At this week's NCCC start, I talked about a real-world tire speed test that was just published in Bicycle Quarterly.
http://janheine.wordpress.com/2012/06/13/bicycle-quarterly-performance-of-tires/ (http://janheine.wordpress.com/2012/06/13/bicycle-quarterly-performance-of-tires/)
The authors found that wider tires roll faster than skinny and highly inflated ones. Further, tire suppleness (threads per inch or TPI of the tire casing) had a major role in tire speed. The more TPI, the faster the tire (and the more expensive). I would add that wider tires inflated to less than max pressure do not chatter down the road, but are both better handling and more comfortable.
Note my contribution to the comments - Of Course I'm right!
I'll also add that wider rims also can help the wider profile and allow for less tire pressure. HED has 23mm wide rims on some off their high-end models (most rims for our skinny 23mm tires are 19mm wide). Having the rim as wide as the tire allows the tire side walls to keep tire shape and rubber on the road, as opposed to having to over inflate (light bulb cross section) in order to avoid pinch flats. When I first got my HED Ardennes I was skeptical about inflating to the recommended 85 psi, but since Jim Hutchings swore by it, I gave it a go and was (and continue to be) simply amazed at how smoothly these roll, and, most importantly, corner, especially on descents. For me, this was counter-intuitive, as normally lower tire pressure seems like it would increase friction and rolling resistance. Getting the right combination of tire width, TPI, rim width, and tire pressure can really make a difference. Don't be afraid to experiment (you can also find these wider rims offered by Bontrager and others- I even have 25mm Araya rims on a 1973 Nishiki International that roll nearly as smooth.)
http://schwalbe.com/gbl/en/technik_info/rollwiderstand/index.php5?flash=1&ID_Land=38&ID_Sprache=2&ID_Seite=143&tn_mainPoint=Technik&tn_subPoint=
Its all compromise, there is the rider's weight to be considered as well.
http://schwalbe.com/gbl/en/technik_info/luftdruck/?gesamt=74&flash=1&ID_Land=38&ID_Sprache=2&ID_Seite=136&tn_mainPoint=Technik
For some additional info, http://www.cyclingnews.com/reviews/hed-ardennes-wheels . Here, many factors - TPI, rider weight, rim width are taken into account. The psi table in Paul's second link above is more "conventional wisdom" which the wider rims dispel. But, it really does take experimentation and each rider needs to decide what level of compromise works best. (fwiw, I use 85 psi on the front and 90 on the rear for my weight, which I'm not revealing here :o)
That's a great article, and Jan does his testing from avery technical and neutral standpoint. But alas, it's something us radonneurs have known for decades! 650b is not just a fad. Wide rims do have an effect too. One of my favorite tires is the 26mm Grand Bois Cerf. It is a high end tire at a nice price. The wheels on my Soulcraft use Velocity's A23 rim, which is 23mm wide. These tires on that rim open up a little more (and will stretch as they age due to the supple high tpi casing) and measure out around 27 - 27.5 mm. I think the biggest thing people miss out on is tire pressure. Like derailleurs, the manufacturers recommendations are quite conservative. Just because they recommend 100 psi, don't do it. I run 25mm GP4000s at 85/90 with no issues. A lot of people like Conti Gatorskins. I've found those tires should be 10 or psi less than recommended. If you are a clydesdale, you should be a on wider tires for sure. YMMV.
OK I have a question for all you wheel/tire buffs.
I'm buying an old bike with 27 inch wheels on it. Yes, 27 inch, as in 630mm bead vs the 622mm bead for 700 wheels.
The best tire I could find for this size wheel is Conti Gatorskin, and I've heard that these roll terribly because they are so stuff, very poor TPI (3 layers of 60 TPI).
Can anyone recommend a better tire for this size rim?
Check out http://sheldonbrown.com/harris/tires/630.html. However, I have not tried any of these. A big selection of, supposedly high performance 27" tires.
That's actually the site I just ordered tires from. :-)
Are high TPI tires more less susceptible to flats?
I've got the Kevlar Gators, and they do not get flats as much as the previous tires, but I still get flats. Anything better than Gators?
Peter,
The answer is yes and no. It depends on what you define as "better". If you are looking for a tire that will have one or zero punctures in it's lifespan, well, good luck with that. Like everything in life, there are trade-offs. Light, fast, durable, comfy? I have found that Gators are marginally more flat resistant than any other tire I've ever used. In my experience, the number of punctures, be it through the tread or sidewall, has been more or less the same as any other tire I have used, making it statistically insignificant. I suppose you could pick up a pair of Schwalbe super indestructible something or others, but they also weigh half as much as the bike. IMO, anything is better than Gators in regards to ride quality. I suppose that in the course of ones lifetime total of cycling miles, it may be true that higher tpi tires do get punctures more, and supposedly it's true because the fibers are thinner and more supple. I would say it makes no difference, and actually a more supple tire may have a lower rate of punctures because of it's ability to deform and roll over debris easier than stiff, low-tpi tires. If, as I have experienced, you only have one or two punctures in the lifespan of a tire, is it really an issue? I myself worry more about the ride quality and road holding ability more than puncture resistance. Sure it sucks to be dropped by the group when you have to stop to make a repair, but it's really just a 4 minute break that a couple stop lights won't sort out in the end.
YMMV
Thanks Robert.
Flat tires seem to happen in spurts for me. Once on my way to Palomar from Escondido I had 3 flat tires.
It takes me more than 4 minutes to fix them, and I'm careful to partially inflate the tube before putting it in the tire to avoid kinks that will cause an instant flat.
It is ok for a tire that is less comfortable and slightly heavier than one that will be more susceptible to flats, if such a tire existed. From what you are saying, which is consistent with what other bikers have said, is that these flats are just part of the sport. I guess I should get the tires that I can change flats quicker -- the ones with flexible walls.
I've tried gel-filled tires (supposedly self-sealing), but they don't really work.
Being paranoid, I carry at least 6 tubes and 2 repair kits with me on most rides.
If you're getting 3 flats in a short sport, chances are the there was debris in the tire the first time you flatted and you just didn't find it, and didn't remove it from the tire.
I have not tried Gatorskins but have heard that they're not a very "supple" ride, meaning not too comfy.
I have not tried a lot of tires, but I can say that I really like Continental Grand Prix 4000 S tires. In the 25mm width. When you ride these with lower PSI, they are _so_ comfortable, and you can ask the other long weekend riders how often I get flats. The answer is, not very often. :-) Knock on wood.
Thanks. I'll look for these tires next time I'm at Bike Empire.
I've made the mistake before of not getting all the debris out of a tire before putting a new tube in, but was careful to inspect the tire thoroughly that time. One of my flats had to do with the tube stem getting pinched. I'm thinking I was just unlucky that day.
Have not had many flats lately.