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substituting 42 for 39 on a double. considerations?(13 posts)

substituting 42 for 39 on a double. considerations?JS Haiku Shop
Apr 24, 2003 6:23 AM
shimano 9-speed. seems chain length would not be an issue. are there any other considerations? TIA!

absolutely no issues; easy no-brainer nmDougSloan
Apr 24, 2003 6:37 AM
that's what i wanted to hear. thanks! nmJS Haiku Shop
Apr 24, 2003 6:39 AM
Apr 24, 2003 6:39 AM
You won't really gain anything, but the ability to go one gearstep higher in the small ring, and lose one gear step on the bottom end. All gear ratios in between are nearly identical. Check it out.

Front shifting might improve just a tad, even if your big ring is pinned and ramped for a 39.

Hopefully he has one in the bike junk box.dzrider
Apr 24, 2003 6:58 AM
I wouldn't buy a new 42 to replace a still usable 39, but if I had a 42 around the house I'd put it on.
How about a 50 tooth up front?Alex-in-Evanston
Apr 24, 2003 7:42 AM
Any idea who makes a Campy 10spd compatible 50 tooth?


How about a 50 tooth up front?Andy M-S
Apr 24, 2003 7:58 AM
Campy makes one. The Centaur triple is available as 50-40-30. You can probably get it through Branford.
If it is a 135mm BCMR_GRUMPY
Apr 24, 2003 9:46 AM
You can have your shop order it from QBP
How about a 50 tooth up front?wielerpret
Apr 25, 2003 1:33 AM
Fine blades are manufactured by Specialites TA (French). The 'Zephyr' types are 10sp Campy compatible. They are much cheaper than Campy and come in several colors. I don't know if or where they are available in the US, though. Good luck. Luke. Amsterdam.
Very minorMR_GRUMPY
Apr 24, 2003 6:42 AM
The big ring is either an (A) or a (B) to match the small ring. In reality, the only problem you might have would be hardly a problem at all. Shifting between the big and small ring while standing might suffer.
whether your legs can handle the hills or not with a 42 (nm)ColnagoFE
Apr 24, 2003 7:23 AM
Apr 24, 2003 8:26 AM
I have heard that some have encountered a "clearance" issue between a 42 ring and the chainstay. Some have indicated that it rubbed, while others have mentioned that a grain of sand would not fit between the ring and chainstay. Other frames, though, do not seem to have a problem. Has frame production somehow changed since the move from a 42 to a 39 small ring?
re: substituting 42 for 39 on a double. considerations?russw19
Apr 24, 2003 8:39 AM
If you are just doing it 'because' then you may want to look at gear inch charts for both setups first to see if you are going to losing anything. See if you are going to have more or less double gears. If more, it's a waste of your time. Unless your 39 is worn and you have a 42 to replace it with... if that's the case, it's another story, but if not, look into it first.

A couple years ago when I was still racing I used to run a 53-40 with a 12-21 setup. Of course that's in Florida, so the small gears weren't an issue. But I had a bunch of double gears with the 14/18 and the 15/19 cogs. I would have been better served to run a 12-23 in the back (this was 8 speed) because it would have run a 20 tooth cog where the 19 was and given me actually 2 more gears. I was doubled at the 19... if I had the 20 it would have been another (very close to being a double) gear and the 23 would have been a bail out.

Anyways, look into it first... see what you lose and what you gain if you haven't yet.