This all very nice, but if having a narrow Q is so important, how are fatbikes or mountainbikes at all rideable? Also many touring bikes have wider MTB cranksets. Considering the use case of touring bikes (massive mileage crammed in short time periods), I'd imagine we'd see a lot more issues with tourists than we do.

I think you're missing the context. First I described why wide cranks cause rubbing by changing the leg angle, and then expanded from there about other physiological effects that can happen as cranks get wider and wider. This is in reference to 'fixing' the OP's clients 'problem' by spacing the pedals out even further on an already wide crank. Which is why I disagree with fixing aesthetic issues by changing physiology.

Old style touring triples aren't necessarily as wide as some current Shimano doubles. And many people are not so sensitive to tread width. But I would also say that the amount of force and the high cadence of a racing bicycle ridden with fairly rigid clipless pedals does make these issues come out quicker than on most other types of riding.

The Q-factor on a FC-R8000 is 146mm. If that's wide I'm worried what's considered narrow and why would anyone want that. My 151mm GRX crankset gave me immediate and concerning knee pain before I spaced out the pedals with 12mm longer spindles.

There isn't much study done on the health effects of Q-factor. I did find one study which found that wider Q-factors increase knee abduction moment. https://pmc.ncbi.nlm.nih.gov/articles/PMC7242219/
However the study was tiny and the four tested Q-factors were 150mm (narrow road bike), 192mm (fatbike), 234mm (what the...?) and 273mm (ridiculous...).

All in all the results were kinda meh, and frankly tiny when hopping from road Q-factor to fatbike q-factors. Beyond that differences were greater but that's of zero relevance in terms of realistic cycling components.

All in all, when considering how small the effects of changing q-factors are with absolutely massive jumps in width, a small spacing of a few mm, even on a "wide" crankset, is going to have absolutely no discernible effect on the rider.

Seems like Q-factor is largely overrated when going wider. Too narrow is a problem because there's stuff in between the legs when riding a bike. One really shouldn't attempt to mimic walking gait width with cycling just like one shouldn't do that when squatting. Completely different activities and all that...

Again, the "problem" in this thread isn't that the Q factor was "too wide", it was that the OP wanted to make it even wider to prevent heel rub.

The other issue with the FC-R8000 is that it has no ankle clearance.


It sounds like you think wide cranks are better. You are welcome to that opinion, but the bike owner in the OP was comfortable, and not suffering from "stuff between the legs" that would have been better had she been riding a fat bike.

How do you know the rider has a noseless saddle?

The problem is nonexistent. Adding a 2-3mm spacer to both sides will not cause issues even if the cranks were mtb-cranks.

Also on the point you made in your previous reply, while road bikes may have steadier pedaling effort, mountain biking causes far higher torque moments at the knee. Touring is also practically road cycling but with much higher volume.

I don't think wider is better. I just don't think people should particularly strive for wide or narrow cranks since it most likely won't make a difference, unless one is going far too narrow or far too wide. There's too much bro science in cycling. When I see statements that saddle height should be X because some former pro made a formula, or one shouldn't widen from already wide cranks (which they weren't), I typically want to know why. And most of the time there is no physiologically or scientifically sound reasoning behind such statements.

Considering how many different width cranksets cyclists riding multiple disciplines have, the idea that a few mm difference, even if done due to cosmetics, would pose ANY ill effects, is laughable.

Your attitude sucks. Most people barely ride. Some people need more Q, some people less, some people aren't sensitive either way.

My point is that the client has no comfort problems, so why potentially induce one by changing a position that is working to address an aesthetic issue caused by the crank design having too little heel clearance.

You point is that everyone is just like you, so let it rip. That's dumb.

Yet what data there is seems to imply Q-factor isn't at all important and detrimental effects only begin at the extremes.

A few mm adjustment would not have induced anything. However a rubbing heel can wreck your shoes. I'd imagine that there are people who would be bothered by the rubbing and start self adjusting to avoid it, which in turn could cause quite large issues.

​​​​​​​I recall specifically writing the opposite. But you do you and all that.

​​​​​​Look, there is no database of medical fit information. No one is collecting it, very few universities are studying it. So you have absolutely no right to claim that you know that tread width doesn't affect people. Your anecdotal assertions about fat bikes are also not data.

I worked for one of the best and most experienced fitters in the US. For some people, tread width matters a great deal. Sometimes they need more, sometimes they need less. But what they need isn't subject to a lot of manipulation. It affects ankles and feet and knees and hips.

The other bit you might have missed is that widening tread changes the hip angle usually, and therefore the foot angle. So even though you are trying to move the heel 4mm, it takes considerably more cleat movement because moving the front of the foot out usually causes the heel to angle in to compensate.

If this thread was started by the rider, I would have explained all that and then said "Hey, try it. This is what to watch out for." But this thread was started by a bike shop employee of limited experience, and that is not someone I'm going to play fitting telephone with.
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elcruxio, I've had chondromalcia patellae the past 47 years; since mid-way through my brief venture into road racing. My knees make it very clear that they do not like wide Q-factors at all. They have never seen a Q-factor that felt too small. (There probably is one but it may not be achievable on a conventional bicycle.) They love 135s. (Velodrome fix gears.) 145 is OK. 155 works for around town bikes. I've been observing this since the late '80s as the super straight Sugino and TA cranks fell out of favor and Q-factors started marching up.

My best custom is set up triple so I can climb anything on these knees. It started out with nice Shimano 105 crankset. But my knees weren't entirely happy. In fact, I started taking my fix gear up the same hills and found my knees liked that better! So I re-did the good bike. It now has ancient, straight Sugino cranks from the old "10-speed" days, a super narrow Phil Wood BB. Not an easy process, I had to install "pins" to keep the chain from falling into the gap between rings. But the Q-factor is way down and my knees love it.

So - I can listen to my knees that make it very clear that I have a choice. Low Q-factors or those modern replacement knees. If I were to follow that "research" and take the Q-factor doesn't really matter approach, I'd have a pair of neat scars on my knees. And after that, you would probably be right.

For me a narrow Q is more comfortable, without any doubt. I disregard minor crank rub.

What REALLY bugs me is the width of modern rear hubs that result in heel strikes - even for my size 44s with cleats aft on the shoes. Never happens on bikes with 126mm spacing.

Having ridden in the rain on the same single since 2000 and the same tandem since 2006, I've rubbed the paint and some of the aluminum off my cranks, thanks to booties and boots and maybe just my Sidis. I can feel the dents in the aluminum with my finger. My fit is fine as are my cranks. 'Much ado about nothing'.

I have my cleats set with quite a lot of toe-out, which makes heel rub quite likely. My solution is +4 mm Shimano DA or Ultegra SPD-SL pedals. The standard pedals cause heel rub, while the 4 mm wider ones comfortably clear. I don’t notice the extra width at all. I don’t think heel rub is a big deal, but I prefer to avoid it if possible.

Maybe cleats or pedals are worn causing some rotation when engaged and pedaling