Gear ratio selection, maintaining power with a lift and bigger tires

I've seen a lot of about gear ratios and how its helpful to go "bigger" than what your change in tire size would be, i.e. use 4.56's when you have 33" tires even though 4.10's would be the closer match.

I would like to ask this a bit differently with an example. I have 2 XJ's. An 01 XJ with 235/75R15's on factory steelies, stock suspension, and stock gears. I also have a 97 XJ with 30x9.5x15's on factory alloys, a 2.5-3" lift, and stock gears. Both have BFG A/T tires. I bought the 97 XJ with a lift and have no stock comparison. What I do notice, is that climbing grades the 97 XJ seems to have "less power". There's a hill I've climbed both with on multiple days (trying to account for any wind) and the 01 XJ climbs it easier than the 97 XJ, and seems to have a higher top speed too. Both seem to have about the same compression. The 97 XJ has a new cat, etc. Out here in Colorado with the high altitudes its not uncommon to run either in 2nd gear near redline on some of these highway grades once you're near/over 10,000'. However, the 97 XJ seems to need 2nd gear a bit more. How much of this could be attributed to the lift/larger tires versus overall powertrain/drivetrain performance.

And, if I do say put 4.10's in, am I likely to "loose" top speed because obviously if I need to be in second near redline, I'm not going to be able to go as fast. Or would the 4.10's eliminate the need to use 2nd gear so its not really an issue.

Because regearing takes time and isn't cheap, I would like a bit more information before I pull the trigger.

Thanks!

sounds like regearing is exactly what you need

The feedback you get will be more useful if you indicate whether the transmissions on these jeeps are both auto or manual, or you have one of each.

Sorry, they are both AW4

You wouldn't need 2nd gear (most likely). 4.10's would be much better.
Are both vehicles originally from the area? Because there are high alt CKP, and "normal" CKP. Also, the 99+ intake was redesigned and flows better.
235/75 VS 30x9.5 difference is minimal. If you are willing to go through the effort, swap the wheels and tires between the 2 vehicles and do the same drive. And report back.

You also have to take into consideration that not all vehicles are created equal. If you took 2 identical, even brand new, XJ's on the same drive almost certain that they would perform at least slightly different.

97 XJ was special ordered for a gentleman in Jacksonville, Fla then it moved to Colorado
01 XJ was bought from the lot in Reno. I bought it from the first owner who I knew.
I suppose I could lift the 01 XJ same as the 97 XJ and report back.

When I've bought crank sensors from the dealer I don't recall a high altitude one. I'm not sure if that applied only to earlier models?

You may be right, my 01 XJ may just be a better perform on the highway. I would say the 97 has more low end grunt and the 01 XJ seems to do better top end. I noticed it pretty much from day one when I got the 97 last year. I think its pretty typical of the log intake. Either would benefit from an effective power boost.

md21722 said:

97 XJ was special ordered for a gentleman in Jacksonville, Fla then it moved to Colorado
01 XJ was bought from the lot in Reno. I bought it from the first owner who I knew.
I suppose I could lift the 01 XJ same as the 97 XJ and report back.

When I've bought crank sensors from the dealer I don't recall a high altitude one. I'm not sure if that applied only to earlier models?

You may be right, my 01 XJ may just be a better perform on the highway. I would say the 97 has more low end grunt and the 01 XJ seems to do better top end. I noticed it pretty much from day one when I got the 97 last year. I think its pretty typical of the log intake. Either would benefit from an effective power boost.

Click to expand...

I noticed this exactly between my 92 and my 99. But the difference 410s will make is actually quite impressive. I had 456 on 33s and now 410s on 33s and the difference is pretty noticeable. With the 410s you'll be pulling hills with ease

trippled said:

I noticed this exactly between my 92 and my 99. But the difference 410s will make is actually quite impressive. I had 456 on 33s and now 410s on 33s and the difference is pretty noticeable. With the 410s you'll be pulling hills with ease

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:huh:

I think you have this backwards. Lower gear will pull hills better. 410 gears are lower than stock, but 456 gears are lower than 410 gears. I think i have this right.

Johnnie Walker said:

You wouldn't need 2nd gear (most likely). 4.10's would be much better.
Are both vehicles originally from the area? Because there are high alt CKP, and "normal" CKP. Also, the 99+ intake was redesigned and flows better.
235/75 VS 30x9.5 difference is minimal. If you are willing to go through the effort, swap the wheels and tires between the 2 vehicles and do the same drive. And report back.

You also have to take into consideration that not all vehicles are created equal. If you took 2 identical, even brand new, XJ's on the same drive almost certain that they would perform at least slightly different.

Click to expand...

Only RENIX engines (87-90) had the high altitude CPS option.

The 99+ intake only works well with 99+ head and ecm programming. It does nothing for older engines. Wasted time and money on this 'mod' myself.

scottmcneal said:

:huh:

I think you have this backwards. Lower gear will pull hills better. 410 gears are lower than stock, but 456 gears are lower than 410 gears. I think i have this right.

Click to expand...

You are right. My post is worded correctly I unfortunately went from backwards in my gear change due to circumstances. But 410s would be noticeable in his case, since he most likely has 3.55s

Yes, stock 3.55's.