Outer Limits 4x4 Board

What sort of pressures do people run at rockcrawling speeds without beadlocks? We run 31 inch MTR's on a hilux, so weight and power are not huge. Has anyone had any bad experiences at excessively low pressures? How low is too low?

I used to run 6psi on my Hilux running 33x11.5 Simex JT2s. Only ever popped 6 beads in about 200mtrs cutting a new trail through a dry rock creekbed. Had never popped one before this and i dont think i did again after it. Had the beads come a little un-seated and get mud,rocks,dirt in them but not completely off the beads.

popped a bead on a cooper STT on a disco at 22psi on rocks.

Steve

I had 35x14.5x15 tsl Boggers on 15x8's and ran as low as 4 or 5 psi and never had a problem!

33x12.5 on 15x7 rims !!
down to 4psi !!!!

These claims are all without beadlocks? Maybe we can go a little lower than first thought then. Thanks for your comments.

Also wondering whether the tyre is most likely to come off at low pressures when there is a lot of wheelspin or just when it is crawling along and under a lot of load (I.e. twin lockers on a rocky trail)?

most times you pop a bead ,
is when there is side load against the tyre sidewall !!

ie... rockclimbing , small ledge , turning into it , POP !!
or in mud , hitting the edge of rut or similar !!!!

the only thing with wheelspin , is turning the tyre on the rim !!!!
very rarely popping the tyre off from wheelspin !!!!

31 mtr
6psi aint lost a bead yet

mtb4x4mad wrote:What sort of pressures do people run at rockcrawling speeds without beadlocks? We run 31 inch MTR's on a hilux, so weight and power are not huge. Has anyone had any bad experiences at excessively low pressures? How low is too low?

Are you running a 7 or 8 inch rim? 8 inch rim might give you a problem on side slopes and full lock downhill, other than that, the rim might spin in the tyre, requiring a rebalance if these tyres are your streeties.

i used to run a set of 32x11.5 BFG AT's, and used to run 16psi on the rocks, never popped a bead, thou i used to pop em when i got home to clean mud and dirt out of them that was causing leaking,

only popped a bead once on sand running 10psi,

now running 33.12.5 MTRs and playing with preassures to find out what works

37x12.5 on 8" rims at 9psi under a short maverick. working OK thus far.

Normally run 10 psi on rocks - accidently run 8 psi a couple of times Haven't lost a bead yet

Oh yeah - - - > 35x12.5/15 BFG MTs (old style) on 15x8s

On the TJ running 35x12.5 on 15x8 non-beadlocks - generally I'll airdown to 10-12PSI....but sometimes 8-10PSI have only popped a bead when farting about at about 6PSI...
As for the swampers (on beadlocks) this I generally run at about 6-8PSI anyways...

On my Zuk I used to run about 10 in the 32 BFg's Lost a bead in a boghole .. After that it came of pretty easy . 33x12.5 swompers in 15x8's popped two beads at the same time at about 6 psi on a hill climb somwhere out back of walhalla both rims spun in tyre .. 35x12.5 bias claws at sub 5 psi seem good .. but only used em on one run so jury is still out.
It also depenmds a bit on how long the tyre has been on the rim and how you mounted em .. if you have used soap ectc to help get em on that soap is still there just waiting to help it slip off as well ... Get a bit of rust in there etc it will stick like the proverbial s@#t to a blanket ..

I have always only gone to 15psi as been to chicken to drop them any lower. Never had a problem though.

33's MTRS on 15x8's

Get a peice of string, measure half and multiply by 2, convert the CM -> PSi and you get your answer.


8, 10 12 might be fine for one person, in one situation, but in others, it might be all pear shaped.


as a rule, 18 is the lowest i would go without tubes or secondairs / beadlocks.

10 with Tubes.

1-2 with Secondairs or Beadloacks

i would go under these if stuck and could see it would help. would do it with caution, and air up straight after, as no tubes or beadlocks, and under say 18 at speed on dirt = BAD NEWS.

Airing up ain't an issue with Co2 quick dab and the pressures are back up to something safe... no more waiting, waiting, waiting for the arb to pump...

Steve

usually run 1.5-2 psi in the front and 0-1psi in the rear.


Thats on a zook with 37 boggers and 8 inch rims

No one has mentioned 10" rims, this must cause the bead to pop at low pressures.

Whats a safe low pressure for 315/75/16 (35") on 16x10" rims ?