re-gearing for 37's ??

[FirstAscent]

I currently have almost new 37's on my Tundra which I'll either save for next vehicle or sell and buy 35's. I really like the look of my 37's on 20" wheels but I am ok with 35's.

It's widely accepted in the Tundra community that 4.88's are the way to go for its 6spd tranny.

 

I'm not as familiar with the Chevy side of things, and now with the new 8spd tranny, would it still be recommended to re-gear for 37's? What about 35's? What would you say is the recommended ratio and what would be the best ratio for 35's and 37's, kinda a middle ground for both?

 

I think the main reason I'd go with 35's instead was just because it's less hassle and I'm not sure I'd want to do a 9+ inch lift. 

 

Thanks everyone!

[lt1z]

Going to need tuning to make a change to the gearing. I would think 3.73 for a. 8 or 10 speed on 37s though.

[JR09country]

3.73 or 4.10s

1st gear ratios for GM transmissions
- 6speed: 4.03
- 8speed: 4.56
- 10speed: 4.70


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[FirstAscent]

Thanks! Yeah this would be for the 5.3L 8spd.

Would you say 3.73 for 35’s would be the best option if I decided against 37’s?

[AJMBLAZER]

4.10’s or 4.56’s. 

[swathdiver]

On 12/18/2018 at 11:11 PM, FirstAscent said:

I currently have almost new 37's on my Tundra which I'll either save for next vehicle or sell and buy 35's. I really like the look of my 37's on 20" wheels but I am ok with 35's.

It's widely accepted in the Tundra community that 4.88's are the way to go for its 6spd tranny.

 

I'm not as familiar with the Chevy side of things, and now with the new 8spd tranny, would it still be recommended to re-gear for 37's? What about 35's? What would you say is the recommended ratio and what would be the best ratio for 35's and 37's, kinda a middle ground for both?

 

I think the main reason I'd go with 35's instead was just because it's less hassle and I'm not sure I'd want to do a 9+ inch lift. 

 

Thanks everyone!

Don't know which model you're looking at so consider the numbers.

 

First, the 8L90 8-speed transmission has the following gear ratios:

1st = 4.56

2nd = 2.97

3rd = 2.08

4th = 1.69

5th = 1.27

6th = 1.00

7th = .85

8th = .65

 

Most of these trucks have a 3.23 rear axle ratio so that gives them a 2.10 final drive ratio in 8th, 2.75 in 7th, 3.23 in 6th, 4.10 in 5th.

 

With a 275-55-20 tire which mathematically is 31.91" in diameter, this would have the engine rpms at about 1550 in 8th at 70 mph or 3025 in 5th at 70 mph.

 

A 35" tall tire would require 3.55 gears to run the same rpms as stock.

A 37" tall tire would require 3.73 gears to run the same rpms as stock.

[JR09country]

Don't know which model you're looking at so consider the numbers.
 
First, the 8L90 8-speed transmission has the following gear ratios:
1st = 4.56
2nd = 2.97
3rd = 2.08
4th = 1.69
5th = 1.27
6th = 1.00
7th = .85
8th = .65
 
Most of these trucks have a 3.23 rear axle ratio so that gives them a 2.10 final drive ratio in 8th, 2.75 in 7th, 3.23 in 6th, 4.10 in 5th.
 
With a 275-55-20 tire which mathematically is 31.91" in diameter, this would have the engine rpms at about 1550 in 8th at 70 mph or 3025 in 5th at 70 mph.
 
A 35" tall tire would require 3.55 gears to run the same rpms as stock.
A 37" tall tire would require 3.73 gears to run the same rpms as stock.

This is good info. So if it was me I would go with a lower gear ratio than stock. So, 3.73 for 35s and 4.10s for 37s. I had 4.88s and 35s with the old 4 speed and loved it.

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[swathdiver]

2 hours ago, JR09country said:

This is good info. So if it was me I would go with a lower gear ratio than stock. So, 3.73 for 35s and 4.10s for 37s. I had 4.88s and 35s with the old 4 speed and loved it.

Consider also that if he was running a 35" tire with a 3.73 rear gear, his final drive in 5th gear would be 4.74:1

 

All those extra gears gives them a lot of flexibility.  More importantly though, I hope they got the bugs out of the 8-speed!

[FirstAscent]

Consider also that if he was running a 35" tire with a 3.73 rear gear, his final drive in 5th gear would be 4.74:1
 
All those extra gears gives them a lot of flexibility.  More importantly though, I hope they got the bugs out of the 8-speed!

Awesome, a lot of great info indeed. I’m looking at the lt trail boss which would align with the numbers you’ve given. I love the look of 37’s but still leaning towards 35’s mainly for ease of fitment.

Were there a ton of bugs with the previous tranny?

[swathdiver]

2 hours ago, FirstAscent said:

Were there a ton of bugs with the previous tranny?

 

 

Yes, the design and or the torque converter.  This happened a lot with '15-'17 models as you can see through searching posts on this forum.  I don't think the later 8-speeds were so problematic but it's worth looking into.  I'm happy as a clam with my 6-speed and have no desire for more or a new truck!

[AJMBLAZER]

Don’t forget that the rpm numbers don’t take into account that the tires are heavier and the truck is taller. That’s why going a bit deeper with the gears is a good idea. 

[FirstAscent]

 
Yes, the design and or the torque converter.  This happened a lot with '15-'17 models as you can see through searching posts on this forum.  I don't think the later 8-speeds were so problematic but it's worth looking into.  I'm happy as a clam with my 6-speed and have no desire for more or a new truck!

Thanks! I’ll do some searching.

Don’t forget that the rpm numbers don’t take into account that the tires are heavier and the truck is taller. That’s why going a bit deeper with the gears is a good idea. 

Ah good point, that makes sense

[FirstAscent]

I was talking with a company that specializes in gearing, they mentioned:
“With the 8spd having two overdrives and 8th being a 0.65 overdrive we’d recommend going with 4.56 gears”

I wanted to get all of your thoughts on that as well, I was kinda hoping they’d recommend something closer to what we’ve been discussing, so now I’m questioning everything to make the best decisions.

[SkiRat]

Ok - so I want to re gear this 19 to 4.30 or 4.56.  I am having a hard time finding a company that offers a kit for a 19

[jweezy]

On ‎5‎/‎3‎/‎2019 at 8:45 AM, SkiRat said:

Ok - so I want to re gear this 19 to 4.30 or 4.56.  I am having a hard time finding a company that offers a kit for a 19

One of the ways some people find what gear ratio you need to run to have the same final drive ratio is by taking the size of your new desired tire and multiplying it by your old gear ratio, that you take that number and divide it by your old tire size. The final number will give you a very close calculation to what gear ratio you would need to get back to that close to stock final drive ratio. This is used a lot in the off road jeep communities and its pretty effective. It keeps gears shifting like stock and economy numbers tamed...… sort of