Author Topic: Looking for a lighter Rohloff bike than my Mercury  (Read 18336 times)

PH

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #75 on: October 25, 2022, 11:21:46 am »
That's where I went wrong with choosing the Mercury - it's designed for at least 20kg more than I'm likely to need (the Mercury is still waiting to be rehomed).
Bike looks great, but I have no idea what you base the above statement on?  Spa suggest the Elan is suitable for the same sort of light camping load that Thorn suggest is appropriate for the Mercury.  Both offer forks suitable for front panniers to increase that. 
I note there's no numbers on your update, a little surprising considering the title of this thread! 
I'm going to guess the frame is 800 - 900g lighter than the Mercury and the fork (Which you could have changed anyway) is another 700g.  I'm also surprised by the change back in wheel size, as you were looking for something faster it seems like a backwards step. 
« Last Edit: October 25, 2022, 11:37:38 am by PH »

Moronic

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #76 on: October 25, 2022, 01:21:35 pm »
John your priorities are very different from mine and it's clear you are on a journey with bike config that is keeping you engaged and riding. That's the great thing. And I suspect you're doing many more miles than I am at the moment. (Poor weather and the excitement of a new to me motorcycle having confined my Merc to the garage past couple of weeks).

I've no idea whether I can reach the ground from the saddle of my Mercury because I've never had reason to try. Yet for you, the desire to do so more comfortably motivates a wheel rebuild.

Your bike looks incredibly good but there's no way I'd be trading my Mercury for an equivalent. But then I don't need a disc fork, and if I did I might be much less satisfied with the Merc. It's fantastic that you are working your way towards what you want, and thanks for taking us along on the ride with you.
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mickeg

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #77 on: October 25, 2022, 09:46:17 pm »
Nice looking bike.

I am pretty happy with my titanium bike, but mine was built for loaded touring so I am sure it is a stiffer frame than yours.  And my wheels were built for the extra weight of four panniers.  Mine is a 3X8 drive train, half step plus granny.  Not Rohloff.

JohnR

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #78 on: October 26, 2022, 09:49:40 pm »
Bike looks great, but I have no idea what you base the above statement on?  Spa suggest the Elan is suitable for the same sort of light camping load that Thorn suggest is appropriate for the Mercury.  Both offer forks suitable for front panniers to increase that. 
I note there's no numbers on your update, a little surprising considering the title of this thread! 
I'm going to guess the frame is 800 - 900g lighter than the Mercury and the fork (Which you could have changed anyway) is another 700g.  I'm also surprised by the change back in wheel size, as you were looking for something faster it seems like a backwards step.
I'll try to address these valid questions.

1. Thorrn's Mercury brochure http://www.sjscycles.com/thornpdf/BUILD8MERCURY650bROHLOFF.pdf states the rider + baggage weight to not exceed 120kg with my Mercury's build (disc fork) or 110kg with the Thorm 853 fork. I'm unlikely to ever exceed 80kg for rider + baggage. Spa give no indication of load limits and just describe the Elan as "It's a light tourer, or you can fit big tyres and hit the trails, or light wheels and join the chaingang" https://www.spacycles.co.uk/m11b0s143p3698/SPA-CYCLES-Titanium-Elan-Mk1-Frameset. The description includes "Paying attention to tube profiles as well as sizes means its stiff enough to be quick, but not so stiff to be uncomfortable". The same wording is used for both the 725 steel and titanium frames. I read through the comments of the frame designer (Colin 531) on the Cycling UK forum https://forum.cyclinguk.org/index.php to help understand both the difference in characteristics between steel and titanium frames and the constraints on frame design.   
2. Thorn states that the Mercury uses Renolds 853 steel for the frames and 725 steel for the stays. The frame of the Elan 725 is 725 steel but it's not clear what steel is used for the stays. 853 steel is 11% stronger than 725 steel https://www.reynoldstechnology.biz/wp-content/uploads/2015/08/rtl_steel_alloys_extract.pdf although both tube diameter and wall thickness will influence frame strength. I therefore assume, without supporting data, that the maximum comfortable load (rider + baggage) capacity of the steel Elan is around 100kg and the Elan Ti is a bit less. I don't want more stiffness than needed for my loading conditions as additional stiffness results in a harsher ride. In reality, an Audax frame would probably have the right stiffness and I investigated the Thorm Audax but crossed it off due to the tyre width limitation.
3. I've done some weighing: My Elan Ti with full carbon forks weighs 12.9kg without the bags shown in the photo and with G-One Allround tyres (35mm on from, 40mm on rear) the Ergotec AHS handlebars and rubber grips, an Aravis saddle, the open Chainglider, bottle cages and small lights. The Mercury weighs 14.1kg in the original condition (Thorn handlebars and Thorn saddle) except it's currently shod with 48mm GravelKing SK tyres with tubes instead of the original 50mm Schwalbe G-One Speed tyres with tubeless sealant. With the same equipment on both bikes the difference in weight would be between 1.5kg and 2kg.
4. I would see the choice of tyre to be a bigger factor in rolling resistance than the difference between 650b and 700c. I fitted the G-One Allrounds on the 650b for two reasons: (a) they are the same sizes as the G-One Speed tyres I had been using with 700c wheels and (b) we are into autumn and the likelihood of mucky roads. I've got a pair of 30mm 650b G-One Speed tyres to try in the spring when the winter muck has cleared but even if they are faster I may conclude they don't justify the likely reduction in ride quality. From my ride logs I estimate that the Elan Ti with the 700 wheels was 0.5 to 1 mph faster than the Mercury. Given that it's reckoned that weight doesn't matter (except when going uphill) then one key factor in that increase is the less harsh ride.

In case you're wondering what I'll do with the Elan 725 frame, there's a winter project to build a bike with a 2 x 10 derailleur drivetrain
and see how it compares. I might decide it's a better option for the summer months than the Rohloff.

PH

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #79 on: October 27, 2022, 12:25:33 pm »
I'll try to address these valid questions.
Thanks for taking the trouble to do so.
You seem to have built a bike that suits you better than your Mercury did, nothing I or anyone else says should in any way take anything away from that. It's just chat!  I swap bikes around fairly frequently, so it would be both stupid and hypocritical of me to to suggest I know what suits anyone else when I can't always work it out for myself!!
However, where we stray from opinion to detail, I am inclined to comment...
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I therefore assume, without supporting data, that the maximum comfortable load (rider + baggage) capacity of the steel Elan is around 100kg and the Elan Ti is a bit less.
There's lots of evidence this assumption is wrong, frame weight, tube diameter and gauge, construction... Leaving that aside, Spa would simply be irresponsible to advertise a bike as an All-Rounder with touring and off-road capability, if it had a designed weight limit that many of their customers will exceed.  The large differences in the Thorn brochure between configurations are sometimes confusing, though it doesn't surprise me the difference a fork will make, it is the weakest link.
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I've done some weighing: My Elan Ti with full carbon forks weighs 12.9kg
That's a reasonable weight for a light touring bike, my Mercury is 1.1kg heavier, though it's a few sizes larger and that includes a rack.  The last build of my Hewitt Cheviot was 12.5kg, though that wasn't the most practical build. I know someone with a Spa Ti Tourer that weighs under 13kg. These are the sort of weight differences I've been suggesting throughout this thread. There's lots of reasons you might prefer the Elan, there is something different about Ti and the lighter the rider the more noticeable that seems to be.  I'm still of the opinion that these sorts of weight differences are not a significant factor in themselves.
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I would see the choice of tyre to be a bigger factor in rolling resistance than the difference between 650b and 700c.
Yes, tyre choice is without a doubt the biggest factor.  However, all other things being equal, bigger wheels roll faster, while smaller wheels accelerate quicker. You must notice this with your Birdy, I do with my Airnimal, the difference between 700c and 650b obviously won't be as marked but it's always there. 
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In case you're wondering what I'll do with the Elan 725 frame, there's a winter project to build a bike with a 2 x 10 derailleur drivetrain
and see how it compares. I might decide it's a better option for the summer months than the Rohloff.
That would be interesting, making the comparison between gearing on the same bike. I have a friend with the same bike who, at some expense, got his down to less than 10kg (Without guards).

JohnR

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #80 on: October 27, 2022, 06:22:39 pm »
However, all other things being equal, bigger wheels roll faster, while smaller wheels accelerate quicker. You must notice this with your Birdy, I do with my Airnimal, the difference between 700c and 650b obviously won't be as marked but it's always there.

I reckon that the Birdy is 10% slower than the bigger bikes. Some of that is due to the 18" wheels but I wonder if other factors such as the dynamo are adding to the drag. In theory the dynamo drag shouldn't be significant but 5W is 5% of an average rider power of 100W.
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That would be interesting, making the comparison between gearing on the same bike. I have a friend with the same bike who, at some expense, got his down to less than 10kg (Without guards).
I won't be looking to achieve the absolute minimum weight (my choice of handlebars won't help in that respect) but, by my choice of gearing (probably 42/24 + 11 - 36) can provide a gearing range that closely matches my current Rohloff build. A few years back I had a Dawes Super Galaxy and the 3 x 9 gearing suffered two major limitations: Too much gear overlap and overall gearing too high for me.

There's a bit of me that has the urge to try fitting a Rohloff on a carbon fibre frame. However, the rest of me questions if that is a good idea as the rear triangle won't have been designed to handle the Rohloff's torque (with the worst loading being in the opposite direction to the force applied for a disc brake). However, should I decide that a 2 x 10 derailleur bike deserves a place in my garage then I may get tempted to investigate the carbon fibre frame option. It won't provide a big weight reduction compared to titanium but every little bit helps offset the effects of the rider getting older. I'm becoming a belated bike fiddle but it's fun applying the accumulated experience to the creation of something slightly better suited for my needs.

martinf

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #81 on: October 27, 2022, 11:03:50 pm »
However, all other things being equal, bigger wheels roll faster, while smaller wheels accelerate quicker. You must notice this with your Birdy, I do with my Airnimal, the difference between 700c and 650b obviously won't be as marked but it's always there.

On good road surfaces, my own experience with 16" and 20" wheel Moultons suggests that wheel size isn't all that important when combined with a good suspension system.

My old 16" Moulton Stowaway wasn't much slower than my 700C lightweight on a long commute after I modified it to take 7-speed derailleur gears and drop handlebars. And some of the difference comes from using inefficient small sprockets, 11T smallest on the Moulton compared to 14T smallest on the 700C bike. When Moulton bikes were first introduced, they managed to break some speed records. I suppose the lower aerodynamic drag of small wheels offsets the lower rolling efficiency at high speeds.

The 16" wheel Bromptons I have now are noticeably slower, probably because of the more upright riding position and lack of front suspension.

On very bad surfaces, bigger wheels are much more efficient than small ones, that's why tractors have such huge wheels.

Comparing 26", 650B and 700C I don't notice much difference if the tyres are similar. My 700C lightweight currently has very efficient (10.3 watts at 60 psi according to the bicycle rolling resistance website) and relatively narrow Continental Grand Prix 5000 700c x 32 tyres, so it is faster on good road surfaces than my Raven Sport Tour with Schwalbe Marathon Supreme 42 x 559 tyres (19.1 watts for the 700c x 32 mm version at 60 psi, so probably more for my wider tyres run at lower pressures). However the Raven Sport Tour copes better with moderately rough surfaces and is generally a bit more comfortable on the kinds of roads/tracks I tend to prefer.
   

JohnR

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #82 on: October 30, 2022, 10:09:10 am »
Mention of rolling resistance reminds me that with the frame changes I've also increased tyre pressures without making comfort worse and getting lots of buzz from the road surface. On the Mercury I was comfortable at 30psi with 50mm G-One Speed tyres and I'm now up to 40psi with with 35/40mm G-One Allround tyres on the Ti frame. (I'm aware that tyre size is a factor in this).

bernhard

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #83 on: September 30, 2023, 10:02:04 pm »
while I realize this thread is about a year old, maybe somebody can benefit from what I'd like to post.
I "upgraded" from an Audax Mk3 to a Mercury Mk3 two years ago. The idea was to get a fast tourer thats close enough to a road / gravel bike while still being comfortable for a few 100km days in a row.

I ended up with a dropbar built that weights in at 13.5kg with pedals fitted.

550S frame
Trek FXD carbon fork
FSA agx k-wing carbon handlebars
CaneCreek ee-silk seatpost
Wheelset: db460r rims, son in front
Schwalbe G-One allround 35mm tubeless
thorn crankset
SKS mud guards
B+M lighting
MKS Allways pedals
Fizik Argo saddle
SRAM Rival shifters + hydro discs
Gilles berthoud front rack


Getting rid of mudguards, lights and dynamo and front rack would shave off another kg or 1,5.
all in all I think the ride quality, weight, comfort and luggage capability are well balanced.
The group I usually ride with - carbon road and gravel bikes - I can keep up with. Sometimes I am a few minutes late for a meeting point, but thats most likely not the bikes fault.

« Last Edit: October 01, 2023, 07:56:33 am by bernhard »

PH

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #84 on: October 01, 2023, 03:12:08 pm »
Bike looks great Bernhard and just from a glance it's not surprising that John's weighed 50% more!
Did you weigh the Audax as a comparison? 

bernhard

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #85 on: October 02, 2023, 06:57:35 am »
I did. The Audax Mk3 was about 800g lighter.
It featured 28mm tyres, tektro rim brakes and a steel fork. I am sure Rohloff + Hydrodiscs adds weight vs the 105/deore/tektro mix I had mounted on the Audax, while frame and fork beeing lighter on the Mercury.

From time to time I think about setting up a lighter bike. Then I remember my 90ies Faggin with Chorus setup that I sold, as I always picked the Audax due to the much nicer ride quality :)

The Mercury fulfills the intended role perfectly: fast day rides and credit card tourer. It is no racer, but then thats not what it wants to be. I think of it more as a sports coupe than a racing car.

PH

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #86 on: October 02, 2023, 01:20:05 pm »
I did. The Audax Mk3 was about 800g lighter.
That is exactly what I would have predicted, kicking myself I didn't include that in the above post! 
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From time to time I think about setting up a lighter bike. Then I remember my 90ies Faggin with Chorus setup that I sold, as I always picked the Audax due to the much nicer ride quality
I've wasted a fair bit of money going down that route over the years. I can sometimes kid myself it was spent, not wasted, because I've had the fun along the way and it not like I'd have done anything else with it...
There is something nice about going for a blast on a bike built for that without all the compromises to practicality.  But the stars don't often align like that for me and the last one I had covered 400 miles in three years. My Mercury does that in a poor month.

JohnR

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #87 on: October 02, 2023, 06:47:14 pm »
Bike looks great Bernhard and just from a glance it's not surprising that John's weighed 50% more!
Did you weigh the Audax as a comparison?
Some of my customisations to my Mercury such as the Ergotec AHS handlebars added to the basic weight nd because the bike cost so much I fitted a frame lock. I slowly figured out that one consequence of the Mercury being built to carry more load than me + minimal baggage meant that the frame was stiffer than I wanted. I was put off the Thorn Audax by the tyre width limitation although using 650b wheels would like increase that limit (but subject to the significantly smaller choice of rims and tyres.

When I bought my Mercury I didn't understand the finer details of bike design. I'm now slightly wiser but still learning. I've just built a drop bars + derailleur bike to see if I can improve on the poor experience provided by my last drop bar bike some years ago. The frame I bought for this build has smaller diameter top and down tubes which have made a significant improvement to the ride quality (although I'm looking enviously at that Cane Creek seatpost).

Moronic

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #88 on: October 04, 2023, 02:37:50 am »

The Mercury fulfills the intended role perfectly: fast day rides and credit card tourer. It is no racer, but then thats not what it wants to be. I think of it more as a sports coupe than a racing car.

Yes! Actually I take a step down the range, and think of my Mercury more as a GT than a sports coupe, but then mine is set up a little more tour-ey, with flat 'bars and a steel front fork with low-rider lugs.

Either way it's a perfectly valid role for a bike to play, and if you're not racing then why ride a racer - at least now that we've got such fantastic alternatives. Great to hear that your Merc does the job you picked out for it.
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PH

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Re: Looking for a lighter Rohloff bike than my Mercury
« Reply #89 on: October 04, 2023, 01:48:18 pm »
I slowly figured out that one consequence of the Mercury being built to carry more load than me + minimal baggage meant that the frame was stiffer than I wanted.  of rims and tyres.

I still think it's a shame you never tried the Mercury in a lighter build, you may have reached the same conclusions though at least you'd be comparing apples with apples. I obviously don't know how your Mercury rode, mine has always been in the Sports Tourer guise, in that spec it losses little to the steel Audax bikes I've previously owned.  So little that I parted with my last Audax bike shortly after getting the Merc.
Isn't the Elan also designed to carry more than the minimum?  Spa describe it as a light tourer (Amongst other things) and the experience of some on the CUK forum stretches the idea of light! I also know at least two Elan owners who previously rode traditional Audax bikes for the same rides.
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The frame I bought for this build has smaller diameter top and down tubes which have made a significant improvement to the ride quality
It's a dangerous game - Taking one factor and attributing too much to it.  It only really works if all other factors are equal, for example - If a frame with slightly smaller diameter tubes was also 20mm shorter and the TT was 30mm lower - Which would be the stiffer? And with the longer seatpost and stem required, which would feel stiffer? I don't know either.
It is useful to consider what suits us, what we attribute that too may help inform our future decisions, it's of dubious value to others. Whole product experience is of more use, even then there's no reason it should match someone else's.  I greatly prefer my Nomad to the Ogre it replaced. I could have a fair go at explaining how I prefer it, I'd struggle to explain why.
Getting back to the weighty subject of this thread. There's 3.6kg difference between my Mercury and Nomad in their current spec, the difference in feel and experience is immense.  I'm sure I've said this several times over in this thread already, weight is a consequence of getting the other criteria right, not the goal (Though it can be fun!)

« Last Edit: October 04, 2023, 01:52:42 pm by PH »