Longer cranks (Zinn)

[stephenmarklay]

I know we have debates the merit of long cranks as far as power, aero etc and but have any of you tried longer cranks to get behind the spindle. I have found I really me to be behind the pedals and it is a bit limiting. I have reasonabley long femurs (nothing crazy) and that makes a 72 seat tube angle or a 30 plus mm setback post best. I have not tried longer that 175 cranks but in wondering if I should?

[pbarry]

Have you used Zinn's crank length calculator? A good place to start.

If you decide to try longer arms, find used ones first before splurging on the high $$ extra long zoot cranks.

[stephenmarklay]

For sure. Since my inseam is not that long (33.75) his calculator says 180-185. So if I were to get a used 180 DA crank and a 72.5 STA I get about 1.2cm vs a 73 STA and 175 cranks. Something anyway a 185 crank might be harder to source.

[Peter P.]

I believe Zinn's philosophy is a 73 degree seat angle works for just about everybody, and shifting the seat angle back to accommodate long legs/tall riders/long femurs closes up the hip angle, causing all sorts of physical problems. Cervelo used to adhere to this concept as well.

His solution is longer crankarms, not slacker seat angles or greater setback posts. He offers an adjustable length crankset that you can "rent" and apply the rental fee to the purchase of new cranks if you so choose.

Anyway, it's something like that. I like his theory and even invoked it when I ordered my custom road frame. I ride a typical 53cm frame where you'll usually find a 73.5-74.5 degree seat angle. I spec'd a 73 degree seat angle mostly because of Zinn's theory. My saddle's centered about the clamp and I ride 170mm cranks. Works like a charm.

[stephenmarklay]

I would think the a good builder could make a bike with say a 72 degree angle with the appropriate geometry to keep you close to centered. I have not really had an issue with tons of setback as far as hitting my knees on my chest but I see how getting your leg up high enough to get over he pedals can be hindered with that much setback.

[pbarry]

I believe Zinn's philosophy is a 73 degree seat angle works for just about everybody, and shifting the seat angle back to accommodate long legs/tall riders/long femurs closes up the hip angle, causing all sorts of physical problems. Cervelo used to adhere to this concept as well.

His solution is longer crankarms, not slacker seat angles or greater setback posts. He offers an adjustable length crankset that you can "rent" and apply the rental fee to the purchase of new cranks if you so choose.

Anyway, it's something like that. I like his theory and even invoked it when I ordered my custom road frame. I ride a typical 53cm frame where you'll usually find a 73.5-74.5 degree seat angle. I spec'd a 73 degree seat angle mostly because of Zinn's theory. My saddle's centered about the clamp and I ride 170mm cranks. Works like a charm.

I get what you are saying and happy you found a good solution. Would a 74 degree STA work for you with the saddle all the way back? I look at centered saddles as lost real estate. ;)

[pbarry]

For sure. Since my inseam is not that long (33.75) his calculator says 180-185. So if I were to get a used 180 DA crank and a 72.5 STA I get about 1.2cm vs a 73 STA and 175 cranks. Something anyway a 185 crank might be harder to source.

You have long levers so match them with a longer crank length. If anything, Zinn's calculator is conservative. Nothing to lose by trying them out.

[sandyrs]

I'm 6'5". I rode 185's for a while on my road bike. Now I have 180s. 175 on MTB and CX. I notice it for about thirty seconds switching between bikes but that's it. I guess 180s are slightly more natural feeling but I don't go to great lengths to find long cranks anymore.

The Zinn calculator also has me at 210mm cranks so take this with a grain of salt. :)

[stephenmarklay]

Thanks! I think I will try 180 as they are not to hard to find. In principle what he says makes sense. However, as with seat tube angle or whatever else there are limits to what is practical. A 210 crank would mean your cranks are so much lower to the ground that you would likely want a higher BB or a 70 seat tube angle would necessitate really long stays.

I think getting a 72.5 STA bike and 180 cranks does not deviate to far and gets me a bit of that behind the pedal feel I like.

[benb]

Zinn's solution moves your CG forward and get more weight on the front wheel which might be beneficial. It also makes it easier to fit on longer bikes.

I've thought about trying this as I've always had a decent amount of setback and the hip angle thing comes into play but it's such an expensive experiment. And the fitter who puts me further back to help with the femurs makes the reach to the bars harder whereas zinn's does not.

If the cranks stay short the next proposed solution IME is always "custom frame" obviously custom frame is also an expensive experiment, and it doesn't help with the hip angle thing.

[Mark McM]

I believe Zinn's philosophy is a 73 degree seat angle works for just about everybody, and shifting the seat angle back to accommodate long legs/tall riders/long femurs closes up the hip angle, causing all sorts of physical problems. Cervelo used to adhere to this concept as well.

His solution is longer crankarms, not slacker seat angles or greater setback posts. He offers an adjustable length crankset that you can "rent" and apply the rental fee to the purchase of new cranks if you so choose.

The hip angle argument makes no sense. If, say you used a crank that was 10 mm longer, you could move your saddle 10 mm forward (because the pedal would be 10 mm more forward when the cranks were horizontal). You'd also have to lower the saddle to keep the same leg extension at the bottom of the pedal stroke. But since the diameter of the pedal circle increases by twice the crank length, then your knee would rise 20 mm more at the top of the stroke as compared to the shorter cranks. The end result would that the hip angle would close more with the longer cranks than with the shorter cranks.

In the past, triathletes had used longer cranks because they though it would increase pedalling torque and power. But now they are moving to shorter cranks, because research has shown that they can achieve the same power, but the shorter cranks also decrease hip angle, allowing for a lower, more aerodynamic position.

Here's an article from SlowTwitch about this:

http://www.slowtwitch.com/Tech/Crank_arm_lengths_for_tri_727.html

[benb]

Who says you have to keep knee extension at the bottom of the pedal stroke the same? That's always a range. Having to lower the saddle because you increased the length of the crank assumes you had the saddle at the maximum of your range with the shorter cranks doesn't it?

The hip angle is also dependent on the position of the bars and using the longer cranks may more may not make some different bar positions available.

[Mark McM]

Who says you have to keep knee extension at the bottom of the pedal stroke the same? That's always a range. Having to lower the saddle because you increased the length of the crank assumes you had the saddle at the maximum of your range with the shorter cranks doesn't it?

The hip angle is also dependent on the position of the bars and using the longer cranks may more may not make some different bar positions available.

So, you are assuming that our position is set up with incomplete leg extension with shorter cranks? That is not usually the case.

But let's say that we don't change seat height with the longer cranks, and only move the saddle forward. Now we have a shorter reach to the bars, so we will sit more upright. But at the same, our legs rise higher at the top of the pedal stroke, exactly as much as the saddle was moved forward. The result is little to no change in hip angle with the longer cranks, so no gain there.

[stephenmarklay]

The hip angle argument makes no sense. If, say you used a crank that was 10 mm longer, you could move your saddle 10 mm forward (because the pedal would be 10 mm more forward when the cranks were horizontal). You'd also have to lower the saddle to keep the same leg extension at the bottom of the pedal stroke. But since the diameter of the pedal circle increases by twice the crank length, then your knee would rise 20 mm more at the top of the stroke as compared to the shorter cranks. The end result would that the hip angle would close more with the longer cranks than with the shorter cranks.

In the past, triathletes had used longer cranks because they though it would increase pedalling torque and power. But now they are moving to shorter cranks, because research has shown that they can achieve the same power, but the shorter cranks also decrease hip angle, allowing for a lower, more aerodynamic position.

Here's an article from SlowTwitch about this:

http://www.slowtwitch.com/Tech/Crank_arm_lengths_for_tri_727.html

This all makes sense and is the way I understand it except you won’t see a 20mm increase the top of the stroke. Only 10mm. It would have to be really strong to stretch a 180mm arm to 190 at the top :)

[Mark McM]

This all makes sense and is the way I understand it except you won’t see a 20mm increase the top of the stroke. Only 10mm. It would have to be really strong to stretch a 180mm arm to 190 at the top :)

The 20 mm is a relative change. With a 10 mm longer crank, the pedals will be 10 mm lower than before at the bottom of the stroke, and 10 mm higher than before at the top of the stroke. If the saddle is lowered by 10 mm to get the same leg extension at the bottom of the stroke as before, the relative difference in pedal rise at the top of the stroke is 20 mm.

[stephenmarklay]

The 20 mm is a relative change. With a 10 mm longer crank, the pedals will be 10 mm lower than before at the bottom of the stroke, and 10 mm higher than before at the top of the stroke. If the saddle is lowered by 10 mm to get the same leg extension at the bottom of the stroke as before, the relative difference in pedal rise at the top of the stroke is 20 mm.

Gotcha

[Waldo]

For sure. Since my inseam is not that long (33.75) his calculator says 180-185. So if I were to get a used 180 DA crank and a 72.5 STA I get about 1.2cm vs a 73 STA and 175 cranks. Something anyway a 185 crank might be harder to source.

I get a 193mm crankset from Zinn's calculator. I happily rode a 190 for almost 10 years before scaling down to 185, which works well for me. I am a pretty normally proportioned 6'1". TA Carmina comes in 185 and, with its interchangeable spider, is an incredibly versatile crank.

[gregblow]

I just got my longer cranks today! Zinn says I am 175-180 range. I went with the 180's excited to ride tomorrow. i will let you know how they feel. Btw, I am on 172.5 now.

[stephenmarklay]

I get a 193mm crankset from Zinn's calculator. I happily rode a 190 for almost 10 years before scaling down to 185, which works well for me. I am a pretty normally proportioned 6'1". TA Carmina comes in 185 and, with its interchangeable spider, is an incredibly versatile crank.

Thank you very much for the info.

[benb]

I get 185 from his calculator.. maybe some day I'll try it. I've never been on a bike with longer than 175. So much of it makes sense, even if some of the arguments against it here make sense too.

For me having knee pain is primarily caused by having the foot too far back at 3 o'clock.. I end up with more setback to counteract this.. that moves me further from the bars. I have a really high seat height, that makes it hard to get enough stack on most frames. Going to a 1cm longer crank would help this a huge amount as I'd end up lowering the seat height by 1cm. More bend in the knee at the top of the pedal stroke doesn't really concern me as your leg is supposed to be relaxed there, more bend at 3 o'clock doesn't strike me as a big concern as the longer crank moves your foot forward and opens up the knee angle to compensate.

It makes me wonder if I wouldn't have to slam my cleats all the way back on my shoes as well if I had a 1cm longer crank.

[stephenmarklay]

I get 185 from his calculator.. maybe some day I'll try it. I've never been on a bike with longer than 175. So much of it makes sense, even if some of the arguments against it here make sense too.

For me having knee pain is primarily caused by having the foot too far back at 3 o'clock.. I end up with more setback to counteract this.. that moves me further from the bars. I have a really high seat height, that makes it hard to get enough stack on most frames. Going to a 1cm longer crank would help this a huge amount as I'd end up lowering the seat height by 1cm. More bend in the knee at the top of the pedal stroke doesn't really concern me as your leg is supposed to be relaxed there, more bend at 3 o'clock doesn't strike me as a big concern as the longer crank moves your foot forward and opens up the knee angle to compensate.

It makes me wonder if I wouldn't have to slam my cleats all the way back on my shoes as well if I had a 1cm longer crank.


I am going to take the middle road with it all. A seat tube at 72.5, a 180 crank, and cleats back.

I am riding my commuter longer and longer distances with flat pedals which allow me to the pedal back under the meat of my foot and it feels great.

[benb]

I am going to take the middle road with it all. A seat tube at 72.5, a 180 crank, and cleats back.

I am riding my commuter longer and longer distances with flat pedals which allow me to the pedal back under the meat of my foot and it feels great.

I might just order those shimano 1-sided touring SPD pedals for my road bike and try that for a bit so I can wear my MTB shoes on all my bikes to start.

I could increase my setback on my Trek (SPD-SLs + 175mm cranks) compared to my All City (SPDs + 175mm cranks) to make up for the close to 1cm difference in cleat position on the road shoes but then I'm right back to reach problems.

The only thing that would really give me pause with getting longer cranks would be scraping them. I've scraped the 175mm cranks cornering before, though not recently. It's never really been terribly scary or even upset the bike much and I'm not racing so I don't really need to pedal through corners so much but I can see wanting a higher BB height with longer cranks. I am using bigger tires than before which might help.. the 2 bikes I remember scraping pedals on were my Giant TCR Composite and my Serotta Concours. Both those bikes never had tires bigger than 23mm so they were running a little closer to the ground although I forget what the BB heights were.

[mhespenheide]

I'm 6'4" and rode with 175's on the road, 180's mountain for a decade or more. Then I got the bug to try longer cranks on the road. I switched to 180's and it took almost two years of riding before I was really comfortable on them at 90-100rpm. First they felt long, then the circles felt bigger, then they just felt a little "off", then finally I got used to them.

Last year I picked up a new bike with 177.5's and they felt immediately comfortable. I've kept them on there and like them a lot.

I like the idea of longer cranks -- really long, like 190mm+ -- but the 177.5's seem to work well for me.


I also like a relatively large bottom bracket drop (75-80mm for a road bike). I don't want to lose that, as I might have to with cranks of the length that Zinn would recommend for me.