Would regearing help with MPG for larger tires?

[dyizhere]

Just a thought. I stepped up to the 265/70/17 already and noticed a hit on MPG already (about 2ish MPG). I understand this is contributed to the increased tire size strain due to the stock gearing, rolling resistance and lastly by the amount of distance covered by the larger tire is not accurately displayed by your odometer. I get all that. I was thinking about going up to 275/75/17's next go around with a lift of course. My question is could you not re-gear the diff to compensate and help the truck think it is running stock 265/65/17's? Anyone have any experience with this? This should fix the power loss and MPG due to gearing disadvantages and secondarily make your spedo/odometer correct again. This should get your engine RPMs back in the RPMs back in the engine's ideal torque band that it was designed to and thus the MPG it was rated at right? You would only be fighting the rolling resistance.

This may have already been addressed already but I figured I'd ask anyways. Thanks!

 

[jwyshrek]

don't forget increase mass of the larger tires.

Regearing will help correct the odometer and the perceived power loss, but not significantly for the MPG.

see this:

http://www.toyota-4runner.org/4th-gen-t4rs/149710-11-2-mpg-avg-after-lift-ride-height-question.html

They are called the laws of physics for a reason...

 

[WXman]

I've regeared a couple of Jeeps. I can tell you there's a lot more involved that just matching the tire size/gear ratio back up again. I think that the small increase in city MPGs you'll get will be over-ridden by the loss of MPGs on the highway from turning higher RPMs...plus the cost of regearing takes a LONG time to break even on.

I would only recommend regearing if you just simply need more pulling power.

 

[ebg18t]

I think that the small increase in city MPGs you'll get will be over-ridden by the loss of MPGs on the highway from turning higher RPMs...plus the cost of regearing takes a LONG time to break even on.

2nd this.

I priced out re-gearing and it isn't cheap. I 'may' do it when/if I do lockers. But I can't justify it on its own.

 

[nevada]

absolutely, without a doubt it will help your mileage.

i run 35's on my 85 runner, and can still get 21mpg hand calculated.

its also better for the engine, and transmission. everything working in the rpm range it was designed to.

 

[JB.]

Just a thought. I stepped up to the 265/70/17 already and noticed a hit on MPG already (about 2ish MPG). I understand this is contributed to the increased tire size strain due to the stock gearing, rolling resistance and lastly by the amount of distance covered by the larger tire is not accurately displayed by your odometer. I get all that. I was thinking about going up to 275/75/17's next go around with a lift of course. My question is could you not re-gear the diff to compensate and help the truck think it is running stock 265/65/17's?

The effective gearing change you just performed (larger tires) already helps your mpg. It just can't overcome the other factors that have dropped it.

You're now rolling at lower rpm on the freeway and the shift points take place at lower rpm. Whatever the mpg drop has been, about 1/2 mpg of that is attributable to the odo calculation adjustment you haven't done yet. Currently, my total GPS derived adjustment is 5% (add 5% to odo). About 2/3rds of that is for the 265/70/17 tire with the remainder being an adjustment for the stock odo setup.

 

[fourwd1]

Just a thought. I stepped up to the 265/70/17 already and noticed a hit on MPG already (about 2ish MPG). I understand this is contributed to the increased tire size strain due to the stock gearing, rolling resistance and lastly by the amount of distance covered by the larger tire is not accurately displayed by your odometer. I get all that. I was thinking about going up to 275/75/17's next go around with a lift of course. My question is could you not re-gear the diff to compensate and help the truck think it is running stock 265/65/17's? Anyone have any experience with this? This should fix the power loss and MPG due to gearing disadvantages and secondarily make your spedo/odometer correct again. This should get your engine RPMs back in the RPMs back in the engine's ideal torque band that it was designed to and thus the MPG it was rated at right? You would only be fighting the rolling resistance.

This may have already been addressed already but I figured I'd ask anyways. Thanks!

Regearing the diffs is the only correct answer. As you surmise, regearing with the proper ratio puts the engine back operating in the power band it was designed to, restoring lost power and mpg, and correcting speedo error.
Since it's not an inexpensive endeavor, it's certainly not worthwhile if you're just running a tire 1 or 2 sizes larger than stock.
Figure about $500 per diff for parts and labor if you pull the diff and carry it into the shop.

 

[ran]

My 265/70-17 Destination A/T cost me 3 MPG.

2007 SE V6

 

[BlackWorksInc]

How does regearing affect top speed?

i.e. I am planning on 35's in the future for the 4Runner, wanna regear it to get some low end acceleration/torqueyness back; but don't want to sacrifice power on the top end either...

 

[Jeremy556]

How does regearing affect top speed?

i.e. I am planning on 35's in the future for the 4Runner, wanna regear it to get some low end acceleration/torqueyness back; but don't want to sacrifice power on the top end either...

This is a total WAG on my part (I don't think my 4r has been above 85), but I'm thinking the 4Runner is going to be drag limited, so regearing this way will probably increase top speed.

Even if it is RPM limited (which I highly doubt), the regearing will greatly improve performance right up to top speed.

 

[nevada]

How does regearing affect top speed?

i.e. I am planning on 35's in the future for the 4Runner, wanna regear it to get some low end acceleration/torqueyness back; but don't want to sacrifice power on the top end either...

theoretically, it would put the top speed back to where it was when stock.

as said above, you may see a slightly higher top speed with the lower/correct gearing. but, the v8 has gobs of torque, so with a long enough road, it may still top out with oversized tires. but it would be WORK.


i dont understand the people that say regearing is too expensive, or that it will take too long to recover the cost. you spent how many 10's of thousands on the vehicle, and then again how much on a lift, and oversize tires?
and yet a $1000 to get it back operating CORRECTLY is too much?

 

[WXman]

theoretically, it would put the top speed back to where it was when stock.

as said above, you may see a slightly higher top speed with the lower/correct gearing. but, the v8 has gobs of torque, so with a long enough road, it may still top out with oversized tires. but it would be WORK.


i dont understand the people that say regearing is too expensive, or that it will take too long to recover the cost. you spent how many 10's of thousands on the vehicle, and then again how much on a lift, and oversize tires?
and yet a $1000 to get it back operating CORRECTLY is too much?

Well, the reason is because the question was asked in reference to fuel economy. You spend money on tires, you spend on a lift, now you're spending on more gas, and then to top it all off you drop $1,500 (the going rate in most places for a regear) to maybe get back 1 MPG? It's just not economical.

If you are WAY lopsided in gearing it will help. I had a 4-cylinder YJ that was underpowered to begin with and it had 33s on it when I bought it. Was getting a hand calculated 13 MPGs. I put 4.88 gears in it myself and started getting 18-19 after that. BIG difference. But that was because it was severely underpowered to begin with.

On my 2011 JK I put 33s on, lost 2 MPGs, regeared to 4.88s, and didn't get back a single MPG. Total waste of money. And on top of that, the regear opened up a whole new can of worms because the extra RPMs of the driveshafts created a vibration issue that turned out to be a nightmare to get taken care of.

I also helped my buddy regear his '98 Tacoma to 4.88. So I have some experience with what the person who started this thread is asking about and just based upon my experience I don't think it's a good idea to drop the cash hoping to get mileage back. He's going to be $1,000 to $1,500 deep in the mod, might have side effects he didn't plan for, and will be very disappointed when he realizes that he didn't pick his mileage back up again.

Getting the engine back into it's powerband is a good thing, but it's not going to make it like rolling on 265/65 HT tires again. You're still fighting the added unsprung weight and rolling resistance and the regear doesn't negate those affects.

 

[fourwd1]

i dont understand the people that say regearing is too expensive, or that it will take too long to recover the cost. you spent how many 10's of thousands on the vehicle, and then again how much on a lift, and oversize tires?
and yet a $1000 to get it back operating CORRECTLY is too much?

For a lot of people, yes.
After putting out a lot of money for tires and/or lift, the money tree may be bare for awhile. Paying a few more dollars a fill-up at the pump every other week can be easier on the wallet than throwing out $1K or more all at once.

 

[BlackWorksInc]

By the way, what good heavy duty Ring and Pinion sources are there for us?

 

[nevada]

Well, the reason is because the question was asked in reference to fuel economy. You spend money on tires, you spend on a lift, now you're spending on more gas, and then to top it all off you drop $1,500 (the going rate in most places for a regear) to maybe get back 1 MPG? It's just not economical.

If you are WAY lopsided in gearing it will help. I had a 4-cylinder YJ that was underpowered to begin with and it had 33s on it when I bought it. Was getting a hand calculated 13 MPGs. I put 4.88 gears in it myself and started getting 18-19 after that. BIG difference. But that was because it was severely underpowered to begin with.

On my 2011 JK I put 33s on, lost 2 MPGs, regeared to 4.88s, and didn't get back a single MPG. Total waste of money. And on top of that, the regear opened up a whole new can of worms because the extra RPMs of the driveshafts created a vibration issue that turned out to be a nightmare to get taken care of.

I also helped my buddy regear his '98 Tacoma to 4.88. So I have some experience with what the person who started this thread is asking about and just based upon my experience I don't think it's a good idea to drop the cash hoping to get mileage back. He's going to be $1,000 to $1,500 deep in the mod, might have side effects he didn't plan for, and will be very disappointed when he realizes that he didn't pick his mileage back up again.

Getting the engine back into it's powerband is a good thing, but it's not going to make it like rolling on 265/65 HT tires again. You're still fighting the added unsprung weight and rolling resistance and the regear doesn't negate those affects.

hahaha. no dude. you are wrong.

driveline vibrations from extra rpms? try again. it wont be spinning faster than when the stock tires, and gears were in place. this is assuming you geared it back to stock.
the vibration was from an improper pinion/driveline angle.

 

[SSt4r]

This is a total WAG on my part (I don't think my 4r has been above 85), but I'm thinking the 4Runner is going to be drag limited, so regearing this way will probably increase top speed.

Even if it is RPM limited (which I highly doubt), the regearing will greatly improve performance right up to top speed.

The 4runners are speed limited (to 118 if I rememberolice but it could go faster so a minor change in the gearing wouldn't affect top speed.
Anyone figure out how to defeat the speed limiter?

 

[Jeremy556]

The 4runners are speed limited (to 118 if I rememberolice but it could go faster so a minor change in the gearing wouldn't affect top speed.
Anyone figure out how to defeat the speed limiter?

I don't think mine will go 118 unless in freefall.

 

[nevada]

By the way, what good heavy duty Ring and Pinion sources are there for us?

are they not just a standard 8"?

i havent looked into the newer ones...

The 4runners are speed limited (to 118 if I rememberolice but it could go faster so a minor change in the gearing wouldn't affect top speed.
Anyone figure out how to defeat the speed limiter?

seriously? theyre limited? makes sense i suppose.

I don't think mine will go 118 unless in freefall.

the fastest ive gone is 80....but, i expect it would top out the speedo EASILY, and have plenty to spare.

 

[nevada]

Just a thought. I stepped up to the 265/70/17 already and noticed a hit on MPG already (about 2ish MPG). I understand this is contributed to the increased tire size strain due to the stock gearing, rolling resistance and lastly by the amount of distance covered by the larger tire is not accurately displayed by your odometer. I get all that. I was thinking about going up to 275/75/17's next go around with a lift of course. My question is could you not re-gear the diff to compensate and help the truck think it is running stock 265/65/17's? Anyone have any experience with this? This should fix the power loss and MPG due to gearing disadvantages and secondarily make your spedo/odometer correct again. This should get your engine RPMs back in the RPMs back in the engine's ideal torque band that it was designed to and thus the MPG it was rated at right? You would only be fighting the rolling resistance.

This may have already been addressed already but I figured I'd ask anyways. Thanks!

also, i dont know if it was mentioned in this thread, but your speedo is now reading slower. its showing less miles than you've actually gone. so that is going to change your perceived fuel economy.

 

[Johnny4runner]

also, i dont know if it was mentioned in this thread, but your speedo is now reading slower. its showing less miles than you've actually gone. so that is going to change your perceived fuel economy.

Exactly. Your fuel mileage won't be correct with larger tires. It will be low b/c the computer thinks you are driving slower / less miles than in reality. This compounds the drag effect of larger tires, more rotating mass and being higher off the ground.

Also I'm pretty sure regearing in a 4th Gen won't correct the speedo b/c the speed reading is taken at the wheel hub, not at the drive shaft (like a jeep).