how much shaving of the brake blocks did you need to do in order to fit the stinger??

im in the market for a disc as my super9 is slightly damaged...

About half. Actually managed to shave them the wrong way so haven't used the rear brake all season...

Ah cool, half is not bad.

Maybe the aero gurus can explain how this works, because I don't see how narrowing q-factor by 17mm changes frontal area of your legs at all. Maybe if you were pedaling like a bow-legged sailor before, but my thighs at "normal" q-factor spacing are pretty much parallel. If I put them 3 cm closer together, I still have just as much leg, it's just placed closer to the frame. So does the aero improvement come not from a reduction in frontal area, but rather from a smoothing of the flow around the legs and/or fairing of the rear part of the bike from air flow? I'm also curious if you did this testing with a disc wheel. Just trying to figure out how this works.

Narrower Q-factor is more aero, but not by the extent Jens is talking about. Ask AeroCoach/Xavier on Twitter as he's done a lot of work with it.

How does it show that?
With those legs you'd be faster with a narrow Q.

Narrow Q did the same for me Jens, I got down to 125 on the p4.

Shame most modern bikes aren't built for narrow Q, it works well for the narrow hipped and is a significant aero saving.

Well I'm way more aero than Jens for one. Also, my track bike CdA is much higher than my TT bike CdA, and that's with a narrower Q. Also, there's just no way I'd be able ride with that low of Q and not break the chainstays.

How low is your track bike Q?
How can you compare your CdA to someone else's, or indeed between your bikes.

I would have thought all the time you have spent with Xav you'd know it would make you more aero, whether you can do it or not is the point Jens is making.

He's making the point that most modern superbikes aren't all that adjustable when it comes to things like Q, which as he has shown for him makes him more aero.
Might not work for everyone, but it worked for me!

I'm not a guru by any means, but I can offer a few points. I got a wind-tunnel documented improvement of ~7 watts going from a q factor of 149 to 132 (17 mm reduction). I think this may have under-estimated the improvement, because it was the last run of the day and I was getting tired and sloppy. In field testing I gained roughly that much again by narrowing another 12 mm.

I think I misled by discussing frontal area. You are absolutely right that your legs' frontal area is what it is, whether they are 120 mm or 2 feet apart. It's really about how the air flow re-attaches. If your legs are way out there by themselves in the wind, the flow isn't going to re-attach as well. How close your legs have to be for flow to re-attach is probably a factor of the size our your legs, the frame, wheels, and a whole bunch of factors. From my experience, I'm guessing there's an inflection point somewhere between 150 and 130, where there is a dramatic improvement. Previously, I did some testing between 165 and 150 and saw very little difference ( As long as your legs are way out there, it doesn't matter if its 155 or 200).

Incidentally, I am puzzled that many people here believe that socks with a strip on them will gain them 5 watts, but think that bringing their legs 3cm closer together does nothing. ;-)

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My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers

It's 136mm on my track bike. Seems pretty easy to compare when they all have known CdAs...

You seem to be missing the point. A Q factor narrow enough to drop my CdA is only achievable on older frames, but those frames are all slower than the P5 (among others). So it's not as if it hasn't been considered, it just makes no sense (especially if you have a P5). And again, with that narrower a Q factor, my heels would just bounce off the chainstays.

I reckon you're just trying to justify buying a p5!

and this all assumes that narrowing q-factor doesnt effect your power production....ultimately its finding the correct balance

You do realise that I never wanted to buy the P5, and was forced into it? It also took 7hrs of testing to get faster than I was on my Plasma...

Thankfully mine went up!

Yeh I know what you mean! Last time I went into my local cervelo dealer that guy holding a gun to my head was a real buzzkill

Did you buy of the back of those idiots CTT wanting to enforce the 3cm??

I cannot speak highly enough of cervelo... the warranty department has been amazing, sent me a new frame with hardly any discussion... lifetime warranty.. granted I've never owned a TT bike before I bought a P5...

Yeah. The target on my back was enormous and I was miles away on the Plasma. Partially my own fault for being so vocal about it, but still BS that cost me a silly amount of time and money.

I agree,
I've had a p2, p3, and now a p4.
An s5 and an S3!

With your wider legs and hips, it's possible that you would have to go in even closer than I did, to achieve significant drag reductions. So yeah, for a lot of people it clearly doesn't make sense. For me, it does.


Well, I'm really old. But also I've only been at this for about 7 months, after a very long hiatus.

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My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers

You'd still qualify as one of the most aero on ST. ;)

Also the issue of not being able to use a crank-based PM. PT Stingers aren't the easiest to find.

I would really be intrigued to know what the interactions are that make this useful for some folks and not for others. I went from 157 to 130 and so far I am just not seeing any change. Today’s run of a/b/a/b tests were remarkably consistent within a second of each other. Which is kind of a bummer because it was as cheap a way of finding free speed as I could have hoped to find.

I feel better now. I have a P3(alu), a P4, and just added a C5 (that bike is soooo fun!).

It might have more to do with the tracking of your knees. Simply moving your feet closer to the crank arms may actually increase drag for the same reason your most efficient hand position for swimming is with slight gaps between the fingers (I.e., the water doesn't flow freely between the fingers so the effective surface area of your hand is increased. Same with the debate between wide and narrow forks. Wide forks let the air flow through while narrow forks count on the air flowing around.

Now your knees and thighs are interacting with the headtube on the bike. Are you more Areo letting the air flow through the inside of the legs or should the knee attempt to "hide" behind the headtube, and to a lesser extent the downtube. Your testing may indicate it doesn't make any difference compared to Jens, but he sure looks tall and skinny. Maybe that is the reason it works for him

I run the narrow Speedplay axles and cleats set about as narrow as possible and my knees graze the top tube. I don't

I am about the definition of tall and skinny and my knees are grazing the top tube, those things are similar. Between moving one cleat and the crankarm/bb change, I am probably 30mm closer together, but maybe I need to be even narrower for it to show any effect Not sure if I am going to try it or not.