CHOICES, CHOICES...
Our choices in the tires we ride are possibly among the most subjective we make. There is often very little empirical data (except maybe price...) that is involved. More commonly our "data" is along the lines of "my buddy says they're the fastest tires he's ridden" or "she said she didn't get flat tires for a year". When you really stop and think about it though - there is a lot of highly personal variables involved in those statements. Let's cut through the clutter.
I've long admired cyclingnews.com's James Huang's technical writing and referred to it often as the best in cycling journalism (although - VeloNews has really stepped it up lately).
One of his latest pieces highlights a tire testing facility in Finland that seems to finally be coming up with some good data on tires in real-world type scenarios and less-so in the controlled laboratory conditions of older tests. The article has some fascinating facts and data; confirming some long-held thoughts and theories of my own and surprising me on a few areas that I had accepted as fact which it seems were not.
FIRST - THE CONFIRMATIONS:
-Wider tires are faster due to less energy lost in casing deformation. The study specifically cites 25 mm tires versus 23mm tires.
-Puncture resistant tires are typically slower, but to different degrees depending upon the stiffness of the material used. Again, based on tire deflection.
-Lighter inner tubes are faster. Lower weight at the periphery of the wheel lessens the moment of inertia and amount of effort required to maintain speed - the same as with lighter tires.
NOW - THE SURPRISES:
-Higher thread-count tires aren't always better. What's simple to understand is they are more susceptible to cuts because of the thinner threads. But, a medium thread-count tire may actually roll faster because the casings are less supple and deform more efficiently. Add their increased cut resistance and they'll make good every-day tires. Still though, consider that while thread count decreases, puncture resistance will increase at the expense of speed.
-Tread pattern matters on the pavement too! Whoa! I get this off-road; it makes sense. But I've always thought of tread patterns and siping on road tires as "negative spaces" in the tread which would limit the tire's ability to conform to the imperfections of the pavement. This in theory increases adhesion with the pavement. Not necessarily so...some patterns will increase adhesion. I now wonder how much this has had to do with tires I loved and hated...
Finally - they may have put one of the greatest industry arguments of the last decade to rest: 29" MTB wheels do roll faster than their 26" counterparts! I however still feel that some 26" geometries allow for better agility, but it may only be a matter of time before someone proves me wrong there too...
Enjoy the full article here:
http://www.cyclingnews.com/features/tech-feature-the-work-of-wheel-energy
Lots of good thoughts shared so far on this one? Care to contribute - leave a comment...
So much of this is counter to our simple minded logic. Kind of like riding a course on my steel rain bike FASTER than on my race bike because the ride was better therefore my fatigue was less, etc. Those 25mm tires FEEL slower, but like CX tubulars roll sweetly along. The TPI was a revelation to me as well..
ReplyDeleteInteresting stuff. And one point to consider--when you count the time it might take to change a flat, the tire/tube combination least likely to flat may be the fastest, if by fastest you mean getting from point A to point B in the least amount of time (not to mention least amount of hassles). This is why I like thorn resistants (which labels me a fred or something, I know, but oh well).
ReplyDeleteDavid-
ReplyDeletePuncture resistance is high on my list of requirements too. Even the Continental 4000 S that I ride in the summer is a relatively tough tire for a high-performance tire. But, in the winter I ride much more resistant tires like a Gatorskin or Armadillo Elite. In the end; you're right: not getting a flat is a lot faster than standing on the side of the road with a pump and inner tube in your hand...
Hi Matt-
ReplyDeleteI have a question regarding inflation of the tires. Friends say to keep the PSI lower which will increase speed and contact with the road. You mentioned tire size and that smaller tires may not always be faster. Would the PSI be comparable-more contact with the road, etc? I tend to inflate my tires a bit beyond what is recommended, they say that results in a bumpy ride, but I would say less contact and conforming to the road-and I get fewer flats. I feel that the bike is faster with a slight overinflation of the tires. Had someone help me with a flat once, he underinflated, ended up with another flat during the same ride. I deal with my own flats now, even though they were just trying to be nice :) BTW, tri bike may be need your expertise soon!
Chris-
ReplyDeleteBring the TTX by the store any time - we'll be happy to help. Repair turn-around is running about 3-4 days right now (yeah, we're a little busy for February).
Now - on to your thoughts on tire pressure: My first comment would be this - a very trusted tech rep for Michelin Bike once told me to never inflate a tire beyond it's max pressure rating. The tire can probably handle it; but it's not designed for it and your rim probably isn't either. Many rims have maximum pressure ratings too (although lesser known) and many are around 125 psi. So, over-inflated Conti, Specialized and Bontrager tires and many Vittoria and Vredestein tires are past the max range for your rims - carrying a far greater change of catastrophic consequence than simply an over-inflated tire...
As for pressure and flatting - I find it is also influenced by tire type and condition. Worn out tires are even more susceptible to flatting at lower pressures and new tires are less affected by pressure as it relates to flatting. So, any uncharacteristic flatting is a good indication to check tire condition. More on this here: http://mattmagee.blogspot.com/2010/08/worn-tires-and-flatting.html
Pressure and performance? Your thoughts are right on: lower pressure in a 23mm tire will add more lateral dimension (width) to the contact patch and make it more similar to a 25mm. But it will also add length to the contact patch - which is the problem with a 23 when compared to the 25. The length of the 23mm contact patch is where the rolling resistance comes from. It is in contact with the ground longer - creating greater friction with the surface and causing a longer section of the casing to necessarily deform versus the wider, rounder patch on a 25. So, a low pressure 23 is closer, but not identical to a 25.
All this is to say; experiment with the pressure to find what works for you without exceeding the max. Different pressure front and back is also acceptable. I usually run 5 to 10 lbs less in the front than the back. This works because there is more weight on the back tire. More in tire pressure here: http://mattmagee.blogspot.com/2009/06/truth-about-tire-pressure.html
Wow - that was a long response! :)
Oh, and don't read too much into multiple flats on a ride and difference in tire pressure. Some flats can't be avoided. Also, your Good Samaritan may not have effectively removed the original cause of the flat from the tire.
ReplyDeleteAlso - to address the "bumpy-ness" of higher pressure: greater pressure causes tires to "bounce" off imperfections in the road rather than conforming and rolling over them. Bouncing is not as fast as rolling. Higher pressure feels faster *because* of the rougher ride. Our brain interprets that as speed: however correct or incorrect that may be.
I think I'm done for now... :)
Matt: It is true that wider tires have lower rolling resistance, but because narrower tires are more aerodynamic they are actually faster (aerodynamics trumps rolling resistance).
ReplyDeleteHere's a nice chart illustrating what I'm talking about.
" -Lighter inner tubes are faster. Lower weight at the periphery of the wheel lessens the moment of inertia and amount of effort required to maintain speed - the same as with lighter tires."
ReplyDeleteI missed that in the article. Where does it say that lighter weight at the periphery of the wheel lessens the amount of effort required to maintain speed? Wouldn't a heavier rim generate a more pronounced fly wheel effect and make it easier to maintain speed?
How does this interact with wider (therefore heavier and less aerodynamic(thanks David H)) tyres?
Plus - and I don't mean to pick unnecessarily but - Most of this stuff isn't new. We've know for some time about rolling resistance. Jobst Brandt has some enlightening things to say on many of the subjects outlined above from a real world point of view.
ReplyDelete