Gearing my bike questions
- Thread starter twister
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That seems pretty low geared to me. (as in pedal fast and not go fast)
I like to base my gear choices off of desired top speed and top cadence (pedal speed) Try this link for example.
http://www.machars.net/bikecalc.htm
I entered 25 tooth chainring and 9,10,11,12,13,14,15 for the rear to see what the results for all of the options would be. It looks like with your gearing at 75rpm you would be doing 17.2 mph. to lower your top speed to 14.1 and accelerate more quickly use 25X11.
25x12 would slow you down to 12.9mph at 75 rpm.
It is a fun calculator.
I had an old scrambler that would wheelie with almost no effort. It was 36 front 20 rear. I actually hated it and geared up for more speed. 36 front 20 rear on a 20" rim is about the same as 25x17 on a 26" rim.
I used this calculator to pick the gearing on my track bike. 48x13 on 700c at 85 rpms give me 24.6mph. That is about as fast as I like to cruise rpm-wise.
I like to base my gear choices off of desired top speed and top cadence (pedal speed) Try this link for example.
http://www.machars.net/bikecalc.htm
I entered 25 tooth chainring and 9,10,11,12,13,14,15 for the rear to see what the results for all of the options would be. It looks like with your gearing at 75rpm you would be doing 17.2 mph. to lower your top speed to 14.1 and accelerate more quickly use 25X11.
25x12 would slow you down to 12.9mph at 75 rpm.
It is a fun calculator.
I had an old scrambler that would wheelie with almost no effort. It was 36 front 20 rear. I actually hated it and geared up for more speed. 36 front 20 rear on a 20" rim is about the same as 25x17 on a 26" rim.
I used this calculator to pick the gearing on my track bike. 48x13 on 700c at 85 rpms give me 24.6mph. That is about as fast as I like to cruise rpm-wise.
That would be in the seventies, gear inch wise. Doesn't seem like a low gear to me, that's on the high end of the scale as far as production line single speeds. Equivalent to one of the old tanks with a 50t drive ring (25 for 1"pitch) and 18 (1") out back. Good when you've got momentum, rough going upgrade. If you use it for general riding and take-off is the only problem, I would start with a small change, 'cause you lose distance with a lower gear. Stunt riding is a whole different ball game.
Depends on the riding purpose I guess. I was never real serious into bmx stuff. I tried skate park stuff and actual bmx racing a little. Deorman is right about it being in the 70's gear inch wise. looks like 77.3. The scrambler I referred to was 39.3 gear inches when I first got it. Mad acceleration to 12mph or so.
Yeah the "classic" bmx gear is in the neighborhood of 55"; the old-school standard was 44x16, and the trend as time went on was towards a smaller drivetrain for grinding clearance; incidentally, 25x9 is a very similar ratio to 44x16. To get similar gearing on a 26", you need to run something more like a 44x20 or 44x22--- or 25x12 with more moden micro-drive components. It seems to me that whoever designed your bike geared it like it had 20" wheels, and didn't take into account that the 26" wheels would give it a higher final drive.... As it stands today in bmx, 25x9 with 20" wheels is pretty much standard...
I thought you'd bought a Fairdale Taj, which their site is showing to be a 31x13 (still high in my opinion, at 63") with a metric-threaded freewheel (boo!)... Depending on what hub your bike has, it may be a pain to switch from what is almost certainly a driver (9t rears are always drivers, as far as I know) to a cassette-type that will take a 12t cog--unless you switch out the rear hub. And, more than likely, it's going to be impossible to find a front sprocket under 22t.
Let us know what rear hub you got, and we can see what your options are for putting something bigger out back. Worst case scenario, if you end up with a 22x9, that'll be around 63.5"--- still high for bmx and jumping dirt in the caverns, but about 10" lower than where you stand now....
72.5" or so, depending on what size his tires are....
Cool. Easy fix. Get yourself a 28 or a 25t front sprocket, and move on with your life. 
My bomber had 44 front and 20 teeth on the rear coaster brake.
With 26" wheel, math was 44tooth/20tooth=2.44 wheel revs per crank rev x 26"=63.44 gear inches. Kinda hard to start out.
Changed front sprocket to 32 tooth (from kids 20" bike) now works out to - 32tooth/20tooth=1.6 wheel revs per crank rev x 26"=41.6 gear inches.
Pedals much easier from start.
From the net:
Mtn bike gearing Steep hills 17-20 gear inches
Technical trails 17-20 gear inches
Dirt roads 20-27 gear inches
With 26" wheel, math was 44tooth/20tooth=2.44 wheel revs per crank rev x 26"=63.44 gear inches. Kinda hard to start out.
Changed front sprocket to 32 tooth (from kids 20" bike) now works out to - 32tooth/20tooth=1.6 wheel revs per crank rev x 26"=41.6 gear inches.
Pedals much easier from start.
From the net:
Mtn bike gearing Steep hills 17-20 gear inches
Technical trails 17-20 gear inches
Dirt roads 20-27 gear inches
@27" on a dirt road, you'd be going less than 5 mph at 60rpm. That seems extremely low, to me. Why spin so hard to go so slow? I ride singlespeed offroad a lot, and i sually shoot for somewhere in the neighborhood of 50" gears.... somewhere between 48" and 52", usually.
