V20 crank length?
- Thread starter TransAm
- Start date
Andrew Wilson
Guru
I’m your size and I prefer 170’s. I run 172.5 on my road bike. I tried 155’s on my Baron but still prefer 170’s. While shorter will let you spin faster, I find a slower RPM ( 80 rpm or so) lets me hold a better line on the V20
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DavidCH
In thought; expanding the paradigm of traversity
Well... I got my best results on a 165mm crank but I am running 155mm. After every ride with the 165mm cranks my knees were in pain. With the 155 my knees are fine. So for me cycling every day with 155 suited me better than 165 health wise. I am 5'10. The 155s make my legs more aero and with the cleats far back in the shoes at an optimum.
LarryOz
Cruzeum Curator & Sigma Wrangler
Many riders find shorter cranks are better for bent riding. Personally going from 175 down to 150 help alleviate my knee pain, spin up faster, and be more aero. There really is no down side that I can see. You do not loose leverage or power and I have tested this various ways. I have tested cranks from 180 down to 90mm. I really like the 140-150 range.
Here is also calculator that can help you figure out what would probably be best for you: http://www.recumbents.com/wisil/misc/crank_angle.asp
benphyr
Guru-me-not
@LarryOz et al. Has anyone come across actual scientific or at least rational reason(s) or testing results for why shorter would be better for recumbent specifically and a bit longer for vertical better? One needs to give knee pain veto power, and after that leverages, torques, body parts lengths and strengths and endurance are going to be different for each individual.
Could it be related to the hip-bottom bracket angle that dictates what part of the pedal stroke is gravity assisted and which part is fighting gravity? That is, the push part of the cycle on recumbent is largely unaffected by gravity while the follow through and dead spot are gravity affected on recumbent. On vertical bike the push force pretty much coincides with gravity.
Could it be related to the hip-bottom bracket angle that dictates what part of the pedal stroke is gravity assisted and which part is fighting gravity? That is, the push part of the cycle on recumbent is largely unaffected by gravity while the follow through and dead spot are gravity affected on recumbent. On vertical bike the push force pretty much coincides with gravity.
benphyr
Guru-me-not
Oh I use 175mm and 165 on my Cruzbike Kit and Qx100 respectively- because that is what they came with. When I switch bikes I can feel a difference. But It is not something that I can quantify or say is significant enough for me to distinguish from everyday variances in my riding.
LarryOz
Cruzeum Curator & Sigma Wrangler
If you are spinning 90+ on average, you should give some 150mm cranks a try - You will be amazed at how much less movement your legs will have both up and down and in and out.
LarryOz
Cruzeum Curator & Sigma Wrangler
As you all know I have reams of testing on this, but I have not seen any "actual scientific" data on it in the cloud anywhere. Probably because of the small amount of recumbent cyclists out there compared to uprights.
I believe this is one of the main reasons:
When a rider is on an upright bike, their hips rock back and forth somewhat as their normal pedal action. This allows their leg greater reach and a larger total diameter of pedal travel which translates to a longer crank. Since part of the pedal stroke is assisted by the mass of the riders body (with some help by gravity and momentum) the length of the crank has greater importance since the moment arm is longer = more power. An upright rider will obviously hit a "size" that will be uncomfortable or even panful for them (just as a bent rider will), although I think it will be at a longer crank length. They will also notice that the longer the crank length the more their legs will have to move which becomes more pronounced as the rpm increase.
I think mashers (low rpm riders) will not have as many issues with longer cranks as spinners (high rpm riders) - that is until they get older and their knees start screaming at them.
My 2 cents,
Larry
I’ve thought about this a lot but also don’t have any real data. A couple of ideas:
1) When I got my first Cruzbike I set it up so that my knee angle at greatest extension would be the same as on my uprights. With this I found that I had weird sensations in my knees on long rides where it felt as though my knee was hyperextending a bit. I think this is because the weight of lower leg and upper leg in the reclined position are both pulling against the knee with the same forces as you would get during hyperextension. I shortened the boom a bit and the problem went away. If the cranks were as long as on the DF that would then make my knee angle at minimum extension too tight which is a common cause of knee pain in cycling...so the shorter cranks help there.
2) Whether you’re on a DF or bent when one leg is going down (with respect to the ground) the other is going up so the two forces should cancel out. On a DF they more or less do because the center of mass of the leg is more or less directly above the bottom bracket. On a bent the situation is much more complicated. There’s a lever effect because the center of mass of your leg is close to your body but the force on the pedals is far away. Fortunately the pushing, more extended leg is further out so the gravity force from the extended leg has a lever advantage on the gravity force on the rising leg but unfortunately because of the more acute bend of the knee on the rising leg the center of mass is being moved through more distance. I think on balance you lose a bit of energy pushing that rising leg up. The shorter the crank the less you lose.
The above may be completely wrong but it’s fun to think about. I’m more confident about the legitimacy of point 1 than of point 2. I thought that @RojoRacing had an interesting observation that, at constant power, his heart rate went up as he increased cadence. This suggests that there’s a cost per pedal stroke when riding a recumbent. I think published studies on DFs have shown that you don’t see this sort of effect when the pedals are right below your legs.
1) When I got my first Cruzbike I set it up so that my knee angle at greatest extension would be the same as on my uprights. With this I found that I had weird sensations in my knees on long rides where it felt as though my knee was hyperextending a bit. I think this is because the weight of lower leg and upper leg in the reclined position are both pulling against the knee with the same forces as you would get during hyperextension. I shortened the boom a bit and the problem went away. If the cranks were as long as on the DF that would then make my knee angle at minimum extension too tight which is a common cause of knee pain in cycling...so the shorter cranks help there.
2) Whether you’re on a DF or bent when one leg is going down (with respect to the ground) the other is going up so the two forces should cancel out. On a DF they more or less do because the center of mass of the leg is more or less directly above the bottom bracket. On a bent the situation is much more complicated. There’s a lever effect because the center of mass of your leg is close to your body but the force on the pedals is far away. Fortunately the pushing, more extended leg is further out so the gravity force from the extended leg has a lever advantage on the gravity force on the rising leg but unfortunately because of the more acute bend of the knee on the rising leg the center of mass is being moved through more distance. I think on balance you lose a bit of energy pushing that rising leg up. The shorter the crank the less you lose.
The above may be completely wrong but it’s fun to think about. I’m more confident about the legitimacy of point 1 than of point 2. I thought that @RojoRacing had an interesting observation that, at constant power, his heart rate went up as he increased cadence. This suggests that there’s a cost per pedal stroke when riding a recumbent. I think published studies on DFs have shown that you don’t see this sort of effect when the pedals are right below your legs.
chicorider
Zen MBB Master
Consider how much climbing you do as well. I'm 5'5" and ran 170mm cranks on a DF bike. I run 160mm cranks on my Cruzbikes, and feel that that gives me the balance between flat-land speed and climbing torque. I tried 155mm for a while on my V20, but returned to 160mm and have stayed there. I was glad that I tried the shorter length because it helped to confirm that 160 felt right for me. In short, be willing to experiment and go with what feels fright to you (and your knees).
I did a long solo ride today (obviously the way I go on about these things nobody would want to ride with me) and thought of an actual “experiment”. If I completely relax my legs on the V20 the balance point is with my extended leg at about 45 degrees up from the bottom and my bent leg about 45 degrees down from the top. That means that in the first 45 degrees of the power stroke I’m actually working against gravity a little bit in addition to propelling the bike. With a longer crank the balance point should be the same but you would have to raise the center of mass of the system more to get to the point where gravity starts helping you again. Of course there are all sorts of reasons you wouldn’t want to have a ridiculously short crank but the energetic cost of a longer crank would be a consideration in finding the optimal length and might be part of the reason that people usually go shorter on a bent than on a DF.
Frito Bandito
Zen MBB Master
I've never had issues on a DF bike putting down power or feeling any pain at all in short bursts or on 150-180km rides with my 170mm or my 172.5mm cranks.
However, with the 165mm cranks on the V20 I've felt some pain in either my left Iliopsoas or Pectineus, or maybe even the Adductor, which was likely caused when the boom slipped and the BB was 3cm further away by the end of the ride. I shortened and tightened it up and it is fine now but there is still residual pain a week later. Yesterday's 65km ride was relatively easy and almost pain free so I am sure it'll recover. What I assume happened is during that part of the stroke where my right leg wasn't able to do its part in getting the power further around, or the left leg muscles were lifting more than they were accustomed to. Or, it could have just been that the BB being too far away caused it to stretch too far or have to lift from a hyperextended position. It's easier to get a DF bike fit dialed in so I would have had the problem solved quickly, but this will take a bit more tweaking since generating power on a recumbent is not entirely the same as for a DF.
However, with the 165mm cranks on the V20 I've felt some pain in either my left Iliopsoas or Pectineus, or maybe even the Adductor, which was likely caused when the boom slipped and the BB was 3cm further away by the end of the ride. I shortened and tightened it up and it is fine now but there is still residual pain a week later. Yesterday's 65km ride was relatively easy and almost pain free so I am sure it'll recover. What I assume happened is during that part of the stroke where my right leg wasn't able to do its part in getting the power further around, or the left leg muscles were lifting more than they were accustomed to. Or, it could have just been that the BB being too far away caused it to stretch too far or have to lift from a hyperextended position. It's easier to get a DF bike fit dialed in so I would have had the problem solved quickly, but this will take a bit more tweaking since generating power on a recumbent is not entirely the same as for a DF.
benphyr
Guru-me-not
Wrong fit or not being used to a particular muscle movement can easily result in damage or pain. When switching to moving bottom bracket recumbent you are changing things with the muscles used. Also in your case the number of kms is high so the repetition of motion would be higher than for me when I learned over the course of months with rides ranging from parking lot practice to 10km max. On a new platform (mbb) you are not going to notice differences as easily either.
With thousands of hours on your DF you would have noticed earlier. Also, the seat would move down bringing the pedals closer which is a little more forgiving than hyperextending the joints.
All this is to say that I believe your experience is not at all related to crank length. If anything the shorter crank length slightly reduced the problems of the boom extending.
Caveat: This is my experience talking not scientific or medical analysis. Hopefully it is helpful.
Frito Bandito
Zen MBB Master
Those are very good points benphyr, and seem very logical. I am sure with anything longer than 165mm cranks the problem would have been more severe, and I didn't even really consider the mbb. I am definitely going to be focusing more on keeping it more stable to prevent recurrence from here on out. It is difficult to limit how hard or far I push on it until the muscles adapt and to the mbb and I can keep it straighter. I will be installing a new groupset soon and it's still strange for me to accept that shorter cranks seem to be better than longer, but I will not go against what everyone seems to agree on.
benphyr
Guru-me-not
I guess to be sure I am being clear. Post #15 refers specifically to @Frito Bandito's situation, emphasizing that the variables involved, being a new mbb rider + the boom sliding out 3cm over the course of one ride, are much more significant than the difference between 175mm and 165mm cranks would make (1 cm) for one ride. It may turn out to be different sizing is what you prefer in the long run but the change to smaller crank length with the V20 seems, even if it is a contributes a tiny bit, like it would be the smallest of the factors identified.
I had read quite a bit of scientific evidence to support the use of shorter cranks on more laidback positions with crank high, although I do not have said information at my finger tips.
1. Shorter crank results in less air flow disruption (smaller circle with the feet)
2. Better hip angle at the top of the pedal stroke.
3. Shorter cranks mean higher cadence, all else equal. This improved capillary perfusion and venous return.
(If you are using Rotor elliptical rings, do your homework......they have to be offset from upright position and 4 bolt shimano won't work)
1. Shorter crank results in less air flow disruption (smaller circle with the feet)
2. Better hip angle at the top of the pedal stroke.
3. Shorter cranks mean higher cadence, all else equal. This improved capillary perfusion and venous return.
(If you are using Rotor elliptical rings, do your homework......they have to be offset from upright position and 4 bolt shimano won't work)
ak-tux
Zen MBB Master
Just incase no one else had already posted:
http://www.recumbents.com/wisil/misc/crank_angle.asp
http://www.recumbents.com/wisil/misc/crank_angle.asp
paco1961
Zen MBB Master
Late to the party but add me to the short crank ranks. I’m 6’1” w 34” inseam. Rode/raced 172.5mm on DF for years. Tried the same on my CB (first recumbent) and could barely walk after my first 50 miler due to knee cap pain. Switched to 155 and have never looked back. Now ride 155 on both S40 and V20
