5.13 Gears, My Thoughts and Real Numbers

[JTdiRtyD]

Increases in mpgs is usually because you're back to using all gears, so it's not truly an increase for the vehicle, it's a situational increase. You're not seeing an increase from 8th gear with stock gears compared to 8th gear with 5.13s, you're seeing an increase from 7th gear stock to 8th gear with 5.13s. Even though your rpms are higher with 5.13s, you can effectively use 8th gear again which is probably roughly the same rpm as 7th was previously.

However, my 2020 Tacoma I saw an overall increase simply because the 3rd gen Taco transmission is utter shit. It's an outdated 6spd, it's programmed for best fuel economy so it always tries to keep the lowest possible rpm based on some shit algorithm that a 5 yr old must have come up with, and because of that the engine is constantly under load trying to keep itself moving (breathe on it and it'll gear hunt for the next mile). When I geared to 5.29s it bumped me about 1-2 mpg average, and bumped about 2 mpg while towing. Prior to 5.29s if I drove in 6th @roughly 1300rpm I would see 14-15 mpg average highway (I would see 15-16 if I drove in 5th @1800rpm). After 5.29s I would see 16 average in 6th @roughly 1800rpm (but now 5th I would see a decrease). The 5.29s brought 6th gear to roughly the same rpms as 5th was, and gave enough mechanical advantage that it wasn't working as hard. All of this was on 32's, one tire size larger than stock. It drastically improved the drivability of the Tacoma.

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[Zachanadandy]

Increases in mpgs is usually because you're back to using all gears, so it's not truly an increase for the vehicle, it's a situational increase. You're not seeing an increase from 8th gear with stock gears compared to 8th gear with 5.13s, you're seeing an increase from 7th gear stock to 8th gear with 5.13s. Even though your rpms are higher with 5.13s, you can effectively use 8th gear again which is probably roughly the same rpm as 7th was previously.

However, my 2020 Tacoma I saw an overall increase simply because the 3rd gen Taco transmission is utter shit. It's an outdated 6spd, it's programmed for best fuel economy so it always tries to keep the lowest possible rpm based on some shit algorithm that a 5 yr old must have come up with, and because of that the engine is constantly under load trying to keep itself moving (breathe on it and it'll gear hunt for the next mile). When I geared to 5.29s it bumped me about 1-2 mpg average, and bumped about 2 mpg while towing. Prior to 5.29s if I drove in 6th @roughly 1300rpm I would see 14-15 mpg average highway (I would see 15-16 if I drove in 5th @1800rpm). After 5.29s I would see 16 average in 6th @roughly 1800rpm (but now 5th I would see a decrease). The 5.29s brought 6th gear to roughly the same rpms as 5th was, and gave enough mechanical advantage that it wasn't working as hard. All of this was on 32's, one tire size larger than stock. It drastically improved the drivability of the Tacoma.

5.13s in 8th is mathematically the same as 7th gear with 4.10s. 0 chance of increased efficiency using the same final drive ratio. Physics is always right. The only way the mpg improves is by doing less work, ie driving less aggressively or slower. And even with 4.10s I see 8th on the freeway when it's flat and there's no headwind which would obviously be more efficient than running extra rpms.

 

[MarkO]

5.13s in 8th is mathematically the same as 7th gear with 4.10s. 0 chance of increased efficiency using the same final drive ratio. Physics is always right. The only way the mpg improves is by doing less work, ie driving less aggressively or slower. And even with 4.10s I see 8th on the freeway when it's flat and there's no headwind which would obviously be more efficient than running extra rpms.

Take a step back and think about the easiest way to get a 100lb tire to start rolling.

 

[JTdiRtyD]

5.13s in 8th is mathematically the same as 7th gear with 4.10s. 0 chance of increased efficiency using the same final drive ratio. Physics is always right.

Which is exactly what I said it does. If some someone was driving in 7th all the time and getting 17mpg, regears and is now driving in 8th and getting 18mpg they will claim they got a bump in mpgs when in reality they didn't. They are sitting at the same rpms getting the same mpgs, just in a different gear.

The only way the mpg improves is by doing less work, ie driving less aggressively or slower.

You mean like decreasing the amount of energy needed to perform the same task through mechanical advantage?


I do agree in 90% of cases out there a person is not going to see an increase in mpgs by gearing lower, but it's not impossible, especially in some vehicles like the Tacoma that are piss poor from the factory because of too high of gearing. Most people are gearing to run larger, heavier tires and thats going to impact mpgs regardless.

 

[Zachanadandy]

Take a step back and think about the easiest way to get a 100lb tire to start rolling.

Which is why I said the only place you'd see any possible gain is in a lot of stop and go driving? How many times are you getting a tire rolling from a stop on a roadtrip? Twice every 4 hours when you stop for gas? The only place you gain anything more than you can from a simple downshift is 1st gear period. The 8 speed keeps the vehicle in the proper power band for the load automatically everywhere else. This isn't a wide ratio 4 speed where you're lugging between gears without low enough axle gears. And even in 1st gear the 4.7-1 ratio is plenty.

 

[Zachanadandy]

Which is exactly what I said it does. If some someone was driving in 7th all the time and getting 17mpg, regears and is now driving in 8th and getting 18mpg they will claim they got a bump in mpgs when in reality they didn't. They are sitting at the same rpms getting the same mpgs, just in a different gear.



You mean like decreasing the amount of energy needed to perform the same task through mechanical advantage?


I do agree in 90% of cases out there a person is not going to see an increase in mpgs by gearing lower, but it's not impossible, especially in some vehicles like the Tacoma that are piss poor from the factory because of too high of gearing. Most people are gearing to run larger, heavier tires and thats going to impact mpgs regardless.

That same mechanical advantage is a downshift away. Final drive ratio is all that matters for load on the engine and mpgs period. 5.13s in 8th, 4.10s in 7th, 3.55s in 6th all offer the same final drive ratio. Therefore the same load on the engine, rpms, and mpgs will result in the same conditions. The engine doesn't know or care what gear the transmission is in or what gears are in the axle. Where you start to lose efficiency with an 8 speed is when you go too far in either direction. Gear so low that the thing is in 8th all the time at any speed above 40mph and at 80mph you're looking for 9th gear... Go the other route and run 4.10s with 42s and you'll likely never see 8th or even 7th. The OEMs have millions of miles tested and mpgs are one of their top priorities. If 5.13s were optimal for 37s every JT with 32-33" tires would come with 4.56s. There's a point where too low is too low and you get diminishing returns. Obviously the difference between 4.88s and 5.13s isn't so big to make some massive difference one way or the other, but 4.88s will deliver better mpgs when driven the SAME every time.

 

[Splenda]

There are many myths in the Jeep world. I refer to it as Jeeptelligence. Sometimes I just stand and list to a group of Jeeptards spouting off all their Jeeptelligence and just smile. There's a reason they make people go to college to be engineers.

 

[smlobx]

Interesting discussion….

I was watching a video this am that talks about Jeep now offering 4:56 gears with the Rubicon X package on the Wrangler which comes with 35” tires AND offers 4:88 as an option!

Since I am usually pretty heavy and running 35’s this gives me more confidence that rehearing is the right choice.

 

[JTdiRtyD]

That same mechanical advantage is a downshift away. Final drive ratio is all that matters for load on the engine and mpgs period. 5.13s in 8th, 4.10s in 7th, 3.55s in 6th all offer the same final drive ratio. Therefore the same load on the engine, rpms, and mpgs will result in the same conditions. The engine doesn't know or care what gear the transmission is in or what gears are in the axle. Where you start to lose efficiency with an 8 speed is when you go too far in either direction. Gear so low that the thing is in 8th all the time at any speed above 40mph and at 80mph you're looking for 9th gear... Go the other route and run 4.10s with 42s and you'll likely never see 8th or even 7th. The OEMs have millions of miles tested and mpgs are one of their top priorities. If 5.13s were optimal for 37s every JT with 32-33" tires would come with 4.56s. There's a point where too low is too low and you get diminishing returns. Obviously the difference between 4.88s and 5.13s isn't so big to make some massive difference one way or the other, but 4.88s will deliver better mpgs when driven the SAME every time.

In my Tacoma, with factory gearing in 5th gear even a slight headwind would cause it to downshift.
5.29s in 6th gear and it took quite a bit more headwind before it would want to downshift.

Factory gearing in 5th gear it would start to gear hunt back and forth between 4th and 5th on slight inclines. Overpass on the highway? It's going to gear hunt.
5.29s in 6th gear and it very rarely downshifted and took larger inclines before it would, and if it did it downshifted one gear and held it until you crest the hill.

May be the same or very close to the same final drive ratio, but the load on the engine was lessened enough that it didn't find the need to downshift. Don't ask me the science behind it, all I know is there was a significant improvement in how my Tacoma performed in all the same conditions. I ALWAYS use cruise control as soon as I get up to highway speed, so it wasn't me changing my driving habits.

There are many myths in the Jeep world. I refer to it as Jeeptelligence. Sometimes I just stand and list to a group of Jeeptards spouting off all their Jeeptelligence and just smile. There's a reason they make people go to college to be engineers.

Toyota engineers had to release updates to their transmission programming because it performed so poorly. Then the update still performed poorly but it was determined they couldn't improve it any further. They went to college, but they also need to stay between the left and right limits of whatever they are told to stay within.


Call me a liar or a Jeeptard all you want, but for 20k miles after I regeared my Tacoma I logged every tank, hand calculated, and almost every tank I saw 1-2 mpg improvement over my logs prior to gearing. Towing I saw the biggest improvements. I almost exclusively use cruise control unless I'm in town. I'm not saying every vehicle is going to see improvements, all I'm saying is there are cases where you can see improvements. If you have a vehicle that doesn't struggle in final gear than you're only going to see a negative impact to mpgs, but if you have a vehicle that you typically downshift to get that mechanical advantage and drivability, then regearing COULD be a benefit. It can increase drivability and at least maintain the same mpgs, depending on the gearing.

 

[Zachanadandy]

In my Tacoma, with factory gearing in 5th gear even a slight headwind would cause it to downshift.
5.29s in 6th gear and it took quite a bit more headwind before it would want to downshift.

Factory gearing in 5th gear it would start to gear hunt back and forth between 4th and 5th on slight inclines. Overpass on the highway? It's going to gear hunt.
5.29s in 6th gear and it very rarely downshifted and took larger inclines before it would, and if it did it downshifted one gear and held it until you crest the hill.

May be the same or very close to the same final drive ratio, but the load on the engine was lessened enough that it didn't find the need to downshift. Don't ask me the science behind it, all I know is there was a significant improvement in how my Tacoma performed in all the same conditions. I ALWAYS use cruise control as soon as I get up to highway speed, so it wasn't me changing my driving habits.




Toyota engineers had to release updates to their transmission programming because it performed so poorly. Then the update still performed poorly but it was determined they couldn't improve it any further. They went to college, but they also need to stay between the left and right limits of whatever they are told to stay within.


Call me a liar or a Jeeptard all you want, but for 20k miles after I regeared my Tacoma I logged every tank, hand calculated, and almost every tank I saw 1-2 mpg improvement over my logs prior to gearing. Towing I saw the biggest improvements. I almost exclusively use cruise control unless I'm in town. I'm not saying every vehicle is going to see improvements, all I'm saying is there are cases where you can see improvements. If you have a vehicle that doesn't struggle in final gear than you're only going to see a negative impact to mpgs, but if you have a vehicle that you typically downshift to get that mechanical advantage and drivability, then regearing COULD be a benefit. It can increase drivability and at least maintain the same mpgs, depending on the gearing.

They actually weren't close in final drive ratio as that's a massive change in gear ratios from 3.73 to 5.29. Also the taco double overdrive is too big a jump from 4th gear 1-1. Going from 1-1 to .69 and then .58 makes 5th and 6th too close together and leaves a huge spread from 4th to 5th which is why gear hunting is such a problem even with moderate sized tires. Add in the mediocre 1st gear of 3.6-1 and there's a lot of reasons why the Tacoma is much better all around with deep gears. The 8 speed is game changing on both ends. With stock 4.10s and the 4.7-1 1st gear its the same as a taco with 5.35 axle gears, tell me again we need more mechanical advantage to get a 100lb tire moving? How's a Toyota go anywhere then? On the opposite end we go from 6th at 1-1 to 7th at 7th at .84-1 to 8th at .67-1. Much more useable and much less spread on the top end. Even with 4.10s our to gear is equal to a Toyota with 4.73 axle gears. Not saying there's no reason to regear ever, but we don't need to go stupid low like a Toyota and if regears are $3k like they are locally the juice just isn't worth the squeeze. It's simple math if you understand it, and it never lies. You can't beat physics. Final drive ratio is what determines everything.

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