Changing Chainrings

[Mike_Commuter]

Morning Everyone...
Well, I'm no stranger to riding a bike around but up until this point I've never really done anything much more than hop up and go, however I've got a quick question that I'm hoping I can get some advice on. I've got a bike that I use for my work commute, it's more or less one of those hybrid ideas where a mountain frame and components are set on some skinny wee tires so that you can cook along on the asphalt rather than the dirt. All very *urban* I'm sure you'll understand, no need for anything more than this for the way that I ride. Rigid, no suspension... very light and overall quite zippy.

But just not fast enough for the long haul.

I want to change the gear ratio away from the mountain style and into something a little more roadworthy... right now I'm pretty much living in the last three gears out of twenty-one available and it seems like kind of a waste. I'm sure that I can buy chainrings which are bigger and that this should solve the problem, but have no real idea about installation or if there'll be any hidden nuances that I'll have to tackle along the way. I'm running out of gears, not strength, and I want to find a way to solve the problem.

Is it as simple as just swapping out the front rings?
Does anyone out there have any previous experience with this operation, simple or difficult and is there anything that I should know about before I begin...?

Thanks very much for any help that you have to offer,

Take care.

Mike_C


(I'm also curious about a good solid brand of front and rear hubs as well, some real gliding low friction jobs if anyone has a favourite that they'd like to recommend)

 

[alfeng]

I want to change the gear ratio away from the mountain style and into something a little more roadworthy... right now I'm pretty much living in the last three gears out of twenty-one available and it seems like kind of a waste. I'm sure that I can buy chainrings which are bigger and that this should solve the problem, but have no real idea about installation or if there'll be any hidden nuances that I'll have to tackle along the way. I'm running out of gears, not strength, and I want to find a way to solve the problem.

Is it as simple as just swapping out the front rings?

(I'm also curious about a good solid brand of front and rear hubs as well, some real gliding low friction jobs if anyone has a favourite that they'd like to recommend)

Swapping your existing large chainring for another can be either exceedingly simple OR excruciatingly tedious -- a lot depends on the crankset that is currently on your bike.

Presuming (and, sorry for not knowing) that the crank is indeed a MTB-type crank, then it probably has a 4-arm spider with a 104 BCD (Bolt Circle Diameter).

The largest 104 BCD ring that I am aware of is a 48t which Shimano makes -- there may be others.

The excruciatingly tedious part will be IF the chainrings are currently held in place with chainring bolts (the latter use a 5mm HEX/ALLEN wrench) OR if they are riveted.

If the chainrings are held in place chainring bolts, then you simply have to undo the chainring bolts, undo the front derailleur cable & move the front derailleur UP on the seat tube (first, note the separation above the current chainring), bolt on the new/larger chainring, reattach & retension the front derailleur cable ...

If the rings are riveted on, then you have to remove the cranks, grind off the rivets, buy the chainring AND the bolts, and then proceed ... it can be done; but, it is tedious. IF THIS IS THE CASE (riveted chainrings), MEASURE THE BCD & ORDER THE REPLACEMENT CHAINRING BEFORE GRINDING OFF THE RIVETS ... OTHERWISE, ... WELL, IT COULD BE AN UNNECESSARY EXERCISE IN BICYCLE MAINTENANCE.

FWIW. I have Shimano (all levels), Campagnolo, and HUGI (now, DT) hubs ... they are all good ... the Shimano DO need to be adjusted properly (which is to say they can be too tight when they come-from-the-factory) AND the lube (grease) can't be too heavy ... but, heavier grease generally means less frequent maintenance.

 

[gclark8]

Not having access to the build of the current bike , its a bit hard to answer. Have you the web page link?

For my friends with entry level 8 speed MTBs I fit 11-30 cassettes on the rear and 28/38/48 cranksets (TX 71) and CO51 front derailleurs. For 7 speeds its 11-28 on the back and the same on the front.

These bikes can achieve over 45kph!

Then its the tyres, 26" slicks,
Conti Ultra Gator Skin 26x28mm ($48)
Conti Sport Contact 26x1.3 ($45),
Conti City Contact 26x1.5 ($43),
AirPro City with Kevlar 26x1.5 ($25),
Airpro, Dunlop, Repco or BiCorp City tyres 26x1.5 ($15).

 

[Eastway82]

Hard to say for sure without knowing the actual spec of the bike, but if the gearing's pretty much standard 7sp mtb as detailed by gclark8 and you're 'living' in the top three gears all the time, it may be that you're just pedalling too damn slow! I see it all the time with commuters and leisure cyclists, grinding along at sub-70 cadence when changing down a gear or two and spinning a bit faster would be better exercise, more sustainable for longer rides, and less stress on their knees. If that's the case, try some higher cadence pedalling (90-100) as an experiment.

 

[Mike_Commuter]

Hey folks, excellent responses and thanks very much to everybody so far.

1. I'll get the exact specs up in a few hours (I'd do it right now but we had a late night and there's company for breakfast) so you'll all have something to mull over with me. Don't be too surprised as it's some deliciously vintage stuff.

2. I might have the terminology wrong when I said living in the 'top' three gears... spinning above 100 rpms is *precisely* the problem as it's just too darn easy to do. I'm using the most difficult three gear combinations to pedal, right up at the very end of biggest front and smallest rear - and they're just not difficult enough. If I'm aiming for a cadence of somewhere around 80 or so then I can definitely handle quite a bit more.

Anyway, eggies and toast and a frowning lover are calling...

Talk to you all again soon and I appreciate the help!


Mike_C.

 

[Sportsax]

I am working on a similar project. This 21 speed 26" dual suspension (3 ring front) MTB has an 750 watt electric hub on the front wheel with a 48volt lithium battery on the back luggage rack. I have been commuting 36 miles per day to work to save gas and get some needed exercise. I have to help out with my legs to assist the electric power or I find myself running out of juice with miles to go. The problem is when I want to go fast to get there and open it up. The electric hub likes to cruise around 25 mph and occasionally hits 30-32 mph. The gears are too low for my pedaling to keep up. I like this MTB rather than a road bike for comfort and the suspension but need a larger chainring than the 42T that is on there. I found a 4 hole 52T online that matches up but had to grind the rivets off to get the 42t off. Last night, I ordered some chainring bolts and spacers so I can install this large 52T chainring on the bike. I'll check back later to update when I get the parts in.