Help me understand gearing
 

Sorry, I just don't get it. My bike came with 42 and 16 teeth. Its too easy to pedal once I get rolling. If I want to go faster I'd have to pedal faster than I physically can. So, do I need more or less teeth in the front or the rear. The simpler explanation the better cause I don't understand all the gear mathematics I've been reading.

More teeth in the front and/or fewer teeth in the rear will give you a higher gear. Rear cogs are generally less expensive than front chainrings. Make small changes, especially if you're changing the rear cog: a one tooth change in the back makes more of a difference than a one tooth change in the front.

gear ratio.

simply divide the front by the rear.
A higher number is faster at the same rate of spinning.

42/16 = 2.625 <- what you have now
44/16 = 2.75 <- faster
42/15 = 2.8 <- faster than 44/16

however, after a certain point, the engine, you, can no longer spin the cranks at a good rate unless you're going down hill.

Thanks John. "Higher gearing" meaning tougher to pedal, all else being equal?

now you've confused me AEO. I thought I'd have to go to 42/18 after John's explanation but now I think I have to go to 42/15.

Its too easy to pedal once I get rolling.
If I want to go faster I'd have to pedal faster than I physically can.
So, do I need more or less teeth in the front or the rear?

he said larger size in the front and/or smaller size in the rear makes for a taller gear.

More teeth in the front will make it harder to pedal and make you go faster. Less teeth in the back will also make it harder to pedal and make you go faster. I'd suggest getting a chainring (the front one) with more teeth. Because it will be easier to installl since you won't need a chainwhip or lockring tool. Only an Allen wrench and maybe a chainring bolt tool.

Thanks everyone! Now I've got it.
Higher, lower, taller....these terms aren't clicking with me. That's why I just wanted to know what would make it harder to pedal. You're explanation is perfect, Danzax. I appreciate the advice on changing the chainring too. I do want to make this modification as simple as possible.

Bigger in front and/or smaller in the rear will be harder to pedal but, if you can turn the cranks, you'll go faster.

just think of it this way (as an imagery)

there's ur big ring (42t chainring) on ur front and a little ring (16t cog) on ur wheel. Every time u make a full pedal rotation on ur big ring, ur little ring rotates 2.625 circles. Get?

now if ur big ring is bigger (imagine something dramatic), then every time u make a full pedal rotation, ur little ring will rotate a lot more circles. Thus, u can pedal at the same cadence as before but go much faster. But at the same time, u'll also need more strength to be able to push down that pedal.

And vice versa, smaller chainring, easier to pedal, but u go slower at the same cadence.

Would 2 identical bikes, one setup with gearing of 42/16 and the other with 34/13 pedal similarly?

yes, they would pedal at a similar rate.

Hence Gear Inches and Gear Ratio's are inaccurate accounts of gearing. Gain Ratio's are where it's at.

So, if giving someone these two hypothetical bikes to ride back-to-back they wouldn't notice any difference in pedaling?

gear ratio is sort of meaningless because it doesn't take into account wheel/tire size, but gear inches is gear inches.

@ JerseyBri: if two bikes had similar gear inches, they'd have similar pedaling characteristics. however, you can have a bmx bike with 20" wheels and a mtb with 26" wheels and if they have the same gear ratio, they won't pedal the same because they have different gear inches.

yes, I suppose that is true, I was mostly just plugging Sheldon B's Gain Ratios. Which take into account Crank Length as well.

Got it. That's why I asked about "2 identical bikes."

I'm good now. I now know...

...to require more effort when pedaling I need to either get more teeth on the front or less on the rear.

...Two bikes, one with 42-16 gears and the other with 34-13, with all else being equal, will pedal identically.



Now, of course, I'm curious why a manufacturer would choose the 42-16 combination over the 34-13. :)

My wife had trouble understanding gearing so I built her up a single speed.

Are you suggesting I try a tricycle?

There are a couple reasons: first, track bikes do not typically use cranks with BCDs that would accommodate a 34T chainring. Although the vast majority of fixed gear bikes sold these days will never go anywhere never a velodrome, the "look" is appreciated by the FG crowd. Second, smaller cogs and chainrings have marginally more friction than larger cogs and chainrings, so if you're in search of the best performance you'd opt for the larger sizes.

Thanks John!