REBEL OFFROAD: Gears - the how, why and what.

Why should I have the gears in my differential changed?
Lets face it. When it comes to our Jeeps and Trucks, bigger tires are a must have. Whether it’s crawling over bigger rocks, getting through deeper mud pits, running over curbs in the drive-thru’s or just because it gives us that more aggressive look – bigger tires do it all. Larger tires affect your vehicles final drive ratio and if you have not changed your differential gears to match the changes in your tire size then your vehicle is not performing efficiently. Your vehicle will feel sluggish and slow to get going. Your motor will lug and your transmission will be shifting around and working much harder than it should. This causes shorter transmission and engine life and puts greater stress on your drive train components.

Adding taller tires or higher-ratio gears reduces engine rpm at all road speeds and gives the truck less mechanical advantage to help it crawl over an obstacle or get moving from a stop. Lower gears increase engine rpm and acceleration/ crawling capabilities. Remember that low gears are higher numerically (4.10 is lower than 3.50).

Now that you have the basics it’s easy to see why adding taller tires can cause the engine to lug below its power band and cause poor performance. To fix the problem, you need to swap to lower-ratio axle gears. But many ‘wheelers want gears that make the overall combination even lower than stock to improve off-road performance or increase a vehicles towing abilities.

5 Reasons To Change Your Gear Ratio.

The benefits of gearing CANNOT BE MATCHED BY ANY OTHER MODIFICATION TO THE VEHICLE!

1. OFFROAD PERFORMANCE WILL BE GREATLY IMPROVED
Even a simple change from a 31″ diameter tire to a 33″ diameter tire will affect the amount of available torque by 10%. Lower gearing will enable you to have far greater control when crawl over rocks and other obstacles with greater control and put less strain on your vehicles other components. This will greatly reduce the risk of breakage to hubs, axles, drivelines and suspension components.

2. STRESS TO THE DRIVELINE WILL BE GREATLY REDUCED
Modern day transmissions cost $600 or more to perform a basic overhaul. Driving with even a 10% larger tire will result in the transmission being under the same load as always being driven on an incline. The transmission may not suddenly fail, but the life will definitely be reduced by thousands of miles.

3. MPG and ENGINE EFFICIENCY WILL BE REGAINED
RPM alone does not affect fuel mileage. An undergeared vehicle (as the result of oversized tires) will result in a substantial loss of fuel mileage. Also, just as with the transmission, your engine life will greatly be reduced. Changing your axle gear ratio will stop the motor from having to work so hard and increase your fuel efficiency.

4. SPEEDOMETER/ODOMETER ACCURACY WILL BE REGAINED
With kits in the $100+ range to calibrate speedometers after tire swaps, it seems pretty important to have an accurate speedometer, which can also be fixed with a simple gear change.

5. TOWING ABILITY WILL BE INCREASED
Changing your vehicles axle ration to a lower gear will increase your vehicles ability to tow efficiently. The engine, transmission and the rest of the drive train components will not have to work nearly as hard when you are towing.

This is where we must now talk about the gear ratio chart for the Jeep JK.



Please contact us to discuss your vehicles axle ratio needs.

Cheers,
Bond
866-900-8841

correction

Quote :

4. SPEEDOMETER/ODOMETER ACCURACY WILL BE REGAINED
With kits in the $100+ range to calibrate speedometers after tire swaps, it seems pretty important to have an accurate speedometer, which can also be fixed with a simple gear change.

Swapping gears will not correct the speedometer in a JK. When you change tire size on a JK, the only way to correct the speedometer is to reprogram the computer for the new tire size.

True - we were referring to more broad base than just the JK. We love the AEV ProCal for speedo recal.

Bond, Great information to have. Thank you.
Gearing is on my to do list. Probably be going to 5.13's.

N2rock wrote:

Swapping gears will not correct the speedometer in a JK. When you change tire size on a JK, the only way to correct the speedometer is to reprogram the computer for the new tire size.

Really? That's odd. How does the whole speedo thing work in a JK then?

Deacon wrote:

N2rock wrote:

Swapping gears will not correct the speedometer in a JK. When you change tire size on a JK, the only way to correct the speedometer is to reprogram the computer for the new tire size.

Really? That's odd. How does the whole speedo thing work in a JK then?

actual wheel speed as measured by sensors at each wheel

redneckhouston wrote:

Deacon wrote:

N2rock wrote:

Swapping gears will not correct the speedometer in a JK. When you change tire size on a JK, the only way to correct the speedometer is to reprogram the computer for the new tire size.

Really? That's odd. How does the whole speedo thing work in a JK then?

actual wheel speed as measured by sensors at each wheel

Yeah- like Geo says- wheel speed is measured at the wheels. So when you swap tires to a different size, you hook up a programmer and tell the computer the new tire size. And it has to be actual measured tire size, not just the advertised size. For example, with my 35's I had to program as 33.25". The speedometer is dead accurate now (checked against my gps and by a radar wall).

Wow, that's interesting. Sounds like an unnecessary pain. Is that for ABS purposes, then, I guess?

Deacon wrote:

Wow, that's interesting. Sounds like an unnecessary pain. Is that for ABS purposes, then, I guess?

Not really a pain at all. Programmers can be picked up for around $150. You simply plug them into the port and make the change- takes less than 10 seconds to do. Which is obviously easier than changing a gear. And they do so much more than just reprogram the tire size. The AEV Procal is the lowest priced one, and it has a lot of other functions that can be changed

When I switched to 35's I never really thought the 4.10's were really that bad, with the exeption of driving into a headwind. I noticed a drop off/lag from the stock tires, but it was something I was content living with. That was until I had 5.38's swapped in. It feels like a totally different vehicle.

My son put 33's on his 98 Jeep and really noticed power loss especially on the highway. He has the 4 banger with manual trans. and couldnt really run on the highway in overdrive. He recently put in 4:88 gears and now can run on the highway with no problem. Really amazing how much difference changing out the gears can make. Has to be one of the best investments you can make on your Jeep.

N2rock wrote:

Not really a pain at all. Programmers can be picked up for around $150.

I meant more along the lines of any time you're swapping axles or what have you. I don't know enough about where exactly the sensor is located, what kind it is, how it works, etc.

I'm curious as to what all the programmer does for you if you have a manual transmission, though. I know with automatics it's supposed to change shift points and such, right?

Deacon wrote:

N2rock wrote:

Not really a pain at all. Programmers can be picked up for around $150.

I'm curious as to what all the programmer does for you if you have a manual transmission, though. I know with automatics it's supposed to change shift points and such, right?

Well of course it fixes the speedo for the larger tire sizes. Other things- you can adjust the tire pressure monitor to any psi you want (even turn it off if you prefer). You can bump the idle up- useful for winching. Daytime running lamp activation/deactivation. Clear codes- some programmers will display the codes too.

The Hypertech will do all of the above, plus things like change the cooling fan turn on temp, change the throttle response (JK's are drive by wire throttle), change the tuning for higher octane, etc.. But it is a much more expensive programmer than the AEV.

Ah, yeah, I forgot how many systems were all controlled electronically in the JK. Things like daytime running lamps never even occurred to me! Thanks for pointing some of that stuff out.

When I get my junk back from George, I'll have a high idle mod in the form of a hand throttle