Hey fellas,

I know there's a bunch of threads out there, and I have read quite a few of them. I just wanted to ask as I don't know if my situation is any different.

I just got a lift with King 2.5s front and rear, TC UCAs, and Icon rear springs. Within a day, I threw on 275 /70 / 17 BFG KO2s onto the stock TRD wheels. The suspension went in last weekend, then the tires on that following Monday. I was told not to do any wheeling till I got at least 400 miles on the suspension. Then go back and have everything retorqued. That happened yesterday. I was ready to get dirty.

I'm in SoCal and often go up to the Cajon Pass to run those trails. I wanted to try out the upgrades so I naturally decided to hit the Cajon Pass. So a couple of things hit me as I was driving up there. First, the 4R was working much harder than I remember it ever having to do. In the week I was to throw on the 400 miles, my MPG dropped from 18.8 to about 17. On the drive up to the Cajon Pass today, it dropped to 15.9. Second thing, the drive does add elevation (although I couldn't tell you how much) and as I heavy-foot the throttle a bit more to keep the speed constant, I see the RPM go to about 3K and stay there, and it never drops below 2K even on the flats.

I'm curious if that's sounds about right to you all. It probably sounds like OCD about my MPG, and maybe some of it is. I knew I was going to lose some mileage but wasn't expecting what had happened today.

Thanks guys for any feedback you all might have.

Bigger tires take more effort to turn. Yes you will lose mpg

The larger tires put your engine out of the optimum RPM range, so power and MPG suffer . To get it back you would need to regear.
Also they throw the tach and odometer off, so your MPG calculations will be off.

LOL ... I understand this. Probably didn't phrase my question clearly?

Guess I gotta read up on regearing. The tach discrepancy I'm not quite understanding. I assume the higher load in rotating these large and more weighty tires would result in higher RPMs, is that not true? Would you explain further please?

Regarding the odometer, and I'll group the speedometer in as I assume they are tied to the same source of information. Anyway, I used to be 2 miles off on my speedometer faster than multiple sources I used to compare the speedo value (e.g., Waze and those speed meters you see on the streets). With the increased tire size, these sources are, if I was to hazard a guess, within .25 MPH. I'm making a big assumption that the speedometer is tied to the same mechanism which drives the odometer.

Going higher and larger tires moves the whole drive train out of the engineering specs. So it has a negative effect on everything. Will also accelerate wear on all parts...

I definitely am planning to keep the rig long-term. Although I've had a 4Runner in the past, this is the first one I've actually put any significant mods into. It's all going to be a learning process for me. Any suggestions you got to help minimize the impact over the long-term, please do share. The drive train impact I'm learning about now

As long as you don't drive like a complete ass hole I'd just drive and not worry. Regular maintenance is all you can do.

Its meant to be driven. (I shouldn't really talk mine is a garage queen and sees the road maybe once a week)

Interesting...i haven’t noticed a shortage of modded Yota’s everywhere running 100% reliable. What empirical data do you have to support your opinion?

If you want a larger tire, but are still concerned about mpg's, the best thing you can do is to shop for a lighter tire. This can come as a P or C load rated tire and/or a skinnier tire like a 255/75/17.

Do you know the load rating on your BFG's?

That's the plan brother. I was hoping against hope that I might lose 2 MPG but it's at 3 now, and I haven't driven up to the mountains but one time...Ha! More than that, I'm hoping I'm not significantly reducing the life of the engine having it run under heavier load.

The BFG's are E rated. I was told the 275s don't come available in any other rating than E. At 265, you have the C and E to choose from. Quite honestly, the 275s kinda suits the lift, if I had to for some reason go back to 265s (or skinny tires), I'd prefer to just put it back to stock height. Yep!

A typo, I meant speedo and odometer

Empirical data is not required, just common sense.

Nothing is 100% reliable, and the only guarantee is there is no guarantee.

It’s physics and engineering… no such thing as a free lunch. Every modification has it’s costs and savings / pros and cons.

People say spacers are fine too, but you are still increasing the amount of leverage there on the hub, which could case accelerated wear of wheel bearings, but the rate in which it would degrade is still dependent of plenty of other factors. That is the cost of a track increase. The savings are increased stability.

With bigger tires and factory spec gearing you just end up lugging the motor a bit more, and it could promote negative effects long terms, but most of us would probably REALLY feel the need to re-gear before getting to that extreme. Going that far "out of spec" is wildly annoying to the user. It's like peddling a bike in the wrong gear.

There are other 275 AT's that are not E rated. Firestone Destinations come in P and C ratings. 265's come in P rating as well. The Firestones are quite a bit lighter than the BFG's. You could probably regain some mpgs with a C or P rated tire.

So the answer is no....you don’t have supporting data other than the old tried and true “common sense” rebuttal.

Load rage E is to much for our light 4runners. I would and did go for load range C after doing lots of research and talking with buddies who made the mistake of going with load range E on their Tacoma’s and 4runners.