Gearing

was thinking of doing the same, when i get a new crank.

hippy I lost to a roadie today. The shame. I totally blame it on my lack of inches.. my gear inches, gutter-minds!
42/16 or 42/18 or whatever the hell the freewheel is means I kinda loose going downhill. Then I got every light into the city.

tut tut tut...

I've never lost to a roadie. Then again, there aren't that many people on bikes in Basingstoke anyway!

You've never raced me.

I'm allowed to lose to roadies because I am one (a pretend one, but one nonetheless)

You'd probably kick my arse in a race, hahaha :)

I rarely do long rides (I wanted to do more in the "summer" but the weather has been rubbish) and only ride 4 miles to work :)

eeehhhh only ride 4 miles to work :)

Yeah, 8 minutes is barely time to warm up ;-)

I'm knackered now, so you might beat me.. but only if you leave Bulmers bottles in strategic locations to distract me..

I need to pick a gear ratio for the condor. The ratio on my current ( geared) bike that i seem happiest with is 50:17.

I've ridden 48:18 when i've tried out other SS/fixed bikes, and that also seemed fine.

any advice? is 50 :17 a good thing to try, or is there a reason why most people have 48 or lower on the front?

i love my 50:17

k, that's one vote then!

is 48 :16 the same ratio? my head is getting confused

on my soma I was 50:16, which suited me as I don't really like spinning heresy I know, but there you go, and I'd just ride in that gear all day long, thought it might be a bit big for fixed as I wouldn't have the coasting breaks so went 48:16 smaller, but more manageable, still a bit nervous dinking in and out of traffic and filtering really slowly can be a bit of a pain - only been riding fixed for a week so hopefully with time I'll feel more secure, friend whose been riding fixed for a couple of years is on i think either 48:18 or 46:18, says it gives him better slow speed control.
my tuppence is get a gear slightly smaller than what you turn on the geared to allow for the lack of ability to coast, ie rest legs.

yeah, that seems sound.

but what i would like to understand better is : what is the practical difference between 48:16 and 46:18? if ti's the same ratio, why choose one over the other?

i use 48x18, seems good around and in town

nimhbus yeah, that seems sound.

but what i would like to understand better is : what is the practical difference between 48:16 and 46:18? if ti's the same ratio, why choose one over the other?

they aren't the same ratio

best to try a gearing calculator, this isn't the one that I used but it seems good enough

http://www.bicyclesource.com/bike/gear/gear-javascript.html

ah, you're right!

cornelius blackfoot best to try a gearing calculator, this isn't the one that I used but it seems good enough

http://www.bicyclesource.com/bike/gear/gear-javascript.html

cheers..

personally i find easier just to divide 48 by 18 to find the ratio, makes a bit more sense in my head for some reason!

anyone tried a Golden Ratio gearing? 1.618 :1 ?

50:31 gets close...

dividing 48 by 18 won't get you the ratio

(chainring x 27*) / sprocket = ratio

*27 if you have 700c

yes it will.

48 divided by 18 is 2.6

the ratio is therefore 2.6:1

am i wrong?

I really like this calculator. It shows you ratios, inches, speed/rpms, skid patches, and equivalent gears, while taking into account crank length, wheel size, and whether or not you can skid both ways...

yeah, that's really good! cheers!

yeah thats the one I was looking for, obviously I didn't look that hard.

glow dividing 48 by 18 won't get you the ratio

(chainring x 27*) / sprocket = ratio

*27 if you have 700c

Not exactly. If you have a 700C with a 28mm wide tyre, it's more like 26.7 (lower gear - easier to spin)

nimhbus yes it will.

48 divided by 18 is 2.6

the ratio is therefore 2.6:1

am i wrong?

It all depends on the size of the wheel/tyre combo.
A ratio of 2.6:1 with a 26" wheel is going to be easier to spin than the same ratio with a 700C x 28mm.

A couple of examples:
[ulist]
[li]26" x 1.5 @ 48:16 = (25 x 48) / 16 = 75 gear inches (tyre circumference is 25" despite being labelled as 26" nominal size)[/li]
[li]700C x 28mm @ 48:16 = (26.7 x 48) / 16 = 80 gear inches (tyre circumference is 26.7)[/li]
[li]700C x 20mm @ 48:16 = (26.1 x 48) / 16 = 78 gear inches (tyre circumference is 26.1)[/li]

[/ulist]

Theres an Excel spreadsheet to accurately work out your gear ratios, a spoke length calculator, tyre sizes and others here: http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3504

I now use 49:18 which is fine for me.

I started off with 42:16 though, then went 43:16, then 49:18. If it's your first time fixed then I reckon it's best to err on the low side to start with. Also depends on how flat your regular routes are.

to find your wheel diamiter
700 cc rim = 622 mm

add tyre width x 2 (because tyre tend to be square

divide by 25.4 (mm in an inch)

e.g

for 23 mm tyre on a 700 cc wheel with a 48 x 16 your gear inches will be

(48 / 16) x ( (622 +(2 x 23) )/25.4 )

Try and use sproket with idealy a prime number of teeth or a sproket chain ring combo with as high as possible lowest demnomiator when the fraction is simplified to maximise skid patches. Clearly not a concern if you don't skid.

There is a mental person out side my window so I ust go now.