justinzane

Instead of gravedigging https://www.bikeforums.net/bicycle-me...ing-sizes.html, I'll start anew.

I want to know what is the largest range possible with a 110mm or 130mm double. Can one have a 48/28 -- like a 48/38/28 without the middle ring? How about a 52/26? What are the functional limitations and tradeoffs? Are there specific makers that cater to oddball setups like this?

On the flip side, what is the smallest difference between double rings that is at all useful? Is there any situation where a 53/48 or a 52/48 is useful?

I know that someone will say "just get a triple" somewhere along the line. I'm not necessarily going to run out an install a max-range double whatever the answers say. I'm trying to get a feel for what is reasonably possible, not the conventional wisdom, not the current trend.

cny-bikeman

The answer on largest range will vary due to type of chainrings, spacing between the two, derailleur, and chain, but I believe 48/28 is impractical due to the steep, low angle climb and drop. The derailleur pushes the chain sideways, not up, and the chainwheels are designed with certain assumptions. The derailleur will not in my opinion be able to push the chain that high, and in the other direction the chain will likely travel right past the small chainwheel due to the steep drop. Other large differences present similar problems. What you will get here is anecdotal evidence that may not apply to your equipment, as there is no definitive answer.

As to the smallest difference there is also not a single answer. With today's 11 and 12 tooth small cogs I don't think 53 is very useful, let alone paired with a 48. How often do you expect to be going 40+ mph when coasting is not the better alternative?

JohnDThompson 

The functional problem is that the wider the range the front derailleur must cover, the longer the cage it needs. With too short a cage, the chain will drag on the derailleur when it's on the small ring. SunTour made a wide range front derailleur with a cage extension for this purpose, but the longer cage proved more flexible and didn't shift very smoothly.

HillRider

The largest difference with a 130 mm BCD is a 38T small ring (the smallest that will fit) and what ever large ring you want, typically a 53. The smallest chainring that will fit a 110 mm BCD crank is a 33T and, again the large ring is limited to what's available, probably a 52 or 53T. So in either case, a 28T chainring is not an option.

As to big gaps, I have run a 53/42/26T chairing set up on a Campy triple crank and the 42 to 26 shift and back were acceptable even with the front derailleur mounted way to high for those rings.

KBentley57

The max difference on most derailleurs is 16t, which is why we have the options 50/34, and 52/36 for compact and mid compact. The ultimate low gearing solutions are on the back of the bike, you can lower the gear inch on a drivetrain more easily in the cassette.

Unless you want a mountain crank, that is.

ThermionicScott 

The manufacturer's spec isn't a binary works/doesn't-work point, it's just where they feel performance drops off enough to warrant the spec. In general practice, the closer two chainrings are in size, the easier they'll shift, and the farther apart they are, the more laborious it will be. Sheldon Brown did something like you propose, a long time ago, and it works as long as you know what you're doing.

Gear Theory for Bicyclists

mconlonx

Yup. One may be able to get away with another 2t difference, maybe 18t, but even then, you'd be looking at shifting issues, like dropped chain on the inside, hard shifting to the big ring on the outside.

dbg

Minimum chainring sizes for 130 and 110 were mentioned. If other BCD's are allowed, the question becomes derailer capacity --and that is a function of derailer design. I'm currently experimenting with a 44-28 (no ramps or pins to aid the climb), and use the IRD compact road triple derailer. It works absolutely fine, BUT I've also installed a chain catcher at the low end and a chain guard at the high side. Shifts appear to be a simple slap on the brifters. I have not been on a long trip yet --which is where the real behavior will emerge. But it seems to be fine and I suspect 44 - 26 would also.

[adding: this derailer appears to be able to handle up to 48 big ring.]
[adding pic]



[adding: not sure I'd want a 48 - 26, but I bet this derailer could handle it.]

HillRider

There is a limit to this too. Current front derailleur's have the inner cage plate significantly deeper than the outer so a minimum chainring difference must be maintained or the inner plate will hit the smaller chainring and keep the derailleur from shifting to the larger chainring unless the derailleur is set too high above the big ring. Older fd's had the two cage plates about the same depth which is why half-step gearing was practical but newer designs don't.

ThermionicScott 

Good point! I'm more used to "road" stuff up to the 8-speed era, but I did notice this when I tried to set up a 48/42 double (not half-step, but an experiment with what I had) on my road bike with a Deore LX triple FD. Because the FD was designed around a 48/38/28 triple, it didn't "like" less than a 9T difference between rings.

SlowJoeCrow

While its rated capacity is still only 16T the Shimano CX70 front derailleur is worth a look for smaller than usual doubles since its cage is shaped for a 46T outer chain ring so it should be a good fit for a 30-46 Randonneur style crank. Also FSA used to make compact double specific front derailleurs with specially shaped cages.

dbg

Just reiterating ...I have found nothing to match this derailer for my wide range sub compact doubles with road shifters. It's capacity has to approach 24 T and max big ring ~48. I've used it in two builds so far and really like it (both with 44 T half step big ring).



IRD Alpina-d Compact Road Triple Front Derailleur - Harris Cyclery bicycle shop - West Newton, Massachusetts

justinzane

Perhaps I should have stated that, but I am assuming that one cannot just throw really different rings onto an existing groupset and expect things to work well. And, I am aware that there are explicit limits on the sizes of rings available for a given crankset. I'm wondering what is possible, with the right choice of components and what manufacturers and product lines are good for unusual setups.

Somewhere or another... Ahh, here... Sheldon Brown references a TA Cyclotouriste crankset with a huge gap between ring sizes. According to this, the official name of these are the Pro Vis 5 and they are possibly no longer manufactured. It also seems to require old, no longer manufactured derailers. Is this a totally unique product line as far as range between rings goes? If not, what else is there? Anything similar that can be bought without scavenging e-bay or garage sales?

I'm assuming that commonplace, new Shimano, Campy, SRAM, etc. derailers will work best with chainrings that are of nearly similar size to what they sell as a complete groupset. However, I'm assuming that what manufacturers list as min/max ring sizes are limits on what they think shifts well, not real limits on what works with friction shifting. Anyone done any actual testing to find out what the real limits are for common front derailers?

Also, while the FD will be far more important in this regard, what difference does the chain and the RD and cassette make?

Seems quite ridiculous to me as well. But my knowledge and experience is very limited and assuming that something is useless is rather silly unless one has a truly encyclopedic knowledge of the subject. I'm not expecting any really wide differences or any really narrow differences to be "practical" or useful for most people. I'm trying to get an idea of the workable extremes and what uses they might have for a select few.

Again, this is not an "I want this on my bike" post, rather I'm hoping to learn from those with unusual experience and knowledge just for the sake of learning. Hope that makes sense.

tcarl

Regarding your other question, the smallest difference, once upon a time (early 1970's and earlier) a common "racing" gearing was the so-called "half step" gearing. A typical set up would be 49/52 chainrings and something like a 14-16-18-21-24 freewheel. The gear ratios on the smaller chainring were half way between those of the larger, so lowest to highest gears would be 1 6 2 7 3 8 4 9 5 10. You probably wouldn't use gears 6 and 5 very often. As straight block freewheels and more gears became more common 42/52 and 13-14-15-16-17-19(-21) became the standard. A touring set-up would be "half step plus granny" - an example being 36/49/52 with a 14-16-18-21-24-28.

I really liked the half step gearing. You could have the "fine tuning" gear change - just change chainrings, or a slightly wider gear change by switching freewheel cogs. The front derailleurs always shifted really smoothly with only the 3 tooth difference. Nowadays brifters, indexing, many more cogs, and freehubs are all great improvements, but with the technology and parts of that era half step gearing worked well. I can just imaging using it today - since they probably wouldn't remember it or understand the reasoning or principle behind it, I can just imaging my cycling buddies reaction to my having a 3 tooth difference in my chainrings. Maybe I'll set a bike up that way sometime just to see their reaction.

fietsbob

in 1985*, a companion from England , riding the California Coast [SF South] with Me, used a Classic TA 50-28t Cyclotourist crankset.

Functionally such a big upshift out of the 28t would be done at the crest of a hill , so the strain on the chain is near zero.

* the freewheel, as I recall he used, was a 13-28t .. a 6 speed would be in that period.



My current rig (folding Brompton) the double is even wider , but the chain is not derailed, there is a gear box in the crankset,
the arms turn at a different rate, faster than the chainring, in Low reduction gear, range.


It ia functionally as if a 50 - 20 t double .. I combine it with a 3 speed IGH in the back wheel.. 6 speed, no overlap, results.

Both being planetary, 3<>4 is a quick double shift.

gsa103

Compact road cranksets are typically designed for 16T. Modern MTB gear sets are 14T max difference. In a light duty application, you could probably run a MTB FD to 16T for on-road use (low load & vibration).

Either way anything beyond 16T is going to be suboptimal. The main problem is the FD not having enough rise to avoid crashing into things.

A better solution is a wide range MTB cassette. With a MTB RD you can run a compact double (or mountain double), and an 11-36 (or even 10-42 [11spd]).

justinzane

I like that spirit! Perhaps I'm just an innate hacker. Perhaps growing up with a grandfather who grew up in the Original Depression and who worked for years at Western Electric led me to see most non-living things as simply objects with engineering potential. The common, "If they don't sell it, it must not be worthwhile." sentiment is somewhat frustrating to me. As is the "If racers don't use it, it must be crap." sentiment.

I just ran into a great guy at the LBS -- I managed to use my last patch and my spare tube in the same ride and needed an emergency replacement -- who has just biked from Portland, OR to Yreka, CA on an awesome frankenbike. He happened to need an emergency spoke. It make me happy and inspired to see a truly serious cyclist who had built up his bike with components chosen individually for his riding style and his budget, not something thrown together by a marketing or inventory management team.

Regarding the meat of your post, I've read about that 1/2 step setup on sheldonbrown.com and elsewhere -- both in historical perspective and on classic bikes now. I can see how that would work really well for certain cyclists on certain terrain. For someone without sufficient leg strength or facing roads with many quick grade changes, it might be a bit limiting. But, somehow it seems that learning to double shift should be pretty easily mastered in a couple of hours of riding. I can't imagine it working for me at the moment, since I do not have the strength, experience or flat roads to really appreciate anything smaller than a 12% difference between gears on most of my rides.

But, thank you for the input!

justinzane

I've been seriously considering doing that. For the kind of riding I do now, I would like to try an 11-28T 7sp freewheel (yes, freewheel) and 28-30/48/chainguard front. Since it seems that the Cyclotouriste/ProViz5 is no longer available except as mismatched pieces on e-bay; I'm wondering what bits and pieces to experiment with. I'll throw up a a different thread for that, though.

I'm embarrassed to admit that I've never seen a folder in person. For urban life, though they sound awesome. And, that is exactly the kind of thing I was hoping to learn -- a "good" reason to use an uncommon gear setup. Thank, fietsbob.

LoveValla

For those still interested in this topic,here a list of non-standard road double "very" compact cranks i know:


Sugino: OX601 and OX901D, 110/74mm.

Renè Herse: 70mm.

Specialitès TA: Carmina and Vega, 94mm (with spider).

Middleburn: Double Incy, 110/58mm (with spider).

White industries: VBC, variable mm (with spider/chain ring).

bulldog1935

here's my compact double built on a Sugino XD2 triple crank, guard + 42/25T
works great with an Ultegra CX70 FD and Microshift R10 RD, 12-29t 9-sp rear

here's the gear analysis
have to plug in 38mm for the tires to see the actual
The overlap fills in the gaps where the custom cassette goes wide.
But for the most part it acts like two 1x9 drivetrains (or two sequential 1x7 and splits out easily at 50")
The crank and chainline work great with a 111mm BB
well over 5000 mi on this in steep hills, and it's a joy - shifting this with index is totally mindless

Max ring size on the CX70 FD is 48T, so this FD would work great if you wanted 48/28T double

I derived the compact double from my cyclotouriste triple, half-steps plus granny 46/42/26T, wide-7 rear 12-32t
Cyclone GT RD, Shimano 600 EX FD - with a low-Q cyclotouriste triple, you use a road double FD, and hard to beat this one.
Chain wrap capacity is one link short, but never a need to cross-chain 12t in the rear with 26T in the front

Here's the gear analysis (32mm tires)
This one needs 121mm asymmetric BB (best) or 126mm symmetric.
over 10,000 mi on this setup, and it's a different joy - get into the big ring as soon as you can and use the half step first for climb

Both double FD make the wide jump with aplomb - a triple FD would just get in the way.

79pmooney

A lot of naysaying in the early responses here. 16t the max that can be done? In 2016? 50 years ago Peugeot was doing that with hard to shift 3/32" chains, no pins or ramps on the teeth and a crude rod front derailleur.

Try it! 50-28 ought to be doable. 52-26 would be fun! 2:1! I'd pick the ring I had to have and just start playing with to other and see how far I can go. Indexing may be a struggle, esp for the upshift. (I will point out that front derailleurs don't lift the chain at all. They push the chain into the path of the teeth of the large chainring. The chain hitting or dragging on the bottom of the derailleur cage in small-small cogs is only an issue if 1) it catches on the cage. (Now that is a real problem. Very fast destruction of the derailleur.) 2) The noise bugs you and 3) Wear to the cage when you use those gears is unacceptable to you or your wallet.

I have used smaller derailleurs than the chainring difference called for many times, running a 53-42-28. I will happily run the 28-13 for a stretch of flattish road on tough climbs rather than double shift twice. Some of those front derailleurs went a long ways despite doing that. (Actually, you probably won't be doing much of that since a large small-small cross-over and a big chainring difference = an automatic shift into a much bigger gear!) What could be a challenge is index shifting which I guess is your current mode. You can step back a few years and install a friction derailleur for the front, perhaps a downtube of stem shifter mounted on the aero bars (if this is for the Fuji Aloha of your intro). Get the SunTour ratchet shifter if you can find one. It will come as a double; I doubt it was ever made as a front only and I don't think I have ever seen a rear only. That shifter should be perfect for the huge shifts you are talking.

Also, use a chain catcher. I use the Deda one and the one that started it (whose name I forgot) on my three triples. If you Google "chain catcher" you will see options that didn't even exist last time I looked.

Ben

fietsbob

White Industries VBC and Compass can put together a 28~50 combination, as well .

You would only Come out of the Granny Gear at the crest of a Hill when you take all strain Off the Chain.

bulldog1935

Mine have like 4" steps on the granny, and it's very easy to shift up and down in the rear as the grade waxes and wanes

I'll use the 50" gears on the granny for approach before dropping to 30" gears as needed.

2lo8

I set up a triple as a 50/30 double once and it did shift. It didn't even shift that badly except that it liked to try throwing the chain, although obviously you're not going to shift under load. The only thing special needed about the FD was it did not have a shaped cage.

I would just run a triple though, the only reason why it wasn't run as a triple is the FD didn't have enough throw to shift all three rings.

If you want optimal performance, you should stick to ramped and pinned matched pairs of rings, within the spec ranges of the FD. There is a noticeable difference on how well things will shift.

jamesdak 

I'm running Wickwerks 53/34 chain rings on my Tourmelet shifting with a standard Dura Ace 7800 FD. It works wonderfully, in fact I think it's the best shifting setup I have on all my bikes. I've yet to have any problem at all.





As I've mentioned before, these shift up to the big chain ring super quickly. Like before I even finish making the throw with the lever.

If interested in the wickwerks here's a link:

https://wickwerks.com/