XJ Tire & Wheel Combinations, Fender Clearance, Lift Requirement, Axle Ratio Chart

[Porch951]

Re: XJ Tire & Wheel Combinations, Fender Clearance, Lift Requirement, Axle Ratio Char

Thanks for the reference!
Where are you getting your "Gas Mileage" figures though? With an AW4, 3.55's, and 30's...mileage sucks!!! I can only imagine it gets much worse with 31's, 32's, and 33's.

Look here: http://www.jeep4x4center.com/jeep-tires/tire-gear-ratio-chart.htm

 

[BarFlyFisherman]

Re: XJ Tire & Wheel Combinations, Fender Clearance, Lift Requirement, Axle Ratio Char

The chart was developed using the optimum RPM range at 55 mph (2700-3000 RPM).

Going with a higher gear ratio, gives you more torque/climbing ability but worse mileage.

Going lower, improves mileage but drops out on torque/towing/hill climbing ability.

That's why you see guys with big tires & lift kits who don't understand gearing ratios (or who haven't swapped their gears) - pushing their XJ's uphill on the highway.

So for a highway XJ, that's taken periodically off road go with the HIGH end of the OKAY range, or 1 ratio above it. For a daily driver that's rarely taken off road, stay in the middle of the OKAY range.

Trailer queens that ride in padded velvet trailers to climb hills can go with outrageously high ratios, as they only perform mid-air refueling while off-road. They are seeking lots of slow speed low end torque. Many even install lower gear transfer cases to drop even lower.

 

[Root Moose]

Re: XJ Tire & Wheel Combinations, Fender Clearance, Lift Requirement, Axle Ratio Char

Say wut?

What is "optimum" about 2700-3000 RPM at 55 mi/h?

The basic rule of thumb goes something like (caveats apply!):

31s, 4.10s
33s, 4.56s
35s, 4.88
Larger, you've built a buggy and should run the lowest ratio your swapped in axles will take.

And then you get the religious arguments about each of those lines.

Another rule of thumb... find out your stock gearing and tire size and normalize against where you want to be. For example, if you want stock-like highway cruising RPMs start by normalizing. Then, depending on the engine and usage go one ratio lower.

Example:

3.55 / 27" = Ratio / 32"

Ratio = 4.2x

Above 4.10 size but below 4.56 size. Added weight, pushing heavy tires, increased aero drag, and hauling a trailer I'd go 4.56 every time with a 4 or 6 cylinder engine. With a V8 or larger... maybe not, which brings us to another point.

Your best bet is to compare what your math says against anecdotal evidence in your local 4x4 club.

Using your 5.12 ratio for for 32" tires in the chart would make for a miserable experience driving cross country for any length of time. Highway cruise nowadays is at least 70 mi/h. I certainly wouldn't want to drive a Jeep geared like that for 8 hours a day and day after day.

To complicate things even further...

Which transmissions are we talking about? IIRC the AW4 and AX15 both had different top gear ratios over their life times. Thankfully, all vintage XJs had 1:1 direct drive in the transfer case in high range.

Picking a higher ratio on a built Jeep in order to increase fuel economy is not going to work. Working the extra weight of a built Jeep against a gear ratio that will take the engine of it's torque range at highway cruise is not going to increase fuel economy. Sure, this is a rule of thumb thing again.

2¢

 

[Alexia]

Re: XJ Tire & Wheel Combinations, Fender Clearance, Lift Requirement, Axle Ratio Char

Say wut?

What is "optimum" about 2700-3000 RPM at 55 mi/h?

Absolutely nothing is optimal about 3,000 RPM at 55 MPH. That is 4,000 RPM in third gear! O_O This is not a Honda Civic Si hitting VTEC, yo!

 

[Root Moose]

Re: XJ Tire & Wheel Combinations, Fender Clearance, Lift Requirement, Axle Ratio Char

Fwiw, I'm doing ~2500 RPM at 115 km/h and wish I was geared higher (lower RPMS).

 

[Boss Cherokee]

Re: XJ Tire & Wheel Combinations, Fender Clearance, Lift Requirement, Axle Ratio Char

I have reviewed a bunch of articles, forums, blogs, and tire/wheel retailer websites to create a comprehensive spreadsheet that shows the most common tire & wheel combinations, fender clearance issues (or if trimming is required), lift requirements, and axle gearing ratios.

The spreadsheet is "locked," but anyone can view it at:

https://spreadsheets.google.com/ccc?...CPafl6IK#gid=0

Please be gentle with me, as a lot of work went into creating this chart. If you think that there are some errors (after considering the footnotes & warnings), then post them here. If enough people agree with a required change then I'll make it so.

Barfly, Nice job putting an information based sheet together. As always there will be critics & chicken littles (the sky is falling the sky is falling) hanging around to squash all efforts made by a person to help others in a project, or starting of one. While I myself am one that does what others say cannot be done I applaud your efforts, time, and research! As I said in my profile or past post, my 1st XJ was built in 90-92 with a V8 auto and Dana 20 on Bronco 4" coils running 35" Baja T/A's for the Hammers which at the time an XJ on 35's was inconceivable let alone 33's.No transfer case low gearing, no Atlas, no Skat box. Marlin crawlers were just starting. I have articles and the following year calendar cover pic to prove it. So I'm not Just saying, I did it!! Your spread sheet would have been welcomed and a good starting point and may have helped save time and trials, so thanks from the true old school wheelers and potential newbies! I hope this encourages you to any future assisting spread sheets you may tackle. As we all already know and you have been obviously reminded of any combination is possible! Remember your from California not all is taken well! LOL


POST QUOTE:
I have had my Jeep and been into off-roading for 8 years now and I have never seen a set of true 33x11.50 or 33x12.50 tires. I'm sure I have seen some metrics that would come close to those specs but never seen any standard sizes. Like coldoath said the rule of thumb for rim width and tire width is 15x7 is good for up to 11.50 while 15x8 can handle 12.50 and a little wider just fine. I have 15x8 rims with my 33x12.50r15 tires. I have read alot of articles too over the years and thought alot of the information provided by those articles were skewed to completely inaccurate. I learned what I know through real world observations and experience.

As far as 33's are concerned they are available in BFG 10.50/11.50/12.50 & 13.50 in M.Thompson but no longer in 14.50.

 

[Boss Cherokee]

Re: XJ Tire & Wheel Combinations, Fender Clearance, Lift Requirement, Axle Ratio Char

Say wut?

What is "optimum" about 2700-3000 RPM at 55 mi/h?

The basic rule of thumb goes something like (caveats apply!):

31s, 4.10s
33s, 4.56s
35s, 4.88
Larger, you've built a buggy and should run the lowest ratio your swapped in axles will take.

And then you get the religious arguments about each of those lines.

Another rule of thumb... find out your stock gearing and tire size and normalize against where you want to be. For example, if you want stock-like highway cruising RPMs start by normalizing. Then, depending on the engine and usage go one ratio lower.

Example:

3.55 / 27" = Ratio / 32"

Ratio = 4.2x

Above 4.10 size but below 4.56 size. Added weight, pushing heavy tires, increased aero drag, and hauling a trailer I'd go 4.56 every time with a 4 or 6 cylinder engine. With a V8 or larger... maybe not, which brings us to another point.

Your best bet is to compare what your math says against anecdotal evidence in your local 4x4 club.

Using your 5.12 ratio for for 32" tires in the chart would make for a miserable experience driving cross country for any length of time. Highway cruise nowadays is at least 70 mi/h. I certainly wouldn't want to drive a Jeep geared like that for 8 hours a day and day after day.

To complicate things even further...

Which transmissions are we talking about? IIRC the AW4 and AX15 both had different top gear ratios over their life times. Thankfully, all vintage XJs had 1:1 direct drive in the transfer case in high range.

Picking a higher ratio on a built Jeep in order to increase fuel economy is not going to work. Working the extra weight of a built Jeep against a gear ratio that will take the engine of it's torque range at highway cruise is not going to increase fuel economy. Sure, this is a rule of thumb thing again.

2¢

Nice to see some positive input! I also agree with the higher choice on ratio as far as your mathematics, especially if you have close choices to step up, for instance: your sum of 4.2 but going up to 4.56. Many do not consider radial, aerodynamic, and greatest amount of driving (Daily driver/trail only/or combination of both). 36x15.50x15 such as I run, give greater noticeable resistance than 36x12.50x15. I know I,ve have them in both sizes. Even though many criticize my wide 15.50 I prefer them for the wide print they give me on the rocks. They are the same as 38's width wise without the rolling resistance therefore not needing lower weaker gearing that a set of 5.13's or higher might bring!