Another Re-Gearing Question

[JMT]

I've got the 4.0L, NSG370 6-speed tranny and 3.73 gears Right now I'm running 31's that are really 30.25. I should be at 4.07 to have stock performance (4.11). I was calculating the numbers for 33's and 35's and I was wondering your opinion on whether 4.56 would work for either. Assuming that most tires are not true to those numbers and a few are, I made these calculations. What do you think? My issue is I can't decide where I want to end up so I'd like to know.

32.25's
Calcs say 4.34 so go with 4.56

33's
Calcs say 4.44 so go with 4.56

34.25's
Calcs say 4.61 so I could go with 4.56 or 4.88 (almost dead on)

35's
Calcs say 4.71 so I could go with 4.56 or 4.88

 

[Rob5589]

It is easier to go by the listed number rather than the actual diameter. 6 spd and 33's, go 4.56. 6 spd and 35's go 4.88.

 

[JMT]

It is easier to go by the listed number rather than the actual diameter. 6 spd and 33's, go 4.56. 6 spd and 35's go 4.88.

I already made the calculations man!

I'm just thinking that if I'm on 31's now at 3.73 and it's very livable, then wouldn't it be just as easy or even easier to live on 35's at 4.56?

 

[StG58]

Don't fear the gear. I have rarely heard anyone say "I wish I had less gear" if they're driving a Jeep.

 

[JMT]

Don't fear the gear. I have rarely heard anyone say "I wish I had less gear" if they're driving a Jeep.

Ok, so what would 33's be like at 4.88? Just want to think about all my options, especially from you guys with more gear knowledge @Rob5589 and @StG58

 

[StG58]

I'll let @Rob5589 answer that one. He's got way more experience that I do on what it would be like. I'm going 5.13's in my SE, and he's running 4.88's in his SE. Different rigs though. Question though. How often do you spend more than an hour running down the Highway at 80?

 

[JMT]

I'll let @Rob5589 answer that one. He's got way more experience that I do on what it would be like. I'm going 5.13's in my SE, and he's running 4.88's in his SE. Different rigs though. Question though. How often do you spend more than an hour running down the Highway at 80?

Never. I cruise 9 miles at 60 daily. Rarely go more than 60 miles and when I do Itravel 60-70mph

 

[StG58]

Never. I cruise 9 miles at 60 daily. Rarely go more than 60 miles and when I do Itravel 60-70mph

Calculate the difference between the different gear and tire combinations you're thinking about. Come up with a correction factor for each, say 1.15 for the 4.56 - 33" combination. You can find a gear among 6 that is kinda close to that RPM. Drive around a little in that gear at those RPM's and that will give you an approximate feel for that tire and gear combination. Does that make sense? Be sure to check 1st and 2nd as well as the higher gears. IIRC, your 6 speed has a pretty deep first gear. You may have a decision between a really low crawl speed in 4lo and general usability in hi range. It's no sin to start out in 2nd in low range though.

 

[Mike_H]

Also not a sin to start in 2nd in High range...I do it often, driving around in my jeep. 1st is so low with with the 4.11 gears that I'm only half across the intersection when I need to shift to second.

 

[Rob5589]

Ok, so what would 33's be like at 4.88? Just want to think about all my options, especially from you guys with more gear knowledge @Rob5589 and @StG58

I think it would awesome. The gear calc puts you at about 2800 at 70. If I were in your shoes, I wouldn't hesitate to go 4.88 over 4.56.

Like @StG58 said, rarely does someone want for a taller gear. Occasionally we would have a customer whine over the higher rpm's on the fwy. But after off road, towing, etc., the whine changed to "this is awesome." We did have several customers not take our advice and go with what they thought or a "buddy" told them to go with. Then they'd bitch us out because they couldn't tell the difference.

 

[JMT]

I think it would awesome. The gear calc puts you at about 2800 at 70. If I were in your shoes, I wouldn't hesitate to go 4.88 over 4.56.

Like @StG58 said, rarely does someone want for a taller gear. Occasionally we would have a customer whine over the higher rpm's on the fwy. But after off road, towing, etc., the whine changed to "this is awesome." We did have several customers not take our advice and go with what they thought or a "buddy" told them to go with. Then they'd bitch us out because they couldn't tell the difference.

That's really interesting! Thanks, I'm about decided to go for 4.88's. I'd never have to regear for sure.

 

[JMT]

Calculate the difference between the different gear and tire combinations you're thinking about. Come up with a correction factor for each, say 1.15 for the 4.56 - 33" combination. You can find a gear among 6 that is kinda close to that RPM. Drive around a little in that gear at those RPM's and that will give you an approximate feel for that tire and gear combination. Does that make sense? Be sure to check 1st and 2nd as well as the higher gears. IIRC, your 6 speed has a pretty deep first gear. You may have a decision between a really low crawl speed in 4lo and general usability in hi range. It's no sin to start out in 2nd in low range though.

Not sure I understan fully, but it gives me something to think about and study. So I'll do it just for interest sake

 

[StG58]

Not sure I understan fully, but it gives me something to think about and study. So I'll do it just for interest sake

Ya, sorry, that wasn't very clear was it.

Here's an example. I know that the Jeep runs at 2800 RPM in 4th with my current tires at 60 mph. I would like to know what it would act like if I had 5.13's in it. So I do the math... 5.13/4.10 and come up with 1.25. 1.25x2800=3500 RPM. But, I'm also going with a larger tire so I need to factor that in. Let's say my current tires go 650 revolutions per mile and the new tires go 625 revolutions per mile. 625/650=0.96. My 3500 RPM's are now 3300 RPM's (The revolutions per mile data is available on the manufacturer's websites) After figuring all that out, it's a matter of selecting a gear that gives me 3300 RPM at 60 MPH. It'll never come out exact, but it will kind of give you a feel for what the Jeep will act like. If you multiply the 1.25x0.96 and get the result, 1.2, you only have one conversion number to deal with.

This won't help you get a grip on what the actual gear and tire size change will do to acceleration, power on the pavement or braking. It will kind of give you a feel for what cruising down the road will feel like.

A spreadsheet is great for doing these calcs because you can do the math for your actual gear ratios and tire sizes.

Or you can ask on here and get a ton of opinions.