Ah, now that is a good question (esp for a nub)!

Hopefully Tom A. will chime in here. I've been very unscientifically toying around with this (front wheel only - still run a wider 23mm ProRace2 clincer on my rear disc for comfort/rolling resistance) with my front Hed Jet90 (old model). Been swapping between a Vittoria Corso Evo 20mm and a ProRace3 in 23mm.

For sure, the PR3 rides nicer and I don't think is any "slower". So, if it is essentially a "wash", the wider tire wins easily because of comfort alone. Yes, the New Jet C2 would solve this dilemma and is on my radar screen ...

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Fatigue is biochemical, not biomechanical.
- Andrew Coggan, PhD

"Vittoria Corso Evo 20mm "

I thought this came in 21 or 23mm?

Nope - Vittoria Open Corsa Evo CX (CLINCHER) is 20mm. Printed on the sidewall and measure at 19.9 on my calipers and seem to fit/line up perfectly with the older Hed Jet rim.

23mm Michelin PR3s measure 22.7 and PR2s at 23.5 (current ones mounted). I've seen PR2s as wide as 24mm and only have 3 PR3s (they all measure just under 23)

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Fatigue is biochemical, not biomechanical.
- Andrew Coggan, PhD

I'm runnng both. Use a 20mm for my front 101 and a 23mm on the rear disc. The rear tire is hidden by a close fitting seat tube cutout. This optimizes frontal area on the front wheel and RR on the rear.

Ric

 
I would think the trailing edge of the rear wheel would need some attention too. But I've seen relatively little talk on that aspect...so what do I know.

Bump for the weekend racers.
So, are we looking at a wash with the offsetting factors? In terms of watts, what are we looking at for each factor? In other words, how much energy is saved with the aero benefit of the narrow tire and how much is saved with the lower rolling resistance of the wider one?

That really depends on the characteristics of the tires you are comparing (both Crr and aerodynamics) on the particular wheel you're interested in...i.e. not ALL wider tires have lower rolling resistance than narrower tires.

Poke around in this thread for some insight into all the variables:
http://forum.slowtwitch.com/...g=aero%20tt;#1742677

That said, it appears to me that really low Crr can "forgive" a lot of aero sins...

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I'd say that you know a lot.... ;-)

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Thanks for that link, Tom. I had seen that thread before, but spent more time trying to decipher it this evening. (Now I have a headache.) You pointed me to the graph that gives the answer (unless I missed something), for a slow guy like me, the rolling resistance definitely "wins."

This is a good question. My limited and subjective experience is that the rolling resistance matters more. I bought some Hed3 clinchers last year and they came with a 23mm tire on the rear and a conti 4000 19mm front. On the stone chip roads I ride a lot on I felt the front was losing me quite a bit of speed in jiggling the bike up and down. I switched to Michelin PR3s (23mm) and they bike felt faster straight away. On nice smooth roads I'm not sure if this would be the case.

You're welcome...just let me know if I can help in any way to lessen that headache :-)

I would say that the curve plot gives "an" answer...not necessarily "the" answer ;-)
The curve shapes and crossover points will change depending on the rider weight and the aero properties of the wheel to which the tire is attached.

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Oh, I meant tubular, I use a 21-28 on the 1080 front wheel

How much real world time are we talking here?

I can't help but wonder if things like this really matter. Sure wheels, helmets, and position are backed by solid data.....but when im lapping guys on zipps with my round tube bike with 20mm wheels (not bragging, there are guys much faster than me, just commenting on what i see at races)....well....maybe im just poor and bitter (ok i am), but is all this crap really worth it?

Cost/benefit ratio seems ludicrously low.

See the other thread on how little time you have lost a race to ...

At the pointy end (or anal end), yes, it does matter.

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Fatigue is biochemical, not biomechanical.
- Andrew Coggan, PhD

No doubt it does at the pointy end (extreme pointy end)....i dunno....just seems like such miniscule gains in the scheme of things. Aero benefits of a 20mm tire over a 23mm tire minus increased rolling resistance....i mean....really?

Basically, it all comes down to this:

You can't buy* FAST...but you can at least buy fast-er.

*("buy" in this sense means either purchasing or selecting stuff that will make you faster...all other things being equal)

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That's funny. I don't think narrow tires cost more than wide ones. Secondly, when one is looking at cost/benefit of bike parts, fast tires are the probably the single best way to spend your dollars.

If you were making those comments about ceramic bearings, I'd be right with you.

That's terms i can understand.

Fast(er).

I like that.

No you're right, I should have been clearer. Just commenting on the whole aero/weight etc side of the industry in general.

Well...in that thread I linked to above, there's a chart that shows 2 tires that have nearly identical rolling resistance (VF Record and Bontrager RXLPro23), yet because of the aero drag differences they have a total drag difference of ~50-75g, or ~0.1-0.15lbs. That translates to roughly 0.5-.75 secs/km of time savings.

So...depending on the length of your bike race, is that "worth it" to you? Only you can make that decision. Heck, even for just a 10 mile TT I'll take the extra 8-12 seconds. I lost out 2nd place in the last local 10 mile TT by just 1 second.

Of course, this whole subject is talking about just one tiny detail, and taken in isolation it may not seem like it's worth it. But, add up a bunch of the same types of "tiny details", and pretty soon you're talking REAL time savings, right?

IMO, going fast in a timed cycling event is ALL about attention to a whole bunch of tiny details.

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the relevant ratio is power:disposable income. luckily the second term rises for most people as they age. for the luckiest, for a few brief years, it rises enough from about 40-46 to offset the effects of the decline in the first term.

I need tires. I can control for many of the variables by saying I'm buying tire X, so am I better off getting the 20 or the 23? All said, yes I'm splitting hairs between finishing 149th and 150th, but why handicap myself any more than time and genetics already have? Even to spend an extra $30-$40 for "good performing" tires vs. "poor performers" makes sense to me if it buys me 0.25-0.5 mph. I agree that $2000 for wheels that would catapult me to 147th place would be a piss poor way to spend my money. Then again, if I could afford them, why not?

Call me a born skeptic, but I find it hard to believe that the little lip on the Bontrager TT tire works as well as claimed. At least w/ a Zipp 808/Veloflex Record combination, the "step" from the tire to the aluminum brake track is less abrupt* than the transition from the aluminum brake track to the carbon part of the rim. It's therefore hard to fathom how filling it in would reduce drag so markedly.

*Measured using the highly precise "drag a fingernail across it" test.

OK..."You're a born skeptic." Are you happy? ;-)

Seriously, as you know, the aero data was from Damon Rinard and relates to a Bontrager Aeolus 5.0 ACC wheel...so, as I've said a few times already, THOSE particular curves are wheel and loading specific. Then again, Damon also said that they saw similar aerodynamic affects from test with the same tires on a 404.

I guess this is one for Damon to field...Damon?

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