What is the best way to determine the correct pressure for a non-stock tire size? I've been running 235/75/16 tires on my Disco close to the pressures recommended on the door for the standard size of 235/70/16. Is there a formula to extrapolate an equivalent pressure on a larger tire from the factory guidelines? It's dealing with volume, so presumably nonlinear (i.e. a 5% increase in tire size does not equate to a 5% increase in pressure). I've seen numbers all over the place on this site from different users so anything definitive would be helpful.
pressures for non-stock tire sizes?
- Thread starter Tugela
- Start date
Found this:
http://forums.lr4x4.com/topic/75943-tyre-pressure-what-is-the-correct-pressure/
Kind of maybe helpful.
http://forums.lr4x4.com/topic/75943-tyre-pressure-what-is-the-correct-pressure/
Kind of maybe helpful.
The chalk method a good idea and quicker than trying to monitor your tire wear in other ways.
......
I usually run 32-34 in the front and 35-38 in the rear. I've never had any real tire wear issues over the years.
No need, just run the pressures at which handling is acceptable and hopefully wear is not much.
Factory recommendation of 28/36 or so is mainly aimed at making trucks understeer ever so slightly.
I haven't done the chalk test, but I got very twitchy over potholes and rough road at speed on 255/85/16s when I had them up around 31/32 in the front. Dropped down to 28 and not had a problem since...
When I first lifted the D2 with 255/85R16's, the shop filled them to about 50psi. Driving it could best be described as trying to balance while standing on a basketball. I dropped the pressure to 42/42 and felt much more in control.
45 psi is a notable deviation from factory recommendations of 28/36: 60% higher in front and 25% higher in back than factory. Why do you choose to run higher pressures and what have your results been?
I am not an expert on this subject, but I have observed the difference in tire pressures recommended on my various bicycles. My mountain bike tires (26x2.2) call for a pressure range of 40 - 65 psi and my road bike tires (700c, 23mm) call for 100 - 140 psi. Intuitively a smaller volume tire requires higher pressure to retain structure. The difference in volumes between my mountain bike tires and road bike tires is huge, whereas the difference in volume between stock D1 tires (235/70/16) and my D1 tires (235/75/16) is relatively small.
Higher pressures:
Taller tires have taller sidewalls, hence running them at near-factory pressures will make them handle sloppily on the highway. An emergency avoidance maneuver is a "no big deal" with high pressure, and scary as shit at 28-35 psi.
In a similar sense, 225/75 will handle better at higher pressures than 235/70.
The higher is the pressure, the less likely the tire is unseated off the rim in a side drift.
As a side benefit, tires with higher pressures are less likely to be damaged by an accidental obstacle like an edge of a curb or a brick on the road (or by sharp rocks off pavement).
Front/Rear:
After installing the front TT, I was horrified by the handling of my D1. The sudden change in road slope in conjunction with a curve appeared as an abrupt switch from a severe understeer to severe oversteer. A simple solution to that, suggested by someone on DWeb (and confirmed by an independent source) was to run the front tires at the same pressure as the rears. In effect, it reduced the straight-line understeer, and as a consequence - transition to oversteer.
The numbers themselves depend greatly on the type of tire used. My LR4, for instance, has C-rated tires with max pressure of 50 psi - so I don't pump them over 42. The guys who run versions of Michelin X with rock-hard sidewalls prefer lower pressures.
My front TT is a lot tighter than the rear, so it may not be as much of an issue in general.
LOl.....I had some narrow 285's on mine before the 35's and I took my Disco to get the oil changed. The "nice" people there aired them up to almost 80 PSI which was max on the side of the tire. I Honestly I really didn't notice driving it to wheel but when I got there I couldn't climb $hit.
I decided to air down and that's when I found out :banghead: