Is there a significant difference between a 47 and a 49 tooth chainring?
 

I am having trouble deciding which one to get, I live in NY, so it is mostly flat, If i were to end up with a 47t chainring because it was given to me, would I notice a difference, could this be adjusted by switching to a different rear cog?

http://www.gear-calculator.com/#

Put in what you are riding, and what you are looking at to get a general idea of what you are up against. I particularly like the MPH @ cadence option.

Noticeable but not big.

If you do skid stops, the 47T ring may give you more skid patches (47 is prime, 49 is not), depending on your rear cog.

47 is far too low, you'll never be able to go fast enough.

49 is far too high and will destroy your knees.

48 is perfect for everything.

:p

Yes, changing the rear makes a difference, more than the front (per tooth).

+1 on everything ^^^^

well wouldn't 47/15 be okay then? I am running 48/17 right now, but the only two choices i have for the chainring i am getting is 47 or 49

You need to read up on gearing. 47 x 15 is a much much much higher gearing than 48 x 17.

nah man

No.

Increasing the number of teeth on the front has the opposite effect of increasing the number on the rear.

If you like your current gearing, changing one tooth on the front makes a very small difference. Changing the rear by one tooth makes a greater difference. You wont be able to achieve the exact same gearing if you change the front by only one, because any change to the rear (in an attempt to compensate) will go beyond.

okay, thanks

play with this:

BikeCalc.com - Bicycle Gear Inches Chart

The time honored way to compare gears is in "inches", ie convert your gearing to the equivalent wheel of the old-fashioned high wheeler. The bigger the wheel, the further you go with one pedal revolution and the faster (up to a point). Hence all high wheel racers were tall (they could straddle bigger wheels).

The math is simple. Divide your chainring teeth by the cog teeth and multiply by 27 (for normal 700c wheels). You can get picky and measure the exact diameter of you wheel. I never do, Life's too short.) So:

47-17: 47/17 X 27 = 75" (No need for decimals here. Your legs can't tell.)
48-17: 48/17 X 27 = 76"
49-17: 49/17 X 27 = 78"

47-15: 47/15 X 27 = 85"
48/15: = 86"
49-15: = 88"

I rarely ride higher than 72". Even in my mid-season racing days many years ago, 76" was about my max. I do have a fixie with a drop long enough to screw on any cog and I have been known to do major descents in 42-12 (= 95"). Now that's fun! But back on the flat? I stop and flip the wheel around. back to the 17t.

Ben

here are some gear charts 47 v 49 and 47, 48, 49
http://bikeforums.net/attachment.php...hmentid=419437http://bikeforums.net/attachment.php...hmentid=419436

I ride 49-19 and have 49 skid patches.

edit: this might be wrong, I am now confused, and don't have the will to figure out if my memory is wrong .

You are indeed wrong. You have 19 skid patches, not 49, but then again what makes you think the OP even cares about skid patches ?

I wear size 12 shoes and have 12 walk patches, so this sounds about right.

38 if you're ambidextrous.

24 walk patches

smaller the rear cog the more pronounced change in ratio.

if u care about rear cog tooth engagement (transmission of power via roller chain), then sizing your front ring as small as posssible is your best choice.

Nope, I only walk using one foot.