I don't think Jan's statement about pressure is true for stiff tires; not my experience, by "feel", anyway.
Kojaks run well at a range of pressures, but I find that (1) they are not the best rolling tires by any means -- Elk Passes are better, as were Parigi Roubaix; and (2) that they work best at 50 to 60 undermy 170 lb. OTOH, the 20" Kojaks on the folder feel far, far *far * better than the Marathon Racers (old ones, if that matters) they replaced. On Thu, Dec 3, 2015 at 8:38 AM, Jeremy Till <jeremy.t...@gmail.com> wrote: > So recently I've been coming to realize that rolling resistance on my > Quickbeam seems to be a bit higher than would befit a bike of its name. > This became readily apparent yesterday when I rode the same route twice, > helping my wife find a bike commute route to her new job and then picking > her up in the evening. In the morning I rode the QB and in the evening I > rode my Surly LHT. Now, by all accounts the Trucker should be slower; it's > heaver, has front and rear racks, a dynohub in front (and the light was on > for all of my evening ride) and is generally built more as a bombproof > vehicle that the light-n-fast hotrod I want the QB to be. But the Trucker > was definitely rolling easier. > > Before you ask: no, nothing's rubbing on the QB, and my chain tension > (fixed gear) isn't too tight. I even recently replaced the crunchy > cartridge bearings in the rear hub a couple of weeks ago, and it's spinning > very nicely now. > > All of this leads me to believe that the tires might have something to do > with it. The Trucker has the most supple tires I've owned so far: > Continental Speed Rides in 700x42. They roll great, and at ~40psi front > and ~50-55psi rear are super smooth. Back in the late spring I put some > 700x35 Kojaks on the QB, hoping to achieve similar riding characteristics, > especially after many on here have had positive experiences with them. > However, I'm wondering if they have higher rolling resistance at similar or > just a touch higher pressures (~45psi front and ~55psi rear). > > Last night I did a bit of literature review on the existing research on > tire pressure and rolling resistance. In his roll-down and track tests for > BQ, Jan has come to the conclusion that tire pressure really doesn't make > that much of a difference in rolling resistance (specifically that higher > pressure does not equal lower RR), and recommends tuning your pressures for > shock absorption and cornering. Others have tested tire rolling resistance > on a drum; this was done by Avocet back in the 1990's and more recently in > a VeloNews article: > > http://yarchive.net/bike/rolling_resistance.html (Jobst Brandt's > interpretation of the Avocet numbers) > > http://velonews.competitor.com/where-the-rubber-meets-the-road-what-makes-cycling-tires-fast > (Leonard Zinn tests current road tires) > > These drum tests basically agree with Jan, but only for highly supple > tires. Basically, the more supple the tire, the flatter the tire pressure > vs. rolling resistance curve. Stiffer tires, on the other hand, do achieve > lower rolling resistance as the pressure increases, although both Jobst and > Zinn point out that they are never as fast as supple tires, no matter the > pressure. > > Now, comparing the Kojaks and the Speed Rides, both have highly supple > sidewalls; if anything the Kojaks are more supple. However, the tread area > on the Kojaks is reinforced with a flat protection belt and is > significantly stiffer there than the Speed Rides. I'm wondering if this > stiffness causes the Kojaks to be more sensitive (in terms of rolling > resistance) to tire pressure, and if I'm running them too low. I'm > certainly running them lower, at least in the front, than the 55psi minimum > recommended by Schwalbe. > > I'm about to go out here and try pumping my Kojaks up to something like > 60psi front and 70 psi rear, but I'm wondering what others, especially > those who have had good experience with the Kojaks (namely the 700x35 > ones), run in theirs. Please give your weight as well. I weigh ~190 lbs > and the QB generally carries a small front load (5-10lbs) in a Shop Sack. > > > > > > > -- > You received this message because you are subscribed to the Google Groups > "RBW Owners Bunch" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to rbw-owners-bunch+unsubscr...@googlegroups.com. > To post to this group, send email to rbw-owners-bunch@googlegroups.com. > Visit this group at http://groups.google.com/group/rbw-owners-bunch. > For more options, visit https://groups.google.com/d/optout. > -- Resumes, LinkedIn profiles, bios, and letters that get interviews. By-the-hour resume and LinkedIn coaching. Other professional writing services. http://www.resumespecialties.com/ www.linkedin.com/in/patrickmooreresumespec/ Patrick Moore Alburquerque, Nouvelle Mexique, Vereinigte Staaten ************************************* *The point which is the pivot of the norm is the motionless center of a circumference on which all conditions, distinctions, and individualities revolve. *Chuang Tzu *Stat crux dum volvitur orbis.* Carthusian motto -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
