Being radical I’ve dropped from my 1990s 40 psi all round to 35 front and 30 rear.
I’m running 2.1 ground controls tubeless and weigh 12 stone in my pants.
Is there a magic formula to working out optimum pressures?

You’ve heard the old saying for torquing bolts? “until it snaps and back it off half a turn”.

I think it’s similar due to the number of variables.
15st rider.
2.35″ reinforced sidewall tyres – tubeless.
30mm internal rims.
160/150 travel bike.
Ridden reasonably quickly down peak district rocky stuff.
23f/26r

Weight in lbs/7 = psi.
Then adjust +/- a bit (mostly -) to suit front and rear, tyre choice etc. Only a starting point, but it’s about right for me.

Yak’s formula gives me about 22, which is about where I am. (22-ish front, anywhere from 25-28-ish rear)

13 front, 15 rear on 29+ mulefoot 50mm rims. I’m 12st 4lb. Keep meaning to go lower, but have visions of tubeless gloop flying out of sidewalls. Yaks formula is way out for me, all although would be spot on for standard tyres.

Will give 25 a go tomorrow.

I’m 12 st 6lbs and I ride with about 20psi front and rear. If I’m at a downhill day on a rocky course, I go up to 25-30. But for my local trails which are rooty, rocky and steep (and slower speed), if I run over 20psi then I lose too much grip.

I’d like to run at 17-18psi, but below 20, I start to feel the rim touching too much. And my tyre start to squirm.

I’ve tried running st 30-40psi, but I just feels like I’m continually bouncing about from rock to rock.

Drop it until the tyres start rolling on corners then add a bit.

About 6 psi front and rear…

Yak’s formula is much easier in English – twice your weight in stone! Bit higher at the back.

Yaks formula +/- 5psi covers my range depending on front/rear, tubes/tubeless.

Twice my weight in stone, bit lower at the front on tubeless.

Get tyre squirm below ~22psi (Chunky monkey on Crests) so that’s the limiting factor. I then tune the rear so they have similarish grip levels, although this changes with conditions so I tend to leave it at ~26 psi as this means the rear normally slides first.

I find when bikepacking I need 29/35psi, and that’s with only 9-11kg of kit added to the bike/me, but without it the bike is squirmy and near impossible to ride

Interesting article albeit roadbased here

[Url]https://cyclingtips.com/2017/05/what-is-the-optimal-tyre-pressure-2/[/url]

If you read down the comments a guy links to a googledocs spreadsheet. [Url]https://docs.google.com/spreadsheets/d/1W_qsdZPfxDoaQ5A94mfTaVdIOrmHtjCQ_zAtHXf6t00/edit?usp=drivesdk[/url]
i couldn’t work out the logic or formulas…what i did find interesting if the methodology is correct is how big an impact front / rear weighting has
I did try the calcs for my gravel bike based on a guess on weighting and the answers worked well for me..10psi lower on rear and 20 lower on front on what i thought were quite low pressures

Yak’s formula is much easier in English – twice your weight in stone! Bit higher at the back.

Good point! I got it from the stans website years ago when I first went tubeless. All in lbs over there.

Yak formula gives me 28.

I habitually run 25 front, 27 rear (tubeless, Spesh grid sidewalls, UK riding from local woods to rocky Lakes).

Will usually go to about 27/30 for rocks or events where I don’t want to puncture (‘Ard Rock, etc.).

All in all, quite a consistent approach here.
I like the weight in stone times two as a rough starting point and it pretty much mirrors what I have.

Is it the same pressure for tubeless or tubed though?

That formula actually works for me and by chance is what I’m running.

Comes out as 31psi.

I use 30 in the front and a bit more in the back up to 35.

Much lower than 30 on the front and I get snake bites.

I’m sure I read something once that did it by tyre “sag” but I can’t remember how much the tyre was supposed to compress under rider weight.

Yak’s formula says 29psi for me.
29×2.3 minions, hard/slippy ground (Staunton) yesterday and was running 17f/19r. As the ground dries up will up the pressures to keep the tyres from squirming in the turns and with higher speeds, bottoming the rims.

That formula is a bit suspect. It will depend on tyre volume.

A 4″ fat tyre will need a much lower pressure than a 700c 23mm road tyre.

Definitely will be lower for bigger volume tyres. Imo it’s ok at around 2.25 width.

colournoise – Member
Yak formula gives me 28.
I habitually run 25 front, 27 rear (tubeless, Spesh grid sidewalls, UK riding from local woods to rocky Lakes).
Will usually go to about 27/30 for rocks or events where I don’t want to puncture (‘Ard Rock, etc.).

Don’t actually use a pressure gauge too often though.

Think I picked it up on here, but the fruit squeeze test works for me. Orange on the front, apple on the back.

Depends on the tyres, trail and condition, UST racing ralph on a wet penmachno about 18 (fantastic levels of grip for a fast tyre), TR racing ralphs on the local hard baked loam about 35.

That formula is a bit suspect. It will depend on tyre volume.

The formula is from Stans, as a starting point for tubeless MTB tyres, not CX bikes, not fat bikes.

That formula is a bit suspect. It will depend on tyre volume.
The formula is from Stans, as a starting point for tubeless MTB tyres, not CX bikes, not fat bikes.

I think most of us took it as such.

70 Kg, 2.3 Maxxis single ply. 17 PSI front, 20 rear. Run that everywhere

Dry condition for normal trail riding I run 29 front 31 rear. Don’t really mess about with the rear but in wet condition drop about 2psi in the front.

I was playing withh tyre pressure the other day, no formulaic approach, just trying different things, I ended up with 24psi up front (any lower and it washed out really easy) and 20psi at the rear.

why does everyone run higher pressure at the back?

I’m riding hardtail BTW

I weigh about 75kg + kit, and ride in the Lakes on 29″ HT and a 29″ rigid.

23mm internal rims- fr 2.4″ 24psi rr 2.25″ 26.5psi

40mm internal rim- fr 3″ 11psi

why does everyone run higher pressure at the back?

Because on steep climbs, nearly all the weight is on the back tyre and you also tend to smash the rear wheel over stuff more than the front so you need a bit more pressure in the back to prevent damaging rims. I weigh about 80 kg with gear and generally run 25 front and 30 rear on 2.35 x 26 tyres FWIW. I could run them 5 psi lower, but I prefer to have a margin for leaks, etc.

why does everyone run higher pressure at the back?

Seated pedalling on the flat the weight distribution is about 30/70 F/R, standing on the flat it’s about 40/60. And when riding the back tyre suffers the bigger loads most of the time, squirming first in berms, rim striking first through rock gardens, etc.

8 psi front 10 rear

That formula is a bit suspect. It will depend on tyre volume.
The formula is from Stans, as a starting point for tubeless MTB tyres, not CX bikes, not fat bikes.

I think most of us took it as such.[/quote]

But it is a very good point, the actual difference in volume between say a 29×2.4″ and a 26×2.1″ is pretty substantial, and both sit within what could be considered “normal” MTB tyre sizes these days… I reckon the formula needs updating to take account of wheel diameter and tyre width.

Except carcass stiffness is equally important and rim width isn’t far behind. And then there’s riding style and rider strength. It’s a starting point, no more no less.

If it feels bouncy decrease, if it feels squirmy increase.

Have stuck to the Stans formula for years and ended up with 31/34 F/R. @.3(ish) tyres on 25mm rims. Now running 35mm rims on 2 bikes, 2.5/2.4WT Maxxis on the FS, 3″ spesh purgatory grid on the B+ rigid. The FS is set to 21/24 the B+ 13/15.

Wide rim and tyre combo is very forgiving of low pressures, even for a fatty like me!

26/28 F/R for me with EXO/Grid/SG tyres. Tubeless on 30m DT Swiss rims.

Anything less I find the tyre squirms when cornering hard & I get punctures.

19 front 22 rear on 2.35 tyres on 29er HT and 26er FS.

13f/16r Maxxis 29×2.25 when racing my Yeti hard tail 59kg

If you’re still running 1990’s tyre sizes stick with 1990’s pressures. Tubeless will allow slightly lower pressure without pinch flats, but the main difference is huge tyres. I run 40psi on my 26×2.1, 30psi on my 27.5×2.3, 18psi on 27.5×2.8 and 13psi on my 26×4.8.
I’m a few PSI higher than is trendy these days but…
[list]
[*]I hate squirm on corners[/*]
[*]I’m 92kg[/*]
[*]I ride fast[/*]
[*]I very rarely crash[/*]
[*]I very rarely puncture[/*]
[/list]
your mileage may vary, but it must be your choice based on your riding.

I normally run 20psi front and rear. although I had a blowout cornering hard at 23mph at BikePark Wales last weekend resulting in a pretty hard crash.

This was on the second of 2 days riding, and having then checked the rear tyre (which was at 10psi), I think they had lost some pressure from the hard riding over roots and rocks the day before.

Moral of the story, check your tyre pressures every day!