Crank arm Sizing?
I am thinking of changing to a crank based PM. I currently have a PT wheel, that I would sell after making that change (if I do). This would be so that I could have different wheel choices with less of an investment of having multiple PT wheels.
Although we have had a bunch of conversations in the forums of suggestion having a compact gearing set up, is there any suggestions you guys may have on selecting the appropriate crank size? On my Tri Bike the crank arm size is 172.5, and I am about 5'11 with a 33" inseam. My thought would be to go a little shorter....170 or 167.5. Although these are minor differences I just wanted to ask to see what advice might be out there.
Any suggestions you guys have would be great.
Thank you for the help.
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There has been a thread about impact of crank arm length to your position and body angles .... can't remember were to find it but I think Al Truscot started it.
It really boils down to how it affects your bike fit.... If your spending the money on a new crank with PM , it maybe time for another bike fit to go along with it!
Here's the other recent thread: http://members.endurancenation.us/Forums/tabid/57/aft/14078/Default.aspx
That thread sort of ended prematurely... I don't particularly agree with the findings of the article. I personally think the flaw in his analysis was keeping constant cadence and assuming force per revolution would need to go up. I think at constant power and constant foot speed that cadence goes up...
I'll try to give more detail in the next couple days as necessary, but also don't want to overwhelm this thread before others chime in.
@TIM..I was thinking on getting a "real" fitting done with my bike this year, so will make sure to hold off on that until after I change cranks to make sure it is right. I guess that in the end I guess I had in my head that shortening the crank arm length would help my position a little to open my hips and help my legs a little bit. I know that these are all incremental little changes, but if I change cranks at least I would be going in the right direction.
@John..Thanks for the link and I read through that, one of the things that I know I have issue with is that Patrick tells me I need to ride with a higher cadence and if this would at least push me in the right direction by a percent or two, and least it is not in the wrong direction...that makes sense right.?
@John
For the heck of it I bought 165's Friday and will get them on my bike next Friday. I am leery messing with anything on the bike but I thought I would give them a try. If you aren't in any hurry I will do a few rides and let you know what I think of the change. If I don't like them you may get a good deal on a Quarq Elsa 165 crank!!!
He can certainly give you a good FACT BASED (your meassurements and position) opinion!!! Worth every penny in my opinion.
www.ttbikefit.com
You certainly can stick with 172.5s if you want. If you have access to (any) 165 mm set, it might be worth getting them on for a try to see what you think. The thread above does have info to look at.
The key thing is that if you adopt the 165s, you will move your saddle up about 7.5 mm (relative to the 172.5). That means your knee on the upswing will be 15 mm further away from your chest if you also raise your front end by the same amount (keeping your drop the same). That opening up CAN lead to greater power just like having less drop can lead to greater power (but this is a less fortunate choice because of the aerodynamic penalty). If you are very comfortable and not too "folded up" to begin with, you can raise your front end by less than the 7.5 mm and increase your drop. That will obviously decrease your hip angle some. Clearly, you could get a fitter involved here.
Thanks for the help, I can visualize what you mean and will look more into having a good fitting done with my bike prior to buying a new crank based PM. I got my bike last year, based on pre purchase suggestions from Todd at TTBikefit and used the suggested measurements he gave me to initially setup everything then slowly moved some things around over the spring and summer to make it comfortable as I got more and more used to it from riding it more and more.
So I will totally get in touch with him to see what I can set up.
Thanks again.
A few quick notes:
Crank Length -- generally, people are setup with the following lengths...generally:
Shorter crank lengths have become more popular on tri bikes in the last 2-3yrs, for the reason's JW and WJ described -- able to achieve a more comfortable hip angle at the same front end drop.
We are big, big proponents of compact cranks. Or, rather, one very, very important that item that 90% of the IM field doesn't pay enough attention to race day is gearing. You can see, through our resources in the Wiki, the IM Gearing Thread, and elsewhere that we don't make that mistake and a very, very interested in making sure you have the proper gears on your bike for your race. This generally means having enough gears for the race...and we follow this with our guidance that you can never have enough gears on the IM bike course.
More gears = higher cadence = a less forceful / less torque applied at the same wattage. That is:
The net is that at IMWI '11 I was at about 4.2-4.3 w/kg, rode a 5:10 bike split with a compact crank and 26-11 gearing, giving me a 34/26 climbing gear for the hills.
@ Rich, now we are cooking with gas. Totally agree with more gears....having a compact at Lake Placid last year was very helpful along with the 11-28 gears. My w/kg is no where near 4, and I would never give up having more gears. Thanks.
Cadence, as the saying goes, is a red herring. Let your cadence fall where it may and let it naturally self select.
Rich is talking more about having the right gearing and not so much the right cadence. He doesn't want you showing up to Ironman Canada with 6,000' of climbing with a 54/42 and 11-23 cassette. You'd be mashing and killing yourself going up the hills at 60 rpm while the smarter athlete will have a better gearing and will be going up the hill at 80 rpm in a much easier gear.
As for overall cadence, just let it happen. Some people spin at 95-100 and others ride 80-85. Practice what feels and performs best for you. Generally, a higher cadence is going to have less muscle fatigue but a higher heart rate. A lower cadence will have more muscle fatigue with a lower heart rate. What's optimum for you is probably not optimum for me. So it's a little trial and error to find what cadence works best for you.
The distance of the bike ride matters as well. You will find across the board that the longer the distance bike ride the lower the average cadence. If I'm doing a sprint/oly my cadence will be close to 90. About 85 for a HIM and 82 for an IM.
Perfect timing on this thread as I assemble my race components during this out season.