"Hybrid-izing" a MTB Chainring limits?
I'm converting a 1992 Bridgestone MB-4 into a fat man's touring bike. What is the biggest functional triple anyone has put on one of these? Also, will I need a different front derraileuer?
Most of that depends on how your derailer mounts. If it is on a braze-on mount, you can't move it up to accomodate larger chainrings. In that case, you could probably file off the braze-on, or just ignore it, and get a clamp-on derailer.
If your derailer clamps on, then you can slide it up to make room for the larger chainrings.
On some bikes, the chainstays flare out quite a bit, and you should check to make sure that a larger chainring won't hit them. That is a very rare problem, though, and you should be fine.
If you can get around any of the issues I mentioned, then you could put pretty much any chainrings on that bike. I think that 48/38/28 or something like that is good for touring. It is higher than mountain gearing, but lower than road gearing. (Actually, I have a 48/36 double on my "road" bike, and that is plenty high. The big 53-tooth ring on most road bikes doesn't get used to its full potential unless riding very fast downhill.) You should probably stick with the mountain bike rear gearing for touring.
Mad bike riding scientist
A trekking crankset (48/36/26) paired with an 11-34 cassette will give you just about all the gears you'll need for a touring bike. I'd probably go with a 22 inner...but that's just me
Originally Posted by GrannyAbuser
The MB-4 has a clamp-on derailer and the 1993 version came with a 46 outer ring so a 48 shouldn't have problems with hitting the chainstay.
Particularly with your sig, why do you think you need a bigger crank? Far more people would benefit more from working to improve their cadence than from buying bigger cranks. For commuting and touring, actually spinning out is/should be a quite rare occurrence. I know I don't do it, and if I don't, then the people I overtake or keep pace with certainly aren't either.
Originally Posted by GrannyAbuser
You have a valid piont dadac however I have always been a torker rather than a spinner. since I'm fat and extremely slow up hills I have found that my best tactic is to attack the downhills where gravity is my friend which gets me that much further up the next hill. I've always referred to this as "getting up on plane" and have found this to be the best way (short of losing weight) to up my average speed and conserve my energy.
Originally Posted by dabac
I have a road bike (Raleigh Technium 753 or 531 [trying to determine that in another thread]) which is a rocket ship with its tall gearing, but is a poor choice for me right now with a double rather than a triple plus I'm afraid of hurting it at my current weight. I also have an ultra heavy duty Surly Instigator for the woods which I won't hurt but is like a Hummer on the street and tires me out.
Lastly I have my MB-4 that I've decked out for comfort and utility and I'm trying to split the difference in gearing and make it my road bike until I get back to a more reasonable weight. Both MTB's have 22/32/42 cranksets and I spin out (my max comfortable cadence is probably 80-ish) on downhills even with the 11-32 cassette. The bike originally came with a 26/36/46 crankset which I broke years ago and then years later I had an LBS replace the bottom bracket. I have an old Sugino 28/38/48 crankset which I tried to put on there but it bottomed out on the frame when trying to tighten it.
I would think that if the bike came with the 46 tooth setup a 48 tooth setup should fit, but it's possible the LBS installed a narrower one than original. I'll have to take some measurments. I just figured I'd post this question before needlessly spending $ on "upgrade parts".
Worst case scenario: I'll deal with the shorter gearing, learn to spin better and/or start embracing uphills as "weight training".