Index Categories:
Tires – Effects of Tire width on aerodynamics
Tires – Rolling resistance
Tires – Clinchers vs. Tubular
From:
bobcowin Dec 31, 2006, 5:13 PM
Question:
Rolling resistance articleThis may have been posted before, but I hadn't seen it. This is a study done on tubulars and clinchers to measure the rolling resistance in terms of watts required. There is a brief discussion (complete with neat Chrysler graphics :-) on the trade-offs among rolling resistance, comfort, puncture resistance, aerodynamics, etc. The fastest clinchers had lower RR than the fastest tubulars; the fastest tubular measured took about 34W, while the fastest three clinchers were all under 30W. The Tufo Elite Jet was an astounding 50-52W, depending on air pressure.
ST postJosh:
I have seen the same theoretical data that you talk about showing higher RR for tubulars than clinchers, but this isn't actually nearly as clear cut a case as that data would suggest. Mainly, all RR tests use a simple machined drum for testing the tires and that is not very true to real life. Some data was taken a few years ago using a different system, similar to that developed at CALSPAN in California. This system is more like a treadmill but the belt is steel with various types of tarmac surfaces bonded to the surface.
In these tests the tubular tires actually fare slightly better than clinchers on more realistic, rough road surfaces; more or less because the structure of the tire allows the tire to conform to the rough surface with fewer losses. The clincher tire on a smooth drum only needs to defore really at the contact patch and partially in the casing, but on rough pavement the additional deformability of the tubular tire carcass seems to be helping out. The other thing to remember for all the tubular bashers is that clinchers only show better or equal in these tests when used with thin latex tubes, these tubes have significantly less RR than butyl so if you want to run clinchers for racing you really have to run latex tubes, which is something that very few people do. Overall that's why the 13 minute over IM distance is not so realistic, if it were you would see it affecting results, and you would have certain pros with wildly different bike splits in similar events when they switch sponsorship between clincher and tubular wheel manufacturers and so on, but it just doesn't happen that way.
I think that the other thing generally not mentioned is that most tubular tires have a puncture resistance belt under the rubber that adds a bit of weight and RR, but improves durability of the tire. Clincher tires that test very well for RR usually don't have similar puncture resistance belts, but these are not the clincher tires most of us want to use and we certainly don't recommend racing on them as a flat will cost you way more time than any RR savings will get you.
Also, the tire bed shape is critical. Older aluminum rims (which are used in many of these older RR tests) would have a large single radius curve shaped tire bed, generally 23-25mm diameter, and eyelets that protrude into the tire bed. These rims can significantly increase RR when a tire is used that has an effective inflated diameter smaller than the rim bed as the entire casing of the tire is deflected at the contact patch. This is made worse by the stitches under the base tape which protrude slightly, requiring additional glue to fill the airspace, and further deforming the casing locally.
With some proper design the tire bed can very closely mimic the tire profile eliminating these problems, and also resulting in the need for significantly less glue as the glue can be very thin on the rim. Also the elimination of eyelets eliminates excess glue as well as what were effectively high-spots in the wheel that show up in testing as an increase in RR. The same 21mm tire will show 15-20% less RR on a Zipp rim due to these design elements than on an older GL330 or similar tubular rim, and that is not at all trivial. This is another reason we strongly recommend 21mm tires on all of our wheels.
We have probably done more work than anybody in studying the tire/rim interface in both clincher and tubular. With considerble work on both models we have ultimately ended up with nearly equal drag on clincher/tubular products. To get there, the clincher rims are generally slightly wider and have a little bit of a different shape, but at least with our product there is no appreciable difference between tubular and clincher in terms of aerodynamics.
As for the inevitable question of why the pros favor tubulars, there are a few very simple answers:
1. they flat less, since most flats in pro racing are pinch flats (the roads are generally pre-swept or somewhat cleaned) tubulars eliminate the majority of flats. Plus road pros race on all sorts of crap pavement and cobbles where clincher tires just don't hold up.
2. in a downhill or fast situation a flat with a tubular is far safter than with a clincher as the tubular flat can be ridden with much less drama. The tubular flat can also be ridden faster and longer giving the team car more time to get to the rider, so he isn't stuck on the side of the road.
3. they can be run at lower pressures. Everybody always talks about how tubulars can be run so high, but really the pros want lower pressures for better grip (particularly in the wet) and more comfort. It is common to see road pros in Europe running 90-95 psi in the rain and 100-110 in the dry, so on the roads they generally ride, these pressures would be very problematic with clinchers.
There is really no clear cut answer here, and as with a lot of things it is largely personal opinion, but there is lots of data showing the superiority of one vs the other and so on, but in reality the differences are quite small. We prefer tubulars as they are much lighter, the tires are more puncture resistant despite being lighter, can be pressure optimized to road surface (can run much lower to much higher), generally have more consistent and higher cornering grip, and when properly glued offer an extra margin of safety. "
Index Categories:
Wheel Aerodynamics – Tire/rim interaction
Tires – Effects of Tire width on aerodynamics
Tires – Rolling resistance
Tires – Clinchers vs. Tubular
From:
????
Question:
Are you pro-tubular simply because it’s cheaper to make a tubular rim? Josh:
I can assure you that I and the rest of the folks have no secret reason for advocating tubulars. Nor are trying to pull the wool over everybody's eyes on this tubular/clincher debate. Since we make and sell all of our products in both, we certainly could care less what you buy or use, but from the testing I have been privy to and worked with there are many real world situations where the tubular will have equal or lower RR, specifically poor road surfaces. Having said that, even if clinchers can surpass tubulars in all RR situations tubulars will continue to be most prevalent in pro road racing due to the safety issues and ability to ride when flat, as well as the weight discrepancy which will remain indefinitely due to the necessary design limitations of clincher rims.
Also some have said that clinchers are an aerodynamic mess. They are not a mess, they are just different than tubulars, so that using the same rim shape for both will leave one of the products lacking when compared. This forces us to design the clincher and tubular versions of a rim as two different products, so that they share rim depth and marketing but from engineerings point of view they are totally different products.
All of our clincher products more or less mimic the performance of the tubulars with the 404 clinchers having a slight advantage actually over the tubies and the 808 tubulars having a slight advantage over the clinchers. To give you an idea of how different things are, however, look at our clincher disc. We really had to work some sidewall curvature into the shape to clean up the airflow off of the tire, and blend the aluminum to carbon interface so as not to have a hard lip between the two as that lip can cause 3-4 watts of drag in some designs. But you can see that the final product essentially looks nothing like our tubular disc, yet the performance is nearly identical.
Our clincher disc photos can be found here:
http://www.zipp.com/Products/Wheels/tabid/85/CategoryID/2/List/1/Level/1/ProductID/104/Default.aspx?SortField=ISBN%2cISBNhttp://www.zipp.com/Portals/0/clincherdischorizontal674.jpgMore infomation on carbon tubular rim construction:
ICT (Inversion Composite Technology)
http://www.zipp.com/Technology/CompositeTechnologies/ICTInversionCompositeTechnology/tabid/97/Default.aspxMore information on our exclusive co-molded carbon/aluminum clincher technology:
M2CM (Multi-Material Co-Molding)
http://www.zipp.com/M2CMMultiMaterialCoMolding/tabid/101/Default.aspxIndex Categories:
Tires – Clinchers vs. Tubular
Carbon Construction – Braking concerns with carbon
From:
corinwright May 8, 07 7:47
Question:
Clincher vs Tubular - Descending and Hot RimsI did my first double gap yesterday after work. Lincoln and Ap gaps in Vermont. Pretty gnarly climbs, but the descents were frightening. The frost has not receded yet, so there were heaves and sinks the whole way down. 20+% grade, switchbacks and bumps caused me to over-use my brakes to the point that I blew my rear at a particularly hairy moment. The rim was so hot that it burned my fingers changing the tube.
Question is, would I have the same issue with my tubulars? I guess that I would risk melting the glue, but would I blow the tire? That's definitely not an experience that I would like to repeat! The hole in the tube almost looks like it was created by a really hot spoke nipple (the rim tape was definitely heat-shrunk to the rim, and there was a small circular hole on the rim side of the tube.
Josh:
It is the heat that causes the butyl inner tube to fail and not the pressure increase, although I have seen people blow clincher tires off of rims due to the pressure increase. We have seen rim temperatures in testing exceeding 325F, which can be enough to raise the air pressure in the tire by 20-25psi, so this can be a blowout risk on loose fitting tires or rims at the low end of the ISO diameter spec. On tubulars the heat is more likely to melt or soften the glue than blow the tube as the tire base tape and casing serve to insulate the tube. The tire rupture on tubulars is more likely going to be that the tire begins to rotate on the rim and the valve is ripped from the tube. I was doing a US Nationals about 15 years ago in Bear Mtn. New York and they started the race at the top of some climb and neutralized the start behind a car for the 3 or 4 mile descent and maybe 20 people flatted or rolled tires in those 3 or 4 miles due to brake heat of having to ride a steep descent at 25mph behind a car…painful.
Anyway, alternating your brake usage or at least feathering out of one brake of the other for a few seconds will lower rim temperatures considerably. Also using brake pads without any abrasive additives like the Zipp pads or even the Kool Stop Black pads will lower temps by as much as 20-30degrees and up to 60 degrees for the Zipp pad which also contains thermally conductive materials. Most pads anymore contain aluminum oxide; the same stuff sand paper is made from, to increase coefficient of friction, but that also increases heat. Also, once the pads do begin to melt they create an insulating situation on the rim where the hot pad material melts to the rim keeping the aluminum or carbon from being able to reject heat to the atmosphere, and also increases the surface coefficient of friction, so that when the part of the rim with melted pad on it comes through the brakes again it is hotter and higher friction which will make it even hotter...a sort of snowball effect.
Finally, lighter weight, or shallower profile rims will get hotter as they have less mass to act as a heat sink, and less surface area to dissipate heat for convective cooling. The more aerodynamically effective a rim is the better it will generally cool as the airflow stays attached to a larger area of rim where it can transfer away heat.