alathIN

Can I run a 38t inner chain ring with my 53t outer chain ring?

I live in flattish Midwest so I usually ride a 53/39 chain ring set and 11/12-25/28 cassette.
But I have an event coming up with two rather steep-ish climbs (Ironman Costa Rica 70.3)

I put a 12-32 cassette on the back and tried it out in some notoriously hilly country to the South of me (Brown County Indiana).
I was mostly OK on long and steep climbs, but still got a bit lower cadence than I would prefer when there was a short section of even steeper slope, or a tight turn on a steep climb.

It's not enough of a problem to want to change out my BB and/or crankset - its 130 bcd so I can't go compact - but I am wondering if I can get away with a 53/38 chainring combo.

I already have a 38t inner chainring laying around. It's FSA, and my big ring is Vision (made by FSA).
My front derailleur is SRAM Rival 2 x 10 (not a yaw model)

Just wondering if that one extra granny tooth in the front might come in handy on the steep bits, and also wondering whether 53-38 is a workable combo.

fietsbob

There have been sets engineered to work best if you don't break them up, for the index shifting function, Like STI,

so a 53 - 39, can function better than the chain ring 1 tooth smaller.. 53, 38.

(there is a % difference you can calculate, 1/38, vs 1/39)

Now If you use friction shifting and accept you have to plan your shifting tactically,

then you may find the options wider..


Flattish ... the Paris Roubaix race is also pretty flat, but there they close up the chainring difference to a 53 - 46..

rm -rf

A 38 chainring won't make much of a difference.

38/39 = 2.6% easier.
Rear cog shifts are anywhere from 6% to around 12% depending on the cog teeth. So switching to a 38 ring is about 1/3 or less of one cog shift.

I wouldn't go purchase a 38 ring, but since you have one, you might as well try it. It's close enough in size that it should work fine.

...

Your current 39/32 lowest gear is the equivalent of a 34/28 low.

39/32 = 1.22 ratio
34/28 = 1.21

For really steep climbs, I like my 34/32 low gear. I can "comfortably" stay seated on 10% grades, and sit on steeper grades if I slow way down and use fairly light pedal pressure at a very low rpm. The next shift, 34/28 is okay, but I have to stand up more often. Standing is fine on short, steep hills, but harder to do on longer steep climbs.

fietsbob

Might consider a new crankset... 50 - 34 is a popular choice, so you can get them in a lot of different price points.

caloso

It will work fine. I have a 53-38 with a 11-28 cassette. I have a Quarq that needed new chain rings and since I had to buy new ones, I thought I might as well get a 38. Yes, it's only a one tooth difference, but sometimes that's all the difference.

Shifting is perfect. Never dropped a chain, not even noticeable compared to the 39.

alathIN

That's exactly what I've got on my touring/commuting/general purpose road bike and I love it.

My tri bike has 130bcd, because it's a Quarq power meter I managed to snap up cheap. It would be a bit pricey to replace - though I don't strictly need the PM for this one event, so I could just grab whatever that fits BB30 I suppose...

fietsbob

that is a 30mm spindle tube, I believe.. (Shimano went with a bit smaller diameter)

Left arm secures those with the tube part of the right arm assembly, I believe, (read your owners/service manual )

I just fix bikes in the shop, don't shop for them.. myself..

caloso

Yup. Exactly my situation.

alathIN

Yes, there is probably an adapter I could use to put my touring/commuter bike's crankset on my tri bike. It's Shimano 105, and yes, it goes together just like you said with the spindle permanently attached to the driveside and the left crank arm bolts on to that.

Shoot, now that I think of it, my commuter/tourer bike does have a 30mm BB, so I've already got a set of the 30mm to Shimano Hollowtech adapters.... I could just switch the two cranksets out.