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Switching from a triple drivetrain to a double(7 posts)

Switching from a triple drivetrain to a doubleHerms
Apr 9, 2002 6:15 PM
In order to switch to a shimano 105 double drivetrain what must be changed on a bike that comes stock with a shimano 105 triple drivetrain. Obviously I would need to switch to a double crank, but is there a lot more involved than just switching the crank.
Thanks a lot, Herms
What you need...Uncle Tim
Apr 9, 2002 6:44 PM
You are definitely going to need a new bottom bracket with a shorter spindle length to accommodate the double. You are going to need a new front derailleur to account for the shorter travel distance of a double. And though you can probably get away with the rear derailleur, the right way would be to get one that's designed for a double crank and has the appropriately shortened cage.

And don't forget the double crankset. You are going in the right direction. I am proud of you.
What you need...sievers11
Apr 9, 2002 7:08 PM
new sti lever
new FD
short cage RD
smaller BB
new crank

Check out excelsport.com
http://www.excelsports.com/products.asp?major=1&minor=5
New STI???Uncle Tim
Apr 10, 2002 1:41 PM
If the set up is for Shimano (Ultegra,105, Tiagra - don't know for sure about DA), there is no need to get a new STI shifter for the front derailleur. Once you set the travel limit correctly, the left STI shifter will work just fine. You'll just have an extra stop which you will need for trim. Unless I am just blanking out, I don't think the STI shifters are particularly designed as "double" or "triple" configurations. For all of the conversions I made, the STI shifters (in the above listed component lines) were all compatible.

And though it may be possible to set the limit screw in a manner that will allow a triple FD to work on a double, I wouldn't even try it. Just to avoid headaches, it's worth the money to buy a new FD designed for the double.
just adjust front derailer to lock granny outcyclopathic
Apr 10, 2002 7:59 AM
Personally I see no reason to switch, 42 middle works better then 39 small IMHO. if you don't need granny don't use it. Weight saving is negligible, and Fred factor.. who cares if you can still drop guys on climbs?

with respect to your question Uncle Tim is right all you'd need 109.5mm bottom bracket (triple is 118), cranks and front der. 105 shifters are double/triple compatible and short cage rear der is only 8g less, should you bother?
If you are strong...Uncle Tim
Apr 10, 2002 1:52 PM
I agree, Cyclo, that if you are strong this would be a workable approach. Though I abhor the triple on a bike, the hills around here mandate that I have a 39 front chainring to match up with the low 25 on the back. Very few hills I can't climb with that combo. But a 42x25 and the equation will change. I prefer the 39 and I would suggest that to all those who are not super strong riders.

I think that if I were to adjust anything, it would be on the big chainring. 53 looks great, but it makes for a relatively big gear. Generally, I don't get on the big ring until 17mph or more, so if the road is rolling, I'm on the small ring. And I never spin out on a 53x12. I would probably find it better to have a 52.

One other thing: I do find the weight difference between a double and triple crank to be significant. I think that on Ultegra, the difference is about 6 ounces. Some scoff at that, but I think it makes a noticable difference.
re: no I am a wimpcyclopathic
Apr 10, 2002 6:51 PM
still 42x21 is all I need on my 27lbs commuter to climb 9% grade. I run 12-27 on my "other" bike and I've climbed 0.8mi 16% avg grade climb in 42 using 24 and 27 cogs.

weight difference for Ultegra is following:
BB 20g
RD 6g
FD 7g
cranks 117g
total: 150g or 5.3oz

105 weight difference:
BB 9g
RD 4g
FD 7g
cranks 79g
total: 99g or 3.5oz
(weights from Shimano catalogue)

according to analyticcycling 150g less for 165lbs rider/bike (which translates into 135lbs rider on 20lbs bike with helmet and 2 water bottles) producing 350wt will save .65s on 10% 1mi climb. 220lbs rider on the same bike and producing 250wt will save .97s. If this is noticable, give me a break.