MikeyMK

I had a crank with two 48t rings on it..

Drew Eckhardt 

12 speed wheels are dished the same as 10 and 9 speed Campagnolo.

That's proven adequate.

sysrq

Half of my commute is nearly flat or with around +/-1% grade, so small gearing steps might help saving some energy for the hills ahead for shifting with rear derailleur only with wider steps.

tomato coupe

I agree, but the post I was commenting on was pretty dismissive in nature.

Darth Lefty 

were they in phase?

Darth Lefty 

For your average rear shift of 116%, a 108% front shift is about half, and about three teeth.

That’s math. My opinion is that this plan is no fun.

79pmooney

Various comments: Those talking of 11 speed or more seem to be missing the point that the OP is riding a 7-speed. There are very good reasons to stick with 7-speed for a commuter. Cheap, reliable, simple. Narrower hubs (not all frames take kindly to 130 dropout widths). Non-index shifting is easy to do with the wider cog spacing and again, cheap, reliable and simple.

I cannot suggest a best half-step gearing for the OP as I have never had nor been tempted to ride half-step. But if I did and I was riding a route I knew well and did a lot, I'd figure out the gears I wanted for that ride and come up with gearing that simplified shifts and gave the best ratios for the route.

My riding style, since my 2nd good bike most of 50 years ago, has been on 52-42 up front (and a 28 inner ring except my racing bike) and a tight freewheel/cassette in back. I've gotten older but all that has done is reduce the front to 50-38-24. Same concept, same shifts, just for slower speeds. Now, this does often "force" me to do cassette-wide shifts but since I use friction shifting I left "force" in quotations because those shifts are far from a hardship. (Another reason I've been slow to get on board with index shifting.)

Speaking of cheap, reliable and simple, OP, have you considered doing to a 110-74 BCD crankset? There are a lot of used Suginos out there with lots of life left in them. That would open the door to a triple, give you more gearing options and keep your jumps down since you could use a tighter FW/cassette. (42 x 32 is the same as a 28 x 21 or 22. A 12 or 13-21 7-speed is fun! All the shifts are sweet, even grinding the toughest hill. (My Money spent a couple of decades on a 50-38-23 x 12-21 7-speed.)

Ben

sysrq

I'm restricted to 42t as my smallest chainring, so wide range cassette is the only option.

noglider 

It's a matter of taste. When I get into better shape, I crave smaller steps between gears. When I'm carrying heavy loads, I want bigger steps, and the same is true when my terrain is hilly.

My own preference is for steps between 8 and 15% change. I had a bike with a 3x7 drivetrain, and the steps were a little bigger than I wanted. When I started making gear charts for a hypothetical change, I realized I was better off sticking with what I had. The other considerations were range (how low the bottom and how high the top) and shifting pattern. I realized that what I had was the best compromise for the time being.

shelbyfv

It's true that obsessing over gear steps in the 11 speed era seems odd. On the other hand, if I had to commute the same 40 mile route day after day after day, I might look for any little thing to make it more interesting

Koyote

One of my old riding buddies used to calculate (in his head) the gear inches of each of his gearing combos as he rode long miles.

MikeyMK

They shadowed perfectly, but chain-cross would knock it out.

Still, it wasn't for use that way of course - one was for the cassette, the other was for an outboard electric motor...

ThermionicScott 

Baloney! What bike are you using that won't allow a sensible crankset to be installed?

Furthermore, a bad half-step setup is worse than anything else. Don't bother if you can't get the right freewheel and chainrings to even out all the jumps.

MikeyMK

He's probably got a 144 BCD crank

Cougrrcj

Ummmm.... I'm a 60+ yr-old Luddite that STILL rides 6-speed rear freewheels on ALL of my 30+yr-old C&V road-ridden bikes. Oh, and three out of four are still 27" wheels vs 700c. My two 'touring' bikes both have triple cranksets. BUT, here along the glacial-scoured/ flattened lower Great Lakes (South Coast of Lake Erie), we don't have a lot of hills, so the biggest 'hills' I see are freeway or railroad overpasses. My 12.5-mile commute is only 140' downhill to work. 12 feet of elevation change in a mile is flat in my book! Here I seldom need any gearing above or below 75-90 Inch-Gears to be in my natural-cadence comfort zone.. As such I can get by with narrow-range six-speed 13-21 freewheels and a chainring of 38-42t on my commuters works. The 'tourers' get 13- or 14t-to 26/28/30.or even 32t freewheels to go with 24/36/46 or 28/38/48 cranksets depending on the terrain expected. No -- I'm NOT climbing the Appalachians or Rockies...

ThermionicScott 

I figured out that much. Maybe you can help him explain why it can’t be replaced with a part that makes more sense.

sysrq

It's actually an ebike with TSDZ2 motor, not the most appropriate forum section I know. Since 7/8 speed chain is the best for middrive ebikes then wide range 7 speed cluster is the best for it. And half-step gearing might get the bike more usable with the motor off. Motor is only for the headwinds and hills.

ThermionicScott 

Ah, that helps shed some light on it. After doing a bit of Googling, it appears the crankset uses a 110mm BCD, so you actually can use much smaller chainrings than 42T (down to 33T): https://www.electricbike.com/tsdz2-7...orque-sensing/

sysrq

But then the chainline gets awful with the smaller than 42t chainring, it's dished to get it as close as possible to the motor.

ThermionicScott 

Hmm, how much is it dished? Can you use chainring bolt spacers to scooch the chainring inboard a little?

Seems to me that putting on an additional chainring would make the chainline far worse in the new big ring.

Darth Lefty 

So you’re saying you were just trolling?

MikeyMK

Am i really? And I thought this was a cycling forum.

No, I was commenting on a closely matched front chainring in a topic specific for it, and seeing who would realise the application of this particular example.

Trolling is when you keep someone going with no fundamental basis, which brings us to your own direction...

MikeyMK

Not really, no. I'm going for square taper, but regardless, it's probably mostly to do with expendable outgoings.

Road Fan

Within the rules of a half-step pattern you can do quite a lot. The trade-off for having to make double shifts and keep track of what you are doing is that none of your gears will be duplicated. I'm not sure how wide your cassette is, but here's one I've been noodling about for local errands and commuting, on a bike with a 126 mm OLD, good for a 6 speed freewheel. For commuting I don't need a lot of speed, but I do want to spin up hills. so as not to arrive winded and soaked.
I also want to use all 12 gears.

Top gear will be between 80 and 90 gear inches, so 52/16 (with 26.6" wheel diameter). Biggest rear sprocket will be a 36. I know from experience I like about a 35-ish inch low gear for this kind of riding - with that 36 tooth big back wheel I will need a 48 tooth. So far gear range will be 35 to 86 inches, freewheel will be 16-36, and chainset will be 52-48

Now how to make it a half-step? Equal percentage jump between rear sprockets. There is some fancy arithmetic, but it can all be done rather easily on Excel. The overall ratio is 36/16 = 2.25. It will be a 6-speed, so there are 5 jumps. The desired incremental factor (or percentage) will be to raise 225% to the power of 1/5, which gives 1.176, or 17.6%. This means if you multiply 16 by 1.176 5 times, you will have the following sequence of IDEAL gear values:

16.000
18.817
22.131
26.027
30.610
36.000

If we round them all off to the nearest whole number, we get a freewheel that can actually be built if the parts are available: 16-19-22-26-31-36. The actual incremental factors after rounding are?

1.188
1.158
1.182
1.192
1.161

The corresponding steps beween adjacent sprockets is 3- 3- 4- 5- 5 teeth. So for a half-step the even factors (17.6% +/- 1.8%) should give you a monotonic increase in tooth jumps as the sprocket gets bigger.

If you shift sequentially from easiest to hardest on the 52 chainring, you'll get 38-45-53-63- 73- 86. The jumps are roughly 10 inches each but they actually get bigger as the gear gets bigger. In older literature this 10 inch jump was sometimes thought of as a "step". If you shift using the double-shift pattern, you'll get 35-38-41-45-49-53-58-63-67-73-80-86. The jumps cluster around 5 gear inches also getting bigger as the gear gets bigger. This 5 inch value is the "half-step."

Notice that the size of the half-steps never gets below 3 gear inches. This was in older days thought of as the smallest jump that would be useful. I'll let the C&V denizens consider their own opinions about how small of a gearing jump is actually useful.

If you want bigger half-steps you have some options: increase the range by raising the small cog back up to 13 teeth. Then the range jumps up to 106 - 35 and you have the upper half-steps of 10 gear inches. This may or may not feel comfortable. For the Sturmey Archer AW fans, it's peanuts. If the range is now just too high, you can go to a smaller set of chainrings 48-43 and now there is only one step of 10 teeth, and you have a range reduced to 98 - 32. I kind of like this one!

Now I want an electronic sequencer to automatically perform the double shifts when I want to sequence up incrementally through the half-steps!

I hope this has been somewhat entertaining!

I have a few sets of TA Cyclotourist or Stronglight 49D arms and I think I have a 43 and a 48 chainring. I'll maybe drop a line to Pastor Bob and see if he can cobble together a freewheel, maybe on a base that I can send him.

Phil_gretz

It's half step gearing, with the rear jumps of 14% and front jumps of 7%. This style emerged in the days of fewer cogs in the rear with wider range jumps, and a half-step double or triple on the rear to give the smoother transitions between. It works a charm once you've learned and committed it to muscle memory. Very nice.

By the way, to the OP, I'd go 42/45 with the rear 14-34 that you've described.