Low Q Factor Crankset

llamafarmer

Hi all,

Having had a bike fit recently, it turns out I need to find a crankset with a smaller Q factor to improve my knee alignment, ideally in a 165mm length.

I currently have a full XT 3x9 drivetrain with 175mm cranks, which I've roughly measured at 174mm Q factor. I want to get this down to something a little closer to my road bike setup which is 146mm.

According to SRAM, their X7 cranks (2x10 and 3x10) have a Q factor of 167.5mm, but they only seem to come in 170mm cranks at the shortest....

Can anyone recommend any alternative cranks?
Does anyone know what sort of Q factor the latest Shimano 2x10 cranksets have?
Can I get away with a Shimano or SRAM 2x10 crankset without changing shifters?

Thanks!

cooldad

Q factor is not something normally considered on an MTB. You move around a lot and don't sit and pedal for hours on end.

llamafarmer

I'm having knee trouble cooldad, so I need to at least consider it.

YeehaaMcgee

Nope, it really isn't worth bothering with on an MTB - you move around the bike, meaning your knees are never really in the same position for long enough.
Do your physio exercises and it will get better over time.

njee20

XX comes in a lower q-factor, not sure about crank length. XTR M985 Race cranks are narrower, and come with short arms.

If you've got a 68mm BB shell it may be worth looking at road compact cranks, limits ring sizes though.

supersonic

Having had a bike fit recently, it turns out I need to find a crankset with a smaller Q factor to improve my knee alignment, ideally in a 165mm length.

Out of interest what did they say? And why?

cooldad

Flats maybe?

paul.skibum

I know nothing about Q factors but I know you can get 165 cranks - CRC have 165mm XT & XTR cranks in stock for both 10 and 9 spd.

But what the other said - I dont think I ever sit in one place long enough to consider knee alignment - uphill you shift around and knee alignment goes out the window, downhill you stand up. Have you thought about going for flat pedals to loosen up the knees? But dotn go for 5:10's and really grippy shoes as they are worse than spds for float.

llamafarmer

I'm getting professional advice on a knee injury I picked up in a crash a while ago, part of which is to make sure my bike set up isn't aggravating things. I went to see a mate who's a specialized bg fitter and suggested I try to improve my crank set up and at the moment I just want to work out what options I have and what is most cost-effective. I've made small adjustments in the past to be a bit more scientific about bike set up and it's worked well for me, I'm a big believer in the importance of a decent fit when you spend so much time in the saddle and turn so many millions of pedal revolutions in a lifetime.

Yes I'm aware of the difference between riding an mtb and a road bike but moving around on the saddle and standing up only effects the alignment in one plane. I do plenty of trail centre riding too, so that's a lot of sit down and spin climbing.

Sonic - shorter cranks to open the angle inside my knee (as viewed from side) at the top of the stroke to let me apply power for the whole pedal stroke - I'm very smooth on the road bike and more 'stompy' on the MTB. Narrower stance to allow my ankles, knees and hips to line up better vertically. A lot of this is more related to quads, hip flexors and ITB I think, but all effect the knees.

Flats aren't going to effect the width of my stance on the bike - I still have to clear the crank arms. I also massively prefer riding in cleats, so that's what I want to stick with for now.

llamafarmer

njee20 wrote:

XX comes in a lower q-factor, not sure about crank length. XTR M985 Race cranks are narrower, and come with short arms.

If you've got a 68mm BB shell it may be worth looking at road compact cranks, limits ring sizes though.

Thanks njee, XX is the same Q Factor as X7 from the data I've found and same 170 or 175mm length options. I'll have a look into road cranks, but don't want to change my ratios too much and I'd be worried about chainstay clearance.

paul.skibum wrote:

I know nothing about Q factors but I know you can get 165 cranks - CRC have 165mm XT & XTR cranks in stock for both 10 and 9 spd.

Yep, that's my simplest option - same cranks as now, but 165 instead of 175. If possible I want to bring the Q factor down as well though, which is why I'm interested in the difference between double and triple.

YeehaaMcgee

llamafarmer wrote:

I'm getting professional advice...

I went to see a mate who's a specialized bg fitter

Professional help, or advice from "a mate"?

njee20

Thanks njee, XX is the same Q Factor as X7 from the data I've found and same 170 or 175mm length options

XX (only) comes in 156mm (IIRC) too, sufficiently narrow that it doesn't clear many frames stays, probably doesn't go below 170 though.

As you infer the issue with a road compact will be the ring sizes - you can't go below 33t on a 110mm BCD, so fine if you run 1x10, but that's not ideal with the whole bad knees thing!

What pedals do you use? You can get super short axles for Egg Beaters which will bring your q-factor down by a good chunk.

Professional help, or advice from "a mate"?

Not devaluing it in the least, but that's a 1 day course open to all of their dealers, I'd heed their advice for fairly basic things, but they seem to be making some pretty severe (and unorthodox) recommendations, I'd take with a pinch of salt.

How tall are you, out of interest?

llamafarmer

njee20 wrote:

What pedals do you use? You can get super short axles for Egg Beaters which will bring your q-factor down by a good chunk.

I use Times, have been meaning to try and compare spindle lengths, but it doesn't seem to be easy to find info. The egg beaters might be worth a look, even if I really don't like them

njee20 wrote:

Not devaluing it in the least, but that's a 1 day course open to all of their dealers, I'd heed their advice for fairly basic things, but they seem to be making some pretty severe (and unorthodox) recommendations, I'd take with a pinch of salt.

How tall are you, out of interest?

Why do you say it's unorthodox njee?

I'd always take it with a pinch of salt, but I've seen my pedaling technique on the video and looked at all the angles with the BG software and the shorter cranks make a lot of sense to me. If I only have to replace cranks, that's not a massive expense, so worth a try and if I can reduce the Q factor by a few mm at the same time, then even better. I don't expect this to cure my knee issue in one shot. Oh and I'm a shortarse - about 5' 5"

njee20

Unorthodox because it's sufficiently unusual that 50% of the drivetrain manufacturers don't make cranks in the length you've been recommended ;-)

It's also something I've seen quite often in bike fits, that very odd crank lengths get recommended.

If you're pedalling at angles and buggering your knees then I'd have thought the shoes would be a more useful investment.

YeehaaMcgee

I don't think that shorter pedal axles would help unless you have inhumanly narrow feet - the crank arms would still be in the way.
I still don't buy the whole Q-factor thing, however.

If you stand, at ease, how far apart are your feet? Heving them too close together seems unatural to me - but I have a very wide stance.

supersonic

This is the thing - you could go to another bike fitter and they'd tell you something completely different. I think a lot of them are scams. If got specific injury problems I'd try and visit a qualified sports physio who specialises in bikes.

But worth a try, of course.

llamafarmer

njee20 wrote:

Unorthodox because it's sufficiently unusual that 50% of the drivetrain manufacturers don't make cranks in the length you've been recommended ;-)

But they do make them and is the reason some don't just low demand? I'm in a pretty extreme percentile in terms of height anyway and plenty of clothing brands don't make clothes that fit me either. It's always seemed odd to me that you buy a small road bike and you get shorter cranks with it, but all MTBs seem to come with 175mm cranks.

YeehaaMcgee wrote:

If you stand, at ease, how far apart are your feet? Heving them too close together seems unatural to me - but I have a very wide stance.

They wouldn't be far apart, I'm short and thin Cycling itself is unnatural though and if I was running I know my feet wouldn't be miles apart.

njee20

I'm in a pretty extreme percentile in terms of height anyway and plenty of clothing brands don't make clothes that fit me either.

You're not though are you, plenty of women far far shorter than you (I'm assuming you're a bloke!?). 165mm cranks are pretty extreme, and like SS I'd take any bike fit that recommends things like that with a pinch of salt. Particularly a very generic one like the Spesh one, again, not detracting from the service they offer.

Struggling to see how very short cranks will deal with knee alignment issues, which are more commonly caused by lateral tracking issues.

The Rookie

I can understand a drift towards shorter cranks, but the difference between 170 and 165mm is only 5mm, and that's only about 1% of your inside leg length, so the difference in knee bend is going to be pretty tiny.

llamafarmer

njee20 wrote:

You're not though are you, plenty of women far far shorter than you (I'm assuming you're a bloke!?). 165mm cranks are pretty extreme, and like SS I'd take any bike fit that recommends things like that with a pinch of salt. Particularly a very generic one like the Spesh one, again, not detracting from the service they offer.

Struggling to see how very short cranks will deal with knee alignment issues, which are more commonly caused by lateral tracking issues.

Ok semantics, but compared to a guy of 6' we're worlds apart, yet we'd probably both have mountain bikes with 175mm cranks as standard.

Out of interest are we talking about the same Spesh fit here? With the full video software set up?

The shorter cranks were to reduce the angle at the knee, the Q factor reduction was for alignment.

The Beginner wrote:

I can understand a drift towards shorter cranks, but the difference between 170 and 165mm is only 5mm, and that's only about 1% of your inside leg length, so the difference in knee bend is going to be pretty tiny.

I'm on 175 at the moment, so that's 10mm they're proposing. The effect is doubled at the top of the stroke, because it allows you to put the seat up 10mm - so hip is higher, foot is lower at top of stroke, angle behind knee is larger at the beginning of the power phase.

84toy

Hey LLamafarmer. Your request is not unheard of. I support the narrower cranks. I've been doing endurance mtb racing for the last 3 years. When I say endurance I mean anything 3hours and over. That translates to anywhere from 35 miles to 100 plus miles of trail time. After that much saddle time a wide Q starts to get to ya. I too have been searching for narrow cranks. Few people consider a narrow Q to be beneficial in mtbing. Thats why it has been only recently that some manufacturers have started developing narrower cranks I.E. Sram and Shimano XTR, and only at the higher end. It seems absurd to me that some one could think that a person who is 5'5" wouldn't need a narrower crankset. Your hips are typically going to be smaller than the hips of somebody who is 6'2''. So wide cranks will obviously be a problem. I notice a big difference with my power and efficiency when I go from my mtb cranks to my road cranks. I wish I could get road cranks on my mtb! Also, not all single track is the same. If its really tech than yes you will be up and out of your saddle alot which may not affect a persons knees. But when your out doing Cohutta 100 in Tenn which is more of a gravel road race up and down the smokey mountains. Than you better believe getting knee alignment in check is important.

You may be stuck with 170s in length with most crank options but the a 156mm Q is obtainable with the nicer Sram/Truvativ. Read the fine print. They may need to be special ordered as the cranks are offered in narrow and wide versions. Keep Fighting the good fight and get those knees better!

84toy

Secondly, I rock 170mm cranks on all my bikes and I'm 5'11''. I get criticized for it all the time. All my bikes are singlespeed, and I race a ss 29er with my 170's. I'm no stranger to long days in the saddle off road. I could never go back to longer cranks. So follow your intuition Llamafarmer. Get 165s if you can find 'em. The 1% that was commented on adds up after lets say 35 miles of pedaling. I got your back dude.

njee20

So wide cranks will obviously be a problem. I notice a big difference with my power and efficiency when I go from my mtb cranks to my road cranks. I wish I could get road cranks on my mtb!

Is that empirical, or just speculation? As I said before if you have a 68mm shell then you can fit road cranks, go for a compact and you can run a 33t ring, you may need to adjust your SS ratio but it can be done, potentially, I'd be surprised if all your bikes were 73mm.

As an aside there are people here who ride for 3 hours plus, you're not unique in that respect! In fact it's unusual I ride my MTB for any less than that!

michaeltrupin

This is an old post, so I’m wondering whether you, OP, are still following. For the moment I’d just like to say that I’m also 5’5” and, tho I don’t have a particular knee injury, I’ve been struggling and experimenting w/ the same q-factor & crank arm length issues (which are totally legitimate). I’ve had some success in making adjustments, and would love to know what u've come up w/ lately, and to chat if you’re still around.

bigflangesmallsprocket

I'm a road cyclist but have had similar issues to yourself, exasperated by slightly odd leg lengths. I can understand for mtbs that a slightly wider Q factor will help stabilize you when you're riding off-road a lot of the time, but if you have issues with your knees then this can be a problem for some.

I'm a little taller than you, but not much. When I were a lad (by gum, by eck, etc), narrow Q-factors were the norm, so not even generally considered. Due to my odd leg length I also tended to ride with my frame slightly lopsided, with my right knee occasionally hitting the top-tube, not a problem when I was younger and more supple, but returning to riding many years later it was definitely an issue. I found that my longer leg had a tendency to try to kick out at the heel, especially under effort, effectively twisting my leg, in order to try to even my stroke and find extra length from somewhere. This had the effect of straining my knee, outer thigh and calf muscles, and heel on my longer leg.

I solved the leg-length discrepancy easily by putting a minimal sized shim between cleat and shoe, which straightened up my road bike; on my hybrid (mtb with rigid forks really) with flatties, I just got two cheap pairs of pedals, the one with a thicker pedal platform for my shorter leg, which had the same effect. Fitting Speedplay frog pedals also helped, so that my heel wasn't straining against limited cleat float.

I've found that modern crank/BB systems generally have a wider Q-factor than traditional ones. Looking down at my legs when riding, I can actually see that my legs want to move up and down in a straight line; works fine down to the knees, but from the knees down my lower legs will be canted outwards toward the pedals. Some people seem to get on fine with this. If you watch cycle racing you may see some riders pedaling in this fashion, looking quite knock-kneed, whilst others have found a position (or have the hip width/physiology) that enables them to pump their legs up and down in a straight line. I don't get on fine with this! My Small Carrera Subway had quite a wide Q-factor and 175 cranks. I swapped them out for some 170's (longer than my 165 road cranks, but still an improvement), and fitted a narrower BB I had lying around. It's not perfect, but much better than my previous set-up. At some point I intend to rebuild an old Jamis mtb frame and fit it with rigid forks, which looks a slimmer frame, and see if I can improve my position again. For the road bike, I did source an ultra small width BB, but removed it when I thought the bearings were failing (found out later it was just not adjusted quite right, so am refitting it shortly). I also got myself a pair of Specialized mtb shoes with canted insoles, which I use for both road and mtb when I have the Frogs fitted. The soles in these shoes are angled to lift your inner foot slightly, encouraging your knees to assume a more inline position.

I am still having problems, but it's slowly improving (last year I rode with no real problems with my knees, but my ongoing back condition, trying to ride too low a road-frame with an aging and less agile back, already damaged from over-use injuries in heavy industry, cut my riding season really short). Another measure I intend to take, upon rebuilding my road-bike (I'm mostly on the Carrera these days) with a more suitable frame, is to adjust my cleat position again. This is in respect to foot placement on the pedals, which I hope will improve knee stability even more. Usual advice for foot position is to have the ball of the foot on the pedal centre. There are some sources that now suggest that, ideally, the ball of the foot should be very slightly FORE of the pedal axle centre. The reasoning: the foot does not sit at the centre during the full range of a pedal stroke, especially when you move around on the saddle during different efforts, including during hills. Your foot can be a fair few cm's above the pedal depending on the shoe/pedal combination, so your centre of balance is altering all the time, decreasing stability. By moving your cleat back slightly, this is reduced, and can improve knee stability, though the amount will depend on your shoe size, so the smaller your feet, the less you'd move back the cleat. Of course, if you're riding on flatties then it's probably not feasible to assume a foot-forward position, but if you move to clipless, it's something to consider. I'm going to try it on my road-bike anyway. Note, I think this may have the effect of bringing your riding positon very slightly lower and more forward, though probably not much you may need to adjust saddle position accordingly. I'm on holiday in a weeks time so I'll be building my new road-bike and testing this one out.

Just a thought ref to crank length. The 5mm increments in crank length actually have a 10mm effective height difference as you have to take into account bottom and top of stroke, there's also the circumference/turning circle of the stroke to take into account. If you have long legs and no knee issues, this may seem like a very small incremental change, but the shorter your leg, the larger the percentage. At the top of the stroke, your knee will be 1cm lower, not much, but think of the accumulative effect on a bike ride that may last hours.

A pretty long post I know, but it's been a real limiter for me in my return to cycling, with enforced semi-retirements along the way (there are bike-fits that specifically address these problems, that often require update fits to check progress, but are quite expensive and wayyy beyond my budget, especially including the kit-upgrades they'd probably want to push on you. I made my shim from a piece of washing-up bowl plastic). This subject seems to be a lot more prevalent on the road-scene. Appropriate crank length and leg length discrepancies are subjects that are returned to time and again in road-cycling fitness magazines, probably showing the older average age of its readers :oops: , Q-factor not so much, but it does get a look in when knee pain and cleat position is discussed.