koolerb

I've been messing around with tire pressure on one plus bike with 2.8's and another with 3.0's. I'm still pretty far from having this figured out. I weigh about 180 lbs, the trails around here range from really smooth surfaces to very rooty and rocky. I lean towards keeping pressures on the high side to avoid pinch flats on large rocks and roots, also to keep up speed on the smooth stuff. But I've also definitely noticed when I go too high I lose the plus size shock absorption advantage and the bikes get bouncy. I've been using pressures between 25 and 40 psi. Very difficult finding the sweet spot.

One thing to note, it seems like there's more of a difference in rolling resistance between the 2.8's and the 3.0's than I would expect. The 2.8 bike rolls really fast, faster than I expected it would. The the 3.0 bike feels really sluggish even when I trying to compensate with higher pressure in the 3.0 tires.

Just wondering if anyone with more experience here can level set my on where I should be.

HTupolev

That sounds really high.

At 200lbs bike+rider, 40PSI is what I run on the rear 2.1" slick on my gravel bike if I'm riding good smooth paved roads. And those are a very supple road tire, they ride somewhat squishier at any given PSI than most MTB tires.

For a 180lb rider on ~3" knobbies, I'm not sure it would make sense to go above the low 20s even good hardpack. On any properly rough stuff, it's probably reasonable to head down into the mid-teens.

It's hard to make precise comparisons of tires that are on two difference mountain bikes.

Aside from their size, are they even the same model of tire? If not, that's probably making a vastly larger difference than the .2" width discrepancy.

koolerb

Both bikes are front suspension hard-tails, wheel base is about the same on each, bike weights are about the same, the wheel width on the 2.8 bike is wider than the wheels on the 3.0 so actual width at the tire sidewall is really close, 70 vs 71 mm. For some reason that 2.8 bike with the wider wheels really rolls. In fact, first lap around one smoothish rolling trail section with a Strava segment attached, I beat my fastest time set on a 26" hard-tail with 2.0's and I wasn't even really trying.

Anyway, thanks for the pressure advice. I'll start testing between 20 and 30 psi. I hear these plus bikes can be really good but tire pressure is critical.

Kapusta

Those pressures sound incredibly high for your weight.

I weight around 170-175.When I was running 2,3-2.4” tires with tubes, I ran around 24 front and 29 rear, even on very rocky terrain.

With 2.8-3,0 tires, I would not think twice about trying 18 front and 23 rear and see how you like it.

Rolling resistence had very little to do with tire size. Tread makes a huge difference on knobby tires, and on tires that are run at low pressure, the casing makes a big difference as well (thin, supple sidewalls roll faster)

beatlebee 

I am running 3.0 on a 29+ with 12.5 psi out back and 12 psi up front. Very rocky terrain and no burping or bottoming out. ~165 lbs

pickettt

Avoid pinch flats? Go tubeless and take a variable out of your equation.

BarryVee

175Lbs here on tubeless 27.5+ x 2.8" Maxxis. 11-18psi max inflation pressure depending on terrain. Rear usually 1-1.5 psi higher than up front. Set with digital gauge. I'm not an "expert"

koolerb

Wow, so you guys are saying even 30 is high. I have some experimenting to do. Thanks for all the advice. I'm actually a road bike rider for the most part so anything under 90 psi sounds low to me.

JonathanGennick 

Could be the tread design, or the rubber compound, or some other aspect of the tire design.

Leebo

Couple o questions. Rim width? Running tubeless? Get a good gauge and do some testing. Start at say 20 front, 22 rear. What tires exactly?

prj71

You shouldn't have to exceed 20psi on 27.5+ tires unless you weigh 300 lbs.

At your weight you should be in the 15-18 psi range.

koolerb

The 2.8's are WTB Trailblazers rim outer width 49mm; the 3.0's are Kenda Havoks outer rim width 39mm.

prj71

Still doesn't matter. No reasons to exceed 20 psi on a plus tires.