Safe deflation limit for 275/55/20 tires

68camaro

Any River...Any Place
Hi, I was wondering what is effective but safe tire deflation limit for a JGC with Zitto Terra Grappler G2 275/55/20 tires/wheels? I run about 38psi on street. No bead locks. Off-road use is mostly forest roads/unimproved dirt roads, nothing crazy, but some areas have very longer steep hills which when wet can be slippery.
 
Last edited:

rkj__

Adventurer
Great question, I was wondering the same thing. I’m used to 265/75R16s, so comparatively, these low profile tires don’t look like they have any sidewall to spare.

I probably would not go below ~24 psi for trails with any rocks. But, I don’t have any experience to back up this guess.

If driving responsibly on sand, you could go into the teens.


Sent from my iPhone using Tapatalk
 

Mundo4x4Casa

West slope, N. Ser. Nev.
The general rule for deflating has to do with two things: 1. Any ".5" tire; i.e. 16.5 or 19.5 has very little sidewall and the wheels lacks a safety bead to keep it on the rim at lower pressure.
so the only way a, .5 tire/wheel would work at low pressure is to use beadlocks. However, lowering the pressure is not recommended by experienced ".5" manufacturers.
2. Lowering the pressure has to do with the height of the sidewall on normal, non, ".5" tires. A tire like the G2 275x55R20 has a lot of wheel and a rather short sidewall and not expected to have much air reduction before any danger is reached. This means: don't lower the pressure unless you absolutely have to get out of trouble. We have a 2011 Grand Chero Limited with 18 inch wheels and enough sidewall to deflate a ways. Of all the possibilities in wheel tire combo for a JGChero, i like our 18's the best, as a wide variety of capacities can be had; a higher capacity than 15, 16, 17. 19, or 20 inch tires that fit a JGChero.
We had good luck with Cooper Discoverer AT-3's with long life and pretty good on snow and ice with big tread blocks, sipes, and tiny voids. They don't look as Macho as mud tires but are quieter and last longer.
The newest version seems to be the best of the AT-3's as they eliminated the crescendo of noise toward the end of tread life.
Since I do a lot of sand and dune running with my 10K pound truck camper, I elected to keep the 16 inch wheels and mount 35 inch tires which give me plenty of sidewall with which to deflate down to about 20 pounds when needed.
 

68camaro

Any River...Any Place
2. Lowering the pressure has to do with the height of the sidewall on normal, non, ".5" tires. A tire like the G2 275x55R20 has a lot of wheel and a rather short sidewall and not expected to have much air reduction before any danger is reached. This means: don't lower the pressure unless you absolutely have to get out of trouble. We have a 2011 Grand Chero Limited with 18 inch wheels and enough sidewall to deflate a ways.
Thanks, because of low sidewall I have always been concerned about airing to far down, I have taken to 22-25 with no problems but haven't tried below there. Our 2004 JGC has 18" wheels and I have thought about switching them with the 2014's 20" to get more sidewall but no decision yet.
 

68camaro

Any River...Any Place
I probably would not go below ~24 psi for trails with any rocks. But, I don’t have any experience to back up this guess.

If driving responsibly on sand, you could go into the teens.
Sent from my iPhone using Tapatalk
About 24 has been my comfort zone, with low sidewalls I worry about going lower but not sure if correct. I guess I can run one and if I blow bead put on spare, testing might be best.
 

rkj__

Adventurer
About 24 has been my comfort zone, with low sidewalls I worry about going lower but not sure if correct. I guess I can run one and if I blow bead put on spare, testing might be best.
In addition to blowing a bead, catastrophically damaging the lip of the wheel is a concern with alloy wheels.
 

Mundo4x4Casa

West slope, N. Ser. Nev.
Thanks, because of low sidewall I have always been concerned about airing to far down, I have taken to 22-25 with no problems but haven't tried below there. Our 2004 JGC has 18" wheels and I have thought about switching them with the 2014's 20" to get more sidewall but no decision yet.
Just be careful of the brake fitment going to a smaller diameter wheel. I just had the brakes done on our '11 JGChero and they are actually 17 inch brakes on 18 inch wheels. The 2012 GC had 18 inch brakes to fit the then 18 inch wheels. jefe
 

68camaro

Any River...Any Place
In addition to blowing a bead, catastrophically damaging the lip of the wheel is a concern with alloy wheels.
Just be careful of the brake fitment going to a smaller diameter wheel. I just had the brakes done on our '11 JGChero and they are actually 17 inch brakes on 18 inch wheels. The 2012 GC had 18 inch brakes to fit the then 18 inch wheels. jefe
Thank you both for heads up. Each will need to be taken into account.
 
Top