Author Topic: Mercury (Rohloff) Gearing  (Read 1062 times)

Luker99hy

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Mercury (Rohloff) Gearing
« on: September 04, 2021, 11:13:55 AM »
Hello all

I'm nearing the 700 mile point on my Mercury Mk3 and have a question about gearing.

The bike is fitted with a 43t chainring and 17t sprocket. I find that I seldom use gears 13 and 14 whilst needing to play 'hike-a-bike' on some steeper climbs. To me, this suggests that, for my purposes, the gearing is too high. I have a 19t sprocket available and I assume fitting it would lower the gearing. Before fitting it I would like to understand the implications of doing so. The act of changing the sprocket seems simple as it is the splined type.

I recall sighting a chart of permissible chainring/sprocket combinations somewhere but cannot find it now. Can anyone signpost me?

Also, is there an idiots guide to understanding Rohloff gearing? I would like to understand what I would actually achieve by changing the sprocket.

Presumably, changing the sprocket would impact chain tension!

As a technical numpty, if it is all too difficult, I might leave it until my first service at SJS.

Best

Ray

 

PH

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Re: Mercury (Rohloff) Gearing
« Reply #1 on: September 04, 2021, 12:23:35 PM »
You would effectively add one lower gear at the expense of one higher, with only a fraction of a difference between current 1st and updated 2nd.
Plenty of online gear calculators, this is my preferred one and simple to use.  I like setting it for "Gear Inches" but you don't really need any understanding of the units to make comparisons, but plenty of online explanations if you want that.
https://www.sheldonbrown.com/gear-calc.html
Lowest ratio permitted depends on your weight, see the long thread as to whether you think you ought to be concerned by that.  43/19 is fine if you're under 100kg. The chart you're thinking off will be in the "living with a Rohloff" pdf downloadable from the Thorn website and I think the gear ratios are listed there as well.
Yes you'll need a longer chain. As it's hardly run in you might get away with adding a link or two.

You might also consider which are your most used gears, how often you need lower and how usable they'd be. You may end up with a compromise, in my case, I might benefit from one lower gear, but I wouldn't want to change where 11th is or sacrifice 13&14.

And - welcome to the forum, apart from the gearing how else are you finding the bike?  How have you got it set up?  wheel size? Photos?  ;)
« Last Edit: September 04, 2021, 12:26:41 PM by PH »

Luker99hy

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Re: Mercury (Rohloff) Gearing
« Reply #2 on: September 04, 2021, 02:58:38 PM »
PH - thank you for your helpful response and welcome to the forum.

Thanks to you I have had a lightbulb moment. I now have enough of an understanding about gearing to make a decision moving forward. At first I did not appreciate the relevance of 11th gear. Having used the gear calculator I am inclined to make the change at some point, probably at service, due to the fact that my most used gear is currently 10th, I seldom use 14th and sometimes need to walk. Having said that, a shift of one gear may offer less benefit than other options such as losing weight! For now, I'll try to ride more in 11th and perhaps build fitness. Due to health related issues I try to keep my HR within strict limits, that will be the deciding factor.

The bike is exceeding my expectations. Having spent too much money, in the past, on trying to make off-the-shelf bikes work for me I now appreciate I was penny wise and pound foolish. I have not changed anything set-up wise on the bike. SJS got it spot-on. Wheel size is 700c with 38mm tyres fitted with lightweight tubes containing sealant. My previous bike was 650b and tubeless. Jury is still out on size and tube or tubeless. Brakes are as recommended by SJS, v-brakes front with disc on rear. Works well. I'm not a fan of clipless pedals so ride flats. My preference is for Hope F20 pedals. Outstanding grip but harsh on the shins if I get things wrong. Saddle is currently the B17 as supplied with the bike. It is comfortable but for the winter I will probably revert to an SQ Lab saddle. I find them very comfortable due to the form and fit. My one regret is not going for a front hub with dynamo. Since fitting an Ortleib bar bag I have lost a lot of real estate on the bars. Just enough room for my GPS unit but no front light. My current bodge is to use a Petzl headlamp that just about fits around the bag.

As for photos, none at the moment. I'll gussy the bike up a tad next week and take a couple.

Thanks again.

Ray

JohnR

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Re: Mercury (Rohloff) Gearing
« Reply #3 on: September 04, 2021, 03:22:26 PM »
Welcome.:) Here's the long discussion about gearing http://thorncyclesforum.co.uk/index.php?topic=4412.0 . It's probably best to start at the end and work backwards. As you've got the 19T sprocket I would suggest that you do the switch and see if you prefer it. It shouldn't take more than 1/2 hour. Read pages 16 / 17 of the Thorn Owner's Guide http://www.sjscycles.com/thornpdf/ThornBikeOwnerManual2Web.pdf regarding adjusting the eccentric bottom bracket (also page 15 relates to chain tension). Take a look at the EBB and check the position. If it's in position A (page 16) then you'll also need a new chain (the KMC X8 is suitable and relatively cheap although the E1 is more durable). If the EBB is away from position A then there may be enough adjustment to accommodate the 19T sprocket. Thorn included the EBB adjustment tool with my Mercury but I have found that if the end of a long Allen key is pushed into one of the holes then it can be pushed around using the crank once the adjustment bolts are loosened.

I also strongly suggest that you gradually learn the basics of bike maintenance. There are plenty of guides on the internet. My Mercury has done over 6000 miles in less than 14 months and I would like to think it is well-maintained, albeit all DIY. I've learnt a few new skills along the way.

Luker99hy

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Re: Mercury (Rohloff) Gearing
« Reply #4 on: September 04, 2021, 08:46:03 PM »
JohnR - thank you.

I have skimmed the Owners' Guide and it is very useful. Must admit to being confused about the EBB. The guide says that a Mercury has a mini eccentric, mine looks like a 'normal' EBB. Perhaps the Mk3 is different to previous models in this respect. The tool supplied with the bike looks like the one used on the normal EBB in the guide. It's due a good clean tomorrow so I will investigate further.

Agree about bike maintenance. My previous bikes were serviced every six months at my LBS. I see the Mercury being serviced at SJS annually therefore I need to develop my skills. First time I have had V-brakes so there is a learning opportunity! Managed to centre them the other day thanks to a Park Tools video on YouTube. Really need to get to grips with brakes as I lack confidence in that critical area.

The joys of cycling with a real bike!  :)

JohnR

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Re: Mercury (Rohloff) Gearing
« Reply #5 on: September 04, 2021, 09:09:07 PM »
I have skimmed the Owners' Guide and it is very useful. Must admit to being confused about the EBB. The guide says that a Mercury has a mini eccentric, mine looks like a 'normal' EBB. Perhaps the Mk3 is different to previous models in this respect. The tool supplied with the bike looks like the one used on the normal EBB in the guide. It's due a good clean tomorrow so I will investigate further.
I think you're right about the Mk 3 Mercury (which I also have) EBB not being the mini. Whichever size it is, it's secured by clamp bolts and not by bolts pushing into the shell (shown on page 13). I think the Owner's Guide hasn't been properly updated for a while.

One benefit of getting progressively more ambitious with bike maintenance is the reduced tisk of getting stranded when away from home. If you haven't yet had the back wheel out of the bike then it is better to practice at home rather than figure it out in the middle of nowhere when you get a puncture. The only challenge is remembering to shift the Rohloff hub to 1 or 14 before removing the Ex-box so it's easier to be sure that the indexing is correct when you refit it. You'll also learn which basic tools you need to carry such as the big Allen key for the front axle.

PH

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Re: Mercury (Rohloff) Gearing
« Reply #6 on: September 04, 2021, 09:18:28 PM »
Must admit to being confused about the EBB. The guide says that a Mercury has a mini eccentric, mine looks like a 'normal' EBB. Perhaps the Mk3 is different to previous models in this respect.
Yes, the idea of a mini EBB was short lived and the Mk3 has a full size one.