GOVERNING ENVELOPE FOR THE OEM
This is partly a function of ( few listed here)
1. Tyre size & vehicle type
2. Tyre construction (material & compound)
3. Tyre type (HT / AT / MT)
4. Load. ( Max axle weight)
5. General usage variances of speed, load , temp etc( not competition etc)
6. Drivability factors and durability...
7. Compliance to MFDD (mean fully developed deceleration)or simply put, distance /time to complete stop.
The above considerations by the manufacturer gives you 29 psi as listed for a vcross 245/70/16
Having said so, this is indicative and need not be followed as gospel truth. Going marginally higher or lower comes with it's own baggage of benefits and pitfalls because the physics is linking each aspect and will not let one piece of advantage come without a flip side to it. So a balance needs to be acquired about what u gain at the cost of what u are loosing and will purely be determined by each user as his priority of one factor over the other. I will not delve into the pros and cons of higher or lower pressure as this is pretty much dug in and established. However temperature plays the monkey here and hence a few words on it.. Primary reason for a tyre to have a temperature rise above ambient when put to general use is the flexing of the side wall. The material absorbs and releases energy each time the wheel rotates once. This is the biggest contributor and each celsius increase will increase the pressure by 0.2 psi or every 5 degrees increases the Tyre pressure by 1 psi.. if you are on stock tyres and rims with recommend pressure, this change is barely noticeable while in use. This is one of the primary reasons to use low profile tyres in competition situations. One other contributor to temperature is "slip". Now I am not referring to visible slip but is a function of friction that lets u go forward Inspite of the fact the wheel is rotating but the patch in contact is stationary ( no relative motion between the road and the Tyre contact patch),. But lateral / longitudinal forces are in action to take you forward. It is a function of friction and slip however when stationary the slip is zero. This really comes to action and contributes to temp rise when accelerating hard, not once but when sustained repeatedly, which is a deviation from real life normal situations and hence is a minor contributor to temp rise. Third of course is the ambient / road surface temp which has a direct impact. Usually very extreme temp variations are not seen in normal use, however if one has checked his Tyre pressure in Drass at Sub zero temps and next day you are down on the gangetic plains at 40 + C temp, you will have to recheck and bring the pressure back to the one you set in the mountains. For those who feel the ride in a vcross is hard can go south on the pressure and visually ensure the bulge is not too much ( no need to put sand bags) and if still not satisfied start by removing the shortest leaf in the leaf spring pack. Remember we bought a truck and it's dna / personality comes with it.... Coming back to what psi, trick is to see a small bulge and suitable ride quality and go from there... U will not go wrong...lower mileage or a bumpy ride... Your personal call Good luck Yield and drive...
Gyan Madan
@ www.prakashgyan.com
