20/02/2015 - Chubby

From our latest email newsletter, Cy writes....

Thanks to everyone who dropped by to have a chat at London Show. We really appreciated it, and had a lot of fun having some good natters about the bikes with lots of people.

But now onto something I mentioned a few weeks ago. You might recall I fired a couple of pictures around when we received a sample set of WTB's new semi-fat (I'm going with chubby) tyres, the 27.5 x 2.8" Trailblazer and some rather lovely KOM i25 rims to put them on. The idea with these is that they're big volume, wide tyres which come up around the same size as regular 29er wheels so you can go chubby on your regular 29er without needing specific frames, forks and the other paraphenalia associated with 'going fat'.

By the time I had got the wheels built (you need minimum 25mm internal width rims for these tyres, hence the i25's) it was nearly show time so I put them on the show Solaris for giggles. They certainly drew plenty of attention and plenty of people were curious about their performance.

Show over, I finally got the wheels in my Solaris and took them out for a first ride on the Wednesday night ride. This was on my local trails around the edge of Sheffield; Houndkirk and Blacka Moor. A couple of big up and downers on fast, rocky trails.

I pumped them up to 15psi front and 20psi rear. First thing on the quick-spin-up-the-road test is that they feel very different to regular tyres on hard surface. They're quite rounded in profile so the transition to a turned handlebar when turning corners was very noticable, like a big camber change. I found the rear tyre bounces a lot when spinning along. Kind of understandable when you have effectively strapped a virtually undamped 1" travel air spring to the back of your bike. Pedaling induced movement was way more obvious than it is on my Rocket with 150mm of suspension. Final thing I noticed was a lot of squirm under braking going down hill on a road.

All this slightly alien feel left me a little trepidatious heading offroad, but just like a jacked up Land Rover will be a soggy mess on the road, but perfectly at home on the dirt, so it was with the Trailblazers. There is this incredibly addictive soft edged, floaty, muted feel to the feedback from the trail, but handling wise the most surprising thing is how unsurprising they feel. You just ride the bike. They roll way faster than they have any right to being so big, but get them leaned over and there's some serious grip to be had. Hats off to the WTB guys who designed this tyre. Proper clever piece of tread work.

Speaking of leaning, that was one thing I noticed is that you don't really steer the bike as such, and I don't know if it's because I've not ridden 29" wheels for a while or not but I seemed to be needing a lot more lean angle in corners than I expected. That said, lean angle is the proper way to get around corners so once I adjusted it was working great.

The big tyre and near 29" wheel diameter meant some pretty serious speed even on choppy terrain. I was a bit nervous of the lack of pressure in the rear; due to there being a day between first inflation tubeless and riding offroad, some pressure had come out and it felt VERY soft at times, and yet I only felt the rim on a rock once. (N.B. subsequent checking suggests this first ride I was running around 10psi front and 12-13psi rear on the ride). It's just a whole different area of perception in terms of the feel of the bike.

In the muddy sections the footprint seemed to spread and keep me on top of the slop with very little slip under power and I had no issues with clogging despite running a front mech and a fork brace style front mudguard on my Solaris.

No firm conclusions yet, but as I'd hoped these big tyres are much more all round usable than any kind of full on fat bike would be, but they seem to offer a good degree of that float which fat bikes are reknowned for. My plan for the next few weeks is to fiddle with tyre pressures a bit on the local loop to see how that affects things, and also get in some trail centre berms-and-jumps style laps at Parkwood Springs to see how they go there, again with some pressure fiddling to see if I can find a good setup. JPJ from A Line Coaching has the medium Solaris demo bike at the moment so I'm planning to get out with him and do some swapping of wheels to see what we both think.