I have a pair of Mavic 33 training wheels with Michelin IM tires on them and pair of Hed3s with conti3000s on them. The Michelins are 23mm and the Contis 19mm. Cnsistently my rides on the training wheels are faster than on my Heds??? Could it be becasue of the tires? My training volumeehas varies, but i am pretty sure I am in the same condition each time I ride. I rode a 65 mile ride four weeks ago at 21mph on the Mavics, and a 75mile ride on the Heds @20.4mph two weeks later. In both instances cadence was about the same and HR within 2 or 3 beats?
While your sample size of two rides can’t determine anything with precision, tire width does matter. Wider tires are usually faster on normal, semi-bumpy roads – the real world kind. Narrow ones can be faster on ultra-smooth roads or velodromes.
Many people (me, at least) find the extra comfort that comes with wider tires makes them faster on long rides due to less fatigue.
there’s something more than just difference in tires going on to cause that much of a difference. but, according to what i’ve read (i think written by dan on this site) tires are most aerodynamic when they’re as close as possible to the width of the rim. the 19mm tires are smaller than the rim; the 23mm tires are very close to the rim’s width. so, yeah, wider tires are supposedly more aerodynamic, but that doesn’t explain that kind of a difference in speed to me.
I don’t see how comparing those two rides qualifies as a test. The lengths were different, so obviously the courses were different. You went a bit slower on the longer ride, not really much more than would be expected. Your speedometer could have lost contact on one of the rides and you could have the distance off a bit. There are any number of other possible differences.
Do a few more controlled tests. We would all be interested in the results.
I don’t know about anyone else but I think that there is no clincher tire out there that is faster than the michelinn tires… not familiar with that specific model, but the pro race tires a freakin fast and hold like no ones buisiness… definately lose out in the durability section though… Right now have heavy belted tires, somedays I wish I was on the michelinns. though.
If you fins that those tires are consistently faster why don’t you switch the tires between the wheels?
A few things. The course was pretty much identical as was weather and wind. I am going to switch the tires around, but the point about comfort over the distance is a very good one. I am riding 75 miles again this weekend, and I will ride the same course as before and see what happens.
I am not complaining though, these ride speed averages are all a great improvement on last year, I am just curious to see if I am losing out on some “free speed” - if there is such a thing.
The difference of those first class tires are to small to be able to check using this kind of test, other variables (wind, temperature, rider form, humidity etc) differs much more.
there’s something more than just difference in tires going on to cause that much of a difference. but, according to what i’ve read (i think written by dan on this site) tires are most aerodynamic when they’re as close as possible to the width of the rim. the 19mm tires are smaller than the rim; the 23mm tires are very close to the rim’s width. so, yeah, wider tires are supposedly more aerodynamic, but that doesn’t explain that kind of a difference in speed to me.
A 23mm rim – on a race wheel? Technical course? Poor roads? Maybe on the rear, but…
Your lead edge into oncoming wind is key – the front tire/wheel combination. Other work has shown that a (very) slightly smaller tire width relative to width may be optimal here, though the dif. is negligible.
But any wider tire-than-rim setup is always going to cost you bigtime.
Under appropriate conditions, I race with an 18mm Conti Grand Prix clincher (hard to find, as sadly they no longer make this width) on a 19mm high profile rim. Don’t tell me it’s not fast, 'cause it is. And even an evenly matched 19/19 on the front is noticeably faster than a 23/23 there.
You can go a little wider on the rear if you like, but if you’re racing TT’s or short tris on good roads, 23 seems to be pushing it. My TT’s are short (40km or under) so even on the back I generally use a 19/20 or 20/20 tire-to-rim setup, using a high end tubular.
But if comfort is a key concern, I’m assuming poor road surfaces, very long races, or inappropriate frame geometry or layout for a TT position (FWIW, the P3’s comfort in TT position is awesome, even on 18 or 19mms pumped to 160). Just my $0.02.
Interesting, Kraig – I’ll go take a look (please don’t yank the link :-)).
One question I always have about wind tunnel wheel tests is whether airflow is tested over a static (non-rotating) wheel, or one that is rotating forward at, say, 28mph. This is directly relevant to tire width, and the distintion is an important one.
The top part of a rotating wheel is moving into the oncoming wind at twice the speed the bike itself is moving (in the example above, at the top of its motion, its going 56mph against the air it’s contacting via friction!).
This has to be a major source of air clash/turbulence – AKA, slowing you down. And, of course, the wider the tire, the greater the surface friction area inducing this turbulence.
Sorry if everyone knows this but me, but how are wind tunnel tests of tires done – with rotating wheels, or with static ones? The latter would greatly underestimate time saving differences by witdth, it seems to me.
Jeez that profile of rim dimensions just makes me sad. It looks to me like the mavic cxp33s are probably more aero than the ksyriums.
Mavic’s hype machine for those wheels has worked so well that, on my last club ride, probably half of the “fast” riders were on ksyriums. I can’t fault them though, they probably just believe what they’re told. I was at my LBS the other day, and the store owner and tri rider was telling me that the ksyrium ssls “just feel faster” than the HED alps I had in my hands. I just shook my head…
Wheels that “feel fast” are wheels that accelerate well. In order for a wheel to accelerate well it needs to have a low MOI and to be stiff.
Ksyriums feel fast because they have a low profile and light rim, making it have a low MOI, and are stiff by construction. Cyclists like them because they are light and accelerate well. That makes them excellent wheels for draft-legal triathlons too.
But you’re right, the CXP33 rim is more aero than the Ksyrium rim. One set of wheels that were a good compromise were the old Cosmic Elites, with a rim close to a 33 and spokes and hubs close to the ones on the Ksyrium.
Just curious if you ever measured any difference between a rotating wheel with and without a fork attached to it. Sort of a related question to the post above, just in a more direct fashion.
Wheels that “feel fast” are wheels that accelerate well. In order for a wheel to accelerate well it needs to have a low MOI and to be stiff.
Ksyriums feel fast because they have a low profile and light rim, making it have a low MOI, and are stiff by construction. Cyclists like them because they are light and accelerate well. That makes them excellent wheels for draft-legal triathlons too.
But you’re right, the CXP33 rim is more aero than the Ksyrium rim. One set of wheels that were a good compromise were the old Cosmic Elites, with a rim close to a 33 and spokes and hubs close to the ones on the Ksyrium.
Paulo
As regards your first sentence: absolutely untrue. Unless you are constantly reaccelerating, as in a rolling set of climbs, or a crit.
If your are racing a reasonable flat TT, you accelerate exactly twice: at the start, and at the turn.
Wheel profile, rim config, spoking, etc. are all infinitely more relevant than weight away from the axis of rotation (which is what affects acceleration). What matters id resistance/drag at race speed. Period.
I have an amazing Saavedra Aero wheel that weighs virtually nothing. Would never dream of using it in a TT, except in a steep uphill hill climb.
If you want to see a really boring video clip of the wheel/fork setup I used and the sounds of a wind tunnel, check out (note that for the tire tests I did, the fork was removed): 400 kb movie
It should also be mentioned that Greenwell et. al, have done the wheel rotation experiment and he states:
“Before commencement of the experimental programme, it was expected that the wheel rotational speed would have a significant effect at non-zero yaw angles, particularly for the trispoke wheels which resemble a rotor system. On analysis of the results it was found that the wheel rotational speed had in fact an almost negligible influence, except for some aspects of the disk wheel axial force characteristics at very high yaw angles.”
So, Greenwell takes the stance that wheel rotation doesn’t really matter. A&M has the ability to do this, so I chose to go after the more “real world” case
If anybody wants a copy of the Greenwell paper (wheel aerodynamics journal article) drop me a line and I can forward it.
Thanks, Kraig! (don’t find clips like that boring at all, BTW).
So is the notion of the top of the front wheel “throwing” air forward off base? Or is it just that – since the point of air friction contact at the top is the tire (not the rim) – all similar tires-on-rims will test pretty much equal in this regard?
If it’s the latter, wouldn’t this still beg the question of optimal tire width? (the issue that got us onto this sub-topic).
A 19mm tire has a width almost 20% smaller than a 23mm – thus significantly less surface area in contact with the air at its top to induce “forward rotational frcitional drag” (for want of a better term). Clearly less friction induced in relative terms – just don’t know how great this effect/difference is in REAL terms…
Would love a copy of Greenwell’s paper, will e-mail you my e-mail shortly.
If you are using the same computer to caculate avg speed. There may be a slight difference in the circumference of the wheels. I know my HED3’s seem to register a couple mm different than my Bontragger training wheels. The trainers have 700X23 Michelins, the HEDs have 700x23 Tufos. The difference could add up over the course of 65-75 miles.
I think the reason that you’re slower on the Hed wheels is pretty simple, you’re not riding fast enough to realize a time savings from the more aerodynamic wheels to offset the time you’re losing from spinning and hauling around their extra weight. On this forum, there seems to be endless discussion on aerodynamics and wind tunnel testing, quoting theoretical time savings when the fact is most of us don’t ride fast enough to really benefit. Call me crazy but I’ve always found that everyone gets a benefit from lighter wheels, whereas only the faster riders, those averaging 35km/h + , seem to gain anything from “aero wheels”, unless they are also lightweight. So if you want to use aero wheels, get the lightest ones possible, such as the carbon wheels that Zipp makes…and make sure you follow Bunnyman’s advice and get tubulars!
Wow Kraig! That’s a mature reply. Just because I don’t believe everything that happens in the wind tunnel applies directly to riding out on the road doesn’t call for a tantrum. It seems to me that weeman, who started this thread, found this to be the case also, and was looking for reasons why it was so. Sorry to burst your bubble Kraig, but other people besides you have opinions to express and reasons for them as well. However, when it comes to racing in a windtunnel, I will defer to your expertise as it’s been a while since I’ve raced there!
Kraig, I guess it would have been better for me to have not stated any specific speed in my post. Obviously, the speed where the trade-off might be is not fixed or predictable, I was just offering up a somewhat arbitrary number to show the ballpark of where I think it may be. I just think a lot of people get the impression from wind tunnel tests, that throwing a relatively heavy set of aero-wheels on their bike is going to make them a lot faster regardless of their speed or terrain they’re riding.
Don’t get me wrong, I trust your math and physics and appreciate we can learn something from the wind tunnel. I would just like to see more practical perspectives as well.
And even an evenly matched 19/19 on the front is noticeably faster than a 23/23 there.