Change Crank, Cassette or Both?
 

My bike is not set up for the hills where I live. I built the bike with a 53/34 crank and a 11/23 cassette. I'm thinking of changing to a 50/39 compact crank or a 12/29 cassette or both. Obviously if one or the other does the trick it would be cheaper but am willing to change both if necessary. Any opinions?

Pretty sure you mean either a 50/34 or a 50/36. Not sure a 50/39 is readily available.

How much trouble are you having with the climbs? A cassette may take care of your problem.

If you're really concerned, I would do a mid compact 52/36 with a 12-27 or 12-28.

If you already have a 34 small ring (compact), why would you switch to 39 (which is not compact) ?

Or the hills are too easy and your gears are currently too low ?

A 12-29 will be cheaper than switching to a 50/34 (you really must have a 53/39 right now) and may be adequate. However, be sure to check if your rear derailleur can handle it.

Change the cassette first and see if that's enough.

It seems to depend on how much you like the smaller gear jumps, or if you don't care about it. Some people have a groove for their cadence, and don't mind shifting more front and back, and so would prefer a compact. If you're happy with bigger jumps, with more range in your cadence, the cassette makes more sense.

Something to keep in mind, changes in the back have bigger effect than changes in the front. For example changing the cassette to 29 (with the existing 53 on front) would be equivalent to changing the crank to a 42 tooth (with the existing 23 cog)

Assuming you've got a 53/39 and are thinking of a 50/34, that would certainly give you lower gearing.

Swapping out your cassette would also give you lower gearing and assuming your RD could cope with the wider range would be quicker and easier - you'd need a few extra chainlinks (or maybe just get a new chain and not faff around with it). If your RD can cope with it you could go to something like 11-32 or 11-34 - you'll get some much lower gearing but the price you'll pay is bigger steps between gears.

If you need much lower gearing you could go all-out and put MTB gearing on it - maybe a 42/27 or 36/24 at the front paired with 11-34 at the back. Going from a 39/23 granny gear to 24/34 would make a huge difference, although you'd trade your 53-12 top gear for 36-11 which would mean you'd have to really thrash the pedals to get up to speed.

You can get an idea of the relative gains by simply dividing the chainring size by the sprocket size.

At present your granny gear is 39/23 = 1.696
A 50/34 would give you a low of 34/23 = 1.478
A 12-29 cassette would give you 39/29 = 1.345
Replacing both would give you 34/29 = 1.172
The silly MTB extreme would give 24/34 = 0.706

The lower the number, the easier it will be to pedal if everything else is equal.

There's no way he has a 53/34 now; I can't imagine anything handling a 19t differential. He must have just mixed up the standard and compact gearing. If he has that sort of gearing there are bigger problems here than climbing.

Sorry for the mistake. That's what I get for not re-reading the post before submitting. Yes I have a 53/39 and thinking of going to a 50/34 compact. I think a 12/27 or a 12/29 is offered in a Record cassette. I like the speed of the gearing I have now but have to compromise somewhat for the hills. Maybe changing the cassette first is the answer.

This. Get the cassette and see if that plus a dose of HTFU gets you through what you need. If it doesn't, THEN think about changing the crank, which is much more expensive. Are you able to get over the hills and just want it somewhat easier, or are they completely too big for you?

I would only spend the money for a Record cassette if I were hoping to set a record on an uphill time trial. Otherwise go for one of the lower models.

Oh, yes, right, get the Chorus cassette (there's no Athena cassette). No sense in wearing out soft Ti cogs to save a few ounces.

I'm able to get over all but one although some were really difficult. I need something easier.

Yes, I built the bike with Record gear but it would be sensible to switch to a more inexpensive model. My riding doesn't warrant top shelf stuff.

The 29t bottom cog will be over 26% easier than your current 23t. The 12-27 will be over 17% easier. Frankly, the 27t would probably be fine, especially if you keep riding and get fitter. Take your pick, but I'd keep the crankset.

Thanks, if that works it would be the best(cheapest) case scenario. What's the advantage of the 27 over the 29 since that cog would only be used on the steepest hills? If 29 is too tall you can always shift down.

The 12-27 goes:

12,13,14,15,16,17,19,21,23,25,27

The 12-29 goes:

12,13,14,15,16,17,19,21,23,26,29

The only difference is on the 12-27, the last two cogs are 2-tooth jumps instead of 3-tooth. That means they'll involve a less-severe change in cadence. How much that matters is up to you; I thought the 12-27 might add an 18t cog in the middle, but apparently not.