Author Topic: A gear ratio question for those knowledgeable people!  (Read 1437 times)

leftpoole

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A gear ratio question for those knowledgeable people!
« on: April 30, 2020, 11:31:29 AM »
Hello,
According to what I have read so far about these hubs and how to get the best use from them, it appears that the best overall useable gear should be gear 11. This I take to mean general rule is to be using gear 11 in everyday use the most. Garbled but as I see it,
I am using gear 12 more than any other gear and am wondering how best to rectify this?
I just would like to know how many teeth on crank would increase the ratio. It is running at present a 16 tooth sprocket with a 39 chainwheel.  8) I have so far managed to calculate using Sheldon Brown chart that a 42 teeth chainring is the nearest to what it compares. Further assistance very welcome.
Best to all,
John
« Last Edit: April 30, 2020, 02:22:56 PM by leftpoole »

PH

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Re: A gear ratio question for those knowledgeable people!
« Reply #1 on: April 30, 2020, 04:46:03 PM »
As I'm sure you've seen from the gear calculator, a 42 would but 11 quite close to where you have 12 now, something like 11 2/3, I think that's as close as you'll get with a change of one component, I haven't looked but it might be possible to make an exact equivalent by changing both chainring and sprocket.
It's correct that 11th ought to be the most efficient on account of it being direct drive.  but before you start making changes you might like to consider just how much more efficient and how much that matters to you.  testing has shown that 8/9/10/11 are all within 1%.  You might also consider how the rest of the range suit you, you might not want to raise the bottom gear, or it might be a big advantage to have a higher top. 
When i bought my Raven, it's primary purpose was as a commuter, the trip home included a long drag, and about a quarter of the way up i had to drop it down to 7th, which is the slowest change and also a big drop in efficiency.  I lowered the gearing to stay in 8th and found it easier without noticing less time in 11th.
https://dorkythorpy.blogspot.com/2014/03/hub-gear-efficiency-vs-derailleur-gear.html

leftpoole

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Re: A gear ratio question for those knowledgeable people!
« Reply #2 on: April 30, 2020, 07:09:44 PM »
PH,
Thanks for your comments. I have obviously used deep recessed brain effort to come to the conclusion I made because you have too, and I trust others with mathematical stuff!
I actually decided to try somehow for the change of chainring because I just happen to have Thorn ring that particular size purchased on a whim brand new from someone on Ebay.
So its looking good either way as, after all 1% is very little.
I will see how I match up after time on my Audax 853 derailleurs .
Thank you again,
John

Matt2matt2002

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Re: A gear ratio question for those knowledgeable people!
« Reply #3 on: April 30, 2020, 07:12:46 PM »
Hi PH
Enjoying your blog.
A nice balance between fact/ opinion and fun.
Thanks
Never drink and drive. You may hit a bump  and spill your drink

John Saxby

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Re: A gear ratio question for those knowledgeable people!
« Reply #4 on: April 30, 2020, 08:36:07 PM »
John,

I've done a gearing change on my Raven, as follows:

>  Began with a 38T ring x 17T sprocket, and then,

>  After two years, changed to a 36T ring at the front. 

That reduced my gearing by about 4 - 5%, and I found myself spending much more time in the upper register, between 8th and 12th gears.

I also ride a derailleur-equipped light touring bike.  Currently, I have an 11-34 9-spd cassette at the rear, and a 22 - 36 - 48 triple at the front.

Have attached an Excel spreadsheet with the comparative gear-inch numbers for the two bikes.  That may be helpful.  The current setup on each bike has a lime-green (!) "Current" above the table.



martinf

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Re: A gear ratio question for those knowledgeable people!
« Reply #5 on: April 30, 2020, 10:52:37 PM »
Hello,
According to what I have read so far about these hubs and how to get the best use from them, it appears that the best overall useable gear should be gear 11. This I take to mean general rule is to be using gear 11 in everyday use the most. Garbled but as I see it,
I am using gear 12 more than any other gear and am wondering how best to rectify this?
I just would like to know how many teeth on crank would increase the ratio. It is running at present a 16 tooth sprocket with a 39 chainwheel.  8) I have so far managed to calculate using Sheldon Brown chart that a 42 teeth chainring is the nearest to what it compares. Further assistance very welcome.
Best to all,
John

To change from a 39T chainring in order to get the future gear 11 to equal the current gear 12 means about a 14% increase in chainring size, so I make that 44T rather than 42T.

That said, your option of 42T/16T would give you almost exactly the same gear range as my own Raven Sport Tour with 50T/19T, assuming you have similar sized tyres (mine are 35 mm). My gear 11 on that bike corresponds to 64 gear inches, or 28 km/h at 90 rpm, so a reasonable speed for me on a lightly-loaded bike on level roads for what I call "sporty" riding. So as you already have the 42T, and so long as you don't mind having a slightly higher gear 1, I reckon it's worth trying. It just means adding some links to the chain and probably adjusting the eccentric.

In practice, I don't really notice much difference in efficiency between the 7 highest gears, and as I tend not to ride on the level for long distances I am not really bothered whether gear 11 is my most used gear or not.

What matters most to me is the lowest gear. On the Raven Sport Tour I wanted to have something low enough to get me up all the local hills without straining my ageing knees and without getting off and walking. Gear 1 which corresponds to 18 gear inches, or 5.2 km/h when I drop my cadence to 60 rpm, has so far been OK. If I ever need something lower I can swap out the 50T in 2T steps all the way down to 40T with my stock of spares. I am not bothered that this would mean losing the highest gears as I currently only use gear 14 downhill or with a very strong tailwind.

I gear my other Rohloff bike (Raven Tour) significantly lower, as I use this bike as a heavy tourer, equipped with front and rear pannier bags for long trips.

leftpoole

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Re: A gear ratio question for those knowledgeable people!
« Reply #6 on: May 01, 2020, 12:09:59 PM »
John,

I've done a gearing change on my Raven, as follows:

>  Began with a 38T ring x 17T sprocket, and then,

>  After two years, changed to a 36T ring at the front. 

That reduced my gearing by about 4 - 5%, and I found myself spending much more time in the upper register, between 8th and 12th gears.

I also ride a derailleur-equipped light touring bike.  Currently, I have an 11-34 9-spd cassette at the rear, and a 22 - 36 - 48 triple at the front.

Have attached an Excel spreadsheet with the comparative gear-inch numbers for the two bikes.  That may be helpful.  The current setup on each bike has a lime-green (!) "Current" above the table.

Hello John,
Thank you. I have looked at your spreadsheet, but as a mathematical novice even at 70 I looked and admired but only partly understood!
Actually truthfully it is interesting and I admire anyone who can calculate these things as well as you have.
Thank you again,
John

leftpoole

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Re: A gear ratio question for those knowledgeable people!
« Reply #7 on: May 01, 2020, 12:17:05 PM »
Martinf,
Thank you and truly remarkable how these differing versions all more or less offer a solution!
Thank you again as I think this might be in the long run the best for my requirement.
I have many medical problems unfortunately which I get and sometimes remission is great and then suddenly back to being unable to ride.
My latest additional and seemingly permanent is Osteoarthritis in both knees. The right knee being very painful, the left somewhat less so. I have been following my Doctors advice all through and now the Pandemic has struck I am I guess at the bottom of a waiting list for next step whatever that is.
So again a thank you and a thank you to all!
John

Andre Jute

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Re: A gear ratio question for those knowledgeable people!
« Reply #8 on: May 01, 2020, 02:36:06 PM »
Have attached an Excel spreadsheet with the comparative gear-inch numbers for the two bikes.  That may be helpful.  The current setup on each bike has a lime-green (!) "Current" above the table.

Well done, John! Clearly your years as a teacher weren't wasted, presenting bite-sized chunks of knowledge so palatably.

Andre Jute

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Re: A gear ratio question for those knowledgeable people!
« Reply #9 on: May 01, 2020, 03:17:34 PM »
...truly remarkable how these differing versions all more or less offer a solution!


Any discussion of gearing on bicycles has as its subtext the search for maximum forward velocity with limited human power. That's what underlies the "most of the time you should be in gear 11 on the Rohloff" dictum so often heard: the search for efficiency. Gear 11 on the Rohloff HGB is the 1 to 1 ratio, the one with the least loss, therefore the most efficient.

That matters to racers, or old racers who can give us the URL for the relevant efficiency tables from memory. But a Rohloff is a bit heavy for racers...

So I would say what matters on the Rohloff isn't strict adherence to wisdom arising from racing, but what suits your age, your health, your accustomed cadence, and your knees best, as long as your most common gear is somewhere near 11, say 10, or 12, 13, 14, more gears higher than 11 because these overdrive ratios will wear the Rohloff less than even gear 11, whereas you don't want to go lower than 10 as your most-used gear for fear of wearing the hub faster. (Actually, I think that, with the Rohloff in particular, that's probably a nicety too far on an HGB of its known longevity, and gear 9 will also be all right, but don't blame me if you have to buy a new Rohloff before your 104th birthday.)

My own original Rohloff setup was 38x16, the 16 being the sprocket that comes on the Rohloff from the factory (and a very good choice too, if you ask me, though I ordered a 17T sprocket as well just to be certain), and the 38 calculated not by reference to gear 11 but to the lowest gear on which with my cadence I can keep my balance. This was necessitated by the practical consideration that my wife wanted to live up the steepest hill in town just when I was about to go in for heart surgery. Fortunately this worked out as gear 11 on the flat once I recovered. In fact, I recovered so well that I was eventually happy with a bigger chainring, which actually put me up into gears 12 and 13, and now, several years later, I still need the lowest gear (now a couple of gear inches higher but no matter) for getting up the hill below the house but I storm around the flat bits (not too many on which a bicyclist can relax) of my countryside in overdrive gear 14. Of course, that also means that I cruise downhill, catching my breath, but there's nothing wrong with that. Overall, it's a smoother ride in the overdrive gears, which helps if you knees are getting a bit sensitive.

So, as you've observed of the advice from experienced tourers, there isn't a fixed "best" point, but a range of suitable options. Choice is good!

So, I'd say, fit what you have or can get delivered, try it, and if it works for you, you can always afterwards blow up a storm of mathematics to justify your choice, or you may take the view that it suits you fine, you're the guy who paid for it, and that's that.

PH

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Re: A gear ratio question for those knowledgeable people!
« Reply #10 on: May 01, 2020, 04:26:35 PM »

To change from a 39T chainring in order to get the future gear 11 to equal the current gear 12 means about a 14% increase in chainring size, so I make that 44T rather than 42T.
You are entirely right, your maths is better than mine :-[

martinf

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Re: A gear ratio question for those knowledgeable people!
« Reply #11 on: May 01, 2020, 07:39:20 PM »
My latest additional and seemingly permanent is Osteoarthritis in both knees. The right knee being very painful, the left somewhat less so.

My own experience of knee problems may or may not help you.

I had persistent knee pain about 40 years ago, to the extent that my GP advised an operation. I didn't fancy that, as I knew someone who had had a knee operation that had left him worse off than before. So instead I :

- changed jobs. At the time I had a job as a bus driver, most of the coaches and buses I took out were very old with fierce clutch mechanisms and stiff brake pedals (and often no power steering, but that didn't seem to cause me any grief).

- switched to spinning a lowish gear on the bike rather than turning a high gear more slowly.

- got proper cycling clothing that kept my knees warm rather than the more fashionable blue jeans that were cold and clammy when wet. At the time, tweed cycling breeches (wool stays reasonably warm when wet), nowadays I generally use synthetic cycling tights in cool weather.

Later on I found out by accident that using 150 mm cranks instead of 170 mm suited me better. I maintained at least the same average speeds and endurance by turning a lower gear faster. Probably possible to do the same with 170 mm, but I find spinning comes naturally with short cranks, and the knee bend is slightly less.

ZeroBike

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Re: A gear ratio question for those knowledgeable people!
« Reply #12 on: May 07, 2020, 04:21:24 PM »

My latest additional and seemingly permanent is Osteoarthritis in both knees. The right knee being very painful, the left somewhat less so. I have been following my Doctors advice all through and now the Pandemic has struck I am I guess at the bottom of a waiting list for next step whatever that is.
So again a thank you and a thank you to all!
John

Obvs your health isnt the best and it goes up and down.  What about an ebike or retrofitting one? 

Have a look for

Tongsheng TSDZ2 Mid Drive Motor

It can be retrofitted to most bikes.  It has a torque sensor so you can set how much assistance you have it give.  (get the version with a throttle as the casing has all the holes in it already and you can then decide to put a throttle on at a later date without drilling the casing)

TBH I was toying with the idea of putting one onto my mtb to get me up hills quicker.. they put a lot more wear on stuff so with mtbs they take a battering anyway.. add weight and speed and you end up with a much lighter wallet!!! but as a short tourer / commuter.. I think it would be great!

Needs constant tinkering .. which is right up your street

pluss have a look at this

https://endless-sphere.com/forums/viewtopic.php?t=93818

Tonnes of firmware stuff you can do to really dial it into how you want it to work... and the times when your knees are fine and your health is good.. take it off.. put it in a box and just peddle.

Its just a thought.  As I say I was thinking of putting this all onto a mtb, but mine is full suspension and the battery dosent fit anywhere nice and the motor really needs to sit at the back and on mine it wouldnt.. and then there is just the whole adding weight thing, components wearing out etc.

Of all the retrofitting systems that exist.. the Tongsheng  one is  the one to look into, its the torque sensor so it means it peddles with you rather than trying to approximate this from cadence and speed.

Anyway, either way hope your health improves!

All the best

Ben

 

leftpoole

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Re: A gear ratio question for those knowledgeable people!
« Reply #13 on: May 07, 2020, 04:48:05 PM »
Ben,
Thank you for the very long well worded response.
Iím grateful.
But please donít ever mention e-bikes again! Iím not going to even try one. Iíd rather give up cycling and buy a proper internal combustion motorcycle. Iím an ex motorcycle rider.
Although some feel e-bikes useful and, no doubt they are to some. But no never not for me.
Thank you so much again.
Best to you and everyone.
John

ZeroBike

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Re: A gear ratio question for those knowledgeable people!
« Reply #14 on: May 07, 2020, 05:02:34 PM »
Oh well buddy.. I sort of know what you mean.  I haven't got one myself, but fortuently Im much yonger than you and in really good health.  I will never convert you but Id say the difference between peddling half capacity vs being on a motorbike in terms of your health is different worlds.

I hate to see you give up cycling.. thats not to say you shouldnt get a motorbike too.

BTW do you remember that rusty old knackerd, beat up old audax you sold me.. just bought the last set of Reynolds steel forks that will probably ever be offered in BRG... I dont even want them, but now they are rare I must have them!!!

You take care mate

Ben