I'm considering changing out my rear gear to get better pulling performance. I have an 08 f150xl 4.2l, 8.8 axle, 33 inch tires, and 3.73 gear . My gear shop says the optional gears are 4.10 4.30 or 4.56. I don't think 4.10 is worth it, however anyone with a 4.3 or 4.56 and this engine combo please chime in. I'm pulling about a 5,000 lb trailer. Thanks

 

I agree, going from 3.73 to 4.10 is not worth the cost. I'd go 4.56 all the way. I have a similar set up to you and that's what I went with. Keep in mind, my truck is not my daily driver. It is only used for towing, hauling, and occasional vacation trips, just for the added comfort and cargo space. If you do a lot of highway driving, then you might want to go with 4.30.

I love this set up for when I'm towing and hauling. There have been times where I wished my RPM's weren't so high, but that was usually only on long road trips on highways, running 70mph+

 

Chris. I spoke with another gear shop and they said they could take my money, but my problem is horsepower (4.2L) not gearing. Glad to hear the 4.56 works for you. I don't drive my truck long distance very often, so I may consider it. Thanks, Scott

 

Do you have a manual or automatic transmission?

 

Just an FYI, for every .25 gear ratio change, the rpm's will change by 300- that should give you a better feel for what you may want.

 

Yea, gears definitely won't help you with gaining any more horse power. But they will help your truck a lot with turning those 33" tires and towing that 5,000lb trailer. Between the re-gearing and custom tuning, I'm quite happy with how my truck performs. It still ain't no v8, but it gets all the jobs done that I've thrown at it.

 

GLC - It's an Auto.
I found some formulas to calculate gearing in relation to tire diameter. Here we go....math in public. My change in tire size (30" to 33") gives me an effective gearing of 3.37 (old diameter divided by new diameter multiplied by 3.73). And requires a gear of 4.1 to get back to the rpm I had originally had. (new ratio= 30/33 x 3.73)
If I use a new gear of 4.56 this should make a difference and raise the rpms about 500 according to Beechkid (I assume that's at 60mph). Any thoughts?

 

If you are towing 5k with a V-6 on 33's, I'd get 4.56's.

http://4lo.com/calc/gearratio.htm

70 mph in OD would be 2275 rpm. With your 3.73's you are at 1860.

 

I also recommend getting some kind of tuning done to your truck if you do re-gear. I remember when I first got my 4.56LS installed. My speedometer said I was doing 80mph when I was only doing around 60mph. I was able to update my trucks PCM with my XCAL2 and it was much happier.

If tuning isn't an option, maybe check and see if the dealership can recalibrate your PCM to at least get it close to recognize those larger tires and change in gear ratio.

 

IMO, the 4.56 would make a huge improvment for you over the 3.73.

Yea, the shop is right the truck does not make much power, but if you've been pulling the same load with 3.73's, you are going to pleased as punch with the difference.

 

After looking at new truck prices....the gear change keeps looking better. I'm looking into an xcal3 custom tune as well. Thx!

 

I'll second that! I'm loving the new trucks and especially the new engine line ups. But when I price them out, I love NOT having a payment even better!

You will be amazed at how your truck performs if you get gears and a custom tune. At least I was, it's night and day from stock.