Fixed Gear Conversion Done Right

By interestor on 06/20/2009. Bike tags: Fixed gear

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Frame / Size / Year:
Motobecane Mirage

Handlebars / Stem:
Bontrager Crowbar chromoly racing stem

Fork / Headset:
Oh, the latest and most fashionable headset

Front Wheel / Hub / Rim / Tire:
27"

Rear Wheel / Hub / Rim / Tire:
27"

Crankset / Bottom Bracket:
Motobecane with Shimano UN-71

Saddle / Seat Post:
Bianchi saddle, Drive alloy post

Pedals / Chain:
Specialized sealed pedals, wide chain

Gearing / Chainring / Misc.:
46 16

Notes:

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.

Solid
brianmillerhotrodding.com

People who friended this bike CONDENADO

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Pretentious much?

Submitted by proudxvxyouth on 07/20/2009.

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.

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Hostile

Submitted by interestor on 07/20/2009.

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.

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what's the seatpost size?

Submitted by evotion on 07/07/2009.

what's the seatpost size?

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Post

Submitted by interestor on 07/20/2009.

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.

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buy a trackbike

Submitted by marcusindenco on 06/24/2009.

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

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It's still a conversion, a

Submitted by simonweiss on 06/24/2009.

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

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If the title of this bikes

Submitted by wes m. on 06/20/2009.

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.

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^ +1

Submitted by mmm_pancakes on 06/20/2009.

^ +1

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+1 on your username, mmm ...

Submitted by gelpicorp on 06/21/2009.

+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.

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huh?

Submitted by gelpicorp on 06/20/2009.

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.

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done right?

Submitted by HipsterGary on 06/20/2009.

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

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Busted

Submitted by interestor on 06/24/2009.

Yeah dammit. Very imperfect.

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1"?

Submitted by joshua on 06/20/2009.

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

0.314960"

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.

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Height

Submitted by interestor on 07/20/2009.

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.

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even less

Submitted by latron on 06/20/2009.

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. :)

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Thanks.

Submitted by joshua on 06/20/2009.

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.

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My only guess

Submitted by latron on 06/20/2009.

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....

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Fair enough.

Submitted by joshua on 06/20/2009.

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.

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Wheels

Submitted by interestor on 06/24/2009.

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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Fixed Gear Conversion Done Right