Here's the deal. I have an S10 blazer work truck, It carries a lot of weight and spends much of it's life in and out of farms and fields. It's 4WD with 3:42 gears. Due to weakness in the rear end with these trucks I've now installed an explorer LS unit with 3:55 gears. Not exactly a perfect match, but since the 4WD is only used in sloppy, slippery conditions, the mismatch hasn't really been a problem.

It's currently running LT 235 75 R15 tires at 50 PSI, which seem to perform quite well for my usage. They're still in good shape so I'm not planning any changes in the short run, but at some point that day will come. I'm wondering is possible to go to a slightly different size on the rear to help close the gap in the gear ratios? I know the difference isn't much, because the spread between the speedometer and my GPS unit is only about 1 MPH at 60. Perhaps any change would be too much? The rears are now mounted on rims to match the Ford axles so tire rotating is no longer an option or a concern.

Any thoughts?

 

I think this calculator can be used to figure out your mystery. Every variable is adjustable, and it also has a tire diameter calculator.

https://www.novak-adapt.com/knowledge/gearing/

There are many such calculators and graphs, but I like that one.

 

Okay, thanks. That gives me something to play around with.

 

Honestly, this all sounds like a not-unreasonable solution.

Your tires are 28.8" (nominal), and by my math you'd need 30" tires to compensate for the new diff ratios.

I believe the closest common size will be 265/70r15, at 29.6".

 

Actually, after dinking around with one of the charts in the link posted above, that's the size I came up with too. Guess I'll take it up with my local tire shop when the need arises.

Thanks all

 

I'd say Go Hard Or Go Home! Lift it and put on 33s!

Now seriously - is the gear ratios gap really worth bothering?

 

3.42 to 3.55 is only a 3.8% difference. It's simply not worth worrying about. Just making a turn will throw the percentage off far more than that on a gears matching truck.
The 3.42 in the front will just slightly pull on the rear, which is better than the rear pushing.

Fun fact: A lot of mud trucks run a higher gear ratio in the front to help pull the front through the mud and to help steer better.

 

I'm not sure I was ever really worried about it. Probably more curious than anything else. I know the mismatch was a concern when the swap was still in the "what if" stages, and I received varying opinions on the outcome back then. I do know the original gearing was less than perfect to begin with. There was an occasion when the transfer case developed a mind of it's own, shifting into 4hi and would not be talked out of it. I had driven a few blocks in that condition before realizing what had taken place. Not exactly a comfortable ride.

The few times I've used the 4WD since the change have been without problem, but I haven't tried it on dry pavement. I think it's probably okay as it is, but thought I'd invite some other opinions. I think a slightly larger tire on the rear might be of some help in certain conditions, but shouldn't adversely affect the gear ratios either.