Q Factor, quack quack..

[Woz]

One of my favorite 1 x 9 set-ups was a 110mm and a LX M560. Got it to just clear the wide stays of a Voodoo by
a fag paper clearance and the chain line was awesome with the outer ring position. In winter it got converted
to SS with no chain line faff whatsoever.

I did file the crank internal tapers though to center it all up, but that's how I roll with bike parts

 

[lensmansteve]

bjellys, I think I've had that syndrome for a while. Nerds of the world, unite. We have nowt to lose but our obsessions..
Leave the paracetamol alone, get something stronger on the go. Mainlining GT85 maybe?

 

[lensmansteve]

Woz, that sounds just the sort of wizardry I like. Tbh, this thread has inspired me to take the nasty four bolt off my just-built Kāstle Degree 8 and drop kick it into the shrubbery, to be replaced by a M550 that I left off because the lh crank only missed the chainstay by a couple of mill. What was I thinking? Afraid of scraping the paint? 107mm UN71 was in the frame when I bought it on here a month or so ago, total bargain, Prestige Superlite, beautiful paint- £45 posted, early Christmas this year.. For me, anyway..

 

[TheAntsPants]

Re:

Aww sh!te! I thought my bike was perfect and now you've got me running to the shed :facepalm:

Seriously though, my favourite advice is to measure the width of your feet when you walk, say, on a sandy beach, ignoring the strange looks from normal folk! That should give you a baseline to work from for what is "natural".

The other consideration for the pedants is that the narrower the Q factor, the stiffer and lighter the bike. And you'll get a fractionally steeper lean-in to the corners before your pedal hits the ground :roll:

A quick back of the envelope calculation tells me a 20mm increase in Q factor (10 on either side) reduces your lean-in by 1.5° (but don't quote me on that!). You decide if it's worth the worry

I'll leave it to someone else to calculate the aero advantage

So, my advice is go as narrow as possible before it feels weird or your heels hit the stay.

 

[Splatter Paint]

Re:

Doesn't everybody try to get the cranks / rings as close as possible to the frame?

SP

 

[24pouces]

Re:

Thr worst Q factor : Mavic mtb crankset : wide spider with parallel arm and an around 130mm axle. So, hankle is hammering the crank when pedaling

 

[lensmansteve]

Morning, all! I've heard that "walking test" Ants, worth doing but we balance ourselves a bit differently when we walk I think. When we run, our footprints almost line up.. But the important thing is that the Q is getting some attention, isn't it? And yes, the leaning over thing can be improved with a narrow Q (and crank length, and bb's height) and the Q alters the feel on corners as well as stability when we're giving it welly. I mentioned that earlier, I think.
Well SP, I think we all know the answer to that one. Didn't you know Shimano come round and fire up your home if you don't keep to their specifications? That's what I've heard anyway..

 

[lensmansteve]

Pouces- Some designs are truly awful. It makes you wonder if they test them at all. What's really sad is that they still sell plenty. Incidentally, crank rub is a common thing. That's mostly caused by cyclists trying to narrow their Q, often subconsciously.

 

[2manyoranges]

...goodness me this is deep therapy. Lost knowledge coming back up to the surface. Q really does matter. I've ridden off road for 30 years and really looked after my knees - other who have not have all sorts of serious cumulative knee and hip problems.

Crank rub is a function of white a few things, of course, including monster wide shoes these days - 5 10 impacts etc. Flats allow a lot of movement (a good thing for your joints) and I went back to using them around five years ago. But if you use clipless, then Q becomes EVEN MORE IMPORTANT (shouty capitals...never mind). And so here we go again with things which are related....boost rears throw the chain line out further - trying to get the right line on my Sentinel build is causing a headache...and using clipless means that getting Q right is essential. It's a bit bonkers to use pedals with no float (if you value your knees) and once you have got pedals with the right float (thank you onZa and Time Atacs) then there's the nightmare of getting the cleats in the right place - actually easy when you set them up with your legs hanging over a table and someone helping out with the alignment.

It's a perspective thing - I imagine my self going along full tilt without any bike at all. Really. Then start adding the bike, bit by bit in my mind. That's what you want, a bike which adapts to you, not something which demands that you adapt to IT.

This image helps you get the right width to bars (wider than we were used to in the 90s), the right seat angle (much steeper than we ever had - and now coming from some of the North American designs), much less 'over the front' (which means slacker head angles and stubby 35mm stems - or less (!!) and less offset on the forks). Modern bikes are sorting many of these - Transition were thought to be mad with their steep seat angle and slack head angle - now everyone's doing it. But few people are thinking of Q - they should.

 

[Woz]

3 pages of Q-factor ramblings and nobody mentioned Graeme Obree. What's wrong with you people!