utoner34

I have Shimano Sora Hollowtech II, 50/39/30T 175mm 130BCD crankset and Shimano HG300 9-Speed, 11-34T cassette.

I would like to get as small granny ring as possible to make those very steep gradients (~20%) easier for climbing.

The problem is that I am not sure how low to go with gears for compatibility issues and where to buy such chainring?

What are your suggestions?

Trevtassie

You can go as low as 24T on the front, chainring wise, but the issue is likely to be the cage on your front derailleur not reaching done far enough. You might need a mountain derailleur. Sunrace do a 11 to 40T 9 speed cassette now. A Deore 9 Speed derailleur works OK with it.

redlude97

Assuming it is a 5 bolt cranlset, then the inner ring is 74bcd most likely. This fits a 26t. Something like this would be a direct swap https://www.amazon.com/dp/B001GSKTNS/ref=cm_sw_r_cp_awdb_t1_U89hBbWW1KG47

DiabloScott

20% grades are never going to be easy.
If you can't make it up in a 30x34 you're probably not going to make it up in a 26x34 either. Those ultra low gears are sometimes needed by people carrying heavy touring loads, but they're not a substitute for fitness or climbing skill.

Good luck on your project though.

berner

This sounds about right to me. I have a triple with a 26T granny. A 24T may or may not work. I can be tricky shifting into and out of the 26T. I've slightly modified (closed up) the derailler.

utoner34

I can make it but this is more to benefit my poor knees.

fietsbob

Do the math.. gear ratios on derailleur bikes overlap a lot.

so once you are in the lowest middle chain ring gear , going to a 24 vs a 30 will give you maybe 3 more lower gears

those being the 3 biggest cogs on the rear cluster..

so any dragging the chain across the bottom of the FD cage
may only happen in those cross chain gears you should avoid anyhow,

& they are deep in the ratio overlap of similar ratios on the middle chainring..







....

79pmooney

I've been running 53-42-26 and similar for years with no issues. If I were you, I'd try it with your current derailleur. You will probably find it works just fine, perhaps noisy in the smaller cogs as the chain drags over the roller at the bottom of the cage. I've done that for years, I do replace the roller with the smallest washers I can fit over the bolt. Steel on steel. Not much drag and neither the chain or the washers are going to care unless you ride that gear for hundreds of miles.

Ben

utoner34

My bike math is poor

You mean I wont feel much difference even if I manage to put 26 teeth on smaller chainring?

clasher

I've not looked at the inside of a sora triple but a lot of the newer shimano cranks use a unique BCD that limits the inner ring to 30T so if you've got a newer 4 arm sora crank I would guess it's only good down to 30T. I'm pretty sure all the older models use a standard 74mm BCD for the inner ring so you can snag one off the internet somewhere to try it. I had good luck with a 28T inner ring but I had an 11-36 out back. 26T might be better than 24, I had a lot of chain drop when I tried a 24T on my triple setup.

79pmooney

Basic "bike math" that will give you gear ratios in "inches", ie the wheel sized you would have if you rode an old fashioned high wheeler or a unicycle. (100" was the high gear of our grandfather's 10-speed. Below 30" is considered mountain gearing. 67" is the classic winter training gear for flat ground.

The formula is" chainring teeth / rear cog teeth X the wheel diameter in inches. (For 700c wheels, using 27" works well.) Your current low gear is:

30 / 34 X 27 = 23.8"

A table of your gears would look like:

......50....39....30....24 (if you choose to go this low)
11.123....96.....-......-
13.104....81.....-......-
15..90....70......-......-
17..79....62.....-.......-
20..68....53....41....32
23..59....48....35....28.1
26..52....41....31....24.9
30...-.....35...,27.0..21.6
34...-.....31....23.8..19.1 (Edit: Wow! This table came out really good first try!)

Don't take this chart as the word of God. I guessed the number of teeth on your cassette. I can usually guess Shimano's choices correctly. I also haven't shown the gear combinations for the extreme cross-overs, indicating them instead as just dashes. You can see that by going to the 24 tooth chainring, you get two real gears lower.

Any bike shop should be able to get you 24 tooth chainrings for the common 74mm BCD standard. Salsa makes one (that I am currently using) and Sugino almost certainly does also. Both should be available to a shop through QBP and can probably also be found online.

The various online gear calculators all do the same calcs as my example. Some do give you the results in gear ratios or other forms, I always liked the (archaic) "inch" system because it is so visual. Now, different calculators arrive at the outside tire diameter differently so the results will vary slightly but the differences will be less than our legs can feel.

2nd edit: install a chain watcher. There are several brands. They all work.

Ben

Jon T

I'm in the same boat with you. I currently have a 32-42-52 on the front and a 13-28 (6 gear cluster) in back. At 63 yo I too, need some help on the hills. I found a 26 t granny in my stash and it will replace the 32. The 52 is being replaced with a 50 (round) as the 52 is now too tall of a gear for me AND I'm tired of the bio-pace oval rings. I love my old Peugeot (bought new in '84) and hope we have many years and miles left in us.
Jon

raria

I have this cranksetTruVativ TouroTriple Road, 30/42/52T
and a Sora 3500 FD.

Do you think a 24/26 smaller ring will work with that FD?

79pmooney

Hard for me to say. I've never run a cassette remotely as large as yours and have never run a Shimano FD except the Dura Ace triple on my best bike.

That said, try it, You have zero to lose. Either it works acceptably or it doesn't. Changing out FDs is no harder after the chainring change than before. Setting up new FDs can be a hassle. Try what you've got before you jump through hoops you might not have to.

I'll guess that your current FD will work quite well except that you will have chain rub in certain combos, maybe a lot. Chain rub will kill FD caged - over hundreds of miles. It will kill the market value of treasured classic FDs that the C&V types lust for. (The Sora is not one of those. The financial risk you are taking might be $5.)

Ben

Carbonfiberboy 

We run 53-39-26 9 sp. on our tandem with 11-34 in the back. Works great. We have an Ultregra FD which shifts fine with no modifications. The 26 is obviously better for climbing steep stuff than a larger ring. One thing which does not work is trying to stand in the 26-34. Not enough momentum. Upshift a few cogs in the back and then it works fine.. I have the same front rings on my singles with much smaller cassettes. That also works great because the low gears are closer together than they would be with a larger ring and a larger cassette.

For others running 9 sp., you can't just swap out the 42 for a 39 without changing the outer ring to one designed for a double, i.e. a 53. Then the 39 works fine. The 26-39 shift is much easier than 26-42.