Gear ratio to tire size chart
Here’s a great little chart to find out what gear ratio would be good for you if you are changing tire sizes. Keep in mind that this is in no way a definitive answer. A lot will depend on what type of terrain you wheeling, how much on-road/highway driving you do, what MPG you are aiming for, etc etc. Also keep in mind that this is a general chart. It does not take into account what transfer case you have.. If your TJ is not a Rubicon you will have a NV231 t-case and 2.71:1 crawl ratio. If you have a Rubicon you have a NV241 t-case and a 4:1 crawl ratio. This has a very big effect when you are wheeling in 4-low! You can get away with a lower gear ratio and still crawl slower than your friends with 2.71:1. On the other side of the same equation you can gear the same as your friends without Rubicon’s and crawl even slower! Another factor to keep in mind is that the tire size listed on the tire itself is not always the actual size of the tire. Some tires in the upper 30′s and 40′s are up to a couple inches smaller than what is listed.
(Click image for full size)
For what I use my jeep for currently, I think right about the higher blue levels would suit me good. For example if I go to a 36″ tire, I would want to be right at 4.88. That would give me lots of gearing for mud and hill climbs, decent power at a higher RPM on the highway, and the usual horrible MPG like I expect out of my jeep (only worse than stock)!
Stock gearing in my jeep is 3.07, and the stock GSA tires are about 28″ in size. 27.7″ x 8.5″ to be exact. That puts it right in the bottom of the yellow area, which gives pretty poor performance on the highway. Add 31″ tires to the mix (my jeep), and the issue is even worse.
July 24th, 2008 at 3:56 pm
another informative post – thank-you
July 25th, 2008 at 5:22 pm
Thanks for the great comments Tammy!
August 1st, 2008 at 5:37 am
Hi Raskull,
First of all – love the site. I notice that you are running 3.07 gearing on 31′s – which is the same boat that I am in. Im trying to decide if this is something that I should do something about. I was wondering if you had any plans to upgrade the gearing – or are you waiting to see what kind of larger tire you end up going to ? Its one of those things that I really wish I had known about before I bought my 04 TJ Sport.
Fox
August 1st, 2008 at 11:41 am
Firefox: I really like my gearing the way it is around town, and it’s ok for wheeling too. I just hate it on the highway.
If you plan on sticking with 31′s forever then it might be something you want to look into, especially if you travel a lot on the highway. Just keep in mind that a regear for both axles could cost you $1000-$1500.
I plan on going to a larger tire size, so I will wait until then to regear.
June 21st, 2009 at 11:29 am
I have a 99′ TJ with and automatic. I need a new carrier but want to go to Numerically higher gears. What is the highest numerically i can go with the automatic?
Thanks
June 30th, 2009 at 11:17 pm
WingNut: What tire size do you have, and what axles are you running?
July 3rd, 2009 at 11:22 am
I don’t think you’re reading the chart right when you say “Stock gearing in my jeep is 3.07, and the stock GSA tires are about 28″ in size. 27.7″ x 8.5″ to be exact. That puts it right in the bottom of the yellow area, which gives pretty poor performance on the highway.”
3.07 and 28″ puts you at 2395 RPM and in the yellow, which according to the chart indicates good highway driving and fuel economy. That setup would be poor for towing and power according to the chart.
July 7th, 2009 at 1:44 pm
I am reading it correct, by maybe the comment is misleading. I had 31″ tires at the time of the writing of this article which means that 5th gear is not very useful on the highway.
With 28″ tires it’s not bad, but I still noticed a huge difference in power in 5th gear with 3.73 gears in other friend’s jeeps. I did get better gas mileage though, so I guess it depends on what your definition of “poor performance” is. I was speaking of power, not mileage.
July 31st, 2009 at 11:05 pm
I drive the Hope Slide hill and highway regularly; I turn off the O/D going up the hill but does little to help; still have the issue of bogging down or running at high RPM to do 90-100KM. I’m going to larger tires so a gear swap is going to be a must; what ratio though?
Based on the chart above, my current stock set up of 3.73 axles and 30.5” tires run just at the edge of highway/good fuel economy and daily driver/best performance. Combined with the transmission gearing (not factored in the chart), I think I need to move a little more away from Highway category to Daily driver/performance to get better power to climb the slide hill. If I run 33” tires, 4.27s would put me into the mid range of best overall performance. I was initially thinking 4.88s but this would put me into the power/poor fuel economy category.
Will the 4.27s fit into my stock carrier etc.. Do you think I’m on the right track to get the best compromise of road/power/furl economy and off-road/crawling performance or should I move closer to the 488s? I do drive a lot of highway so economy is a concern.
current set up:
Front: Next Gen. Dana 30 Solid Front Axle
Rear: Next Gen. Dana 44 HD Rear Axle, Limited Slip Diff
3.73 Axle Ratio
T-case 2.72
Tires: P255/70R18 (measures 30.5” height)
August 20th, 2009 at 11:55 pm
With your axles and 33″ tires a 4.56 gear ratio is widely considered to be the best option available.
Yes, if you can find a set of 4.27 gears for your axles, it would fit in the stock carrier just fine.
October 31st, 2009 at 9:42 am
I ended up going with 4.88s with the 33″s that actually measure 32″. I am quite happy I went a little lower with the ratio and not with the 4.56
As the JKs 3.8L is a little underpowered, the gears give me more torque where I need it. The fuel economy has suffered but not as much as I expected. Based on the computer, roughly a 15% decrease. Next mods will be high flow exhuast, cold air intake and performance chip. These will increase horsepower futher and if the advertized stats are correct, I might even get back or close to stock fuel economy.
November 11th, 2009 at 2:45 pm
At what speed is this chart bassed on?
November 30th, 2009 at 7:29 pm
08JKSahara: Good to hear! Good luck with the future mods.
Steve McCallon: I honestly don’t know. It’s safe to trust the coloured areas to get a desired result still, but unfortunately won’t help you in trying to hit a certain RPM at a certain speed. You can figure that out yourself fairly easy though. Try this out:
1: Test out your jeep at the speed you wish, say 60mph.
2: Make a note of your RPMs (we’ll say 2000rpm)
3: Divide the RPM you marked down by your gear ratio, then multiply it by the ratio you are thinking of using. (2000 / 3.07 * 3.73 = 2430) Voila!
December 6th, 2009 at 8:41 pm
Nice posts. Keep it up.
September 27th, 2010 at 1:14 pm
I own a 04 jeep wrangler unlimited automatic with a Dana 30 front with a Detroit locker and 4:56 ring and pinion the rear is a Dana 44 with a Eaton e locker and 4:56 ring and pinion i ran this set up with 33″ Goodyear mtr’s and was a great set up i also run a banks monster cat back exhaust with a k&n cold air intake and was very happy i live near the cajon pass on the way to Vegas and begin one of the steepest grades in the u.s. i would take it no problem at 70 to 75 miles an hour. with the od on and air conditioning with power to spare.
I recently put on 33 inch superswamper boggers and it has since lost a noticeable amount of power on the highway i can now take the pass at 60 to 65 with the od off. i can’t believe a simple tire swap can be so drastic.
Off road is not a problem at all i installed a tera low 4 to 1 gear reduction kit and in 4 lo it is down right scary.