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Crank Arm Length on Small Phantom

Hi All. I'm new to the forum and just bought a Phantom. I have 20 years of riding DFs but this is first bent. I've done a few Target parking lot rides, one feeder road through rollers where there is little traffic and graduated to using my SpeedPlay padels yesterday without too much drama. Seemed like my steering was much better yesterday-no parked cars, or curbs attacking me!
Question: It looks like the cranks on the small Phantom is 170mm. I ride 170-172.5 on my DF bikes. It was my understanding that most bent riders used much shorter crank arms than DFs to spin easier. I don't know if this is true or just something I read. Is it common to put 170s on a small frame bent designed for short riders. I thought maybe LCD intentionally used same length cranks as a DF due to upright sitting position because you can get more leg power into the stroke than a seat with a high degree of incline. I'm 5"5" with an ex seem of 38. It seems I have the boom about where it should be for leg extension and bend in knee. It also seems my knees come close to my chest. Don't know if this is how the bike is designed or whether I'm not set up correctly.

Hi Bowzette -

Some recumbent riders prefer shorter crankset lengths than is the norm for upright bike riders. But there is no consensus about this, and many riders are happy to use the same sized cranksets that they would use on traditional upright bikes.

I tried using 145mm BMX cranks for a month or two, but could never adjust to them. I then tried 155mm cranks, and although they felt weird at first, after a month or so of riding they started to feel OK. My motivation for using the short cranks was to fit my clodhopper feet inside of a very small front fairing. I do not think the short cranks made me any faster or slower.

Some riders say that knee problems are helped by switching to shorter cranksets. I have been lucky with my knees so far, and have not felt the need to use them for this reason.

Another thing that recumbent riders sometimes do is to position the cleats of their clipless pedals farther down towards the heel than is the norm.

My advice: ride the bike the way it is now. Do not mess around with different components, wheels, etc. Just get the bike adjusted properly, and start riding. Time and miles will tell you whether or not your choice was the right one for you. If you put in some real miles, and decide the bike is a keeper, then you can start playing around with modifications.

Safe riding,

I figured it out. The new Phantom II small frame has 160mm crank arms and the large chainring is a 48 not a 52. I apparently have an older model that has 170 crank arms and the large chainring is a 52. I would rather have the 52 than a 48.

I'd recommend sticking with the 48. Unless most of your rides are downhill, embedded in a peloton, or with a strong wind at your back, you're not going to be spending much time in 52x11. Depending on how fast you can pedal, you won't spin out until you reach 38 mph or so.

For the rest of the time, the 48 chainring will give you a great all-around gear selection, allowing you to stay in the big ring a lot. IMHO it's nice not to have to shift to a smaller chainring to get up small-to-medium climbs.

With the "short" cranks you should be able to spin, making up for some of the gearing on the top end that you feel you're missing.

Remember that above about 30 mph, it takes a lot of work to get incremental speed gains due to wind resistance.

Hi I've been riding My Phantom for a few years, 5600 miles or so. Keep it simple!!!! I'm 5'5 and 71 years old. Don't change a thing. Spd clips a MUST!!! DOUG DANIELE

Thanks Doug. I put my SpeedPlays on Sunday and rode without drama :-) I plan on taking some hills on this evening.

Looks like some good ideas have been covered. I would agree to keep it as it is for now and get time and miles on the system. Comming from a DF with similar size cranks should make these feel good enough.

On the 38, my knees come in under the handle bars but not near my chest. They extend to where my legs are almost straight but my knees are not locked.


Since you're 5'5", you could go to shorter cranks. I'm 6'4" and I use 175mm cranks on the P38 and 170mm cranks on my Phantom. I get good leverage and proper knee extension with both.

What you don't want to do is hyper extend or over bend where the knee is nearly flat with full pedal extension or worse yet, when you bring the knee back, have it bend to less than 90 degrees. Either of these extreme's can cause serious knee issues down the road. If you experience continuous knee pain after several rides, you may want to consider shorter cranks or different gearing.

I ride with guys who are over 6ft who use 160 to 155mm cranks on P38's and have no trouble maintaining a high cadence. Good luck.

thanks for the comments Scooter. I have adequate bend in the knee and the few miles I've put in hasn't bothered my knees. But it does "feel" like my knee is coming too far back. I will pay close attention and see if this is the case. I was a bit surprised LCD put 170 cranks on a small frame bike set up to spin. Now they put on 160s.


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