Greenstreak

I have an aluminum Specialized Allez that I bought used about 14-15 years ago. I'm not sure what year model it is. It has Shimano Tiagra components.

Also, it has a 59x39 crankset (two rings) and a 12x25 cassette (nine rings) . This makes it hard for me to go up long steep hills. I have a ride coming up that will involve a lot of mileage with lots of steep hill climbing.

How feasible would it be to change the gearing to make it easier to add hills. Maybe by adding a smaller third chainring? Would this be a good idea or bad idea?

Looking for suggestions for the easiest to implement, most cost-efficient solution. All suggestions are welcome. Thanks!

(Note: I am new to these forums and this is my first post. If this is in the wrong subforum, let me know and I'll move it.)

Andrew R Stewart 

The easiest way is to replace the cassette with one that has larger cogs, or an easier gear. Your current rear der likely won't work well with any large cog more then 27T and that's not a big reduction of ratio anyways. What many have done is to also replace the rear der with one that is Shimano 9 speed compatible. My wife and I have a few bikes with Shimano Deore or XT rear ders just so we can get up the Finger Lakes hills. The different der can let you run a 32, 34, or even 36T large cog/low gear. I suggest replacing the shift cables/casings and relubing the shift pods too at this time.

My own solution also includes a triple crank. But since loving one's ft der isn't trendy I'll shut up. Andy

Jon T

I put a triple on my old Pug road bike 25 or so years ago. Rear cluster is a 6 speed 13-28. Front WAS 32-42-52. The rear is the same but the front now is a 26-42-50. There aren't too many hills I can't ride up any more. I don't go fast but I make it.
Jon

nomadmax 

I have an 86 Allez SE that has a 34/48 Shimano crankset, 11-34 9 speed SRAM cassette, Shimano Deore 9 speed RD and Campy Ergo 10 shifters on it.

shelbyfv

Yes, 9 speed mtb cassette and RD. Maybe an inexpensive 50-34 crank like https://www.merlincycles.com/shimano...set-62076.html (though out of stock at this vendor.)

DiabloScott

This is the right forum, and this is one of the most common questions, so have a search because there's a lot of good info in here already posted for other people in your position.

You didn't say what kind of shifters you have; that will affect your options.
Compact crank and MTB rear derailleur with 32or34 biggest cog would give you about as low of a gear as you could want.
Pick out some components and then post your idea here for review.


And low gears give you some room to work with, but they will not compensate for lack of climbing fitness - make sure you get in lots of climbing rides before your event.

davidad

You can use this site to see what gear ratios will satisfy your needs. Bicycle Gear Inch & Shifting Pattern Calculator

TrojanHorse

Old tiagra RDs can only handle about a 26 tooth large cog on a cassette, so you're very limited. (basing this on my wife's tiagra triple)

I purchased one of these: https://www.amazon.com/gp/product/B003Q40IRW
and a 9 speed cassette (11-32) and she's in business on hills.

Note that there are several versions of that deore RD, you want the one with the barrel adjuster and you want the GS cage version. (medium cage)

mitchmellow62

OP: The RD-4500 Tiagra short cage rear derailleur (my guess for your derailleur) had a recommended largest sprocket of 27 teeth. A 12-27 cassette would only lower your lowest gear about 8%.

The derailleur has a total capacity of 31 teeth. So with the current cassette you could replace the 53/39 crankset with a compact 50/34. Your lowest gear with the compact crank would be about 13% lower but your highest gear would also be about 6% lower. I believe your bottom bracket is square taper. Square taper compact cranks are relatively inexpensive. You'd want to be sure that the compact crank you choose uses the same length bottom bracket. You'd be able to reuse your chain, perhaps shortening it a little. (The '03 Allez Sport came with "mostly" Tiagra but the rear derailleur was 105. The short cage 105 has a total capacity of 29 teeth and if your's is 105 it would still work.)

If you go to a much wider range cassette (much greater than a 27 tooth large cog; i.e 11-32) you will need a long cage derailleur and a new chain. A 32 tooth large cog lowers your lowest gear by about 18%.

If you go to a triple crankset you will also need a new three speed left brifter, a different spindle length bottom bracket and a new chain. A 30 tooth small ring lowers the lowest gear by about 30% using the current cassette.

Spend some time with a gear calculator to see what these changes do to the full range of gears/speeds. Also, check Ebay, Amazon, some of the online bike stores and your LBS to get an idea of cost for the outlined options. Be careful, many of us obsess over the "correct" gearing (you couldn't tell, could you? lol).