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Fixed Gear Conversion Done Right

Bike tags: Fixed gear
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Motobecane Mirage

Bontrager Crowbar chromoly racing stem

Oh, the latest and most fashionable headset



Motobecane with Shimano UN-71

Bianchi saddle, Drive alloy post

Specialized sealed pedals, wide chain

46 16

Here is a vintage Motobecane Mirage fixed gear conversion. This has proper sized 27” semi aero rims with a fixed hub. These have even less rolling resistance than the smaller 700c wheels.

How many times have we seen dangerous “fixie” conversions with all kinds of corners cut? One of the most common fatal errors that the inexperienced make is to put 700c wheels on an old 27” frame, dropping the bottom bracket half an inch. These damned fixed gears are hard enough to force through a sharp corner. Dropping the ever-moving pedals even lower is a big sacrifice to make for style.

This old French frame has a new sealed cartridge bottom bracket and new aluminum BMX racer seat post. Those Specialized sealed ATB pedals are remarkably smooth strong and light.

Crank story: I put a new cartridge BB of the correct length, not realizing the new FSA crankset I have would be pushed out too far. Whoop. So I had to reuse the stock crank, which is quite light and good. I put the FSA chainring in the inside position. Actually, I think it turned out well.


People who friended this bike CONDENADO, BananaNinja


WTF How did I attract all the mouthy pussies to criticize this old bike. It is like there is some gay mafia who specifically advocate wrong sized wheels on old conversions. I have upset them

Here we have stylie posers concerned that my quick release doesn’t look like an actual track bike. Asshole, you think I’m going to race this thing, oh right, you are only concerned with the style.

I just made this clunky old bike more fun to ride. I sought and found the correct sized wheels. Maybe I should paint one orange to satisfy these readers.


Well, the rear wheel's position in the dropouts, the extra chainring, and the awful stem covered in rust lead me to believe that you cut corners as far as componentry is concerned. Also, your inability to compare drivetrain componentry and your surprisingly tenacious drive to increase the difference in size and rolling resistance between 27" and 700c wheels lead me to the conclusion that you also cut corners when learning about these bikes.

With a setup like that I highly doubt that you're doing ANYTHING fast, much less taking corners at speed. I doubt that BB height is a major concern.

I'd be more worried about adjusting your saddle and working on bike fit.

A major concern

Thank you for your useful reply. It is very important to criticize a rider’s axle position and stem finish.

Though I am having a hard time understanding what you mean by “drive to increase the difference in size…”, I am glad you have made that asinine conclusion. Demonstrating your poser attitude definitely clears up how much credence one might give to your opinions.

And attempting to insult my speed ability is a bold hater’s technique; and especially relevant considering that cantankerous hacked together ancient fixed conversions are well known for their high speed capabilities by jack asses like yourself.

Additionally, it is valid that you are concerned with my bike fit.


Thanks. Actually, I like to align the recommended air pressure mark with the valves on my bikes.

Pretentious much?

I'm pretty sure the quick release on the front wheel of a fixed gear could be considered to be a cut corner.

Throw in a half link on that chain, too. It would uncut another corner.

As someone else has stated before me, a fixed gear conversion is one giant cut corner.

I do have my own conversion with 700c wheels that I ride quite regularly and as long as I pay attention, pedal strike is never a problem.


Nice. You pretentiously nit pick my bike, then admit you ride a low performance show bike yourself. Nice balance.


Yeah, I am surprised at all the hostility here. The "done right" tag is really in response to all the crappy dangerous conversions I see on the street here in Brooklyn. Most of the bikes I see on Velospace are top quality customs.

what's the seatpost size?

what's the seatpost size?


That seatpost is 25.4mm. There are a lot of bmx racing posts available, even carbon fiber. That aluminum one really lightened up the top end.

buy a trackbike

muuch2 do over nothing.congrats on yer sweet turn down the suck.

It's still a conversion, a

It's still a conversion, a bag of suck.

If the title of this bikes

If the title of this bikes page was fixed gear conversion I dont think anyone would bust your balls. Putting the "done right" on a fairly standard conversion bike... doesnt quite make sense to me.

^ +1

^ +1

+1 on your username, mmm ...

+1 on your username, mmm ... made me fire up my gridle.

yeah, my thoughs exactly on the title. it probably would offend pretty much everyone on here. i have a schwinn who is waiting on her 700c wheels. but i'm not offended, and i still think it's a nice looking bike.


isn't hacking a multispeed bike frame into a SS/FG track bike sort of cutting corners on the whole? why not just get a purpose built track bike. oh well. i like old lugged steel bikes. if it is repurposed and ridden, then that is the important thing.

done right?

you sure did "cut corners" on the cranks tho.


Yeah dammit. Very imperfect.


A 27" rim has an ISO width of 630mm, while a 700c wheel is 622mm. That works out to...


Putting new 700c wheel on a 27" frame isn't dangerous nor is it cutting corners, and lowering your bottom bracket about the width of a pencil isn't going to make you crash.


Your theoretical calculations are impressive. However taking a measuring tape to the two different wheels with tires reads .49". I already have to be careful with cornering; it is bad enough riding a conversion with the low road bottom bracket versus a proper track frame with a high bottom bracket. But putting 700c wheels in a 27" frame drops it too much and you will crash if you like to take fast corners.

even less

The rim diameter difference is 8mm, but that's only 4mm difference in radius -- 0.15748". I just measured a pencil width and got 0.28". So, about 56% of a pencil width. :)


I forgot to account for the fact that we're talking about radius here. That makes the 1" claim even more absurd.

I'm also a little unsure how he figures that his 27" wheels have lower rolling resistance than an equivalent 700c wheel.

My only guess

is that a larger diameter wheel will turn more slowly for any given speed. That's not rolling resistence but less "drag," perhaps. Given the fractional difference between 27" and 700c, however....

Fair enough.

Decreased rotational mass is certainly not the same thing as lowered rolling resistance, though.

If lower rotational mass is what he is after, then given the relative scarcity of good 27" tires and the virtual disappearance of high-quality 27" rims from the marketplace, your rotational mass will likely be higher than a comparable 700c wheel due to increased material weight. But since I don't know anything about these "semi-aero" rims, so I can't speak with real certainty on that - they may be lighter than a fart.


27" wheels do have more material and are heavier, unfortunately. Negatively affecting acceleration and deceleration - very important aspects on a fixed gear. = rotational mass

A larger diameter wheel will roll over street imperfections easier than a smaller wheel, and keep its forward momentum better. = rolling resistance

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