Minimum difference in tooth count between chainrings
 

I have a road triple (52/42/30) that came on my touring bike and have since realised the 52t outer ring is slightly overkill, only time it gets used is with a heavy tailwind. Curious as to what the minimum difference between teeth count is. Would 46t be too small? Any more than a 48 and would make more sense to just replace the crankset. any advice appreciated, thanks.

Small chainring differences of 3-5 teeth were par for the course until the seventies, when 53/39 became dominant.

I still ride with half step (4 teeth difference) + granny on my touring bike, so I know assure you that it'll work. However, with narrow chains you want to be sure that the tops of the inner ring's teeth are below the shoulder on the inside of the outer ring. This is to ensure that the chain can't be trapped in the wider space between the rings.

FixedFiend626, A problem that could arise is the backside of the FD cage will interfere with the middle ring when shifting to the outer chain ring, if the difference between the middle and outer chain rings isn't great enough. I have a FD meant for a 52-42-30T triple barely clearing an eight tooth difference, but it's also working on a smaller diameter 24-34-42T chain set.

I'm guessing that you're credit card and/or lightweight touring with that crank set. A less expensive option is to use a cog on back with one or two more teeth. For example:
48/15=~86 gear inches
52/15=~93 GI
52/17=~82 GI.

Brad

I'll be more certain. Interference by the inner cage plate of the front derailleur WILL occur unless you have a very old fd. Most relatively new front derailleur designs are made for a minimum chainring tooth difference of 10 teeth or more and have deep inner plates.

The half-step gearing FBinNY refers to was common up to about the mid 80's when 7+ cog freewheels and cassettes reduced the need. Before that, front derailleurs often had shallow cage plates and would clear even a four tooth difference. I had a 1985 Bridgestone with Sun Tour ARX derailleurs and the front derailleur permitted me to use a 46/42/26 triple crank. Nothing I've owned since then will work with that gearing.

The more I read about these issues, the more I'd like to see 46/30 doubles become common. We're suck with 50/34 (on 110mm bolt-circle diameter) for current compact double cranksets, so 34t is the smallest chainring they can handle. But even 50t is larger than I need unless I'm on a fast group ride. For riding solo, if I spin out of a 48/12 gearing, I'm already in tucked descending position and not pedaling.

A long-term hope is that one or two bike companies resurrect their forges for 94mm BCD cranks aimed at the mountain bike market. Just using the two outer rings and a narrower bottom bracket.

I know this is not exactly what you asked but my 1960 Schwinn Continental has from the factory a 48 small and a 50 large chain ring. Seems to shift just fine that way. Roger

No doubt, but it came with a front derailleur shaped to allow that small tooth difference. New ones aren't.

You also shift it by reaching down between you knees and push a lever left to right to upshift and vice versa to downshift. The nick name for them was "suicide shifter." Roger

One thing I failed to mention is that Im running a bottom-pull, down-swing derailleur and due to the waterbottle bosses being lower than usual I can only lower the derailleur by about a cm so that kind of solves that potential issue (of backplate hitting). Whether itll be too high to actually shift it to the 46 might be an issue. might have another top-swing derailleur in the parts bin.

The last paragraph you wrote I literally have no idea what youre talking about. Credit card with that crank set? and thing about gear inches? its not a singlespeed.. quite confused.

I run a 48-45 setup on my road bike (with a moderately-spaced cassette), in order to get true split-shifting. If I plan to do a lot of hills, I can always switch my rings to 45-42....

You didn't mention what cassette tooth counts you use, and how many cogs in the cassette.

A 46 and a 42 would only be about a 1 to 1.5 cog shift. For instance,at 85 rpm:
the 46-19 is 16.1 mph, between
the 42-17 at 16.5 mph, and
the 42-18 at 15.6 mph.

So the middle 42 and large 46 would be pretty much interchangeable.

I'd suggest a 39 middle instead of your 42, and keep the 52 for those occasional long gradual downhills or big tailwinds. My 39-12 gear is good up to the low 20 mph range, so I'm rarely shifting to my 52.
It will lower the middle gear's mph range by about 1 mph, a little more at faster speeds.
It's about 7% easier.

It depends on your typical cadences and road speeds, of course.
EDIT--and touring with a load needs lower gears than this.

I mentioned my 11-speed 12-25 cassette with my 52-39-39 in another recent thread. I only use the 52 on mile or more downhills.

What this says is the bike seems to be geared as a "credit card tourer" meaning it is lightly loaded and you carry only extra clothes and sleep in motels and eat in restaurants. Hence the need for a "credit card" and you can get away with fairly high gears. The opposite is "loaded touring" where you carry a tent, sleeping gear and cooking gear as well as your personal stuff. Loaded touring bikes typically have much lower low gears.

Ahhh.. ok, funny.. havent heard that one. Mainly just ride it on long rides, not into the skinny-tire, hunched over roadies anymore.

Running a 11-32 9-spd cassette with 32c Compass tires set to 65. Def not changing out the 42 as I use it most of the time. I guess I see what youre saying but why keep a ring on that I only very rarely actually use whereas a 46 would get used continuously?

If you are going to a smaller largest ring, you leave the FDER where it sits.
I made my 22-32-44 into a 22-32-36.
I tried lowering the FDER, but it interfered with the middle ring and wouldn't shift to the smallest.
The pic shows how ugly this is.

Yes, you have a modern front derailleur of the type Hillrider warned against above. The dropped inner cage plate interferes with shifting when the tooth difference between rings is too small. What you need is a vintage front derailleur designed to work with half-step gearing, e.g.:

https://cdn.shopify.com/s/files/1/01...railleur_1.jpg

N.B. Campagnolo isn't the only one available, althpough it is among the best quality. Similar units were made by Huret, Simplex, SunTour, Shimano, and others. The important feature you're looking for is the shallow inner plate as seen in the picture above. This allows you to lower the derailleur enough to place the outer plate just a couple millimeters above the outer ring's teeth, for best shifting performance.

Credit card touring is a term usually associated with being very lightly loaded (cargo) and often used where no camping or cooking is involved, but rather using motels and restaurants.

The last paragraph was to show what could be done simply by down shifting the rear. The 15T and 17T rear gears were just middle, more or less, examples of the gear inches of what is available with the 52T chain ring and how minor the 48T change could be. Gear inches apply to all bicycles, not just SS bikes.

Brad

I was running a similar setup. A Shimano TY22 FD?, 22-32-36 chain rings with a 19T single speed freewheel on my commuter.

Shifted perfectly. FD sits a bit high, but it would crunch quite nicely into gear even under load. I miss that setup actually, I now run 24/38T crank with 14-28T 6 speed freewheel and rarely use the FD any more.

[MENTION=129516]FixedFiend626[/MENTION], One mismatch that stands out to me is the 11T top cog in the cassette. You maybe able to do more good by selecting a cassette that will actually match well with the 42T and the 52T chain rings. Generally a 13T top cog was standard fare with a 52T chain ring. If you seldom use your 30T chain ring and 32T bottom cog, you can close up your ratios using a 13-28T cassette.

My distance roadie uses a 52-42-30T crank set coupled with a 14-25T 9S cassette. While it's generally flat in my area, there are a handful of tough climbs that I have used my bottom gear to climb.

Brad

I agree but good luck finding one. Shimano made some Junior cassettes with 14 and even 15T small cogs and Campy makes 10-speed 13x26 and 13x29 cassettes but finding any 11-speed cassette with anything but an 11T or, at best a 12T small cog is nearly impossible.

A true "credit card tour" is when you carry NOTHING on the bike past your wallet, phone, small snack, and possibly a wind/rain jacket, and you PAY the hotel to ship your luggage to the next stop. This is very possible in Europe, not so much in the U.S.

The only advantage I see is that the 42 with 46 is kind of a "half step" gearing. So you could shift the front to get a gear halfway between. But normally that's not really worth the effort of a front shift.

Here's your proposed setup attached below. 32c tires. 30-42-46. 11-32 9-speed.

46 chainring in blue. For the same gear and cadence, this is only about 2 mph faster at 20 mph, and 1 mph faster at 10 mph than the 42 ring. It essentially covers the same range as the 42.
42 chainring in black.
30 chainring in red.

Cool, thanks for that. So it really isnt that big a difference, kind of my intention in the first place, even if somewhat redundant. Maybe ill just go for a BBG bashguard instead, idk

We think of those things as "organized tours" where your accommodations, meals, and daily destinations are all preplanned and scheduled in advance and your luggage is waiting when you get there each day. Vermont Bicycle Tours and similar organizations operate these and there are lots of them in the US. RAGBRAI, Bike Virginia, and similar "Tours" do about the same thing. For that matter, many of these are paid in advance so, in theory, you wouldn't even need to have the credit card with you.

I think of a "credit card tour" as one where you carry your own personal clothing and other items but stay in hotels/motels or with Warm Shower hosts and eat in restaurants or buy prepared food. Your route can be less defined and you don't necessarily have a schedule to keep.

Sorry, but an 'organized tour' is something completely different. Major full-service European hotels have offered luggage forwarding to guest for centuries (going back to people who were doing pilgrimages, then later hiking tours, and today cycling tours). That is the true definition of 'credit card touring'; one where you have the money to pay somebody else to move your luggage, so that you don't have to carry it. You also do not need to be limited by a set schedule if you have a day of bad weather, or you decide to change your route in the middle of your tour.