Jeep Wrangler Forum banner
  • Hey everyone! Enter your ride HERE to be a part of JUNE's Ride of the Month Challenge!

1 - 8 of 8 Posts

·
Premium Member
Joined
·
663 Posts
Discussion Starter · #1 ·
I’m trying to get an idea of performance based on my own experience and using the table provided. Let’s say I’m used to a Jeep with 3.6 auto, 3.21 gears and 32” tires. That puts me in the yellow at 3 squares below the beginning of the green level. Would it be a fair statement to say that the performance I’m used to with that setup would be equivalent with the gearing and tire size that keeps me in the yellow at 3 squares below the green? For example would 36” tires with 3.73 be roughly equivalent in performance to my example above


64211B21-E8EE-4E7E-8799-480AD39A9FC7.jpeg
 

·
No Whining now....
Joined
·
257 Posts
IMHO (or maybe not so humble) -- Yes, I would think so; but why would you not go for the green?
Personally I'm on 37s with 4.88 on an auto trans. No problems as daily driver and it's a blast to crawl with.

No whining now...
 

·
Premium Member
Joined
·
663 Posts
Discussion Starter · #3 ·
I’m not saying that’s what I’m shooting for. Just trying to get more feel for the charts and alll the info out there on regearing
 

·
Registered
Joined
·
4,110 Posts
Yes. But 3.21 and 3.73s actually don't fall into "performance" categories. :D
I've found those charts to be pretty reliable in terms of RPM to tire size.
What's not reliable though is using the yellow or green to estimate MPG.
 

·
Registered
Joined
·
3,430 Posts
As you go up in tire size, you add more than rolling diameter and that has an effect on real world performance. Weight plays a very small part. Rolling resistance of bigger, wider tires has a bigger impact. Aerodynamics plays a part on the freeway (it gets worse as you go up in tire size and drive faster). If you were to get the RPMs with bigger tires back to exactly where they were with the smaller tires the Jeep will feel like it has less power. That's why you should generally go numerically higher on the ratio when you regear for bigger tires.

As a result, the color coding is off on that chart. The color bands should shift as you go up in tire size.
 

·
Super Moderator
Joined
·
6,791 Posts
I agree with derf. While the gear ratio itself may be similar the decrease in performance from larger heavier tires also needs to be part of the equation. To get the same level of performance with a larger tire size you actually have to go past just maintaining equivalence in gearing.
 

·
Registered
Joined
·
625 Posts
As you go up in tire size, you add more than rolling diameter and that has an effect on real world performance. Weight plays a very small part. Rolling resistance of bigger, wider tires has a bigger impact. Aerodynamics plays a part on the freeway (it gets worse as you go up in tire size and drive faster). If you were to get the RPMs with bigger tires back to exactly where they were with the smaller tires the Jeep will feel like it has less power. That's why you should generally go numerically higher on the ratio when you regear for bigger tires.

As a result, the color coding is off on that chart. The color bands should shift as you go up in tire size.
These charts are sort of set up that way honestly. Although maybe not enough. In the first column 2160 rpm is green. Under 5.13s 2277 is a hundred RPM higher, but is now yellow. Its a small difference, but as people here often point out, there isn't that huge of a jump between on set of gears to the adjacent set either.
 

·
Premium Member
Joined
·
924 Posts
A simple formula for doing this is to take your old gear ratio, multiply it by your new tire size and then divide that by your old tire size. That will give you your new gear ratio, like 4

In case you didn't know the formula.. neat video to watch

 
1 - 8 of 8 Posts
Top