Gratuitous Gearing Guesswork....

New dude - tried searching - no luck - soooooo, question time! I have a shiny new 2017 TRD Off road with the automatic and 3.90 gears (which I think are 8.75” diffs f/r right?). I fitted a new set of Maxxis 265/75R16 E-rated MT tires which are 1” taller/heavier/stiffer than stock. Fuel economy dropped a mpg or two and I can tell acceleration has been ever-so-slightly affected (even more than the annoying ECT). Being the OCD mod nerd that I am, I had a glass of Bourbon and got to wondering about life, love, and gear swaps. My thinking is thus: swap a set of factory 4:30’s from the manual TRD truck into mine and - BAM! - instant awesomeness! Has anyone done/tried this? I know they’re “only” 32’s but did I mention I’m OCD when it comes to mods? The gear conversion charts I see on teh internetz all show the ideal gear ratio for 32’s is something like 4:12 or 4:10 (give or take) which nobody makes so I’m wondering if 4:30’s might be a bit too low. I’m assuming since I’d be using factory parts it would be a fairly straightforward (albeit wallet draining) swap involving the ring & pinion only. Is it or is there some hidden complication I’m missing (such as with the E-diff)? Would it screw up my highway cruising or no? I suppose my ultimate goal would be to get as close to the overall factory gear ratio as possible while keeping my sweet new tires. Thoughts?

 

look at the Mega 4.88 thread (JerryTaco post). Most of your questions/concerns are there and some cost info. 4.88's which is your only option for the TRDOR. Good luck.

 

They are both .20 off... I’d say just suck it up until someone comes out with 4.10’s

 

Its been considered but with double overdrive gears 4.88 is not as tall as it would seem.

99% of gear charts were written for Jeeps and vehicles without OD. Sure we have a 1:1 4th but we also have 2 OD gears...

 

First, welcome to Tacomaworld!

Now, the bad news. The first law of Thermodynamics, loosely phrased, says you can't get something for nothing lol. In your example above, this means that if you are going to put bigger heavier tires on your truck, you have to pay with something! No matter what gear ratios you use, you will lose efficiency (mpg) when you do this. That is your "payment" to the real world of physics. Now, you might get better drivability for yourself, you might get better torque or something, but you still will lose efficiency. The only way to gain that back is changing your operating parameters, like shedding weight, driving at 55 mph instead of 70 mph, etc. Otherwise, enjoy your (less efficient) new vehicle!

 

4.30 would be great if you never plan to go larger than 32" tires. I suggest you do the math yourself and make sure you take the extremely high OD ratios of the AT in to account.

If you do what you propose, you will end up with a 5th gear ratio in the AT that is nearly identical to the 6th gear ratio in the MT. So you are definitely not too high in the final ratio. With the 4.30 you will still cruise at 75MPH @2,000RPM in 6th.

If you went 4.88, your 6th gear would still be slightly higher than an MT. You would cruise at 75MPH@2,250RPM in 6th. Still not obnoxious.

It would be worthless to even consider a 4.10, even if available. Your highway cruise would change about 75RPM versus a 3.90.


I would agree with he above statement. A gearing chart that only considers tire size is worthless and probably meant for a Jeep with a 0.85 or 0.7 Overdrive ratio. The Tacoma has an astronomical 0.58 Overdrive ratio!

 

Assuming OP found a wrecked MT Off Road model...the front and rear diffs would be a direct swap, correct? So in theory, 4.88's aren't the only solution, you just gotta find a wrecked MT OR that isn't missing the front and rear diffs. Now, what the cost would be compared to 4.88's, who knows.

 

Pfft, your science has no place on Tacomaworld. It's common knowledge that regearing increases MPG, HP, Torque, shortens your 0-60, nets you 1000 EAF points, smooths out drivetrain vibrations, and gets you laid more.

 

duh. not even duct tape can fix what you have. ignore.