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Old 06-23-2010, 12:52 PM   #1 (permalink)
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am i crazy tire sizes

ok i have been driving an old 81 toyota 4wd long bed to work. ever since my 98 taco 4x4 was bought back due to frame rust( the size of a quarter) but that is a different story.

the truck i am driving is has a 22r motor 2.4l (144.4 ci) motor, and a weber 2 bbrl carb, i really like the sound of the second opening up. but that dont help mpg. it is a straight axle 4x4 with 4.88 gear instead of the 3.90 and has 31x10.50-15 tires instead of 225/75/15,
right now at 65 mph i am punching 3000rpm.
do u think a set od 33x10.5 r15 or 32x11.50 r 15 tires would yield better mpg?
with a 32 and my gears the rpm would be about 2800 at 65mph
and 2700 rpm at 65 with the 33's



stock 65 mph would be 2600rpm.

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Last edited by taco; 06-23-2010 at 01:03 PM..
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Old 06-23-2010, 02:44 PM   #2 (permalink)
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I think the tread style would be more important than the size for something like that.
M/T's being the worse, then A/T's, then All Seasons. I guess if they make low RR tires in that size that would be the way to go for mileage, but then it would hardly be a truck. ):

You're compensating for speedometer error when you say MPH at RPM right? Why not just go back to stock gearing?

PS: Love the 'new' truck. Makes me want my samurai back.
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Old 06-23-2010, 04:17 PM   #3 (permalink)
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The first and most important question is what do you plan on using the pickup for?
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Old 06-24-2010, 05:55 AM   #4 (permalink)
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First, the Flotation sizing (looks like: 33x12.50R15LT) means the tires are built like LT type tires - which have a very low priority for rolling resistance. You would be better off with passenger car tires - ones that the size looks like: 225/75R15. Those will sometimes give good fuel economy, sometimes not. It depends on what you select.

To put it generally: Flotation and LT metrics are designed for "Trucks" and that means more attention to tread chip and chunking resistance, high unit loading (more load compared to the physical dimensions), etc. These thiungs are directionally away from good fuel economy.

So unless you are going to use your truck like a truck, you would be better off with passenger car tires.

And if your concern is gearing, why not select a larger passenger car tire - like a 235/75R15 (If they will fit!) Not only would the gearing be better, but directionally, this would be better for rolling resistance.
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Old 06-25-2010, 09:28 AM   #5 (permalink)
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i bought the truck with the 4.88 installed i dont have the stock 3.90.

a 235/75/15 is a 29 inch tall tire, that is way to small to help with my low gearing.
except for a few tires, the taller u go the wider u go also...

main use is 130 mile round trip to work, my drive is 65 miles each way of curvy two lane roads that have a 55mph speed limit. with the occasional off road trip, but nothing to hard.

yeah i am compesating for speedo error. the speedo says i am doing 62 when i am at 55mph according to the gps.

thanks.
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Old 06-25-2010, 11:00 AM   #6 (permalink)
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BFGoodrich All-Terrain T/A KO

Several of my friends have had good luck with these, the 33" range from 9.5 to 12.5 widths, max sidewall on most sizes is 50psi.

If your not hitting too many good sized sharp rocks you might consider an LT tire.

edit: When you go on your trails drop the psi down to about 30-35psi so the bumps don't beat you and your truck up... trust me.
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Old 06-25-2010, 03:31 PM   #7 (permalink)
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yeah that is the only tire i have found that gives ma an a.t tire and that size.

i dont think running on 12 psi would stop it not beating u up off road. much harder than my old 98.
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Old 06-25-2010, 03:36 PM   #8 (permalink)
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Quote:
Originally Posted by taco View Post
yeah that is the only tire i have found that gives ma an a.t tire and that size.

i dont think running on 12 psi would stop it not beating u up off road. much harder than my old 98.
Depends on the trail, I got bruises from one when running 20 front, 15 rear, but then I wasn't always driving on only the tires.
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Old 06-26-2010, 12:00 PM   #9 (permalink)
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but do u think tires that large would help my fe?
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Old 06-26-2010, 10:37 PM   #10 (permalink)
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As a general rule, larger tires give better rolling resistance provided you keep the same inflation pressure. However, you may find that you need to drop the inflation pressure in order to keep the truck from bouncing - and there isn't any data to tell us what happens when you do that.

Nevertheless, the larger diameter is going to help change the gearing of your truck in the right direction. Given how many miles you drive, it jjust might be worth looking at changing the rear gear ratio. That obviously is not helping your fuel consumption.

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