Frame and Crank Lengths

Monching has been riding a 50cm size frame with 172.5 mm cranks and he wants to know if they are the correct length. He hasn't told us his leg or thigh lengths so we can't really say, but we do give him our thoughts on sizing

Question: Good day bicycling, what is the best road frame geometry for my height I'm 5'5" tall, I own a trek road frame aplha SLR that has a 50cm seat tube, is it big for me or just right? What is the correct length of a crank arm for my height? I'm using an ultegra cranks that has 172.5mm length, is it ok for me? I've tried a 170mm cranks but it seems to be very hard for me to spinhigh gears compared to a 172.5mm cranks. Thanks!

Good day Monching,

For me to tell you if your frame and your cranks are the correct length you need to tell me your inside leg length, this is the most important measurement for frame size. The length of your thigh is the important information for your crank length.

OK, so without this information what can I say? The basic thing is, are you comfortable on your bike? If the answer is yes then don't worry about it, you have the correct size bike. Maybe your position could be tweaked to get a little more power out, but that would take someone to have to see you riding, or to be assessed on a bike set up system. Small changes could be made, but the most important thing is that you are comfortable.

As to the crank length, I think you have summed it up by saying that you that you couldn't get used to the 170's, but feel good with the 172.5 mm's then those are the ones for you. I and a friend both tried 172.5 mm cranks, we are both the same height and our frames are set to nearly the same saddle height. He loved the longer cranks, but I hated them, two things we learnt, one his thighs were longer than mine, so he had the leverage for the longer crank and two I pedaled more easily than him so the shorter cranks suited my style of riding more. He stayed with the 172.5's and I returned to the 170's and we were both happy. So stick with the ones you have.

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