Cycling UK Forum

How do I calculate the gear ratios for the Trek District 4 equipped which comes with an Alfine 8 hub and chainring of 50T and rear sprocket of 24T? I am trying to compare to a similar hybrid with a derailleur. I can calculate derailleur ratios but despite having the Alfine numbers - 0.53 to 1.61 range - am lost. Please don’t refer me to Sheldon Brown et al. as trying to understand them almost made me give up cycling!
Thanks for any help you can give!

http://www.gear-calculator.com/?GR=SNI8 ... 4&UF2=2220

That compares it with a derailleur set up using 50/34 chainrings and an 11-34 10 speed cassette, but you can change any of the parameters.

Thanks slowster for link but my ipad wont open this site as it deems it not secure, despite several attempts. Basically what I need to know is...
The Alfine ratios are 0.53. 0.64.......1.42 1.61 according to several sources, none of which gives chainring or sprocket sizes so what are these ratios?
The Shimano Deore 11-46 ten speed with a 42t chainring, by my simplistic calculation gives gear ratios ranging from 0.26 to 1.09. And as I typed that I realize that doesn’t seem right, not sure.
I know wheel size etc are variables but I am comparing the Trek Dist 4 with an otherwise very similar bike.
Should I just ask the online sales to do the comparison for me as they are the ones I want to buy from?

Click on the image above to enlarge it. It shows what the Gear Calculator results look like, i.e. a visual representation of the Alfine gear range on your bike, and the derailleur set up for comparison.

'Gear inches' are shown, which is the most common way of describing a gear, and allows for comparing the gears of bikes with different wheel sizes. It's not essential to know exactly what gear inches are*, rather they are just a useful relative measure of different gears. For example, if you consider that the bottom gear on your bike is not low enough, then you need a bottom gear lower than 30 inches. Similarly many cycle tourists would want a 20 inch bottom gear or even lower if touring in the mountains with full camping kit, and conversely they would mostly consider any gear over 100 inches to be unnecessary for their needs.

* https://en.wikipedia.org/wiki/Gear_inches

The Alfine ratios are 0.53. 0.64.......1.42 1.61 according to several sources, none of which gives chainring or sprocket sizes so what are these ratios?

Those ratios are the range and intervals provided by the Alfine hub. The actual gears they provide will depend upon the sprocket and chainring ratio used with the hub. So a 54 tooth chainring and 18 tooth sprocket will give a range of gears that is 50% higher than a 36 tooth chainring and 18 tooth sprocket, i.e. 54/18 = 3 vs 36/18 = 2. Conversely a 36 tooth chainring and 18 tooth sprocket will give the same gears as a 42 tooth chainring and 21 tooth sprocket (36/18 = 42/21 = 2).

First question, what is the rear wheel and tyre combo?

50 divided by 24 = 2.08
If you are in direct drive, multiply 2.08 by the wheel/tyre diameter.

For instance, if that is 26" it will give you a direct drive of 54.08 gear inches.

0.53 of that gives a bottom gear of 28.66 gear inches.
1.61 of that gives a top gear of 87.07 gear inches.

If your rear wheel/tyre combo is different, substitute the 26" to what ever you measure it as.

Sarjoy wrote: ↑25 Jun 2021, 2:57pm I can calculate derailleur ratios but despite having the Alfine numbers - 0.53 to 1.61 range - am lost.

Calculate it as if it was one gear on a derailleur, 50 x 24, and multiply that by the Alfine ratio. 5th gear is direct drive, 1:1 so will be exactly the same as 50 x 24 on a derailleur bike.
It might help if you said what units you're familiar with.

Thanks to everyone for all your answers and helpful info. It will take me some time to go over it - I didn’t realize there was so much to consider when computing ratios.

Sarjoy wrote: ↑25 Jun 2021, 7:46pm Thanks to everyone for all your answers and helpful info. It will take me some time to go over it - I didn’t realize there was so much to consider when computing ratios.

I'm sorry we haven't been more help, I'm not sure I've grasped the question, maybe I'm not the only one. If you say what you've worked your derailleur gearing out to be, it wouldn't be hard to give you a direct comparison.

Thanks PH but you have all helped me. I hesitated to give too much info as I didn’t want to ask for too much help and thought I would be able to work most of it out once some things were clarified. I will have a go and get back to this thread if necessary and if that is ok.

Sarjoy wrote: ↑25 Jun 2021, 4:06pm
The Alfine ratios are 0.53. 0.64.......1.42 1.61 according to several sources, none of which gives chainring or sprocket sizes so what are these ratios?
The Shimano Deore 11-46 ten speed with a 42t chainring, by my simplistic calculation gives gear ratios ranging from 0.26 to 1.09. And as I typed that I realize that doesn’t seem right, not sure.

If you're wanting a comparison, for the deore you're dividing the wrong way around, so it should be from 0.91 to 3.82. Those numbers represent wheel revolutions for one pedal revolution.

The alfine numbers are fine except they all need to be multiplied by the 50/24 (i.e. 2.08) which gives you 1.1 to 3.35

That sense checks out as the total 'range' of the deore cassette is 418% (46/11) while the range of shimano 8 speed hubs is ~307%.

Thanks Stevek. I knew something wasn’t right and you have helped a lot. I have tables of gear inches now but I really wanted to understand the hub figures with chainring etc in themselves.

I know you've ready said that Sheldon's gear calculator does your head in but we've all been there (expect for those of us who sailed through their Maths A level and shot on to ace nuclear physics, of course...) but hang in there, grasp the nettle and soon you'll be comparing gear options like a pro! As has been recommended up-thread, gear inches are a common choice of unit to use. And again as has been remarked, an understanding of what exactly a gear inch isn't strictly necessary, as all you're doing is comparing one set of numbers with another. Here's the choices I would make to calculate the gear inches for my Moulton, which is fitted with 20" wheels and an Afline 11 speed.

Another way to look at it you could replace the Alfine with an 8 speed derailleur block.
Then divide the Alfine sprocket by the gear ratio to get the corresponding derailleur sprocket.
That gives you roughly a 15-17-20-24-28-32-37-45 block.

Luck ..........

Thank you simonineaston and Tigerbiten for two more good suggestions.

simon... you have an Alfine 11. I am only considering a hub because I came across the Rohlhof years ago when looking for a new touring bike. This is still my plan but right now I just need to get back cycling after 4 years off so am looking at hybrids. The Alfine appeals because of low maintenance - i.e. cleaning! - but I am a bit wary of the belt as I know chains are easier to fix etc. And in the current climate parts are in short supply. Lastly my current level of fitness and hills around here make me wonder if the Alfine 8 goes low enough. I am trying to avoid buying another overgeared derailleur bike - 27! - but I have found some great 10 and 11 speed derailleur hybrids available with a large rear sprocket I am sure would get me up anything round here. Would appreciate anything you can tell me about your Alfine experience.

anything you can tell me about your Alfine experience

I've been using the 11 speed Alfine for about a year. I'm using it on a Moulton TSR frame which has 20" wheels, which as has been pointed out up-thread has a direct effect on the gear ratios available, specifically lowering overall range ('cos the tyres travel less distance per revolution than larger wheels, which requires less effort).
With regard to the suitability of the 11 speeds, by happy concidence they suit me & my riding style almost perfectly, having a lowest gear of 21" and at the other end of the effort scale, a highest gear of 89". This over-all range would be too low for most club riders, but is fairly typical of a traditional tourer. As you can see, this is achieved from a Shimano compact chainset with 42 teeth and one of their standard rear sprockets, with 19 teeth. So far, so good. Although I've considered using a belt, I've concluded that the relative difficuty with which I could make changes to over-all ratios by changing the front or rear driver sizes meant it made more sense to stick with sprockets and chain.
With respect to the build-quality and the fit & finish, the Alfine seems to me to be an excellent product, well-made and straightforward to use. I am very pleased with the way it performs, with one or two reservations, which I list next.
Gear selection is very dependant on the way the control cable is set-up and maintained, largely because the indexing takes place at the control lever. There is no indexing in the hub itself, so the cable has to be set up exactly right. There is the rare tendancy (noted elsewhere on this very forum) for the indexing not to confirm to the alignment marking system used by the makers to allow the user to preset the cable length. See here for example. This means that occasionally, the user can experience missed or catching gear engagement, even when the alignment marks are correctly aligned as per the maker's set-up guide. However, this appears to be the exception and not the rule - it is also fairly easy to work-around by simply lengthening or shortening the cable by using whatever barrel-type adjustment the bike is equipped with.
Although I can't comment usefully as I have not subjected my hub to lengthy or harsh treatment, I read that users have mostly found the product to be both reliable and robust.
The last issue I can report on is the availability of control levers, or rather lack of. We're all used to having a super-wide choice of control levers for use with derailleur gears, from so-called brifters, through rotary grip-shifters, old-fashioned down-tube levers and all sorts in between. The choice for use with the Afline hubs is pretty much one of three, Shimano's own double-action trigger, or a third-party brifter from Microshift and the bar-end option from Jtek. This limited choice has a knock-on effect on availability and price, which naturally limits experimentation.
Another thing which will become apparent to the user fairly quickly is weight distribution. Whereas the weight of a multi-ring derailleur sytem is distributed fairly evenly across the length of the bike, most of the weight of the hub system is concentrated in the hub itself, meaning a cycle equipped with an Alfine will feel back-heavy compared with an equivalent derailluer-equipped bike.
All-in-all though, I'm liking my 11 speed Afline a lot and wish I'd taken the plunge earlier. Hope that helps.