Jaynen's Black Gen 3
- Thread starter Jaynen
- Start date
magoh76
Adventurer
I know what you are talking about. Thinking about some spacers in the future, especially if I get a lift.
It's been a few days since this was posted, but I'd still like to recap a warning when switching to LT tires from OE "P" tires. Basically, LT tires will typically require a higher inflation pressure to keep the same load rating as the original P type tire, and an even higher pressure to be able to handle a higher load. This guide is long, but worth a read for anyone switching from OE "P" tires to LT metric (no relationship with Toyo, just really like this guide, which is pretty much universally applicable):
http://toyotires.com/tires-101/load-and-inflation-tables
In a typical example, if you have P245/75 R16 (usually 109 load rated) at a factory recommended 32 psi pressure, each tire can carry 2271lbs, and that's the max, higher pressure won't usually give them a higher load capacity. See pg. 16 on the linked pdf.
Now, if you switch to a LT235/85 R16 and keep the same pressure your tires can now carry 1700lbs each. You've just lost ~25% cargo capacity! This is mostly due to construction and heat management.
Now, the upside is, your new LT's will usually be at least "D" or more typically "E" rated, and now you can go to higher pressures. Per the table on page 20, you'll see you should go to at least 55 psi to be near your OE load rating (2331 lbs). Any less than that your load carrying capacity is less than the original "mall-rated" P type tires. Of course, if the tires have the usual "E" rating you can now go to 80lbs and enjoy >3000lbs per tire for a comfortable safety margin over your vehicle's Gross rating (which of course, shouldn't be exceeded).
I'm no tire expert and I know everyone has a different experience and opinion (especially on that last comment with regards to the truck's GVWR). There are also a million caveats (passenger & cargo load, terrain, etc) but I think that's the main reason you saw such a jump in MPG from increased pressure, your tires were probably underinflated at 3X psi. Also, every disclaimer ever uttered may apply here: Closed course, unprofessional driver, these are only my comments which should not be taken as a rule by anyone ever, and you should always consult your owner's manual and obey all traffic laws, keep hands and feet inside the vehicle when moving, etc, etc).
HTH.
jeep-N-montero
Expedition Leader
You do realize that 1700x4=6800 right? This is 1000 pounds greater than the GVWR of any Montero ever sold, not something I would even remotely worry about.
Indeed it is :sombrero:
Sort of (about 800lbs per my numbers), but you're right, hence my disclaimers.
I don't mean to derail the thread, just thought that the increase in MPG's was quite dramatic and the difference in pressures required for a given load for LT tires may be a large contributor. In any case, 22-23 mpg is awesome (these were rated at 18 IIRC), I'm lucky if I see 19-20 at 65mph or so. I wonder if Jaynen's 32" tires make for more efficient highway cruising vs stock 30.5-31".
The door sticker has pressures for "E" rated tires which I don't think come in passenger variants only LT but these pressures are still like 35ish? The size different for rotational reasons is only 3% not enough to be whats causing the dramatic shift in mpgs. Normally around town and stop and go traffic I am averaging close to 15 with a low around 10. (I have been experimenting with using non premium vs premium since its a premium recommended not required vehicle)
I will say that weight of your wheel/tire combo is usually one of the biggest factors. On my TDI jetta I went to 225/45/17 wheels and tires from the stock 15"s and my mpgs stayed the same because the wheels and tires were lighter even though the wider wheel package had a higher rolling resistance.
So narrower tires+higher psi to reduce rolling resistance I think is going to be where the gain is seen
I will say that weight of your wheel/tire combo is usually one of the biggest factors. On my TDI jetta I went to 225/45/17 wheels and tires from the stock 15"s and my mpgs stayed the same because the wheels and tires were lighter even though the wider wheel package had a higher rolling resistance.
So narrower tires+higher psi to reduce rolling resistance I think is going to be where the gain is seen
jeep-N-montero
Expedition Leader
Keep in mind you need to add about 5-6% to the odometer reading to compensate for the decrease in revolutions per mile with a larger diameter tire. For example, when I went to the 235's on my diesel truck it was a 4% decrease in rotation, so instead of 400 miles per tank it would be 416 miles.
My father in law has run his BFG AT on his superduty at high PSI for years. I think you would have to massively overinflate to get any sort of crowning issue (which is the only thing I think overinflation would cause) at least on my tires 45 is still way below the max you can run. My old rule of thumb was 90% of the manufacturers max for the tire
off-roader
Expedition Leader
Per BFG, the proper way to determine correct inflation pressure is to weigh the rig on a truck scale. One with the kind of scale that tells you the weight at each axle or maybe even tire. Then call up your tire maker and ask what the proper inflation should be for your particular tire at that weight.