BACK40 returns!

[LukeTheJoker]

Alright, time to finish this one!

For those that don't remember this is a super heavy duty 26" Off-road/BMX/Klunker/Bomber that I started in the 2016 Off-Road build-off. Hit a few timing issues when I had to take a month off that couldn't be avoided.

Frame geometry was designed by @OddJob, he helped me get a long, stretched out cockpit but still in a compact wheelbase, with very short chainstays even though those tires are oversize 26x2.5 Kenda Nevegals in 'Stick-E' compound.

The wheelset itself is pretty cool, starting with 48 hole Odyssey Hazard sealed bearing and oversized (14mm solid axle) hubs with thread on disc brake adaptors (203mm Avid Cleansweep discs) and a 14 tooth freewheel on the rear, they are spoked up using a 48 spoke 4X pattern and sleeved spokes to double walled and eyeletted tandem/touring bike rims.

The rear dropouts are sliding for chain adjustment and lock with 3x 8mm Allen head bolts each, cranks are DiamondBack Chro-Moly 3 piece with a 30T TuffNek chainring.

Old build thread: http://www.ratrodbikes.com/forum/in...ing-but-withdrawing-from-the-build-off.96123/

As it sat at the end of the ORBO:

As it sits now:

Basically exactly the same!

Not actually much to do to finish it:

-Finish welding on the fork dropouts.
-Brace the loop bars to the seat tube.
-Brake caliper mounts front and rear.
-Brake cable guides.
-Test ride.
-Strip, paint, assemble, stickers...

I could have got it finished by rushing at the end of the ORBO, but I have fallen in love with the bike, and the fit is perfect for me, so I wanted to spend the time to do it as best I could rather than rush the final steps. So, building will start again here in the coming days!

 

[josh_from_ga]

I can't wait to see the finished product!

 

[LukeTheJoker]

I can't wait to see the finished product!

You and me both!

 

[Funkme]

Another one. Whats that 3 in(2 by you and 1 by a mate). Going to be hard to keep up.

 

[MazdaFlyer]

I still like the frame profile on this bike, smooth!


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[LukeTheJoker]

Another one. Whats that 3 in(2 by you and 1 by a mate). Going to be hard to keep up.

Ah, but I will be fighting summer and fire-ban days... You can keep up, I know for sure, looking forward to seeing what you have planned!

I still like the frame profile on this bike, smooth!

Me too!

 

[OneHorsePower]

this build , so happy to see you'll get it finished , can't wait to see the results

 

[LukeTheJoker]

this build , so happy to see you'll get it finished , can't wait to see the results

Me too!

 

[OddJob]

Luke, I just had a rush seeing that pic again of BACK40! Dagnabit that is one cool bike! And don't throw those blueprints away on that frame design....I would love to own one of those custom BACK40 frames by @LukeTheJoker ! Even if the shipping is sky high

 

[MazdaFlyer]

Luke, I just had a rush seeing that pic again of BACK40! Dagnabit that is one cool bike! And don't throw those blueprints away on that frame design....I would love to own one of those custom BACK40 frames by @LukeTheJoker ! Even if the shipping is sky high

What is the wheelbase dimension? Watch out for knockoffs!


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[OddJob]

What is the wheelbase dimension? Watch out for knockoffs!


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I just looked for a schematic that we put together in the planning stages that Luke had sent me on my computer and could not locate it. Perhaps when he wakes up to the new day he can share that Ed. The wheel base itself isn't extremely short, but the chainstay length is very compact! I can't wait to see him riding it, hopefully on some varied terrain, i.e. climbing uphill to see if that front end stays planted!

 

[SILVERKINGPC]

Lukester... I was watching this closely when you 1st started it. The frame is really unique: a combination of a TT bike, a Klunker, a prewar and an MTB all at once. I can now see OddJobs hands in it being he's a cyclist. And again, I am still waiting for someone to pull off the custom disc brake caliper mounts w/o an adapter , which can cause huge headaches and frustration getting right.
Are you going with post-style caliper mounts or your orig. idea? skpc

 

[LukeTheJoker]

Luke, I just had a rush seeing that pic again of BACK40! Dagnabit that is one cool bike! And don't throw those blueprints away on that frame design....I would love to own one of those custom BACK40 frames by @LukeTheJoker ! Even if the shipping is sky high

I already looked into shipping, and it is not possible, the frame is too tall to fit the dimensions allowed by AusPost!

I may have something in mind to solve that issue down the road though!

What is the wheelbase dimension? Watch out for knockoffs!

Pretty much exactly 1 meter from memory. (40")
I am fine with knock-off's too!
In fact maybe I will post all the dimensions and angles in a diagram later on so that others can make them?
I could even draw up a blueprint and get it copied out to send to anyone who wants to build one or get it built...

I just looked for a schematic that we put together in the planning stages that Luke had sent me on my computer and could not locate it. Perhaps when he wakes up to the new day he can share that Ed. The wheel base itself isn't extremely short, but the chainstay length is very compact! I can't wait to see him riding it, hopefully on some varied terrain, i.e. climbing uphill to see if that front end stays planted!

14" Chainstay length with those tires, would be less with something smaller...
The dimensions are perfect for me, big cockpit but very nimble!
I am hoping for a full ride video at the end too!

Lukester... I was watching this closely when you 1st started it. The frame is really unique: a combination of a TT bike, a Klunker, a prewar and an MTB all at once. I can now see OddJobs hands in it being he's a cyclist. And again, I am still waiting for someone to pull off the custom disc brake caliper mounts w/o an adapter , which can cause huge headaches and frustration getting right.
Are you going with post-style caliper mounts or your orig. idea? skpc

I think you summed up the frame design perfectly!
Been thinking about post mounts actually, it would not be any more work than an IS mount with an adaptor, so I may as well!

 

[LukeTheJoker]

Pretty sure I still have the build board somewhere, so a blueprint/diagram should be no hassle.

 

[LukeTheJoker]

Just been playing with Back40 getting my head into gear to work on it in the coming days and I have hit a small issue...

The rear hub has the flanges a long way apart to give the best possible strength on a BMX bike, but that does mean the spokes sit closer to where the brake caliper runs, and of course I wanted to run some flashy calipers and went with double adjustable Aquila's which are fairly fat, then wrapped the spokes to make them even thicker... I think you can see where this is going...

It is only just touching the spokes, and only on the rear wheel, so the way I see it I have three reasonable options:

1: Change to a thinner caliper. (But I really like the Aquila's and have already swapped in new sintered copper pads.)
2: Add a narrow .5mm spacer behind the spin on disc mount. (There is more thread outside the mount so it will not weaken the bond.)
3: Add narrow washers behind the disc at the bolts. (Easy and cheap, but loses the effect of the nice ridge that centres the disc.)

Not sure which way I will go yet, but it is not a big hassle with any of those solutions. Will probably go with option 2 as there are no downsides...

Should have some progress soon!

 

[OddJob]

Option 2 washer spacer gets my vote as well. Quick diagnosis and problem solving once again Dr Luke!

 

[LukeTheJoker]

I stripped the disc off and it turns out these adaptors are not the style with the location ring, so option three may be a good call too, either way will work fine, I can't space it out too far though or it will hit the chainstay, just see what spacers I can dig up tomorrow and go with whatever works!

 

[LukeTheJoker]

Had a good day on Back40 today, so much so that as soon as I find a chain, it is ready for it's first ever test ride!

Started with the brake issue while it was fresh in my mind.

Found some 1mm thick steel from an old sign and traced the disc mount on to it:

Drilled the holes and cut it from the sign:

Some time with a grinder and file gave me this:

Perfect fit:

That solved that issue!

Then I moved on to capping the tops of the fork tubes, welded on some mudguard washers:

Finished and cleaned 90%:

Same on the bottom and finally welded on the drop outs:

Then closed off the open ends of the chainstays at the bottom bracket plates:

Found a nice piece of curved flatbar that looked nice for the seatpole brace, I didn't want something too chunky, so this got the nod:

Welded:

And that was it for today, just need to find a chain for the test ride, and if there are no issues it will be on to the brake mounts and final clean-up before paint.

 

[LukeTheJoker]

Looking at this with the bike reassembled:

It looks too small and flimsy compared to the rest of the frame, so I will change it up next work day...

 

[OddJob]

I like the curve of the brace, but agree that it should be more 'beefy'. If not for looks, at least for strength when cranking side to side up the big hills....