Thursday, June 2, 2011

Grand Bois 26 mm "Cerf" tires

After the data presented by VeloNews on the effect of going from 23 mm to 25 mm tires, at the same pressure, on vibration reduction (measured with accelerometers: see this post) I was inspired to get fatter tires for the MDR ride (which I described last post). Bicycle Quarterly has published several reviews and tests of the rolling resistance of randonneuring tires, and the Gran Bois tires, "hand-built" by Panaracer in Japan, have always tested well. Jan Heine, the publisher and main contributer to Bicycle Quarterly imports these tires and sells them through his web-based retail business, Compass Cycles, so can be said to have a profit interest in reviewing these tires positively. Neverthless, his reviews are well written and his tests are well documented, so I had good reason to believe him when he said they are supple, have good rolling resistance, and are comfortable. When I saw them for sale in Box Dog Bikes in San Francisco, that sealed the deal.

Bicycle Quarterly advocates fat tires: they consider 28 mm excessively narrow, let alone 26 mm. But by the standards of MDR these tires are fatties: most riders were using 23 mm tires. As the VeloNews test showed, fatter tires smooth out bumps even at the same pressure as thinner tires, but the advantage of fatter tires is you can run them at lower pressure for the same tire deflection (and pressure of the bead on the rim) and so can gain considerable further reduction in shock transmission from the lower pressure. So I was interested in going against my inner racer and running these tires at lower pressure than I've used before: only 80 psi.

So despite the $66 price tag (on which I get a 10% discount as a member of the San Francisco Bike Coalition), fairly pricey for a tire I'd use for anything short of racing, I decided to take the plunge.

scale shotThis tire weighs in at 241.5 grams (I tared the rubber band)

As with all thins which go on my bike the first thing I did was weigh them. Fatter tires tend to be overbuilt for puncture resistance, since it's assumed their users aren't interested in either rolling resistance or weight. Partially due to Jan's influence, however, the Grand Bois range is built for speed as well as comfort, however, and so I wasn't surprised when for their width the weight came out to be a very competitive 241.5 grams on this sample:

I then mounted them on some clincher wheels I picked for the tour. Each had Velocity Aerohead rims which I've not found to be particularly tight. Despite this, and despite the fact my front rim had VeloPlugs instead of rim tape (in theory allowing the tire to settle deeper into the rim), it wasn't easy mounting these tires: I had to use my tire iron for the last bit. But once I did so they popped right into place.

side viewThey look beefy from the side

I was using a Challenge latex tube for the front wheel, a Ritchey butyl tube for the rear. Latex tubes don't patch quite as easily as latex, so I was hedging my bets with using the single latex tube. The latex tube worked out fine, so next time I'd run the Challenge tubes front and rear.

I gave a quick spin on the road in front of home with my wheels with my 23 mm tires with whatever was left of the 100 psi I'd pumped them to at some point in the undocumented past, then put on the wheels with the 26 mm Grand Bois tires on and repeated the test. The difference was striking. I'm sure Jan would claim the massive shock transmission of the 26 mm tires sapped the strength straight out of his legs, but by my standards the improvement in ride quality was palpable. I wondered if I'd ever want to go back to 23 mm except for when I use tubulars, which is only in races.

Once concern with tires larger than 25 mm is brake clearance. This simply wasn't an issue on my Ritchey Breakaway with Rival brakes. There's plenty of room.

profile viewThey are curved, not flattened, at the contact point, with still plenty of clearance for my Rival brakes.

Another concern with fatter tires is sluggish cornering. The profile of the Grand Bois Cerf is what I'd describe as parabolic near the contact point: a relatively tight radius. I've used other tires with flatter profiles and you really feel the width of the tire. However, these tires cornered as well as my 23 tires, from what I could tell.

So I set off on the tour. I wish I could describe the silky smooth ride the tires provided, but the reality is that I quickly took them for granted, and on the relatively rough pavement encountered during parts of the route, I felt not only discomfort in my unpadded saddle (to be expected I suppose) but also through the handlebars. Of course the discomfort would have been worse with high pressure, narrower tires.

The Cerf tires have been said to be prone to puncturing. However, during the 370 mile tour we went over a glass-strewn highway shoulders, through potholes, and I even went "off-menu" for a 7 mile dirt and gravel road. At the end I don't even see a nick on these tires. Maybe I was lucky.


Coastdown contest early finishers, photo taken by winner, Alan Armstrong.

In Bicycle Quarterly Jan likes doing coast-down tests for checking rolling resistance. Our tour had our own version: on a hill outside San Luis Obispo it's traditional to have a coasting contest: one stomp of a pedal then it's into a tuck for the often slow speed ride until momentum runs out. Obviously excessive rolling resistance would be a disadvantage on this test, while body weight is an advantage in overcoming wind resistance. Everyone finishing ahead of me was heavier, and all of the light women finished behind me on this contest, so from this there's no indication my 26 mm tires at 80 psi added any substantial rolling resistance.

There were only a few nontrivial descents on the tour, but even with the cross-winds I had no handling issues on these. I once had serious stability issues riding 28 mm Michelin tires which have a different shape than these tires.



A second highly nonscientific test happened today, where I commuted to work for my first nontrivial ride after MDR. I rode SF2G Bayway, where I traditionally put in a good effort on Cortland Ave to check my fitness. I took 4 seconds off my Strava-best time on the hill, reducing my PR from 57 to 53 seconds. Of course last weekend's tour played a role here, but it's safe to say the wide tires or the 80 psi pressure don't seem to be slowing me down much. And for the rest of the commute the smoother ride on familiar roads was familiar.

So I give them a very positive review. The only disadvantage is they're on the tight side, so I'd not want to have to change a flat on the road with cold fingers, especially if I was under time pressure. But hopefully the wider tires make a pinch flat, at least, less likely. So these tires are a keeper.

6 comments:

Garrett Lau said...

I think I weigh the same as you, so rolling resistance might have mattered in the coasting contest.

djconnel said...

Wow -- I'd forgotten you'd pipped ahead of me. So much for the supremacy of my tires :).

Garrett Lau said...

OTOH, I also beat Jeff, and I tied with Jon, so maybe it wasn't just the tires.

djconnel said...

Peter claimed he was able to use the cross-tail wind to his advantage by going downwind, going upwind when the wind was reduced due to being in the lee of a building, then going downwind again after leaving the shelter of the building. Peter's always using his head...

niggle said...

Hi, I would be very interested to know what the actual measured width and height of these tyres is (and the internal rim width was). Not sure whether to go for 26mm or 28mm Cerfs, my current tyres are at the limit for clearance. They are '28mm' Vittoria Rubino Pros, but actually measure 26mm wide.

djconnel said...

These measured right at 26 mm on my 19 mm rims. On 23 mm rims maybe they'd be slightly wider. I've been using them ever since this post, paying more than some alternatives, because I really like them. On my other bike, which I use mostly for organized events I have Michelin 25 mm tires and also like those, but I think the Cerfs have more durable treads and so are better suited for my day-to-day bike.