Why GM decided to release the TrailBoss with an insignificant 32-inch tire baffles me, especially since other GM models that are less geared for off-roading are released with 33 inches. Be that as it may, the other problem is the TrailBoss wheel arches are known to be rather narrow which limits you somewhat when fitting bigger tires.
Table of Contents
Biggest Tires on A Stock Chev TrailBoss (W/Without A Lift)
Fitting Spacers & Lift With 33” Tires On Your TrailBoss
In stock form, the TrailBoss comes wrapped in 32×10 tires which is, in many owners’ opinions, not the best size for this big truck. So, when upgrading from a 32×10 to a 33×12 on stock rims you will experience a massive amount of scrubbing inside those wheel wells.
You will have to do quite a bit of trim on the plastic fenders which isn’t ideal if you plan on selling the truck later down the line. Any tire bigger than the factory 32-inch versions is going to require a lift kit or at least a spacer kit up front.
The perfect setup would be a small 1.5” spacer or lift kit combined with a negative offset rim/wheel to make those 33 inches fit and function properly offroad without any scrubbing offroad or at full lock.
Bigger Than 33-Inches on A Lift
If, for example, you run something bigger than a 33-inch and only opt for a 1.5-inch spacer while running factory rims/wheels you could get away with about a 295/70/18 which is the equivalent of a 34.3-inch tire. In this instance, you will need to trim the mud flaps hidden inside the wheel well. You will also need to remove the bracket that is tucked away behind the fender liner.
The upside with the spacers is the amount of stability you get on the TrailBoss. The truck’s handling is greatly improved with less body roll giving it a more planted feel when cornering.
What needs to be trimmed when fitting oversized tires on your TrailBoss? Well, there is a bracket that is located directly behind the mudflap that needs to be removed. You also need to trim a bit off from the inside and systematically trim your way outward until the rub is eliminated.
Do it in stages, only trimming little bits at a time to avoid cutting away too much and leaving unsightly spaces/gaps in your wheel wells.
For this job, you will need a decent heat gun and Dremel Cutting tool. If you don’t already own one then I would recommend you check out this Top-Selling Infrared Thermo gun on Amazon with almost 17000 good ratings. Also, for trimming fender liners I recommend investing in this Dremel Variable Speed Cutting Tool (Amazon) It will give you better control than an aggressive grinder leaving your trimming looking a lot more professional and neat.
If you drive a Silverado your job is a bit easier. There is no need for drilling or cutting too much and can get away with a simple zip-tie. Tie the hole in the fender liner (from discarded hardware) to the hole that the bracket used to be mounted to. Job done!
Fitting Aftermarket Rims/Wheels to your TrailBoss
The stock tires are 32-inches, and 10-inches wide which is rather puny for such a butch truck. It doesn’t do the truck justice to be cruising around with such tiny wheels. The problem with the TrailBoss is that it has a very narrow wheel arch which makes it rather difficult to simply upgrade to a 33-inch tire without any additional mods.
Here is where the aftermarket rims/wheels come in. Any rim/wheel with a more negative offset will push those tires out more, thus creating more space in the back of the tire to clear the UCA (Upper Control Arms) as well as the inside of the narrow wheel wells. The wheels will stick out a bit, but it will negate the need to cut up your wheel wells and do any trimming on the arch flares.
Let’s say you opt for a 33-inch by a 12.5 then you’ll be hitting a sweet spot between looks or aesthetics and improved offroad capability. That’s exactly what you want! You don’t want to have to throw tens of thousands at the truck just to fit bigger tires.
User Experience & Feedback
I’ve got 295/70R18 Falken Wildpeak AT3W tires on my 18-inch Trail Boss wheels. Just a tiny bit of rub on the mud flap occasionally when reversing with steering near full lock. I don’t have any lift or leveling kit, just factory Trail Boss suspension.https://www.trailboss.org/threads/biggest-tire-on-stock-boss.62/
I put Toyo 195/70’s on mine. So, 34X11.5 roughly. I had to remove the mud flaps when I added Bushwacker fender flares. When I added the tires I had to remove the mudflap brackets and add 2″ wheel offsets. When that was done I had no tire rub. Before the spacers It rubbed bad. Hell of a racket. I’ve read on the GM forums that you could put 195/70 without any rubbing. Anyone who says that is wrong.https://www.trailboss.org/threads/biggest-tire-on-stock-boss.62/
I run 295/70 yokahoma x-at, on stock 18. No rub, no spacers. Places them right at the outside edge of the fender. Spacers would put them outside and look great IMO. With spacers, the 295/65 will fit.https://www.trailboss.org/threads/biggest-tire-on-stock-boss.62/
The TrailBoss is an excellent platform if you want a truck that’s ready to hit the trails. A Simple big-tire upgrade will allow you to tackle those tracks with confidence without having to spend tens of thousands on the truck to get it capable and trail-ready. Follow the above-mentioned guidelines before fitting 33-inch or 35-inch tires and you should be ready to smash trails you never thought possible with your humble but very capable TrailBoss!
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