Gearing Choices

[John Tolhurst]

Here is my recommendation for Silvio gearing.

Background Facts and Observations.
1) For sporty riding at 15 mph plus you need close range shifting because a small increase in gearing produces a exponential increase in effort required for the same cadence. This is why sporty bikes need close ratio clusters.

2) For comfort and confidence on a long steep climb you need very low gearing.

3) The recumbent position calls for shorter cranks because the hips are not at liberty to help move the legs as they are on an upright. So on a cruzbike recumbent I recommend shortening the cranks to 165 if 175 suits you on the upright, or a similar proportion if you take other sized cranks on an upright.

4) Sheldon Brown's gain ratio concept allows integration of crank length variables with other gearing variables. http://www.sheldonbrown.com/gain.html

5) The gearing that we wish to achieve is defined as 175 cranks with a triple 52/39/30 with 10-speed 12-13-14-15-16-17-19-21-24-27 Cassette. This gearing setup produces the following gain ratios:

30 30.0 % 39 33.3 % 52
12 ... 4.8 ... 6.2 ... 8.3
8.3 %
13 ... 4.4 ... 5.7 ... 7.6
7.7 %
14 ... 4.1 ... 5.3 ... 7.1
7.1 %
15 ... 3.8 ... 5.0 ... 6.6
6.7 %
16 ... 3.6 ... 4.6 ... 6.2
6.3 %
17 ... 3.4 ... 4.4 ... 5.8
11.8 %
19 ... 3.0 ... 3.9 ... 5.2
10.5 %
21 ... 2.7 ... 3.5 ... 4.7
14.3 %
24 ... 2.4 ... 3.1 ... 4.1
12.5 %
27 ... 2.1 ... 2.8 ... 3.7

That is, gain ratios of 2.1 through to 8.3.

Recommendation

Crank Length 165mm
Compact Double of 34 50.
Custom Cluster as noted in the listing below.

This combination gives a spread of 2.0 to 8.4, just slightly wider than the benchmark we were aiming for.
34 47.1 % 50
12 ... 5.7 ... 8.4
8.3 %
13 ... 5.3 ... 7.8
7.7 %
14 ... 4.9 ... 7.2
7.1 %
15 ... 4.6 ... 6.7
6.7 %
16 ... 4.3 ... 6.3
6.3 %
17 ... 4.0 ... 6.0
17.6 %
20 ... 3.4 ... 5.1
20.0 %
24 ... 2.9 ... 4.2
20.8 %
29 ... 2.4 ... 3.5
17.2 %
34 ... 2.0 ... 3.0

Conclusion
The above gearing combination (165mm cranks on a compact 34/50 double with a custom 12-34 cassette) give a number of advantages.
1) you get over 420% of gearing with just a double chainring, so less shifting of the front.
2) most casual or group riding will be on the large ring, so again less shifting.
3) large steps in the lower gears will make quick starts possible with less shifting.
4) large steps in lower gears are suitable to a leaning forward full body use of the bike, then as speed and cadence increases, the gearing steps shorten up and aid a high spinning cadence.
5) crank length will give optimum use of the front wheel drive while still promoting spinning.

This is my recommendation for gearing the Silvio. The only weakness in the argument is the availability of high quality 165mm cranks.

Suggestions most welcome. :geek:

 

[Hotdog]

It sounds great in principle, but how easy would it be in practice? Are ten speed custom cassettes ranging up to a 34T cog available? I could see the rear derailleur being an issue too, a 34T cog and an overall range (front plus rear) of 38T points to a MTB derailleur to me but are they compatible with road shifters? I not suggesting it can't be done, I just don't know much about this stuff and am curious to find out what would be invovled

 

[JonB]

I can not follow your calculations, What wheel did you choose?
"For 700 X 20 / 20-622 tire with 165 mm cranks"
i get 2.5 - 8.4 and not those 2.0 you speak of.

Not being a roadie, and not caring about weight, i would consider using a sram dual drive to get a bigger range or get the same range with a closer gearing. Or choose a Nuvinci gear hub and get a infinitely variable gearing. Possibly combined with a schlumpf highspeed drive.

Sram dual drive will get you ratios from 1.8 to 11.4.

Nuvinci + schlumpf highspeed drive will get you from 2.0 to 7.0 and using the highspeed mode from 5.0 to 17.6.

 

[Hotdog]

JonB wrote: I can not follow your calculations, What wheel did you choose?
"For 700 X 20 / 20-622 tire with 165 mm cranks"
i get 2.5 - 8.4 and not those 2.0 you speak of.

20mm tyres are rather non-standard, if you try it again with 23mm wide tyres (as used on most road bikes) you'll get the same numbers that John gives.

 

[John Tolhurst]

Hotdog wrote: It sounds great in principle, but how easy would it be in practice? Are ten speed custom cassettes ranging up to a 34T cog available? I could see the rear derailleur being an issue too, a 34T cog and an overall range (front plus rear) of 38T points to a MTB derailleur to me but are they compatible with road shifters? I not suggesting it can't be done, I just don't know much about this stuff and am curious to find out what would be involved

Yes, a rear derailleur to take 34t is another possible weakness of the model, however RDs for triples have longer cages I think (don't they?), since there is a larger difference on the front. 52-39=13, so difference in length is 6.5 links or 3.25" On the other hand, a triple is 52-30=22, or 11 links or 5.5" which is an extra 2.25" to manage with the rear derailleur cage. Readers will recognize I am working from principles here, my familiarity with components is not great.

 

[John Tolhurst]

JonB wrote: SNIP..
Not being a roadie, and not caring about weight, i would consider using a sram dual drive to get a bigger range or get the same range with a closer gearing. Or choose a Nuvinci gear hub and get a infinitely variable gearing. Possibly combined with a schlumpf highspeed drive.

Sram dual drive will get you ratios from 1.8 to 11.4.

Nuvinci + schlumpf highspeed drive will get you from 2.0 to 7.0 and using the highspeed mode from 5.0 to 17.6.

My view is that the design of each bike must be singlemindedly focussed on a particular bike concept and rider type. Think of it this way, you will never succeed in the art of cooking if you try to add every nice spice to the pot. It doesn't work that way, instead you have to be highly selective. :idea: The idea of the Silvio is to reinterpret the road bike. Matching a compact double to a close-wide cluster on 165 cranks is already very very radical if your frame of reference is road bikes as they are commonly sold.

 

[Hotdog]

A little browsing around unearthed wide range 10 speed cassettes from Interloc Racing Designs available in 11-32 (Shimano compatible), 11-34 (Shimano) or 12-32 (Shimano or Campagnolo) but they don't have the closely spaced top end, so not quite the gearing you suggested. Their FAQ and Sheldon Brown's pages do say a a 34T cog would require an SGS ('MTB') derailleur but that's OK as they apparently will shift over a 10 speed cassette with road shifters. GS ('road triple') derailleurs are generally good for rear cogs up to about 30T, whereas SS ('road double') manage up to 28T. So it does seem that something very similar to the interesting gearing you suggested could in fact be put together from available components.

 

[JonB]

Hotdog wrote:

JonB wrote: I can not follow your calculations, What wheel did you choose?
"For 700 X 20 / 20-622 tire with 165 mm cranks"
i get 2.5 - 8.4 and not those 2.0 you speak of.

20mm tyres are rather non-standard, if you try it again with 23mm wide tyres (as used on most road bikes) you'll get the same numbers that John gives.

Do you mean For 700 X 23 / 23-622 tire with 165 mm cranks ?

i still get 2.5 as the lowerst gain ratio.

34 47.1 % 50
12 5.7 8.4
8.3 %
13 5.3 7.8
7.7 %
14 4.9 7.2
7.1 %
15 4.6 6.7
6.7 %
16 4.3 6.3
6.3 %
17 4.0 6.0
11.8 %
19 3.6 5.3
10.5 %
21 3.3 4.8
14.3 %
24 2.9 4.2
12.5 %
27 2.5 3.7

But i think i found out why. John uses a 34 tooth in the back. I stop at 27 because thats what John used at the road bike calulation.

 

[JonB]

johntolhurst wrote: My view is that the design of each bike must be singlemindedly focussed on a particular bike concept and rider type. Think of it this way, you will never succeed in the art of cooking if you try to add every nice spice to the pot. It doesn't work that way, instead you have to be highly selective. :idea: The idea of the Silvio is to reinterpret the road bike. Matching a compact double to a close-wide cluster on 165 cranks is already very very radical if your frame of reference is road bikes as they are commonly sold.

But since the frame design itself is already pretty radical, taking that step i would not mind doing other radical things. But then again, my frame of reference is not road bikes.

 

[John Tolhurst]

The main issue with this proposed gearing is the shift structure from the big to little chainwheel and back. Because of the wide spacing of the compact double and the close ratio of the small end of the cluster, you must shift 4 or maybe 3 cogs at the cluster to get the next ratio. On my current bike with standard road gearing, the down shift on the rings is accompanied by one upshift on the cluster and that gets me into the next lowest gear. On the proposed gearing, that technique will work on the wide end of the cluster, moving you from the 50 / 26 to the 34 / 22 but its still a little bit of a stretch. Mostly you will need to go up two on the cluster and one down on the rings. You can get this rhythm going with a little practice. But on the close end of the cluster, it might be one down on the rings and three up on the cluster. This might create a pause in the power delivery, or a distraction to accomplish the shift which might cost you a bike length on a climb. If that bothers you. You seem to have to ease up momentarily on shifting just because of the disruption to the cadence that occurs when shifting up front.

 

[Mark B]

JonB wrote: But then again, my frame of reference is not road bikes.

I understand better, now, since I found a picture of you and your bike!

:lol: :lol: :lol:

Mark

 

[John Tolhurst]

Hotdog wrote: A little browsing around unearthed wide range 10 speed cassettes from Interloc Racing Designs available in 11-32 (Shimano compatible), 11-34 (Shimano) or 12-32 (Shimano or Campagnolo) but they don't have the closely spaced top end, so not quite the gearing you suggested. Their FAQ and Sheldon Brown's pages do say a a 34T cog would require an SGS ('MTB') derailleur but that's OK as they apparently will shift over a 10 speed cassette with road shifters. GS ('road triple') derailleurs are generally good for rear cogs up to about 30T, whereas SS ('road double') manage up to 28T. So it does seem that something very similar to the interesting gearing you suggested could in fact be put together from available components.

Yes, well we can calculate the difference between the shortest chain and the longest. It will be 0.5(34-12+50-34) = 38/2 = 19t or 9.5 inches

Sheldons rear derailleur page talks of capacity, which appears to be the difference between the smallest and biggest at each end, without halving. The Ultegra 10 Speed GS "Triple" for example has a capacity of 37, so we might expect it to work on this proposed gearing - almost. Just stay out of the 50-34, or cut the chain long and stay out of the 34-12.

 

[Mark B]

I know that compact is all the rage right now, but I'm not sold. I did some research on this, talking to riders and mechanics and my take on the whole deal is that compact drivetrains are driven by people that want the low gearing without sacrificing the coolness factor of a double crankset. :roll: The sacrificial lamb, of course, is your high gear. I spoke to a friend of mine that not only wrenches, but is probably one of the stronger riders in this area. He told me that the low gears are great for the climbs, but the setup leaves a lot to be desired for descents and flatland pacelines where you might fall out of the slipstream. Once you're off, you're off, forgetaboutit.

The other thing about the compact drivetrains is the inherent need to crosschain. The "experts" will tell you that the narrower chains are more flexible and can make the reach easier. The mechanics will tell you they're replacing way more chainrings than they used to. It seems the extreme angles, coupled with the narrower chain and rings cause the chain to eat away at the sides of the chainrings, wearing them paper thin in a relatively short time. As an example, he randombly grabbed a severly worn chainring right off the bench.

My own personal observaion is that I hear and read about more and more people breaking the ten speed chains.

Call me a skeptic, but I think the old rule of thumb of never, ever crosschain still applies, but is not practical with compact drivetrains.

That is what you call MY two cents worth.

Mark

 

[JonB]

Mark: funny picture.

John and Mark:
loosing power, even for a moment and falling behind is exactly why i suggested a sram dual drive or a nuvinci gear hub. With the sram you can keep the chain on one chainwheel at the front, and then use the internal gear hub to change fast. If you choose your rear cog set wisely, you might get a very small range shifting, and if you combine that with 2 or 3 chainwheels in the front you might get a wide range with very small steps between the gears.

The nuvinci hub will give you INCREDIBLY small steps between gears and you can apply power all the time, as well as change gear while standing still. Combining that with a schlumpf drive will get you a single chainwheel infront and a wide gear range with those INCREDIBLY small steps between the gears. The only problem i see is the weight.

 

[Mark B]

JonB wrote: Mark: funny picture.

That would be a great donor bike for a conversion kit, if it weren't bass ackwards. :lol:

JonB wrote: The only problem i see is the weight.

I also have an irrational fear of overcomplicated, infernal geared hubs. If I can't look at it and figure out how it works without a pilots license or an engineering degree, I tend to shy away from it. I'm a simple guy with simple tastes.

IMHO, I believe the triple drivetrain is the most simple, elegant and workable drivetrain currently available. I believe a quad up front would be even better. You can track the chain relatively straight all the way from low gear to high gear without putting undue stress on the drivetrain components. But, that's just me. I tend to believe most people cannot wrap their minds around the concept of trying to keep the chain relatively straight.

I like to think I'm forward thinking, but I don't see the compact drivetrain as moving forward. I see it as a tool to sell more parts. I'm not buying it; I would have been fired from Shimano years ago because I would have jumped up and down on the boardroom table, screaming at the top of my lungs about what a dumb idea this was.

Mark

 

[JonB]

Mark B wrote:

JonB wrote: The only problem i see is the weight.

I also have an irrational fear of overcomplicated, infernal geared hubs. If I can't look at it and figure out how it works without a pilots license or an engineering degree, I tend to shy away from it. I'm a simple guy with simple tastes.

I tend to agree, but i believe that the Nuvinci hub is as simple as it gets. Just some balls rolling against the side of the hub http://youtube.com/watch?v=kVPjhmTThPo

Mark B wrote: IMHO, I believe the triple drivetrain is the most simple, elegant and workable drivetrain currently available. I believe a quad up front would be even better. You can track the chain relatively straight all the way from low gear to high gear without putting undue stress on the drivetrain components. But, that's just me. I tend to believe most people cannot wrap their minds around the concept of trying to keep the chain relatively straight.

You also have to keep it clean. A Nuvinci gear hub keeps the chain STRAIGHT. The Freerider i bought has a single chainring infront and an 8 gear rear cog casette. Thats not straight. When it is worn out next spring, or the year after that, i will most likely get a Nuvinci gear hub. If i need a bigger gear range before that i will probably try a schlumpf highspeed drive infront.

 

[MrSteve]

I'm extremely impressed with the NuVinci transmission.
It makes obsolete all discussions concerning ... all other transmissions,
especially discussions concerning optimum gear ratios, number of chain rings,
deraileur cage length and so on.

The only debatable points left, in favour of standard transmissions, are weight and cost.

(The NuVinci transmission has balls. There: I said it!)
:twisted: :twisted:

-Steve

Edited by my conscience....

 

[Mark B]

yakmurph wrote: The only debatable point left, in favour of standard transmissions, is weight.

Yes and 11 pounds is a BIG consideration. I guess I'd have to play touchy-feely with one and ride one before I came to a solid conclusion. They're in Fallbrook, so maybe they'll be at the Redlands Classic expo.

Mark

 

[John Tolhurst]

The nuvinci is beautiful, no argument, but we are talking here about Silvio gearing options, a bike based on the concept of reflecting the values of the road biking community as far as possible. Maybe that means a triple, rather than my proposed gearing setup.

As I understand it, the chain will be no more or less angled across than if a standard double were used. A triple offers greater possibility for chain parallax (if I can borrow that term)

It is important to note in this gearing model that 175/165 (1.06) is equal to 53/50 and about equal to 52/50 (1.04), so the actual gain ratios across any cluster you choose are the same or about the same if you swap your 175 double to a 165 compact double on the big ring at least. In fact I would like to run a 165 x 50-37 on a 12-28 cluster on my Silvio. :evil:

 

[Hotdog]

johntolhurst wrote:
Yes, well we can calculate the difference between the shortest chain and the longest. It will be 0.5(34-12+50-34) = 38/2 = 19t or 9.5 inches

Sheldons rear derailleur page talks of capacity, which appears to be the difference between the smallest and biggest at each end, without halving. The Ultegra 10 Speed GS "Triple" for example has a capacity of 37, so we might expect it to work on this proposed gearing - almost. Just stay out of the 50-34, or cut the chain long and stay out of the 34-12.

The problem with the Ultegra GS comes back to the maximum cog size, which is a seperate (but correlated) issue to overall capacity. As you say, the 37T overall capacity is fine (these ratings are generally conservative, and you'd only be pushing the limits if you cross chained to the maximum extend possible), as is the maximum front difference (22T), but in common with the other road branded Shimano derailleurs it's only rated for a 27T largest cog. They're known to in practice work fine with 28T cogs, however if you went much larger than that it's likely that regardless of the B-pivot adjustment the jockey pulley on the derailleur will come into contact with the cassette when you try to use the large cogs. To go above 28T at the back you really need to cross over to the MTB branded components, say an XT GS, but I don't see that as a big problem. The distinction between 'road' and 'MTB' parts is really just branding, 'MTB' rear derailleurs are commonly used on touring bikes, for example.

The NuVinci hub is interesting, but I'll be waiting for it to evolve a little more before I get excited about it. Continually variable gearing is nice, however the current model is very heavy and has a limited overall range, and in the few reviews I've seen it's been said to be hard to shift under load. These things will probably improve with further development, but for the time being I don't see enough advantage over other geared hubs. Shimano Nexus 8-speed hubs are lighter, cheaper and with greater overall range (I've got one on my old commuter, great bit of kit), the only downside relative to the NuVinci is a few biggish jumps between ratios. Rohloff 14-speed hubs have a really good overall range (over a factor of 5), are lighter still (and with a lighter model in development), and have evenly spaced, reasonably close ratios, the main downside with those is they're extremely expensive, but by all accounts they outlast any other sort of transmission several times over so maybe not such bad value in the end. Internally geared hubs definitely have their place, I think they're great for commuting/touring/utility bikes and as the technology continues to develop they may become more widely used, but it's hard to argue that any of the currently available hubs is a better solution than a derailleur drivetrain for a performance orientated road-going bike.

 

[cycleguy]

One of the changes made to my gearing this week was changing the large front chainring to a Shimano. The bike shop was stating that the Shimano chainrings have much better shifting due to their chain guides that help it up to the large chain ring when using a compact setup. It's just a large jump with a compact chainring (34 -> 50) This new chainring made a big difference when I tested it on the road today, much smoother.

My rear cluster goes from 34 down to 11.. using a Shimano Deore XT rear derailer. I have lots of steep grades around here and wanted the extra power...seemed to work really well today.

Harold