Short cranks are popular with many recumbent trike riders because they help you spin faster and also decrease the pressure on your knees. In general, for any given rider, the shorter the cranks are, the easier it becomes to spin a rapid cadence. HERE is the late Sheldon Brown’s article on the subject. And HERE is a short article about short cranksets and knee pain. And HERE is yet another article by Mike Burrows. And HERE is an article on how to determine (calculate) the crankarm length you need.
As far as I am concerned I think every pedal powered bike/trike should come equipped with crankarms which offer multiple positions for the pedals such as shown in the picture below. Then riders of all size can choose what is best for them. That just makes sense to me!
Shortening crankarms can be accomplished by replacing the crankarms or by using adapter plates with predrilled and tapped holes such as shown below. No matter which you choose none of it is inexpensive.
I personally really like the idea of the multiple hole add ons like I have pictured above and below. They offer all those positions. They space out the pedals a bit further widthwise. They are easy to install. And I would imagine that they are a less expensive way to go. However, from what few I have found online the cost is a whole lot more than I thought they would be … like within $25 of the cost of a new crankset. It is reported that these don’t stay tight and often times don’t fit the crankarms correctly.
Note: (1.5 years later after first writing this article) For what it is worth I now have a set of Ride2 crankarm shorteners (see further below) and have not had any problems at all with them.
Here is a video which explains the need and benefit of shorter crankarms.
There are various manufacturers of these crankarm shorteners and each is different from the other.
Adjustable crankarms are also available.
Yet another option some people go with is drilling and tapping new holes in the existing crankarms. So long as the crankarms are made in such a way that this can be done and the person doing this knows what they are doing this is by far the cheapest option. All that is involved is the labor to accomplish it. Definitely this must be done right or one would ruin an expensive set of crankarms. Ideally this should be done in a machine shop where accuracy in spacing and alignment be more ensured. Also the hole should be flat faced by milling the surface. Doing all this by hand would be more difficult to get it straight and accurate although it could be done. I have contemplated doing this to my crankarms. This should only be done on aluminum crankarms.
This person will professionally shorten crankarms. It is not inexpensive to have it done, but it is cheaper than buying an all new crankset. The two pictures above are examples of his workmanship.
Just a note here for those who ride tandem trikes: “Any tandem team needs to come to terms with the cadence issue. With practice and patience, most couples can work this out on a standard tandem. Some teams, particularly those who are not well-matched in leg length or pedaling style may benefit from use of different length cranks for the captain and stoker.” … from Sheldon Brown’s article.
Also from Sheldon’s article he states: “For reasons that are not completely clear, many recumbent riders benefit from shorter-than-usual cranks. Some people who have no knee problems on upright bikes find that their knees pain them when they ride a recumbent. Shorter cranks can often alleviate this, though it isn’t clear that the long cranks per se are the cause of the problem.
One theory is that the knee pain results from pushing harder, “lugging” in a too-high gear. With an upright bike, if you push very hard you are lifted up from the saddle, so you know you are doing so. With a recumbent, where you are braced against the back of the seat, it may not be so easy to judge how hard you are pedaling, so you may just over strain your knees by pushing too high a gear without realizing it.”
HERE is an article with information on what length of crankarms we should use based on our height. It only goes down to 5 foot 5 inches and up to 6 foot. HERE is another one with a chart showing inseam and corresponding crankarm length.
I used the calculator found HERE to determine the crankarm length I should use. Of course, it is only as good (accurate) as the measurements are you put into it. According to the results shown in the image below I should use about 135 mm crankarms. My trike came with 165 mm crankarms.
Note: The thing I have noticed about these various charts and calculators as they all come up with considerably different results. For myself I have found crankarm lengths ranging from 130 mm to 160 mm. That is a considerable difference and seems rather absurd to me. I guess this is why this subject matter is so controversial. Anyway, I am fully convinced that shorter people need shorter crankarms as do those who have knee joint issues.
One of the statements made on one the websites follows: “I think the main thing that this suggests is that the TA chart, which at first glance seems so radical in suggesting either very long or very short cranks, is in fact on the conservative side, and that short people especially might consider getting even shorter cranks than those recommended by the chart.” I tend to agree with this. I have found I do much better with shorter cranks than what some recommend for my inseam. I prefer the 130 mm crankarm length over the 155 mm length some show for me. I am short and have gotten shorter as I have aged. I have always had a short inseam. I have lost 1.75 inches in overall height thus far in my elderly years.
HERE are YouTube videos on the subject of short crankarms.
One thing to keep in mind, nearly everything written about this subject was written concerning bicycles and not tadpole trikes. I am no expert so I can’t say much about this. I can only speak from my own experience. As a short person who has had knee joint issues the shorter crankarms have been a God-send. My only regret is I didn’t switch to them many years earlier.
When it comes to short crankarms these are the options that I am aware of. Shorter crankarms just might be your ticket to help you …
ENJOY THE RIDE!
P.S.- (Dec. 2016 … 1.5 years later) I have purchased and am now using the Ride2 crankarm shorteners and really like them. Right now I have them mounted on my wife’s 2 wheel recumbent bike which is set up on an indoor trainer out on the enclosed patio. It is winter here where I live and too cold and too much snow to attempt riding my tadpole trike. I will install them on my trike when better weather comes along and I can go out riding it. I have also just undergone the surgical procedures for knee joint replacement on both knees so these crankarm shorteners really are helping during my rehab therapy. Right now I have the pedals in the next to the shortest holes which is about 106 mm I think. I expect to move them out further as time goes along. The various holes shorten the crankarms by 24, 41, 59 and 76 mm. So with 165 mm crankarms these adapter plates provide 141, 124, 106 and 89 mm settings. As you can see there is no 135 mm option. The closest I have is the 141 which is likely to be what I end up using in due time as I fully regain my range of motion.