Almost everyone understands that brakes are necessary to safely drive a motorized vehicle. Hopefully most people understand that the brakes that come from the factory on your vehicle are more than adequate for your vehicle as long as you stay within the manufacturers stated ratings for weight, tire size, and towing.What seems to escape many people is the need to upgrade your vehicles braking ability when you start to modify it with larger tires, heavier equipment, and if you tow extensively.
Moment of Inertia
I am not a physics professor nor am I a physics expert. I am going to use the simple calculations to illustrate a point about additional weight and why larger brakes are a benefit. Let’s use a 32 inch tire and wheel combination package that is approximately 100 pounds. We will then upgrade to a larger 37 inch tire and wheel that weighs approximately 145 pounds.
Using a very simple equation to calculate moment of inertia: Mass * D2 (Distance between axis and rotation), the MOI for the smaller combination is 625 kg m2. Comparing that to the larger combinations at 1305 kg m2 you can see how much additional force is required to change the direction of motion.
In simplest terms in order to stop the vehicle in the same distance the larger wheel and tire combo either requires over twice the force, or it requires a much longer stopping distance. Once you begin to add additional weight to the vehicle from heavier suspension parts, to armor, and other accessories this gap increases even further. Upgrading your brakes in this scenario is the difference from avoiding and accident or being right in the middle of it.
In a previous article I wrote about this subject there were several comments about brakes being unnecessary for crawling and several other off-road scenarios. I didn’t delve into the comments to argue these points knowing I would eventually address them in an article like this one.
Automatic transmissions are becoming the norm for off-road use. Simpler to operate, hit the gas and go control allows more people to enjoy the off-road experience. One of the downsides is you can’t always take power away from the drive wheels. In a manual transmission vehicle simply press in the clutch and you have lost all forward or reverse drive. With an automatic that’s not always possible. Linkage bind, driveline stress, and more make shifting into neutral a scenario that isn’t always possible. In order to prevent the vehicle from moving you need to use the brakes.
I bet that when you lifted your vehicle, added larger tires, and beefed up your protection you probably added a numerically higher gear ratio to recover some lost acceleration and performance. Now you not only have more weight and aforementioned MOI, you are also using more power to try and twist the wheels. A good friend has this exact scenario, modified Jeep with all these parts and the brakes are not able to stop the vehicle when it is on 4LO. Unfortunately for him there isn’t a simple kit to add larger brakes but we will figure out a solution.
The same thing occurs when you need to hold position on a rock or a hill climb without rolling backwards or forwards until you are ready.
If you bought a vehicle specifically for towing and never modify it the most you should have to do is buy new brake pads frequently. If you bought a big old truck with plenty of power and then add that 6 inch lift, giant mud tires, LED light bars, and used a tuner to add a bunch of power you still need to stop that behemoth. Still want to tow 20,000 pounds? Then you really need to get better and bigger brakes, for everyone’s safety. If you need more power to tow it, you need more power to whoa it. Clearly that should be a sales tag line for some company. It’s the perfect mantra for what we are talking about, larger better brakes will save your life and possibly mine.
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