For an amateur, the advice is to avoid extreme choices in length and to refer to a table with anthropometric values. Braking lesson with Pedro Gomes. Cornering on a bike at high speed is something that new riders are. Nowadays the powermeter crank is where everything starts for a ride. Having dominated for decades, 26in wheels now see little interest b.
Visit also. Other factors, like pedaling style, have to be considered as well. Back and knee pain are often signs of improper bike fit, and can point to crank length concerns.
Buchanan says that a history of low-back or calf issues on the bike can be an indicator that a rider is on too-long a crankarm. But before you mess with crankarm length, adds Buchanan, take a look at other likely causes of pain and cramps, like turning a high-enough cadence or building core strength.
How hard or easy an individual gear feels depends on three things: the combination of chainring and cog size that actually produces it, the wheel size it rolls on, and the crank length that turns it. So if you do end up changing crankarm lengths, it will change your gearing as well. The relative jumps between gears stay the same, but the overall range will feel slightly easier to pedal, or smaller, with shorter cranks and harder with longer ones. A related consideration: Since Shimano and SRAM only make crankarms between and mm, going outside that range means you might also need to buy new chainrings, or even a different bottom bracket.
An obvious note: This is just an illustrative example, not a crankarm length recommendation for 5-foot-2 riders. The main points to consider: handlebar height and saddle setback. Handlebar height is always set relative to saddle height. That 5-foot-2 woman moving to mm cranks will raise her seat about 7. So her handlebar will be lower relative to her new seat height, and she may want to raise it. Always make these changes in consultation with your fitter, and keep track of all original fit measurements so you have a baseline for comparison.
Finally, consider that you may decide not to make other changes. If the inseam X 0. This would cause problems in that Shimano and Campagnolo only make cranks longer than mm Equally, someone of average size like me at cm with an mm inseam would need to use a mm or similar crank and only T. Anyone much over 6 feet cm is likely to have longer inseam than that again. Custom crank lengths are available in up to mm in 1mm increments from several sources but there is potential for problems when longer than standard cranks are fitted to production frames.
Really long cranks would need bottom bracket drops that are higher i. So realistically, either a custom frame would be necessary for many, OR the entire bike manufacturing industry would have to completely change their approach to frame design. Smaller riders could be closer to the ground as shorter than normal cranks mean that the bottom bracket height and hence standover height of a frame could be reduced while still maintaining adequate pedal to ground clearance around corners.
This can only be of advantage to the short legged. Chainstay length and the clearance between foot and front wheel become potential issues for users of extra long cranks as well.
This means that the literal application of inseam x 0. However some of the issues that can occur with small riders on c wheeled bikes, like lack of standover clearance and poor foot to front wheel clearance would be lessened with shorter than conventional cranks if either custom or redesigned production frames were available.
There are some other potential considerations:. Inseam length and leg length are not the same thing. Inseam is measured from the ground to crotch. Leg length is measured from the ground to the top of the femoral head.
Whether there is a consistent ratio between leg length and inseam length I am not sure, and would be surprised if it is the case. So any formula would have to start with choosing a particular measurement frame of reference. Leg proportions : The longer the lower leg for a given leg length, the higher the knee will rise for a given crank length. This can place practical limits on crank length particularly for riders who have the ability to ride with their handle bars low.
Having your upper thigh foul your rib cage when on the drops is not conducive to performing well in the long term. Foot length : Depending on foot size and assuming a middle of the road pedaling technique, the longer the foot relative to leg length, the further the rider can reach to the pedals.
This should probably play some part in any equation based on proportions. Flexibility : If a rider is tight in the hamstrings they cannot effectively have as high a seat height as would be possible with more flexible hamstrings. The lower the seat height for a given leg length, the higher the knee will rise for a given crank length. Potential for an increase in knee problems : Longer cranks bring the potential for greater loads on the knee.
Note: Shear force is when the upper leg tries to push forward over the top of the tibia and fibula. A longer crank for a given rider increases shear force disproportionately for the following reason. For sake of argument, assume a change in crank length of 10mm. To maintain the same effective seat height as measured from centre of pedal hole in crank to top of seat , the seat post will need to be dropped 10mm further into the frame.
That will mean however, that the knee will rise 20mm higher at the top of the pedal stroke. As you read in e. All of which was great. The story was quite different in fast bunch rides and crit racing though.
Never mind ground clearance issues, I worked around those. The problem was high speed. As any crit rider knows, there are periods where the rider must be able to sustain high speed usually desperately trying to hold on to a wheel. Because I could not apply the extra leverage through as many degrees of crank arc as I could with a shorter crank.
Torque analysis confirmed this. I went from being a reasonably smooth pedaller at high load with shorter cranks to being a far less smooth pedaller with longer cranks.
In the type of racing where there are plentiful changes in speed, this was a large disadvantage when the pressure was really on. Your experience, if you choose to experiment, may well be different to mine, particularly if you are REALLY long legged or your type of riding differs from mine. Femur length in inches should be the same as crank length in cm alternately, femur length in cm divided by 2. This is based around the idea that the upper leg is the major lever when applying force to the pedals and that the lower leg is the connecting rod and plays little part.
Without going into the merits of this statement, the practical consideration is how to accurately measure femur length. The only definitive way would be with a CT scan or similar. Femur length can be measured from bony landmarks but you will probably get differing results depending on who measures it as it is relatively easy to make mistakes with this method.
The idea of femur length being a determining factor sits better with me than inseam length as it reduces the chances of the upper leg fouling the ribcage, but even so, flexibility, foot length and bar height and intended useage should play a part in your crank length choice to some degree. Various tables, with often conflicting recommendations of crank length to leg length.
If you want to really search around, there is a lot of this stuff out there. Some of it is in cycling books, some of it from crank manufacturers and so on. The problem is that many disagree and give wildly differing recommendations leaving the reader no better off.
I have seen successful elite riders effectively use various proportional crank lengths from Eddie Salas using mm for his mm inseam very close to the American idea of 0. Experimenting is not as easy as it should be because of the cost of changing cranks. Adjustable length cranks are available in length that range up to mm and custom length cranks can be made in 1mm increments up to mm that I am aware of for those that are interested enough to pursue it.
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