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I have a 1979 2wd f100, this is an old farm truck with a warmed up 6cyl, and actually gets pretty good mileage. In the spirit of that, given recent gas prices, I plan to make my next tires a taller set.
I simply want to know how tall of a tire I can use, at normal, narrow widths. My research brings me to a 235,85,15 however, I've been wrong before. Also, id be interested in pics of trucks on stock rims with bigger tires.
Last edited by Liddykitty; Jun 15, 2022 at 05:09 PM.
It’s a trade off, taller tires will roll you further per revolution, and turn less RPMs at a certain speed. However, they are heavier and take more power to get turning. If your tires are in decent shape, I’d just roll what you have. These trucks will never be a Honda Civic from a fuel mileage perspective, be it an I6 or not. I have 235/75/R15 on my 68 F100 with the 240/3 speed and they ride well. Very common size so relatively cheap. I think the BFG rugged trails I have now were like $85 a piece from the Wally World, but that was a few years ago.
Just doing a Tire Rack search, I do not find a 235-85x15.
It appears 265-75x15 is about the tallest, equaling the wider and heavier 31-10.50x15s at 30.7. Again, I'm not checking all brands or sites.
If you go to 16" wheels you will find the 215 and 235 85 series which gets you to 30.4 or 31.7" diameters.
Beyond that, you start getting into LT tires in larger sizes that gain weight to the point where some of them are almost double the weight of a P235-75x15. No MPG gain trying to turn those.
What tire do you have now?
As with a lot of mods, it's hard to really save gas, and if you save gas, you may not be saving money overall.
Right now i have 235,75,15s, I have no interest in a wider tire. This thing is so light it's will spin if a dog pees next to it, need the narrow tires in the rain or it will hydroplane worse.
Im not sure where i got the idea 235 ,85,15s existed, probably thinking of 16s. Now I'm thinking of 245,75,15s, about a half inch taller and wider.
I'm not planning g on replacing them now, just whenever I buy a new set, my current tires are fine.
Lowering rpms never sounded like a bad thing to me, especially in an inline, ive got the toqure. I get 22 mpg on a good day, without traffic.
Last edited by Liddykitty; Jun 20, 2022 at 11:53 PM.
Great looking truck you got there Liddy! I wouldn't change a thing, maybe 245/75's, I went with 265/70/15's on my 66 just because I like a fat tire in the wheel well, glad to hear you're getting 22, I get about 18 running down the hill to Fresburg n back, but it's a little more "hilly" here. For me, swapping from 3.00's to 3.50's in the rear end brought my power and mileage up, so you don't want to get to far out of the rpm range for the 6.
Thank you, nice truck, I like some meat on my tires, my truck does work on the farm and I do like a tall tire. Easy to plug, cheap, low psi, what's not to love? These things don't handle anyway lol.
Not sure about the rear end, the trans is either a rat or a ran. The motor is warmed up a bit though, chevy rockers, smog delete, more open exhaust, and tuned well. I have plenty of power for something bigger.
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