New here...Do I Need to regear for 35's with 3.73 gears

[Aftershock00]

Uh huh, the Nitto web site says mine are 34.2, they measure MAYBE 33.1 installed. There is not one metric tire that has ever measured installed what the diameter claimed, and I have been thru a few. They measurements they give must be on the narrowest rim listed and at full pressure with no load. When you start inputting tire size to correct speedo to GPS then it becomes obvious something is off. I have to run 32.6 tire size to get the speedo within 1 mph of GPS.

I see what you're saying now. I just went out and measured. From left to right, tires measured 34"... Maybe a C hair under. If I measure up and down, tire measures around 33.75, obviously because of flat spot where tire meets ground.

Still, this doesn't affect how much added tirediameter there is because of stock tires claim to be 31", then they are really 30". So it's still the same net gain, no?

 

[cerberusiam]

Yes, there is a net gain and that is about all you do up in size and not have other issues. A 33" with 3.73's is a good all around choice, even towing heavy. A 34" tire is not bad, good for efficiency and light to medium towing. When you get to true 35's then you start to notice the power difference a lot more, also, that is when it becomes almost necessary to mod the transmission. The 68RFE is better as you have more gears to choose from but it is still being leveraged more with a lot of TQ, that have been the downfall of every LD piece of the drive train form the start. Like I said, based on what you are using the truck for that should be a good choice and you should not have problems. It will feel better and shift better once you correct the speedo and add a little power which will likely help the trans last longer also.

 

[Aftershock00]

Be careful what you wish for with a manual transmission. I have met with too many owners that thought the truck didn't have any power and thought something was wrong. With the auto you have a great advantage over the manual because you have torque multiplication going on in the converter. Off the line the auto will smoke the manual all day long. The engine will be just as happy at 1500 as 1800 and you can't hurt it, but it may not be in the sweet spot for fuel economy if your worried about that.

So I know lugging is not good for any engine and puts extra wear on bearings, Rods, etc, whether it be a two stroke, a four stroke gas or a diesel, the question I have for you guys is... If 1500 rpm isn't considered lugging, what rpm is considered lugging/unhealthy for the engine?

 

[cerberusiam]

1500 is still in what is considered the idle range so if you are under anything other than minimal load then it is lugging it. The question about what rpm is lugging has other dependencies so it is not a one size fits all answer. Once you drop under 180 rpm's you are really out of a working range and starting into defuel mode. If you want to see where the engine will perform in your truck you need to put it on a dyno to get fuel for what it programmed to do, anything else is just guessing.

 

[Aftershock00]

Hey guys, thanks for all the replies. So I have my bullydog gt installed and corrected the speedo. I still feel like 6th gear drops in way too early and 4th and 5th should wind out a little more during conservative driving.*




Is there any way to make the transmission relearn when to shift? I know these trannies are less electronic than ford, but I'm still not feeling right about the lugging. Yes, I could just lock 6th out, and or use tow/haul mode, but I'd really like to have the truck drive normally without adjusting anything, Atleast when I'm driving without a load.*
I was thinking of switching to 305/65r18 which is 33.6" tire according to nitto terra grappler g2. Maybe these would be the perfect combo of fuel efficiency and use ability. I really think 4.10 gears would solve my problem but I can't justify that kind of an investment on an 08, when I'm hoping to buy a 2018 when it come out

 

[HankC]

I had the same question a few years ago and debated about the 4.10s. I've been running 35" TOYO Muds for 5 years now and I love it! I have the 3.73 gears, various Carli Suspension components, stock trans, H&S tuner on MILD, engine is stock minus the Banks intakes. With the tuner I adjusted the speedometer. I like the way my truck rides. I'm no speed demon nor do I drag race up the highway. At my highway cruising speed (70 to 73mph) my engine runs at 1800-1850rpm. Most of the high-speed diesel generators I work with aboard merchant ships run at or around this speed.

I believe its just personal preference and application.

 

[cerberusiam]

That is stock programming for NVH and CAFE ratings with the added larger tires. If you want to change that you will have to reprogram the transmission control to customize it.

 

[Aftershock00]

I guess I'm just curious if going down 1.5 inches in tire diameter would even be noticeable. *According to bulldog, I have to set tire size to 33.1 inches for speedo to read accurately.*