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Old 04-16-11, 06:00 AM   #1
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Swapping out mountain for road chainrings, what would it take?

I have an old rigid framed mountain bike that I'm in the process of converting to a drop bar commuter/utility bike. Just about the last thing I'm less than happy with is the gearing.

I'm not spinning out or anything, but in the hardest 1-2 gears I'm pretty comfortable going 70-80 rpm on the flats. Sure I could work on spinning faster, but I'd like to know I have a couple of harder gears to go to if I wanted.

It's got a 14-28 6 speed freewheel in back and a mountain triple up front (biopace 24-36-46, I think). I'd thought about switching to a 7 speed freewheel but that doesn't appear as if it'd give much extra on the low end.

Then I was thinking about what if I changed the chainrings to a road triple? Would that give me that harder gearing I'm looking for? I don't spend much time in the granny ring, so I doubt going from 24T to 30T would cause me much problems, but maybe the bigger outer ring would give me the illusion of extra speed being possible?

I don't know how much work this would be to do (or if it'd really give me a few extra gears for when I get in better shape), so I thought I'd ask and see how feasible it would be. I don't want to sink a ton of money into this, but I say that every time and now have well over $500 into a bike I dropped $100 on on craigslist.

Is it as simple as buying some new rings and swapping them out? Or would I have to replace the whole crankset as well (necessitating knowing what kind of cranks to get, I assume). And a new FD? I think I've read that there are two types. Mine has the derailleur cable going under the bottom bracket if that makes a difference.

Oh and feel free to treat me like the complete idiot I am. If this is a stupid idea or won't really give me any extra gearing, feel free to say so.
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Old 04-16-11, 06:15 AM   #2
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It's possible you may get by just replacing the chainrings and raising the front derailleur a bit. A good first move would be to spend some time with a gear inch chart. Figure out how big of a big ring you think you want. Then check the internet to see if you can find the rings that you want resonably priced. If you don't have a crank puller, you can usually replace the larger two rings with the crank still on the bike.

You may encounter an issue with the arc of the front derailleur cage. On a bike as old as yours, however, I'm thinking a 48 or 50 chainring should be a pretty easy bolt up.
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Old 04-16-11, 09:31 AM   #3
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Older MTB's had frame geometry that was fairly close to road bikes, so swapping out just the outer ring shouldn't be a problem. Just make sure you can move the FD up the seat tube a little to account for the bigger front ring. As stated above, you might also have some issues with the FD 'arc' and if it can handle the jump through all three crank rings. You state you only have a 14T small gear in back? Is it possilbe to change the freewheel to something smaller? 12T, of maybe 11T? FWIW: I did something similar to a mid-1990s MTB and simply swapped the whole crank for a new, inexpensive compact double (big ring went from 42T to 50T). I need to get a new, longer chain if I want to use the lowest gearing (I probably won't), but the FD does work with the new double crank, just shortened the FD cable and adjusted it so it won't go to the 'now-invisible' granny ring!
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Old 04-16-11, 10:25 AM   #4
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A secondary reason I swapped the crank was to get shorter crank arms. Went from 175mm to 170mm, which is a much more comfortable ride for me.
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Old 04-16-11, 10:38 AM   #5
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A 48 tooth ring and a 13-x freewheel will yield a decent top gear of 92 gear inches which is pretty ideal for commuting and touring... my Kuwahara Cascade is a 26 inch wheeled tourer with a 28/40/48 and a 13-34 7 speed block that has a tighter 13-18 range and that huge bailout option.

A lot of mid eighties mtb's came with a more hybrid like gearing with that 28/38/48 set up which worked well with the 14-28 blocks they were equipped with.
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Old 04-16-11, 10:47 AM   #6
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All you have to do is check bolt diamiter and count 4 or 5 bolts, Bike Island had cheap fsa rings, 30$. You will lose the bio pace, or go to ebay and look for 110 BD (bolt diamiter)50 tooth ring. I'm just guessing that it's 110, and don't worry about 6-7-8-9-10spd chain rings they all will work with 8spd chain.
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Old 04-16-11, 01:38 PM   #7
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As others have said, this might be an easy switch. I swapped a 28/38/48 for a 30/42/52. I did some measuring first to make sure I'd get the right BB so that the rings wouldn't hit the chain stay. But the installation and front derailleur adjustment was very easy.

Switches to the big ring were never very crisp, so I recently switched to a Shimano FD-R443, which is designed flat bar setups with road rings. Shifting is smoother than ever now.
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Old 04-16-11, 04:25 PM   #8
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If you're not actually spinning out on the 14T small rear combo then I can't see why you want to go to the expense of switching either end. The suggestion that you have "faster" gears is only that, a suggestion. If you are not spinning out the 46+14 combo easily then you won't even be able to comfortably use a higher gear inch ratio except when trying for a speed run down a slope. Is that one time situation worth spending the money needed to do the change?

There's a lot of fun and reward to be had from modifying an old bike as you've done. But you need to stop and think about where the cost of such projects goes past the point of sensible return. I'd suggest that buying new parts to do a crankset and deraileur change would be WAY over the top for this bike. But if you could score the bits needed from a junk box at the LBS for cheap then sure, why not in that case. Otherwise the money that would be used for new(er) and more costly upgrading would likely be best saved towards a new(er) bike which will have a nicer frame, better components and suit you better all around.
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Old 04-17-11, 05:58 AM   #9
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BCRider, I think you've got a good point. I enjoy fiddling around on it, but I've probably reached a point where I need to stop. Especially since it appears as though the chainrings appear to be riveted to the crank.

They don't look like they're in the best of shape (unless the teeth are supposed to be uneven like that), but you're probably right in that I've just about reached the extent to which I should modify the bike (and long since pasted the value I should have spent). It did really well helping me carry 50+ lbs of groceries home last night, but I'd probably be better off saving my money for a new bike and trying to convince my wife that there's good reason for me to have 2.
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Old 04-17-11, 07:39 AM   #10
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I need to get a new, longer chain if I want to use the lowest gearing (I probably won't),
FWIW, I'd strongly recommend getting a chain that will cover your big/big combination even if you don't think that you'll ever go there. If you ever accidentally shift into that combination it'll bend your derailleur arm into the rear spokes.
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Old 04-17-11, 08:11 AM   #11
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BCRider, I think you've got a good point. I enjoy fiddling around on it, but I've probably reached a point where I need to stop. Especially since it appears as though the chainrings appear to be riveted to the crank.
If the chainrings are riveted, as many lower-line cranks are, that's a show stopper right there. Your only alternative is a complete replacement crank and possibly a new bottom bracket as well as a longer chain.
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Old 04-17-11, 12:50 PM   #12
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Yeah looking closer it's a shimano 200gs crankset and a ty70 (tourney) front deraileur which were both near the bottom of the end models from 91-92, so I think I'm just going to stop where it is.
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Old 04-17-11, 01:10 PM   #13
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Since the crankset/BB/FD would be expensive to replace, keep your eye out for a newer rear wheel with a Shimano Freehub. You can then get a cassette with an 11T which would give you a significantly higher top end. This might cause problems though if you have indexed shifting. Friction should work fine.

If you're patient wheels show up frequently on craigslist (at least around here) in the $20-$30 range.

46/14 - 82 gear inches
52/14 - 92 gear inches (if you went the chainring route)
46/11 - 104 gear inches

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Old 04-17-11, 01:43 PM   #14
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If you're not actually spinning out on the 14T small rear combo then I can't see why you want to go to the expense of switching either end. The suggestion that you have "faster" gears is only that, a suggestion. If you are not spinning out the 46+14 combo easily then you won't even be able to comfortably use a higher gear inch ratio except when trying for a speed run down a slope. Is that one time situation worth spending the money needed to do the change?
My thoughts exactly. Save your money. The only possible change I could recommend is a freewheel beginning with a 13. A larger big ring will only reduce shifting performance.
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Old 04-17-11, 02:11 PM   #15
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FWIW, If you ever accidentally shift into that {big/big** combination it'll bend your derailleur arm into the rear spokes.
Don't do this. It is hard on the wheel, may wreck the derailleur and probably bend the derailleur hanger. My X taught me that trick. She was so PO'd about it the asphalt started to boil on her walk into town.
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Old 04-18-11, 08:55 AM   #16
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Since the crankset/BB/FD would be expensive to replace, keep your eye out for a newer rear wheel with a Shimano Freehub. You can then get a cassette with an 11T which would give you a significantly higher top end. This might cause problems though if you have indexed shifting. Friction should work fine.

If you're patient wheels show up frequently on craigslist (at least around here) in the $20-$30 range.

46/14 - 82 gear inches
52/14 - 92 gear inches (if you went the chainring route)
46/11 - 104 gear inches
Not a bad idea. Since I think I'm going to stick with what I've got for now I can keep looking and see if an older 26" rear wheel with a freehub does appear eventually. If I do find one will any freehub do or or are there different ones for smaller (fewer speed) cassettes vs the new 9-10 speeds? In an ideal world, it'd be 130 mm spaced as that's what my rear spacing is and I'm not sure how much work it'd take to spread it out further than that (especially for changing a flat on my commute) especially with my heavy rack fighting the spreading in addition to the frame. Maybe that's a non-issue though.

Like I said, though, I'm not in a huge rush anymore as I probably should work on improving my fitness on what I have (though I didn't leave the largest chainring on my rides over the weekend). Plus I have a set of new (well NOS) 6 speed indexed 105 dt shifters I just got in the mail and haven't had time to put on the bike yet, so I'll want to get my money's worth out of those before I go and get something new.

The new chainring idea was something I was just thinking of because, once I get some time to sit down and do it (not easy with an 8 week old who needs lots of attention), I'm putting on new brakes, moving the brake levers, putting on Kelly take offs and the new shift levers on them, and the requisite re-cabling of brakes and derailleurs and bar taping - hope to do a better job this time, and figured if I was putting on new cables and adjusting the derailleurs anyway, now was the time to do it. But yeah, I can work on getting in better shape throughout the year on what I have and get to the point where I'm comfortable spinning at 100 rpm with what I've got and then I can change gearing out this fall or something if I happen to pick up your suggested new wheel on CL between now and then. Thanks for the advice all.
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Old 04-18-11, 08:56 AM   #17
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By the way, in my picture (bad as it is) some of the teeth look smaller than others. Does this mean the rings are worn out, or are those the things that they do to make shifting easier? Or is it just too hard to tell because I had so low light and was using my crappy ipod camera?
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Old 04-18-11, 10:36 AM   #18
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By the way, in my picture (bad as it is) some of the teeth look smaller than others. Does this mean the rings are worn out, or are those the things that they do to make shifting easier? Or is it just too hard to tell because I had so low light and was using my crappy ipod camera?
Almost all modern (i.e. anything after the late-'80's) chainrings have shaped teeth and often ramps and pins as shifting aids. They are perfectly normal and intentional. The only exceptions would be chainrings for single speed, track and fixed gear bikes where no shifting occurs.
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Old 04-18-11, 10:57 AM   #19
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I thought about the used freehub and cassete wheel as well. But he's got a 6 speed freewheel at the moment and last I heard cassetes start with 7 speeds. So a wheel switch would likely result in the need for a new shifter at the very least and likely a matching rear derailleur. So again the cost would suddenly go sky high and all the clues shown so far suggest that this was very much a budget price bike in it's day.

Tinkering to make such low end bikes more suitable and better fitted are one thing. We all like to do that or we wouldn't be posting on this forum. But the wise tinkerer knows when to stop pouring cash into a project when the core components of frame and other major parts are just not that good.

Himespau, you need to start "The Perpetual Hunt" for the shops in your area as well as garage sales and the like for old cheap bikes that have good frames at their heart. For example I bought an old unwanted slightly chipped and rusty Norco road frame one time for $14. I bought it because it passed my fingernail "thwack" testing of the main triangle tubes as being the hollow ringing sound made by thin chrome moly tubes rather than the dull sound made by high tensile steel "water pipe" tubes. That frame ended up being built into my first single speed which I then road for a lot of years as one of my commuter and errand bikes. While "only" single butted that frame gave me back all I put into it and sent it to the wheels. It was a great bike to ride. I only finally sold it to a friend when I celebrated my up coming retirement by buying a Redline 925 to replace it. Last I heard from my motorcycle buddy that single speed is still being used regularly and with great enjoyment.

Another bike shop back corner find I've still got is another Norco frame from the days of fine quality steel frames. $40 got me a Rampage frame done in triple butted Tange Prestige tubes. This built up into a really fine bike that I've used for both street as well as some trail riding with a quick wheel swap. It doesn't look like much to see but that bike has the heart of a warrior and works in all the best ways that a bike should. Total cost wasn't much as I was able to build it up using a lot of parts already on hand. And none of the parts is all THAT high end. The mid grade Deore stuff for the most part.

So it is more than possible to build a great bike for cheap. But doing so starts with getting to know a good frame when you find it. To that end I suggest you start by learning the sound made by various quality levels and metals tubes when given the fingernail "thwack" test. Labels works too if they are still on the frame. But if they were re-finished to make them look less desireable then a lot of times the labels are painted over or not there at all. In such cases the thwack test may well be what tells you that you're holding a possible winner frame.
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Old 04-18-11, 11:27 AM   #20
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I picked up a tiagra triple crank made for a square BB for less than $30 deliverered on ebay. It works great on a 1990ish GT mountain bike.
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Old 04-18-11, 11:41 AM   #21
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Tinkering to make such low end bikes more suitable and better fitted are one thing. We all like to do that or we wouldn't be posting on this forum. But the wise tinkerer knows when to stop pouring cash into a project when the core components of frame and other major parts are just not that good.

Himespau, you need to start "The Perpetual Hunt" for the shops in your area as well as garage sales and the like for old cheap bikes that have good frames at their heart.
Will have to take your advice and start going through goodwill/garage sales. Not sure about the bike shops around here having much in the way of deals, but it's something to consider. One place had a used basement sale a couple of weeks ago, but the only other lbs I've been to here that wasn't a corporate chain sold mostly used bikes and seemed a bit high in their pricing for what they were selling. I'll have to look around a bit and see.

I do appreciate Rocket Sauce trolling the Boston Craigslist and posting what he feels are good deals in another thread and have been looking through those for a long time, but I'm sure the really good deals would be gone.

Being 6'3" or so, I haven't so far seen a lot in sizes I'm looking for. I think the bike I have now says it's 22.5" and it feels a bit small (the reach feels better now that I've got maybe 7-8" of post showing and a 140 mm stem, so I'm guessing a 58 cm is the absolute smallest I'd be looking for a more like a 60-61cm, which don't seem to pop up on the CL as much as the smaller sizes. Maybe a garage sale will give me better luck.

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