I’m going nuts with 3.21s and 35” tires

Slutzk · Oct 2, 2023

Man, this is so weird and crazy to me b.c i have read this time and time and again! So knowing i got a 3.21 i was pretty bummed and mad i didnt go with the 3.92 b.c i knew id put tires and level it, just figured i don't tow like that so don't need it. So i finally put new tires on my truck with the Bilstein level front and back. (Toyo ATIII 35x11.5r20) and i have had absolutely no issues whatsoever with hunting between 7th and 8th. maybe what @JerryBsizzle said its likely people don't recalibrate and it throws the transmission off. but if I'm on the highway/freeway flat, or even going up north through mountains to go to Payson from Phoenix (AZ) and once im in 8th i never go back down to 7th unless i brake behind someone. werid and unsure but ive never had this issue with 3.21 and im pretty happy about it.

JerryBsizzle · Oct 2, 2023

DJ menace said:
I used alfaobd to recalibrate my speedometer after upgrading my tires to 295/60r20. Only time will tell if updating the tire size on my BCM alone will work. If not, I'm going to buy rough country's speed recalibration tool. It apparently not only calibrates the speedometer but adjusts the ECM to modify the shift point base on the tire sze.

Both of mine were done by the dealer. They built both trucks, and on the first one I had the issue of hunting for gears and I used the GPS on my phone and saw the speedometer was off. So I brought it back, they did it on the spot and it worked perfect after that. On this latest truck I picked everything out and had them do all the work. I made damn sure the speedo recalibration was on there.

Just think about it. When you put bigger tires you are taking less revolutions to go the same distance. Your computer thinks you are going slower than you actually are (because of less revolutions). My OEM tires were 661 revolutions per mile, the tires I have now 603. If your truck is hunting for gears and you haven't recalibrated you probably should start there. Like my old boss would say, "when you hear hoofbeats think horses, not zebras".

DJ menace · Oct 7, 2023

An udapte: my truck drives much better after I changed the tire size using alfaobd. I've heard that Jscan works pretty well to but I've never used it. Overall, I'm happy with the outcome with my 295/60/20, which is close to 34x11.5x20

Slutzk · Oct 7, 2023

DJ menace said:
An udapte: my truck drives much better after I changed the tire size using alfaobd. I've heard that Jscan works pretty well to but I've never used it. Overall, I'm happy with the outcome with my 295/60/20, which is close to 34x11.5x20

Glad to hear. it sounds like.... from just research, other folks and this forum. that if folks recalibrate there speedo its not an issue. but those that dont seem to have hunting problems from 7th and 8th. not saying thats 100% true or debunked but seems to be a trend with people that do it, dont have a problem reguardless the gear ratio

Belle44 · Oct 7, 2023

Agitated said:
I knew when I installed the 35s I would lose some cruise rpm and effective gearing but I really did not expect the truck to be hunting between 7-8th gears on flat ground. This is killing me. I am aware I can just get some shorter tires but the current stance I have is important to me. I asked my dealer to price out a loaded 3.92 new rear housing and front section but they arent even sure it is available and if so what the cost will be. This crazy there is no aftermarket support for these axles.
I think my best bet here is to either find someone to switch and pay for the labor, or trade in on a different truck. But my truck is a good one so i hate to roll that dice. For now i have to keep hitting the steering wheel gear limit button and lock out 8th gear.
I made a big mistake.

Just get the OBDMX+ with the security cables also you have to buy the alphaOBF program change the size of the tire and the Speedometer presto problem solved

gomango392 · Oct 7, 2023

Agitated said:
I knew when I installed the 35s I would lose some cruise rpm and effective gearing but I really did not expect the truck to be hunting between 7-8th gears on flat ground. This is killing me. I am aware I can just get some shorter tires but the current stance I have is important to me. I asked my dealer to price out a loaded 3.92 new rear housing and front section but they arent even sure it is available and if so what the cost will be. This crazy there is no aftermarket support for these axles.
I think my best bet here is to either find someone to switch and pay for the labor, or trade in on a different truck. But my truck is a good one so i hate to roll that dice. For now i have to keep hitting the steering wheel gear limit button and lock out 8th gear.
I made a big mistake.

Never had this problem with my 4th gen on 35s and 3.21s it almost always went into 8th gear on the highway. Having so many gears, they will always search for gears no matter the gear ratio. My 23 with 3.92s and 35s searches sometimes as well, depends on the roads.

6of36 · Oct 7, 2023

gomango392 said:
Never had this problem with my 4th gen on 35s and 3.21s it almost always went into 8th gear on the highway. Having so many gears, they will always search for gears no matter the gear ratio. My 23 with 3.92s and 35s searches sometimes as well, depends on the roads.

Fourth gens, and fifth gens, are totally different animals. A LOT more electronics.

gomango392 · Oct 8, 2023

6of36 said:
Fourth gens, and fifth gens, are totally different animals. A LOT more electronics.

Hmm, they have the same engine and transmission though, plus the 5th gen is slightly lighter. Either way, I notice zero difference between the 3.21 and 3.92. If I didn't order my truck, I'd never pass on a truck on the lot for having 3.21s. It was foolish not to spend the 195 for the 3.92 upgrade but it'd not a make or break deal for me. Heck my 5th gen feels a lot slower than my 4th did.

Wirerat · Oct 8, 2023

gomango392 said:
Hmm, they have the same engine and transmission though, plus the 5th gen is slightly lighter. Either way, I notice zero difference between the 3.21 and 3.92. If I didn't order my truck, I'd never pass on a truck on the lot for having 3.21s. It was foolish not to spend the 195 for the 3.92 upgrade but it'd not a make or break deal for me. Heck my 5th gen feels a lot slower than my 4th did.

5th gen 8hp75 has several tweaked gear ratio changes vs the 4th Gen 8hp70. The 1:1 and OD gears were the same but the lower gears changed a bit.

This video describes the changes.

gomango392 · Oct 8, 2023

Wirerat said:
5th gen 8hp75 has several tweaked gear ratio changes vs the 4th Gen 8hp70. The 1:1 and OD gears were the same but the lower gears changed a bit.

This video describes the changes.

well this video explains why the 5th gen feels so much slower than the 4th lol

Mountain Whiskey · Oct 8, 2023

DJ menace said:
An udapte: my truck drives much better after I changed the tire size using alfaobd. I've heard that Jscan works pretty well to but I've never used it. Overall, I'm happy with the outcome with my 295/60/20, which is close to 34x11.5x20

Glad it worked. Now just imagine how much better it would be with 3.92 gears!

DJ menace · Oct 9, 2023

Belle44 said:
Just get the OBDMX+ with the security cables also you have to buy the alphaOBF program change the size of the tire and the Speedometer presto problem solved

I agree with this statement and alfaOBD practically pays for itself! I've used alfaOBD to recalibrate the tire size, and to reprogram a few things. However, I used the veepeak OBD scanner, which was like 15 bucks on amazon.

theblet · Oct 9, 2023

Wirerat said:
5th gen 8hp75 has several tweaked gear ratio changes vs the 4th Gen 8hp70. The 1:1 and OD gears were the same but the lower gears changed a bit.

This video describes the changes.

Watched the video. 3.21 wins again!!

6of36 · Oct 9, 2023

theblet said:
Watched the video. 3.21 wins again!!

View attachment 168977

You are going to get MountainWhiskey riled up again

Mountain Whiskey · Oct 9, 2023

6of36 said:
You are going to get MountainWhiskey riled up again

We all know better than to believe YouTube videos!

6of36 · Oct 9, 2023

Mountain Whiskey said:
We all know better than to believe YouTube videos!

See.....I knew that would get you going

But I agree about all those videos. Anybody can post anything on the internet.

theblet · Oct 10, 2023

Mountain Whiskey said:
We all know better than to believe YouTube videos!

Anyone who can speak for that long must know what they are talking about tho

Redz72 · Oct 10, 2023

theblet said:
Anyone who can speak for that long must know what they are talking about tho

Yes he did sound like he knew what he was talking about. And he also said at the end, if you’re putting bigger tires on your truck, like 35’s, def go with the 3.92.

Upon further review, the call has been changed on the field to 3.92 for the win (with bigger tires)!

Ramroo · Oct 10, 2023

theblet said:
Watched the video. 3.21 wins again!!

View attachment 168977

Duh

theblet · Oct 10, 2023

Redz72 said:
Yes he did sound like he knew what he was talking about. And he also said at the end, if you’re putting bigger tires on your truck, like 35’s, def go with the 3.92.

Upon further review, the call has been changed on the field to 3.92 for the win (with bigger tires)!

Eh

Lol

I’m going nuts with 3.21s and 35” tires

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