gear ratio help

kennypowers

New Member
Joined
Mar 5, 2009
Location
Wilmington
I am about to put a high pinion dana 30 and a dana 44 under my tj. I am torn between what gear ratio i should get. I plan to upgrade to a 4.oL within the next 6 months. The next tires I will buy will be 36"s, however I proabably won't buy them for another year. (currently have 33's and a 2.5L) I also have to use this vehicle as my daily driver. But I want to have enough power to pull a trailer with ease. I dont need to go faster than 60mph. I was thinking about something like 4.10 to 4.88? Any suggestions???
 
4.56's would be about right. I run 35's with a 4.0 and 4.56's and am very happy. I have a friend with a 2.5 and 33's and 4.88's and he is not very happy with it. I guess it really depends on what your going to do with it though.
 
I'd go with 4.88s if you plan on turing 36s with that 2.5L. Are you auto or manual?
 
this should help you decide. http://www.quadratec.com/jeep_knowledgebase/article-26.htm

assuming you have the stock 4.10 axles in it now with 33's, you probly dont have the power to pull. so, you got 2 choices basically.

1. do the axle swap with either 4.56 or .88, hold off on the 4.0 swap until you get the 36's, unless you just like to pay for gas.

2. hold off on the axle swap, do the 4.0 swap, and put the axles in when you get the 36's.

I think that is good reasoning, If im misleading in anyway, feel free to set me straight. hope this is helpful.
 
The reason I am doing the axle swap first is because my front dana30 is currently broken. I already have a hp dana30 and dana 44, so I might as well do them both.
I want to get gears that will be good with my 2.5L and 33's.
I also want the gears to be a good match with a 4.oL and 36's. (later plans)
 
Auto or manual?
4.56, 35's and a 4.0 in a 5spd is perfect. 38's need 4.88's, but 36/37's are kind of gray area. Considering you won't ever go over 60 (I wish I could do that, would prevent a lot of tickets...), I would go with 4.88's.
 
Its a 5sp manual.
Does anyone know what will happen to my gas mileage with lower gears (going from 4.10 to 4.88)... I dont know if Im understanding it correctly. Im thinking my gas mileage might increase with lower gears because my engine wont have to work as hard, but my "top speed" will decrease.
Anybody have a manual 2.5L with 33's and 4.88's : What rpm's are turning going 60mph?
Anybody know about a 4.0L with 35/36's and 4.88's : Same question?
Thanks for the help
 
kennypowers said:
Its a 5sp manual.
Does anyone know what will happen to my gas mileage with lower gears (going from 4.10 to 4.88)... I dont know if Im understanding it correctly. Im thinking my gas mileage might increase with lower gears because my engine wont have to work as hard, but my "top speed" will decrease.
Click to expand...
I agree on both counts, its hard to say, just have to do it and see. Keep in mind your speedo is off since you changed tires size. On a related note, you say you only go 60 MPH, but you are probably actually travelling faster.
kennypowers said:
Anybody have a manual 2.5L with 33's and 4.88's : What rpm's are turning going 60mph?
Anybody know about a 4.0L with 35/36's and 4.88's : Same question?
Thanks for the help
Click to expand...
Check out the Find RPM calculator near the bottom of this page...http://www.rocky-road.com/calculator.html
I'll use 0.785:1 OD ratio (AX15 is 0.79, NV3550 is 0.78)
engine doesnt matter
60 MPH...
4.10 and 33s-->1966 RPM

4.88 and 33s-->2340 RPM
4.88 and 35s-->2206 RPM
4.88 and 36s-->2145 RPM

Keep in mind, these diameters are true diameters...most tires actually measure under their advertised 'diameter'. Most of the major manufactures will list actual diameter (on the suggested rim width) on their websites.
 
I think I figured my speedometer to be 10% off. Through the use of multiple GPS's haha.
Example: 30mph = actual 33mph. 50mph = actual 55mph.

I understand that with lower gears I will be turning higher rpms relative to lower gears at the same speed. My questions are: Will just changing my gear ratio make my speedometer incorrect? (not changing tire size, just gears) and... Does anyone know what will happen to my gas mileage specifically? (from experience or knowledge)

Thanks
 
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