Gear inch/ratio question

I've just changed to 48 x 18, more comfortable for fixed than the 48 x 16, which was perfect for single-speeding.

i'd reccomend 44:16, itd about perfect for the town.
44:15 was tempting

15T is a weird size though.

dogsballs 15T is a weird size though.

Not as weird as 15.5 T

49x18 on one, 48x19 on the other. i still need to take some effort on spinning faster on the 48x19 but i do really like it, and it's on my conversion frame so it rides really comfortably. the other one is the track frame more like blasting around.

i really liked 48x18 but i'm loving the skid and it gives you only 3 patches. that's why i changed it over to even-odd.

edmundane i really liked 48x18 but i'm loving the skid and it gives you only 3 patches. that's why i changed it over to even-odd.

Is that voodoo fixie-maths? It may work as a general rule of thumb, but it's a bit cargo cult. A hypothetical 60-15 would have only one skid patch, despite being even-odd. By contrast, my 49-19 gives 19 skid patches*, and that's odd-odd.

• Or would if I did skid. Which I don't.
  

Yeah and 53x18 has 18 patches..

Check out these easy to read tables and get that 17T on the back! :)

http://www.fixed.org.au/2006/11/

leeww [quote]dogsballs 15T is a weird size though.

Not as weird as 15.5 T[/quote]

Weird how? Riding a bike without gears and freewheel with only one brake on the London streets when a hundred years of bicycle development have given us the option of a chainring and sprocket combination for every conceivable occasion...

That's fucking weird.

The Rule is:
If you have the ratio ie mine 44:16, and you divide it down to the smallest possible divisible fraction, then you have the potential numbe of skid patches.
SO 44:16 = 11/4, so 4 possible skid patches.
17 doesn't divide by anything. that is why it is good for your tires (17 skid patches possible).
I would change to 15, which would give me 15 patches, but i love the ratio as it is.

running 48x18 with a half link, normally would be 3 skid patches, seem to have the right length of chain because now got 17, and i like the 72 inch.

I don't know how to compare gear ratios to each other. I'm rather confused.
I use 46 on the front and 16 on the back and its pretty hard to brake, and hop about and skid, without yanking quite hard on the bars.
I tried my friends yesterday and he has 48 on the front and 19 on the back, and his bike was so easy to ride. It was way more fun and I really preferred it.
So here's the question: if I want to change my bike so it rides the same as his, do I need to replace the chainwheel as well as the rear sprocket? I can't really afford to do this right now.... Or can I just replace the rear sprocket with a different one which will work in a similar way? If so, how many teeth do I need?
How do you work this stuff out?

gear inch!

I think changing to a 17t sprocket on the back is a cheap step in the right direction.
Someone is gonna start talking gear-inches now:
EDIT - too slow again! 17 is a prime number which is also a nice thing.

If you go 46x18 you'll be about 67.5"

You're mate's 48x19 is about 66.7"

That's close enough not to notice the difference.

And as a bonus, in 46x18 (on 23mm tyres) 80rpm is 16mph, 90rpm is 18mph, 100rpm is 20mph, etc...

PS. You're currently riding about 76"

Thanks for that. Out of interest, how did you calculate that? What maths are involved?

Here is a quick-n-dirty relative comparison of gear ratios:
48/19 - 2.526 - your deam bike
46/16 - 2.875 - you now
46/17 - 2.705 - in - between chooice
46/18 - 2.555 - 18th cog is the cheapest way to get a feel similar to your friend.

Damn too late

you can use this gear inch calculator to figure out the ratio, better to change the rear sprocket, the only problem might be finding on big enough to get a similar gear inch

46:16 = 77 gear inches
48:19 = 68 gear inches

so you'd need

48:18 = 69 gear inches

so swap out the 16 for an 18 and you should be coolio

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

juliettyspaghetty Thanks for that. Out of interest, how did you calculate that? What maths are involved?

I use chainwheel divided by sprocket multiplied by wheel diameter (nominally 26.4" for 700C, or thereabouts).

This gives you the gear ratio - if you multiply this by pi, you get the distance travelled per complete pedal revolution.

Trust me, 46x18 is what you want, and it's also a magical gear that lets you ride up Ditchling Beacon 3 minutes faster than everyone else :p

yep, 46 x 18 , i agree

easier maths (though less info revealed):
divide chainring teeth by sprocket teeth.
your ratio - 46:16 = 2.875, your pedal one revolution, your wheel moves 2.875 revolutions. smaller end result means easier to pedal.
46:17 is nice.
as a side note, if you can get prime numbers into the mix you get more skid spots.

BringMeMyFix [quote]juliettyspaghetty Thanks for that. Out of interest, how did you calculate that? What maths are involved?

I use chainwheel divided by sprocket multiplied by wheel diameter (nominally 26.4" for 700C, or thereabouts).
[/quote]

[nerdmode=on] This actualy gives you the equivalent diameter of the front wheel of an ordinary (i.e. penny farthing) bicycle. [/nerdmode=off]

.

I'll meet you in the midday sun - bring your mad dog and your neanderthal gear ratio...

As well as 46X18 you could get pretty much the same result with 40X16 so now you have the dilemna as to which to change.

The rough and ready gear calculator is BIG divided by LITTLE multiplied by 27 (nominal size of 700 wheel).

Good luck.

my brother rides 46x16 and you don't want to end up with legs like his. 46 x 18, as others have suggested, would be a pretty good gear and will make skidding nice n easy