bemilyc

Hi forum posters,

I'm looking to replace the crank on my bike before a long tour. The goal is to increase my gear range on the low end, since I'm expecting some hills. Unfortunately I have to change the whole crank because my current crank is an obsolete bolt circumference (118) and it's impossible to find replacement chainrings.

Doing online research I've found references to the TA Cyclotouriste or ProVis 5 cranks, which were double cranks that could replace a triple crank minus the middle chainring - with chainring teeth combinations of, say 28/46, or 26/42. Apparently they stopped manufacturing these in 2005 or so.

I like the idea of this wide-range double rather than a triple crank, and so I am wondering if anyone makes these anymore, or a comparable product?? (But also, if there were mechanical problems you know of that made these a poor choice, I would appreciate hearing about that too...)

Thanks in advance for the help.

desertdork

Velo-Orange has been working on their Grand Cru crank.
https://velo-orange.blogspot.com/2010...cru-crank.html

Also check out Sugino PX as an option.

sstorkel

Most road bike front derailleurs are spec'ed for a maximum 16-tooth difference between the large ring and the small ring. You might get away with a slightly larger difference... or you might not.

tacomee

There are standard crank sizes for a good reason.....they work. Sure, some folks make goofy double cranksets with huge differences in chain ring sizes, (I have personally done this), but it's nothing but hassle and your gearing might not work for you.

Touring bikes generally have a compact triple (110 and 74 BDC) or a standard MTB triple. There isn't a good reason to mess around with anything else. Not to say I don't build crazy stuff for no good reason once in awhile.

ajs26

I've had bad gearing on my bike for over a year now. My crank was a 48/39 and I had a 11-23 cassette. As my cross bike got built up to be more of a touring bike it naturally became heavier, especially with fenders, saddlebags, stronger wheels, 700x38 tires, etc. Once I actually put stuff in the bags and took some longer trips I really regretted not having lower gearing.

I started by changing out my heavily worn 11-23 cass. for a 12-26. That helped somewhat, but hills, wind, and a loaded bike needs more than just 3 extra teeth on the cassette.

Long story short. I finally decided to get a new crankset. I couldn't decide between a triple or double with a smaller than 39t small ring. I ended up getting a Sugino XD700 48/34 double. Search for Sheldon Brown's gear-inch calculator. The numbers may not mean alot to you but they will give you an idea of what your bike has and what your bike could have, as well as the % of spread between each and every gear.

Chris_W

I also run 26/42 on my touring bike, and 28/46 on my road bike. With 9 or 10 cogs on the back, there is no need for the middle ring. In the Long Distance Cycling sub-forum of this site, such combinations are often discussed and are referred to as "super compact" doubles (as opposed to the standard 34/50 road bike compact cranks). There are several mountain bike cranks that have been released in the last few years that are designed as mountain bike doubles, some of which have 27/42 chainrings (but there are many other combinations), these have previously been only high-end, expensive cranks, but SRAM is about to release some more reasonably-priced versions this summer. These MTB cranks would work for touring if you are OK with the wider Q-factor of a MTB crank and you have a 135mm rear hub to get the chainline right. If it is more of a road bike setup, or you just prefer a narrower Q-factor, then you can get this gearing by using only the inner and middle positions of a road triple crankset and using some custom chainrings - TA Specialites makes some very nice ones. When using the triple-as-a-double, just make sure that the chainring that you place in the middle position has the shifting ramps designed to be in that position, and the chainring bolt recesses on the inside of the ring, such rings are available in up to 46-tooth sizes from TA. You can either leave the outer chainring position empty, and so you'll need some shorter chainring bolts, or get a chainguard to put in the outer position to keep your pants / leg away from the chain (the Salsa Crossing Guard is good at a decent price).

This setup is then similar to the old "half-step-plus-granny" gearing that was reasonably common when cassettes only had 5 or 6 cogs. Now that 9- or 10-speed cassettes are the norm, the two half-step chainrings are not needed, and can be replaced with just one.

I've used a lot of different front derailleurs with this type of setup, designed for double or triple cranks, road or mountain bike models. All have worked OK, but all work better if you have continuous control over the front derailleur, as with a down-tube or bar-end shifter, which allow a lot more control than just having two indexed positions.

LeeG

I took a Sugino triple and put a 30 t on the inside with 44 t on the middle with chainguard on the outside. The 44t in the middle position can run the whole range of the cassette and with 32t or 34t on the cassette I get the low gears I want. 90% of my riding is on the 44t with a range from mid 30's to 90's, on the 30t I've got mid 20's to 30's taken care of.

LHT in Madison

I have a road triple and changed the inner 30 (or 32?) to a 24 so that I have a 52/42/24. Shifting from the 24 up to the 42 is not a smooth shift. I don't know if it is the ramps and pins being designed for a different chainring or if it is the big jump from the 24 to 42. If you are not used to such a big jump, be prepared for shifting that is less smooth than desired.

Garthr

Road FD's are under rated in a big way. I use a 9sp 105 Double FD with a 24t difference, it's rated for 15t or so.

OP will have no problems with a 9sp road double, or older. Shimano brand, that is, I don't use others.

sstorkel

I think it's a mistake to say that any FD will be able to handle a crank with a huge difference in size between the small ring and the large ring.

When doing something like this, you really have to look at the drivetrain as a whole. There's only so much chain slack that the drivetrain can take up while you're shifting, and that duty is handled by the rear derailleur. If the difference in size between the big ring and the small ring is too great, the RD won't be able to take up the slack and shifts from the big ring to the small ring become problematic. Running a long-cage road RD or MTB RD probably gives you the best chance for success if you want to run the FD out of spec. In my experience, friction shifting seems to be more forgiving than indexed shifting. And you can hedge your bets by installing a Jump Stop or Dog Fang.

nun

With a 110 double, the smallest inner ring you can do is 33 and given a 16t difference you can go up to a 49 outer. With a 94 double (ie TA Carmina) you can do 46/30. However, for touring I think 33 ro 30t are a little high so the most obvious thing to do is to simply use the inner and middle positions of a 110/74 triple. This is what I do and run 42/26 rings. You have to be prepared to have a larger than usual gap between the derailleur and the 42t ring though. I use a 105 double FD and a long cage MTB RD

https://wheelsofchance.org/2009/08/28...-the-question/

The Smokester

I wonder why you really want the double. If you get a Specialites TA Carmina triple you will have a small Q, a choice of rings from 20 to 50 teeth, a choice of crank length from 155 to 175mm, and excellent shifting.

LHT in Madison

I commented above that I use a 52/42/24 triple, for that I use a vintage Suntour high normal front derailleur. Front bar end shifter is friction. Rear gearing is an Sram 11-32 eight speed cassette.

If you really want to use a double, go ahead. But, I really like my setup with a triple. It offers the gearing you are looking for and a bit more gear choices in the midrange to high end. The highest two gears are too high for typical riding but they can be nice to have for those rare long shallow downhills that you occasionally encounter.

I don't use the smallest rear two cogs with the smallest (24t) chainring, don't use the largest two rear cogs with the largest (52t) chainring and with the middle (42t) chainring do not use the smallest or largest rear cogs. This results in a total of 18 gears that I actually use. In my case there is another reason that I do not use the smallest two rear sprockets when I use my 24t chainring, the rear derailleur (XT M739) does not take up all the slack in the chain.

From smallest to largest, gear inches with my 37 X 700c tires is as follows:
20.7,
25.5,
31.6,
36.8,
41.4,
44.6,
47.3,
55.2,
64.4,
68.4,
72.5,
79.8,
82.9,
89.8,
96.7,
102.6,
119.7,
130.6.