I own a 1990 Jeep Wrangler. I bought it with 30 inch tires already put on. (Larger than stock). It has obviously changed my gear ratio and the car only maxes out at 60-65 mph now. (It has the 2.5 liter 4cyl) What type of work can I do to change the ratio other than change the axle? If I have to change the axle, what should I get? Do I need to get a new front one since its four wheel drive? Any suggestions are appreciated.

Larger diameter tires should actually increase your top speed since you travel farther per wheel revolution.

Larger diameter tires also has a negative effect on your acceleration and braking ability unless you change the gearing and install bigger brakes.

Yes, it would require a new ring and pinion gear for both the rear and front differentials.

Perhaps the previous owner already changed the gearing and did so with a particularly high gear ratio like one would install for rock crawling.

thanks man. Any idea of how to determine what size to get? And a price idea?

First off, are you red-lining the tacometer or does it not have enough power to go any faster? Those earlier 2.5's didn't have hardly any power. Even the newer ones (2000-up) weren't that great. A buddy of mine had a 2000 with 31's and it wouldn't got past 65 unless you were going down hill. On long hills it would bog down as low as 50-55mph. Before you go throwing money at re-gearing, I suggest you first figure out which side of the tracks you're on. More than likely you have a 3.07 rear and front designed for 29in tires. 30in tires do not necessitate any gear change, just a slight boost in power. Not much you can do for bolt-ons. Just try to free up your airflow in and out of the engine and do a tune up. Other than that, maybe a cam. Rather than typing it all out here's a good link to help you determine your current ratio.

FAQ - How do I determine my gear ratio? - JeepForum.com

I would suggest in your position (having a 2.5), that the gearing should be as follows: 31in 3.73, 33in 3.90, 35in 4.10 (and if you're brave enough) 37in 5.13 minimum.

If you do re-gear, have a professional drivetrain shop do the work as you have to know how to set the pinion depth or your new gears will eat themselves.

If it was me, I wouldn't go any bigger than 33in tires on the 2.5 and run 4.10s in them. I always err on the side of more grunt on the low end and being able to turn the tires cuz honestly, bigger tires at high way speeds get get pretty hairy at times. It's not a porsche, it's a wrangler. Hope this helps

thanks a bunch. compared to some other forums ive read, you really know your stuff

it is nice information of Wrangler which has great features.