Bicycle Mechanics - 39T Chainring on 105 Triple?
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12-04-01, 08:08 AM
I need to replace the middle (42T) ring on my 105 triple. I would like to replace it with a 39T so I can have exactly the same gearing as my other bike except for the 30T on one for when I get to the hills. I know that the middle and large rings on Shimano cranks have special tooth designs, ramps, pins, etc., to work with specific other rings. In other words, there are two different 52T rings, one designed for use with a 42T and one for 39T. The 42T middle ring also has ramps, etc. As far as I can tell the 39T Shimano ring is intended for use on the double crankset and does not have ramps/pins since you will never shift up to it from a smaller ring. Does this mean it won't work at all or just that the shifting up from the 30 might be a little slower? Ditto for shifting from the 39 up to the 52 if I don't replace the 52 right away with one intended for use with the 39? Using 105 STI 9-speed shifters and front der.
As long as you maintain the proper spacing, the STI should be able to move the chain. It just won't be as smooth a shift as with the ramps.
12-05-01, 12:50 PM
Thanks, lj. I stopped by my LBS on the way home, and my buddy there said the same thing so I picked one up. I got the 42 off without removing the crank, but the 39 is too small. So, no problem, right? Just pull the crank with the old crank extractor. AHH, but wait, this is a recent 105 bottom bracket with hollow axle, nothing for the puller to push against. Sooo, Rainman has to buy yet another tool, the new type extractor, which is not a problem except, as usual, a 3 minute job is going to take a couple of days! I'm just going to stop by the shop and use theirs this time, but I told my buddy to add it to the growing list of things to order for me.
12-05-01, 01:23 PM
Long time no see, I've been busy with my web sites and havent been around lately,,, boy things sure have changed.
Yep the 39 will work just fine you probably wont notice very much diffrence, I used one on a double for quite a while, it was just a little slower to up shift.
Ok untill next time .
12-05-01, 01:41 PM
Oh by the way Rainman, click over to my new site, I moved from MSN (yuck) to Angelfire. See what you think about it, I know its not your cup of tea ..... but you know openions are good no matter where they come from .. LOL.
I have freely mixed/matched/swapped 39, 40, and 42T rings with 50, 52, and 53T outers, without worrying about "A" and "B" designations, ramps, pins etc. (Heck -- most of my bikes do not even have ramped or pinned chainrings, and they shift just as well. I think the ramps, etc. are mostly marketing hype, particularly for those of us who pedal gently while shifting.)
12-05-01, 04:58 PM
Thanks, Steve, I'll check it out.
Stopped by the LBS to use the crank extractor. Slapped the chainrings on and hit the road. Oh, I didn't abuse the LBS by doing this. As a matter of fact, they would have installed the new ring for me since I bought it there, but I wanted to do it. AND I had them order an extractor for me so I can start pulling the rings for regular cleaning. I hardly noticed a difference in shifting. I used an Engagement Ring brand. Uniform teeth and no ramps, pins, etc. The nice new 39T ring made me faster, too, which I can't figure out since I was on the big ring all the way home. :D Stopped the chain noice, too, from the worn teeth on the old ring.
So Yorick is running silent again except for the buzz of, I guess, the pulleys anytime I am using the big ring. Is that normal? I don't hear it on the middle ring.
12-05-01, 05:26 PM
Yep that's pretty normal, the faster chain travel + the extra tension cause the noise. If you feel like it install some sealed bearing pullys, these run quiter and faster to, less friction you know.
I used to use them on the old Bianchi crit. bike all the time, loved them! been thinking about it on the Cannondale Mt. Bike.
12-06-01, 12:35 PM
Just a note about the 105 cranks. Do yourself a favor and go for the self-extracting bolts. They are such a time saver and have no ill effects. I have them on my XTR cranks and would hate to go back to square spindle/crank puller setup.
12-06-01, 02:14 PM
Can you replace the stock bolts with self-extracting bolts, or does the self-extracting capability require specific crank arms? These cranks have the cap shaped crank bolts that are also the dust cap and require an 8mm allen wrench to remove. Can I just purchase different bolts?
12-06-01, 02:49 PM
Self extracting bolts are very nice, and should work with your cranks. They do make things easy when removing, just be sure to thread them all the way on. You will need a spanner wrench, or (another) special tool. Agggggghhhhhhh! Will the tool buying madness never end? I'd just buy the tiny little cap that slides into the hollow spline that allows a standard crank puller to work. That's what we use at our shop.
12-06-01, 04:17 PM
It's trivial, but the spanner is less expensive than the extractor. IMHO I think the convenience of self-extracting bolts is well worth it. One night while fine-tuning my BB spacing, I removed and reinstalled 2 sets of cranks 3 or 4 times each. I probably wouldn't have bothered if it weren't so easy.
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