I will be getting a set of compact cranks for my Tri bike but am having some trouble making a decision regarding crank length. Both my Tri and road bikes have 172.5 mm cranks, but with all of the recent talk regarding crank length I am thinking of going for shorter cranks. FWIW my inseam is 80 cm and the BB to saddle length of my Tri bike is about 73 cm. The Shimano compact cranks I am considering can be purchased with 165 mm or 170 mm cranks.
172.5 is probably as long as you want to go for that inseam, but for a tri bike you could easily go with 165s and probably not notice any difference. I’ve used the formula of .21 x length of inseam in mm, thus 800 x .21 would yield a 168, so anything from 163 to 173 would probably fall within your comfort range.
Chad
i’ve just switched form 172.5-53/39 to 170-50/34 - so far i’ve
found it much, much easier to spin fast, up to 120rpm, but man,
do i miss the leverage when the road turns up. on the flats, my
average speed over my mostly flat course is up 2-3mph. i took
a guess and decided not to switch cassettes to compensate for the
loss in leverage. hills are a bit easier, but obviously slower.
i think i will be doing a bit more off-the-bike leg work, like presses,
lunges, plyo to take better advantage of the improved spin rate.
(riding an '08 QR Caliente very steep, w/the trishuttle)
So 165s of 170s will feel pretty much the same. What if I told you that I get tightness in my right glute which may be caused by my current position. Do you think that this would be a good reason to choose 165s as this should open up my hip angle somewhat as compared to 175s?
I went from 172.5 to 170s and loved it. Better spinning motion less lactate build up and much more comfy in aero position. I could go shorter probably but im happy with it for now.
I was planning on getting the compact cranks mainly because it would allow me to maintain a higher cadence up steep hills. I would have thought that speed would not be impacted on flats or hills with compact cranks. I am a bit surprised by your experience.
I was planning on getting the compact cranks mainly because it would allow me to maintain a higher cadence up steep hills. I would have thought that speed would not be impacted on flats or hills with compact cranks. I am a bit surprised by your experience.
i do actually maintain a higher cadence up the hills, but it certainly
feels like more work(i.e. i need more power) i switched primarily
to open up the thigh-torso angle and also to relieve some of the
pressure on my aging knees. it is likely that i was too cramped,
included angle was too extreme(knees close to chest) flying on
the flats is brilliant, but i now need to work on sustaining 105rpm
at 22mph for longer than 2 minutes.
Go back to your 53/39 and get some 165mm cranks. It will give you more hill speed and still give the feeling of a high cadence. You can get some cheap Tiagra cranks for $40.00 or so to try it, it will work.
I swap back and forth between three bikes; an old mtb with 190mm PCs, my road bike with regular 190s and my tri bike with 180s. I don’t even think about the differences anymore. I like the long cranks for hills and out of the saddle riding, but prefer to spin very fast on the tri bike. I get tightness in my glutes as well when I don’t ride the tri bike often enough because my hip angle is a little more closed than recommended because I have adopted a semi-superman position. 165s might open up you hip angle enough to help, or not; it’s only 7.5mm. Moving your seat forward can help with that as well, if you bike is designed for it.
Chad