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Mountain biking 2019

scott43

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La riviere diable.. Mont Tremblant. I survived the bug feast...
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Erik Timmerman

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I've been playing with different tires as of late. My Fuel EX comes with Bontrager XR4 Team Issue 2.4. I got some XR4s in a 2.6. First put them front and back, then did one of our big climbs yesterday and decided it was a big fat NOPE for the rear-I felt like I was riding in molasses. I really liked the cornering security I felt with the 2.6 up front, however. I'm going to put the 2.4 back on the back and run the pressure a tad lower than I have been.

On that note, for a 2.4 and 2.6 tire with a 130 pound rider, what pressure would you folks run? Particularly on the big chunky rocks that we encounter at Snowbasin? (Think, big, sharp baby heads, sometimes elephant heads, with some loose thrown in for good measure?) I want to run them as low as I can without killing my carbon wheels, because that extra squish and grip really helps me. I've been hearing I could go as low as 13 in the front. I ran them at 14 yesterday.

14 sounds really low, but if it’s working for you... As a point of reference my daughter weighs the same and is running 20 psi in 2.5” DHFs.
 
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AmyPJ

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14 sounds really low, but if it’s working for you... As a point of reference my daughter weighs the same and is running 20 psi in 3.5” DHFs.
If I run 19, I'm bouncing off the rocks like a ping pong ball. Unfortunately, adjusting rebound can only do so much. We have a special kind of rock gardens here.
 

Erik Timmerman

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Here's a couple of pictures from the Poconos home of rocks, roots and rhododendrons. We managed to avoid all of the poison ivy and ticks (I think) and sometimes were surrounded by the sweet smell of honeysuckle. We pre-rode on Saturday then I stepped aside as the kids raced on Sunday. Fun course in a surprising place at the end of a cup de sac in Stroudsburg, PA. After a few hours of racing the kid had a new jersey and some other swag. What I think she liked more was this japanese food truck! It was delicious. After that we ran amok in a fireworks outlet (the guy in front of us spent $4500 in there!).
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Erik Timmerman

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If I run 19, I'm bouncing off the rocks like a ping pong ball. Unfortunately, adjusting rebound can only do so much. We have a special kind of rock gardens here.

Sounds like you found a good spot. I'd just look for those warning signs - the rim pinging off the ground, and squirmy sidewalls the air up appropriately. If you never feel either, drop a pound until you do - then go back up.
 

AmyPJ

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Sounds like you found a good spot. I'd just look for those warning signs - the rim pinging off the ground, and squirmy sidewalls the air up appropriately. If you never feel either, drop a pound until you do - then go back up.
Egads if my rim ever pings, I'm in trouble! I know it has happened in the past when I had aluminum wheels.
I want to run as much as possible because of climbing efficiency. I've actually contemplated climbing with more pressure, then releasing some for the descent. There are a few rides where I could pull that off.

I want a bike that farts as hard as I do.

What in the actual? Was that some kind of promotional video, or someone goofing off with a promotional video?
 

4ster

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I've actually contemplated climbing with more pressure, then releasing some for the descent
That’s what I do most of the time, especially if I begin on pavement or smooth dirt. 30lbs on the initial climb, then 20lbs the rest of the day.
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Ron

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the lower the psi, to the amount you dont squirm or bottom out, the faster you will roll. its been proven over and over.....

since I can't ride, I loaned my yeti with 2.6 Maxxis reckons to my friend who races in local competitions, I lowered his psi to 17 front/18 rear to start, on his first ride he set almost all new PR's first his climb up and blew his times away on the down, he was coming off his bike with 2.35's and psi's of 25/27. he was amazed how much faster the bike rolled, especially over rocks/roots
 

AmyPJ

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the lower the psi, to the amount you dont squirm or bottom out, the faster you will roll. its been proven over and over.....

since I can't ride, I loaned my yeti with 2.6 Maxxis reckons to my friend who races in local competitions, I lowered his psi to 17 front/18 rear to start, on his first ride he set almost all new PR's first his climb up and blew his times away on the down, he was coming off his bike with 2.35's and psi's of 25/27. he was amazed how much faster the bike rolled, especially over rocks/roots
It'll definitely help while climbing chunky stuff, but on smooth stuff? I have my doubts and my legs sure felt like they were working extra hard, and I was really wishing for a 30t or 28t chain ring on the climb on Sunday. On the downhill, no doubt it helps, especially with the confidence. But I'm definitely skeptical that the 2.6s don't create unnecessary drag on climbs, particularly smoother climbs. Although, I also tapped out on a climb that I normally make BARELY. I made it about 30 feet from the top. I felt like I was riding in molasses with the 2.6s running at 16 psi.

Was that his first ride on the Yeti? I'm so curious about going faster with lower psi (to the right point.) I want to read more about it!

Another thing I've read about and observed--a 2.6 Maxxis is not as wide or tall as most other 2.6s??

Anyway, tire pressure seems to be one of those kind of mysterious things that always leaves me scratching my head. I mean, you'd think it'd be pretty cut-and-dried, but it's definitely not!
 

AmyPJ

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Here's a couple of pictures from the Poconos home of rocks, roots and rhododendrons. We managed to avoid all of the poison ivy and ticks (I think) and sometimes were surrounded by the sweet smell of honeysuckle. We pre-rode on Saturday then I stepped aside as the kids raced on Sunday. Fun course in a surprising place at the end of a cup de sac in Stroudsburg, PA. After a few hours of racing the kid had a new jersey and some other swag. What I think she liked more was this japanese food truck! It was delicious. After that we ran amok in a fireworks outlet (the guy in front of us spent $4500 in there!). View attachment 75980 View attachment 75981 View attachment 75982 View attachment 75985 View attachment 75986
Look at her go! So fun watching the kiddos blossom.
 
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Ron

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I (and others) have posted up several articles and studies on roll (CRR) resistance and aerodynamics (cda) but..... here's a broad stroke overview

*wider tires roll faster than narrower ones. (not necessarily at the same psi, in fact as the road surfaces increases in roughness, lower is faster.)
* lower psi is faster in relation to hysteric and suspension losses but at certain points, psi won't make any real difference but is more comfortable. in the case of mtn biking, lower is faster subject to above and safety.
* on speeds above ~15pmh, (obviously, now we are talking gravel bike-road bike) aerodynamic forces begin to overtake relative roll resistance
* there are two points at which a tires psi is optimized - hysteric and then suspension. that psi does not occur at the same point
* the tire to rim ratio is optimized at ~105% (rim depth is critical, 45mm and deeper rims are best) meaning the rim needs to be wider than the width of the tire. the gains/savings are significant and of course as speed increases, the forces are cubed. the ratio can be mitigated to an extent by deepening the rim allowing the air to reattach, also, there is some off-set when using wider road tires ~28 with deeper wheel 45mm plus where the CRR can offset the aero plus the added depth of the rim allows reattachment.

Maxxis 2.6

again, you have to run the proper width rim, a Maxxis 2.6 is designed around a 30-35mm internal width rim and inflates to a full 2.6 tubeless of course,


TREAD PATTERN the tread pattern will have an equally dramatic effect on the CRR as well as weight on the climb! 2,6 rekons weigh almost the same as a 2.35 Schwalbe NN so the added footprint (contact points) and much smoother and closer packed knobs roll faster and require lower forces to roll forward, there is some offset to initial forces to spin up due to the added height but rolls easier to lower CRR, wider contact points and better tread pattern,

it also changes a 27.5 tall tire to ~28.35 tall tire
 
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Lauren

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On that note, for a 2.4 and 2.6 tire with a 130 pound rider, what pressure would you folks run? Particularly on the big chunky rocks that we encounter at Snowbasin? (Think, big, sharp baby heads, sometimes elephant heads, with some loose thrown in for good measure?) I want to run them as low as I can without killing my carbon wheels, because that extra squish and grip really helps me. I've been hearing I could go as low as 13 in the front. I ran them at 14 yesterday.

I've got 5-10 lbs on you, and running 2.8s (Maxxis Rekon in the back, Minion DHF on the front...absolutely love the combination). They normally hang out around 20-24 psi, more or less...I go mostly off of feel. I'll normally pump them to about 24, then squeeze them, let a little out, squeeze again, and repeat until I'm happy...super scientific.
 

Lauren

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try them at 16-18.....

They may end up in that range by the time I get them to a point I like. I'll have to be a bit more accurate next time I pump them up and see what psi I actually run at.
 

Lauren

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...and of course, the accuracy of your pump :). most hand pumps are widely inaccurate.

Haha, I was going to say the same thing. I trust mine to put air in my tires, but not much beyond that.
 

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