Drivetrain Upgrade and Modification
 

I've got a 1990 Trek 1400 that will be getting a drivetrain upgrade before spring. Below are the current and planned drivetrains. I'm trying to avoid having to change the rear derailleur which is a short cage 105.

Current: Square taper 105 with 52-42 biopace rings and traditional bearings. 11-23 Hyperglide 7-speed cassette. 105 short cage rear derailleur with max of 33-tooth span.

Planned: DuraAce 53-39-30 triple with Octalink BB. 13-23 Hyperglide 7-speed cassette. If I figured this right (53-30) + (23-13) = 33 should work with the short cage derailleur. I should gain significant climbing gears on the low end and bring my top gear down slightly as the 52 x 11 was a lot for me except on downhills or with a good tail wind.

Does anyone see any problems with this arrangement for mid to long distance riding on rolling hills and occassional moderate climbs? If I find this to come up short on the low end I could change to a long-cage rear derailleur and a 12-28 cassette, but I'd rather not if I don't need to as the current derailleur is in great shape and I don't do long, hard climbs at this point.

gearing for hills
 

Greetings Myosmith,

Last January, I was contemplating some gearing changes on my Felt F80 road bike to make it easier for me to climb the hills on my normal routes. I started this thread to ask questions about varoius possibilities including changing front ring sizes. If you read through all of that, you will see that I landed on what I believe to be the best gearing for my old tired legs. My ratios may not be what you are looking for but should give you something else to consider when trying to get a bike geared for hills. In the end you will have to decide for yourself based on your strength, endurance, severity of your hills, normal wind speed, and probably a few other factors to get your bike just right for you.

In a nut-shell, in case you don't want to read all of that other thread, the changes I made took my F80 from a 52-42-30 / 12-25 combination to 52-41-28 / 12-27. I am now quite pleased with the way my bike performs on the terrain I have to tackle with my level of conditioning. :thumb:

Hey Myosmith,

I'm using a 48-36-26 triple with a 14-25 9sp cassette and a short-cage rear derailer. This is similar to your proposal in that the calculated derailer capacity requirement is also 33 : [(48-26) + (25-14) = 33] The rated derailer capacity is 28 I believe, but by avoiding cogs 1 and 2 when in the big ring and 8 and 9 when on the small ring all is well and shifting is quite good. Go for it!

Regards,
Bob P.

IF your chain wrap capacity is 33 teeth, you're good to go.

But- isn't a short cage DR only good for about 29 teeth????

Yes. 31t if you push it and your derailleur hanger is long.

Why would you go to all the expense of a triple conversion and then cheap out on the rear derailleur, requiring you to use sub optimal gearing? A 105 triple rear (5700) is like $55. After shifters, crank, bb, and front derailleur it's not that much more. Using a narrow range cassette with a triple means that you will be forced into the small ring early and will have to use it more often. I think triples are great for a lot of people but I can't deny that the shift to and from the granny ring is slow. It's not something you want to do a lot. A 12-27 would be better.

Also the DA triple stinks. It uses proprietary chain rings so you can't change gearing and replacing them when they wear is expensive. Ultegra 6600 had standard BCDs and chainrings. 6700 does it like DA. Avoid.

Front derailleur and shifters aren't getting changed and BB needs it anyway. DuraAce wasn't my first choice but I got the crankset in new condition cheap at $89 which was about the same as replacing the rings on the old square taper 105 crankset. My other option is to remove the inner chainring on the DA and run it as a double with a 13-28 cassette which would reduce the required capacity of the rear derailleur to 29. I'm finding conflicting information on the 105 ss derailleurs with listed capacities of 29 in some places and 33 in others. Some list the max rear cog size as 28 tooth and some as 32 tooth. Did this change with different incarnations of the 105 SS derailleur? If so, how do I determine which I have other than just trial and error?

Now someone correct me if I'm wrong, but the Dura Ace triple cranksets accept standard outer and center 130 BCD chainrings (with caveat to follow). The proprietary part is that the DA center chainring won't fit other 130 BCD cranks because of the tabs to which the inner chainring attach, and the inner chainring is some goofy BCD that only works with the DA center chainring. Therefore you could replace the outer and center chainrings with any 130 BCD chainrings but would have to settle for using the crank as a double.

[QUOTE=Bob Pringle;13771888]I'm using a 48-36-26 triple with a 14-25 9sp cassette and a short-cage rear derailer. This is similar to your proposal in that the calculated derailer capacity requirement is also 33 : [(48-26) + (25-14) = 33] The rated derailer capacity is 28 I believe, but by avoiding cogs 1 and 2 when in the big ring and 8 and 9 when on the small ring all is well and shifting is quite good. Go for it! [QUOTE]

I think that's a recipe for disaster.

A better plan is to make sure your chain is long enough to safely cover the big/big combination and not worry about the little/little. You only use the granny ring for climbing steep hills and shift out of it when you reach the top. Consequently, you only use the granny with the 2 or 3 biggest rear cogs. Even if you happen to shift into a combination that causes the chain to go slack, it won't damage your bike.

Accidentally shifting into the big/big with a too short chain is much more likely. It can also cause serious damage to your chain, derailleur, wheel, frame and maybe even you in about one second.

+1 Even if you know to avoid the big-big combination, some day when tired or distracted you may try to use it and it MUST work.

The other guys know more of the technical details, but I think you'll really like the triple once it's on there. :thumb:

Yup. It generally happens on a nice day when everything is going right. You start up a little hill and gradually shift into lower gears in back. When you feel resistance you attribute it to the hillgrade and push a little harder with your legs. OOPS!

(sum of big minus sum of small) .. (53+23)-(30+13) is more how chain wrap up is calculated,
might destroy the RD if you use too little chain and shift it into a combination demanding more chain.

Fit the longer cage RD, so it takes up your chain-slack of having adequate length.

reusable quick links favor trial and error, using a chain too long, at first,
then removing a link , or 2, till its right.

Or use the big/big chain measuring method:
1. Wrap your chain around the biggest front chainring and biggest rear cog bypassing the derailleur.
2. Figure out the shortest place you could rejoin the chain.
3. Add 1 inch of chain (2 links) to that length.
That's the shortest chain that will safely cover the big/big gear combination and derailleur arm length doesn't matter.

OK, lots of good advice to work with. Thanks.

How is this for a plan? Install the DuraAce triple with the proper BB for a triple but set the front derailleur low limit screw so that I can currently only use the middle and outer rings. Install a 13-28 rear cassette. Keep the current short cage derailleur and adjust chain length accordingly (big+big+1"). If I decide a really need the inner ring, I can pop for the $80+ for a new 105 long cage derailleur and readjust the lower limit screw on the front derailleur to let me into the small ring.