Any Chromoly frames with a low seat-tube height?

spinningmagnets

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What is the common width on the BB of Downhill, Dirt-jumper, and Trials bikes? Specifically I'm curious if there are any ChroMoly frames that have a low seat-tube, so that a Thudbuster suspension seat-post would fit. The GNG kit is designed to use a 68mm wide BB, and then inserting a 73mm BB-cartridge so the excess threads can provide a mount for the two side-plates. And what are the BB-cartridge options where two stout aluminum plates could securely attach?

A 1-1/8th head-tube is desirable (to allow a wide variety of suspension forks), but not essential.

Trialsbike.jpg

I know its "possible" for a bike shop to narrow a wider BB-tube using a "facing" tool, but I'm hoping to identify an easy-to-copy combination, with minimal mods needed.

Spring is almost upon us, and I'm looking for a hardtail project frame as a base to develop a BB-drive using a converted BMC/MAC hub as a non-hub. Thanks in advance...

GNGbb3.jpg
 
Not sure what your question is about. FWIW, I have a 26" Trek MTB chromoly frame size 13.5". That's the shortest seat tube I have seen on a 26" MTB.
 
http://www.konaworld.com/bike.cfm?content=shonky
 
I've seen some good deals on Azonic Steelhead hardtails. There were a few years where hardcore hardtail bikes were pretty popular. Many were made from aluminum, but there were some nice steel ones, too. Most had short seat tubes with relatively long top tubes, and the rake angles were usually a little more slack than a typical cross-country bike. Most were designed for a 4-5 inch suspension fork. There are plenty of others out there in addition to the Steelhead, and those bikes aren't nearly as popular as they used to be. So, you can probably score a good deal on one. Here in Albuquerque, someone has a well-built Steelhead on Craigslist for $400, and it doesn't seem to be getting any bites (as it has been reposted a few times.) I'm hoping to build a setup similar to a CNG using a hardtail frame that I have lying around. Seems like it would be a fun bike!
 
I have an early 90's 26" Iron Horse AT80 with a great cromo steel frame that is 14" - plenty of room to fit a thudbuster there - seems most bikes are alloy these days but should be able to find a smaller cromo framed bike at yard sales or craigslist for a song...
 
why not a spring seat like a good quality brooks instead the thudbuster? timeless and reliable for a lifetime.

very interested in ur project. godspeed....
 
sjacome said:
why not a spring seat like a good quality brooks instead the thudbuster? timeless and reliable for a lifetime.
X2 - I am using a Brooks B67 on my current project - classes up the bike and provides great support and comfort...
 
spinningmagnets said:
...so that a Thudbuster suspension seat-post would fit....
This is tangental, but I would beware of Thudbusters - at least those with the single saddle rail tension bolt.

I've had a failure on one that would have killed me in traffic. No bumps... just riding along on a smooth flat surface.

I called Cane Creek and the guy there gave me the usual "Well, you must be the only one having a problem..." BS.

Shortly thereafter, I corresponded at length and gave testimony in support of a guy whose life was basically ruined when his failed.... and he won the lawsuit...

Now I've got 3-4 27.2mm Thudbusters laying in a drawer somewhere...
 
Was the problem with the bolt? If so, that's an easy part to replace.
 
I don't have anything against Brookes saddles, I've only heard good things about them. I already have a Thudbuster, and I like it. This is the first I've heard about a weak bolt on the Thudbuster. If you could describe which one, I will replace it with something stronger.

I worked at McDonnel-Douglas for a few years as a hydraulic tech in a department where we stressed aircraft parts in a lifetime cycle profile, and also a "one time" bend-it-till-it-breaks testing profile. Two visually identical bolts can have widely different levels of strength depending on a variety of factors. Computer aided design has greatly sped up the process, but a careful and close examination of the aftermath of a parts failure is still useful (I believe the proper engineering term was "looking at the broke shit"). Important aircraft bolts in a crucial location have paperwork showing the metal batch that the raw bolt was made from, and some are scanned by non-destructive testing (magnaflux, fluorescent dye/black-light, X-ray, etc). Now I make drinking water.

I want to make a BB-drive like the GNG, but using the converted MAC/BMC, and hopefully having all the benefits and none of the weaknesses. What are the best frames for this? and do those frames have a common BB style/width?

edit: Thanks for the responses...
 
PeteCress said:
Chalo said:
Was the problem with the bolt? If so, that's an easy part to replace.
Yes. The bolt sheared catestrophically (or however you spell it....).

The issue is not with replacing a bolt. The issue is with being killed or terribly injured.

I mean you can replace the stock bolt with a graded industrial fastener that is strong and reliable enough for the job. If the bolt is the point of failure, you can replace it before it has a chance to break. If you have weak fasteners attaching your handlebars or brakes, you could also be hurt or killed when they let go. So don't use weak ones.

One-bolt posts with 8mm bolts are proven to work in the long term, though some such posts now have 10mm bolts so the fastener quality is not so critical.

A long time ago, I broke the bolt in an SR Laprade post. I had been overhanging the saddle with a Torque Platform offset cradle, so it was under unusual stress. I arrested my fall before my butt hit the rear tire, and nothing came of it.
 
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