Everybody’s first upgrade, more often than none are increasing tire size. Some even upgrade without adequately considering the consequences.
Am I against upgrading? of course not, but you need to study what upgrades you will need in order to get a well balanced upgraded vehicle.
Let’s start from the beginning
When you buy your vehicle, it comes with normal tire size, let’s say: 255/75R17. When you reach 65 mph, in 6th gear, your revs are around 2400 rpm. The speedometer shows 65 mph, and the fuel consumption could be in freeway around 18 mpg.
Next, you decide to upgrade a bit, maybe 35’s, thinking that should be ok. Then you noticed, that to get up to 65 mph, you need to stay longer in 5th gear, and when in 6th gear, your revs are now 2100 rpm. Now your MPG is down to 16 mpg and lack climbing power.
Why? The bigger tires, without proper re-gearing, are changing the entire interaction between your engine and the translation of force to the ground.
If you want a normal daily driver, you will want to be right in in the threshold between yellow and green. If you plan to do 50/50 freeway off-road then you might want to be in the middle of the green. But if you are building a pure off-roading vehicle you want to be on the blue.
Now look at this chart below, gather the information you need from your vehicle (What’s your differential gear ratio, and whats your current tire size in inches) and figure out what’s your prefer setup.
Cons
If you decide to upgrade the tires of a stock vehicle, and you think that getting new gears might be sufficient, think again. Depending on the size you are upgrading to, you might need to upgrade other parts of your rig. For example, a stock JK, on 31s, with a 3.21 gear ratio will run on 35s, but won’t be a good off-roading vehicle. It will lack power when climbing, and won’t be responsive at all. Been there done that.
Consider what your ultimate goal is before starting to upgrade. Don’t think that a gradual list of upgrades is a good short term plan. Think ahead. You will save money.
If your ultimate goal is to run with the big boys on 40s… well, the list of upgrades just exploded astronomically. Don’t kid yourself; you will need new axles, new gears, new brakes, new lift, and new shocks… to mention just a few parts… If you like me think you still want a daily driver that performs well offroad and has a good balance, maybe 35s or 37s is sufficient. Then you might get away with just re-gearing and doing a lift.
Often, bigger tires are just a matter of preference for the look of the vehicle, but if you aren’t able to afford the necessary upgrades, unfortunately, you will end up hating the results.
Pros
The most significant impact larger tires will provide is clearance. Clearance is the distance measured from the lowest point in your vehicle to the ground. If your rear axle is the lowest point, measure from the bottom of it to the ground to get your clearance.
The second biggest benefit is the ability to sort bigger obstacles with ease and increase your break over angle.
More traction when offroading and braking, especially if deflated, those bigger tires will have a surface of contact to the ground, multiple times larger compared to a smaller tire.
Wider tires also increase wet performance, and also better feedback from the steering wheel, usually returning to a neutral position when the driver’s hands are removed.
Keep in mind this article was based on my own experience with my Jeep JK 4 door. Each vehicle has different sweet spots for what works better, study your vehicle, and find out what works better for you.
See you on the trails, big tires, small tires, whatever you choose, just have fun and stay safe.
By Big AL PDX
email:bigalpdx@oregonoffroadrecovery.com
follow BigAl at @bigalpdx
videos: YouTube Channel
