Demet

OK long story short, I'm trying to convert this 70s Motobecane into a badasse single-speed. I'm just starting out so know very little about this, but have the bike, a stand and have been acquiring tools as I go.

I bought these wheels before I decided to go singlespeed, so I'm wondering if they will work, or do I need a different one? I'm fine if I need to buy another rear, as I want one that will take a bigger tire, ideally a 38mm I think.
https://northwestbicycle.com/product...0c-rear-j64194

So if I need a new rear (or both) this is what I know/need:

• 17-23mm rim width will allow 38mm tire, based on charts I have found.
• I want black, and no advertising/branding, or very minimal.
• Rear spacing on the bike is 126mm (above wheels are 130 and I can squeeze them in)
• I would ideally buy this wheel from Amazon as I have a credit there I'd like to use. But can buy elsewhere if need be.
• I think I want to do a flip-flop hub as I'm just starting and not sure about fixed yet ;-p

Any recommendations would be really appreciated, my mind is mush trying to decipher all the variables! Here's a picture of the bike when I got it, have new brakes/levers to put on, added basket, waiting for new quill and stem so I can get handlebars where I want them....

ThermionicScott 

The wheel in your link has an 8-10 speed freehub. Don't buy that, get a real singlespeed wheel.

JohnDThompson 

What diameter wheels are currently in the frame? Most SS/FG wheels you'll find will be 700C (622mm bead seat diameter); if that's what you bike currently runs it ought to be trivial to swap them in. If they're 27" (630mm bead seat diameter) you may need to get longer reach brake calipers to run a 700C wheel.

The low-budget option would be to simply install a single-cog freewheel on your current wheel (assuming English-spec hub thread).

Demet

Yeah I already bought those before I decided to go SS/FG, just wondering if I can still use them. But I will to find the right ones, but wider so I can do bigger tires.

Thanks for your feedback, yes I already bought long reach calipers, actually just fitted them to the frame. Ditched the 27" wheels so I could gain some space for bigger tires, and a LBS told me those older chromed wheels are less good in rainy Portlandia ;-) So now I'm trying to find the right wheels, at least the rear, could use the front I already bought, but ideally I want 17-18mm wide wheels which gives me options on larger tires. But I don't know exactly what kind of hub/cog deal/thing I need. I think i want a flip-flop hub so I can ease into the fixed life.

ThermionicScott 

I don't have any direct experience with them, but I've heard good things about Velomine. It would be hard to top a deal like this: https://www.velomine.com/index.php?m...oducts_id=2099

Demet

Cool those look good, I can do a flip/flop hub on it? Do you know what the interior width of the rim is, I can't seem to find that information?
EDIT: Found reference to internal width of 17.5mm so that will work for me. Thanks!

ThermionicScott 

Yeah, anytime a hub is listed as fixed/fixed, it also has the ability to run a freewheel on either side.

TugaDude

I can vouch for Velomine. Good guys, good service. Don't hesitate to deal with them. I bought a number of items from them and zero complaints. If you stay with existing wheel it may or may not need to be re-dished. Reasonably simple to do yourself, but you could have it done, and re-tensioned for probably $20.00 at a LBS.

rustystrings61 

Velomine for the win here - sealed Formula hubs laced to Sun CR-18 rims, which will support wider tires nicely, all at a good price. The all black version appears to be out of stock but I bet it won't be for long. FWIW, I had been considering laced up a set of CR-18s to some hubs I have on hand, but I can almost buy a complete set of these for what spokes and rims will cost me.

IAmSam

OP, if you went to the page rustystrings61 linked, did you happen to look around Velomine and maybe notice that they also have single rear 27" track wheels, including one on the wider CR18 rim? If you haven't gone too far on changing your bike up yet - getting one of those would be probably be the simplest way to singlespeed your bike.

Or...

I think you may have already bought a geared rear wheel? Then please stop buying more wheels/sets you don't need or understand. You want to make a singlespeed, not fixed, bike right? Then just buy any of the myriad singlespeed kits out there on the google and throw it on that gearie wheel you may already have. Or...you could just buy some spacers & a cog, & save a few bucks.

Have fun, good luck...

Demet

Thanks guys, I ended up buying the the H Plus Son wheels recommended above. I could have just used the ones I already bought but I realized they were not made for the bigger tires I want, so they are on CL now. I already have new long reach calipers on the bike so I'm committed to the 700c conversion, for the little bit of extra room for my bigger tires. Going with 35mm Marathons, instead of the 38mm, just to be safe with fit.

Now trying to understand and find the right rear cogs - one freewheel and one fixed. Going to convert the chainring next so I know size and spacing... thanks for your help!

Demet

OK could use some more help if anyone has a moment. Have wheels and tires are on the way, and would like to order parts for the drive train. From what I understand I will need:

• Rear fixed cog
• Rear freewheel
• Chain

Can i reuse my existing chainring and crankset? I'll post pictures. Chainring is 52 tooth and is 46mm to the centerline of the bike. There is a 5mm gap between back of chainring/crankset and face of bottom bracket (see picture). And there's 6.5mm gap between protruding parts of the chainring and the chainstays. Should I get a shorter axle? It seems like 46mm is going to put the rear cog/freewheel way out there??

I wouldn't mind buying a new chainring/crankset if need be.


It's hard for me to understand how I will be able to position fixed cog and freewheel so that they line up with the chainring. I guess once the wheels get here maybe it will be more clear, but looking at the pictures it seems like the threads for the cog/freewheel are in a fixed position?

Wheels I ordered, asked them to space rear to 126mm: https://www.velomine.com/index.php?m...oducts_id=2099

Thanks for any help!

TugaDude

Here is a link where you can input all of the various information and determine the "gear inch" value for a singlespeed.

https://sheldonbrown.com/gear-calc.html

Notice too that the Sheldon Brown site has a section on singlespeed conversions and that will help answer chainline questions hopefully.

Chainline may not be as big an issue as some make it out to be. In a perfect world, you certainly want your chainline as straight as possible, but if using 3/32" chain it isn't as important as if you will be using 1/8" chain. The 1/8" chain is not as flexible laterally and wants to be in a straighter line. 3/32" chain is used with derailers and bends all over the place without causing issues so long as you don't "cross chain". So if you are using 3/32" chain, get it as close as practical, but don't sweat it too much.

I copied this for you from the website's page on singlespeed conversions.

"
You can check the chainline by installing the hub in the bike, with no chain installed. By placing your head just in front of the chainwheel, you can sight along the chainwheel and see back to the rear hub, to see if the chainwheel lines up exactly with the rear sprocket. If it doesn't, re-arrange spacers or change the bottom bracket axle as necessary. You might also hold a yardstick or other straightedge against the side of the chainwheel, reaching back to the sprockets.

• Except on a bicycle with vertical dropouts and a chain tensioner, the chain is adjusted for as little slack as possible without binding, by "walking" the rear wheel forward or back in the dropouts.
• Chainwheel choices can affect their longevity.
• Chainwheels also can often be centered to keep the chain slack the same as the cranks turn.

There is detailed information on these topics in our article about derailerless drivetrains."

Notice that Sheldon has a gear ratio calculator and what he calls "gain ratio" calculator. Worth pondering. He makes a good argument.

Demet

Thanks for this info. was very helpful and I've made a lot of progress. Have the bike running now, but need to adjust ratio. Currently have 52t chainwheel and 18t freewheel (which is White Industries I got of CL for a good price so would like to use it), and 165mm cranks, Might first try longer cranks, maybe 175, and see how that affects gear ratio. I like how much power I have when cruising on level ground, but starting from stop is a bit tough, would like to improve that a bit. Using Sheldon's calculator is really helpful, thanks again!

Philasteve

I don't think crank arm length would change much. If its hard to start from a dead stop or hard to get up hills, just buy a bigger cog.

TugaDude

You are welcome, glad it is helpful. A lot of people will use a smaller chain ring for the front. I generally will use a 46. Then after you've done that you can monkey around with the rear cog size. Freewheels are available in a variety of sizes, but good ones are spendy so going from one to another to another is prohibitive. White Industries is top-notch. Good pawl engagement.

I agree with the post about the cranks. I don't think the added leverage is going to help much. Also, if you ever choose to go fixed, longer cranks on a bike with a relatively low bottom bracket is potentially dangerous going around corners.

Demet

Thanks guys, well using Sheldon's calculator I get 6.0 'gain ratio' with 52t chainring, 18t freewheel and 165mm cranks that I have now. If I change to 175mm cranks I get 5.7 gain ratio, which seems to me like it would be a significant difference. The 6.0 I'm using now is not that bad, I don't need a lot more starting power, and I like that I can go fairly fast if I want to. I guess I should figure out if my BB is low, high or what!

If I change to 46t chainring, but keep 18t freewheel and 165mm cranks, I get 5.3 gain ratio. Wish I could try it easily, but I'm worried it will be too spinny?? Well, I'll figure it out and report back ;-) Thanks!

rustystrings61 

I got curious, and since I still think in gear inches, I went back and ran the numbers on Sheldon's calculator. If you run 700 x 38 tires with 46x18 gearing, that would give you a 69.8-in gear, which is essentially a 70-in gear. Just for a historical perspective, that's close to what was the stock FIXED gear on pre-built British bikes sold out of catalogs, with typically a lower single-speed freewheel on the other side of the hub.

F.J. Camm in his 1936 book Every Cyclist's Handbook recommended around 65 gear-inches for men for a single-speed road bike, 60 gear inches for ladies. This was for general road work, including club runs and long rides.

Demet

So i went with a 46t chainring and it seems to be a good fit., with 18t White Industries freewheel. Thanks for the recommendations everyone! Here's a pic from first ride yesterday. I was concerned about the fenders as they barely fit, but no rubbing as of yet. Not happy with the stem/handlebars yet. Not sure where I'll go with that but it doesn't feel comfortable quite.

Also a bit concerned as chainline is about 14mm out of alignment. New crankset is further out then old one. But it seems to work OK, no bad noises and chanin doesn't seem to want to jump off. I'm using an 1/8" chain. Should I be concerned?

ThermionicScott 

14mm is too much. Did you ever replace your bottom bracket? The new crank is probably designed for a shorter one.

I would level out that saddle, too. You're probably sliding forward on that thing.

Demet

Thanks, I'll look for a shorter bottom bracket, I can hear a little noise now for sure. And good call on the seat, I am slipping forward a bit! ;-P