Buck01

I was getting between 19 and 21 MPG.
When I figured that milage I did NOT take into account the 31x10.50 tires I was running.

Then I found the milage calculator that someone here created.(sorry cant remember who)


I went back and recalculated some of my milage.
Taking into account the tire size difference.

I went for 20.39 MPG not counting tires
to 20.65 counting the tire difference.

not alot of difference.

I did a 3 inch BL and put 33x12.50 tires on. So I decided to see how bad I was doing on milage now.

I have only run one tank so far.

I am getting 17.36 MPG counting the tire difference.

so far it looks to be a 3 MPG hit with the bigger tires.

The questions becomes....

If I regear....will I regain that 3 MPG or more?

and how many miles will it take to offset the cost of regearing????

ALOT I would imagine.

Just thought I would share a little info for those thinking of going to bigger tires.

MadCityRich

How are you counting the tire difference? You should end up with about a 10% correction factor between 31 and 33 inch tires. Thus, if your odometer says you went 100 miles, you really went 110.

MadCityRich
'95 3.0 pickup
5 spd
4.88 gears
31x10.5
big ass rear bumper
manual hubs
other crap

kyle_22r

you may get it back, as regearing takes a lot of the load off your engine.

Buck01

Madcity
I am using this milage calc. That would be a 20% correction from stock. Correct?
http://midiwall.com/4Runner/mpg.html

Kyle
I understand I MAY get the milage back by regearing. Is it worth it and how many miles\tanks of gas would it take to offset the cost of re-gearing?

midiwall

Umm, the math behind that page is really simple and it doesn't take into account things like the rolling resistance in the tire compound, actual surface area on the road, etc.

I mention this 'cause you moved from 31x10.50 -> 33x12.50. Outside of a basic 2" in diameter change, you also added 2" in width, so the overall contact patch of the tire is much larger, thus increasing friction even more.

Like was talked about in the thread where that calculator was introduced, it is _NOT_ designed to show MPG differences, it's designed to ONLY take into account ODOMETER differences based on the simple diameter difference in the tire.

I should probably mention all that on the calculator page.

AH64ID

Are you using the rolling radius of a tire when you convert the difference? My 35" BFGS only roll as a 33.7" tire. That will affect your math a little. BFG says their 33 is a 31.7 rolling radius tire. And 225's are ~ 27.5. That equates to a 15% differnce from stock, assuming your speedo was accurate stock. On another thread we are discussing speedos and people are saying they read fast from the factory. The best way to tell is to use a GPS, borrow one if need be. Then you will know for sure what %age your speedo is off. Between 31's and 33's there is about a 6% difference.


Midiwalls claculator is great, but you have to use rolling radius there too, which is why his base calibration is 30.6. You would put 27.5 there and 31.7 in the current tire size.

There is no way to tell if you would gain all the mileage back, and there is no way to tell how long it would take to pay off.

I am able to get 18-21 with my 4" susp lift and 4.88's with 33's in the winter. I get about the same with 35's in the summer, but I also take about 400lbs of sand and chains out of the bed.

With a regear your truck will drive closer to stock as far as performance, 33's are heavier and will take more to turn regardless.

AH64ID

But regardless of differnces is road resitance, it pretty cut and dried as far as how much the odo read and the amount of fuel you burn. It is a good way to accuratly tell your mileage, just not a way to estimate what you would get if you did go to larger tires. Regardless of gearing, bigger tires take more to turn.

midiwall

Agreed...

Buck01

Midiwall
but if that corrects odo readings then it should be a fairly accruate MPG calc too right?

I am not saying these numbers are exact but as close as I can get them given all the variables.

AH64ID

I have been following that speedo thread also.

I think these numbers are as close as I can get for measuring MPG.

I am not to worried about performance or MPG right now. I was just offering my results for others who are thinking about lift and tires. However flawed the measurement is.

I like the way the truck looks with the lift and tires.

I am looking at a couple of 488 3rds. If I can get them at a decent price I will install them. If not it will wait for now.

It would be nice to be able to figure the cost of regearing and the miles and amount of gas that would be saved to see how long it would take for the gears to pay for themselves but I am not sure how to even begin to measure something like that.

midiwall

Yeup, but it's not a prediction tool. I think that's where things got off kilter in the other thread. It'll correct the ODO reading for the difference in tire circumference, but not predict the mileage you'll get when moving to 40" swampers.

Buck01

Gottcha.. : )

AH64ID

I was thinking about this on the way to work...so here goes... this is all realtive, you can change the numbers to what you spend/see.

So for the sake of the math lets say its 1,000 to put the gears in, gas is 3/gal, your tank is 15 gal and you get 1 more mpg from the swap, 17 to 18. So you are able to go 15 more miles per tank, for the same cost right. At the new mpg, 18, thats essectially .83 galons saved, or about $2.49 per fil. Each fill is now 270 miles. So 1000 bucks divided by $2.49 is 401.6 tanks, or (tanks * miles/tank) 108,433 miles until you break even. Now half that for 2mpg increse, still 54K. You get the idea.

And yes, the looks are much better with a 3" and 33's. I am more go than show, but I LOVE how my rig looks on 35's.

Also if you have been following the other speedo thread you saw the link to my spreadsheet.. Play with that. You can get lots of info from it.

One last thought... I dont know how much you wheel so this might not work but... If you dont use 4wd very often and arent a wheeler you could just buy the rear gears when you get a deal, then find a deal on fronts.

kyle_22r

it'd be worth it for the performance alone.

AH64ID

Agreed. I had to run stock gears for about 3K one summer when my 4.88's were in the shop, mad I was HAPPY to get my gears back...

Buck01

I dont see that MUCH difference around town. Of course I am not racing from light to light either. The big difference is on the highway...the truck is REALLY gutless there.

AH64ID

Gears help on the fwy, but not as much as I would like....

Buck01

AH64ID

I use 4WD drive fairly regularly but not for trail riding or anything like that...I use to get to and from the house...

I live on a really nasty little cow path of a road...1 mile up hill to the house..

the rain runs down it and makes a muddy mess. This is bad enough..then in the winter the snow gets on it and stays forever..no sun hits the road...then a warm spell and it starts to melt then freezes overnight and then a really fun ride down the hill in the mornings.

I had thought of the idea of just doing the rear for now. Great minds think alike.
I just know if I did that then I would need 4WD and not have it.

I know if it was muddy enough I could probably use the 4wd with different ratio's but dont really want to chance it.

Buck01

AH64ID

On the note about cost of gear swap. That makes me think even more about the benefit of gears. If I have to put another 108,433 miles on the truck. That would be well over 300,000 miles. Now I hope the truck lasts that long but that is a lot of miles.......

Of course when you figure how much I have spent on the truck already I guess it isnt to bad.

lol : )

-MaTTi-

I noticed any differences between stock w/265/70R15 and BL+33x10.50R15. I still get 25-27 mpg at summer time. Gears are 4.10:1.

AH64ID

[jealous] I was trying to figure out how you get killer mileage, ah yes the whole compression ignition thing [/jealous]