Tire Pressure to start at? How low or high?- Mtbr.com
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  1. #1
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    Tire Pressure to start at? How low or high?

    Bike: Basically stock 2019 Fathom 2
    Wheels: Giant AM 27.5 tubeless setup, 30mm internal width
    Tires: Maxxis Ardent Race 27.5x2.4
    Bike weight: Weighed by me at 28.6lbs
    My weight including gear 170lbs
    Trail: SingleTrack, HardPack, a little rooty, with some loose pack, small drops and a few small jumps, minimal rocks.

    Where would you start your tire pressure?

    Thanks for sharing your knowledge/experience!

  2. #2
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    Sit on the bike and reduce rear pressure till the cornering knobs on the back tire just touch the cement in your driveway (you'll need someone to look for you). Note the pressure and subtract a few PSI for the front. Vary from there to try different pressures.

  3. #3
    No Clue Crew
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    Or just start at a relatively "normal" pressure -- 25f/30r -- and adjust to your liking.
    Just like a raindrop, I was born to fall.

  4. #4
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    I'd say start at 20 psi and start decreasing until you feel rim strikes then add a pound or two. Right now I'm running 16 psi rear and 14 front on 2.4 tires in pretty rough terrain.

    Higher pressures tend to ride roughly and bounce around. As you start decreasing pressure you'll notice a point where the ride markedly improves and the tires are deflected off line less. Around this point, a few psi +/- will make a big difference. If you're hard charging over sharp edges, you'll need more pressure.
    Do the math.

  5. #5
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    I should weigh my bike one day but I'm guessing it's around 30lbs and I weigh just shy of 160lbs with my gear and pack.

    I too started with 25 front, 30 rear, now I'm down to 20 front, 25 rear. I may go down a couple more lbs of PSI but right now, that 20/25 is working well. Good traction, not too bouncy and I don't have to worry about taking a sharp edge or drop on my rims.

    Edit: Running on 27.5 x 2.4mm Maxxis Ardent EXO tires.

  6. #6
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    I might be 160 wearing a hydration pack.

    I run 20-22 in the front based on my gauge.
    Usually a few lbs more in the wear. The size of tire, for me, isn't too sensitive to slight pressure changes. Meaning I can't tell a difference between 20 and 22 in the front. I tend to run it on the harder side (like the 22) if I'll be riding sharper trails with rock more aggressively.

    I'm on 29 by 2.33 grid sidewall Specialized tires. They are a little more stiff than a Control sidewall by Specialized. Your sidewall will affect the pressure too.

  7. #7
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    Thanks everyone for your input. Looks like I am at 27 rear and 22 front for now. Might try to go lower but for now this seems good for me.

    Sent from my Pixel 3 XL using Tapatalk

  8. #8
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    I'll play. 6'4 285 loaded up. Got a new rip 9 rdo. Running 29 x 2.5 dhf front, 2.5 aggressor rear on i45 carbon rims. Other bike is a Krampus with same rims. I run those at 19 rear 17 front. Any suggestions for the 2.5's?

  9. #9
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    Quote Originally Posted by maamcgui View Post
    Thanks everyone for your input. Looks like I am at 27 rear and 22 front for now. Might try to go lower but for now this seems good for me.

    Sent from my Pixel 3 XL using Tapatalk
    Also keep in mine there are differences in pressure gauges. Find what works for you and work with that on your gague. Same pressure reading from another gauge could net you a different ride quality.

  10. #10
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    Quote Originally Posted by maamcgui View Post
    ...Looks like I am at 27 rear and 22 front for now...
    You really won't know the benefit of going lower until you try it. As I mentioned, there's a point below which there's a big difference, and not much difference above that until you get there.
    Do the math.

  11. #11
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    Quote Originally Posted by Lone Rager View Post
    You really won't know the benefit of going lower until you try it. As I mentioned, there's a point below which there's a big difference, and not much difference above that until you get there.
    So you are saying I still need to get lower?

    Sent from my Pixel 3 XL using Tapatalk

  12. #12
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    Quote Originally Posted by Forest Rider View Post
    Also keep in mine there are differences in pressure gauges. Find what works for you and work with that on your gague. Same pressure reading from another gauge could net you a different ride quality.
    ^^^^ That's a solid point there. I've got 5 different gauges at home and two are similar, give or take a couple pounds, the others sway as much as 12psi from the lowest to highest reading. If you have multiple gauges, put a piece of masking tape on 'em and write down the pressure reading should you need to revert to those gauges at another date ie primary one broken or lost.

  13. #13
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    Quote Originally Posted by maamcgui View Post
    So you are saying I still need to get lower?

    Sent from my Pixel 3 XL using Tapatalk
    "if in doubt, let it out"

    You don't KNOW what too low is until you start getting rim strikes or squirmy tires. The point of the above mantra is to drop pressure little by little until you have no doubt anymore what too low is. It's sorta like when setting up your suspension. You want to try settings at the extremes so you know what "too much" or "too little" damping is, before you work on finding an intermediate that you like.

    On my 29er (2.6 WTB Vigilante/Trail Boss, which have pretty stiff sidewalls, on 30mm rims), I'm at 12psi front, 17psi rear.

    I run a tire insert in the rear so I can push the low end without risking rim damage. Different inserts let you push that lower limit further or not. I'm using Huck Norris, which doesn't really let you run aggressively low pressures like some do. Pressures basically stay the same with them, and they soften impacts to the rims. Cushcore, for example, lets you run lower pressures than you otherwise might because they're thicker, firmer, and they support the sidewalls of the tires.

    I tried going lower when I first started riding this bike, but even before getting a bunch of rim strikes, my tires were really vague and squirmy. So I raised the pressure until that sensation went away.

  14. #14
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    Ive never ran a tubeless tire above 24psi. Anything close to 30 is for tubes and cyclocross.

  15. #15
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    Quote Originally Posted by Lone Rager View Post
    I'd say start at 20 psi and start decreasing until you feel rim strikes then add a pound or two. Right now I'm running 16 psi rear and 14 front on 2.4 tires in pretty rough terrain.

    Higher pressures tend to ride roughly and bounce around. As you start decreasing pressure you'll notice a point where the ride markedly improves and the tires are deflected off line less. Around this point, a few psi +/- will make a big difference. If you're hard charging over sharp edges, you'll need more pressure.
    Pretty much what I'm riding. I'm 160 pounds before coffee and just got back from a couple of days in Moab. Navajo rocks was fine at 16 rear (29x2.5 Aggressor) and 13 front (29x2.6 DHF alphabet) and I ran 1 psi more front and back on TWE + Jimmy Keen with 3 liters of water and some gear/snacks. Turned out that extra 1 psi wasn't needed. I run the same, generally on 29x2.4 Nobby Nics as well, on the Wasatch Back. It's what I run on 27.5x2.6's too.

    That's on my digital gauge. My floor pump reads differently.

  16. #16
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    I give 'em a squeeze and if they feel firm I ride. If they feel mushy I give 'em a couple pumps. Could not even start to tell you what pressure is in each.

  17. #17
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    You're not going to get far when you're low enough to get rim strikes in the rockiest segments of your ride. Put a gauge and hand pump in your pack and do the experimenting you need. Your terrain description and weight suggests you can go quite a bit lower.

  18. #18
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    Quote Originally Posted by eb1888 View Post
    You're not going to get far when you're low enough to get rim strikes in the rockiest segments of your ride. Put a gauge and hand pump in your pack and do the experimenting you need. Your terrain description and weight suggests you can go quite a bit lower.
    That is the plan. Just wanted an idea of where to start.

    Sent from my Pixel 3 XL using Tapatalk

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