Re:Tyre Pressure for 215/75/R15 ?

wrote:

As it's a gen4 the offset of the factory wheels is actually negative 22 

Factory alloys on a gen 4 have an ET/offset of positive 5

Yes we found that out a while ago. I thought I had rectified all the mention of the 22 offset.

wrote:

Yes we found that out a while ago. I thought I had rectified all the mention of the 22 offset.

You did somewhere, must have been a different topic.

Ideal tirewidth (section width) for 7 inch is 245/75 or 255/75
But 205/75 is minimum adviced by the tiremakers.
So your 215/75 is within what they allow.
Max section width " allowed" is 285/75.
Made calculator for that, after contact with a tyremaker, and is also dependend on Hight/Width division, called Aspect ratio.

Needed cold pressure for onroad use is depended on load on tyre and speed used. All to not overheat any part of tyre when driving that reference-speed constantly.
Reference-speed for Q R S T H V speedcode is 160kmph/99mph.

If you give of that tyre next, I will make a pressure/axleload list for you.
1. Maximum load or loadindex.
2. Kind of tyre to determine the reference-pressure
Standard load personscartyre AT 36psi
XL/reinforced/extraload AT 42psi.
Given on sidewall the maximum allowed cold pressure between 44 and 51 psi, and an ocacional XL// 60psi.
C-tyres and LT-tires almost always give reference-pressure behind AT on sidewall
3. Speedcode, less important, have my own system for that.

Then also give if you want it in KG or LBS, and in psi or bar or kPa.

Then you "ONLY" have to determine the axleloads acurate, the most tricky part in it all, and your responsibility.
Carmakers use max permissable axleloads for that, if they not give it higher for energy-saving or responcibility reasons.

End 2007 this " pigheaded Dutch selfdeclared tyrepressure specialist" got hold of the officially used formula and system for calculating needed tyre-pressure, and went running with it.

I have old list of Michelin, in wich pressure loadcapacity list for a specific tyre, for 110 kmph ( K speedrated) down to 20kmph onroad, and for mud/sand about 50% of pressure for 20kmph( 12.5mph) onroad, wich then is maximum allowed speed.
For on track about 80% of the pressure for 65kmph onroad, wich then is max allowed speed.
I write " about" because that is what I made of the lists, would like to know the real system the tyremakers use for that.

Sorry to necro an old thread. I got my new Jimny with Kumho LT215/75r15 they inflated to about 35 psi when they installed them. reading up a general rule of thumb was when going from P to LT tyres add up to 15 PSI from whats noted in the door.

They actually seem to run just fine at these pressures on road if I go for what it says on the door they look like they are a bit flat tbh. I dropped to 15 for sand driving and didnt go above 50kph (mostly around 40 tops)

are people really still saying use what it says on the door for LT tyres when the Jimny comes with P rated tyres normally ?

For starters, I would have tried to avoid LT tires on a Jimny, they are built for "light trucks" (which is what the LT means), so they are heavier and have stiffer sidewalls.

Moving on, I have no idea where you read that you should add 15 psi when going from P to LT, but whoever came up with that needs their head examined, if anything, you're going to need to drop the pressure not raise it - the sidewalls are stiffer, the tires are designed to carry more weight, which the Jimny doesn't have.

If you want to play with the tire pressures, find yourself some chalk and a quiet straight stretch of asphalted roadway - use the chalk to mark a wide band across the entire width of the tire and then drive as straight as you can for a short distance - get out and examine the chalk mark - where has it been wiped away? if it's the center of the tread the pressure is too high, if it's both edges of the tread, the pressure is too low, if it's one edge of the tread, there's an alignment problem.