So as the title says I switched to a 165mm crank on my new Speed Concept. I went from a 175mm crank on my 2011 Speed Concept. I am riding a Shimano Ultegra DI2 6800 53/39 crank. After riding for the past 2 months, I have noticed that I am having a hard time finding the correct gear for my preferred cadence while riding on the flats or downhills. I have noticed on downhills that I am looking for an extra cog (Spinning at over 110 cadence) but I am already in the 11 cog. I was assuming that this was due to switching to the 165mm crank. I am currently running an 11-28 cassette, but am wondering if switching to an 11-25 or 23 (have the 23 already on my disc) will help me on the flats at least due to the 16t cog, but I know that won’t help on the downhills. I was thinking about going to a 54t chainring, but was not sure if a dura-ace 54t ring would work on an ultegra crank (assume it will since they are both on the 110mm bolt pattern and 4 arms). Advice? Thanks in advance.
Well, the 11-23 certainly has less big jumps than the other cassettes, so it might help you in finding the right gear on flats. Going up hills, you can always use the small ring, and 39/23 is acceptable to a lot of riders, depending on what kind of hills you’re climbing. As far as spinning out, 53x11 even on a 165mm crank is moving pretty good. If it’s a huge issue, the 54 would be a good option, though I’m not sure if the 9000 ring would go on 6800 crankset (probably not).
spinning in the 11 you will actually be moving your feet slower with the 165 than you were with the 175. cadence would be the same at the same speed, but foot moves not as far, smaller radius=small circumference
I wouldn’t worry about downhills. Just enjoy the ride if you are spun out. For the flats I would swap cassettes assuming you don’t need the climbing gears. I am sweet spot sensitive to cadence so I always run an 11/23 on my TT bike unless I’m doing a hilly long course. Most rides around home I don’t even need the small ring. That 16t cog is right in my sweet spot and if I don’t have it when I’m pushing hard I get really aggravated. I have a few times swapped over to a 52-34 up front just to hold the 11/23 cassette on a hillier course. The front shifting isn’t super smooth but it keeps my top end and tight gearing with some climbing gear too.
spinning in the 11 you will actually be moving your feet slower with the 165 than you were with the 175. cadence would be the same at the same speed, but foot moves not as far, smaller radius=small circumference
This
You could throw a 54 on there but you’ll have to assess just how much that’s worth to you. For me, personally, if I’m spinning out 53/11 I’m going faster than I’m comfortable with on a bike. YMMV.
If you’re spinning out your 11 cog then it’s not because of shorter cranks. You need a bigger top end gear, which means a bigger chainring or you can switch to even shorter cranks.
Switching to shorter cranks actually increases the gearing / resistance. Think about it this way - using a longer wrench gives you much greater leverage / lower resistance than using a very short wrench.
Recently I switched from 172.5mm cranks to 165mm cranks; I was running a 50 big chainring and 12-23 10-speed cassette. Because the switch to shorter cranks increases my gearing, to get the same gearing as before with 165mm cranks I would need a 13-25 cassette. Or I could keep the 12-23 cassette and use a smaller 48-tooth chainring.
Switching to shorter cranks actually increases the gearing / resistance. Think about it this way - using a longer wrench gives you much greater leverage / lower resistance than using a very short wrench.
No, gearing is not changed unless you change the cassette or chain rings.
torque = crank length * force.
for a constant torque, you can either increase the crank length and lower force or decrease the crank length and increase force. Neither changes gearing which is the ratio between the number of teeth on the chain ring and the cassette cog.
If you go to a shorter crank and maintain equal torque to what you rode with a longer crank, then that additional force pushes straight up into you knees.
Switching to shorter cranks actually increases the gearing / resistance. Think about it this way - using a longer wrench gives you much greater leverage / lower resistance than using a very short wrench.
No, gearing is not changed unless you change the cassette or chain rings.
torque = crank length * force.
for a constant torque, you can either increase the crank length and lower force or decrease the crank length and increase force. Neither changes gearing which is the ratio between the number of teeth on the chain ring and the cassette cog.
If you go to a shorter crank and maintain equal torque to what you rode with a longer crank, then that additional force pushes straight up into you knees.
Ok, maybe I used the wrong term. Given everything else equal, switching to shorter cranks = more resistance; it’s harder to turn the pedals (given everything else stays the same). That’s what I meant when I said shorter cranks increases your gearing. The articles I linked explain everything better than I did.
EDIT: I just re-read those articles and they both state that yes - crank length has a significant effect on gearing. So I stand by my original statement: shorter cranks increase your gearing. If you want to maintain your same gear ratios with a shorter crank, you need to change either your chainring or your cassette (or both) to compensate for the increased gearing of the shorter cranks.
I can’t see any reason why changing to a shorter crank would change gearing. The gearing is based on the cassette and chainring like the other poster stated. I can understand it may take more resistance to pedal with a shorter crank because of the smaller lever but it would not change the actual gearing.
I can’t see any reason why changing to a shorter crank would change gearing. The gearing is based on the cassette and chainring like the other poster stated. I can understand it may take more resistance to pedal with a shorter crank because of the smaller lever but it would not change the actual gearing.
the crank is part of the overall gearing.
The OP either has 650 wheels or doesn’t really have an 11
I can’t see any reason why changing to a shorter crank would change gearing. The gearing is based on the cassette and chainring like the other poster stated. I can understand it may take more resistance to pedal with a shorter crank because of the smaller lever but it would not change the actual gearing.
If it takes more effort to turn shorter cranks (given everything else stays the same), then your gearing has changed. It would be the same if you shifted to a smaller cog (or two, depending on how much shorter your cranks are). The end result is the same - it’s harder to turn the pedals. Thus - resistance / gearing has increased.
Let me add another thing - when I switched from 172.5 to 165 I was an idiot and actually thought the opposite. That shorter cranks decreased your gearing and that I need to switch to LARGER gears to compensate.
I went from 50-38 chainrings with 172.5mm cranks to 53-39 chainrings with 165mm. Cassette was a 12-23 10-speed. Boy oh boy was I in for a shock - due to the double whammy of shorter cranks (increased gearing) + the larger chainrings (more increased gearing). The whole 2 weeks I rode that setup on the trainer I don’t think I even had a need to shift out of the small chainring once.
I sold the 53-39 and when I actually researched out what was happening I was able to get a sensible chainring / cassette combo with my shorter cranks.
If you’re spinning out your 11 cog then it’s not because of shorter cranks. You need a bigger top end gear, which means a bigger chainring or you can switch to even shorter cranks.
Switching to shorter cranks actually increases the gearing / resistance. Think about it this way - using a longer wrench gives you much greater leverage / lower resistance than using a very short wrench.
Recently I switched from 172.5mm cranks to 165mm cranks; I was running a 50 big chainring and 12-23 10-speed cassette. Because the switch to shorter cranks increases my gearing, to get the same gearing as before with 165mm cranks I would need a 13-25 cassette. Or I could keep the 12-23 cassette and use a smaller 48-tooth chainring.So wait, you’re going to increase your cadence to go the same speed? Mechanically the “gearing” has not changed due to the shorter crank arm, using the same mechanical 50t ring & 12t cog with the same cadence = same speed. Keeping the 50t ring and changing to 13t small cog you will go slower at the same cadence. Same goes with keeping the 12t cog and changing to a 48t ring, slower at the same cadence.
Heres the Cobb example, which is in-line with what Ive encountered.
**“During one particular study, Martin and I recorded athletes’ oxygen consumption while cycling on a stationary bike in the lab. We used crank lengths of 145, 170 and 195 mm; pedaling rates of 40, 60, 80 and 100 rpm’s; and intensity levels of 30, 60 and 90% of lactate threshold. ** “We found that the power produced (i.e. force applied to move the pedals) during exertion accounted for 95% of oxygen consumption (V02). Changes in crank length and pedal rate had the capacity to alter oxygen consumption or efficiency by about 3%. “Furthermore, this study demonstrated that the body requires more oxygen as pedal speed (speed of the pedal along its axis of travel – NOT cadence) increases. So, for any given pedal rate (cadence), pedal speed will therefore be slower with shorter cranks, resulting in a decreased oxygen requirement.
Since I’m predominantly a roadie who has been using a 53-tooth chainring with 175-180mm crank arms, Cobb offered that I might want to mount a 54 or 55-tooth chainring if I moved to shorter cranks. This didn’t make sense to me – or McDaniel – initially, as it seemed to contradict the whole leverage component of the discussion. A shorter crank implies a shorter lever, which would imply that a rider need exert more force to turn the same size gear. However, Martin and his colleagues’ findings implied that longer cranks did not yield more power, and that shorter cranks yielded more efficiency in the form of less oxygen uptake. Which meant that factoring in all aspects of biomechanics and physiology, with pedal speed perhaps the most significant, the issue of leverage was no longer the primary consideration. That was the change in paradigm. For example, let’s say a rider has determined she is efficient (and has likely become comfortable) turning a certain size gear with 180mm cranks at a given pedal rate, yielding a particular pedal speed. Now she switches to 165mm cranks and settles back into her comfortable pedal rate, but even after several rides feels that something is amiss. We know that her pedal speed has decreased, because she’s now turning shorter cranks at the same pedal rate as before, so we – like Cobb –make an educated guess that what feels different can likely be attributed to the fact that her oxygen uptake has been reduced. In other words, there is now less metabolic cost (i.e. she is not working as hard) to turn the same size gears!
Okay okay, I read the article about crank length and gearing posted on slowtwitch by Greg Kopecky and played around with Sheldon Browns calculator. It looks like i can get pretty close to my old gearing by switching to an 11-25.
jackmott, I do have an 11 cog and I am on 700 wheels. I know what I have.
