The high gearing will put more stress on the trans, but not a huge deal if not hauling heavy loads and it's not 'gear hunting' on the highway, which I assume it would.

On my '99 F-350 V-10 I went from stock 4.30 to 5.13 with 37s. That put the overall gearing to about equal to a stock tire with 4.10 gears, I think 5.38 woulda been the closest to get back to stock 4.30 ratio. The weight of the tires still made it work harder than a stocker, but it was much better than with the 4.30s. Highway cruising with 4.30 it would drop to 3rd on the slightest hill and 2nd pretty regularly, and it was pretty sluggish off the line.

 

 

 

Changing the gearing doesn't put any more stress on the transmission. It doesn't change the amount of power produced by the engine that is transmitted to the transmission.

Stewart

 

 

Were you happy with 3.73s before? A 2V V10 + 3.73s to me is not a great combo to start with IMO, but I like deep gears on gassers with high RPM outputs. 4.30s should have been there with stock 31s, so a lot of people just simply wouldn't be happy with the setup you started with, much less the one you moved to. If you like it, run it.

Transmission wise it's a temperature thing, the numerically higher gearing increases the span of each gear, so you can have hunting problems and increased TC unlocking. If he watches temps and does a 6.0 cooler, that's probably mitigated. Think of a manual where someone was forcing you to shift a few hundred RPM sooner on every shift, you get a lower power output and might not match up with your power bands. The V10 likes to spin to make power, so he might be cutting himself down at the top trying to stay in OD and the trans keeps dropping to 3rd to boost RPMs. There's a lockout of OD button for a reason, and he should be running a TFT gauge anyway since it's a 4R100.

 

I agree with that.

That can happen. For the same vehicle speed the engine is at a lower RPM and that can cause more frequent downshifts and unlocks.

That's not a good analogy. The transmission will shift at the same RPM regardless of differential ratio. The engine will be in the same powerband as before but at different vehicle speeds. If the vehicle speed is the same as before the transmission may not shift to as high a gear as it would have before.

 

 

New tire diameter in Inches / Old tire diameter in inches x desired gear ratio = what you need to buy

In your case:

35 / 31.6 x 3.73 = 4.10 gears
35 / 31.6 x 4.10 = 4.56 gears
35 / 31.6 x 4.30 = 4.88 gears

People run 3.73s and 35 all the time without issue, it's more noticeable as the truck now downshifts more often and has to work harder to tow. This is why I re-geared Rudolph and added a modified valve body to the trans. The valve body and lift were done first, then came the re-gearing a year later. 11 years and 332K later, the trans is still happy and hasn't grenaded. (knock on wood)

 

I have the 3.73 gearing on my 2000 V10/4wd and have just taken off the 35in tires (removing a big lift). We've made several road trips while pulling our small toyhauler, a loaded 8x22 enclosed trailer, our ski boat, and empty. I wasn't happy with how it towed when I bought it last summer, so I also installed a tuner from 5Star that helped with the shift points and holding gears longer when put in towing mode. I can tell you this: at our elevation of 6k ft, it doesn't often stay in overdrive with that size of tire. If there is any headwind or hill to climb, it'll downshift. I also run a Scangauge II on my steering column and monitor the fuel rate, economy, and TPS sensor. For my rig, it will not stay in overdrive with 35in tires on flat ground if the TPS is reading anything more than 34-35. That means the giant butterfly valve in the throttle is open more than 34-35% (WOT is 100%). I'm taking the rest of the lift off after I get back from vacation at the end of the month and will install a small tire. Hopeful that I'll be able to keep overdrive for longer periods of time with the 87Perf tune. Rarely do I run the 91Tow as my loads are not usually heavy enough to need it. I also have 87Eco, but is useless with 35in tires and 3.73 gears.

 

 

5 Star tune will change your shift points to optimize when your tranny shifts. You won't really see much difference in power output from the engine...the V10 is already doing about what it's going to do. I think if you called 5 Star and explained the situation, they might be able to work up a tune that was specific to your needs. I didn't like my Ex with 3.73's and stock tires and, since I'm planning on 35's later, changed to a 4.88 ratio. It's a lot more fun to drive, tows like a John Deere, and I lost about 1 mpg. I'd say 4.56 gears if you're not planning to tow and 4.88's if you are. JMHO...

 

If you really want to enjoy good performance from the giant gas powered wagon then I 110% agree with the above advice. In my opinion, having driven and towed with my V-10 EX with 3.73, 4.39 and 4.88 ratios I can say without question deeper gears totally change the rig's performance and personality in a very positive way, The standard 3.73 ratio is only what would consider "adequate" for this motor and the heavy EX, I know that I wouldn't be very happy with any numerically lower ratio than 3.73 (I wasn't all that thrilled with them to be honest).

 

I have a 2004 V10 and 3:73 running 35/12.5/20 I was looking to change to 4:30 this should be good for highway and close to stock