This is one trend I can speak to directly. I've been running my Scalpel with 39i/WTB Ranger 3.0" up front and 29i/XR2 2.5" (2.35" claimed) out back for over six months. I couldn't fit anything bigger in the back with adequate clearance, so it's not a true 29+ bike. A byproduct is that the head angle is slacker by about half a degree.
The goal was to have more grip and better rollover. The bike came with 18i rims and Schwalbe 2.1" RaRa tires that measured out to 2", which made for a firm, unpleasant ride that required constant line vigilance even on mild terrain. I could rarely sit and spin. Front-end breakaway was abrupt.
I initially replaced the Ralphs with a Forekaster 2.35 / Ardent Race 2.35 combination. Not bad. Considerably better grip and probably ideal for XC, but still short of rollover. (I'm in the Southeast, it's just constant roots.) Hence the new wheelset (carbon, exactly the same weight as the original despite the width difference.)
Some impressions:
Weight differences are marginal. The Ranger (and Chupacabra, a very similar tire) is 880g. The Forekaster, probably the lightest tread pattern I'd want up front in a regular size, is 735g. Bonty's XR4, more like 780g. The extra weight and inertia is noticeable, but modest.
Steering is slower. Not so much on 70mm and 80mm stems (with 780mm bar, 70.5D HA, 45mm offset), but when I went to 90mm to bring my weight forward (the bike came with ~110mm), it took a few miles to stop blowing turns. Very stable. Lethargic, even. It takes more body english to chuck the bike around.
Tire pressure is enormously important. I verify my Ranger is at 14 PSI before every ride. More pressure makes for a bouncy ride and less grip. It's still better on both counts than a smaller tire with a similar tread pattern, but (at suboptimal pressure) a smaller tire with bigger treads would be preferable. Undershooting by a few PSI results in autosteer that makes the bike totally unrideable. There's no question that some negative Plus experiences arose from poor setup.
Traction is way up in dry conditions. (I don't ride when it's wet.) I can brake whenever; the limiting factor is always weight balance and the Lefty packing down. If my body position is right, the bigger tire sticks like flypaper on most terrain. Dusty loose-over-hard flat turns are still challenging; it's actually better if there's some chunder for the tire to deform around and grab.
(Cont'd)
Nov. 6, 2017, 2:23 p.m. - Alex D
This is one trend I can speak to directly. I've been running my Scalpel with 39i/WTB Ranger 3.0" up front and 29i/XR2 2.5" (2.35" claimed) out back for over six months. I couldn't fit anything bigger in the back with adequate clearance, so it's not a true 29+ bike. A byproduct is that the head angle is slacker by about half a degree. The goal was to have more grip and better rollover. The bike came with 18i rims and Schwalbe 2.1" RaRa tires that measured out to 2", which made for a firm, unpleasant ride that required constant line vigilance even on mild terrain. I could rarely sit and spin. Front-end breakaway was abrupt. I initially replaced the Ralphs with a Forekaster 2.35 / Ardent Race 2.35 combination. Not bad. Considerably better grip and probably ideal for XC, but still short of rollover. (I'm in the Southeast, it's just constant roots.) Hence the new wheelset (carbon, exactly the same weight as the original despite the width difference.) Some impressions: Weight differences are marginal. The Ranger (and Chupacabra, a very similar tire) is 880g. The Forekaster, probably the lightest tread pattern I'd want up front in a regular size, is 735g. Bonty's XR4, more like 780g. The extra weight and inertia is noticeable, but modest. Steering is slower. Not so much on 70mm and 80mm stems (with 780mm bar, 70.5D HA, 45mm offset), but when I went to 90mm to bring my weight forward (the bike came with ~110mm), it took a few miles to stop blowing turns. Very stable. Lethargic, even. It takes more body english to chuck the bike around. Tire pressure is enormously important. I verify my Ranger is at 14 PSI before every ride. More pressure makes for a bouncy ride and less grip. It's still better on both counts than a smaller tire with a similar tread pattern, but (at suboptimal pressure) a smaller tire with bigger treads would be preferable. Undershooting by a few PSI results in autosteer that makes the bike totally unrideable. There's no question that some negative Plus experiences arose from poor setup. Traction is way up in dry conditions. (I don't ride when it's wet.) I can brake whenever; the limiting factor is always weight balance and the Lefty packing down. If my body position is right, the bigger tire sticks like flypaper on most terrain. Dusty loose-over-hard flat turns are still challenging; it's actually better if there's some chunder for the tire to deform around and grab. (Cont'd)