Are you adding a set of wheels and tires to your vehicle that are heavier than stock? If so, you might be wondering how they will impact the performance of your brake system. In this article, we’ll explain:
- Why wheel and tire weight has an impact on brake performance
- What math shows with regards to weight increases and brake performance
- What you can do to counter the impact of heavier wheels and tires on your brake system
But before we get into the details, here’s a quick summary: When you replace your factory wheels and tires with a set of aftermarket wheels and tires that are bigger and heavier, your vehicle won’t stop as well.
We estimate that a 10% increase in overall wheel size works out to a 10% decrease in brake performance. We have also estimated that a 10lbs increase in wheel and/or tire weight works out to a 1% decrease in brake performance. We call this the 10-10-10-1 rule of thumb.
First, Why Do Heavier Wheels and Tires Increase Brake Distance?
If you increase the weight/mass of your wheels and tires, your brake system won’t work as well. If you’re a physicist or engineer, you can think about angular momentum and how it’s impacted by increased mass at an increased radius.
But if you’re not an engineer or physicist, there’s an easy way to think about wheel weight and braking. Imagine that your wheel and tire combination is a dog, and that the dog is running at you full speed. Would you rather stand in front of this 30lbs dog running at you full speed (photo dog1.jpg) ?
Or stand in front of this 120lbs dog coming at you full speed (photo dog2.jpg) ?
The point? The heavier a wheel is, the harder it is to stop it (or start it, for that matter). And when we’re talking about wheels and tires barreling down the highway at 75mph, a slight increase in overall weight can have a profound impact on brake system performance.
The bigger and/or heavier a wheel is, the harder it is to spin. Once it’s spinning, the harder it is to stop. Mathematically, the relationship between brake force (torque applied on the rotating axle) and wheel diameter and/or weight is roughly proportional.
- If you increase the radius of your wheel and tire combo by 10%, the amount of braking force needed to stop your vehicle will increase by roughly the same amount (eg, 10% more radius = 10% more braking force required).
- If you increase the inertia (rotating mass) of your wheels, tires, rotors, axleshafts etc by 10%, the amount of braking force applied to each set of wheels, tires, and axle needs to increase by roughly the same amount.
Of course, there are a lot of factors here, but the relationship between brake force (torque), wheel size, and rotating mass is linear.
tl;dr; The bigger and heavier your wheels are, the worse your brakes will work.
Wheel Size Matters More Than Wheel Weight
As our math shows, a 10% increase in the radius of a wheel will reduce brake system performance by an equal amount. If, for example, you have a Jeep Wrangler with a stock 17″ wheel wearing 245/75R17 tires, your overall wheel radius is 15.7″ inches. Upgrading to a wider 17″ wheel with 315/70R17 tires will increase the overall radius to 17.2″ inches, which is just about 10% greater than stock.
So, if you’re considering a wheel and tire upgrade, it’s a good idea to calculate the overall diameter of the wheels and tires you’re looking at with the OE wheels and tires. If the radius is 10% bigger, stopping distances will increase by roughly the same amount.
Wheel Weight Impacts Stopping Distance Too
Since the torque needed to stop your wheels is proportional to inertia, a 10% increase in the rotating mass of your vehicle will decrease brake system performance by the same amount. But defining rotating mass isn’t easy.
Rotating mass is hard to define because all the parts parts of your vehicle that are rotating when you drive down the road – the driveshaft, axle shafts, rotors, wheels, tires, and miscellaneous parts – are “rotating mass.” In order to figure out the inertia of all of these parts, you need to know both:
- How much each part that’s rotating weighs
- How big the part is, and where the weight is in the part? Is it uniform, like an axle shaft, or is all the weight at the outside, like a driveshaft?
All the parts that rotate on your vehicle have inertia. When you increase the weight of any of those rotating parts, you increase the amount of force it takes to stop your vehicle.
Obviously, calculating the rotating mass/inertia of your vehicle is very difficult. And because every vehicle is different – with different size axle shafts, rotors, driveshafts, etc. – rotating mass can vary quite a bit.
Suffice to say, rotating mass is higher on heavy duty vehicles. If you have an F-350, your vehicle has more rotating mass than a Miata. But there’s no hard-and-fast rule here. If you double the weight of your wheels and tires, you’re going to make your brake system less effective.
Most drag racers find that a 10 lbs increase in wheel weight costs them about a tenth of a second in a quarter mile. This works out to about 1% more stopping distance per extra 10 lbs of weight at your wheels.
So, with the understanding that this is a very rough estimate, you can assume that every 10lbs you add in wheel/tire weight increases stopping distance 1%. Maybe more, maybe less – depends on the vehicle.
How To Improve Braking Distance After Installing Heavy Wheels and Tires
If you’ve installed a set of wheels and tires on your vehicle that are bigger and/or heavier than stock, there are a few things you can try to improve your brake system performance:
- Upgrade your brake pads. This is the simplest and most obvious solution. Go with a pad that’s designed for a heavier vehicle and/or for heavy duty use (like off-roading, towing, or racing).
Replace your brake pads with a set of pads specifically designed to stop oversized wheels and tires.
- Upgrade rubber brake hoses with braided stainless steel. Upgraded brake lines are a good idea for nearly any vehicle – braided stainless steel lines don’t flex nearly as much as rubber. This means your brakes grab harder and grab faster with braided stainless steel brake hose.
- Upgrade your rotors. A good set of rotors are made from a high quality steel, are designed with specific cooling features for your vehicle, and are the exact right size and thickness. A cheap set of rotors are made from scrap metal, lack cooling features, and are often a slightly different size than you need. While most OE rotors are good, there are aftermarket performance rotors available that perform better.
- Install a big brake kit. If you’re looking for the maximum brake system upgrade, you need to remove the factory calipers and rotor and go with a big brake kit. Typically, these kits include both upgraded dual piston calipers as well as an overiszed rotor that’s paired up with a larger brake pad. These kits can make a huge difference in brake system performance.
The 10-10-10-1 Rule Of Thumb
If you’re trying to estimate the impact that a set of new wheels and tires will have on your brake system, follow our 10-10-10-1 rule of thumb.
- A 10% increase in overall wheel diameter works out to a 10% decrease in brake performance
- A 10 lbs increase in wheel and/or tire weight works out to a 1% decrease in brake performance
If a wheel is 8% bigger than stock and weighs 40lbs more than stock, it will reduce brake system performance about 12%:
- 8% increase in wheel size = 8% decrease in performance
- 40 lbs increase in weight = 4% decrease in performance
- 8% + 4% = 12%
Basically, bigger wheels are bad for your brakes, but big and heavy wheels are really bad for your brakes.
A 10% increase in wheel size works out to a 10% decrease in brake system performance. A 10lbs wheel/tire weight increase works out to about a 1% decrease in brake system performance.
While our 10%/1% brake system rule of thumb is only an estimate, a quick search on Google or Bing shows that many consumers report poor brake system performance after installing new wheels and tires. If you’re looking for a quick and easy way to estimate brake system performance impacts, our 10-10-10-1 rule is a good place to start.
NOTE: If you have a set of oversized wheels and tires, be sure to check out our products. We’ve designed our products for vehicles with big wheels and tires.