Can I convert this Columba bike (which I own)?

[CruzinSusan]

Bike has 26" tires, so its lowest crossbar height is 26". I've already ordered "Ape Hanger" handle bars for it.

Also, it has a 7/8" stem, if that's the thing that holds the handlebar. But I don't understand from John Tolhurst's notes, terse item #5 on "Choosing a y-frame bike for converting..." how to procede -- what are the details to do this acquiring?

There are many detail pictures of this Columba on this page...

http://www.2ksilver.com/catalog/product_info.php?products_id=101&osCsid=dj4r97uo00rdr2f4c08fdbckb3

Thanks for considering.

 

[Charles.Plager]

I expect you might have

I expect you might have difficulty getting the seat on there so that it can still fold. I'm sure there are games you can play to mitigate that. The seat height could be an issue depending on how tall you are.

(I'll let those who know much better than I respond to the rest).

Good luck!

Charles

 

[Doug Burton]

Charles is right

Several Dahon 20" folding bikes have been converted, and they have a similar hinge in a similar place on the frame. It takes a little fiddling, but it can be done.

DefJack is one of our most experienced conversion builders, and he has converted a folding bike before. Perhaps he can fill in some details about your donor bike and mounting the seat.

Cheers,

Doug

 

[defjack]

(No subject)

 

[defjack]

  Heres how I did my Downtube

Heres how I did my Downtube I Cut the seat bracket but you might not have to as the Downtube was a small frame.I think your conversion would be just fine if it is the RJ26A as the top tube is pretty flat. Jack

 

[Charles.Plager]

Hi Defjack,
Cool bike!  What

Hi Defjack,

Cool bike! What do you have to do (with respect to the seat) to fold it?

Thanks!
Charles

 

[defjack]

  You have to take seat off

You have to take seat off easy with 1 screw and QR on seat post.

 

[Doug Burton]

Good Onya, Jack

Thanks for posting that photo.

 

[CruzinSusan]

Thanks for response guys...

I've ordered convert kit, and will post my progress.

 

[Charles.Plager]

Sweet.  We're going to want

Sweet. We're going to want to see pictures. Remember to take some as you're putting it together.

Good luck and I'm looking forward to seeing the completed bike!

Charles

 

[CruzinSusan]

Top tube too high

Ooops - the flat foot problem!!

After reading all detailed measurements in this post ..., I tested just the seat assembly to see how bike would feel, stopped at a traffic light. The crucial measurements are from seat post to near edge of seat bottom, (5.5" for perhaps a minimal recline) plus 12" more to front edge of seat bottom -- so about 18" from seat post may be a kind of common constant for all of us.) It seems to me, from this point to the ground is the measurement that matters.

Well, anyway on this Columba this 18" point has pushed the front edge of seat up the rising toptube to almost 30" above pavement. And this makes reaching my heals down flat to the ground impossible. Attempting this stab down results in the broad Cruzbike seat cutting into back of my thigh.

I've concluded, if I still want a foldable Cruz convert out of this Columba, that retains a good reclining posture, I'll need an Electra Townie type comfort saddle with a normal bike seat's nose or horn. This will provide clearance for my skinny thighs when going flat-footed. This saddle (I have one) has even more padding than Cruz seat, and comfortable cups for the sit bones, and was engineered for flat-footed biking.

So project is pushed back a little to fabricate a Townie seat bottom mount, and of course, since the Cruz backrest will then also need a mounting for its bottom edge, this bottom mounting will need to double-duty with a couple of attachment hooks somewhere so the Cruz back rest can be slipped out for bike folding.

 

[CruzinSusan]

Seat pan install phase on Columba

Found a 20-50 year old saddle - it looked like an old piece of furniture -- or was designed like an old car seat -- but it is cushy and has a metal base, easily bolted to the Cruz mount. Then I added a firm gel cover.

('Course, I'll only know it this is a keeper after the first 20mi.)

 

[CruzinSusan]

Seat back install phase on Columba

Again, all this custom stuff is to preserve Columba's foldability, and not reject it because of its high top tube and 26" wheels.

 

[Charles.Plager]

Hi,
Keep the posts coming.  I

Hi,

Keep the posts coming. I want to see pictures and a ride report when it's done.

Cheers,
Charles

 

[John Tolhurst]

seat mount the other way

You may want to test having the seat mount the other way, so as to lift the front of the seat up, which will keep you located better against the back rest.

 

[CruzinSusan]

SEAT MOUNT AS DESIGNED

Yes, thank you John, I'll try it. It's helpful to know your intent for that mount. I saw it mentioned in the instructions, but guessed the strongly rising top tube on this Columba could use the backward compensation, ...didn't consider the rump's potential forward drift.

 

[CruzinSusan]

Front derailleur doesn't mount on TFT

Shemano's front derailleur wrap-around clamp expects a 31.5mm OD tube, but Telescoping Front Tube is 35mm. I'm surprised a forum search didn't pop many other non-mechanics posts on this.

Does anyone know a simple work-around, before shopping for another front De.?

 

[John Tolhurst]

34.9 clamp size

I think you can get 34.9 clamp sizes for Front Derailleurs.

 

[CruzinSusan]

What's needed here is a better tiller!

Tell me if I'm wong, but while my first impressions are still fresh, will you permit me to suggest...

This bike is quite dangerous in the period (or beyond) when riders are yet unaccustomed to the difficulty of straightening a crooked glide path, on short notice. Once this Cruzbike conversion begins to veer off, far more muscle and energy will be required to regain control of its heavy front end -- than the prior leisurely cruise forward would have suggested. (Easy to imagine some demon is wrestling you sidwise into the ditch -- or worse, the closely passing traffic!)

Perhaps a somewhat similar physics problem, and it's layman's solution is discussed at this site...

http://byyb.org/gaffrig/200510/article%20scott%20widmier.htm

But with the (above) success that Scott Widmier had, in mind...

I wish you better-engineering heads could find a way to test and compare the 'tiller/rudder' stress needed to straighten the bike's glide path, using the two available alternates:

1. the Freerider handlebar & mounting, (EX: well pictured by Rose Sundet) vrs.

2. the various positions where handlebars try to lever from behind the headtube, into the cockpit

I'm finished with CruzinSusan (with a sexy handlebar version in position 2.) But after the first 30 miles, and several near disasters -- I'll be riding my other bikes for a while, until I can resolve this 'tiller/rudder' question.

 

[CruzinSusan]

Handlebars set for comfort - but poor leverage against front

As seen in cockpit photo below, gripping those rising bar ends like a steering wheel, while either bracing or resting forearms on the brake grips -- this is quite comfortable for straightaways. And it also helps to stabilize glide path, and fight the the heavy front end when needed.

But once a slight turn to the side begins, (intentional or otherwise) the pressure still builds against coming out of that turn.

So my question is, will buying that Freerider handlebar, positioned as it is, centered over the front axle, give me any more leverage to fight that pressure-to-turn issue?

It's assumed from the many related posts regarding riding/handling that one gets better at this fight, and legs and body learn to do what arms would otherwise be doing, etc.

But would it not be best to install all this with the optimum fulcrum location, and the maximum leverage on it?