Bike build vs. new bike for my son - need advice
 

My younger son (just turned 12) has outgrown his 20" columbia mtb that has served him well cruising the neighborhood and light off-road duty. He has held off getting a 24" wheel bike and is now big enough for a regular 26" wheel with a 13" frame.

I have an extra Trek 930 mtb from around 1997-1998 that is too big for him (18" frame), but it has pretty good components (Shimano stx). He can actually ride it ok with the seat down, but it is way too tall and not safe (he has to stand on his toes to straddle the bar). Is it worth buying a 13" mtb frame and switching all the components over from the trek? We went looking at new bikes today and I really struggle to spend $350 - $400 on a qulity bike that he will outgrow again in a couple years and the components don't look any better than the 10 year old stuff on the trek.

It looks like a 13" aluminum mtb frame runs about $150 at performance bike, but I'm not sure if the standards have changed for head tubes, bottom brakets, etc. to allow me to pull all the stuff off the trek. I'm pretty mechanical and enjoy projects (especially with my son), so that part doesn't bother me.

Does swapping the parts to a small frame make sense or should I just go get him a new bike? What are the likely gotchas and what can I expect to buy (besides the frame)?

The head tube size should be the same, as well as the rear dropout spacing. Seat post size, BB width and front derailleur clamp could all be different.

I think SVR has nailed it. I just did a frame swap for someone. I ran into exactly what svr mentioned as far as seatpost and front derailer.

Brakes are another thing to watch for your. I'm guessing your 1998 bike has rim brakes. Just be sure to buy a frame that takes that style.

But the overall concept of moving parts from one frame to the other is good. I bought my son a nice Rockhopper some years ago. Since then, I've done two frame swaps -- both times to larger Rockhopper frames that I bought on eBay -- as he's grown.

Also watch out for suspension fork crown height and head tube height. If your head tube is much bigger, your old fork steerer might not be long enough. And you can also run into trouble if the two frames are designed for different amounts of suspension.

I would have to say if you can do the work do it... even if you cant...
you already have donor bike...
what you'll be out the price of a frame?
can re-sell on ebay... or CL...
.
i am thinking of doing the same thing to get a 29er rollin...

I did the frame swap thing for my son and I'm about to do it again. I do ALL the work. If you have to go to a LBS, it's not worth it. If you're buying a new frame, it's probably not worth it. A used frame is the way to go.
Have you considered buying a used bike off of CL?

Just like roccobike said, look on craigslist for a used rig that will work for him. Here in Atlanta, I have seen quite a few 13 in bikes for sale on there for pretty cheap. If in your area you cant find any. If you know how to do the work yourself, it might not be to costly to do a swap on a new frame. But why would you want to put old outdated parts on a new frame? :twitchy: Most people do the opposite "new parts on older frame" .

Thanks for all the feedback. I bought a new 14" aluminum mtb frame on sale from performance bike for $112 (and I get 20% back in points, so not too bad). The bottom braket is a different size on the Performance frame (68mm vs. 73 on the trek), so I'll need to switch that out. Also, the head tube is 120mm vs. 100 on the Trek, but I think I am OK there because there are some spacers under the stem now. I'm also using this as an excuse to buy a proper work stand, which I've wanted for a long time. It should be a fun project and I'm hoping my son can do a lot of the work so he can learn a little bit.

Any recommendations on a reasonably priced bottom bracket?

Compared to the new bikes I was looking at for him, the parts on the old Trek 930 seemed comparable if not better. The STX group is an 8 spd while I'm suprised to find most of the new lower-end bikes are only 7 (not that it's a big deal either way). The only thing that is a bit dated from the 930 are the grip-shift style shifters, but they work fine. Also, the old rockshox fork might be a little tired, but seems to work OK.

good comps are good comps no matter how old they are...

grwoof, your doing good!!!

and a new bike stand heh heh!!!

post pics!

STX morphed into Deore in 2000. If you look at the exploded views of STX and Deore M510 hubs, you'll notice the cones are the same - one level better than Alivio, and one level worse than Deore LX.

A Shimano BB-UN26 would be well matched to STX level components. Only $12 here:
http://www.universalcycles.com/shopp...2&category=347

You might need the 68x110.

Its easy in this case to agree with everything thats been said so far.

Buying a new or complete bike may have been your best option, even if you did swap out all the parts.

The frame and fork set is also a good way to go, as long as all your parts will fit (ie fd clamp, bb, crankset, headset, etc).

Not meaning to sound discouraging, just being realistic.

Good luck, have fun and show it off when your done.

I can't seem to find the 68x110 in stock. The bottom bracket on the donor bike was a 73x110, so does this mean I have to go with a 68x110? Would a 68x113 not attach properly to the crank or would the pedals just be set a little further apart?

In that case you could use the more expensive UN54 - which seems readily available in 68x110. Another option might be the even cheaper BB-LP26.

The 110 spindle width is not symmetric - which I learned the hard way. Your cranks will have been made to account for the non-symmetry. I think going from the 110 to the 113 will get longer only on the right side. This will push the right pedal out further than the left.

Thanks Laura, I would not have thought about the wider BB being asymetrical. I think I'll just go with a un54. Performance bike carries it for like $25 before discounts, and I can always return it to the local store if there is a compatibility issue.

grwoof as probably one of your biggest supporters I have to ask...

where are the freekin pictures?

I like as we go type stuff vs. here is the build now we're all done...

Well, I just got notification that the new frame shipped today, so I'm still in a bit of a holding pattern until at least next week.

I guess I should have taken pics of my son pulling all the old parts off the Trek last weekend. The parts are in boxes, but here is a pic of the donor bike and the new workstand. I threw in a pic of my newish road bike, so sorry if that's bad form on the MTB forum. I ended getting a Park PCS-10 stand , which seems well built and has a very nice clamp.

The disassembly was easy and my son was able to do most of it. The only thing I didn't really have the 'official' tool for was removing the headset, which just took a little persuasion from a hammer and large screw driver. It made it much easier that the handlebars could stay in tact with the shifters and brakes. No problems so far, just hope everything goes back together as smoothly. At this point, I think the only things I will need to get are the bottom bracket, a new seat post clamp, and a few of those thingies that go on the end of a cable when you cut it (when I shorten them). I'll also put some new brake pads on just for good measure.

don't ask me about etiquette here I am new!

yay! pix! nice roadie!