fixed/fixed vs fixed/freewheel
 

I am working with my son to build a fixie. Wanting him to have flexibility.... I want him to go (and as I amy buying he will go ;) ) flip/flop so he has a choice.

What are pros/cons of going fixed/fixed and using bmx style cog/free wheel vs going fixed/freewheel?

Thanks from a C*V type dad with a soon to be fixei 13 year old

im not sure i get what you are asking, especially about the bmx style cog thing....


this might be something you already know, but here we go:
most fixed gear/singlespeed back hubs has one side you can run a freewheel cog, and the other side you can run a fixed gear cog held on with a lockring. these are called "flip flop" hubs because you can flip the wheel around to go from freewheel (coasting) to fixed and vice versa.

if your son is new to fixed gear, definitely make sure it has AT LEAST a front brake, and i would advise to have him get used to the bike first with the freewheel side then flip it to fixed once he is accustomed. and make sure if running fixed the peddals have foot retention.

Fixed/Fixed is the most versatile. You can set it up as:

1) Fixed/Fixed
2) Fixed/Free
3) Free/Free

And, yes, it's ok to mount a single freewheel on fixed cog threads, even though the freewheel threads are wider than the hub threads.

As to BMX (metric), the only "advantage" is that you can mount a freewheel with less than 16 teeth, however, that's mainly because BMX bikes have smaller wheels, which effectively lowers the gearing. You should not need anything less than a 16T freewheel for your son, and fixed cogs go all the way from 12T to 22T.

and TT does it again.

Beat me to it.

The 'fixed' thread has the smaller, left handed thread for the locking ring. The fixed/free hubs have one side with the fixed set up but only the right handed thread on the other.

As my esteemed colleague above mentioned, you can run a bmx cog on the fixed threading - there are enough threads there to do so, though if you're absolutely definite that you'll always have a freewheel cog on your bike, a fixed/free hub would be better because it's the correct part for the job.

However, if you get fixed/fixed, you can run anything you like.

You can run a track cog on a freewheel thread - you simply do it up really really tight and use a bb locking ring against it. These are called 'suicide hubs' because the locking ring, being on the same thread, isn't overly effective as a locking ring and excessive back pressure can spin the cog off (it's fun ... not btdt).

My tip?
Buy fixed/fixed - it's what's going on my Hillbrick ... but if you can't get it, you won't be sad with fixed/free because not many people flip the wheel around to use the other cog anyway.

Richard

I like to learn more about the difference between BMX flip flops and fixed/free flip flops.

I am considering a suicide hub on my 27” wheel or getting a (under $40) Redline BMX flip flop 20” wheel and build a new 27” or 700c wheel out of it on a frame with 130 mm dropout.

Do fixed/free flip flops have same diameters on both side, just a matter of left handed thread for the track cog and right hand thread for freewheel?

What about BMX flip flop, my impression is both sides are left hand (?) threads of different diameters? The seller says both sides appear to be the same diameter. Do they make a fixed/free flip flop for BMX? Are the 14 mm axle a different size than what I would need on the road wheel?

Do track cogs have left handed threads or it doesn’t matter as it’ll go on both left and right handed threads just depending on which direction you turn it?

Track cogs have right hand threads, just like freewheels. It's the lockrings that have left hand threads. Regular freewheels have the same thread size a fixed cogs (1.375" x 24 tpi), but there are some smaller BMX freewheels that have 30mm x 1mm threads.

I don't know if this will help at all, but it goes a little like this:

Your flip/flop hub has threading on both sides, one for a fixed cog and lockring and the other side for a freewheel.

The fixed side looks like this (this is looking rearward, drive side is left)

__-----[|. the "_" are reverse threading, the "-" are normal right handed threading and "[|" is part of the hub the spokes connect to.

The track cog goes on the "---" and the lockring goes on the "___".

The free side is similar, but it's just

-----[|. again, "-" are right handed threads, and [| is part of the hub the spokes connect to.

I'd say grab the fixed/fixed Hub, like they have said you can run a freewheel if you want. And if he ends up being a fixie kid he'll enjoy having 2 different ratios if he absolutely needs them. I'm enjoying having 2 different fixed cogs right now. I got a 16t and 17t.

Thanks to Cash36 for the explanation of the fixed/free hub.

What about the BMX flip flop, does it have reverse threading on both side for the lockring?

As there are 2 sizes of axles for BMX, the 14mm axle will not fit the dropouts on a road bike dropout. Is there a way around it?