# IGH and rear suspension



## fokof (Apr 24, 2006)

I'm a HT fanboy. Just spend the last 3 months with a major backpain so I'm starting to think of a soft tail , getting old......

I have a Rohloff for the last five years and there is no way I'm going back to derailleurs.
So i'm wondering how much that extra weight near the rotating axle is affecting the rear suspension.
I'm a CX guy , no downhilling or big jums , I'm probably gonna go with a soft tail 2"-3" rear sus.

Has anyone passed from derailleurs to IGH on the same frame ?
What was the "real world" difference ? 
I know the theory but am curious to know how it REALLY affects the reas sus.

Thanx


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## bsdc (May 1, 2006)

I've gone from derrailleur to IGH on the same frame. It's not an issue, especially if you aren't totally loading and unloading the suspension on something like a jump. One might argue that you need to adjust your suspension a little to account for the extra weight of the hub, but I never found I needed to do this.


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## fokof (Apr 24, 2006)

The rear was not less responsive on fast small bumps because of the extra weight ?
( fast responsiveness )


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## Deserteagle99uzi (Sep 15, 2008)

I can't say I have personal experience in this exact area. However that being said I have changed around my FS quite a bit since I first got it. I have an old rockshox ario 2.2 and I had to adjust the pressure slightly when I first replaced the wheels. I had some junk stock sun rims and cheap hubs, replaced with big fat rhyno-lite's laced to XT hubs. I picked up quite a bit of weight, however the overall change to the suspension was pretty minimal tbh. I realize the weight difference between traditional deraillurs and a rohloff is a bit more than this but the weight is completely unsprung so essentially it's like getting a beefier rear triangle or slightly heavier wheels. Most would say the majority of 29er owners out there haven't worried about "compensating" for the extra weight in the rear due to larger wheels/tires. Therefore, unless you are doing perfectly launched and balanced jumps that have you in the air for more than a second (basically just DHing and DJ) I REALLY wouldn't worry about the small weight difference. 

I know a lot of people think they can tell a real difference in center of gravity and weight balance but I would be willing to bet those same people probably couldn't tell the difference between 4 bikes setup w/a mix of deraillur and IGH drivetrains blind.


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## bsdc (May 1, 2006)

fokof said:


> The rear was not less responsive on fast small bumps because of the extra weight ?
> ( fast responsiveness )


You know, it may be that I'm just some big, dumb, insensitive lug, but I didn't notice any real change when I added a Rohloff to my bike. Maybe some people are suffering from The Princess and the Pea Syndrome.

I say just put it together, ride it and make whatever adjustments are necessary. I seem to recall reading about someone suggesting you could lower the compression dampening and quicken the rebound to compensate for the heavier hub.


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## Timbo (Jan 8, 2004)

The hub's extra weight compared to a normal drivetrain adds unsprung mass to the system. The important part of this is that the extra mass acts as a damper. This "mass damping" is actually exploited in some areas of engineering. For example, tall buildings in earthquake areas often include a large mass connected via pistons to the rest of the building to help damp vibrations. Also, Formula 1 cars employ mass dampers in their suspension/aero systems.

You should of course minimise unsprung mass as much as possible and rely on the shock absorber to provide the damping. Obviously with a hub gear this isn't possible, but you can compensate for it by reducing the damping that your shock does, both rebound and compression. The mass of the hub is giving you some damping for "free" which acts whenever the hub moves relative to the frame, so both in compression and rebound.

In short: use as tunable rear shock as possible and reduce its damping settings compared to what you would use on a normal drivetrain.

As far as the centre of gravity thing goes, it's definitely noticeable (at least for me), but only when I'm doing jumps or doubles etc. It has the effect of moving the pivot point of the whole bike backwards so bringing the front end down on landing is more effort... in my experience. For just regular riding you don't really notice the weight redistribution though.


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## rockyuphill (Nov 28, 2004)

I've been running a Rohloff on a Kona A with the 34:13 gearing for a few years now, and it does add more intertia to the rear end, it takes a couple of extra notches of rebound damping to keep it under control, and it is a bit sluggish in response on chatter and washboard. The smaller front chainring and 13T rear cog reduces the leverage to compress the shock under pedal loads with the concentric BB.


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## fokof (Apr 24, 2006)

Thanx for the amswers , interesting points.



rockyuphill said:


> , and it is a bit sluggish in response on chatter and washboard.


That's what I was worrying about. 
Is it very noticable compared to a standard rear wheel, or something more subtile ?

As for the change of center of gravity , I'm already used to it on my HT.


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## Speedub.Nate (Dec 31, 2003)

I've never built a full suspension bike without throwing a Speedhub on it immediately, so can't draw a comparison. That I haven't found the extra weight to be a noteworthy compromise of some sort doesn't really address your question, and I suspect Timbo and Rocky's comments are valid.

But consider the Speedhub's effect on a hardtail, which itself is a suspension system working under your legs and arms. The rear wheel has to track these same washboard sections, and your legs are acting as the damper to keep that in check. You've got a couple extra pounds of mass centered in your rear wheel that you've got to keep in check, which isn't insignificant -- even compared to the total weight of your bike (vs. just the unsprung mass of the rear triangle on a duallie).

At least by switching to full suspension, this work is being handled by the shock, not your legs, and the unsprung mass is reduced as compared to a hardtail's "suspension system." So even if the extra mass of the hub is a compromise to full suspension, my theory is it's less of a compromise than when compared to a hardtail.

Way back when, Thomas of Rohloff USA told me of some German paper -- could have been a magazine article, could have been a study of some sort -- claiming the added weight actually helped suspension systems. I never did find that paper, and sure would like to read it if anybody has it. Personally, I'm skeptical of his claim.


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## Deserteagle99uzi (Sep 15, 2008)

I was leery of bringing sprung and unsprung mass into this thread but it looks like I should have. Coming from the engineering world I can relate to the damping effects of the extra weight. As long as you are using a decent shock with adequate adjustment options this extra damping should be relatively easy to compensate for. 

I also almost wrote in my first entry "If any country might have studied the effects of extra unsprung weight on a bike it would be Germany" and it appears that hunch was right. Lots of the raw data on recreational (and professional) mechanical systems is often of German origin as typical industrious and function minded German thinking still runs many parts of the mechanical world around Europe. I have found similar studies to what is mentioned for mass damping on cars (VW) as well as real raw data about drag and efficiency on bike tires (mostly relating to pressure and tread depth). It would not surprise me at all if Rohloff had a collection of data relating to the damping effects of the extra weight. 

If you don't want to be bothered trying to dig that up I would take it on faith that a large German company most likely researched this very subject to a point of no contention. I would think that a retuning of your rear shock is probably all that would be necessary.


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## OldMTBfreak (Apr 8, 2006)

I have a Rolly on my 5" travel Titus ML. I rode it with full XTR kit for 3 years, then changed to the Rohloff. I didn't notice any change in the bike's performance. I was worried that the increased unsprung weight would make the bike handle bad. I really couldn't tell any difference. The full-squishy did require a chain tensioner and a chain guide to prevent tossing the chain on the downhills. I love the Rolly, I'm never going back to a deraileur. It will pay for itself in 3-4 years.


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## rockyuphill (Nov 28, 2004)

The extra weight being concentrated at the hub in the rear swingarm will only have a noticeable effect on the high speed transient surfaces like bigger cobble and washboard at speed. It's like running any other suspension system with more damping, it tends to pack up a bit. You need to accelerate the extra mass and slow it down again, so the extra damping tends to not allow the full compression and rebound between successive hits. On any other surface but cobble and washboard I've never noticed any issue with the extra hub mass.

With the concentric BB pivot on the Kona A there is a bit of pedal induced compression, but in the winter with studded tires, that just shaves the peaks off pedal input torque, a bit like traction control, so it makes the Kona A / Rohloff combo my favourite ice bike.


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## sealcove (Apr 26, 2004)

What kind of FS bike are you thinking of? Keep in mind that with most (but not all) FS designs, chain length changes throughout the travel. As such, you will need to live with a chain tensioner. Some are more kludgy than others... what you may settle on will depend largely on how much chain needs to be tensioned. If you haven't chosen FS bike yet, I would consider one where chain length is constant (then you can use a EBB).


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## rdhfreethought (Aug 12, 2006)

fokof said:


> Thanx for the amswers , interesting points.
> 
> That's what I was worrying about.
> Is it very noticable compared to a standard rear wheel, or something more subtile ?
> ...


It is very noticable, and indeed quite obvious. If I was racing, maybe I wouldn't use one. But I hate breaking chains, and I haven't broken a chain yet with the Alfine, and no lost chains either.

Does it matter, or affect the way I ride? In a word, no. If I did 500 runs with the Alfine, and 500 runs with a cassette, would their be a measurable difference. Probably. But I am not interested in such a slight difference in time due to the added inertia. I think the added weight on climbs is much more significant. If you can swallow that, then the difference in inertia, although obvious, will not likely matter much.

PS: it is also more sluggish in the air, so tailwhips and the like will be more difficult.
PPS: btw approaching a full year on my Freeride bike.


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## OldMTBfreak (Apr 8, 2006)

After looking at several tensioners and chainguides, I decided that the Rohloff parts were the best. The chain guide acts like a front deraileur. Most all FS bikes have chain growth issues; not a problem, use a tensioner. A two wheeled tensioner can handle more "slack" in the chain.


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## finch2 (Nov 13, 2009)

rockyuphill said:


> The extra weight being concentrated at the hub in the rear swingarm will only have a noticeable effect on the high speed transient surfaces like bigger cobble and washboard at speed. It's like running any other suspension system with more damping, it tends to pack up a bit. You need to accelerate the extra mass and slow it down again, so the extra damping tends to not allow the full compression and rebound between successive hits. On any other surface but cobble and washboard I've never noticed any issue with the extra hub mass.
> 
> With the concentric BB pivot on the Kona A there is a bit of pedal induced compression, but in the winter with studded tires, that just shaves the peaks off pedal input torque, a bit like traction control, so it makes the Kona A / Rohloff combo my favourite ice bike.


Maybe a 29er wheel with rohloff would minimise the washboard effect?


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## fokof (Apr 24, 2006)

I wouldn't think so ,on a 700 wheel the extra weight compared to a 26" is at the extremity , where rotating mass effect is more apparent.










The main reason I really don't like 700 wheels for MTB.


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## finch2 (Nov 13, 2009)

sure, there would be a little more weight, but rotating weight won't be a factor for unsprung mass, and compared to the rohlofffor static weight, negligable. The longer wheel patch would play a big role in small chatter especially with lower pressures....all a moot point though if you don't like 700c


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