questions about 31s

to all the guys out there running 31s i have some questions. what are you getting for gas mileage, what is your rear end geared at, and is there anything i should know before I run 31x12.5x15 on 3.75 BS wheels

 

I'm waiting for a set of 31/10.5-15 and I'm running 4.88. The 30/9.5-15 tires I bought are actually 28.2 and while fine, the true 31 that are really 30.2 will be even better. I did my gear calculations using 30" as actual size, unreal they are off so much.

I'm 2-300 rpm higher at 70mph than I was shooting for with the 28", so the new rubber should be as good as it'll get with this trans.

Don't put too much credence in mpg, with the 4.10 and 28" gears, my odometer was off more than 10%. I just fill it now, lol. It gets what it gets but it's not far off if at all from before as it sits now.

I'll let you know by weeks end how they feel.

 

So the reasoning for that high of a gear ratio was the calculations? how was the performance with 4.10?

 

I used the calculator as a guide for top cruising speed/rpm. I'm a moto guy, long time car modder too. One thing I've learned, gear low with street cars and trucks. My two Mach 1 mustangs were 5 speeds and 4.30 and 4.56 for the second one.

I operate between zero and 75 mph. My Mustangs would still do +150 mph with those gears, but drive ability was excellent. Most cars n trucks are geared way too tall for the EPA mpg test, not real world driving or fuel economy. I had equal mpg with small tires and 4.10 gears. Real world.

With 4.10 and stock tiny tires, it was excellent. With the 28.2" tires, it was slightly better than stock tires and 3.31, but not much. With 28.2 and 4.88, it romps like a 4 cylinder trophy truck, the nose actually lifts when you gas it. Downside was I was cruising at 3400 rpm sometimes in faster scenarios.

The actual 30" tires will bring it down a few hundred and still be responsive around town and allow better towing and hauling.

They arrive tomorrow so hope to have them on the truck then.

Btw, for off roading, I'd want even lower gearing with the 30s. Our trans isn't great in regards to gear range. I'd prefer a wider spread, lower first and taller fifth. We have to work within this parameter so that's that.

My JK jeep had actual 33" tires and 4.88, but a decent 6 speed manual. It could crawl in first, I started on the street in second, but still had a tall enough sixth to cruise at 75 easily.

 

I have 31s and 4.10 gears and the truck gets basically what I got when it was stock. Drives like it's back to stock as well.

I drove the truck with the standard gears and 31s for a while and you basically dont use 5th gear ever, and hills are a bit of an adventure. It's not crazy bad and i know a lot of guys on here have no problem running it without 4.10 gears, but it's perfect with them. Got a good deal from another TW member with a PreRunner, bolted straight on, did it with a buddy in a few hours.

 

Try it with the stock size tires on the rear axle jtye!

That's how it should be stock!