172.5 cranks vs 170
KateS
Posts: 12
Hi, I'm pretty new to road cycling and loving it. I'm a 5'7 female with an inseam of 80 cm and ride a Boardman Comp (men's). I'm having a lot of knee trouble since a 40 mile ride last year....possibly a classic case of too much too soon. I had a professional fit last Nov when I bought clip in pedals and was told the bike and my position were fine. I was identified as having tight leg muscles, particularly the ITB band and given stretches to do and have bought a foam roller. I've been doing the exercises since Xmas most days and cycling about twice a week...mainly on my trainer. Still having trouble so was wondering if swapping my 172.5 cranks to 170 may help. The fitter didn't mention them as a problem. Not sure if I would be wasting my money and that I just need to be a bit more patient with my stretches! Any advice gratefully received!
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doing a bit of research on this at the moment myself, I'm 5'9'' and have been fitted for 165mm cranks, the fitter is into biomechanics and reckons most people's cranks are too long resulting in a lot of knee problems.0
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Personally, I don't think it will make any difference whatsoever. Try reading this very interesting article:
http://bikedynamics.co.uk/FitGuidecranks.htm
I reckon the pains you have are because you are not getting the right massages (strecthes for the ITB don't work very well). Why not have a couple of sessions with a decent sports physio? I go to see one every now and then and it is money well spent. Foam rollers are good for ITB but they are only a poor substitute for a proper and specific massage. I have managed to learn how my physio massages the ITB and then taught my wife, who helps me when it is playing up (no sniggering at back please).0 -
Try the formula below, it may help you out.
1. Crank length should be inseam measurement 0.216 (or inseam measurement in inches x 5.48 yields crank length in millimeters – same thing)
The size you need may not exist so many people including me ride with cranks longer than recommended with no real problems.0 -
diamonddog wrote:Try the formula below, it may help you out.
1. Crank length should be inseam measurement 0.216 (or inseam measurement in inches x 5.48 yields crank length in millimeters – same thing)
The size you need may not exist so many people including me ride with cranks longer than recommended with no real problems.
...or you could try 170s anyway and see how you get on!0 -
You won't notice any difference, don't bother.
I'm sceptical about how good your "professional fit" was if they thought that the position you had set up was fine because you're a beginner so the chances of you having it spot on first time are very low.Red bikes are the fastest.0 -
Following a bike fit (motivated to get it due to knee pain) I was recommended to go from 175 to 172.5 and it made a huge difference. I felt much more able to spin comfortably and so reduce load on my knees. It was such an improvement I am tempted to go down to 170 - Don't know the provenance of that formula but it comes up 170 for me.0
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I have two bikes with 170 cranks and two with 172.5. I regularly ride all of them.
I can't tell the difference - the other differences between the bikes (very slight differences in weight, wheels, tyres, geometry) are noticeable but the 2.5mm of crank arm length is not.0 -
Thanks for great advice so far everyone...I may have mislead about the bike fit...when I said my position was fine I meant after the fitting! I'm starting to think of looking for a relatively inexpensive chain set on eBay to try it out, maybe start with 170 to see how it goes. I find that raising or lowering my saddle by only a mm or so does make a difference to where my knees hurt.0
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Where is your knee pain? The other year I was suffering and thought it was due to tight ITB, but even though my ITB was tight, the problem actually turned out to be my calf. A few physio treatments and things were a lot better.
I have to conciously remember to stretch and foam roll my calves and thighs. It's maybe worth seeing a sports physio for an hour to see if they can identify any issues.0 -
I think it is likely a problem with set up rather than crank length causing you pain. Even a "professional" bike fit can can get these things wrong. I've had (left) knee trouble that was made worse by a bike fit, as the fitter moved my saddle forward (less setback) to achieve what he though was a good knee over pedal spindle position.
I solved the problem by keeping my saddle quite far back (this felt natural to me) and moving my cleats pretty much as far back as they will go, reducing the amount of work the calf's do, and i think reducing forces on the knee. Also make sure they are aligned straight and you have cleats with some float.
172.5's may well be too big for, i ride them at 6'3", but i think this is more likely to reduce your efficiency rather than cause injury. That said if you are set on buying new cranks to experiment get some 165's, it doesn't seem likely that 170's will be optimal if 172.5's are causing injury and you might actually notice the difference.0 -
My knee pain generally comes on after about half an hour, mainly in my left knee at the side, but sometimes the side of my right knee. I have noticed the front/ top to hurt when I lower the saddle and the back of / calf to hurt when I raise it. Although I've noticed as I'm stretching more I can raise my saddle more, I guess they are working slightly! I do notice some difference when I stretch properly before and after riding in that they don't hurt as much. I don't/can't go by the knee over pedal, as my right femur is about 7mm longer than left (determined by MRI a few years ago due to hip pain while running). I've moved my right cleat further back to compensate for this, seems more comfortable.
While I'm writing, does any one know if I could run a Shimano compact chain set with SRAM Apex gear shifters and cassette? The bike came with a FSA Gossomer compact and I've been looking at SRAM Apex or Rival Compacts...but there are a lot of Shimanos available ob eBay...0 -
Did the person doing the bike fit suggest shims/wedges or alter the position of you cleats on each foot individually? Did they know you have a significant femur discrepancy?
Maybe its worth persevering with the higher saddle, your calf muscles may just hurt because they aren't use to the effort, were are joint pain pretty much only gets worse. This might be worth a read:
http://www.stevehoggbikefitting.com/bik ... knee-pain/
Yes you can run a shimano chainset with sram, just make sure the bottom bracket is compatible.0 -
KateS wrote:
While I'm writing, does any one know if I could run a Shimano compact chain set with SRAM Apex gear shifters and cassette? The bike came with a FSA Gossomer compact and I've been looking at SRAM Apex or Rival Compacts...but there are a lot of Shimanos available ob eBay...
It depends on what type of bottom bracket you have, but I think you will have either BB30 or GXP, neither of which will work with Shimano hollowtech 2 without adapters.
Bottom brackets are cheap though. So if you have GXP you just need a hollowtech 2 BB which is easy. If you have BB30 then you'll need an adaptor though, as the frame is different.
Once the BB is sorted, a shimano chainset will work with your SRAM setup.Red bikes are the fastest.0 -
Great, thanks for this info, I think my BB is a FSA MegaExo but happy to change those parts to go with a new chain set if necessary.
To answer Vecfluxx I did tell the fitter who said as it was the femur it wasn't such a problem and shims etc wouldn't help much...I guess with my feet clipped in my knees are the same height, as lower leg is fine, just my right knee is further forward then my left.0 -
KateS wrote:My knee pain generally comes on after about half an hour, mainly in my left knee at the side, but sometimes the side of my right knee. I have noticed the front/ top to hurt when I lower the saddle and the back of / calf to hurt when I raise it. Although I've noticed as I'm stretching more I can raise my saddle more, I guess they are working slightly! I do notice some difference when I stretch properly before and after riding in that they don't hurt as much. I don't/can't go by the knee over pedal, as my right femur is about 7mm longer than left (determined by MRI a few years ago due to hip pain while running). I've moved my right cleat further back to compensate for this, seems more comfortable.
While I'm writing, does any one know if I could run a Shimano compact chain set with SRAM Apex gear shifters and cassette? The bike came with a FSA Gossomer compact and I've been looking at SRAM Apex or Rival Compacts...but there are a lot of Shimanos available ob eBay...
If your knees are aching at the side there is a good chance that this is because your legs are 'collapsing inwards at the knee'. This can be corrected, well tried really easily if you can lay your hands on some wedges that go under the insole that come with specialized footbeds (insoles). Basically, it corrects the slope across the width of your foot, imagine the big toe sides of your feet being chocked up a bit.
There's these things called LeWedges that achieve the same by wedging the cleat but the LeWedges are more expensive and a bit of a fiddle.
See this below and see if this is a possibility of what is happening to you??? (the Specialized things I am about only raise the inside of the foot by 1.5mm, but its enough to have good effect)
EDIT: I notice above that vecfluxx has said much the same
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I'd say 50% of the women riders I know run cranks that are too long (in my opinion).
Or put another way, 50% are shorties yet run 170 cranks.
That's not so say yours are too long. 5'7" isn't 'short', and you may have long legs but trying 170s can't, well, hurt.
As the comments above suggest, a bikefit isn't gospel. Just because you've had one doesn't mean you can stop thinking about fit and comfort. Experiment!
seat height, layback, seat angle, bar height, stem length, crank length, cleat position, insole shape, even bar width and shape are all adjustable.Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer0 -
Agree with some of the above comments that bike fitting is not a precise art it's worth getting a second opinion if you are still having problems.
The best bike fitters usually invest a lot of time and effort in the cleat and shoe setup - angled wedges, arch support, shims, pedal axle length. If the fitter didn't spend much time on that sort of thing it might be worth getting another fit with someone else. Did they check that your knees were tracking straight when viewed from the front? One way of doing this is to shine a laser at the front of your knees while you are cycling and then tweak the setup to try to minimise sideways movement.
I also have one leg longer by about 7mm and have one cleat shimmed, but it's my tibias that are different lengths, not my femurs.
Also agree that if you are thinking of trying different cranks 2.5mm is not really enough to notice and I would try going from 172.5 to 165mm.0 -
Great advice everyone! Taking note of all of this, will certainly check out shims and wedges, especially the in shoe ones, sounds an easy why to try. Yes been thinking of trying another fit...the fitter did video from the front buy I messed with my cleats since anyway! A second opinion can't harm. I have a Specialized concept store by me and was wondering about their Body Geometry fitting services...anyone had any experience of this?0
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KateS wrote:Great advice everyone! Taking note of all of this, will certainly check out shims and wedges, especially the in shoe ones, sounds an easy why to try. Yes been thinking of trying another fit...the fitter did video from the front buy I messed with my cleats since anyway! A second opinion can't harm. I have a Specialized concept store by me and was wondering about their Body Geometry fitting services...anyone had any experience of this?
If you're anywhere near a Retul centre, go for that Red bikes are the fastest.0 -
DiscoBoy wrote:KateS wrote:Great advice everyone! Taking note of all of this, will certainly check out shims and wedges, especially the in shoe ones, sounds an easy why to try. Yes been thinking of trying another fit...the fitter did video from the front buy I messed with my cleats since anyway! A second opinion can't harm. I have a Specialized concept store by me and was wondering about their Body Geometry fitting services...anyone had any experience of this?
If you're anywhere near a Retul centre, go for that
I would say go to a good Retul fitter that you can ask people about. I had one done and have since undone 75% of what he did. I ended up in more pain. I personally think Retul with all it science needs to be balanced with experience as well. My fitter was newly trained and did a group of us at work. e have all undone what he did 2 years ago.
KateS, just for reference I am 5'7" and run 172.5 cranks on my road and TT bike. I got back into cycling 4 years ago after not doing it for over 10 years. The bike came with 172.5, so I haven't known any different. As mentioned above the only time I have had knee trouble was over trraining for Paris to London and it turned out to be my right calf muscle being tighter than a very tight thing that had been tightened by Sir Tightens-a-lot0 -
There is a fairly comprehensive article about ITB in Cycling Weekly this week. Interestingly, crank length was not mentioned once but bike/shoe setup and stretch/massage came up again and again.0
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Cleat position could be off, take a look at this with ref to knee pain I found it useful after buying new shoes and getting knee pain when I previously had none.
http://www.bikeradar.com/gear/article/t ... t-2-17445/0 -
Thanks all! Definitely taking note of all this, very interested in the wedges for in my shoes, may give these a try as I do roll in on my feet a bit. Took the plunge on a cheap chain set on eBay with 170 cranks...will give it a go, as suggested, it won't hurt! Also took my bike to a LBS who helped readjust my cleats and raised my saddle. Things do feel a bit better, combined with all the stretches. I think I also need to stop trying too much too soon!0
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I swapped out the crank on my main bike from a compact with 172.5mm crank arms to a double with 165mm crankarms and even though I am pushng a larger front ring I can accelarate and climb a lot better than before. Its allowed me to raise my seat a bit more and bring it forward into a more natural angle.0
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I've experimented with 175's, 172.5's and 170's (I'm 5'8), and I prefer the 170's by far.
Much more comfortable to spin with, I would say my cadence has increased about 10%, and my performance is noticeably better.0 -
I went from 170 to 165mm cranks after a recommendation from Mike at Bike Dynamics and it made a huge difference. People forget that the turning circle is double the crank length difference so a 2.5mm change equates to 5mm overall. Your seat will be higher as the pedal is closer to the centre of the cranks when at the bottom of the stroke and your clearance at the top of the stroke will be increased with the raised seat height and shorter crank length to the centre of the cranks. Assessing the difference was done with a power metre using the same gearing and cadence to reduce any variables in pedal stroke and effort. The effort with the shorter cranks was much easier. The angles that Mike works with to do your set up were closer to achieve with the shorter cranks.I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.0
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diamonddog wrote:Try the formula below, it may help you out.
1. Crank length should be inseam measurement 0.216 (or inseam measurement in inches x 5.48 yields crank length in millimeters – same thing)
The size you need may not exist so many people including me ride with cranks longer than recommended with no real problems.
Does anyone know where I can get some 192mm cranks?0 -
There was a bike fitting conference recently where (I think) it was scientifically proven that crank length doesn't make a difference. Prob. more info via Cyclefit and their twitter feed from that conference. Poss. the route to go down is shims/wedges/footbeds which cyclefit do also Adrian Timmis(?) in Derby is spoken of well. Trek are tutored by Cyclefit so a Trek store may be able to help.M.Rushton0
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I'm 172cm (5ft 7.5") with 76-77cm inseam and I have bikes with both 170mm and 172.5mm cranks. I can't tell the difference between them, other than BB to top of saddle measurement is 2 or 3mm lower to compensate. Cadence is no different in practice. I'd say save your money and look at either saddle setback or saddle height to eliminate the pain, don't move the saddle too much at once either.0
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I guess this is similar to mfin's response - but the source is Bikeradar...
http://www.bikeradar.com/gear/article/t ... t-2-17445/0
