Installing bigger tires is one of the most common modifications ATV owners make to their machines. The majority of riders do it to improve offroad performance; some do it for looks, while others may be hoping to increase their bike’s top speed.
But when it comes to tires and speed, bigger is not always better.
Installing bigger tires on an ATV can increase the top end speed when riding on a straight flat. But it will also negatively affect low and mid-range acceleration and handling, making the bike slower in most riding situations. It will add more stress to the bike suspension and drivetrain.
Taller tires tire can increase top-end speed – in theory
When we’re talking about a bigger ATV tire, we typically refer to a tire that is wider and has a larger diameter than the one you are replacing. This is often referred to as the tire being taller, measured from ground level to the tire’s top.
Installing a taller tire will increase the ATV’s effective gear ratio due to the more extended circumstance of the tire. For each rotation of the axle, the bike will move a bit further.
The circumstance of a 26-inch tall tire is 81,6 inches, while a 28-inch tire has a circumstance of 87.9 inches. This means that the bigger tire will move 6.3 inches farther than the smaller tire for each time the axle rotates.
As long as the ATV has the engine power required to keep up, a bigger tire will increase the bike’s top speed, at least in theory. As speed increases, so will wind resistance and drag.
Smaller and medium-sized ATVs will not always have the adequate horsepower to increase speed over a certain point. Where this line goes varies from model to model.
Bigger tires have a larger rotating mass resulting in loss of low-end torque
Bigger tires are also heavier. At least when comparing different sizes of tires of the same brand and model.
A more massive tire requires more engine power to start rolling due to the larger rotating mass. Also, you have an increased effective gear ratio, as discussed above.
These factors add more strain to the engine, resulting in a loss of low-end torque and reduced acceleration.
Bigger tires are harder to spin in the mud
Huge mud tires are a must to get through the gnarliest mud pits, but they do rob a lot of horsepowers.
Unless you have made the necessary modifications to accompany your bigger tires, the ATV will likely have difficulty maintaining the same speed through the mud as it did before.
Poorer handling will make cornering slower
Most people install bigger tires on their ATV to improve off-road performance by increasing ground clearance.
But with a higher ground clearance comes a higher center of gravity. A higher center of gravity will leave the ATV more unstable and more likely to tip when cornering at high speeds. You will not be able to corner as fast as you were with stock tires.
Bigger and heavier tires are also harder to steer, making the ATV less agile and maneuverable at the trails. This also negatively impacts how fast you can ride.
How to maintain acceleration, speed, and handling when installing bigger tires?
We’ve looked at how installing bigger tires can negatively affect acceleration, low-end torque, and handling. Luckily there are ways to reduce these downsides by making various modifications to the ATV.
The problem can be knowing what modification you need for your specific setup. To answer this question, you need to ask yourself what type of riding you do the most.
A stock ATV is tuned for acceptable performance in a wide range of riding applications. Some like slow and torquey rock crawling, while others like high-speed trail riding or dune racing. An ATV that is set up for speed is not ideal for crawling and vice versa.
Also, you need to consider how much bigger the tires are from stock. A small increase in size does not require the same modifications as a massive increase.
There are many varying opinions on this topic, and there is no definite answer that fits all. But to give you a general idea, here are some general guidelines I’ve learned from reading and watching the content of some of the major players in the business.
The average rider that increases tire size by one inch
This is your typical ATV owner that uses his ATV for a wide range of riding applications but wants to go up one inch in tire size for a slightly better grip and flotation.
Recommended modification: None
As a general rule, you can increase the tire diameter by one inch without making any modifications to the ATVs drivetrain. Most ATVs will have enough space in the wheel wells to allow one inch bigger tire without getting rubbing issues.
Already at one inch bigger tires, you will start noticing some of the negative side effects a bigger tire has on low and mid-range performance, but not more than what is acceptable to most people.
High-speed riders that go up two or three inches in tire size
This category is those that enjoy dune racing, high-speed trail riding, or mud pit bashing. With a two to three-inch increase in tire size, the low and mid-range performance is taking a significant impact. You may have a hard time reaching the REV levels where the engine performs it’s best.
Recommended modification: Clutch kit
A clutch kit will be the best option for those with a maximum of two to the inches increase in tire size from stock and like to go fast.
By installing a clutch kit on your ATV, you will make up for the power loss and slow response you get from installing bigger and heavier tires. It will improve low and mid-range acceleration, and a quicker backshift will give you a more crisp throttle response.
See it as a recalibrating of the clutch to make up for the shift ibn gear ratio due to the larger tires.
This is achieved by optimizing and controlling at what RPM the clutching phase happens. That is when the belt travels from the bottom to the top of its travel on the primary clutch.
In other words, you are increasing the engagement RPM, typically from 1900 to 2100 or 2300, depending on what spring-weight you choose. This will make sure you stay in the engine’s power band.
A clutch kit contains stiffer springs and lighter clutch weights. It is not recommended to use one without the other.
Note that you will lose a few mph of top speed with some clutch kits when running stock tires, but some may even get an increase in top speed due to lighter clutch weights.
Look for a quality kit that is specifically made for your machine. A flexible kit will work well with both stock and bigger tires without a significant top-end speed loss.
A quality clutch kit from some leading providers like Dalton or EPI will set you back around $300, which is not that bad considering the benefits.
Check this video to learn if you need a clutch kit or not:
Slow speed, high torque riders that go up two or three inches in tire size
These are the typical rock crawlers that do a lot of technical riding that requires a lot of torque and belt grip at slower speeds.
As soon as you go up two to three inches or in tire size, you will start to notice a significant loss in low-end grunt due to the extra tire weight and a gear ratio that is off.
Running at low speeds will add a lot of extra strain on the drive belt as it cannot position itself properly on the clutches. The belt will heat up and wear out much faster than usual.
Recommended modification: Gear reduction kit
Those that prefer high torque, slow speed technical riding will likely be better off choosing a gear reduction kit over a clutch kit.
A clutch kit is not ideal for this riding style, as it won’t give you the necessary belt grip.
Even with stock tires, you may benefit from a gear reduction as even the low range gearing is a bit high for rock crawling on most ATVs.
With a gear reduction kit, you will allow the stock clutches to operate where it performs best, even at slower speeds. It will take some of the load off the clutch and belt, making it easier to turn tires, axles, etc.
There are two main types of gear reduction kits to look in to:
- Portal gearboxes mounted to each wheel. This option is likely the best for those that ride slow.
- Internal transmission gear reduction. This option is likely best for those that run massive tires but like to go fast.
Check this video by Hunterworks Inc to learn more about the difference between clutch kits and gear reduction kits.
High and low-speed riders that increase tire size with more than three inches
When increasing the tire size even further, the gear ratio will be way off, leaving the engine and transmission unable to keep up. You will begin burning belts regularly, especially when riding at lower speeds.
Recommended modification: Clutch kit and Gear reduction kit
When increasing the tire size more than three inches from stock, you should consider getting both a clutch kit and a gear reduction kit.
There is a limit to how much of an increase in tire size a clutch kit will handle before you get to the point of diminishing returns. With huge tires, you may need a gear reduction kit to take some of the load of the clutch and belt.
While gear reduction is ideal for slow speed riders at any tire size, it may also benefit high-speed riders that run massive tires.
Installing wheel spacers can make the ATV more stable
Wheel spacers will not only give you better clearance that allows for installing wider tires or installing chains on stock tires. They will also improve the stability of the ATV, effectively reducing the roll-over rate.
The extra ground clearance gained from installing bigger also makes the machine more susceptible to tipping, especially when cornering. Wheel spacers will move the tires outward, effectively improving the sideways stability of the ATV.
Keep in mind that wheel spacers will increase the stress on wheel bearings and joints. Therefore it is not recommended to install thicker spacers than necessary to achieve required clearance and stability. ½ inch up to two inches are the most common thicknesses used for ATVs
Check this post if you want to learn more about the pros and cons of ATV wheel spacers or how to choose the right wheel spacers for your ATV.
Other potential downsides of installing bigger tires
Increased drive belt wear
The added strain on the original clutch setup will increase heat buildup and belt wear.
A clutch kit will optimize the gear ratio, effectively reducing belt slip and clutch heat buildup. But even with a clutch kit, the OEM belt may not be able to handle the added strain of bigger tires
Consider getting a heavy-duty or severe duty drive belt specifically made to handle larger tires and aftermarket clutch kits.
If you’re having problems with your ATV belt slipping, I recommend reading this post.
Premature driveline and wheel bearing wear and failure
Due to the increased angles and extra weight, the CV joints, U-joints in the axles, and A-arm bushings will wear much faster. The CV joints may even snap straight off on your first ride running bigger tires.
To encounter this issue, you need to install heavy-duty wide-angle axles.
The added stress of bigger tires will also make your wheel bearings wear out faster than with stock tires. If you regularly drive in deep mud, I recommend getting a wheel bearing greaser to prevent water from getting into the wheel bearings, causing rust and even faster wear.
Tire rubbing on suspension components, brake lines or body panels
Most ATVs will handle one inch bigger tires without any rubbing issues.
But with even bigger tires, you may need a set of wheel spacers and do some fender cutting to provide enough space for the extra rubber.
It may void the manufacturer’s warranty
Due to the added stress on the ATV driveline and suspension, many manufacturers and/or dealers have restrictions against increasing tire size without voiding the warranty.
You may be allowed to go up one or potentially two inches, but to be sure, I recommend you ask your dealer in advance.
There are better ways to make your ATV go faster
If your sole goal is increasing acceleration or top-end speed, some options may be better suited than installing bigger tires.
If maximum acceleration is your top priority, you will be better off going down a size from your stock tires.
The reduced effective gear ratio will improve low-end torque and acceleration, leaving your competition behind on the drag strip.