Looking to upgrade to 33" fat A/T tires on my 96 E350 4x4. Interested in opinions on what gearing I should be running with that size tire? Van came with 32" tires, so wouldn't necessarily have to regear for 33s? I don't know what the current gearing is. Also a consideration is that if I'm going 70 I'm speeding by at least 15, max legal speed limit on Maui is 55. That being said I like goodish gas mileage and not too much a fan of engine drone. Ultimately I would like better seat of the pants feel though.

Sean

 

You are increasing your diameter by 3%. I do not think you need to re-gear unless your van is already struggling with the 32s. If you have 3.73 and change to 4.10, your gearing will be 10% shorter.

Knowing your engine will help. I have a 2010 4x4 E350 with 4.10 gears and 5.4l gas V8. Currently running 275/70/18 (about 33.5") lightly loaded and it moves well.


There are a lot of AT tires. They usually penalize economy. Noise depends on the tire itself. I have Michelin LTX AT2 (Do not look AT) and are very quiet. I used Cooper AT3 on my previous van and they were quiet

 

Engine is 5.8l V8.

 

Another question is does your van have a OD transmission? It should have a E4OD in it. That's what my 96 has. But some 4x4 conversions end up with a C6 3spd auto.

Like @GreeVan said If you are happy with your van's current performance/acceleration then you should be fine. It sounds like you would like your van to have some more off the line acceleration. Then steeper gears may be in order. If you van currently has 3.55's or 3.73's I would step up to the 4.10/4.11 gears. If you have 4.10/4.11 gears then step up to 4.56. Going to a steeper gear doesn't mean it is going to hurt your mileage. If your current gearing bogs the engine down then a gear change could actually improve mileage.

 

Any time someone asks what gears they should change to when they change tire sizes I answer to try it with the old gears first. If you like it with the old gears you've saved yourself $500 - $1000 per axle. And if you don't like it you'll know that all the money you're shelling out is for a reason.

But with only a 3% difference in tire size I'd be willing to bet that you won't notice a difference. If you're happy with your current gearing I'm sure you'll decide it isn't necessary to regear with that insignificant change.

 

I feel the same way. But the last sentence in his original post, he said he wants to improve the seat of the pants feel. So if he feels that way about it with his current tire size, it's only going to get worse with bigger tires ( only marginally so ) . So that means more gearing or more power.

 

Yeah, it needs more off the line already in my opinion.

Is there a way to determine what gearing is in the axle currently without opening it up?

I think the transmission is a 4 speed but not 100%, haven't been able to drive it much yet and transmission is having issues.

 

Assuming an open diff, jack up one back tire, put the trans in neutral and the e. brake off (chock the wheels to keep it safe).

Rotate the tire two full turns and count the number of times the driveshaft goes around. You'll need to be pretty precice with your 2 turns and especially with driveshaft revs if you want an accurate number. But generally, a little over 4 driveshaft turns will be 4.10, 3 3/4 turns will be 3.73, 3 1/2 turns is 3.55, a little over 3 turns is 3.08. I wouldn't guarantee that you'll get a perfect reading to order a matching set, but it'll get you in the ballpark.

Note that with 4x4 you can do the same thing with the front axle with the trans in park/gear abd the e. brake set by jacking up one front tire, locking both front hubs and leaving the t.case in 2WD.

And with a limited slip or locker you jack up both tires and turn the tires 1 revolution while counting driveshaft revs.

 

Even easier is just to get under the rear and read the ID tag on the differential cover. The ratio is stamped on it. If it's got a trac-loc, an "L" will be stamped in the middle of the ratio (i.e: 3L73

 

... if the axle hasn't been modified. In a stock van that's a pretty safe bet. But in one that's been converted to 4WD I'd check what it really is rather than what it says it is.

 

Nothing he's said tells you that's the case. Chances are it's never been modified.