Anatomy of a donor bike

[arharker]

I am considering conversions for myself (6'2") and my wife (5'4"). I am selfishly going the kit route because I enjoy projects. The problem is sorting donor bikes. It is obvious to me why a good "Y" bike works well (Trek or Fisher, etc.).

The Y on the Joshua is more pronounced than the Trek Y5. The Cannondale Super V is even more radical. When does this become an impediment to a successful conversion?

I have seen nice looking conversions on a Mongoose, K2, or Specialized frame where the "Y" seat support takes off from a radically sloping top tube. On other bikes the slope of the top tube is decreased, "raising the bar". When does the combination of higher top tube, larger bike and my inseam render a conversion impractical? I have been looking at a Marin East Peak Ovation that has the raised top tube, but is only a 15" frame.

Lastly, some bikes appear to have the perfect conformation, but the frame dimensions seem restricted. For example the Schwinn S-20 has a nice "Y" frame, but the frame seems extra bulky. The Specialized FSR models have the right conformation, but seem constricted in the areas where you might want to have some flexibility in attaching the seat. Does the conversion kit have the flexibility to deal with such issues?

I am reasonably good at problem solving and engineering on the fly, but I hate to make stupid or fatal mistakes because I haven't understood some critical issue.

 

[pagetuner]

Unless you have already done so, I would recommend that you go ahead and order at least one conversion kit so that you have the pieces right in front of you as you do your shopping. Even if (as I judge from the examples you mention) you have no idea of settling for a department store bike as I did for my kit, you could bring the seat bracket and base to a department store and get a clear idea of what various angles of top bar mean in terms of seat base angle, distance from headset, distance from seatpost, etc. Holding real pieces up to real bikes also will help with basic choices like 24in or 26in wheels, suspension or not, etc. If you are careful with your wrenches, you could even bring a department store bike home for the return period and partially assemble it.

And of course you may consider that the $50-$100 price of a department store bike is money well spent as a "first draft" of your kit. Once you have built the kit and run it for a while on the department store base, you will know in what ways and what dimensions you want your "keeper" bikes to differ. Then you can put the department store bike back to original configuration and use craigslist or your local freecycle program to make it disappear.

Since you enjoy this kind of project, I'm sure you will find as I do that there is nothing like having the actual parts in hand. The Cruzbike kit is amazingly flexible, so we all look forward to seeing what you do with it, especially since you are aiming to produce two ends of the size spectrum.

 

[Mark B]

My dept. store bike is both boon and bust. On one hand, it was fun to build, rides OK and gets lots of looks. On the other hand, it weighs a ton and while it doesn't ride heavy, it is. I'm actually OK with it because I use it like my weight trainer for when I ride the Silvio on the weekends. I look at it, though and think about what could be done differently. I think about doing some cut and paste work since I have a friend that is a frame builder. The thing is, by the time I do all that, I have a Sofrider wad of cash in a bike that is probably still going to be heavy. If I had the capital to start it up, I've considered building a frame that the conversion kit would bolt right up to. My framekit would come with a fork already set up with dropouts and would do away with the conversion plates that bolt to the fork. In my mind, that's the one weakness in the kit. The plates are too thin, so you have to shim the inside with washers so the rear derailleur can reach the small cog. Also, I've never been able to get mine to index shift reliably, so I run it in friction mode, which works great.

Don't think I'm capping on the conversion kit, because I'm not. For the money and what you get, it's a great value and a cheap way to find out if FWD is for you. As genius as it is, there are a couple inherent weaknesses, is all. I've found that living with the weaknesses is bearable and I truly enjoy my conversion, which serves as my work commuter. I plan to try a few more frames before I'm done, maybe even a custom built one, if I can find or build the right kind of fork.

Mark

 

[Doug Burton]

Hello...

" I am selfishly going the kit route because I enjoy projects. "

You will be thoroughly entertained by the kit. The possibilities are many and you can build exactly what you want. You can go crazy mixing and matching parts. It turned into the best hobby I've ever had.

"The Y on the Joshua is more pronounced than the Trek Y5. The Cannondale Super V is even more radical. When does this become an impediment to a successful conversion?"

The seat base is designed to give you 12 degrees of seat pan angle adjustment. With deep Y frames, usually we end up with the seat mount straddling the base of the Y. It works fine that way.

"When does the combination of higher top tube, larger bike and my inseam render a conversion impractical?"

Generally the bike is easier to handle at a stop if the seat height is 3 inches or more below your inseam measurement. A clue to a good top tube is when the seat mounting area is below the bottom of the steering head tube when viewed from the side.

"Lastly, some bikes appear to have the perfect conformation, but the frame dimensions seem restricted. For example the Schwinn S-20 has a nice "Y" frame, but the frame seems extra bulky. The Specialized FSR models have the right conformation, but seem constricted in the areas where you might want to have some flexibility in attaching the seat. Does the conversion kit have the flexibility to deal with such issues?"

Some kit builders have gained seat location flexibility on bikes with short top tubes by bending the seat tube to allow more seatback recline. Each frame seems to present advantages and issues. Please have a look at the various photo resources we have to see what others have done.

"I am reasonably good at problem solving and engineering on the fly, but I hate to make stupid or fatal mistakes because I haven't understood some critical issue."

Don't sweat it. There are plenty of folks around who've built bikes and there's a whole pile of "been there, done that" to dig through. We love talking about this stuff.

Glad to have you!

Best,

 

[arharker]

Thanks to all who have replied,

I appreciate your helpful suggestions; the most practical being that I just dive in and try this. There are heaps of pointers in there as well that have helped me eliminate a number of candidate donors. The sellers are probably becoming weary of my very specific questions.

I will buy a kit and probably start with a smaller cheap bike for my wife. She is much less particular about what she rides as long as it is comfortable. That will be the real test. That will also give me time to get a feel for the kit and find a suitable bike for myself. I just wanted to be first.

Thanks again for your guidance,

Alan

 

[arharker]

Took the plunge today. Ordered the conversion kit and took possession of my first donor bike. I found a '01 GF Joshua XO, minor scratches, perfect working order. Cost me $200 with local pick up. Here we go!

Alan