Tyre pressure… How low is too low?

And, is a heavier/ stiffer carcass tyre less compliant?

Ok, that second one is a stupid question. Obviously a stiffer sidewall makes for a less compliant tyre but what I mean is, does a stiffer sidewall necessitate a low pressure to make the tyre conform to roots and such like?

I’ve been running Maxxis EXO for years and years and years now. Never felt the need for heavier carcass tyres. Even though the Internet tells me that an ebike needs DD tyres and cush core otherwise I’ll explode in a spectacular fireball.

I’ve ended up with a Bontrager SE6 on the front. The SE has reinforcement across the whole tyre so is bound to be stiffer right?

Anyway, I started off at 21psi which is roughly where I’d have had a DHF and it felt mostly ok but was deflecting off rocks and roots and made even mild off camber stuff feel pretty sketchy. Just riding on a rocky bit of a bridleway saw the tyre pinging sideways.

I started letting air out (a quick, pssst at a time) and once it felt better I measured it at 16psi yesterday (Surrey end of the North Downs) and it felt much better. If anything, I reckon I could go lower.

The tyre didn’t feel squirmy and I wasn’t bottoming the tyre and hitting the rim. If I did, I didn’t notice.

16 just sounds too low? It always felt like the 20/21psi that I’d use in the Minion was borderline too low for a 2.5″ tyre.

Is this the effect (benefit?) or a stiffer tyre?

I’m kind of thinking that so long as its not squirming around or dinging the rim, then it must be fine.

The downside to 16psi was more drag. Noticeable while pedaling and definitely reflected in battery consumption. I’m also not sure that it was actually any better than the EXO Minion. It’s like I’ve got a heavier tyre with more rolling resistance for some sort of performance benefit that I don’t really need.

Anyway, this is a bit of ramble.

Is 16 psi too low? And donwe reckon that I made my bike slower and heavier just for sake it?

Have you compared the readings on your gauge with someone else’s gauge? It may not be accurate

16 just sounds too low? It always felt like the 20/21psi that I’d use in the Minion was borderline too low for a 2.5″ tyre.

As above, gauge readings can vary wildly, but as long as your gauge is consistent with itself, then it gives you a reference point. Whether it’s ‘accurate’ with reference to an absolute point doesn’t really matter unless you’re using some sort of external guide like an online tyre pressure calculator – interestingly I found the values from the Schwalbe and Silca ones wildly different when I checked against them the other evening.

This stuff is always quite personal and relative to your riding style, terrain, the nuances of particular tyres etc. I just start off with a reasonable figure – the Silca tire(sic) pressure calculator’s not a bad point, and drop pressure in one or two psi steps until it feels about right or not and adjust accordingly.

I think the bottom line is that if 16psi on your gauge works, then fine. Yes, stiffer sidewalls will give more support, why wouldn’t they. If the tyre feels too ‘slow’ like that, add a couple of psi and see how it feels. But don’t get fixated on absolute values, ultimately as long as the pressure police don’t carry out a raid and bust your for offences under the Tyre Pressure Act, you’ll be fine :-)

If your dinging the rim or the tyres rolling in corners it’s too low.

Good point on the gauge.

It’s a digital Topeak gauge.

I’ve never really considered its accuracy. I’ve always figured accuracy is less important than how consistent it is. It’s always been consistent in the sense that setting a tyre to an indicated 24psi gives a tyre that feels consistent each time I ride. I used to use it for the pressure in my fork and again, it always felt consistent.

If we ignore the psi values I’ve mentioned then, I’ve ended up end with 25% less pressure in the new tyre vs the old tyre. They’re the same volume (near enough) the difference is that one is reportedly stiffer than the other which is something I’ve not really ridden before.

To be honest, the actual PSI doesn’t matter at all really. Yestersay, I went by feel and only stuck the gauge on towards the end of the ride so that I had a reference for next time. I was suprised to see 16 where I would usually see 21.

I guess that leaves the question as, does a stiffer tyre need significantly lower pressure than a less stiff tyre for it to confirm to rocks and roots? At the starting PSI, the tyre was pinging off things which got better at a lower pressure. I’m not ruling out that it could be just be that the tyre is less sticky.

18 psi on specialized butcher 2.6 felt fine but the tyre rolled off the rim twice and wrote off two helmets.

So for me 18 on my topeak guage is too low.

20 has been fine for 3 years.

I run as low as 11psi in a 2.6 ikon o a 29mm rim on my xc bike. Not an ebike though and im light.

The number doesn’t really matter, as long as the tyre doesn’t roll and you don’t beat up your rims too much. I run sub 15 psi on my dh bike if conditions are slow and wet

Have you tried the sram tyre pressure chart ? This gives a good staring point for type of riding/bike/rider weight/rim size etc,

What tyre pressure for…? 🤣

As always, myriad of factors at play, terrain, tyres themselves, rim depth/width, riding style, rider weight. All of which makes it highly subjective and without understanding the above (and more) about each individual making suggestions it’s hard to get a coherent understanding.

My take is as low as you can get it without tyre rolling/being unseated/puncturing. Bearing in mind the impact on rolling resistance as the tyre gets softer. Random psi recommendations on their own are largely pointless

No idea about pressure in mine, but if they’re squirming and giving that drifty feeling then I add more.

The number on the actual gauge doesn’t matter. As said above, if your dinging your rims or they keep rolling off the rim then they’re too low.

WRT the effect of lowering pressure on rolling resistance, there is definitely a sweet spot. Too high a pressure can make rolling resistance increase as well as too low.

How do you get away with Maxxis Exo for years and years? Do you ride a hover bike?

Maxxis EXO front and rear here for years, including 150mm travel trail bikes and racing Enduros. Run at circa 19/23 psi. No issues.

I’m also firmly in the ‘you lot are carrying far more tyre than you need’ club.

I’d rather spoon my eyes out than carry DD tyres!

Well it takes all sorts. During lockdown when everything was out of stock I wasted money on multiple Exo tyres. Minimum 25psi.

They’re so fragile but even when they’re not being slashed open the flimsy sidewalls feel awful to ride.

I had an se6 on the front of my Rail, absolute beast of a tyre, I didn’t get on with it and now run an exo Assegai. But yeah, I had it down way lower than usual for the same reasons you said and didn’t die. Sorry, can’t remember what I run it at though, but it was low. Down sarf as well so surrey hills etc, never ripped an exo. I must be sh#t

Tyre pressures are very subjective

I run Maxxis DD front and rear on my e-mtb, bike weighs 24kg and im 101kg at the momment

I found Exo casings were easily damaged due to having flints and small rocks where i ride and the Exo sidewalls didnt feel supportive

For years i found that running 30psi in the rear and 25psi in the front was spot on for me and where i ride, recently bought a new pump and pumped my tyres upto the above pressures and they felt awful, too hard and no give, bouncing over roots

I reduced the pressures by 5 psi in both tyres and they felt spot on, exactly how they felt at 30psi and 25psi on the old pump, so im guessing my old pump was over reading by 5psi

I did look at fitting a insert so i could drop the rear down to 20psi, but they seem like too much faff, pain to fit, even worse a pain to remove trail side if you need to fix a sidewall slash with some card/litter and fit a tube to get you back, then you have to carry the sealant covered insert back too

Tyre strength depends on so many variables though. I used to run on Exo fine until I started snake biting them. That was due to my speed increasing without a corresponding increase in skill. Also not being attentive to tyre pressures. 🤷🏼‍♂️

In my fairly uneducated opinion, it’s very hard to give advice in specific pressure numbers. It depends on how hard you ride. As others have said, if the tyre is not squirming or rolling on corners, and you’re not dinging rims, then the pressure sounds fine to me. I tend to ride about 15psi on 2.6” tyres on my local trails, where I know pretty well what’s coming (on the trail). And I don’t ride very fast or hard. I try to ride “light”. But if I’m riding harder/faster, then that’s too low. And other riders who I know well – they could never run at those pressures, because they ride much harder and push their gear much harder than I do.

If your dinging the rim or the tyres rolling in corners it’s too low.

+1

Within reason just keep dropping it until there’s a problem.  That’ll compensate for any stiffness in the tyres too.

Bigger tyres and wider rims mean less pressure than was normal when 2.1″ tyres were normal (and they were rarely 2.1″ anyway).

Heavier riders need more pressure as we tend to both hit edges with more force and likewise cornering takes more force for a given speed.

The surface impacts on it too, at trail centers I tend to run higher pressures as the surface is generally very grippy compared to roots and mud, and if not, the berms don’t need much grip anyway.

I play around with tyre pressures a lot. It is important, makes a huge difference. I carry a pump because I sometimes let air out when I get to the interesting bits of trail and pump up for the dull slog home. But for 25+ years I’ve been doing it via the thumb squeeze method, and the how it feels method.

I recently got a digital tyre pressure gauge (cheap, to make up postage on an order from a certain former bike retail company) and was shocked to find the numbers were way out of whack compared to what I hear people talking about and what my track pump says.

I chose to ignore it and ride my bike.

Wasn’t there  a rough calculation method for tyre pressure?

“Wasn’t there a rough calculation method for tyre pressure?”

Twice your weight in stone in psi, -1 front, +2 rear was the one. It’s still a good starting point. Go down 1-2 psi at a time until it squirms or pinches or feels too draggy. With stiffer casings you can go lower (and need to go lower to get as much grip on wet rocks/roots). Inserts give you a bit more leeway, reducing squirm and pinching at lower pressures.

When it’s really wet and slippery I’ve got down to 17 psi in the front with a Hillbilly Grid 2.4 and Rimpact insert, at about 12.5 stone. In the dry I need that up at 19 and then maybe 20 if it’s rocky and fast and dry. Rear 1-2psi higher with a similar tyre and Rimpact Pro insert. Ebike about 2-3 psi higher than on my 160mm hardtail.

That’s using the Topeak digital gauge for consistency.

Pressure numbers are only the starting point in my opinion. It’s how you like the bike to feel and how much you prefer grip over rim life. Like everything, it’s a compromise.

An old piece of advice that I still use is:

“you should feel the rim once or twice a ride only, then you have your tyre pressure set just right”

I’d start at 25psi rear and 20psi front, on a ~2.3″ tyre, then adjust it to what feels best.

On my 3.0″ tyres on my Stooge, I’m more like 15psi on the rear and 13psi on the front, just for reference.

Note: if I’m doing a long ride, and value puncture resistant over grip, I’ll go for +30psi for a ~2.3″ tyre.

If your dinging the rim or the tyres rolling in corners it’s too low.

This.

I find I run higher pressures than many people – but I run mid-weight tyres, I’m a chubster, and ride a hard tail, usually on rocky trails…

Depends what I’m riding. In the peak (straight line, rocky stuff) lower feels nicer until you ding IME.

On the other hand, bermy stuff feels terrible with pressures too low – you never know when the tyre will give way.

Low pressures are a bit like a comfy armchair. Feels nice and, well, comfy. But maybe not super high performing if you’re trying to ride on the edge. Armchairs are terrible for riding on the edge.

FWIW, I have run 2.4  26″ Barons with tubes at 14 PSI on the Les Gets 4 Cross. I’m quite a big chap @ 105 kg. Narrow rims too. I survived. It was a bit squirrelly in places. How I avoided snake bites I’ll never know.

I run mine softer than most people, but imo as long as you’re keeping the air in and the tyres on and the rims intact, it’s not “too low”, anything other than that is a valid matter of taste and is going to be influenced by what you ride, how you ride it, what you weigh, what your tyres are, allsorts. There’s no wrong way to have fun.

I’m 10 stone, generally ride pretty light with a lot of body movement and unweighting etc, and I like coil suspension so for sure that makes a difference! I don’t hate the feeling of squirmy tyres as some do, I don’t struggle to ride through it in corners frinstance, so I’m usually about 16psi both ends with decently wide rims, even on the hardtail. I just prefer the feeling of a softer tyre, that extra conformity and small-bump smoothing, it just inspires more confidence and lets me use the grip I have better. And I basically pick tyres that work with that softer feeling, rather than letting my tyres dictate how I set up pressures, because I don’t care if my tyres are having a good time.

Maybe I’d be faster with more air, but who cares? Even when I was racing I was midpack, it’s not like it made any meaningful difference.

Thanks chief! Spot on :)

Usual advice is keep going lower until it feels too low.

The actual pressure you run is so reliant on so many elements that it’s irrelevant what other folk use, but, if you’re riding the same trails, same weight, with the same-ish tyres etc then it’s worth seeing what pals run (using the same pressure gauge).

As for the OP, they’re in the Surrey Hills, so it’s not like they’ll be charging over rock gardens or the like.

For me with Michelin Wild Enduro’s in the Tweed Valley I’m circa 15psi front, 17-18psi rear.  Even my gravel bike is only 30psi.