Bicycle Mechanics - What all is needed to upgrade from three to two ring crank set?

Hi there,

I have a 06' Trek 1000 with a three ring crankset I'd like to swap out for a newer 105 two ring crankset. The current setup is a square BB. I'm looking to go two ring, since I have never used the granny gear and never plan to do any hill climbs with this commuter. Also, it'll be easier for me to tune-up I figured.

My question is, what all do I need to buy aside from the crankset? I figure the BB. Also, what do I do to align the derailer from three to two ring?

Perhaps I should look for a used or NOS square crankset?

Thank you!

Some of us don't believe that would be an "upgrade." :p

Hi there,

I have a 06' Trek 1000 with a three ring crankset I'd like to swap out for a newer 105 two ring crankset. The current setup is a square BB. I'm looking to go two ring, since I have never used the granny gear and never plan to do any hill climbs with this commuter. Also, it'll be easier for me to tune-up I figured.

My question is, what all do I need to buy aside from the crankset? I figure the BB. Also, what do I do to align the derailer from three to two ring?

Perhaps I should look for a used or NOS square crankset?

Thank you!

All you have to do is decide on which crankset you want and order the compatible length bottom bracket. Up to you whether you go used or NOS on the BB, but you don't need to do - the age of the bike has nothing to do with putting on a double in this case - 6 years is not exactly ancient.

The derailleur setup is the same as you would do for a new derailleur - correct height, align with chainwheels, limit adjustment and then cable adjustment - all per Park procedures.

BTW- unless you don't like the middle and outer chainrings on the current crankset, all you'd need to do for the upgrade (?) is remove the granny and the bolts holding it on. Of course you'd have to remove the right crank first, since the granny can't be worked past the other rings.

OTOH, if you go to larger outer chainrings, it may present a FD problem since there's a good chance your bike was supplied with a FD who's cage's curvature was matched to the ring on the bike. This isn't always the case but is pretty likely if going from a 46 or 48t to a 53t. so check before buying that new 105 crankset.

I'd recommend leaving it alone. When you're ready buy a new bicycle.

It's really no easier to tune up a double than it is a triple. There is only one additional adjustment for the indexing and that is the easiest one.

The only reason I can see for the swap would be to go from a standard triple to a compact double. That could save you a bit of weight, but you said this is a commuter that won't be used on hills so that begs the question "Why?". If you don't want the granny gear in play, just set the low adjustment screw on the FD to lock it out and use it as a double. I did this with an NOS DuraAce triple on a bike that was designed for an older 105 standard double and the stock FD didn't quite reach the granny gear. Months later I swapped the FD to an Ultegra for a triple and now have the full range, but it worked just fine as a double with no modification and no empty bolt holes.

I'd recommend leaving it alone. When you're ready buy a new bicycle.

That is a big cost difference there...

Also, the reason for this change is because I bent the large and medium chainring. It didn't take me all that long either, say less than 1000 miles? My assumption is that has to do with the cheap crankset that is currently on the bike. I could be wrong, as always.

Hi there,

I have a 06' Trek 1000 with a three ring crankset I'd like to swap out for a newer 105 two ring crankset. The current setup is a square BB. I'm looking to go two ring, since I have never used the granny gear and never plan to do any hill climbs with this commuter.


Swap the cassette for a 12-13-14-15-16-17-18-19-21-23 before you do that. The one tooth jumps through the 19 cog feel good.

Although 30x28 or whatever came with the bike is way smaller than you need, 39x23 may not be and by switching to the double you may eliminate your ability to have both the most pleasant flat ground cogs and the low gear you need.

That is a big cost difference there...

Also, the reason for this change is because I bent the large and medium chainring. It didn't take me all that long either, say less than 1000 miles? My assumption is that has to do with the cheap crankset that is currently on the bike. I could be wrong, as always.Well, bent chainrings is not a cheap crankset issue as a lot of cheap cranksets have steel chainrings that are 3x stiffer than the alloy ones.

First, check that the chainring bolts are tight. Then check the crankarm fixing-bolt in the centre. A loose one is very common source of wobbling rings. These bolts need to be tightened to 25-30 lb*ft torque; pretty much requires an automotive-style ratchet-wrench with at least 10-12" handle.

Next, you can bend the chainrings so they're straight. Looking down from the top and using the front-derailleur cages as a guide, you can use an adjustable-wrench (Crescent) to grab the chainring at a bent spot and bend it back in or out:
http://4.bp.blogspot.com/_Y9sYeduiCGM/THnNvN64OZI/AAAAAAAACMc/KNxbCvTsN58/s1600/chainringstraightening_jimlangley.jpg
http://4.bp.blogspot.com/_Y9sYeduiCGM/THnNvN64OZI/AAAAAAAACMc/KNxbCvTsN58/s1600/chainringstraightening_jimlangley.jpg

Finally, to go to double, you can remove the 3rd chainring. Depending upon the crankset, you can typically remove the outer two rings 1st, then unbolt the granny and wiggle and work it out over the crankarm. Then put the outer two rings back on. No need to remove crankarm.

That is a big cost difference there...

Also, the reason for this change is because I bent the large and medium chainring. It didn't take me all that long either, say less than 1000 miles? My assumption is that has to do with the cheap crankset that is currently on the bike. I could be wrong, as always.

Takes a lot to bend chainwheels - I did not see it very often over a long time in the bike biz. Hard to tell why - I would think it would take either an accident or some pretty outrageous pedal mashing. I'm not familiar with the crankset that came on the Trek

First, check that the chainring bolts are tight. Then check the crankarm fixing-bolt in the centre. A loose one is very common source of wobbling rings. These bolts need to be tightened to 25-30 lb*ft torque; pretty much requires an automotive-style ratchet-wrench with at least 10-12" handle.

Everything is quiet tight.




Next, you can bend the chainrings so they're straight. Looking down from the top and using the front-derailleur cages as a guide, you can use an adjustable-wrench (Crescent) to grab the chainring at a bent spot and bend it back in or out:



Great idea, I'll check this out when I get home.

Thanks!

Takes a lot to bend chainwheels - I did not see it very often over a long time in the bike biz. Hard to tell why - I would think it would take either an accident or some pretty outrageous pedal mashing. I'm not familiar with the crankset that came on the Trek

It is a combination of both I fear. I had an accident a while ago, but I have recently started riding alot more. Since then, I've picked up to clicks per pedal rotation. One at the small bend in the ring, the other when it is at the other end. I have completely diassembled and reassembled the whole drivtrain, relubed and torqued all the screws, including the chainring screws.

Crank set is Bontrager Sport, 30/42/52 teeth.

http://www.bikepedia.com/QuickBike/BikeSpecs.aspx?Year=2006&Brand=Trek&Model=1000