Q Factor and Riders with Hip Problems

[doffcocker]

Hello there.
So I think I've mentioned in previous posts that I suffer from a condition called Legg-Calves-Perthes or Perthes disease which I have on my left side. Just to give you an idea it's a loss of blood supply to the pelvic and femur bone that causes pain and restricted range of movement in the area. For some people it affects their right side, for some it is both, for me it is my left.
Now back in October I bought a new bike (I'm pretty sure I've mentioned that) and since then I have experienced a lot of what I would call Perthes related pain, discomfort and limping, but until recently I had never linked this much to the new bike for a couple of reasons.
I have had the condition since I was 11 and cycling has always been a very much physio/specialist approved activity along with swimming - unlike things like running and other high impact sports - and having been a daily cyclist for a few years now and not had any issues at all when I was riding the old bike, just started to assume that cycling could basically do me no wrong at least as far as this issue was concerned.
I have also done a lot of swapping and changing since buying the new bike as well in terms of saddle height, fore/aft, tilt, handlebar reach, so I always thought that if there was any bike related aggrevation to the area this would eventually settle down once I finally found a riding position I felt firmly comfortable with but that hasn't been the case.
Then recently by accident I came across this concept of q factor which I'd never heard of before let alone took into consideration in terms of how it could be a factor in both my preferred riding position and the impact on my hip.
Just to illustrate the effect the condition has on my range of movement, I am able to extend my left leg sidewards significantly less than I can my right, and any sustained over-extension can bring about pain and limping later in the day. Sitting crossed legged has always been very uncomfortable, in fact it's nearly impossible to fully pull off. I can also cause myself problems if ever there is too much downward extension, for example foot stamping type motions, so I'm obviously aware of the problems a saddle that is too high could pose.

So anyway, let's call old bike Bike A (see picture, light blue frame) and new bike Bike B (see picture, darker blue frame).

I've read up on how to measure q factor and I make it that Bike A is about 160mm where Bike is 180mm and now I'm starting to notice certain other things that make me think this could be a problem.
Firstly no matter how high/low the saddle height, I can't seem to stay central on it, my backside always seem to gravitate toward the right side of the saddle. I have always been predominantly right footed but I don't know if that somehow normalises the fact.
Secondly, it's always on the left side downstroke that I feel a twinge as the foot reaches the bottom of the stroke. It's as though at that point my foot is uncomforably outstretched to the side.
Obviously I don't expect anyone to understand my condition and give advice accordingly, but I just at the very least want to know if I have an options in terms of maybe swapping the crank arms for some that are straighter and allow for a shorter saddle to saddle distance.
I've never actually changed cranksets/pedals/arms before, is it normal and straightforward enough for people to do so?
Thanks.

[TheBomber]

I’ve long disliked chainsets with large q factors so keep a close eye on what I have: a road double at 145mm and an MTB triple at 164. To me 180 would be horrible. It sounds so extreme that whatever else you fit will lead to a lower number.

[853]

I was also born with a hip problem in my left leg that restricted movement and gave me problems with Q factor. I therefore have some understanding, and considerable sympathy, for your situation.

Just so that we're clear about how to measure Q Factor, I have attached a photo from cyclingnews to illustrate it below. The easiest way to measure it is to take off the left hand crank and re-attach it 180 degrees away so that it is in the same position as the right hand crank - this makes it very easy to measure and avoids error.

I found square-taper bottom brackets, (the older type of bottom bracket, still used on cheap to medium priced bikes), to be very useful as not only do they come in various lengths, they can also be filed so that the cranks fit further onto them. I found that with a road crankset with a Q factor of around 145mm I could reduce this to around 135mm ( you can't really go below this, as the inner-side of the cranks will then strike the chainstays!)

[TrevA]

Swapping chainsets/cranks is a fairly easy job if you have the right tools, which vary according to the design of the chainset (square taper, Octolink or Hollowtech). If you don’t, then it might be a job best left to a bike shop.

[853]

I've never actually changed cranksets/pedals/arms before, is it normal and straightforward enough for people to do so?

Yes, but you will need some specialist tools that are fairly cheap to buy.

My recommendation is to see if you have a cycling friend who does their own mechanics, as they will have the tools and the knowledge and experience.

It goes without saying that a good bike shop could do this, but they will (understandably) charge you and if you are doing several alterations the costs could mount up.

[doffcocker]

Thanks a lot for this.

Just to clarify, is it ever OK just to swap the crank arms without faffing with the chainring?

Obviously I already know that the arms (and pedals even) from the old bike are a fine fit for me, it'd be nice to think I could just do a switch.

[tenbikes]

I mainly ride fat bikes with massive Q factors. BB are 100 and 120mm.

Right hip pain has gone after 20 years, left knee pain has improved.

YMMV.......

[slowster]

There are a few things you need to be aware of and familarise yourself with before doing what you propose.

Firstly, the concept of chainline. Read this article - https://www.sheldonbrown.com/chainline.html.

Although the Q factor for road double chainsets can vary significantly as you have found, the chainline for all of them will be 43.5mm. That is because road front derailleurs are all designed around that chainline. If the chainline is altered significantly, the chainrings and thus the chain will be too far inboard or ourboard to match the arc of movement of the derailleur cage, resulting in poor shifting.

I think your two bikes might well both have square taper chainsets, but you might only be able to swap the chainsets between the bikes if they both have the same square taper axle length (or very close, e.g. a couple of mm or so). In other words, both chainsets with the square taper axles on their bikes will give 43.5mm chainline. If the axle lengths are different, then swapping the chainsets will result in the chainlines changing.

Therefore, if you want to swap the chainsets, you would need to check whether the axle lengths are the same, and if not you would probably need to swap the bottom bracket cartridges as well.

Just to clarify, is it ever OK just to swap the crank arms without faffing touching the chainring.

If the two chainsets have same sized chainrings (with the same number of teeth), it makes no sense to remove or swap the chainrings between the cranks. Moreover, chainrings can only be swapped between different cranks if they all have the same bolt circle diameter - details here https://sheldonbrown.com/cribsheet-bcd.html.

Removing and fitting square taper cranks is straightforward providing you have the appropriate tools and follow the instructions. If you are careless it is very easy to strip the threads from a crank and destroy it. See the Park Tool article and video in the link below:

https://www.parktool.com/en-int/blog/re ... hree-piece

If you do not have a square taper cranks on both bikes, the link below will tell you how to identify what you do have.

https://www.parktool.com/en-int/blog/re ... ll-a-crank

The link below explains how to remove and fit various types of bottom bracket, including a square taper cartridge unit.

https://www.parktool.com/en-int/blog/re ... n-threaded

As you have already been advised, it may be best to get a bike shop to do the work, given the cost of the tools.

[853]

Just to clarify, is it ever OK just to swap the crank arms without faffing with the chainring?

Obviously I already know that the arms (and pedals even) from the old bike are a fine fit for me, it'd be nice to think I could just do a switch.

Potentially, you could take the cranks off one bike and put them on the other.

I say potentially, as it is dependant on the cranks, and bottom bracket axles, on both bikes being the same type. It wasn't clear from your photos whether they are both square-taper types, but I suspect they may well be. If you can show us some photos of where the axle meets the crank (on both bikes) then it may be possible to determine this.

If they are both square taper then you could get a crank removal tool and swap them over. As I said previously, however, if you can show your bikes to someone who does their own cycle mechanics then they would be able to do it for you, if it was possible.

If it is possible, then it is worth getting a crank removal tool. I say this because from my experience it took several attempts to get something I was really happy with. Whilst I think you're trying to keep the cost down, it may be worth considering a different crank length (shorter I would imagine) as this is what I had to do with my hip mobility issues.

[LuckyLuke]

Hi, I’ve had a gammy right hip on and off over the years. I’ve found narrower cranks more comfortable.
Lower Q (for a triple anyway) are Spa’s TD-2 cranks at 159mm. (153mm for a double.)
In this age of 36T and 40T etc cassettes, a low Q compact double could work? If you don’t mind the jump between rings.

Over the last 10-15 years, before settling on Spa TD-2 triples I tried the following:

-Campag square taper compact doubles (low 150ish mm IIRC). I liked the low Q but not really the jump between chainrings.

-TA Pro Vis 5 ‘Cyclotourist’ ultra compact double. Lovely low Q, ?140s, but better suited to older frames aesthetically and functionally. I found the cranks could foul the chain stays or the chain itself, if the chain stays were beefy, and / or the frame was spaced for 135 OLN. Still a big jump between rings too.

-Stronglight ?Impact triple cranks. These were around 155mm Q and felt great, but they needed an ISO (Campag) BB, which were more expensive than JIS (Shimano), and eventually I needed a smaller middle ring than the BCD would allow (38T smallest).

Best of luck, hope it works out and you are cycling pain free again.

Best wishes,

Luke

[LuckyLuke]

PS SunXCD and Velo Orange make copies of the Pro Vis 5, at 145mm and 149mm q factors respectively (doubles).

[531colin]

............
Firstly no matter how high/low the saddle height, I can't seem to stay central on it, my backside always seem to gravitate toward the right side of the saddle. ..........
Secondly, it's always on the left side downstroke that I feel a twinge as the foot reaches the bottom of the stroke. It's as though at that point my foot is uncomforably outstretched to the side................

I think the first thing you should look at is how you sit on the saddle, before you even think about Q factor.
I have "always" made a bigger bum bone dent in leather saddles with my right sit-bone than with my left. The reason is because I tilt the bike slightly to the left as I ride, so that I see more of the right side of the front wheel than I see of its left side; this is despite the fact that I am left eye dominant, so I should expect to be looking out of my left eye, and seeing more of the left side of the front wheel. (and presumably i lean my body to the right to be in balance))
I had a poor time a few years ago; left cleat set with maximum "heel out" rotation, and cramp-like pain in left calf from holding my foot "heel-out" against the limit of the float in the pedal. A pedal extender on the left pedal cured the problem (ie wider Q factor, on the left side only)
However, I found I can keep the bike upright provided I check frequently, particularly as I get tired, and this is at present a better solution.
I can lend you a pair of pedal extenders if you think it might help diagnose your difficulty.....for example, your left foot could be uncomfortably close to the midline, not uncomfortably outstretched to the side.

[531colin]

.............
Lower Q (for a triple anyway) are Spa’s TD-2 cranks at 159mm. (153mm for a double.)..............
-Stronglight ?Impact triple cranks. These were around 155mm Q and felt great, but they needed an ISO (Campag) BB, which were more expensive than JIS (Shimano), and eventually I needed a smaller middle ring than the BCD would allow (38T smallest)......

Stronglight impact are JIS ....the cranks are actually made by Sugino, they are either XD2 or TD2 .....they are exactly the same cranks as the Spa cranks, one or other of them has all 5 chainring bolts visible, the other type has one bolt behind the crank arm.

Stronglight Speedlight cranks were rather elegant and I think a bigger bolt circle diameter than the XD2/TD2; although they were only for 2 chainrings as I recall.

[fixer]

You can measure the q without taking the crank off.

Measure: left crank to down tube (or seat tube), seat tube diameter, right crank to down/seat tube, add together.

In practice, it's easiest to use calipers and measure to the far side of the seat tube then subtract the seat tube diameter.

[tenbikes]

Pedal extenders are definitely worth a try.
My touring bike is the only one I have which has a 'normal' Q factor, so I have fitted extenders to widen it towards the fat bike Q which I find so comfortable.