Indoor training, part 6: The flywheel effect

I’ve had the Minoura LiveRide LR340 turbo trainer for a while now and I’ve used it with both Hyro, my cyclocross bike with 700C wheels, and Bino, my 20″-wheeled folding bike. A few buckets of sweat later, shared between these two bikes, I started noticing a few differences.

At this point, I’ve documented numerous times the more rapid rate of tire wear from the smaller wheels – and the larger resulting mess that comes with it. It turns out that’s not the most telling difference between the two bikes.

With Bino, I find I can crank up the resistance and use much heavier gears. I regularly dip into the higher end of the gear ratio spectrum. I’ve gotten to the point where I can sprint in the 50×12 top gear combo at the final flat-out interval of a workout…and push as hard as an indicated 60.8 km/h on my cyclocomputer.

I have no idea how I’d sprint to this speed on a folding bike. My limit on the road is around 44 km/h, at which point I’d be pretty spun out.

Even in my 50×12 top gear, it’d take my legs a pedaling cadence of 154 RPM to get to this indicated road speed. Yes, that’s not sustainable for long periods, and most likely very hard to do out on the open road due to aerodynamic drag, but I’m mentioning it to illustrate my case.

On Hyro, though, it’s a different story. I use nowhere near half the LR340’s total resistance range, and despite using the same cassette and chainrings as Bino, I usually never breach the halfway point of the cassette. Beyond 50×19 or 50×17 are gear combos that are too big for me to push my pedals to on a turbo trainer. My indicated road speed also peaks at a significantly lower 52.5 km/h.

V-max on Hyro while on a turbo trainer.

It’s entirely possible that the two bikes are giving me slightly different workouts, and I pin this down to their rear wheels acting as flywheels of different sizes.

With Bino, the smaller 406 mm rear wheel acts as a flywheel that is much lighter and quicker to spin up with pedaling the cranks. The consequence is it takes much more resistance from the turbo trainer to give the training load called for by sprint intervals. Hyro’s 622 mm rear wheel, on the other hand, has more mass and needs more energy to get going…but requires less out of the turbo trainer to give roughly the same training load.

In practical training terms, I think that indoor training with Bino is more of a test of souplesse, or pedaling smoothness. With the smaller wheel size, I find it is much easier to accelerate and decelerate simply by changing my pedaling cadence. Peculiarly, with a change of bike, I find I could get the same kind of training coaches used to recommend getting a roller trainer for. Bino also has a slight edge for really high cadence work. Mounting Hyro’s bigger rolling stock on the LR340 will allow me the low-cadence training that replicates endurance climbing efforts, as well as getting used to holding low positions for faster riding.

Without hard data, and sharing just my palpable differences training between the two bikes, I feel like I may just be blowing a load of hot air. For that reason, I would love to quantify all this difference with a power meter. Unlike heart rate or speed, where external factors such as aero drag or physical condition can affect readings, power meters are more “insulated” and are better at actually quantifying your training load and output – a watt is a watt is a watt. Unfortunately, while they have been coming down in price almost constantly since 2012, they’re still too rich for my blood.

Reprise: Schwalbe Marathon Racer tires, 20″ x 1.5″

After four years, Bino was due for a change of footwear. Part of the reason why I stuck him on the turbo trainer at home was simply in anticipation of this fact.

The smaller 406 mm wheel size means greater rolling resistance and a faster overall wear rate, since the tires’ tread circumference makes more revolutions to cover a given distance compared to, say, Hyro‘s 622 mm. This was demonstrated in dramatic fashion by the sheer amount of rubber dust generated by my rear wheel whenever I used Bino on the turbo trainer.

Soon enough, it was also made crystal clear to me by how badly worn the rear tire got. At first the tread’s profile got flatter, with more of a pronounced step between the center and the shoulders. Later, the biased threads of the tire carcass were beginning to peek through, some of its carbon black oozing out and slipping on the turbo trainer. At this point, Bino sorely needed new rubber on his wheels and was definitely unsafe to ride on the road.

The outgoing Impac Streetpac 20″ x 1.75″ rear tire. You can see how much it’s flattened on its center tread.

The threads on the casing are starting to show due to the impregnated rubber having worn away. These aren’t roadworthy any more.

I paid a visit to Tryon in Makati and bought a pair of Schwalbe Marathon Racer tires. Bino’s outgoing front tire was also a Marathon Racer, but of a previous generation. The appearance of the sidewall logos, tread pattern, and other features were quite different between them, but they do share the Marathon series’ signature puncture protection.

FEATURES

  • 20″ x 1.5″ (ISO 40-406 mm); also available in 16″, 18″, 26″, and 700C wheel fitments
  • “Level 4 Raceguard” double-layer nylon puncture protection belt
  • “SpeedGrip” rubber compound for good handling
  • “LiteSkin” full-length reflective sidewall
  • Wire bead
  • 67 TPI casing
  • Maximum load rating: 75 kg per tire
  • Claimed weight: 340 g per tire
  • Pressure range: 55-85 psi

IMPRESSIONS

According to the marketing spiel, Schwalbe’s Marathon tires were specifically built for toughness and long service life, for applications ranging from touring to commuting. The “Racer” is so-called because it is the lightest model of the Marathon range – not really for its competition chops. Reinforcing the commuting bent, this was the first tire I heard of that had reflective sidewalls, although my original outgoing pair didn’t as they were of an older vintage.

The new Marathon Racers I got had beads that were ridiculously tight. This particular set was perhaps the toughest pair of tires I’d ever fitted onto my custom LitePro x Newson Sportec wheelset with 14 mm internal width, especially the one I mounted on the front wheel. Every time I used my bead jack to wrestle the tire up and over the rim, the wire bead would just walk itself right out of the bead hooks somewhere else. It was a frustrating ordeal that resulted in at least one tire lever getting sacrificed to the tire mounting gods. Eventually I ditched the bead jack and used every other trick in the book to finally seat this tire on Bino’s front wheel, after much cursing, the process leaving me a sweaty mess.

The “arrowhead” tread pattern on the current generation of Marathon Racer tires. Some people have already tried these tires on a turbo trainer and were put off by the noise due to the broken center tread.

Despite the deeply cut directional blocks on the tread, the Marathon Racer is strictly an on-road tire. Not that you’d want to take a folding bike like Bino to the trails anyway; it’s just not made to withstand that sort of riding. At 60 psi front and 70 psi rear, grip is fairly good, even in the wet. They lend themselves well to the deep lean angles that small-wheeled folding bikes excel in when cornering at speed, even on shiny concrete parking floors where traction isn’t so great compared to paved asphalt or concrete roads. They will relinquish grip quite quickly when cornering or braking on wet steel surfaces or wet leaves, though.

Normally I’d go into more of the minutiae of tires, but any discussion about the rolling resistance these tires offer is moot, at best. Neither is any discussion on ride comfort much of one. The 20″ wheel and tire combo is never really going to roll or cushion road acne as well as a 700C combo, and I don’t think this will change much with the kind of tire you mount. That said, since starting my indoor training in January, it’s no hardship for me to maintain an average pace of 17-20 km/h around my usual commute loop, so the Marathon Racers do seem pretty efficient.

These tires sure look good in profile. Most of it is down to the reflective stripe aping a gum sidewall.

Given how much swearing it took to fit these tires onto Bino’s wheels, the Marathon Racers should make up for all that gruntwork with their puncture resistance. For the most part, they do. Even on my old set, I had only ever one puncture.  Best to carry a beefy set of tire levers with you if you run these on your folding bike, not the ones that come with your multi-tool…and make sure your rim strips or rim tape is up to snuff to avoid punctures from inside.

With the air volume of an inner tube under it, like most other tires, it should stretch out and loosen up a bit over time, allowing for easier dismounting and remounting…I hope. Fingers crossed.

With my camera’s flash fired, the reflective sidewalls really pop as a couple of rings.

Finally we come to the reflective sidewalls. I think they’re nice, and any feature that boosts visibility to other road users, especially at night, is worth considering. They’re not perfect, however. The reflective stripe on mine doesn’t follow the circumference of the tire so well – it has a few wiggles along its length. I’d also prefer that Schwalbe broke these down into four long segments instead of making the tire one reflective hoop, because when the tires are in motion, the reflective segments are more eye-catching and convey a sense of the bike moving much better.

The outgoing Schwalbe Marathon Racer bought back in 2013 that served as Bino’s front tire. It’s worn, but the difference in tread pattern is still notable compared to the newer pair.

VERDICT

Schwalbe’s Marathon Racer tires, in a sense, are ideal for small-wheeled folding bikes such as Bromptons or Dahons, where wheel removal, tire dismounting, puncture repair, and tire remounting can be such bothersome procedures that any measures taken to avoid all that faff are worth your money. Virtually unknown in mid-2013, my old pair went for PhP1,300 apiece; with their popularity rising in the past few years and manufacture moving to Indonesia, they can now be found for PhP1,000 each.

Despite the “Racer” name, I don’t really consider these ideal for competitive use. They’re jack-of-all-trades tires; durable, grippy enough, resistant to punctures, and mid-pack in width. For really fast folding bike riders, Schwalbe’s diamond-patterned Durano or full-slick Kojak might be better options, while comfort seekers might be better served by their balloon-like two-inch-wide Big Apples. For ultimate puncture protection, everything else be damned, Schwalbe can sell you a Marathon Plus.

Indoor training, part 5: Turbo trainer tweaks for a folding bike

Previously I wrote about how Bino, my 20″ folding bike, interacted with my Minoura LiveRide LR340 turbo trainer. Officially, with the Z-adapter installed, Minoura says it can support a bike with 24″ wheels, and this became apparent when the threaded shaft on the adjustment knob simply ran out of room to squeeze against Bino’s 20″ x 1.75″ Impac Streetpac tire.

Another issue I ran into was the much greater amount of rubber dust particles generated by the smaller wheels. Because the circumference of the 20″ x 1.75″ tire is smaller, it goes through more revolutions at a given road speed compared to Hyro’s 700C x 28 mm or 700C x 32 mm rubber…which directly translates to much faster wear. The rubber dust particles themselves fly out over a larger area because the wheel is suspended much higher off the floor, making cleanup a chore.

So, I had two issues that need resolution.

I took a page out of Steve’s playbook and fashioned an extension for the adjustment knob’s threaded shaft, in order for the resistance roller to get more pressure against Bino’s rear tire. Basically I took a large brass dome nut and slipped it over the end of the adjustment knob shaft. It didn’t matter to me that the threads between these parts were incompatible with each other – all I needed was to give it a bit more length.

With the dome nut stuck on the end, I got more consistent and more positive pressure on the rear tire, and I was even able to reinstall the large cone spring that should have been there in the first place. This also opens up the option of using narrower tires for turbo trainer duty instead of being stuck with the 1.75″ width option. Schwalbe’s full-slick Kojak at 20″ x 1.35″, in particular, is a good candidate, although I might need to swap to a bigger nut.

See all that gray inside the box? That is all rear tire dust.

Addressing the problem of rubber dust particles was even simpler. All that took was a large cardboard box. Every time I use the turbo trainer, I basically put the cardboard box as close to the rear wheel and resistance unit as possible, so it catches all the rubber that gets flung off. The box flaps rest on the rear fender so there’s no rubbing anywhere.

These two simple hacks solved my problems. They’re not going to do much about the accelerated actual tire wear, though – that’s just a fact of life when using a small-wheeled bicycle on a turbo trainer, I guess.