prathmann

Yes, the 16t difference spec. can be pushed a little. I have 60t/42t rings on my Bike Friday using Shimano 105 components.

Jeff Wills

I hope you noticed that the "early responses" were from 2014.

prathmann

And my Bike Friday with the 18t difference is from 1994.

Sy Reene

That is an interesting premise. I don't see this ring/combo mentioned too often. Might be interested in trying these, but they (wonder if a technical reason?) don't seem to offer in campy 4-Bolt.

kcblair

Glad we're on this subject. I'm restoring a BS500. Freewheel is 14-32 (6Spd) and front 52/42. I'm replacing the 42T with a 34T. I'm sure that is out of Suntours specs, but I'm aware of cross chaining, so this shouldn't be an issue. Thanks KB

TigerMom

thanks. This totally helps to know this part exists @jamesdak!

HerrKaLeun

A while ago a forum member posted link to a SRAM PDF that explained why their double chainrings shift so well. I just can't find it anymore and if anyone knows what I mean would appreciate link - was a really good paper.
Anyway, main point is that they keep the chainrings in a ratio of 3:2. Meaning the small chainring has 2/3 of the number of teeth of the larger one. In my case a 28/42 etc. They said that gives 4 natural overlap points where the chain glides on the ramps from tooth to tooth. It seems most if not all their double cranks follow that 3:2 rule. I know they had to say their design is good, but it made sense. I can attest that it shifts very smoothly (better than my old 3x crank with 22/32/44).

Obviously other ratios also work and as attested above it seems to work well. but if you can, sticking with the 3:2 rule may be good. Obviously this limits your range.

TigerMom

Thanks for letting us know that Wickwerks has a double chain ring that uses 53/34!

My tandem has a triple Ultra (52/39/30T) and is NOT shifting to the smallest 30T chain ring on an uphill (even while soft pedaling). I'm thinking of getting rid of the 30T and changing out the 52T to 53T on my triple front derailleur (we need more upper end gears for the flat rides also). Could I then set the limit screws to stop at the 34T after buying the Wickwerks 53/34 chainring?

Then I was going to change out my rear cassette to 10-42T while using the Shimano XTR long derailleur as some other people on this forum is doing in order to get more uphill gear range. What do you all think?

fietsbob

See my post # 15..


You really only would get out of your mountain climbing smallest chain ring at the top of the hill ,

as you prepare to coast down the other side, and have no chain tension while making it go up to the big chainring.






.....

tomtomtom123

I have done 44/24 with TA chainrings and 46/26 with spa cycles chainrings. The spa cycles shifts a tiny bit better. Shifting is fine but setup of the index FD requires patience to get it right. Was able to do it with both a Shimano FD and SRAM YAW FD. Chain catcher on the inside is required.

I tried 46/24 on the workstand and it seemed to work, but I did not ride it.

The outer most 3 cogs are not usable on the small chainring because the chain will rub on the outer chainring, so you need a cassette wide enough to overlap those gear range. This may be 4 cogs depending on the thickness of the chainrings and the center to center spacing between the 2 chainrings. You can add spacers to widen the distance to stop chain rub on 1 more cog, but too much spacing may cause bad shifting. Aim for 7.6 to 8.0mm and adjust with DIN 988 shims of 0.2mm thickness, $3 for a bag of 100 shims.

bldegle2

I am running a 50/33 on a 5 bolt 110 BCD on both of my road rides. The 33 is a special ring made in France, an engineering marvel. Running a GS derailleur 11/34 cassette in the rear on both. So I would say 17 would be the max or one will run into problems with chain wrap formulas...

Tigermom, what rear derailleur are you running to get the `19T differential to work?

tomtomtom123

You should look at the specs for your RD to find your chain wrap capacity.
https://productinfo.shimano.com/#/sp...r%20Derailleur
The formula is not difficult. cassette difference, plus the chainring difference. Your chain wrap is 40T. Compare it with the Shimano specs.

I have a 12-34T 10 speed cassette, with 44/24T chainrings, so my chain wrap is 42T. I have a Shimano RD-4700-GS with long pull cable ratio. It has a chain wrap capacity of 41T. The outermost cog when on the big chainring just barely drags the pulley cage. It will depend on how close you are to the next length of 1 inch chain link.

Even if the outermost cogs drag while on the big chainring, it doesn't matter for me, because with a 20T jump between the double chainrings, the outermost 3 cogs will have chain rub anyway. So I don't use those 3 cogs.

bldegle2

Thank you for the information. I don't know if either of my current front derailleurs would work properly/smoothly with a 20T differential plus I would have to recrank to take the smaller rings. I am considering a 48/32 setup to keep the ratios on the front rings in spec and shifting smooth, as I age having the gears makes all the difference. I have played with chain lengths on my setup, any longer and chain will rub rear cage/jocky wheel in the most relaxed position, any shorter and big big will not work. Have played with 'b' stop setttings. I have a dag tool, hanging it right always helps. My only rides are road bikes I build, no dirt, no gravel, just road. Anything I comment on is coming from that 2 x 10 experience only, so it may not crossreference to different setups/uses, my bad.

The bike stand is the messenger/bible when doing dress rehearsals my best advise.