1998 blazer, 4dr 2wd. I have the 3.08 rear end and since i put my other wheels on it (which are heavy as hell), i can tell its in a bind. Well i have someone who will swap me some 4.10 gears in my rear end. What do yall think i should do? Im stuck. I want my take off and dnt wanna blow my transmission. I regret putting those heavy tires on it, but snt have the money to put something else on it.... If i do it, how much will me mpg's drop? Any idea where my rpms would be at 60?? They're around 1500 right now. The bigger tires reduced it.

 

What size tires are you running?

 

I had the stocks, which were 205/75 15s i believe. And i went to 275/40 20s. The rims are heavy as hell.

 

You'll definitly have a hit on highway MPG, but it may actually help for city driving. It all depends on your driving needs and style. 3.08 to 4.10 is a huge jump in gear ratio though. You could easily run 33" tires with that low gearing. Wouldn't it be easier to find an axle with 3.42 or even 3.73 gears? Those are very common in the S-series trucks, are ususally cheaper than having your axle regeared, and it's not a big deal at all to swap the whole axle.

 

x2 on the axle swap, a lot easier, but i would stay away from 4.10, that would be too steep
and will probably be over reving the engine so MPG would suck..
Alex if the tire size from the ground to the top of tire is 30" or taller then go with the 3.73 gears
if above 33" then go with the 4.11, i went back and fully read all the posts, i did not notice at first you are running 20"s

 

The 3.43 gears would be about right, 3.73 would be good for performance, 4.10 may be a bit high for highway use. There is a carrier break in the 7.5" axle if memory serves, 3.08 down, 3.23 up, so it may not be a direct swap for gears. 4x4 axles are wider than 2wd axles if you are considering that route as well.

 

Thanks guys! I was thinking about staying away from it! Id like a 4x4 rear end, but want my fronts to stick out too. And the tires already have spacers. I really want the 3.73s. I like having the take off. I normally dnt push it past 90. So mainly i just need take off. BUT id deal with the 3.43s. Looks like ill be hitting up pull a part soon! :P thanks again everyone!!

 

Hahaha. Forgot i can edit!

 

There are some calculators online that will tell you your rpm at speed based on gearing and tire size. I have 3.73's in mine, and with a 235/75/15 (28.88") it runs right at 2,000 rpm at 60 in overdrive and torque convertor locked up.

Your 275/40/20's work out to a few tenths shorter than mine (28.66") While 4.10s wouldn't absolutely kill you on the highway (thanks overdrive! lol), a set of 3.73's would be much more pleasant.

 

3.42's run 2000 RPM at 70mph & 23mpg.