bostonnj15

i am trying to decide on what gears i want. i am going to be running a 33 inch tire but i am going to move up to a 35 size tire later. i was wondering about how fast will the top speed be with the 4.56 gears

MasterShakeXJ

maybe like 60 or so? not entirely sure.

76ANTHONY

not very....
but if your puttin on 35's it will be for the trail right, nobody puts 35's on a dd, do they?

sk8ertht540s

i am putting 35s on my jeep and a 7.5 from rubicon express and im going to drive my jeep every day

BowtieGuy3

Here's the easy equation:
The higher the gears numerically, the quicker you will go. Higher # gives more low end torque and puts your engine in its power band faster, but you will wind out quicker.

The lower numerically, you won't be as quick, but top end increases. The lower the # it takes more to get to the engine's power band, but you spend more time in it.

For example:
At Bristol and Martinsville, we'd run anything from a 6.20:1 to a Trip 6:1
Daytona and Talladega we'd run a 2.86:1 to a 3.10:1.
Bristol tops out at 100mph
Dega tops out at 205mph.

So, the larger tire you go, you correct by having a numerically higher gear to spin those.

There is a formula for tire size vs. gearing and RPM somewhere, I don't have it handy...

xer0

http://www.s-series.org/htm/calc/ratiotable.htm

chart and formula

76ANTHONY

wow, just doesnt sound like the ideal dd to me. but sounds like it'll look cool as heck

BuckB91XJ

Here's my two bits. I have 4.56 gears on my XJ right now with 32" tires, 4.0 HO and the overdrive automatic. I get 21-22 MPG on the highway as long as I cruise right around 70-75 (2300 rpms). If I bump it up to 80-85 (2600 rpms), I get 18 mpg. I actually was planning ahead when I installed these gears. 4.56 gears are too low for 32" tires. They are actually your optimum for 33" tires and in my opinion, 4.88 gears are optimum for 35" tires. I do agree with the guys that I wouldn't go any bigger than 33" tires for a DD. I had 35s on my Toyletta and it would bounce your guts out on the highway. I think 35s on an XJ would do about the same.

BuckB91XJ

I'm really not sure just how fast you can go with 4.56 gears, but with the 32s I can bury the 85 mph speed O and still have about an inch or 2 of pedal left. Here is the gear to tire scale in my humble opinion:

3.55 - up to 30"
4.10 - 31-32"
4.56 - 32-34"
4.88 - 34-36
5.13 - 36 and up

I have only seen tires bigger than 35" on a few daily driven XJs. Example, there is a guy in town where I live who wrenches at our local off road shop. He has an XJ on 39" tires but, he told me he can't do over 35 mph safely. It is trailored to the trail and he NEVER would drive it on the road.

93XJLI

wtf is going on here again?

anyway, I agree with Buck on the gearing. I have 33s and 4.56s and love it. I dont drive too fast so I could've gone 4.88s even. At 60 I'm running 2200, 70 2700. Why do you need to know how fast you'll go? Drag racing on the weekends you aren't wheeling? I have a few friends who DD 35s, and another (who is a mod here actually...) who up until recently was DDing 37s. If you set up your **** right, you can DD large tires no problem

BuckB91XJ

I'm hoping he was wondering about top speed, with lower gears, so he could gauge mileage or his ability to sustain highway speed. I'm with you. It's all about the crawl ratio and just enough gearing on the other end to DD to work without going broke buying gas. No need to drag race my XJ on the weekends. It would cut into my 4wheeling time too much.