Quarq & Moving To a Shorter Crank Length:



2011 SWORKS

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Apr 19, 2011
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Guess this is more of a bike fit question but it involves my PM.
My Quarq PM is compatible with the stock sworks 172.5 crank that came with my bike. I am pretty sure I am going to order a shorter 170mm FSA SL-K crank & here is why...

Received a bike fit from the shop where I purchased my 54cm bike. Looking back now, it is clear that these people should not be fitting anyone one a bike. Clueless would be an understatement after recently experiencing a Retul bike fit.

After riding a few months I began experimenting on my own with stem height/length and seat height/fore & aft. Using a plumb bob I figured out that the Sworks seat post with a 20mm setback did not allow me to move my saddle far enough forward to get my knee (I measured just behind the patella & try to intersect the plumb bob with the pedal axle).

So, I purchased a "Zero Setback" seat post that allows me to get much closer to a correct position as verified with a 3-D Video Retul bike fit I received two weeks ago. However, even with the new seat post my saddle is almost all the way forward & my shoe cleats are all the way forward to get my knee in the correct location.

I dislike the fact that the cleat position could be putting too much pressure toward my toes and not the ball of my foot as well as having the seat post so far forward makes me think there could be a little flex in the saddle rails & just not the optimal position.

So.....Here is my thought. I would gain 2.5mm of adjustabilty by moving to the shorter 170mm crank. I've run many of the suggested "crank length calculator equations" and the numbers imply there would be no performance loss with the 170mm crank.

Forget about the cost factor. Optimizing my fit to prevent injury is more important than dollars.

Lastly, I will have to send my PM back to Quarq to be calibrated for the new crank, correct?

I believe the bad news is that what all of the data is telling me is that my 54cm frame is too large???? Damn that is an expensive mistake. If that is true, I would love it if Specialized would hold their dealers accountable for selling an $8,000.00 bike to a customer in the wrong size and provide me with a proper sized frame.

Hmmm, maybe I will forward this to the Specialized customer support?


Thanks for your input.
 

alienator

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Jun 10, 2004
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2011 SWORKS said:
Guess this is more of a bike fit question but it involves my PM.
My Quarq PM is compatible with the stock sworks 172.5 crank that came with my bike. I am pretty sure I am going to order a shorter 170mm FSA SL-K crank & here is why...
Received a bike fit from the shop where I purchased my 54cm bike. Looking back now, it is clear that these people should not be fitting anyone one a bike. Clueless would be an understatement after recently experiencing a Retul bike fit.
After riding a few months I began experimenting on my own with stem height/length and seat height/fore & aft. Using a plumb bob I figured out that the Sworks seat post with a 20mm setback did not allow me to move my saddle far enough forward to get my knee (I measured just behind the patella & try to intersect the plumb bob with the pedal axle).
So, I purchased a "Zero Setback" seat post that allows me to get much closer to a correct position as verified with a 3-D Video Retul bike fit I received two weeks ago. However, even with the new seat post my saddle is almost all the way forward & my shoe cleats are all the way forward to get my knee in the correct location.
I dislike the fact that the cleat position could be putting too much pressure toward my toes and not the ball of my foot as well as having the seat post so far forward makes me think there could be a little flex in the saddle rails & just not the optimal position.
So.....Here is my thought. I would gain 2.5mm of adjustabilty by moving to the shorter 170mm crank. I've run many of the suggested "crank length calculator equations" and the numbers imply there would be no performance loss with the 170mm crank.
Forget about the cost factor. Optimizing my fit to prevent injury is more important than dollars.
Lastly, I will have to send my PM back to Quarq to be calibrated for the new crank, correct?
I believe the bad news is that what all of the data is telling me is that my 54cm frame is too large???? Damn that is an expensive mistake. If that is true, I would love it if Specialized would hold their dealers accountable for selling an $8,000.00 bike to a customer in the wrong size and provide me with a proper sized frame.
Hmmm, maybe I will forward this to the Specialized customer support?

Thanks for your input.
I really can't say anything about how you were fit to your bike. It is essential, though, during such fits that the LBS person and the customer communicate. For instance if you don't tell the LBS dude that you're not quite comfy, then the dude won't know to change the fit. Also, no matter the fitting system--Retul, Fit Kit, or any other--a bicycle fit is just a starting point. It's not something that will deliver the perfect fit every time. In fact I'm willing bet that many, maybe even most, bike fittings aren't finished when the session is done. Instead after the fitting smaller more incremental changes are made to optimize the fit. Also, the fit you get from Retul, for example, may be no better than a fit done by an LBS staff member who just eyeballs you on the bike. As for changing the crank length to alter other fit parameters isn't the best thing to do. You should only use crank length changes to achieve an ideal or more ideal cadence. While it may not sound nice, if did a test ride on your bike, you can't blame the LBS for the fit after you take the bike home.
 

2011 SWORKS

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Apr 19, 2011
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Originally Posted by alienator .


I really can't say anything about how you were fit to your bike. It is essential, though, during such fits that the LBS person and the customer communicate. For instance if you don't tell the LBS dude that you're not quite comfy, then the dude won't know to change the fit. Also, no matter the fitting system--Retul, Fit Kit, or any other--a bicycle fit is just a starting point. It's not something that will deliver the perfect fit every time. In fact I'm willing bet that many, maybe even most, bike fittings aren't finished when the session is done. Instead after the fitting smaller more incremental changes are made to optimize the fit. Also, the fit you get from Retul, for example, may be no better than a fit done by an LBS staff member who just eyeballs you on the bike.
As for changing the crank length to alter other fit parameters isn't the best thing to do. You should only use crank length changes to achieve an ideal or more ideal cadence.
While it may not sound nice, if did a test ride on your bike, you can't blame the LBS for the fit after you take the bike home.
[SIZE= medium]I would have to disagree with all of your points except the part about communication. [/SIZE]
[SIZE= medium]When the custom bike fit promised by the LBS turns out to be as bad as mine was, are you suggesting it makes sense to then go back to that incompetent individual for more advice on adjustments to the bike fit? If the LBS hadn’t included the “custom fit” in the price of the bike purchase I would have demanded a refund. Instead, I decided to do my own research and attempt to make my own adjustments based off of information from books.[/SIZE]
[SIZE= medium]Maybe you were attempting to be dramatic with your example of a LBS staff member eyeballing a fit being comparable or maybe even better than a "structured fit" such as Retul?[/SIZE]
[SIZE= medium]While there are many suggested tolerances & theories on suggested bike fit parameters, using some sort of QUANTIFIABLE method of fit will always be better than your "eyeballing" example. By no means am I suggesting this will be the perfect fit and not need return visits to tweak, but the bike should have any one of the suggested methods of recommended parameters applied. Come up with a starting point using some sort of logic. I will then gladly purchase whatever custom pieces needed to make the bike fit me like a glove. [/SIZE]
[SIZE= medium]And to assume that a test ride is all that is needed to assume you’ve been sold the proper sized bike is just slightly off base. I would guess that it can take hundreds of miles riding in the wrong position before a pain develops to let you know something is not quite right. Especially if the rider has about 8 months of riding experience under his belt such as I did at the time of this bad fit. I wasn’t sure what a correct fit feels like, as this was my first one. [/SIZE]
[SIZE= medium]I made no issue with the LBS and gladly purchased different sized stems, zero offset seat post, and I even purchased different carbon bars that brought the hoods 9mm closer to attempt to make this frame work. It is only now that I have exhausted all the fit options short of the shorter crank that I will attempt to go back to the LBS & Specialized for a new frame. I’m not saying for free. I just want to enjoy this sport at my fullest potential and with the least amount of chance for injury on the highly cusomized bike I paid top dollar for. [/SIZE]
 

Alex Simmons

Active Member
Mar 12, 2006
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Not entirely sure why you posted here on the power training forum, since i. it's OT, and ii. specific advice on bike fit over a forum is notoriously difficult to sensibly provide.

If you did not have a good experience with your bike fitter, it would still be worthwhile letting them know. As for retul etc, they are just fancy rulers. They do not guarantee a good fit. They simply accurately measure a set up whether or not it is bad or good. If a fitter emphasises the measurement tool over the actual process of fitting, that's a warning sign they are likely masking their lack of experience or understanding of what's more important.

Here are some thoughts on bike fitting you might want to consider:

http://www.stevehoggbikefitting.com/blog/2011/09/perspectives-on-fitting/
 

CyclinYooper

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Jan 9, 2011
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I've used two local bike shops for fitting. After being fit at the first (using the BG Fit system), I was constantly uncomfortable. After switching to the second (which used Fit Kit), I felt much better! I can't tell you whether it was the "system" or the "fitter," but the difference was night-and-day. While working through my fit issues with the first shop (I was trying to resolve constant hand pain), the fit guy kept telling me things like, "well, you need to ride more..." and after a few months, I got tired of hearing it and tried another recommended shop.

I guess my point is maybe you can find another LBS, or even a serious cyclist buddy to give you another opinion? It sucks, because you'll probably have to pay to get fit somewhere else, which will cost you.

People on here are pretty good at diagnosing fit issues. Can you describe exactly what was bothering you? Some one may chime in with a recommendation.

Here's a good link someone else gave me: http://bikedynamics.co.uk/guidelines.htm

Scott
 

alienator

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Jun 10, 2004
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2011 SWORKS said:
 Maybe you were attempting to be dramatic with your example of a LBS staff member eyeballing a fit being comparable or maybe even better than a "structured fit" such as Retul?
While there are many suggested tolerances & theories on suggested bike fit parameters, using some sort of QUANTIFIABLE method of fit will always be better than your "eyeballing" example.
Uh-huh. I was dead serious. You can read into it what you will. I'm not sure why posted at all, other than to rant. You seem pretty sure that you've got it all figured out. "Structured fit" means nothing, especially when there is zero data to support your claim about Retul. You can a fit as good as Retul by using a plumb bob and a pair of eyeballs. It's not important whether you believe that or not. For many years cyclists were fit to bikes without things like Retul, Fit Kit, or the Specialized process. Since you are apparently an expert on fit and what you can't do, you won't have to inconvenience yourself by coming back to ask questions here. Congratulations.
 

danfoz

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Apr 12, 2011
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Curious if you have short legs proportionately or are under 5'7 not being able to make a 54cm work. Ever get a bad haircut (done by a professional)? Bike fit works the same way. Btw, at 5'9" I've successfully arrived at a good fit on 10+ different bikes ranging from 52cm to 56cm by "eyeballing" using the standard baselines currently available on hundreds of websites, and dozens of books. Measured to the mm of course. Fitting should be a reciprocal process (i.e. feedback intensive), as soon as someone, some tool, or some methodology tells you how it is, the purpose has been defeated.

Edit: no one wants a bike that doesn't fit right especially if it cost $$. My oversize models were hand me downs as washing dishes after school wasn't the best way to raise capital. If they fitted you with 172.5's, and if that was not way off base, you're probably not a hobbit. Call specialized, if they give you any lip tell 'em you're off to look at a Volagi. But seriously I rode an SL3 for a season, a 54 with a 90cm stem, maybe you are a bunch smaller.
 

lanierb

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Aug 12, 2004
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Hey Sworks- It sounds like your bike maybe is too big, which sucks. As for going to a 170, there's no reason not to do it. There's a current movement among TT'ers, even larger ones, toward 165s (to allow more power in a very aggressive aero position) and everyone I know that has done it has reported no issues. A smaller crank means higher torque for the same gearing so you may need slightly smaller gears than before (and a slightly higher cadence), but probably you just won't really notice the difference.

Additionally, all Quarq's use cranks with a removable spider (at least all up until the very latest announced red crank which I'm not sure about). So all you have to do is get new crank arms, remove the spider from the crank arm on your existing crank, and attach it to the new arm. You don't even need to send the crank in for calibration. Nothing will change there.

Since new crank arms are expensive I might recommend going in to a good professional fitter first to verify your fit requirements. You can get a good fit for somewhere around $200, sometimes $300, and it's well worth it but particularly for someone like you who is having some issues. You may find that you don't need a new crank, in which case you will have actually saved time and money.
 

alienator

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Jun 10, 2004
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lanierb said:
A smaller crank means higher torque for the same gearing so you may need slightly smaller gears than before (and a slightly higher cadence), but probably you just won't really notice the difference.
I think you misspoke. With all else equal, shorter crank arms will produce less torque, both at the crank and at the rear wheel. That's from the physics point of view. Of course, as a lot of riders already know, body position can significantly impact how much power a cyclist can deliver at the crank. That is the reason why when, in the off season, a can coach and rider may spend significant time to maximize said rider's output while minimizing that rider's drag.
 

2011 SWORKS

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Apr 19, 2011
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Originally Posted by lanierb .

Hey Sworks- It sounds like your bike maybe is too big, which sucks. As for going to a 170, there's no reason not to do it. There's a current movement among TT'ers, even larger ones, toward 165s (to allow more power in a very aggressive aero position) and everyone I know that has done it has reported no issues. A smaller crank means higher torque for the same gearing so you may need slightly smaller gears than before (and a slightly higher cadence), but probably you just won't really notice the difference.

Additionally, all Quarq's use cranks with a removable spider (at least all up until the very latest announced red crank which I'm not sure about). So all you have to do is get new crank arms, remove the spider from the crank arm on your existing crank, and attach it to the new arm. You don't even need to send the crank in for calibration. Nothing will change there.

Since new crank arms are expensive I might recommend going in to a good professional fitter first to verify your fit requirements. You can get a good fit for somewhere around $200, sometimes $300, and it's well worth it but particularly for someone like you who is having some issues. You may find that you don't need a new crank, in which case you will have actually saved time and money.

Just got off the phone with Quarq.
They told me the Quarq PM I have will only work with Sworks specific cranks due to the interface.
In other words I could not use an FSA crank with this Quarq which I would not have guessed. He told me if I wanted a shorter crank it would have to come from Sworks to be compatible with the Quarq. Interesting.
I've always found myself wishing I had a compact crankset when I'm doing a lot of climbing.
I run a standard 53/39 up front & a 11/27 cassette. 2.5mm smaller circles with a 170mm crank I'd be spinning up front sounds significant to me. I'm getting a bit sidetracked, but would using a 170mm crank make the 53x11 gear feel more like a 53x12 gear?
New Sworks crank arms are $300.00. Waiting on a call back on availability.
I think I might just try the 170mm crank arms. It would be cool to record all my power meter readings in each gear with the 172.5mm Vs the 170mm at fixed RPM's.
 

alienator

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Jun 10, 2004
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2011 SWORKS said:
I'm getting a bit sidetracked, but would using a 170mm crank make the 53x11 gear feel more like a 53x12 gear?
Actually using shorter crank arms will reduce the amount of torque produced at a given force applied to the pedals. Think of this in terms of gear ratios, where a higher gear ratio is one that is more difficult pedal and a lower gear ratio is, of course, one that is easier to pedal. In going from a 53/11 to a 53/12, the gear ratio goes down approximately 9%, so pedaling gets a tad easier. In going from a 172.5mm crank arm to one 170mm long, the force needed to turn the crank in a given gear will increase by about 1%, so the pedaling will seem a bit more challenging. This assumes of course that you can feel the difference between the 172.5 and 170mm cranks.
 

swampy1970

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Feb 3, 2008
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Originally Posted by alienator .


I think you misspoke. With all else equal, shorter crank arms will produce less torque, both at the crank and at the rear wheel. That's from the physics point of view. Of course, as a lot of riders already know, body position can significantly impact how much power a cyclist can deliver at the crank. That is the reason why when, in the off season, a can coach and rider may spend significant time to maximize said rider's output while minimizing that rider's drag.
I think he meant that you need to give it a bit more push for a given gear at a given rpm of you reduce crank length.

From my own experience with different crank lengths I tend to naturally increase cadence when crank length decreases. There's probably a relationship between pedal velocity going on there in some form or other...
 

2011 SWORKS

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Apr 19, 2011
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Originally Posted by alienator .


Actually using shorter crank arms will reduce the amount of torque produced at a given force applied to the pedals. Think of this in terms of gear ratios, where a higher gear ratio is one that is more difficult pedal and a lower gear ratio is, of course, one that is easier to pedal. In going from a 53/11 to a 53/12, the gear ratio goes down approximately 9%, so pedaling gets a tad easier. In going from a 172.5mm crank arm to one 170mm long, the force needed to turn the crank in a given gear will increase by about 1%, so the pedaling will seem a bit more challenging. This assumes of course that you can feel the difference between the 172.5 and 170mm cranks.

Ok then I had my thinking backwards. Just tried to order the crank arms and Specialized has them backordered till March-April.
 

lanierb

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Aug 12, 2004
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Originally Posted by alienator .


I think you misspoke. With all else equal, shorter crank arms will produce less torque, both at the crank and at the rear wheel. That's from the physics point of view. Of course, as a lot of riders already know, body position can significantly impact how much power a cyclist can deliver at the crank. That is the reason why when, in the off season, a can coach and rider may spend significant time to maximize said rider's output while minimizing that rider's drag.
Yeah I misspoke. I meant that with a shorter crank you need higher pedal force (not torque) at the same cadence to maintain the same speed. This tends to make people choose a slightly higher cadence (and lower gear) instead.