I really hate shifting the front chainrings, and I tend to do it A LOT here in maryland, where we are up to our ears in rolling hills. However, there are not a whole huge amount of really huge hills. hence the double chainrings on my bike now. I am really lazy though, and even with a crisp-shifting front shifter, I HATE doing it. I was riding today, and I did some long division in my head. I realized that I could go with a 45 tooth chainring and an 11-32 cassette and have the same low gear as a 12-27 cluster and a 53 tooth outer ring. I would lose 9 gear inches, however, in my top end that I would never miss.

now for the practicality, I was thinking that I could use a triple bottom bracket with my double crank. I would mount the 45er on the spot for my inside ring, which would line it up with the middle of the cassette. I was thinking that I might just drop the front mech completely, and use a standard aero lever on the left side. In addition to having easier shifting, I would have lighter weight...though thats not really the point. I suppose it would be an added bonus.

the big question, though is whether or not this would cause excessive chain and sprocket wear, since the chain would be in different directions? I'm not sure.

Any comments would be appreciated. just to add, my front mech IS adjusted correctly. no one can deny that a front derailleur takes longer then a rear to shift...

My buddy has his Pinarello cyclocross bike set up that way...

Wouldn't worry about excessive gear/chain wear. Your main concern will be the chain jumping off the chainring when you hit any bumps or potholes in the road. I ride a single chainring setup on my cross bike, without a front derrailleur, to do this you really need a chainring guard on the outside, and a "third-eye chain watcher" on the inside. Then you will be good to go.

Looking to do the same thing on my cross bike but with a 42/11-32.

One thing you need to consider is whether your derailer can handle a 32t cog. Most road triples can only handle up to 27t cogs. You'd likely need a MTB rear derailer.

****, this is getting to be an even more expensive proposition.

and a MTB derailleur would shift badly too. rats.

velo demon, what rear derailleur are you using? what cassette?

where can I find a cadence to speed calculator?

I run a 42/ 12-32 on my cross/tourer and just keep the front deraillure on really low so the chain won't come off. It is an 8 speed shimano cassete w/ xt rear and Suntour XC front derailleur. I put the 42 ring on the triple like you want to do but I believe 42 is the largest you can go here...

why is 42 the biggest I can go? the middle ring is the same BCD as the outer, and I don't need it to match up for shifting...

there are a few companies who make non-standard sized chainrings for 130 bcd. the best thing to do is find a chainring made for a 3/32 chain, or whatever the width of your chain is (usually 3/32 does fine). the other thing you should do, and you probably already know this as you mentioned wanting to put a 45T ring on, is get a chainring made for single speed use. it will seriously cut down on losing the chain, as the teeth aren't machined to shift better.

sheldon brown probably has a bunch 130bcd chainrings in a bunch of different sizes. rocket rings have a pretty good reputation. they may not look super cool, but they'll get the job done.

there's no reason why you'd have to get a MTB derailluer for this set-up, especially if you're going to keep your current cassette. with a 45T or a 44T chainring, you ought to be fine with a 12-25 cassette and a short cage RD.

most of the time these types of modifications work better with 7 speed cassettes and lower, because of the rear spacing and the slightly wider chain.

you could probably keep your bottom bracket too and just line the chainring up so it's in the middle of the cassette, or biased to whichever end you think you'll use the most.

it shouldn't add excessive wear on the sprocket, as long as you get the right width.

good luck with it and remember that you can usually get anything to work as long as you take the time to troubleshoot.

My XT rear derailer shifts very well.

Oh ok sorry mine is different and I remember shopping for a single set up and thought that 42 was max??? Confused? But go for it I think you will like it. I have a single barcon to change gears very simple and I think good for cx racing ...