[Closed] Plus sized tyre pressure

Too many variables. Define "plus" for a start...
😉

For a proper wide tyre on a proper wide rim I'd say 12-18 psi. That's a massive range though.

Even a formula is a guide at best*, you still have to do the experimenting bit, and it's dependant on more than just your weight and tyre size....terrain, weather, riding style/skill, tyre carcass, rim width etc..

So just experiment, you'll get a better understanding for what works and what doesn't too so win-win

* at worst it's a counter-productive way of legitimising 'guessing'.

You will just have to go out with a pump and a gauge and experiment for yourself.

What feels fine your you wont for another even if they weigh the same on the same bike. A lot is down to style of riding.

Colin: These are 650b @ 3" - WTB Trailblazer and Bridger.

@amedias - I realise that one size (sic) doesn't fit all but I find the Stans formula pretty close for me. Well close enough that my lack of skill isn't going to tell the difference between say 29 & 30 psi. But at the pressures these are recommended 1psi is circa 10% step change which is significant

I'd start at 15psi then. As you say, 1-2 psi at these pressures can make quite a difference but I don't think you're getting the full benefit of Plus once you start pumping them up to 20psi.

20psi was a spurious example, I've seen pressures around 10-12psi quoted for much heavier riders than me but there's no context as to what terrain or style of riding they are on.

Easier (and quicker) to start from 15psi than from 20.

Start at 15 and adjust from there, depends on tubes or tubeless, casing, rim width and person preference.

This on your Solaris Whitestone?

@Normal_man Yes, going to give them a go. Been thinking about getting some 650b+ wheels for a while and bit the bullet last night.

Cool.

Look forward to hearing how you get on. I was tempted but ended up buying a fatbike for n+1 instead.

Nae room for a fat (or indeed another) bike in the house! So this is a low space, low cost way to increase variety. N+(a bit) if you like.

I'm definitely a biffer and 20 psi is definitely 'high' on 2.7/2.8" 650B+... (on roverpigs 'old' cotic wtb wheelset).

With a Solaris you'll struggle with 3" for width on forks (I've got a fag paper either side of mine (with a 2.8" nobby nic and rebas)).

@metalheart. Hmm. I'll have to see - I'm fitting Trailblazer 2.8" to the rear which is what Cy Turner used when checking things out on the Mk1 so that end should be OK.

20 was just a figure out of the blue, Cy mentions "13 front/16 rear" as his preferred setting and he's slightly heavier than me.

Yeah, sorry, rear is a Trailblazer 2.8 (not a 2.7, duh). Plenty clearance on the Mk 1 frame wi that. RP had a nobby Nic on the back (Schwable 2.8 definitely bigger than the WTB),

I was out for a scoot this evening and I'd say I was running 15/16 front, 18 back. But I'm definitely in the heavyweight category atm... 😳

I was a little disappointed to find that it wasn't quite as easy as pull one set of wheels and slap in the other. Disk calipers could do with recentring and the rear cassette is probably half a click out too. But it still runs... only had one ping of something between the tyre/fork stantions... Probably something to with hubs built 3 years + apart I guess.

I'd have to say I did pretty much enjoy the semi fat outing. I was swapping with my mates Soul27.5 from time to time, definitely preferred the semi!

12psi in my 2.8 TB for general bimbling.

But a Topeak digital gauge though, as 1psi makes a difference at such low pressures.
Some fat bike rider will be along soon, to mock such high pressure, & explain how he runs his fat bike tyres under vacuum.

http://www.bikeradar.com/mtb/gear/article/are-27-5-wheels-and-tyres-better-than-29ers-47047/

I think Seb's approach here is a good one - find a good berm and lower the pressure each run until it squirms too much, then go back up one step. If your pump allows it I'd start at 25psi and drop 1psi each run. Try going back up just 0.5psi once you hit squirm level. He ended up at 18.5F/19.5R psi on 3.0 tyres and 40mm rims.

Hadn't considered the recentring, maybe some rotor shims on one or other of the wheels would sort that out. I don't see me swapping wheels on a daily basis so sorting out the indexing shouldn't be too much of a pain so long as I remember to do it 🙄

Have a Topeak digital gauge already so covered on that score.

Wheels and tyres are on their way, the wheels are in the local depot and just waiting for them to move to the "out for delivery" stage.

Regards recentring, as both hubs are evo II's they're close. Should be just a case of loosening caliper bolts, aligning and tightening up... As I said, they actually run, front has a slight skiff at one point but no drag. Just OCD. Rear mech acted up a little on the third cog, more so in the middle CR but not so bad I had to stop fix it... 😳

@chiefg: if I'd started at 25psi the front wheel/tyre wouldn't turn in the fork brace! To me, 20 psi 'feels' about the same as 35 on a 2.25 29er.

I'm pretty sure I could drop pressures but I'm kinda 'risk averse' so happy to err on side of caution for now. Not really stuck it down anything remotely serious down yet.

ETA: definitely post up your findings whitestone, I for one (at least) am interested!

Good advice up there! Get a digital gauge definitely. I find I can run from 10-15 psi in my 3" Chronicle EXO tyres. For really high, rocky descents it needs to be 15 or I get punctures but for more mellow, woody stuff I can run a bit lower and it feels really nice.

watches with interest.. as a non-buffer bit looking at +

kcal - Member
watches with interest.. as a non-buffer bit looking at +

I run13-14 on a trailblazer, 12-13 on a 2.8 NN on the Solaris. I find they need to go up to about 15 on the suspension bike to feel right. 73kg kitted up.

Really, it's just how it feels to you, how hard you corner etc. I ride my full sus harder than the Solaris, and the roll I was getting at lower pressures was a bit disconcerting. Start at 15 and go down. My rims are only 29 & 35 internal so wider rims will feel different again.

@Whitestone,

As long as they're round, you'll be fine.. 🙄

Well I'm 19st and run 2.75" dirtwizards on 50mm rims at 25psi which is about spot on. Tried 29psi on forest track and that's too much.

I have 12psi 3" purgatory front and 15psi 3" GC rear. This is on a Stumpjumper 6fattie.

OK, I've now got quite a few Km done on them and have a feel for where their pros and cons lie [b]for me[/b]. Settled for the moment on 12psi on the 3" Bridger on the front and 16psi for the 2.8" Trailblazer on the rear. I'm currently back on the 29er wheels as I've a couple of long rides coming up that they'll be better for overall.

Generally the pros and cons match up with what people say about fat bikes: insane amount of grip but some unnerving undamped suspension. I've got a test loop of 23Km and 600 metres of ascent, varying surfaces from road to armoured trail with grass, boggy bits and loose rock thrown in at various places for good measure. Given a trail with loose material scattered around and the contact area and grip of the tyres, particularly the front, mean you ride over stuff rather than get pushed around it, even more so if it's a climb.

The undamped suspension nature of the back tyre in particular nearly had me over the bars - I hit a series of bumps at just the right speed to match the resonant frequency of the tyre responding to the terrain - really noticeable on a hardtail 😯 . Occasionally I'd notice a bit of squirming at the back particularly if you happened to ride along an edge of something like a water channel in the trail.

It's quite likely I haven't got the pressures right for me just yet so will work at that over the coming weeks.

Sounds like you need/want to up the pressure several psi tbh.