just lock out 6th with the 4,30 gears and it should pull better than your past 3.73

 

Gman what where you running for tires on your present and previous truck?

Denny

 

It's just 6% higher rpm. You would have to figure in the leverage advantage of the 4.30 somehow. I think it was chuck that gave the analogy of its like using a longer handled ratchet. Very good analogy.

 

My biggest problem is with those "invisible" grades, you know the ones that look like you are on level ground, but the truck is dropping to fourth just to keep up to 60. The Colorado Plateau on I40 is one that comes to mind. Would 4:30 gears make a difference there? I'd sooner a take a mountain pass than one of these types of roads. Add in a strong headwind and third is very likely.

 

If you can search my posts, in 2016 I posted some charts I put together showing rpm differences vs the 4.3 and 3.73 with various tire sizes. They get buried in the pages with all the activity on the site.

 

Do you guys think 4.30s are enough for 34.4" tires, or even 35s?
I just got a 6.2 that has the factory 20" wheels with the 34" tires and am considering a regear. I can tell the engine has plenty of power, but my gears are really hindering the performance. I know the feeling of too tall gears all too well with past Jeep's that had large tires and tall gears. A regear makes it feel like you dropped in a much bigger engine.

My question is because if I have the 34s and possibly going up to 35s should I just get 4.56 since I'm already regearing?

It's kind of ridiculous, only been on the highway once, but it was running crazy low rpms at 70.


I'm also considering those gears because it is a work truck, it's either towing or plowing 95% of the time. I'm only in the highway with the truck once a month tops, mostly on 45-55 mph rural roads

 

I would strongly recommend 4.56 with a 35. This will have you geared just a hair higher than my dads '16 truck which is 4.30's with the factory 245/75r17(31.5"). Very powerful truck and it has no issues running down the interstate. I'm going 4.88's with 37's and would not hesitate to run 35's in the future, even with the 4.88's.

 

I'm happy with my 4.30 and 35x12.50x20's. At 55-60 mph my hwy cruising mpg is incredible, but as soon as I near 70 it starts to really drop. Tough call on 4.30 or 4.56 for what you do, but if there is not a price break for the 4.30, I would lean towards the 4.56. Either way, you will be happy with the swap.

 

I think it's aerodynamics of a brick that really start killing mpgs above 65-70, not the rpms so much. I always noticed when riding a motorcycle without a windshield, this is the speed when you really start feeling the power of the wind.

 

I've been reading a lot about gear changes in these trucks. I've had the gears changed on a previous truck (1985 Toyota, put in 5.29 gears) and it was an amazing difference. I've got 34" tires right now on my '12 F250 CCSB 4x4 and will likely go up to 35s soon. I'm debating doing a gear change, but I'm also trying to decide between 4.30, 4.56, and 4.88s. If the 4.56 and 4.88s were ford options (not aftermarket), I wouldn't even be considering the 4.30s. Since I can never see myself going up to 37s, I'd probably go with the 4.56s as I think that would be plenty for my needs.

 

Yukon is cutting the 4.56 and 4.88 gears. Nothing wrong with Yukon brand.

 

You seem to be the gear expert from reading some of your responses.. Do you happen to know the carrier break over point? At what point do you need to get a new carrier?

On my current Jeep it had 3.07 gears from the factory and to go up to 4.10 I had to get a new carrier. I could have gone to 3.55 without a new carrier

 

No break over point on the rear. Yukon sells thick cut 4.56 and 4.88 for the front if your coming from 3.73. The break over point for a Dana 60 is listed as 4.10/4.56. I think the factory 4.30 gear is a thick cut, so the same carrier either way.


Edit: I'm far from an expert, but I've been doing a bunch of research on this for myself.

 

Yeah, I don't have a problem with the brand. I'm sure they're fine. My preference is to stay with Ford parts though when possible for various reasons.

 

6th gear in my F250 4x4 CC SB with 3:73's is relatively useless if I have anything behind me. An empty 20 foot 14,000 gvr bumper pull equipment trailer and a headwind and you can all but forget about 6th gear. 5th holds nicely but I'm getting around 7.5-8 mpg with an empty trailer running against a headwind at 65 mph.