paulb_in_bkln

Perhaps someone knows why an IGH would have eight gear choices? I don't mean eight in particular, it's that it's an even number that I'm getting at. I thought IGHs would be odd numbers, each gear combination providing two ratios, plus a direct drive, which produces an odd number as the total. Even the Roholff 14, as I understand it, has that number because it combines two seven speed mechanisms.

Andrew R Stewart 

Then there's the classic Bendix 2 spd kick backs and SA FMs and FWs. Andy

Dan Burkhart 

In the case of the Shimano Nexus/Alfine 8 speed, what you have is a planetary unit with 3 sets of sun and planetary gears, a direct drive to the hub shell that is defaulted to when none of the sun gears are coupled to provide a reactionary gear, and a low range reduction unit at the input end that is bypassed in high range. The three speed planetary carrier with it's direct drive default provides four ratios, which is doubled by the high/ low range unit at the input end. 4 x 2 = 8.

Dan Burkhart 

If you manage to digest that video, here is another showing how a Sturmey Archer 8 speed works. You will note that it is entirely different, using combinations of 3 overdrive stages to achieve 8 ratios, the lowest of which is one to one.

fietsbob

and those 7 speeds are actually 3 , 3 speeds* _ 3 x 3 is 9, but 2 are bypassed because they the same 1:1 gear ..
so only 11th remains as 1:1 & .. In reduction geared low range its 4th of the same 7..

* a narrow medium and wide..

S-A AW3 is 1, 3 speed 1st & 3rd are inverse fractions.. 3/4 & 4/3






...

HillRider

Dan, Those are excellent videos and do indeed demystify what to most of us were indecipherable "black boxes". Thanks for the lessons.

GamblerGORD53

So which one is better and faster???

Dan Burkhart 

Thank you. They are a fun project to help me from going bonkers during our long winters.

Dan Burkhart 

Better? I vote Shimano. Faster? Depends partly on the input ratio, but mostly on the engine.

fietsbob

Faster? Alfine 11 speed , Because It goes to 11 This Is Spinal Tap (1984) -- (Movie Clip) These Go To Eleven







...

paulb_in_bkln

Thanks for the explanation! It has been awhile since I looked at the video and soonest opportunity I will watch it again. I can't say I've become a great fan of my Nexus Inter-8, but when it's working properly, I like it.

tcs

Even gears: Lots of two speed IGHs, beginning in the 1880s. Currently, Sturmey-Archer X-R*4, Pinion 12 & 18, Rohloff 14, Sturmey X-R*8, Shimano Nexus & Alfine 8. In years past, F&S Torpedo Universal 4, Sturmey 'F' 4, SRAM G8, Sachs Elan 12, Shimano Nexus 4...

tcs

Well, the Sturmey 8 is less expensive, easier to disassemble & re-lubricate, has more even gear steps, and the harder the ride (steeper hill, heavier load, stronger headwind) the more efficient the ratio.

Dan Burkhart 

The SA has more even gear steps between the middle 6 gears, but there are big steps from first to second and seventh to eighth.
My own experience with the two is that I have the sensation that the Sturmey Archer 8 speed has less efficiency loss than the Shimano. It just feels like it runs more freely with less drag.

tcs

Alpine gearing pattern, used on millions of 'ten speeds' back in the day. Off hand, any production derailleur geared bikes with gear steps like the Shimano 8?

fietsbob

Might be a math challenge to sort out tooth counts, % and ratios, on your chosen cassette....

Perhaps the Mega range jump, 24 to 34 is one situation ..

Dan Burkhart 

I'm not saying it's a bad thing. In fact, having a bailout gear and a downhill, goin' home gear can be useful.

bajajoaquin

paulb_in_bkln

Because first gear is direct drive?

tcs

Funny, nobody ever talks about efficiency in different cog combinations with derailleurs...

That, and more.

Understand, this isn't 'right' or 'wrong', it's just a design choice.

Okay, so theoretically and generally in actual practice: direct drive is most efficient. Each planetary gear train introduces more spinning, intermeshing parts. Large % gear stages are marginally less efficient than small % gear stages.

So you're riding along in 5th gear. With a Shimano 8, you're in direct drive. That's great, you know, flat, level cruising, often-used gear. Then the going gets just a bit tougher, and you shift to 4th. Now you're in a two stage gear, gearing way down and then part way back up. So on down, until you reach 1st, where you're merely running your power through that one, big step down gear train.

So let's say you're riding along in 5th gear with your Sturmey 8. Your power is flowing through two step-up gear trains. Well, phphtt, it's an average gear you use a lot. But then the going gets a bit harder and you shift to 4th. Now your power is going through a single gear train. Theory says this is an improvement, which is good, you know, because the going got harder. Well, and so on, until the road gets steep and you're carrying a load and there's a headwind, and then you shift the Sturmey to 1st, a.k.a. direct drive.

All designs represent compromises, and they're not right or wrong, just choices.

P.S. The late, lamented Sachs/SRAM S7 hub covered about the same range as the Shimano 8 and Sturmey 8, and didn't have any dual- or triple-stage gears.

tcs

Well, the engineers chose to design it in that way - it didn't just happen. Other hubs (the Shimano Nexus 7 & 8s, the Sachs/SRAM S7, G8 & G9, the Rohloff 14, even the old Sturmey Sprinter 7) don't have an Alpine gear pattern. All but the Shimano 8 have fairly even steps.