4.88

[luke87]

as soon as i get my 4x4 swap done I'm planing on running 4.88's gears with 35's. i know gas mileage is gunna go down the drain, but i also want to be able to keep up with traffic in socal.

I'm keeping my 2.5. but i I'm building it and putting a aftermarket cam, headers, cold air, and possibly a throttle body( even though i know it doesnt help much).

my question is..with the gears that i want to run, will i be able to go at least 70? i have 30's with the stock d35 right now and i can go about 80.

are 4.88's too much for a daily driver?

[mjeff87]

is yours TBI or MPI (since you mention throttle body swap)? I'm turning (well, trying to anyway) 33X12.5" now on 4.56's, and it's just not cutting it on the road. It crawls well enough, but on highway I'm all but floored and inbetween 4th and 5th with the slightest elevation....and mileage is in the 10-12 category :oops:

 

and I'm nowhere near the 70 mph range, more like 60-65

 

Jeff

[Eagle]

my question is..with the gears that i want to run, will i be able to go at least 70? i have 30's with the stock d35 right now and i can go about 80.

are 4.88's too much for a daily driver?

"Too much?" As in, too deep a ratio with 35" tires? More likely, "not enough," but let's see.

 

You don't say what tranny you have or what year MJ, so I'll assume it's a 5-speed manual with 4.10 gears. Stock tire size would have been probably 205/75-15 or 215/75-15. Using the 205/75 as a baseline, with 4.10 gears you would be turning 3607 RPM in 4th gear at 70 MPH, and 2705 RPM in 5th gear at 70 MPH.

 

Unfortunately, my tire & gear spreadsheet doesn't even include 35" tires, because when I made it up several years ago I never thought anyone would put 35" tires on a street XJ or MJ. The biggest I have data for is 33" tires, so I'll post that and you can extrapolate. 4.88 gears and 33" tires, in 4th gear you'd be turning 3638 RPM at 70 MPH and in 5th gear you'd be turning 2729 RPM at 70 MPH. In other words, VERY close to the same RPMs as stock tires with the stock 4.10 gears. Jump it up to 35" tires, and you will effectively be running less gear than stock. You'll have a hard time holding 70 MPH on the highway, not because you're over-revving the engine but just because the engine probably won't be putting out enough power to handle upgrades.

[Eagle]

Y'all forced me into it. I just Googled up the BFG tires web site and updated my spreadsheet to include 35" tires.

 

New data, for 35x12.50R15 (and almost identical for 35s on other rim diameters) will be 3410 RPM at 70 in 4th gear, and 2558 RPM in 5th gear.

[mvusse]

Using those numbers, 5.16 gears would be equivalent to 4.10 and stock tires. 5.13 is the closest common ratio, but thinking about getting all that extra rotating mass going I personally would opt for 5.29 myself, if not more.

 

I'd also definitely look into a brake upgrade to be able to stop that much tire.

[tjbliley]

I run 35's with a 2.5/ax15/np231/Dana30/Dana35/4.88's and my end ratio is stock. Which means that it will go whatever it should go if it had stock tires and gears. It pulls up hill and I have 5th gear on the highway, can do 80-85 if I have too. You just need to remember if you have that size tire your COG is altered a great deal and that much speed can cause more problems........Voice of expereince there.......You may just want to cruise around 65-70 and enjoy the ride.

[Eagle]

Using those numbers, 5.16 gears would be equivalent to 4.10 and stock tires. 5.13 is the closest common ratio, but thinking about getting all that extra rotating mass going I personally would opt for 5.29 myself, if not more.

 

I'd also definitely look into a brake upgrade to be able to stop that much tire.

4.88 is the deepest ratio available for the Dana 30, unless things have changed when I wasn't paying attention. Last I knew, even 4.88 was available only aftermarket, because Dana-Spicer won't go beyond 4.56 due to the small size of the pinion.

[mvusse]

I'm new to the jeep thing, so I looked it up. Dana 30 also has 5.38 available, but the 35 for the rear only goes to 4.88.

 

If the rear axle would have been a 44, 5.38 would be a possibility, but there's nothing in between 4.88 and 5.38.

 

I don't even know if a Dana 35 will survive 35" tires for very long without breaking something.

[tjbliley]

I'm new to the jeep thing, so I looked it up. Dana 30 also has 5.38 available, but the 35 for the rear only goes to 4.88.

 

If the rear axle would have been a 44, 5.38 would be a possibility, but there's nothing in between 4.88 and 5.38.

 

I don't even know if a Dana 35 will survive 35" tires for very long without breaking something.[/quote]

 

It will last as long as you want it too. You just have to take care of it and don't drive like an idiot.

[xjcrazy09]

If you were to put a rear locker in...it will up your chances of breaking something

[86FUBAR]

I'm new to the jeep thing, so I looked it up. Dana 30 also has 5.38 available, but the 35 for the rear only goes to 4.88.

 

If the rear axle would have been a 44, 5.38 would be a possibility, but there's nothing in between 4.88 and 5.38.

 

I don't even know if a Dana 35 will survive 35" tires for very long without breaking something.

 

If my memory serves me right and nothing has changed lately that i don't know about the 5.38 u mentioned are for standard rotation (low pinion) and or eariler model 30's and those won't work with the revers rotation 30's that most of us are running , further more i wouldnt recomend runing more than a 4.88 because the pinion starts to become extremly small and is then the weak link in the drive train

[luke87]

well right now i havent done anything to my axels. i still have 2wd and a 4 speedwith the 2.5 tbi. I'm planing on a d44 in the rear and d30 up front with a 231, and a 5 speed that is available at the junkyard.

 

but what I'm hearing i should be ok with 4.88's. i don't need to go 80. ive already accepted the fact that I'm def not the fastest truck on the highway. I'm just wantin a decent dd and offroader to keep up with everybody.

my future setup should be good right?