145 mm cranks

[vosadrian]

Could you tell us what your current setup looks like? I live in a hilly area too, so any tips would be helpful.

My setup is 6870 Di2 with 52/36 front rings on 155mm crank arms (BBK off ebay). Rear cassette is the stock cassette mine came with which I think is 11-36? I said 30 above but I was incorrect.

So I have 1:1 with 36 front and 36 rear. I can get up some 15% short climbs with that setup, but I would be putting out big power to do that so can only do it for maybe 30 seconds. With this setup I have to choose my roads carefully and avoid sustained steep roads. I can climb up to about 10% sustained with this gearing, but I need to be fairly fit to do 10% being at full exertion. 7-8% is OK. 5% and below is nice. For me I live on the plateau NW of Sydney that is about 200m elevation. I regularly go near sea level, so the longest climbs are about 200m of elevation gain over varying % gradient. Mostly the longest I would climb would be about 15 minutes. My body type is a good climber for about 5 minutes and then I start to feel it. I climb OK but more of a punchy short climber of around 5 minutes than long climbs.

On the top end I have 52-11. On some of the long 1-2% declines I can pedal to about 65kph comfortably and 70kph if I am motivated, but there are a few steeper long downhills I could go quicker if I had longer gearing... But I think I need 12 speed with a 10T to do that and still be able to climb as above.

 

[ak-tux]

@Karl42 I hear you. Once again I see how personal the change in crank length is regardless of what the calculators say about "ideal" crank length. While I am fortunate that I don't have any pain issues, I have compromised my riding position from what is ideal, but it's livable. A shorter crank could bring it closer to ideal.

I've given in to my curiosity and ordered "Cruz Bike" branded cranks from AliExpress. today. I ordered a 165 mm set and a 160 mm set for about $35 each and a 42T GXP chainring for $18. So I'm under $100 total for this experiment. When I'm done with them, I'll be happy to offer them here to any forum members that want to do their own tests.

$90 for science! Looking forward to your findings!

Anyway, I had the privilege to compare 170mm vs 165mm becuase the Cruzbike S40 came with a 165mm SRAM Apex1 crank. Previously I had a homemade recumbent (cruzbike copy) with 170mm cranks. First impression, was my average cadence went up. From around 85-90rpm to about 92-100 rpm. Secondly it felt abit harder to pedal the same gear. I had to shift down to a relatively easier sprocket across the range for the same percieved effort.

I don't know about other people but for me, it needed some getting used to. Unfortunately, the SRAM Apex1 crankset has a proprietory bolt pattern and does not allow easy use of third party chainrings. So in my desire to change the chainrings I went back to a low-cost 170mm crankset(from AliExpress). I felt at home with them.

However, I keep wondering, maybe I should have given the 165s more time and maybe fine-tuned the boom position e.t.c. Unfortunately, I also later invested in a 170mm left sided powermeter which is not compatible with the SRAM Apex1 crankset. Besides, I don't like messing around with my bike fit once I find a comfortable position. I will, however, consider testing shorter cranks using my old homemade recumbent.

Later, once I have all the necessary components, I will hopefully use my indoor trainer to compare them. Power would and is still the most objective way to compare the performance. Yes, Iam just curious.

 

[Damien]

On some of the long 1-2% declines I can pedal to about 65kph comfortably and 70kph if I am motivated, but there are a few steeper long downhills I could go quicker if I had longer gearing...

I’ve never gone faster than 65 km/h on descents. I’m just too scared because emergency braking or a crash at that speed would have serious consequences. I'm lightweight, so I don't accelerate as fast as my heavier friends, and luckily I don't have to worry as much about braking – but still, I’m a bit of a coward.

 

[JerseyJim]

I’ve never gone faster than 65 km/h on descents. I’m just too scared because emergency braking or a crash at that speed would have serious consequences. I'm lightweight, so I don't accelerate as fast as my heavier friends, and luckily I don't have to worry as much about braking – but still, I’m a bit of a coward.

There's a big difference between being a coward and having a well developed sense of self preservation. In your case, I think the latter is the prevailing condition. Unless you're in a race and the risks match the stakes, there's no need to go much faster than 40mph/65kph. It's certainly fun to ride fast, but everyone has their limit.

 

[vosadrian]

I’ve never gone faster than 65 km/h on descents. I’m just too scared because emergency braking or a crash at that speed would have serious consequences. I'm lightweight, so I don't accelerate as fast as my heavier friends, and luckily I don't have to worry as much about braking – but still, I’m a bit of a coward.

For sure there are serious consequences, and everyone does their own risk analysis. In this instance, I am riding on a motorway with no cross streets and a wall barrier on the road side and 2-3m of verge I ride in with the traffic on the other side. The road is very straight and good road surface with good visibility. No risk of a car or pedestrian coming out of a driveway or side street The only real risk is if I lose control of the bike for some reason... or if I hit an object on the road. I feel very stable on my V20 at these speeds and have been up to 90kph (coasting) on steep descents and do not feel a lack of stability (I have been over 100kph on my upright and feel less stable). So the big risk is hitting an object. about 18 months ago I was riding the same motorway in a flat section at night and I hit something hard and came down. I was doing about 45kph when I hit it and I never saw it due to night and my lights not being as good as I thought. I smashed my front wheel and needed to replace the rim. I managed to keep the bike upright to slow it down to about 20kph before I slipped the front wheel and came down on my side and got some gravel rash that was much more minor than I expected. I managed to get a tube on the cracked rim and pump it up enough to ride home, but not my favourite riding experience.

So my risk analysis has changed. I will still happily go to high speeds on this road, but only if I can see clearly >50m down the road. So not at night with lights. But in good light, no problem.

I ride both an upright high end road bike and my V20. For me the upright does the hills (windy canyon roads) and the V20 is for flattest and fastest roads I can find. My target every ride on the V20 is going fast. Getting PRs... maybe a Strava KOM. Getting the highest average speed I can. You don't get that hitting the brakes down hills. I must say, unlike many here, I enjoy riding my upright more. My V20 has a purpose (managing back pain and going fast), but I enjoy riding a DF more as I have more freedom with it.

 

[JerseyJim]

I swapped out my 170 mm cranks for a set of 160 mm cranks. The experiment was to see if there was a perceptible difference between the 170 and the 160 cranks and if using the shorter cranks improved my bike fit. I didn't change anything else. My setup is a 42T chainring and an 11-46 12 speed cassette.

These are the CRUZ bike cranks from AliExpress. The trademark infringement notwithstanding, this is a decent crankset, especially for 35 USD. Not great, but decent. I still would get a higher quality one to run daily. One note is that if you are running the chainstay that clamps on the bottom bracket cups, you will need a 3 mm spacer on the drive side crank to get these cranks to work if you choose the "Dekas" chainrings. The inside of those chainrings will touch the clamp part of the chainstay without a spacer. The good thing about using a 3 mm spacer is that the spacing between 12 speed cogs are about that distance, so you're just altering the chainline down the cassette by one cog. It actually improved the chain angle for the highest gear. If you're running the updated chainstay, there's no problem.

As far as bike fit there was a small difference. My thigh still touches the bar but much lighter than before. If I want to get the full 10 mm clearance I need to move the boom out around 5 mm, which is the equivalent of raising the seat on an upright bike and something you would do when switching to shorter cranks. I'll end up doing that later but I just wanted to see what swapping out the cranks would do. What it tells me so far is that from a fit perspective and what I'm looking to achieve, 165 mm cranks would be inadequate.

The first difference I noticed in pedaling was that it was easier to spin at a higher cadence, and in fact I naturally wanted to do that. It was easier to do the "scoop" at the bottom of the pedal stroke to keep the spin going. There was less perceived muscle effort to turn the pedals over. It wasn't super dramatic but it was there. As a result of the higher cadence it was easier to maintain a given speed as it didn't take a big muscle effort to correct a loss of momentum.

The second difference I noticed when climbing the overpass to get to the park. While I did have to shift into one gear lower gear than I normally would, I found that spinning that gear felt easier and it felt like less effort to maintain my forward momentum. It felt like less muscle effort and that the muscle force I was using was more sustainable. Also, even though I was in a lower gear, I was climbing at a speed close to my normal speed on that overpass.

Once I was in the park and doing my laps I played with being in top gear and one gear lower. 11th gear at a higher cadence and less pedal pressure actually translated to a slightly higher sustainable speed than with the 170 mm cranks and lower cadence in the same gear. It seems applying a force at more revs per minute beats a greater force less at less revs per minutes when it comes to pedaling efficiency.

I climbed the small hill in the park using different techniques just to see the effects. I shifted down to 10th gear as the lowest climbing gear a couple of times. I also climbed it in 11th and 12th gear just to see how it felt. In general it was easier to maintain a consistent climbing pace in the lower gear and easier to spin than mash. Mashing was still possible in 12th gear but there wasn't really an advantage to that versus spinning in 11th gear. If I was approaching the hill in 12th gear I would carry the momentum as far as I could before loosing my cadence and then shift to 11th gear. That's my usual technique anyway, but it seemed like I could maintain a higher overall speed with the 160 mm cranks.

On the high speed sections of my lap in top gear, my maximum speed decreased from the 170 mm cranks. I can normally do a max speed of 29.5 mph where with the 160 mm cranks I managed 27.5 mph. So there was a 2 mph loss in top end but that's attributable to the effective lower gearing with the shorter cranks. I could change gearing to make that up but for the type of riding I do, it's not necessary. If I was racing and I needed that top end, I would just use a bigger chainring.

I did my normal laps and headed back home. Again, I wasn't trying to go fast but I was playing around with the gears and what I could get out of them at a higher cadence. Once I got home I saw that I beat my last PB by 10 seconds. That's 10 seconds over about a shade more than 21 miles. That's significant, especially since I hadn't optimized anything. I just swapped over the cranks.

Incidentally, that's the second time I set a PB in less than a month on the S30. I'm loving this bike.

Overall, the 160 mm cranks made a good first impression. I attribute the PB to being able to stay at a higher average speed for longer. I seemed to be able to do that with less muscle fatigue. I was in a higher heart rate zone than usual but that makes sense with the higher cadence.

All of this is anecdotal with the exception of the objectively measured time differential. Even though it's the end of the season and I'm probably at peak cycling fitness for this year, I don't think I had 10 seconds in me using brute force. Given how I felt at the end of the ride, I think the gains are best explained by efficiency. In any event, this was an unexpected result. I'll be living with the 160 mm cranks for a while. There are enough positives to continue the experiment.

 

[Robertas]

Yesterday installed new Croder 145mm 46/30 instead of Shimano 165mm 50/34 crankset, also moved BB 20mm forward as new crankset is shorter for 20mm. Today made 70km ride and found these things:
1. much more easy to start from stop especially in uphills
2. higher cadence and more steering control, thus less fatigue in uphills.
3. I can easily drive with one hand now, even sometimes without hands for short time.
4. regarding speed on flat sections- did not decide maybe to install 50/34 with 145mm cranks, how it will perform, compared with current 46/30, it should be easy install as both sets are BCD 110mm.

 

[JerseyJim]

4. regarding speed on flat sections- did not decide maybe to install 50/34 with 145mm cranks, how it will perform, compared with current 46/30, it should be easy install as both sets are BCD 110mm.

Could you clarify what you experienced with speed on flat sections? Was is slower or the same for you as your previous setup?

Edit:: Actually I see now that you have the smaller rings on not the bigger set. Once you get the 50/34 installed I'd be curious to see the result.

 

[Damien]

That crankset looks great in the picture. I’m thinking about getting the same chainring setup, 46-30T, paired with an 11-34T cassette. A few questions come to mind:

Why did you choose the 145 mm crank arm length?
How’s the quality?
How long did shipping to Lithuania take?
Which bottom bracket did you use – did you buy it with the crankset or just a standard one?

I’m also considering Croder – it’s a shame they don’t have a power meter version available right now. I’m wondering if 145 mm won’t result in a significant power loss on climbs.

 

[Robertas]

Could you clarify what you experienced with speed on flat sections? Was is slower or the same for you as your previous setup?

Edit:: Actually I see now that you have the smaller rings on not the bigger set. Once you get the 50/34 installed I'd be curious to see the result.

Did not special segment sprints yet, but according feeling speed is lower than 165mm setup, today installed back 50/34 chainrings, so now my final setup is 50/34 145mm, cassette 11-42, will do the test soon.

 

[Robertas]

That crankset looks great in the picture. I’m thinking about getting the same chainring setup, 46-30T, paired with an 11-34T cassette. A few questions come to mind:

Why did you choose the 145 mm crank arm length?
How’s the quality?
How long did shipping to Lithuania take?
Which bottom bracket did you use – did you buy it with the crankset or just a standard one?

I’m also considering Croder – it’s a shame they don’t have a power meter version available right now. I’m wondering if 145 mm won’t result in a significant power loss on climbs.

Was not easy for me in long climbs with 165mm, I`m heavy, maybe that is the reason.
I`m not expert but I would say the quality is very good
1 week from UK
BB T47 - it was in my V20C frame set, so was nothing to do with BB, Croder fits very well.
From my one 70km ride experience - in climbs 145mm gives more watts indeed

 

[vosadrian]

On the high speed sections of my lap in top gear, my maximum speed decreased from the 170 mm cranks. I can normally do a max speed of 29.5 mph where with the 160 mm cranks I managed 27.5 mph. So there was a 2 mph loss in top end but that's attributable to the effective lower gearing with the shorter cranks. I could change gearing to make that up but for the type of riding I do, it's not necessary. If I was racing and I needed that top end, I would just use a bigger chainring.

Hi @JerseyJim ,

This contradicts my experience with shorter cranks on both upright and my V20. In both cases fitting shorter cranks increases cadence and effectively makes the gear longer (as you need to go to a shorter gear to go the same speed at higher cadence). In the top gear on my bikes with shorter cranks I can go faster as I can support higher cadence with the same gear ratio. At the other end I find the shortest gear to be longer, so I struggle more up steep hills where I am in the shortest gear the bike has. Of course anywhere where I am in the middle of the cassette I can adapt for the change by changing gears, but once in the biggest end of the cassette there is no option to go for a shorter gear.

I find it odd that you had lower top speed with the shorter cranks and claim the gearing is lower.

 

[ak-tux]

Hi @JerseyJim ,

This contradicts my experience with shorter cranks on both upright and my V20. In both cases fitting shorter cranks increases cadence and effectively makes the gear longer (as you need to go to a shorter gear to go the same speed at higher cadence). In the top gear on my bikes with shorter cranks I can go faster as I can support higher cadence with the same gear ratio. At the other end I find the shortest gear to be longer, so I struggle more up steep hills where I am in the shortest gear the bike has. Of course anywhere where I am in the middle of the cassette I can adapt for the change by changing gears, but once in the biggest end of the cassette there is no option to go for a shorter gear.

I find it odd that you had lower top speed with the shorter cranks and claim the gearing is lower.

I also concur with @vosadrian . With all else equal, the shorter crank should make the top gear feel harder than the same gear with a longer crank.

My experience was on a 165mm crank versus a 170mm. My cadence was slightly higher, about +5rpm, on the 165mm cranks and I could achieve a slightly higher speed on the same gear ratio that was on the 170mm crank. Needless to say climbing felt harder on the 165mm cranks for the same lowest gear compared to the 170mm ones.

 

[JerseyJim]

I find it odd that you had lower top speed with the shorter cranks and claim the gearing is lower.

At the end of my summary I did say the what I communicated was anecdotal. That means, this is what I experienced at the time of the ride and my impressions. I did not say my results would or should be universal.

Given that, my top end speed is what I measured and I compared that against what I have measured in the past. 27.5 mph vs 29.5 mph.

My conclusion regarding the reason my top end speed was lower may be flawed, however I think it is sound. Reducing the length of a lever arm is going to reduce the torque. Torque is force times distance. For the same force I produce with my legs, the 170 mm arms are going to result in more torque than the 160 mm arms.

Power equals torque times angular velocity, or the torque times the cadence in revolutions per minute. What that means is that one can reduce the torque and produce the same power by increasing the cadence to compensate.

With the 170 mm cranks, I produced some power "P" at some cadence "C". With the 160 mm cranks I can produce the same power "P" as with the 170 mm cranks if I pedal at some cadence "C + x" where "x" is the additional rotational rate needed to compensate for the lower torque produced by the shorter cranks.

So all that said, my experience was that my top end was slower and I concluded that there was an "effective" reduction in gearing, "effective" being the operative word here.

I say this because if I was not able to produce the additional rotational rate "x" in my cadence to compensate for the lower torque, the effect would be the same as spinning a lower gear. I wasn't in a lower gear - in fact all the gear ratios have remained the same from my previous crankset - however, without compensating for the loss of torque with a properly high cadence, I'm not going to produce the same power. It's clear to me that at the upper end of my power output, I'm limited by how quickly I can spin. This may improve as I adjust to the shorter cranks. However, for that ride on that day at that time, my top end speed was 2 mph lower.

You say that the fitting shorter effectively makes the gear longer (higher), but actually if you spin at the same rate as your longer cranks, the reduction in the lever arm reduces the torque and you are producing less power (torque times cadence) If you produce less power you won't be going faster, you'll be going slower, and that's like being in a lower gear.

You can also look at this from the other side of the equation. You can keep the cadence the same and compensate for the reduction in torque due to the shorter lever arm by increasing the force applied. Then to get the same power as the longer crank arm you need to apply more force. This can feel just like being in a higher gear, requiring more muscle to get same power output. In reality, the gear ratio is the same, the cadence is the same but it feels harder because you're using more force.

Again, how much additional force you will need to apply to reach the same torque as your longer cranks depends on the power you need to produce, but the equation is the same. To produce some power "P" you can either hold the cadence steady and increase the force and therefore the torque or you can hold the torque steady and increase the cadence, or you can increase both.

 

[vosadrian]

When doing your top speed comparison, you should not be doing it in the same gear. I bellieve you did it in the same (top) gear.

If you were doing 29.5mph on the top gear of your bike with long cranks and you were at a comfortable cadence, and you then reduce the crank length to shorter cranks and go in the same gear, you will do the same cadence, and as you rightly state, if you produce the same force on the pedals, you will have less power. The thing is you are now spinning too slow for the shorter cranks. You are grinding when you should be spinning. The legs do not typically sense cadence. We typically sense pedal speed and interpret that as cadence. The pedal speed (linear speed of the feet pedaling) will reduce if the cadence remains the same but the crank is shortened. Typically we will get the same feeling of pedal speed by lifting the cadence if we go to a shorter crank. This is why most people will equal or exceed their power when going to shorter cranks. They typically automatically lift the cadence to match the pedal speed and as a result the power is similar with similar pedal force and speed as the torque is reduced but the cadence is increased to compensate.

A better test would be if you do not limit your top speed test to being in the same gear. Just choose the gear that has you spinning a cadence at the upper end of your comfort zone. Do that for each crank length. Typically you will be in a shorter gear with shorter cranks and produce similar power and get similar top speed. In fact, if you adjust your fit accordingly (you need to change the length between pelvis and crank to account for change in crank length), you will typically be more aerodynamic also, so may pickup some top end speed even if you make the same power. On an upright bike, if you reduce the crank by 10mm, you would normally lift the saddle by 10mm to get the same extended knee angle. This will in fact reduce the knee angle at the top of the stroke, and typically means you can run you bars a little lower relative to the saddle to get more aero. On a bent, the shorter cranks do not extend as high or as low so typically reduces the front area or your legs as your knees do not bend as much and your body stays flatter.

 

[JerseyJim]

When doing your top speed comparison, you should not be doing it in the same gear. I bellieve you did it in the same (top) gear.

If you were doing 29.5mph on the top gear of your bike with long cranks and you were at a comfortable cadence...The thing is you are now spinning too slow for the shorter cranks. You are grinding when you should be spinning.

I don't have a video, but I think if you had seen my top speed runs, you wouldn't say I was grinding. I was definitely spinning my little heart out.

You assume that I did the top speed run on my longer (170 mm) cranks at a comfortable cadence. Actually I was nearly spun out when I reached my top speed - as you would do if you're going all out. Likewise I did the same with the 160 mm cranks. It makes sense that if I couldn't raise my cadence any higher than in the 170mm run, that the shorter crank run would be slower for reasons I've already explained.

Granted, I don't have a cadence sensor on the bike just yet, however I've done enough structured training (years of TrainerRoad) to know if I've lifted my cadence while riding or if I'm bogging down. At no time was I grinding during the high speed run. My cadence was easily over 100 and probably closer to 120.

I'm not sure if I follow the logic of not being in top gear for the max speed test. In any event I'm not looking for the best crank length for top speed runs. At the time I put the cranks on for that initial ride, I wanted to see what differences I could feel riding as I would normally. Top speed isn't a critical factor. When I'm doing a brevet, the only time I'm anywhere near those speeds is when going downhill. I did the speed run mostly out of curiosity and my own amusement. There's no way I'm going to be doing a max effort like that while randonneuring.

I've since done a few more rides and adjusted the boom. I've reclaimed a little bit of room for my legs in front of the handlebars, although I'd still like a bit more. Right now my legs are at optimum extension for me so that does it for moving the boom. Likewise, I wouldn't want my arms bent any more than they are now.

So far I'm able to maintain higher average speeds with less leg fatigue. I've also found climbing at a more consistent pace easier than before.

I like what I'm feeling with the 160 mm cranks, so for now I see no need to go smaller. This feels right and I've already reaped some benefits so I'm going to go with it and see how I do.

 

[vosadrian]

I'm not sure what gearing you have. I have 52-11 as my top gear (with 700c tyres). 29.5mph is around 48 kph. For me I would be doing a cadence of around 80 which is too low for my 155 cranks. So I thought you may have been grinding.

I'm glad that the short cranks work for you. I don't agree with your explanation that you have lost speed due to lower torque. Especially if you are spinning as fast you can, the shorter crank should have you feeling less maxed out on the cadence at the same speed... and if going slower it should not feel you are pushing the cadence at all. But everyone is different and it sounds like an edge case it you were spinning at your top end. A better top speed test would be with suitable gearing to have you in a normal cadence range. Most of my testing I do with a power meter which is really helpful to see how the higher cadence helps with the power. Typically power equates well to top speed regardless of gear/cadence etc. Same power on flat road will get to about the same speed.