An unfashionable gearing set up?

[Pale Rider]

Some fascinating stuff in this thread, even if I only partly understand some of it.

Seems to me there's too many technical trip wires in half step gearing.

Best course of action for the OP is to buy a factory bike with gearing that most closely suits his needs, and just put up with being half a gear or half a gear inch out now and again.

 

[Ajax Bay]

I've been looking to replace an ancient touring bike with 2x5 gears and have looked at 1x11 systems but I've had another idea for a 2x10

Besides the 'ancient' bike quoted what other geared bikes have you tried, OP? You've spawned an interesting discussion, but I'd like to think you can take into account practical as well as theoretical aspects of this. And the heart of the issue is a clear statement of requirement, which I thought you'd achieved in the OP but now you are 'adapting': the scourge of many real world projects where requirements creep is endemic.
Bear in mind you'd get a 6sp 14-28 block screwed onto the freewheel, no trouble. With a 6sp 14-16-18-21-24-28 block and a 50-34 compact (all cheap, off-the-shelf, chainset fashionable) you can have a range: 32" up to 96" and perfectly reasonable steps (practical average 14%).
http://www.gear-calculator.com/?GR=...,28&UF=2150&TF=90&SL=2.6&UN=KMH&DV=gearInches

 

[Tigerbiten]

If you want true custom gears then 7 speed gives you more options.
Ditch all the sprockets off the 7 speed body.
Then take apart an 11-36 9 speed.
Ditch the 11 sprocket and the 13-36 cluster will now fit on the 7 speed body.
You may well need a new lock ring for it to work.
With the right front derailleur and bottom bracket you can then half step a 50-34 compact double for 104"-25.5".
Very non standard but it's a good option if you're stuck with a 126 mm frame.

Luck ............

 

[steveha]

Besides the 'ancient' bike quoted what other geared bikes have you tried, OP? You've spawned an interesting discussion, but I'd like to think you can take into account practical as well as theoretical aspects of this. And the heart of the issue is a clear statement of requirement, which I thought you'd achieved in the OP but now you are 'adapting': the scourge of many real world projects where requirements creep is endemic.

I've not ridden any other bikes for many years. I think by now I would have rented something from the LBS but they aren't doing renals until 2021. It does occur to me as I lack experience with anything at all modern, I ought to buy something half-decent second hand, discover more and trade it in for the forever bike next spring. Might actually turn out cheaper.

The reason I'm "adapting" is that the solutions in this thread (by myself or others) either don't meet my requirements or have been identified as infeasible

 

[Ajax Bay]

Try to clearly state your requirement plus tolerances.
Longest gear (and how much shorter)
Shortest gear (and how much longer)
Maximum %age step between gears (average plus tolerance/acceptable deviation)

 

[steveha]

Try to clearly state your requirement plus tolerances.
Longest gear (and how much shorter)
Shortest gear (and how much longer)
Maximum %age step between gears (average plus tolerance/acceptable deviation)

OK
Longest gear 105 tolerating down to 99
Shortest 22 tolerating up to 27

Step %

• Above 75", 8% but accept 12%
• Below 40", 12% but accept 24%
• Mid range, on one ring accelerating, 12% but would tolerate up to 18%
• Mid range, with double changes and thinking 7% but would tolerate up to 10%

A strategy I just thought of but may not be practical:

1. Buy a bike with wide range 1x11 or 1x10
2. Ride it for a bit
3. If I'm getting really irritated with the big steps. experiment with adding a slightly different chainring and a changer.

Thanks!

 

[Ajax Bay]

Get a super compact (46/30) and and 11-32 cassette.
That gives you what you need (25" to 110")and can be handled by a medium cage derailleur - see this calculator:
http://www.gear-calculator.com/?GR=...5,28,32&UF=2135&TF=100&SL=2.6&UN=KMH&DV=teeth

https://www.chainreactioncycles.com/shimano-tiagra-hg500-10-speed-road-cassette/rp-prod137768
Here's a 9sp:
http://www.gear-calculator.com/?GR=...1,25,30&UF=2135&TF=100&SL=2.6&UN=KMH&DV=teeth
The stumbling block (to meet your 'step' criteria) tends to be that manufacturers have this unaccountable fetish for making the smallest sprocket an 11t and missing out the 13t . The cassettes would be better with a 12t smallest. I get round this by buying an 11-30 and swapping out the 11t for a 13t (between 12t and 14t obv). This gives me a climbing gear length of 25" but long enough at the other end for the gentle downhills.

 

[Tigerbiten]

OK
Longest gear 105 tolerating down to 99
Shortest 22 tolerating up to 27

Step %

• Above 75", 8% but accept 12%
• Below 40", 12% but accept 24%
• Mid range, on one ring accelerating, 12% but would tolerate up to 18%
• Mid range, with double changes and thinking 7% but would tolerate up to 10%

Thanks!

I'd look at the 42/26 sub compact chainsets from somewhere like Spa Cycles.
42/11x27"= 103" for a top gear and 26/28x27= 25" for a first gear.
So a 42/26 double mated with a 11-28 10 speed will give you almost what you want
The 11-12 and 12-13 steps are about 8% but under 10%, so that ok.
The next biggest step is 15-17 at 13.3%.
After that it's 21-24 at 14.3% and 24-28 at 16.7%.
You can go for slightly higher gears with a 44/28 or lower with a 40/24.

Downsides:- slight power loss and slightly faster wear rates due to very small chainrings and having to jump 3-4 sprockets for the next gear when changing chainring.

Luck .............

 

[steveha]

The stumbling block (to meet your 'step' criteria) tends to be that manufacturers have this unaccountable fetish for making the smallest sprocket an 11t and missing out the 13t . The cassettes would be better with a 12t smallest.

Agreed! You need small steps at the top end I think but manufacturers have other ideas!

 

[SkipdiverJohn]

You need small steps at the top end I think but manufacturers have other ideas!

The large sprockets are mostly used to accelerate up to speed in, or for short periods to deal with gradients, so it is not necessary to fine tune a gear ratio in the same way as at the top end where the rider may be on the flat but the aerodynamic drag is close to their max sustainable power output. It is more important for a rider to optimise their cadence when they have very little left in reserve, than it is when they are not putting out anything like their max torque.
We've all had the situation with five speed 14-28T freewheels, where on a flat clear road 4th is just a little bit spinny but as soon as you go up to 5th, and go down 3 teeth from 17 to 14 on the freewheel just a tiny change in gradient or wind is too much to maintain the gear, and you end up dropping back down to 4th again. You don't tend to get that problem if riding in 1st gear on the 28T cog then you change to 2nd and go down to 24T.

 

[Ajax Bay]

I just think that most cassettes with an 11t but no 12t would be better off with a 12t smallest, unless you're racing. A 50t chainring will allow a gear length of 113 inches which is enough for mortals.
There has to be a 'first' two tooth step and that is where the biggest step will be, until you hit the 'first' three tooth step.