I'm posting here because I've browsed the SS sub-forum and there doesn't seem to be a lot of techincal information there so hopefully someone here can help me.

I am seriously interested in converting my bike to a Single-Speed. I've got semi-forward facing dropouts so my frame is designed to work as a SS. Part of my reasoning is curiosity about the feel and efficiency of a SS drivetrain, part is recapturing the nostalgia of childhood and a very simple bike and part is the fact that my bike riding is geared toward building or maintaining fitness and SS seems a good way to go.

I've been experimenting with riding in a single gear and not only is it doable, but I'm enjoying the experience. My research on SS's indicates that they are more efficient, for various reasons, and that a gear ratio of "x" on a derailleur bike will feel different (more difficult) than the same gear ratio on a SS. How big a difference is this? Are we talking a couple of gear-inches, 4-5 gear inches, or even 8-10 gear inches difference? I've been riding in a 61.5 gear-inch on my 3x9 drivetrain but what would the SS equivalent be? Would a 65 gear-inch SS feel the same? A 70? I checked the Surly CC SS and it has a 67.5 gear inch ratio so it seems I'm in the ballpark for what is common.

I guess my main question is when I find a gear on my 3x9 bike, how do I translate that to the same "feel" on a SS bike?

The laws of ratios pretty much control these questions. With the same gear size the differences of a multy speed system in the same ratio as a single speed are far smaller then one thinks. Portions of a % point of efficiencies, depending on pulley friction and chain lines. The differences are far more perceived then real. Of course when your in the final sprint for the gold medal any minor difference counts. Are you doing this? The chain tension of your single speed set up will have a larger influence then the der tension/pulley wheels. BTW you say that the frame is made for single speed set up. The vast majority of forward facing drop out bikes I've seen/sold/worked on were not thought as a conversion possibility, back in the day. Can you explain more? Andy.

So my current 61.5 gear-inches is probably going to feel very similar on a SS drivetrain? That makes it easier.

Maybe I used the wrong terminology. The seller of my frame uses the term "forward facing dropouts" and Surly calls the same dropouts "semi-horizontal" and both indicate they accomodate SS drivetrains. I seem to have mixed "semi" from "semi-vertical" with "forward facing". If you are familiar with a Cross Check, that's the type of dropouts I have.

I'd be surprised if you could tell the difference in efficiency between SS and derailer drivetrains, particularly if the derailer has BB pulleys.

It seems a bit absurd to mention efficiency in the context of SS; far more efficient to be in an appropriate gear.

The thing with converting to SS is you gotta play around a bit. What size rear cog and front chain ring do you feel best in? You can easily change the rear to something your shooting for. I run mine at 52/19 and it's good around town, a lil tough on some hills.

Huh, I'd use something like 42/18, myself.

But then I spin like a pro, not mash like a noob

This.

While there is some power loss to running a chain around the derailleur pulleys, it's a tiny loss because there's virtually zero tension in the chain's lower loop. The perceived advantage of SS vs multigear is mostly in the rider's head.

I've been riding fixed and derailleur bikes for 45+ years and. like many, appreciate the snappier feel of the fixed gear, especially in the city. Though when I was young, strong and foolish, I did centuries in the hills of Connecticut and PA with the fixed gear (no more).

Possibly one reason fixed feels snappier is that the wheel pushes the pedals through the dead spot. Another is that it forces you to ride more aggressively in rolling terrain, having to sprint hills since you can't afford to lose speed on climbs.

I have 43x16 fixed, like a little lower with freewheel cuz I can coast on downhills.

34x17 is my SSMTB gear.

And yeah, it's all feel, no real efficiency difference. No pulley noise and no chainslap in the rough stuff are a couple of SS niceties.

any combination that lets you arrive at that GI will do..
41:18? TA is a French company makes some odd and even tooth count chainrings.
144bcd is normally 42t or more.. but, I see : via Peter white cycles

144bcd
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[TD="width: 355"]41 tooth for Super Record cranks:[/TD]
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Track cranks are often 144 bcd

though a 42t would be more common, so cheaper.. then 144,135, 130 or 110 type would, almost, do..

For single speed there is a split in what you ought to do between fixed gear and free wheel single speeds.

For a fixed gear, unless you want to be spinning out when going down hill, you'd want between 70 and 80 gear inches.

For a freewheel, you can go lower and be alright. I'd say down into the 60's.

But, on to your question. A gear in a geared system will typically feel slightly higher than it will on a single speed drive train. I rode around in the jagged hills of West Virginia on a 46x15 freewheel, and found it absolutely perfect for climbing, descending and sprinting--of course, that was 82 gear inches.

On my former fixed gear bike I ran a 39x14, which on my wheels ended up as 75 gear inches. Just about perfect for not spinning out on the downhills out here in the Rockies.

But now I'm riding all geared bikes again.

Maybe that'll help.

Just out of interest, what ratio would you run on a fixed 700C bike, FB?

I'm certainly not interested in a fixed-gear bike, although I can see the perception of more efficiency in that system, as mentioned above. It sounds like converting to a SS probably isn't worth it based on what I've learned here and I would be better off just riding in one gear on my multi-speed bike. The "idea" of a simplistic drive-train that makes the bike more streamlined is still appealing to me but I would have to expect a significant, real difference in how the bike feels to justify conversion.

Thanks!

The Cross Check wasn't "designed' to be a SS/fixie but it is certainly suitable for building up in either format. The dropouts will easily allow setting the proper chain tension.

I kept a 47t chainring on the bike (I like prime numbers for track bikes) and usually used a 17t sprocket for general street and road use. I could climb in that sprinting short hills, or biting the bullet on longer ones, and got pretty adept at fast descents.

If I knew I was headed for a fast flat course on open road, I go down to 16t, and sometimes even 15t but I really had to be feeling my oats for that.

I also have a 51t chainring used it once in a while, but tended to get lazy and not bother changing rings. In fact it took a lot for me to switch to the 16t in back, so the bike was 47/17 99% of the time.

There are a few things here that sorta muddies the water. For someone who has both a geared bike and a SS bike, these will most likely be two different bikes. So when a rider switches from one to the other, he's not only switching drivetrain set up but also, frame, fork, wheels, riding position cockpit configuration, different tires etc. It'd be real difficult to keep track of which perceived differences(apart from lack of chain slap) that are coming from where.
Next is that us humans can be quite good at noticing relative differences, but quite sucky at absolute values. Something that'll turn out very minor in hard data can have a huge impact on the subjective experience.

And on top of that: since you have done your homework, you already know what to expect. That'll often turn into a self fulfilling prophecy. In formal testing, it's common to go to quite some lengths to prevent the test subject(s) from knowing what might happen.

An SS bike will certainly force the rider to vary his pedaling quite a bit more, and they're nicely forgiving under harsh riding conditions - if that's what you want.

I'm with dabac here, that most differences you feel when converting a given bike from derailer to singlespeed (not fixed) are placebo.
But it's important to note that ANY EFFICIENCY GAINED BY GOING SINGLESPEED IS MORE THAN LOST BY FORCING YOUR BODY TO PEDAL AT INEFFICIENT RPMs when on terrain or wind conditions that aren't perfectly optimized for the gear that you chose.

(Things are a bit different with fixed-gear because the chain will actually push the cranks forward through dead spots in the pedal stroke, so it definitely feels different unless you have a super-efficient pedal stroke.)

That said, riding a singlespeed is fun, and requires minimal maintenance. My bad-weather road bike is a singlespeed (with fenders) that I ride with impunity in downpours. I highly recommend it. Just not for efficiency's sake.

As for gearing a singlespeed, it's a compromise between a small enough gear to make it up hills and a comfortable cruising-speed gear with a tailwind or slight downhill. You can test this out well enough on your geared bike.
If you go fixed, since you can't coast you have the added concern of a gear big enough that it won't force you to spin out on a big downhill, which is one of the scarier feelings I've had on a bike.