Triple to Double Crank
 

Is there any practical difference between a triple crank (50.39.30 Shimano 105) with the small chainring removed vs. a standard 50.39 105 double?

hmmm, I am not that educated on cranksets and gear inches and all that mumbo jumbo. But logically speaking when you take away that small ring you basically take away the easiest gears you can have, simply meaning when you go up a mountain you cant rely on your small gears to get you up, so your going to mash on that 39. Thats the way I see it, but I am not an expert. Thats why I rather have a triple.

I never use the small ring and I recently had to replace the shifter with a double instead of a tripe. Not that it's a big deal, but I'm inclined to pull the 30T ring off of there to avoid any confusion in the future, not to mention avoiding the shame of being seen on the road with a triple.

I was going to buy a double crankset to replace it, but now I'm wondering if that makes any sense.

Yeah, because it is sooooo shameful. :rolleyes:

You must be very strong rider than, I cant live without my triple and small ring.

Isn't there a way to dismantle your triple and make it a double, Im sure there is a how-to post on here or even a youtube video on it. If I were you I would try to convert my triple to double, rather than spend money on a new crankset.

Didn't you get the memo, line?

Hey, I paid my dues. I rode around with that thing for a year until I didn't need it any more.

A double and a triple use different bottom brackets, so I'd imagine your Q-factor and chain line would be different, but it probably wouldn't be a huge deal.

Very strong is realitive. I do not consider myself a big engine, but I rode from Alpine NJ to the top of Bear Mountain and back on Sunday and never came off the 53. I did cross chain some on the climb up Bear, but for the most part I never went below the 53/21.

And I did not stand on Bear either. I sat and spun at about 80 rpm.

Lots of people, at least in this area, never need the 39 (or 34 if you have a compact) and we are nothing special.

I'm not very strong. I do live in a very hilly place, but once I got comfortable climbing the tough hills out of the saddle, I never went back to the granny gear.

Since my bike already has a triple BB (assuming there is such a thing), then my modified triple crank should work fine. I'll just be removing a chainring that I never (and now, can't) use.

The chain-line while using the big ring on a triple is an issue. Bending the chain to reach the cogs near the wheel will wear the chain and reduce the power to the wheels. The big ring on a double is in about the same location as the middle ring on a triple. Cross-chaining still needs to be avoided, but the chainline is less drastic.

Michael

Alright, that's the kind of information I was looking for. Will I need a new BB if I get a standard double? I think the 105 triple crank has a spacer that you put on but that isn't needed if the crank is a double (same installation sheet, as I recall).

That raises another couple of questions: If I take out the spacer, will it bring the big ring into the center? And if so, will I have cross chaining issues with the smaller cog?

To be honest, back when I had a functioning triple, I rarely got off the center cog anyway. And that's still where I spend most of my time.

Q-Factor and chainline are different between a double and a triple.

Some manufacturers also produce Triple-specific front derailers.

If you remove the inside ring on the triple you can just get a bottom bracket for a double crankset.

Yes, remove the spacer and it'll work. You'll also need to adjust your front derailleur high/low so it doesn't drop the chain. Other differences is the rear derailleur as it's probably a long cage one and your chain is probably longer than a double chain. But unless your shifting is poor after changing it to a double, I wouldn't worry about it until these parts wear out.

Personally, if it was me and I wasn't having any shifting performance issues, I wouldn't worry about it the way it is currently. If you don't use the small ring, simply don't use it. Tell yourself it's a double and have fun riding.

Your BB will be off and it will give you a pretty limited gearing dues to cross chaining and your front derailleur will be quite jerry rigged if it's triple specific. That being said i did several thousand miles like that but eventually switched to an ultegra double and BB(ebay for 65 shipped) and a double FD

Just FYI, I have gone between a Double & Triple and also ran a 1X10 for 4000 miles;

http://i289.photobucket.com/albums/l...drivetrain.jpg

and this Sram Cyclocross double w/ 46t & 38T chainrings;

http://i289.photobucket.com/albums/l...asilver022.jpg

Drivetrain changes were made mostly to experiment. The Sram Cyclocross 46 & 38t double worked fine, but I rarely used the 38t chainring. I installed a 44t single chainring and used that for 4000 miles with a 12-27 10 speed cassette. This set-up forced me to charge up every hill out of fear of bogging down. The range also required a rapid cadence at higher speeds. I put a 50, 39 & 30t triple crankset on the bike this month. My plan is to ride more hilly Century rides next year. I use the 39t chainring 80% of the time and only need the 50t above 26 mph. The 30t chainring is really not needed, but will be used as a convenience a few times a month.

This compact with a 12-27 cassette should work well: http://www.backcountryoutlet.com/out...-Crankset.html

You will also need BB cups for about $40. Your existing derailluar should work OK after adjusting it. You will be switching beteen the 50t & 34t chainrings more often than when you depended on the 39t middle ring on your triple.

Michael

Michael

Not sure where some folks are coming from - I switched out the exact same triple crankset you mention above with a 50/34 Ultegra SL and did not change the BB. I did go to a double FD though. Q factor is different and the shifting is smoother, but you wouldn't get those small benefits with your proposal.

I just replaced mine and now it shifts like butter -- even during the week that I still had the 9 speed cassette and old shifters. You can get a 105 crankset for $100. Like you, I never used the 30 ring and even replaced it for a while with a 34, which was even too low.

The instructions for the BB-6700 I used for mine indicate the spacer is used if you have a triple and is not used if you have a double. Same BB, though. Look up the shimano pdf.

So, thinking about this some more, I come to the following conclusion:

Leaving the spacer on the shaft, means that my primary ring would be the 39T, with the 50 used mainly when I need a higher gear at the top end.

If I remove the spacer, that shifts the 50T into the middle, making it the primary ring, with the 39T serving as the granny gear.

I'm assuming that a standard double uses the latter configuration, i.e., most of the time is spent on the larger ring.

Have I got that right?

Yes, ...and...

If you remove the spacer, the outer and inner ring can each use 9 out of 10 of the cogs on the cassette. You need to avoid the big-biggest combination, in this case to 50t outer ring with the largest cog. You also need to avoid using the small-smallest combination, in this case to 39t inner ring with the smallest cog.

I have a 105 triple with a 50t, 39t and 30t. I have a 12-27 10 speed cassette. I use the 50t when traveling above 24 mph for longer periods. If I removed the spacer, I could use the outer ring when traveling above 15 mph. I use the 39t from start-up to 26 mph. If I removed the spacer, I would stay off of the smallest cog and switch to the big ring at 23 mph.

When in the 15 to 23mph range, I would be able to use either chainring without a problem. This is the best reason for converting a triple to a double, IMO.

Michael

I guess you use the small ring or walk up the hill.

I would imagine that a double is lighter than the triple. Other than that, I don't see many high end road cranks using triple. Yes, it will be easier to climb with that smallest ring.

I've been using it as a double for about 2,000 miles, no problems. I left the spacer on the shaft, which makes the 39t ring my main cog, with the 50 coming into play at higher speeds. I also have the original triple FD, which works OK, but I think a dedicated double FD would be better. In any event, I plan to swap in a dedicated double crank and FD one of these days. I have another bike that can use the 105 trip. That would be Granny's Trek.

I think thats true although I wouldn't do it that way. I ride for a junior team and the biggest gear thats allowed for sprints is 52/14 so we have to work on high cadence drills in the winter. we are not allowed to use our big rings all winter. I have a compact 50-34 crank and i could not keep up with the pedals with my 34/14 so I put my old 11-23 on and I could spin that up to about 30MPH so I would use the 39 as the main chainring, 39/11 or 12 will work fine for 90% of any kind of hill in the east san francisco bay region I live in.