walterGT67

Im very interested..

Robert

Around town I am running about the same, but I have dropped about 1 mpg on the highway. I suspect further drops once I upgrade the tires.

opdsgt

My first tank returned 15 mpg around town. No sustained highway driving yet, not enough to calculate efficiency anyway.

AZ Outlaws

Under dawg... I saw your link to this thread in another post. Thanks for your review too!! I'm going with 4.56 gears on 33's. Didn't feel comfortable with the 4.88 gears and a lot of highway driving out here.

I'm paying $1,200 out the door at a reputable 4x4 shop for Yukon 4.56 gears, a carrier and bearing kit. Anyway you slice it, going from 3.21 to 4.56 on 33's will be a great improvement, I'm sure.

2climbbig

I don't get why a 6-speed needs to be re-geared for 35 inch tires. 6th gear with 4.88s is equal to 5th gear with 4.!0. The Auto it makes a big difference... The stick, it just makes your pinion weaker. I don't see any real advantage.

opdsgt

Outlaw, you're going to LOVE your setup with 4.56s. It makes a world of difference, both on pavement and off.

climbbig, sorry, don't know if your post was intended for me... and even if it was, I can't make heads or tails of what you're saying or asking. Sorry.

Doc_D

I know what you're saying and to some degree I also struggled to wrap my brain around this a little bit.

2climbbig is saying if 6th with 4.88s turns the same RPM as 5th with 4.10s why not just drive around in 5th gear and save yourself $1200? He's basically saying just always be 1 gear lower than you'd normally be it's all the same.

The first problem is, when you are starting from a dead stop you cannot be one gear lower than you normally would be.

The second problem is that you are turning your close ratio 6 speed into a wide ratio 5 speed. That means unless you rev the gears out when you up-shift you can fall out of the power making it feel even slower.

To put it into perspective, on 35" tires and 4.10s my jeeps theoretical top speed is 181 mph if it could make it to redline in 6th gear. With 35" tires and 3.73s it's 199 mph. With 3.21s and 37" tires it's 245 miles per hour That's a ton of wasted gearing that will never get used.


So I think there really are good arguments for regearing a 6 speed.

Here is the one thing I have a hard time wrapping my head around. If anyone can answer this brain teaser for me I'd appreciate it:

Two identical jeeps (except for gears) with 35" tires and 6 speeds are driving side by side at 40 MPH.

Jeep A has 4.10 gears and is in 3rd gear (1.72:1 ratio) turning 2350 RPM.
Jeep B has 4.88 gears and is in 4th gear (1.25:1 ratio) turning 2350 RPM.


Both jeeps put their foot to the floor at the same time. Does one jeep out-accelerate the other?

Doc_D

Actually I made a mistake on the gear calculator I was using. It would take a 5.642 gear ratio in Jeep B so that it's RPM in 4th gear were exactly the same as Jeep A's in 3rd gear at 40 MPH. And after looking at the numbers it seems like in that case they would accelerate at exactly the same rate. They would both redline at exactly the same speed as well.

2climbbig

You got my point and agree with you about 1st gear. But, the problem folks have with the engine is not in first gear... its passing while on the highway. I go to hotsprings to off road all the time and if I need to pass, climb, or tow my camper, I use 5th gear. If I am not towing, driving in the mountains, or passing, then 6th gear is great and saves me gas.

With a stick, you can always find your power curve and don't necessarily need lower gears.


That said, this is only true up to 35" tires. if you are going to 37" tires, you defiantly need to regear since you would be jumping between 4th and 5th gear. And that would be a major pain in the back side.

bpbat21

I m glad to see that you are happy with your gearing. I was throwing around the idea of regearing. When I talked to the mechanic, he wanted to go with 4 56. I will be getting 35s soon and do a lot of off roading, with high way driving as well. In your opinion, what would I be happiest with. Its a 2008 manual.

Thanks guys
Ben