edeslaur

285/75r16s. With 4.10, 13-13.5mpg, OD wasn't useful until around 80mph

With 4.88s, 12.5-13.5, OD now useful, but truck won't go as fast as easily. BTW, OD is 20%, jump between gears is a smidge over 16% (I had 20 here, that was wrong).

During the 200 mile breakin, TPS went bad. New TPS barely had enough adjustment to work (all the way down), but it tests fine per
http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

Please tell me I can get back to easy 90mph and 16-17mpg like I had with 4.10s and both 225/75r15 and 245/75r16s.

The speedo went back to beIng right, FWIW.

T_F_E

easy 90? with 31's and 4.10 I dont think that 60 is always easy....

xxxtreme22r

there is a big difference in weight between 33's and 225's, just sayin.

highonpottery

iTrader: (1)

^and more wind resistance from the extra height.

JBurt

And make sure you're using the right way to figure out mileage. The 33's are about 13% bigger than stock so when you take your milage that you've driven, multiply that by 1.13 before you divide it by how much gas you put in. You have to do a similar operation for the gears but I've never sat down to figure it out. Stock gears for me.

Plus the 33's are a lot heaver so you're rotational mass is increased, which makes a big difference.

If you really want to make sure you're getting the best mileage, make sure you're truck is running right, i.e. plugs, wires, air filter, maf claning, tb cleaning, seafoam, compression test, etc.

edeslaur

Mine's a turbo.

Gearing-wise, 285/4.88 (33") combo is easier to push than 245/4.10s (~31" tall). And it is definitely easier than 285/4.10, which pulled 90 just fine.

Gas MPG is my main concern at the moment. I figure I solve that, my top speed issue will get resolved too.

highonpottery

iTrader: (1)

If you want better gas mileage stop driving at 90mph or get a commuter car. My corolla does 90+ just fine and gets 35mpg. How about driving a tank at only 70mph and see what happens?

I also think tuneup may help. You *should* be back near where you were with stock tires and gears, but maybe 1-2mpg less due to much more rotational mass. So that's somewhere around 15mpg.

4x4climber

If your concerned about gas milage stop going so friekin fast! geeze. i guarantee... you drive 65mph and you will get 17-20mpg with your setup. i get 20mpg at 60-70mph... anything over that and it goes down REALLY fast. These trucks don't mind rpm's as much as they do trying to go fast. BRICKS are NOT aerodynamic.

and do yourself a tuneup if ya havent done one lately..

if you are concerned about gas mileage THAT much buy a spare car. a 1990 mazda protege 4 banger... my buddy consistantly gets 40-41mpg in that thing. with 5 guys n a full trunk or empty...

me:33x12.5x15 bfg m/t on 4.10 with steel wheels and i haven't seen LESS than 15... and that is romping around haulin booty and offroading included in a tank......

edeslaur

Thanks - please let me know if I missed anything:

Rotational mass is definitely higher. 33s would be lighter than these 285s are. But it shouldn't make a significant difference to top speed
http://www.w8ji.com/rotating_mass_acceleration.htm

New motor, new turbo, has been running great. Only change was bigger tires, then bigger gears and a 3" lift at the same time (yes, I didn't point that out and yes, it will affect my top speed and mpg).

285*.75*2/25.4+16 = 32.8"*pi=103" circumference
225*.75*2/25.4+15 = 28.3"*pi=88.9" circumference

That's 16% difference between stock and what's on there now, by calculation. I get tires aren't exactly what they say on the sidewall, for instance very early Kumho ATs 31s were actually barely 30" tall.

245s were easy to push around. They were bigger than stated, nearly 32" tall unloaded. But we'll keep the same methodology.
245*.75*2/25.4+16 = 30.5"*pi=95.77
95.7/103=7% less circumference than the 285s.

Given all that, 4.88s should have brought this truck back to much better than 245 performance since the jump from 4.10s to 4.88s is 16%, more than double the difference between the 245s and 285s, and the same from stock to 285s.

However, the speedo reads a couple mph high at 50mph (that's as much as 4%) after 4.88s and 285s.

So... gas MPG.

With 33s and 4.10s - miles*1.16/gallons = true mpg
With stockers - miles/gallons = mpg
Currently - miles/1.04/gallons = true mpg (if you go by speedo instead of measurements).

So I'm just ignoring the 4% loss (speedo reads high, so I have to take out the about 4%, which would mean less than 12.5-13.5) to get my current 12.5-13.5mpg and just doing straight math since that's what gears and tires say it should be.

Air resistance for sure is a factor at higher speeds (it did go up 3" with the lift I failed to mention, but I don't have a quick and dirty way to calculate difference).

Since my commute doesn't get over 50mph, wind is not that significant a factor in mpg, especially since I'm following others (even less wind concern) and climbing hills.

At 90, it sure can be since wind force is 9x stronger at 90mph than at 30mph.

But it doesn't explain a 3-4mpg loss in my commute tho.

Unfortunately, I didn't pay attention while I was babying the gears since i was running with the front hubs locked and with it in 4wd on the higher speed stuff.

I think it's related to the TPS since it's not quite right yet, and it went out during the gear breakin period.

But it tests out, so I'm not sure what to make of it.

edeslaur

Yer. Note my driving has not changed since I bought the truck.

2 problems.
1. Gas MPG commuting (no 90mph) has dropped a lot.
2. top speed has dropped a lot. I don't go 90 everywhere.

My motorcycle pulls 40-48mpg, but that doesn't help me when I go to the desert in my 4Runner with its 17 gallon tank.

xxxtreme22r

if your geared, mpg has to be calculated a different way. I have to think about for for a little bit though. Also keep in mind if this is a mix of highway/city driving you might be somewhat in a window where your gas mileage would stay the same overall.

For example city mileage would improve from 4.10 to 4.88 since it's now easier for the engine to turn those tires, while highway mileage would drop since you'd be pulling a higher engine rpm at speed.

Running 33's with 4.10s here and my city mileage is around 13-15 mpg (corrected) and my highway mileage is about 23-25 (corrected) and this is with a 22r and not a 22re where the 22re mileage would actually be better. If I were to jump to 4.88's I'd be willing to bet my city mileage would go to about 18-20 while my highway mileage would go to about 20-23.

tj884Rdlx

i recently regeared to 4.88s for my 33s. there wasn't much improvement in MPG.

remember that regearing only manipulates the RPMs at which your engine turns for a given road speed.

changing the rear diff ratio will allow your engine to turn at closer to stock RPM to MPH ratios. any improvement in MPG will only come from YOUR CHOICE to take advantage of the fuel economy found at lower RPMs.

but if you're putting your foot into it, pushing the truck to cruise at higher MPHs, any gas savings you could accrue would vanish. you're still attempting to push a brick through the wind with a ~100HP engine.

keep it under 65 MPH and you'll see the MPG improvement you seek.

my 4R had 235/75s when I bought it, and i went up to 31s, then to 33s which i ran for a year before regearing 4.1 --> 4.88. the gear change resulted in better acceleration and better match of power curve to shift points, but not much in mileage improvement.

so i then investigated tweaking the timing, and increased to about 8*. THAT improved power "feel" and mileage a little.

only taking it easy on the skinny pedal will improve your MPG. incidentally, with a NEW 22RE rolling about 15k mi, on 33x10.5s, i'm getting 14-17 MPG. 17 ONLY when i stay off the interstates and keep it under 55 MPH throughout the whole tank of gas.

4x4climber

You are from Sandy Eggo correct? We should go off-roading sometime.

4x4climber

if you bought that tps at autozone or carquest or napa or something i mite have to bust out the pistol whip... and tell ya to at least try an oem one... a used working one...

as far as aerodynamics. if you are goin 55 in a brick you have ALOT of wind resitance. 70 you have a crap load.. pick it up off the ground even a little bit and it makes a big difference.try coasting down a minor grade at 45... then 55... then 65... then 75.... in neutral.... let me know where you start to DRASTICALLY slow down from wind resistance..
I would say a 3" lift could definitley drop you a couple mpg. if you are an ifs truck it would make even more difference... since your cv's are also gonna be dragging more and the extra angle... every little thing makes a difference.

btw.... 285's are more like a 32... depending on what brand you buy you may get the 32.8 they are supposed to be but i doubt it. 33's are usually at least 32.5 inches. my 33's are 33's when on my truck from ground to top of tire. always measure them inflated and mounted...

i still think with all that said that if your truck was running good and had new wearable parts and a tuneup and good fluids in everything and all that... you should be getting 15-16