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Technical Q&A with Lennard Zinn – Tire talk

  • By VeloNews.com
  • Published Jul. 29, 2008
  • Updated Feb. 23, 2011 at 12:56 PM EDT

By Lennard Zinn

Zinn has been using Hutchinson tires on Mavic Ksyriums with the NoTubes system

Photo:

Tubes, tubulars or NoTubes?
Dear Lennard,
I’m currently running Campy 10-speed and am interested in running Hutchinson Tubeless Tires. It appears that the only officially approved system is the Shimano Dura-Ace wheelset, which is obviously not an option for me. My question is will a wheelset with rims that do not have pierced spoke holes on the interior (like the Mavic Ksyrium SL, Campy Shamal Ultra or Fulcrum Racing Zero) suffice and is there anything special that has to be done to make them work?
Phil

Dear Phil,
I’m riding Hutchinson Fusion2 Road Tubeless tires with Stan’s NoTubes sealant in them on a pair of Ksyrium ES wheels, and they work great. I just rode them Sunday on the gnarliest mountain road ride around Boulder – lots of fast downhill switchbacks on steep pavement and lots of really rough, rocky dirt roads (Flagstaff to Gross Reservoir to Magnolia via CR68 and back to Boulder Canyon). I was tentative on them at first, since I have had bad experiences with standard road clinchers set up tubeless this way blowing off of the rim, but now I’m totally confident with them. No worries on the dirt about thorns, no worries on the rocks about pinch flats and now no worries on the fast corners about the tire blowing off of the rim. I’m using the NoTubes valve stem with removable core in order to squirt in the sealant.

I think the key is that the Hutchinson carbon-fiber tire bead is so tight and unstretchable that it hooks in and stays hooked in. The Shimano rim is specifically designed to fit the tire bead and sealing flap, but there are other hook-bead rims that seem to fit the outer profile of that tire bead as well. A sealed rim like my ES and the others you mentioned makes it easy to set up, but you can get sealing tape from NoTubes so that you can do this on any road rim.
Lennard

Tubulars vs. clinchers
This debate on which is faster, a tubular or a clincher, rekindled again here, may never be settled. There are great arguments on both sides. Perhaps it is telling enough that some riders have been successful on both types of tires.

That at least indicates that the differences are slight. For a little background, please check out Rolling Resistance followed by Rolling Resistance Redux
Lennard

Dear Lennard,
Does your conclusion regarding the rolling resistance advantage of clinchers over tubulars take into account (a) the surface the wheels are being tested on, and (b) the additional rolling resistance created by the separate tube in clinchers?

Everything I’ve read/heard, including a piece on Zipp’s Web site states that any marginal rolling resistance advantage of clincher’s is erased when you take into consideration real life road surfaces and the additional resistance created by the tube in a clincher. This fact, when coupled with the factors you mentioned in your recent post, is why most pros go with tubulars and why Zipp’s top tech guy recommends them.
Dustin

Dear Dustin,
I think that it is clear from all of the links here, that tubulars perform worse relative to a clincher on a smooth roller than on a more realistic surface. To eliminate enough variables to make something measurable also often means throwing out the baby with the bath water; it is not easy to come up with an accurate rolling-resistance test that exactly simulates real-world riding conditions.

If you study this more, I think you’ll find as I have that the answer is not as black and white as we would all like it to be. I was as dyed-in-the-wool of a tubular devotee as you could find until this debate started in my column a couple of years ago. I was certain that tubulars always were going to be faster. But now I’m not so sure.
Lennard

From Vittoria

Dear Lennard,
I don’t know which is the starting document from what it all started, but I’d like to make clear what many tests (not only those by us) state: tubulars roll better than clinchers.

The reason why is inside the casing, and it’s all about one word: flexibility. A more flexible casing is able to absorb vibrations as well as bigger hits with road roughness (such a small piece of stone or general dirt or discontinuity of the road surface), instead of transferring them to the rest of the system (rim ? spokes ? hub ? fork ? headset ? frame ? rider).

Attached you can find a slide that sums up this very simple concept in just two images, nothing more is needed to explain it. It comes from physic: the deformation of the casing absorb the energy that comes from the hit, and that is in the opposite direction of the bike’s rolling.

The influence of casing

Photo:

This means rolling over the obstacle faster.

This is true at any ‘sizing’ you consider the matter, from little stones you find of the road, to micro-roughness of a tarmac surface, to the bigger rocks you hit on a mountain bike (but here the compromise with strength play a major rule).

Stating that, the difference from a clincher to a tubular stays in his connection with the rim shoulder: the bead area of a clincher, pushed by the air pressure too, makes a stiff junction between the two parts (rim and casing), losing most of the flexibility we have just told. A tubular simply doesn’t have it, and in fact the overall flexibility and also the way it deforms are much different and much more ‘smooth.’

This is the main reason why keeping all the other parameters the same, a tubular will roll faster than the same clincher version, by heritage.

Furthermore, a tubular holds an higher pressure than a clincher, and thanks to this properties it can still be comfortable and flexible enough at that high pressures, multiplying this concept to even more advantages in the case of track riding.

That’s all. We can spend hours talking about all the other factors that play into determining rolling resistance (rubber compound is another important one), but I don’t want to go out of topic.
Samuele Bressan
Vittoria & Geax Product Manager & Designer

Dear Lennard,
I suggest you look at http://www.biketechreview.com/tires/AFM_tire_crr.htm. The range of Crr for tires in the preceding (done on a PVC drum), are similar to the range of Crr for clinchers & tubulars in the Chester Kyle study, published in Bicycling, May 1985. The Kyle study was done on smooth asphalt & low speed trike.

It is obvious that the steel drum used in the Tour magazine study magnifies the differences between tires, the question is how much. Tubulars do not perform well on a steel drum because of the small contact area and resultant squirming or glue compression. The difference on the road is minimal. In a test done by Triathlon magazine in September,2006, the same six sew-ups, eight clinchers were tested on both a concrete indoor track, and a steel drum. After adjusting for tire load and speed, the range of variability (defined in watts) for the six sew-ups on the drum was 2.24 times higher (my calculation) than on concrete. For clinchers the range of variability was 1.76 times.

Bottom Line “Rolling resistance is very close on smooth road surfaces between clinchers & tubulars. Individual tires of either group may have better or worse rolling resistance.”
Terry

Dear Lennard,
Riding tubular tires at the track is a cultural imperative (like shaving your legs)
Richard


Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, and “Zinn and the Art of Road Bike Maintenance,” as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.

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