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Discussion Starter · #1 ·
Hey singlespeed weirdos,

Ever wonder what gear ratio will get you that tuckd rear tire for instagram?
Do you have noodle legs, want a bigger cog, but not sure your slider has room?
Wondering how to get that big chainring to big cog combo for marginal wattage gains?

Me too. I was hoping to crowd source some expert opinions to help to validate this chart:

1941916


I would really appreciate if you could measure your chainstay length (to the mm) and see if your gear ratio falls within this chart. General comments appreciated. For example: do you run your chain with a lot of slack? Is your prefered ratio missing from the chart? etc...

A couple notes:

Thanks!
Daniel
 

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Discussion Starter · #3 ·
Thanks for the suggestion. I think that tool is better for finding the magic ratio for your fixie conversion. I want to make a chart specfically for mountain bikes: even chainrings, realistic gear ratios, full 20mm slider lengths.

I am need to get some real world validation on how people set up their bikes (with chain stretch , and slack tension, etc).
 

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I don't have a singlespeed, but this intrigues me. Is the 'problem' that the chain length is fixed to a round number of inches, so the wrong gear combo might mean you can't take up the slack in the sliders?

Why not just use a chain tensioner and be able to run any combo you want?
 

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In the past I made spreadsheets based on the Park rigorous equation and your calculations seem to match mine pretty well. I don’t use any of the combos in your chart, but I do know that my spreadsheet works, so I assume yours would too.

You should plan to run some chain slack, especially if you mount your chainring on a spider where it can be difficult to perfectly center the chainring causing tight spots at certain crank positions. Also, my chains tend to tighten up a bit when they get dirty, so I leave a little extra slack when tensioning a clean chain.
 

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I don't have a singlespeed, but this intrigues me. Is the 'problem' that the chain length is fixed to a round number of inches, so the wrong gear combo might mean you can't take up the slack in the sliders?

Why not just use a chain tensioner and be able to run any combo you want?
The eehouse both tells you what combos of charings and cogs will work for a given chainstay length but also how many links you'll need. A worn chain is usually a minimal adjustment for EBBs or sliders if any. In the SS world chain tensioners like singulators, rohloff, or melvins are fighting words(except on FS SS where for most suspensions chain growth is a thing).

OP, I can verify the eehouse accurate on the 4 or 5 bikes I've used it on, so if you match that should be good. I've never had a chain stretch so far that it couldn't be adjusted.
 

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Thanks for the suggestion. I think that tool is better for finding the magic ratio for your fixie conversion. I want to make a chart specfically for mountain bikes: even chainrings, realistic gear ratios, full 20mm slider lengths.

I am need to get some real world validation on how people set up their bikes (with chain stretch , and slack tension, etc).
I understand what you are looking for and ran into that when I built up a Kona Unit several years ago. The gear combo that I had initially intended on using had a new chain banjo string tight with the sliders in the shortest positions and by adding a link, put the sliders out towards the end where I was not sure I would have enough adjustment for chain stretch. A pain in the a$$, because then I had to order different gears. Every thing you are looking for can be done with this tool. I have used this tool to figure out chainring/cog combos on two different singlespeeds and actually found out about it from another person here on MTBR also using it for that reason. When I bought my Karate Monkey frame, I knew that it has a 423mm chainstay length. I entered 34 in the largest and smallest chainring data spots, entered 20 for both cog positions. Tire size is irrelevant for calculating chainstay length as far as chain links and gearing. Adding the chainstay length measurement just sets a reference on the scale. If I want to be real anal about it, I can play with the chainstay numbers to see exactly that the chainstay length is 42.47 cm for 47 links and 34/20. Scrolling to the right, I can see that by adding a link, my chainstay would now be 43.47 cm. Still usable on my dropouts. I used this information to find what gear combination would give me the shortest possible chainstay length I could run on my KM. There is even a place to add in chain stretch to the calculation. If I decided to run 32/19, which is similar in gear inches as 34/20, I can easily see that I would end up having to slide my wheel back @ 10mm for a 43.45 cm length, putting my wheel about in the center of my dropouts. Useful information for me, because I have thought about trying a larger tire on the back, but would need to slide the wheel back some for better clearance.

Nothing wrong with what you are doing and I guess it would give a fast reference. There is alway some level of comfort before throwing down cash on parts, to actually hear from somebody with first hand experience on what you want to do.
 

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Thanks for the suggestion. I think that tool is better for finding the magic ratio for your fixie conversion. I want to make a chart specfically for mountain bikes: even chainrings, realistic gear ratios, full 20mm slider lengths.

I am need to get some real world validation on how people set up their bikes (with chain stretch , and slack tension, etc).
I've only used the eehouse tool for MTB singlespeeds, and with great success. That said, one recent revelation for me was half link chains…. The advent of narrow/wide rings made 1/2 links and odd tooth number chainrings unusable/unavailable (especially in oval).

Found out about readily available and affordable (albeit heavy) chains like this - KMC HL710 BMX Bicycle Chain... Amazon.com : KMC HL710 BMX Bicycle Chain (1-Speed, 1/2 x 1/8-Inch, 98L, Silver) : Bike Chains : Sports & Outdoors

Works perfectly on a Wolftooth oval and cog. Gotta believe it'll work on Absolute Black, et al. Game changer for me :)

Sent from my iPhone using Tapatalk
 

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I like the visualization but I think each segment should be annotated with link count, and range should mean some amount of vertical slack. I did the math some years ago. Key is how much slack you want in chain.

In bottom equation S is desired upward deflection in mm.
Ft is teeth in front ring.
Rt is teeth in back cog.
CSL is center to center distance from bb to rear axle

this gives necessary chain length in mm, convert to inch and round up to nearest whole number.

1945233
 

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Rippin da fAt
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I've only used the eehouse tool for MTB singlespeeds, and with great success. That said, one recent revelation for me was half link chains…. The advent of narrow/wide rings made 1/2 links and odd tooth number chainrings unusable/unavailable (especially in oval).

Found out about readily available and affordable (albeit heavy) chains like this - KMC HL710 BMX Bicycle Chain... Amazon.com : KMC HL710 BMX Bicycle Chain (1-Speed, 1/2 x 1/8-Inch, 98L, Silver) : Bike Chains : Sports & Outdoors

Works perfectly on a Wolftooth oval and cog. Gotta believe it'll work on Absolute Black, et al. Game changer for me :)

Sent from my iPhone using Tapatalk
When it comes to chains and SS, I have been using the 710 since 09, when my trials bike was in need. That trials bike will destroy most others in a matter of a few sessions.
 

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@natzoo full-time singlespeeder, on mtb and gravel, here. I've been using that tool for over a decade on my bmx bike and everything else. It works! it should be perfectly sufficient to help you validate if that chart is correct. you can use the chain wear field to help as well. I tend to like a tukt rear wheel on my mountain bike (for wheelies!) and I picked a 30/19 gear combo instead of a 32/20 because it allows me to run my CSL at about 425 instead of 431mm.

I've never trusted chains made fully of half links. they are popular among the trendy fixie/bmx crowd, but riders who have been around a while and care about how their bike perform know that they stretch like crazy by elongating.
 

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I had a bit of an epiphany the other day that might be helpful to some of you. I've always tried to make the most of keeping my rear-center short. much of this mentality comes from riding bmx, where keeping the rear wheel tucked to make the bike spinny and flickable. I was never really good at bmx other than a few tricks and I could not hold a steady manual for more than a few feet when I knew people who could effortlessly manual for blocks at a time with enough momentum.

I've always set up my bikes with the shortest possible chainstays, which means picking a gear combo that allows a few extra mm of tucktness. on my Karate Monkey, the eehouse tool accurately predicts that a 34/20 and 30/19 will be darn close to the shortest setting in the dropouts at 423mm. 34/20 is a bit tall for me so I opted for 30/19 for now. as the chain wears, that length gets a little longer but keeps it under 430mm. that seemed grand.

I can't help to try to hotdog my way through boring parts of trails, so I go out of my way to hop, manual, and monster truck over every unnecessary obstacle on the trail. I've been trying to get better at holding long, stable manuals and practice these on stretches of road that connect our urban trail systems. I was doing just this the other day and noticed that I tilt my toes down and even forward, adjusting my heels up and down to balance myself. this makes the bike very twitchy—sensitive to small movements and prone to losing balance. also relevant: I'm 5'9"/ 175cm tall, so I'm not tall enough that tipping back a little bit should make a huge difference.

I have been trying to drop my heels so my body would settle into a more stable position. this seems to be the collective wisdom of our age: that dropped heels, especially while riding flat pedals like I do, makes your ride more stable. but dropping my heels instantly sends my center of mass back quite a bit, enough that doing so makes the bike "loop out" (tip over backwards) with alarming speed. dropping my heels means I need to shove my hips forward in an awkward stance (looks like I am humping my top tube) or tap the rear brake to keep from falling off the back. that's when it dawned on me: the rear-center of my bike is short enough that I have to stand on my tip-toes the loft the front end.

of course, rolling along on your back wheel for more than a few quick meters is not terribly useful on the trail. it's fun, but rarely practical. however, I suspect that my ability to do this says a lot about how stable and predictable my bike will be when it counts at speed on the trail.

I tried an experiment: on yesterday's ride, I knew the route would be long and technical in spots, but with very few extended climbs (or what passes for climbs in Austin), so I swapped my 19t cog for a 18t. this pushes my rear wheel out only a few millimeters, but I'm surprised by how much small adjustments in BB drop and rear-center can make in how a bike handles. maybe it was partially mental, but I immediately felt like the bike was more balanced on the rear wheel. I also felt a bit more front-tire traction in flat, loose corners and surprised myself a few times with my ability to maintain momentum on corners that usually have me on the brakes as I am fighting for traction and over-shooting the apex.

my previous beliefs about how bikes fit and handle have been shaken recently. I'm going to get a new chain (it's time) and try one ride with the axle way back to see how far the tradeoff takes me.

disclaimer: this is just me thinking out loud. I am not an engineer or a particularly skilled rider. rear-center is just one of many variables that affect how a bike handles. having a bike designed with singlespeed applications in mind also means you get to experiment with this dimension as an added bonus. try it!
 

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Rippin da fAt
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Mack, it sounds like you are actually noticing subtleties in bike configuration and what works for you, what doesn't. Now the experimentation begins in earnest!

In my case, I was building frames and forks back in the early 80's and doing all kinds of tweaks. BB drops and caster angles were frequent flyers on the experiment plane, so to speak.

There is a larger array of things that along with CS length, make a major difference. It isn't any one thing, but many.
In my builds, I made one change at a time to keep things under control. Multiple changes and you cannot determine what went good or bad as readily. Those were for times.

Now, manuals are euphoric.., Plain and simply put. I enjoy every one I do! Are they useful and such, who cares! I'm enjoying the high. (Endorphins and adrenaline) Manuals for a short distance are very useful, as are the venerable bunnyhop.
 

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I’d love to understand bike dynamics better.

Old bike has 450mm csl, running new bike at 426mm. I’m still not looping out when climbing, climbing is fantastic. Yes easier to manual, easier and funner to pump through turns…

but I’m also finding I’m losing front tire traction in swoopy corners. Finding myself going wide out of corners on wet trail. Actually fell in my wet driveway trying some pump turns and found myself off trail twice on my first ride. Trying to see if I can just not press too much weight to the rear. Never felt this with old bike but it has higher top tube so I could never be as free with rearward motion.

I love the new bikes handling but having to adapt my riding to the 1” shorter stays.
 

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Rippin da fAt
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I’d love to understand bike dynamics better.

Old bike has 450mm csl, running new bike at 426mm. I’m still not looping out when climbing, climbing is fantastic. Yes easier to manual, easier and funner to pump through turns…

but I’m also finding I’m losing front tire traction in swoopy corners. Finding myself going wide out of corners on wet trail. Actually fell in my wet driveway trying some pump turns and found myself off trail twice on my first ride. Trying to see if I can just not press too much weight to the rear. Never felt this with old bike but it has higher top tube so I could never be as free with rearward motion.

I love the new bikes handling but having to adapt my riding to the 1” shorter stays.
eri, you need to move your weight accordingly. CS length determines how much and for how long weight shift is needed. You are either dynamic or static at times and it will let you know, with practice what is necessary.
This is the point that your bike needs your input, wheel loosing traction, loosing contact with the planet.

No worries tho' cause you got this! Practice with a given bike and all is good.

For the locations that you want to be in the saddle, one with a slightly wider nose and more cush will make riding forward easier to tolerate. Something like a Chromag Trailmaster is good for this. Saddles made of stone or steel make climbing like a saddle made of barbed wire! Just another ingredient that may lend to a good experience on the trail.
 

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eri, you need to move your weight accordingly. CS length determines how much and for how long weight shift is needed. You are either dynamic or static at times and it will let you know, with practice what is necessary.
This is the point that your bike needs your input, wheel loosing traction, loosing contact with the planet.

No worries tho' cause you got this! Practice with a given bike and all is good.

For the locations that you want to be in the saddle, one with a slightly wider nose and more cush will make riding forward easier to tolerate. Something like a Chromag Trailmaster is good for this. Saddles made of stone or steel make climbing like a saddle made of barbed wire! Just another ingredient that may lend to a good experience on the trail.
Thanks! I’ve been playing with weight, am still pretty surprised what a difference an inch of csl makes. Problem is to teach my muscles to do something new, definitely what works on the one bike doesn’t work on the other. I’m starting to feel the understeer more quickly, but ones it starts it’s hard to escape. The motion of rocking forward means pulling the bars which further unweights the front.

This is single speed so I’m standing when I descend or corner. I can easily weight rear by jumping back from neutral, now I’m learning to rock forward before and during turn then finish with pump. Still that motion is quite slow for me, I’m not fast enough for cones in the driveway but I’ve found neutral.

I’ve got a trail master ltd. Great saddle, a great big couch. It’s coming apart after years of wet riding and the new ones are expensive!
 

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Rippin da fAt
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Eri,

Something I tend to do is stay fairly close to the seat I move fore, aft and side to side. But mostly within a couple inches of seating. Lower center of gravity makes handling like Velcro.

what can be done with cs x can be done with cs y. Just happens to be a change in body English and technique. In time it becomes automatic for you. Ride and practice! Don’t pass the opportunity to redo a section to sort it out.
 
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