Gear Reductions—A Quick Guide on How Portal Lifts Work

GDP Portal Gear Lifts give you a lift and a gear reduction in one package, and they let you choose between a 15%, 30%, and 45% gear reduction. That’s a lot of choices! And you might have some misconceptions about what a gear reduction really does or why you’d want a small gear reduction instead of a huge gear reduction.

Never fear! We’re here to answer some common questions about this mystical force that lets your cousin ride like a pro, but leaves you getting winched out of the mud. We’ll help you understand why gear reduction is important, why you might need it, and how you can get it. Spend some time reading now, and you will be talking ratios and torque with the best of them later.

Why Should I Care about Gear Reduction Ratio?

You should care about gear reduction because it helps to create more torque.

Ah, torque.

Here’s another word most of us claim to understand, but just in case you don’t—allow us to explain it. Torque is the amount of power that your engine produces to turn your tires. Simply put, the more torque your UTV can produce, the easier your engine can turn your wheels (which leads to faster acceleration). Less torque leads to higher top speed, but slower acceleration and less power.

Do I Need More Torque?

More than likely the answer is yes, especially if you’re considering getting lifted with a set of portals. Even more simply put, if you’re going to put larger than stock tires on your machine, you definitely need more torque. How much torque you want depends on how you ride. A side-by-side that rolls off the showroom floor usually has a clutch and transmission set up for a balance of speed and power based on stock equipment. Your average ATV/UTV rider might find this completely adequate, but if you are all about hitting the trails and getting the blood pumping, you’ve probably already upgraded your machine. The list of upgrades that can potentially affect the performance of your ride is long, but we are going to focus on one of the biggest culprits: tire size.

How Does Tire Size Affect My Torque?

The biggest torque killer with larger tires is the distance around the tire, or the circumference. When most riders say bigger tires, they are talking about their height from the ground. This is how tires are sold. The size of a tire = the height of the tire from the ground. But by increasing the height of a tire, you also increase the distance around the tire. If we think about the tire as a gear, it takes more force to roll a bigger tire one revolution because it needs to travel a further distance.

An Easy Way to Determine the Gear Reduction You Need

You can skip reading this next part and use this gear reduction calculator, or you can keep reading and learn something new. We suggest you keep reading.

If you marked two tires, one 25″ and one 32,” and rolled them both together for a total of one complete revolution (or the distance it takes for that mark to travel from the ground all the way around and back again), the 25″ tire would travel about 78.5 inches while the 32″ tire would roll about 100.5 inches. Trust us on this one—it’s math. (If you want to know more about the math, check out this article on determining gear ratios.) To roll that bigger tire the extra distance, your engine has to work harder because it needs to spin it more to achieve one revolution. In this example, if we figure the percent increase from 78.5 inches of travel to 100.5 inches, we find that you are losing 28% of your torque. This translates into a loss of acceleration and power.

And now, my friends, we have come full circle. If you want to make up for that loss caused by your bigger tires, you need more power. You need a gear reduction! How much reduction do you need? The simple answer—enough to replace what you lost by increasing your tire size. If you go from a 25″ tire to a 32″ tire, you would need a reduction of about 28%.

How to Choose Which Portal Gear Reduction You Need

We list the recommended gear reductions for each tire size (and the lift you’d need in addition to the portals to achieve those tire sizes) at the bottom of each of our 4″ and 6″ portal pages. These recommendations are specific to each machine and they tell you which gear reduction you’d want to choose to get back to (roughly) stock max speed.

It’s a very basic way to optimize your speed and your power/acceleration with bigger tires. But you don’t have to follow it. For example, most mud guys aren’t worried about hitting their max speed through a mud hole—they stick it in low and crawl through crazy deep mud on monster tires. They want the biggest gear reduction they can get, not the most balanced one for bigger tires. That super-high torque lets them plow through mud like it’s nothing.

The same holds true for rock crawlers. More torque is more preferable than power balanced with speed. Getting up and over huge boulders is more about pure power than speed.

With trails and dunes, a smaller, more balanced gear reduction might do just fine. With tires that are just a little bit larger than stock, the smaller gear reduction can get your power back and keep you moving as fast as possible.

I’m Sold. How Do I Reduce My Gear Ratio?

One of the best ways to reduce your gear ratio (and get a bigger gear reduction) on your UTV or ATV is to install a portal gear lift kit. Odds are if you’re thinking about bigger tires, you’re already thinking about a lift and now you should be thinking about a gear reduction—a GDP Portal Gear Lift gives you both and more.

Advantages of GDP Portal Gear Lift Kits:

1. They’re Easy to Install

Unlike a transmission kit, there isn’t a need to replace your factory gears. Instead, a portal gear lift is attached to the end of an axle at the wheel hub. The reduction and increased power come from the gears that are built into the box that operates at the wheel. This makes installation much less time consuming and accessible to all riders.

2. The Additional Power is Applied Directly to the Tire

Portals transfer the force of the engine more closely to the object being turned (the tire), so there is less stress on the axles, differential, drive shaft, and the transmission—even less than a stock machine. A transmission gear reduction, on the other hand, can cause more stress on your drivetrain components since they’re subject to even more torque than stock.

3. You Retain Factory Steering Geometry

You probably need more torque because you added bigger tires or a lift. Remember? That means you also probably put your axles to work at an angle that they aren’t used to because they are now connected to your wheel hubs from a different height than factory. This can cause a lot of stress and wear. An advantage of going with a GDP Portal Lift is that it relocates the axle centerline so you retain much of the factory steering geometry.

4. Increased Ground Clearance

Not only are you going to get more ground clearance from your bigger tires, but if you use a portal lift gear reduction, you will also get an increased height of 4, 6, or 8 inches (depending on which lift you choose). This is a big advantage that you won’t get by simply putting in a transmission gear reduction kit.

5. Higher Reduction Ratios

Finally, SuperATV GDP Portals allow a greater reduction than any transmission kit. This is really important if you have extra heavy tires or need additional torque for heavy rock crawling or climbing. The GDP 4″ Portal Gear Lift provides a 15 or 30% gear reduction, the 6″ GDP Portal Gear Lift gives a 30 or 45% gear reduction, and the 8″ GDP Portal Gear Lift comes with a 45% gear reduction. If you need a lot of torque, the only way to easily achieve it is with SuperATV portals.

Updated by Kavan Wright on 1/30/2020.