Up to this day I don't know which has more of an effect on power. a bigger chainring or smaller cassette for climbing and acceleration.

I've been told that the cassette in one tooth bigger makes a difference of 2 teeth, or would need 2 teeth less if you went with a smaller ring up front instead.

The cassette is your perspective said the bike shop mechanic But i don't know which one makes the most difference.

When you say you want more power.... what do you mean? speed?

jbucky1
https://www.buckyrides.com

ATMO, depending on what you are doing depends on what chainrings or cassette you run. Also depending a little bit on weather you like to spin or mash to an extent.

for example on one of my bikes I use a 53/39 chainwheel and a 11-27 cassette and I like to climb on it. In this case I'm a bit of a masher but it works for me, and I do a lot of climbing. some would say run a compact or semi compact chainwheel and I would be spinning more, more efficient, maybe even faster.

jbucky
https://www.buckyrides.com

Just keep it in the 53-11.

Neither. If you want more power you'll have to train more.

Yep, in this case, it isn't about the bike (or any part of it).

Assume you use "more power" to mean "more mechanical advantage", or lower gearing.

You can use gear inch calculators, but I just look at percent change between sprockets.

So, say one has a rear cassette with a 11T and 12T sprocket. Shifting from 11T to 12T reduces one's gearing by about 9% or (1T/11T) * 100%

Now, jump to say a 30T and 31T sprocket on the cassette, and the change is much smaller (1T/30T)*100% = 3.3%.

On the front chainring side, going from say 39T to 40T, one gets even a smaller change.
(1T/39T)*100% =2.6%

Typically with the larger sprockets, one changes by several teeth to make up for the diminishing returns.

The crossover point is where the front and rear sprockets are the same size (1:1 gearing), so a 30T front and 30T rear, or 40T front and 40T rear.

Once you have gone beyond the 1:1 gearing, then you'll have more benefit from doing small changes on the front.

So, say you have 40T in the rear, and 30T in the front. A 1T change will be more significant in the FRONT.

There are several limitations that you'll run into including front and rear derailleur capacity and chain wrap which may make some combinations easier to build than others.

Since the largest 1T changes happen with the smallest rear sprockets, there are advantages of starting with say 10T or 11T in the rear. So, a 10-40 rear cassette will effectively give a 4:1 gearing range ratio.
A 13-39 rear cassette would only give 3:1.

Simple math.

Th gear ratio is just that; the ratio between the driving and driven gear. So set up the fraction and compare.

36/28 = 9/7 = 1.29

if we add 2 to the rear or subtract 4 from the front, we get

36/30 = 6/5 = 1.2 or
32/28 = 8/7 = 1.14

So in this case, we see that dropping 4 of the 36t ring is a slightly bigger change than adding 2 to the 28.

So, rather than some rule of thumb, do the math yourself and know.

BTW- if you want to convert to gear inches, which compares to the effective diameter of the rear wheel if the pedals were attached directly, multiply the ratio by the diameter of the rear wheel.

53-11 is a 130-inch gear and pointless for anything except a tandem.
A smaller chainring will narrow all your gear steps, IMO, making any bike sweeter and more versatile.

Here is Mike's gear calculator with a gear analysis for a wide compact double I run that covers 24" to 96" in narrow steps.
Especially look at the gear steps on the semi-log graph. Plug your own gears in there and see what differences you get by changing "on paper" first.
Try to keep the overlaps as few as possible, and try to keep all your gear steps below 10".

TreyWestgate, Power is determined by the rider and has nothing to do with the bike. On a fixed gear bike the transmission delivers one gear ratio, or put another way, a single value of torque multiplication between the rider and the rear wheel.

On bikes with multiple gears, multiple values are available to deliver torque to the rear wheel. Bottom gear can deliver more torque to the rear wheel for a set output of power than top gear. The old saw that 1T in back equals 2T in front only will apply to a few combinations, it's really a sliding scale...math is at the core of everything.

Brad

depends on what your smallest chainring and biggest cog are. If they're the same, then the changes will be about the same.

For instance say you have a 34x34 low, for 26 GI.

32x34 will give you 24.5 GI
34x36 will give you 24.6 GI

Chainring change would make just a hair more difference.

Using less than 13 teeth on the cassette bends the chain at a sharp angle, engages a very small number of teeth, which equals slightly bigger mechanical losses and faster chain and sprocket wear.

Using bigger chainrings with bigger cassette sprockets gives more weight and slightly worsens acceleration (higher inertia).
Bigger chainrings and sprockets also affect ground clearance - if riding over obstacles this matters - so more important for off road bikes.

Add the effect of cross chaining - some combos engage more teeth, but with a great cross chaining.

So there's no definite answer, except the one you find for yourself: which gear ratios you most often use, which shifting patterns etc.
Do you mind 2 tooth size gaps between adjacent sprockets at the fast and the slow part of the cassette?

I explained basics of bicycle gearing and gear ratios in this article, with some links to on-line gear calculators:
Bicycle gear ratios - speeds, gear inches

FWIW. I agree completely. People seem to be taking this thread seriously Check out the "General" first page for some history. Guess I can post this emoticon since it's on the BF approved list.

To extend the above remarks, your use of the term power, talking about a larger chainwheel or smaller cog, and your reference to climbing and acceleration don't make sense at all, especially when put together.

1. The amount of power has nothing to do with gear combination or ratio. Power is the amount of work done (mass x distance) per unit of time. In other words, moving the same weight the same distance in less time (more speed) is more power.
2. A larger chainwheel or smaller cog both increase gear ratio. Gears are essentially spinning levers, and the higher the gear ratio the longer is the distance between the pivot/fulcrum and the load. A longer distance toward the load (less toward you) means you can move the load much more/faster with a given movement on your part, but it also means you have to exert much more force to do so. So a higher gear will only mean faster speed if you are stronger (or more efficient).
3. Acceleration and climbing both require lower gears. Technically if you are going 5 mph on the flat and keep that speed up a hill you are accelerating according to the meaning in physics.

If you are wanting higher gears there's a good chance you are already riding higher gears than is advisable in order to reach your goal of more speed/power. For a variety of reasons it is better to first adopt a higher crank spin rate (coupled with a lower gear) on a bike - generally above 75rpm or so - both to go faster and to get faster. You can also increase the power delivered to the pedals in relationship to your effort by making sure the bike is set up so as to be as efficient as possible for your body dimensions.

Incidentally, differences in bike/component weight, tire rolling resistance, stiffness of frame, etc. all pale next to the engine when it comes to better performance on a bike.

we're good - I was just throwing it out there. I always try to give people the best answer I can. This is the internet, where sarcasm never works and all emotion is internalizing.

Acceleration is the change in velocity with respect to time. If you climb a hill at constant velocity acceleration is zero. There will always be a very small acceleration and deceleration through a pedal stroke but this has nothing to do with climbing a hill.

cny-bikeman is correct here. All climbing is acceleration and a test of whether you recognize planing in your good steel frame.

I'd use this one....

As everyone more or less agreed, the mechanic was right for "normal" gearing on road bikes.

It's not "power", but the physics explanations offered here are a bit mangled and I think not important to your question. I'm sure you meant "mechanical advantage", as in a lever or block and tackle.

We don't really know for sure what the mechanic said, as "the cassette is your perspective" is too ambiguous to even discuss, and neither do we know what the OP meant. Whether the OP was trolling or serious, it resulted in useful info for others as well. The physics explanations were good enough for the purpose.

Do More Leg work in the Gym, for More power ..