Urambo Tauro

Here's a good old trick for fine-tuning tire pressures:

Start with a good alignment and a ballpark guess tire pressure. Mark the tire with a line across the width of the tread. You can use chalk or a silver Sharpie. Drive it, and see how the chalk wears. Try different pressures until the chalk wears evenly. That's how your tires will wear.

Stoenr

Good to see Norm still educating here! I cant seem to find my book that listed the tire size, load rating and the load capacity at said psi. Dont see it online either. Might need to go to my old workplace and see if they can toss me a spare one just for these questions.

ucinn

Well, got the tires mounted now...got to get the pressure right before training the TPMS sensors. If I train them at a certain pressure and then change the pressure later, can they relearn with the sync tool or is it a one and done thing? I didn't realize so much went in to figuring out tire pressures...wow

Norm Peterson

That 35 psi OE pressure does change things a bit.

Front: 98SL @ 35 psi ==> 100XL @ 37 psi
Rear: 98SL @ 35 psi ==> 99SL @ 33 psi

Yes, a 100XL tire is actually "smaller" than a 98SL tire (it matches up with a 96SL tire up to the limits of the SL table). Not at all what you might expect.


I found the tables on line, but it's been quite a while so I don't remember where I found them or what I searched on to get to them. But I kind of cheat anyway, once I got the tables into a little Excel spreadsheet that does all the heavy lookup stuff. I still haven't found the TRA tables, which are for P-metric tires (which aren't the same as either SL or XL).


Norm

ucinn

k, for now I have it at 33 front and 35 rear, I will change them later. The rear tires don't say SL or XL on them so I just figured that meant SL...am I wrong or would thy also be XL's since they are the same brand and model as the fronts?

Norm Peterson

It is SL, which takes a little detective work with the tables and this little scrap of a screen shot from Nitto's 'Invo' page to find. The 'Max Load' number can be tracked back to match one of the tables. One of the reasons I put the max load as a displayed value in the spreadsheet was to simplify this kind of search.


Norm

ucinn

Thanks Norm.. I really do appreciate all the help. I will adjust tonight and reinitialize the tpms sensors for the new pressures.

proeagles

If you want to get real fancy, get a tire pyrometer and measure the tires after normal driving. Take measurements from the outside, inside, and middle of the tread. If the the temps are pretty much the same, you have good tire pressure. If the outer sides are higher, then too low, if the center is higher, too high, adjust accordingly. That is assuming you don't have an alignment problem with too much camber or toe.