulics work in any position you mount them - it's a sealed unit, so the positioning doesn't matter. In most bikes the rear one is almost horizontal, sometimes upside down (worked on a few bikes with that), while on the fork it's almost vertical, or sometimes leaning towards laying upside down (like in my 14 RRB Build-Off).
The bigger & stiffer the disc the better. A friend of mine is running 203mm on his e-bike with 4 piston Magura caliper designed for downhill riding, and that thing has so much stopping power that it bends the fork (But actually it stops his 89lbs bike with him weithing something like 220lbs, from going 32mph in a jiffy). If You're planning on running in speeds less than 19mph a 180 on the front & 160 on the rear might do the trick.
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