Crank length (170 vs 165), shorter rider, 48cm bike, dual use bike road & triathlon

Hello, I am 5’4" and ride a 48cm Cervelo S3.
I am not sure but I think my cranks are 170mm. I can’t find any markings on the cranks that confirm the length.
This is my only bike and I would use it for both road riding and triathlon.
I was curious to hear feedback if I should consider running 165mm cranks all the time?
I definitely don’t want to swap cranks depending on the ride I am doing that day.

If I should look at 165mm cranks, how do I shop for them in the second hand market and confirm they will work/fit on my bike. I always like to save a bit of money if I can but don’t want to buy a 165mm crank if it is not compatible with my bike.

Thank you for any feedback and guidance you can provide.

If you have a stock bike, you should be able to ask Cervelo about the crank size. I am 90% confident it is 170mm. What kind of cranks do you have? I am surprised you cannot find the length marked if they are Shimano.

I have two bikes, 165 and 170 cranks. I am (barely) 5’6 riding size 52 frames. I can’t tell the difference.

In terms of buying them, if you are in the US, Craigslist or eBay. Facebook groups would work in many international markets. In general, Shimano cranks will be compatible with each other, but you can let us know what your current cranks are (or take photos of them).

I wouldn’t hesitate to go shorter.
I’m 5’8” and I have 145mm cranks on my tri bike and 165 on my road bike. If you have to go with only 1, I would go with the shorter.
From the feel standpoint, I can’t tell the difference and there is no difference in power. It does allow me to have a better position on the TT bike.
I do have a 155mm Cobb that I’ve been meaning to sell. Open box but never used. $200 plus shipping if you want.

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I’ve only used 165mm cranks on track bikes to save hitting a pedal on the boards. I don’t believe you’ll feel much difference to 170s on the road. I’ve known riders going longer for greater leverage, but not the other way, unless it’s to spin a lot faster.

I use 170 cranks and am 5’ 11". I do prefer them over usually stock 172.5 for a variety of reasons. 165 should be fine for you. As others mention, even shorter cranks could be even more preferred, but 165 is more commonly available by major manufacturers, if that is a concern.

I think my cranks are stock, 3d rotor? IMG_20190629_070351|281x500

I an 5’8" with an inside leg of 29.5". I moved from 170 to 165 for my TT bike and definitely noticed the difference it allowed me in position, but did not notice much difference in pedaling.