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Discussion Starter #1
I've been wanting to do a chop for awhile, am a little inspired by Pampadori's XS, and am sure someone on here knows more than me so...

Hardtails; How, how much do you fixture? My idea would be to nail the lower tubes down in a way that you could still get the motor in and out for chain alingment and whatnot. I suppose you could just use the rear wheel to hold the axle plates parallel? Actually my first idea was a massive fixture to hold everything, but am probably overthinking it.

Raking the neck; A pet peeve of mine is builders who put too much stretch in the rear for the stock neck. Looks to me that cutting the neck would be easier than the hardtail. So if you're going for a certain number, like you've seen a bike to copy, just zero off the lower frame cradle? Why do builders using custom frames still use offset triple clamps? Why not get it all in the frame?

What are realistic tolerances for chain and wheel alignment? Realizing it's a welded assembly it's not gonna be 100% true, so what's good enough? I had a buddy tell me years ago that he was working with a Kosman Pro Stock chassis that the front wheel was offset 1/2" from the rear. I realize that that bike only had to go in a straight line, but that seems not good.

Or if anyone knows where to go to look for this information that'd be cool too. Thanks in advance
 

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some tips i've been told:

don't do straight cuts, but rather at a 35 degree angle. spreads out the load and better looking welds or something to that nature.

have a peice of pipe inside the tubes about 3 inches or so and then drill a hole thru the frame tube and then fill it in with weld. (hard to explain but it makes the frame much stronger.
use DOM tube.

trueness, get it as close as you possibly can.

but i didn't weld my frame, i was chicken shit about it. if i did it over again, i would have just for the learning exp.
 

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rule of thumb for a 530ish drive chain is it will live just fine with 1/8" offset yet still parallel

running one out of alignment (one sprocket not parallel to the other) is another story and a dumb one at that

My guess is your buddy's bike had the rear wheel offset 0.5" and not actually the drive chain

in the states that I am aware of that actually check rear wheel offset from the geometric centerline......

as part of their safety inspection

they generally allow 0.250"

which means many stock production bikes, even some of the GP race heritage variety

could not pass

some have as much as the 0.5" you mention

within reason..... rear wheel offset from the centerline will only make a difference in how the bike turns from one side to the other

and it takes quite a bit for a seasoned rider to be able to perceive any difference

some of the fat tire choppers have the rear wheels offset as much or more than 2"

and you can definitely tell the difference when turning from right to left on those bikes


the offset tree question followed with the reasonably invalid question about why not get it all in the neck.......

think about the feedback and feel of a zero offset tree...... then one with 2 inches offset....... then one with a theoretical 10" offset

then note that even most short wheelbased and steeply raked GP type bikes will have at least some tree offset.........

and some zero offset trees will have provisions to fix the axle leading or trailing.......

oh and yes you are wanting to overwork yourself getting fancy with jigs

I've seen plenty fine frames done with virtually nothing resembling a jig

even seen fine ones that were welded up using a plumb bob, level, large protractor, chalk lines on the concrete

etc
 

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I don't have much chopper experience. I rode a few customer bikes when I worked at a shop after doing tune ups and tires. The 2 things I disliked the most about them was Ape hangers and the way the front wheel would flop from side to side from raked out extended front ends. Other than that some of them were kind of cool.

Ken
 

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Discussion Starter #5
I used the wrong terminology talking about the triple clamps. Here's what I mean, this bike has a 40 degree neck and six degree clamps. Why not just do a 46 degree neck?

 

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"Raked" trees offer the long bike builder two benefits

1) they bring the trail numbers back into the realm of reality providing useful feel of the road and sane levels of rider input to steer the bike...... amazing is how light the steering can feel on a 75" + wheel base bike having more than 45 degrees of effective rake when raked trees or offset bearing cups are used

2) even more effective rake for an even longer bike

keep in mind that at some point....... let's say 45 degrees effective rake

and I'll point out that some veteran long bike builders leave sliding hydraulic forks alone when building anything over 38 degrees.....

hydraulic sliding forks become a less than brilliant front end choice for a couple good reasons

that is if you really like riding, want full effective use of your front suspension, and want the service parts to last a long time

Sugarbear was likely the first to do looooooong bikes with lots of rake using springer front ends having zero trail

I've never ridden one but having spoken with some that have

they tell me some of his nearly 8' long bikes having nearly 60 degrees rake require steering input levels no heavier than a stock bike

they turn very well and are quite stable too

he accomplished this with rocker center lengths and careful axle placement on the rockers

Rosko....... I have spent many years trying to gain ultimate control over my brown pearl maker

the results are as such now that I can slightly undercut your very reasonable single pearl pricing

while providing discriminating and demanding clients with an entire brown pearl necklace of the very highest quality
 

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no no no, I sell them
 

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come get this one and make something out of it

 

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Discussion Starter #12
Hack,
Thanks for the offer. I've thought about using a sportbike rear wheel, seems like a cheap way to get a big tire. But I've been told that a hardtailed bike will ride better with a narrower rear and a bias ply tire. I know how stiff radials are so I kinda wonder about that.
 

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people say lots of stuff

but the tire width and stiffness is really beyond perception when riding a rigid

what's really nice on that bike is that when you sit on that gel pad seat

it's suspension is every bit as cushy, yet firm, as a fine pair of Ohlins on a swingarm

the front suspension is pretty dayumed sweet too

I pretty much want good tires front and rear on a rigid because when you push them hard thru the bouncy curvy stuff

I want every chance possible the tires will stick


hard to beat real sport bike tires for that

or at least modern tread patterns with bubble gum compound

so I'd advise dismissing the notion you really need skinny or inferior tires

just my two coins on the subject

I have a few other available projects even closer to done but none quite as affordable as a UJM starter kit

that blue thing has a really wicked engine

I forgot the internal specs but I'm going to revisit and re-inspect it so I can honestly and accurately disclose just what goodies are inside

I broke 130 on it when it was nearly 100 pounds heavier and it could have pulled more gearing then

anyhow....... good luck and feel free to ring me if you get stuck or need to consult while in the middle of something

I answer if I'm awake or not in the midst of cavorting like a wild beastie and generally running amok
 
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