# BMX vs Mtn cranks for ss need help



## J Ro (Jan 13, 2004)

Greetings, I am building up a new bike that will be used for DJ and urban riding. I want to have it as a single speed. I see all these new bikes using the "micro gearing" and was wondering if I should attempt to go lower than 32 X 18 that I currently ride. I plan on using the rear hub I already have which is the standard mountain (shimano non singlespeed) freehub so, what is the lowest cog I can run? I like the look and burliness of the BMX cranks and I see that can can go lower than 32 in the front if I run the BMX cranks. 

I was thinking of running the BMX cranks with a 30 ring up front and either 18 or 16 in the rear. 

Also,I am new to the whole BMX sprocket system. I see ones that have a hole the bolt on the sprocket goes thru to attach to the crank arms ans others look like they have no such whole? I was thinking of running the FLy Racing cranks but am unsure which style of sprocket use as they come arms and bb only?


----------



## J Ro (Jan 13, 2004)

Here are the style cranks I was looking at.


----------



## jaykay (Jul 1, 2010)

If you are using a Shimano type cassette hub as you say, the lowest cog you can run is 12t. Shimano only go down to 14t though (DXR), so you'll have to use another brand such as Redline etc. if you want to go lower than 14t. 12t is pretty weak though so I wouldn't recommend it!

As far as sprockets go, I am not totally sure as I've never used that crank - but it seems that Tree and Animal sprockets will fit. Really, you just need to know the spindle size. By looking at the cranks, they look to use a bolt-on sprocket, but if the spindle is splined then you just need to find sprockets with a matching spline count and diameter :thumbsup:


----------



## cmc4130 (Jan 30, 2008)

J Ro said:


> Greetings, I am building up a new bike that will be used for DJ and urban riding. I want to have it as a single speed. I see all these new bikes using the "micro gearing" and was wondering if I should attempt to go lower than 32 X 18 that I currently ride. I plan on using the rear hub I already have which is the standard mountain (shimano non singlespeed) freehub so, what is the lowest cog I can run? I like the look and burliness of the BMX cranks and I see that can can go lower than 32 in the front if I run the BMX cranks.
> 
> I was thinking of running the BMX cranks with a 30 ring up front and either 18 or 16 in the rear.
> 
> Also,I am new to the whole BMX sprocket system. I see ones that have a hole the bolt on the sprocket goes thru to attach to the crank arms ans others look like they have no such whole? I was thinking of running the FLy Racing cranks but am unsure which style of sprocket use as they come arms and bb only?


30/14 would be a more normal BMX gear ratio, because the "classic" bmx gear with 20" wheels was 44/16. 44/16 X 20" = *55 gear inches*. . you can go a little more or a little less, but that's the standard. typical microgear setup is 25/9. 25/9 X 20" = 55.5 gear inches. most bmx'ers would consider 32/16 X 26" (or 52 gear inches) to be a little too spinny.

the most popular after-market cranks in bmx are Profile. http://www.profileracing.com/ . you can run the regular bmx cranks on an mtb . . . but if it is a euro bottom bracket shell that is wider, then you need to buy the 6" spindle (rather than 5.75" spindle).

the hollow chromoly spindle comes in 6" for mtb:
http://www.profileracing.com/estore/product.php?productId=343&categoryId=20 it's a great way to lighten up your crankset.


----------



## J Ro (Jan 13, 2004)

Thanks for the quick replies. 

One other concern I had was thickness between the front and rear rings. Do I need to be concerned about using different thicknesses? I see some BMX Sprockets that look super thick. Will they work OK with say a WTB or Dimension brand rear cog? Would I need a different chain?


----------



## cmc4130 (Jan 30, 2008)

J Ro said:


> Thanks for the quick replies.
> 
> One other concern I had was thickness between the front and rear rings. Do I need to be concerned about using different thicknesses? I see some BMX Sprockets that look super thick. Will they work OK with say a WTB or Dimension brand rear cog? Would I need a different chain?


I don't know the specific answer as to those cogs . . . but I do know that there are different size chains and there can be some compatibility issues between mtb cogs and bmx chains.... Check out empirebmx.com re: chains typically used for bmx sprockets:

https://www.empirebmx.com/store/empire_SupplierCategoryProducts.asp?idCategory=1006

Then look up your WTB/Dimension cog.

What frame and fork are you building up and what hubs/wheels are you using?? If you're talking about switching over everything (except cranks) from an xc bike . . . . you may be better off looking at complete dirt jumpers.

Something like Atomlab or Halo complete dirt jump wheels might be worth the investment:
https://www.bti-usa.com/public/category/WH/WHMD/AL

https://www.atomlab.com/storehubs.html


----------



## jaykay (Jul 1, 2010)

J Ro said:


> Do I need to be concerned about using different thicknesses?


You don't have to worry at all. Even though some sprockets are way thicker than others, usually the teeth on BMX style SS sprockets are made for a 1/8" chain. So you just need to make sure your rear cog is also 1/8".

In all honesty I've mixed this stuff up in the past when I haven't had the right spares and have run a front 3/32" sprocket and a rear 1/8" cog and a 1/8" chain with no problems - probably not recommended for long-term - but it works just fine


----------



## J Ro (Jan 13, 2004)

This is the the combo I am considering. According to the The Tree Fort Bikes website the cranks come with a euro shell 68 bottom bracket.


----------



## gbosbiker (Mar 10, 2009)

you probably already made your choice on cranks but i run 25-11 and its perfect for me. i run bmx cranks as well


----------



## Demo-9 (Mar 24, 2006)

Personally I love Profile cranks and Profile splined chainrings. I would highly reommend that combo. The Profile splined uses the same inner spline interface as Tree does. The cranks are indestructable, simple and easy to put on. I love my set-up. Curently running 25/10 on 24".


----------



## J Ro (Jan 13, 2004)

Thanks for the additional replies. 

I chickened out and went with mountain cranks vs BMX cranks because I was concerned about the spindle being long enough. 

I post pics of the bike later. :thumbsup:


----------



## tim_w_sage (Jun 3, 2011)

Another vote for the profile setup. The spline drive is sweet.


----------



## jaykay (Jul 1, 2010)

Damn, that's a bummer man. I much prefer BMX cranks over MTB cranks - for no other real reason than the amount of abuse they can take. I'm biased though, I started on a BMX and my fav ride is still a BMX so I've been using BMX cranks for a long, long time.


----------



## cmc4130 (Jan 30, 2008)

jaykay said:


> Damn, that's a bummer man. I much prefer BMX cranks over MTB cranks - for no other real reason than the amount of abuse they can take. I'm biased though, I started on a BMX and my fav ride is still a BMX so I've been using BMX cranks for a long, long time.


agreed. all i said is get Profiles, but order a 6" spindle from Profile. it's that easy. but i'll keep an open mind. lots of different cranksets are probably rad.


----------



## Dekes (Jan 3, 2007)

Get a wide base cog in the back like chris king, surly, wtb, on one, ... etc.


----------



## Dr boo boo (May 28, 2007)

Is it better to run an outboard bearing bottom bracket or the standard euro bottom bracket with the profile cranks? They will be going on an NS Subrban.


----------



## Kid718 (Jun 26, 2011)

New guy here...first post. I am here to learn about DJ bikes...but bmx I know about. I am about 250 lbs, and have been thrashing on profiles for a long time. Never cracked one. I currently run the spline drive profile set up on a 24" cruiser I have, and it's fantastic. Cannot recommend it enough.


----------



## cmc4130 (Jan 30, 2008)

I know this is an old thread, but just came across it again.

Here is a visual depiction of why a person may need a 6 inch spindle if he is putting a BMX crankset on an MTB.

Profile BMX gives the option of buying a 6 inch spindle. Most BMX cranksets use something a little shorter, like 5 5/8" or 5.75".

The issue is not so much the width of the bottom bracket shell, in this case 73mm on the Black Market Mob vs. 68mm on a typical bmx. The issue is the chainstay width.

Because Mtb's have wider spaced rear hubs, they often have chainstays that are set wider. Therefore the crank arms have to be spaced wider to get clearance. If you run a typical BMX spindle, you won't be able to space the crank arms wide enough (unless they're barely hanging on) to get clearance with the chainstays.




























Look how much narrower the chainstays are on this Liquid Feedback 24" BMX:


----------

