Hey everyone,
I’ve been having an issue with my jeep losing major speed on any incline. I have a 2013 sport unlimited with a 3” lift on 37s, but here’s the deal it doesn’t matter how big the incline is but it starts losing speed ranging from 10-25 MPH. If anyone knows what the issue is would be greatly appreciated!

 

I'll ask the obvious, what gearing do you have in the axles? Is this something that just started happening? 37s are a lot of rolling mass.

 

Yep a lot of folks just do not realise how much power heavier wheels suck from the engine and then there is the lower ratio of taller gears effect having the larger diameter tires. That's why supercar manufacturers put lightweight wheels on their cars to reduce mass and unsprung weight.

 

Of course gearing is the first question to answer. If it is stock 3.21 or 3.73 then you will lose significant power, particularly if the computer has not been reprogrammed.

 

It just started doing it gears are stock still and computer has been reprogrammed for larger tire size.

 

Did it just start doing it because the tires were just added, or you had these 37s for a while and there has been a definite change that you believe is engine/transmission related? No stock gearing, even 4.10s in a Rubi, are enough for 37s regardless of having the proper size programmed in the computer. Being over-geared might feel fine on flat land, and especially if you don't care about acceleration, things like inclines and headwinds really take their toll on the transmission.....similar to how towing a trailer will dramatically affect how the vehicle performs. I guess what I'm getting at here is it's hard for us to determine thus far if you're just talking about decreased performance from the larger diameter and heavier tires or if you're implying an engine/transmission issue. Since you have a manual transmission I'm wondering if the speed loss you're referring to is simply staying in 6th gear and you're losing speed, or if you're downshifting to lower gears and still losing speed.

You'd really benefit from a regear regardless.