3rz auto gearing advice

Hello just looking for some advice from everybody on rear gearing. My truck is a 3rz auto on 265/75r16. The main issue id like to solve is I actually get worse hwy mpg than city which i think is due to dropping 2 gears at every overpass and one gear on some uphills that seem flat.

These trucks in auto came with 4.56 gears im wondering if 5.29 or 4.88 would be better? From my calculation the 5.29 would correct my speedo without having to change the speedo gear so was leaning towards that.

Any advice?

 

My '02 Tacoma Ext.Cab w/ 2.7, Auto w/ECT ,4x4 w/ 265/75r16 Goodyear Wranglers Ultras has 4:56 Grs. I AVG. 16-20 Mpg. but a little less in Winter Temps. I Always have the ECT OFF unless I'm cruising for a long time on Xpressway Type driving . Eliminates the Up/Downshifting. Hope this helps.

 

I only use ect power on for towing. I used to average 20mpg combined but always had better hwy mpg now i get like 19-20 city and 16 hwy lol. Thanks for the info though i never really thought of something like that button affecting downshifts

 

It sounds like your math is off. 265/75r16 is only a teeny bit bigger than stock (I'm assuming stock was 265/70r16)--not enough to warrant a jump from 4.56 to 5.29. Part of the reason a 265/75 is popular is that mot people don't feel the need to regear (or do any other mods) to support it.

I like http://www.grimmjeeper.com/gears.html for comparing different tire size/gear combos.

How are you counting MPG? Remember that the odometer is also affected by tire size and gearing changes--if you're using the odometer and gas pump to calculate MPG at fill-ups, your numbers are skewed.

 

The trucks speedo has always been off 8% with the 265/75 it is off 12% my mog is adjusted accordingly. This is measured via an otc genesis shop scanner direct from the vss and a gps for the actual vehicle speed. Aside from dumping the two gears on uphill which is insane cuz im in florida, the truck drives just fine and is up to date on all tune up procedures including diff and trans fluid. The calculation i was referring to is that a jump from 4.56 to 5.29 would adjust the speedo the 12% that it is off and make it perfectly accurate

 

I have a reg cab auto 4x4 with 4.10 gears on 31x10.5 ko2’s. I get 15 city and like 16 hwy. I always turn on ect with freeway and hilly places. It’ll hold the gear longer as opposed to lugging it trying to get up to speed on a hill. Your truck though is close to stock so id say 4.88 if you want more torque off the line but your rpms will go higher and you will actually get worse gas mileage. If mpg is your concern then I wouldnt regear.

 

Well the reason for the regear is to keep it in gear longer so it would affectively lower rpm on the hwy and increase it in city but at 70mph i spend a fair amount of time at 4k+ rpm cuz it jumps down to second gear

 

I know I have probably beat this horse to death, but using current commercial grade GPS for something like "actual speed" is flat out incorrect. Positioning has gotten a ton better- most devices will say they are accurate within 5m (16.4') now, but that is a best case scenario condition. In practice, and especially while trying to do something like measure speed of a vehicle on a road way with other vehicles, buildings, trees, overpasses, etc in the way, the accuracy is far worse. The software between the receiver antennas and display is doing a lot of tricky things to make it seem more accurate and smooth, and they've gotten pretty good at it. But you still could be anywhere in a 5m (best case scenario) radius from ping to ping.

 

Ah, so maybe your truck didn't have 265/70r16 from the factory. I thought that was the standard size by 2002, but I could very easily be wrong about that. Maybe it had 225/75r15?

Assuming it had 225/75r15 with 4.56 from the factory, then according to the Grimm Jeeper calculator, you should be in the following RPM ranges in 4th gear at 70mph actual speed:

225/75r15 w/ 4.56 -> 2690rpm

265/75r16 w/ 4.56 -> 2400rpm
265/75r16 w/ 4.88 -> 2575rpm
265/75r16 w/ 5.29 -> 2790rpm

Based on that assumption and math, either 4.88 or 5.29 will get you closer to factory; neither will get you exact. I'd guess that either will drive fine. 4.88 will probably get you slightly better fuel economy. 5.29 will probably get you better driving experience at speeds under 70mph, but you'll be spinning almost 3200rpm by the time you reach 80mph.

Sounds like you've done your homework already, you just need to choose what you want.

 

Ok thanks for the help i know with the original tires it was supposed to be 2000rpm at 55mph now its about 1900. I know with the 3rd gens everybody seems to do 5.29 because of the transmission hunting issue i might just go with the 4.88 seems more common on 1st gens was hoping to find some people that had experience with the 5.29 on first gens but most people I found are third gen or 4Runner.

 

Don’t have a 1st gen, so take this for what it’s worth. I do understand gearing and most vehicles are the same in that regard so long as you take into account the pertinent engine, trans, axle and tire details.

If your tires were originally 225/75R15, they would be 28.29”. 265/75R16 are 31.6”. I take an inch off each when using the gear calculator as I’ve found most tires are around an inch short. I’ve had the best real world rpm calculations that way.

225/75R15 (27.29” entered in calculator) on 4.56 gears equates to 2790 rpm at 70.

265/75R16 (30.6” entered) on 5.29 gears equates to 2887 rpm at 70.

265/75R16 on 4.88, equates to 2663 rpm at 70, i.e. worse/lower than stock.

I’d go 5.29. It’s a 4 cyl, it has minimal power and doesn’t mind revving. I’d let it rev and enjoy the slightly higher torque advantage vs what the truck had stock.

 

Your gonna get worse gas mileage, the rpm will go higher every shift. Get a sc if you hate the shift points, or just live with it with ect like me.

 

You sure it came with 4.56 gears? Have you verified? Most came with 4.10. 4.56 sounds like it would be perfect in your case.

 

Sorry should have been more specific, its a 2002 and from what i have found they stopped using 4.10 on the 3rz when they did the update to the tacoma in 01 with the exception of manual 4x4. But to be certain i have both checked the door code and spun the wheel after chalking.

 

These are generalizations based on my observations. They are not guaranteed to be true, but they're reliable assumptions in my experience...

4cyl+auto gets 4.56
4cyl+manual gets 4.10 pre-2000 and 4.30 2000+
v6 gets 4.10 regardless of auto or manual

(for whatever it's worth, 3rd-gen 4Runners seem to follow the same pattern, except that the TRD trim got 4.30 instead of 4.10)

The auto and manual have significantly different overdrive ratios (4th in the auto is 0.71, 5th in the manual is 0.85 for the 4cyl, 0.84 for the v6), so an auto needs a final drive one ratio higher than an otherwise-equivalent manual to keep similar RPM on the highway. In other words, given the common ratios of 4.10, 4.30, 4.56, 4.88, 5.29, an auto with 5.29 final drive will maintain similar RPM at highway speeds as an otherwise-comparable manual with 4.88.

 

this is about right just that my 97 reg cab auto 4x4 base trim came with 4.10’s. I believe later models like 01-04 got the 4.56 gears. I would like to regear to 4.56 gears even though I have 31’s, but I’m able to live with the downshift. Truck came with 28” tires stock.

 

Yeah, my assumptions are less reliable with earlier model years. Some poor trucks even got 3.93 in earlier years. I think a lot of that has to do with 28/29" tires being more common in those earlier years and 31" tires being more common in later years.