Editor’s Note: Last week, we ran a guest column headlined The Tire Pressure Revolution from Bicycle Quarterly Editor Jan Heine summarizing BQ’s tire pressure research and findings. Some of your comments on the article asked for feedback from Jan about specific aspects of the research or tires. His replies follow. – John Marsh
Is 25 mm the optimum?
It depends. On smooth roads, you don’t gain speed by going wider, but on rough roads, wider tires definitely are faster. And they are more comfortable. With wider tires, you gain comfort, speed and fun on scenic backroads, without giving up speed on smooth roads. Sounds like a win-win to me!
Rotational weight can be compensated for by going to smaller wheels. A 42 mm-wide 650B tire has about the same rotational inertia as a 30 mm-wide 700C tire.
However, the effect of rotational weight is not as important as many think. Otherwise, racers would use the smallest wheels the rules allow (55 cm, or 10 cm smaller in diameter than a 700C x 23).
Many builders and racers have experimented with smaller wheels, but found no benefits. Even sprinters, who would benefit most from the faster “spin-up” of smaller wheels, ride 700C, probably because it offers better handling than smaller wheels (a topic for another day).
In any case, the weight difference isn’t huge, because much of a tire’s weight is in the beads. The difference between the Compass Extralight tires in 32 mm and 28 mm widths is less than 30 grams. If you are concerned, get extralight inner tubes, and your tire/tube combination will be lighter than before.
How to recognize a supple casing?
That one is a hard one. You’ll notice it when you ride the tires on the road — there is much less “road buzz.” When you shop, look for high-end tires used by racers, like the Vittoria CX, Challenge, Dugast or FMB tubulars, and, of course, our Compass tires.
Rim width isn’t a huge factor for the tire widths we are talking about. A wider rim will make your tire a bit wider and possibly a little more aerodynamic, but for most of us, we can just stick any tire that fits our frame/fork on the rims we have.
More data, methods, statistics, etc.
The article I wrote for RBR was just a summary of our research. For those wanting the full story, including methods and statistical analyses, it was published in Bicycle Quarterly Vol. 5, No. 1; Vol. 5, No. 3 and Vol. 11, No. 3.
Snapshot: How Miami Plans a Bike Corridor from Underutilized Land
For any urban planners among our readership, or for those of you involved in bike advocacy in cities without much cycling infrastructure, here’s an interesting read.
It’s a case study on how Miami, Florida, plans to convert 10 miles of underutilized land beneath its elevated MetroRail train system into “an iconic linear park, world-class urban trail and living art destination” – complete with a dedicated two-way bike path.
Details of the project, called The Underline, can be found at https://www.theunderline.org/.
‘A Complete Portfolio of Power Meters for Multiple Locations’
That’s how PowerTap announced the launch last week of its upcoming foray into both pedal-based and chainring-based power systems to go along with its long-time hub-based offerings.
The new P1 pedals, slated to hit the market in May, will cost $1,200, with each pedal powered by a single AAA battery providing about 60 hours of runtime. The pedals are Look Keo-compatible and weigh in at 398g per pair, more than Garmin Vector power pedals in weight, but less in price.
PowerTap’s new C1 chainrings, priced at $700 and slated for market in early summer, are compatible with 5-bolt cranksets and will come in the following combinations: 50/36, 52/36, and 53/39. No true compact combination (34 low gear) is available because of space limitations; the power sensors and transmitter take up too much space in the spider.
The chainrings – proprietary rings made by FSA – come as one piece and are powered by a CR2032 coin cell battery providing about 200 hours of runtime. As for weight, the rings are said to weigh about 150 grams more than a standard set of FSA rings.
Both the P1 pedal system and C1 chainring system are Bluetooth- and ANT+-compatible.
PowerTap also announced a new disc-based power hub, called the G3 Disc, and a newhead unit that offers Bluetooth Smart connectivity to wirelessly upload data and interface with the latest smartphone tech.