Gear options for a crank bike - what's the mose versatile or robust.

[flecc]

If one could assume (and I assume we can't) that in each case the middle gear of each unit (let's just assume that the ones with an even number of gears have a middle gear) resulted in the bike moving exactly the same distance per revolution of the pedal crank

As a matter of interest almost all hub gears including the NuVinci have a direct drive 1 to 1 gear roughly in the middle with reduction or increase to the gears either side. The exceptions are the Shimano Nexus 7 speed which has no direct drive, all 7 gears being indirect through the epicyclic gears, and the peculiar Sunrace-Sturmey 8 speed hub gear. The latter has the direct drive as the lowest "gear", with all the other 7 being above. The logic is that it makes the lowest gear for climbing the most efficient, but the downside is that the highest gear as the most commonly used is the least efficient.

 

[JimB]

I've found this to be very helpful and informative and realise that I've pretty much made the decision on which bike spec I would like for myself I'm still considering a second bike for my wife whose bike riding style and aspirations are a bit different to mine.

Whilst I love gadgets (including electronic ones) and am quite happy using the 24 gear set on my current bike she would be a lot happier not having to bother with them at all.

Manifold Valley and a couple of other test rides organised will hopefully help us finalise things.

JimB

 

[DavePat]

For anyone interested in the comparative ratios and ranges of certain types of gear systems have a look at this PDF link I found on the Nuvinci website. Gear inches are still beyond my comprehension.
Sorry I dont know how to post the actual chart but maybe someone else can.

http://www.nuvinci.com/Docs/GearInchChart_N360.pdf

Dave

 

[Artstu]

For anyone interested in the comparative ratios and ranges of certain types of gear systems have a look at this PDF link I found on the Nuvinci website. Gear inches are still beyond my comprehension.
Sorry I dont know how to post the actual chart but maybe someone else can.

http://www.nuvinci.com/Docs/GearInchChart_N360.pdf

Dave

Thanks for that, it highlights a bugbear I have with my 8-speed hub, the big gap when dropping from 6th to 5th, I'll try and get an 11-speed hub next I think.

 

[flecc]

Gear inches are still beyond my comprehension.

Dave

Gear inches first arrived with the original "penny-farthing" bike Dave. It was the diameter of the large wheel which, because the pedals and cranks were directly on that wheel, gave an indirect indication of how far the wheel would go for a single turn, though that needed to be multiplied by Pi (3.14) to give the actual number of inches travelled.

Of course that inch measure's real use was that it represented the gear ratio, since a larger wheel went further for a single pedal stroke than a smaller wheel, it was a higher gear and needed more effort than a smaller wheel turn.

When the "safety bicycle" (our modern type) was invented, the gear inches of the wheel needed to be multiplied by the up-gearing of the front to rear chain sprocket to give the same indication for comparison with the penny-farthings still in use. For example, if the bike had 25 inch wheels and the chainwheel had 45 teeth and the rear one 15 teeth, each turn of the pedals turned the wheel three times. Therefore the wheel diameter of 25" had to be multiplied by three to give the 75 inch gear that it had. In other words, it was like a penny-farthing with a 75 inch front wheel.

So to work out the gear inches on a particular gear of a derailleur bike, its just necessary to divide the chainwheel teeth by a particular rear sprocket number of teeth and multiply the result by the overall wheel diameter.

To do the same for a hub gear bike, one must first find the ratio comparisons of that hub gear. For example, the Nexus/Alfine 8 speed hub gears have these ratio steps up and down for the eight gears, fifth gear being direct drive:

1.615
1.419
1.223
1.000
0.851
0.748
0.622
0.527

To get the gear inches for a particular gear, just divide the chainwheel number of teeth by the rear sprocket number of teeth, multiply the result by the wheel overall diameter and then multiply that result by the ratio of the gear from that list for your hub gear.

For example, a Nexus 8 equipped 26" wheel bike with a 48 tooth chainwheel and 16 tooth rear sprocket would be this gear inch ratio in fourth gear:

48 divided by 16 = 3, then that 3 times the 26" wheel = 78, then that 78 times the 0.851 for the fourth gear = 66.378, a 66 inch gear.
.

 

[jackhandy]

....simples....