A Treatise on the Perilous Pursuit of Truck Modification
Being an Account of the Mechanical Miseries and Pecuniary Ruin Awaiting the Uninformed Enthusiast
(In Which the Reader Shall Discover the Unfortunate Effects of Rubbing Tires, Misaligned Suspensions, and the Ill-Advised Offset, Leading to a Melancholy State of Repair and Great Expense)
Driving a truck at the Bonneville Flats is like piloting a brick across the surface of the moon. There’s no grip, no sound, just an endless white void and the faint, terrifying feeling that at any moment, the universe might tear the wheels right off. And yet, somehow, it’s glorious—because nothing this big should go this fast.
Ah, the allure of the ultimate truck build. The growl of oversized tires, the defiant stance of a towering lift kit, and wheels so pristine they could double as living room furniture. It’s the stuff of dreams—or so it seems. Because, let’s face it, one wrong decision in your build process, and your off-roading fantasy could turn into a wallet-draining, garage-haunting disaster.
Take the lift kit, for instance. Slap on the wrong one, and suddenly your suspension is working overtime—wearing out faster than a teenager’s first set of brake pads. Add in improperly chosen tires, and you might find them rubbing against your cab mounts like sandpaper on a priceless painting. That’s not just irritating; it’s catastrophic. And let’s not forget wheel offset, that sneaky devil. Get it wrong, and you’ll discover that your handling now feels like trying to steer a runaway shopping trolley—while your drivetrain groans under the strain of your choices.
In short, your dream truck can quickly morph into a Frankenstein’s monster of mismatched parts and costly repairs. The moral of the story? Measure twice, buy once, and for heaven’s sake, consult someone who knows what they’re doing. Otherwise, you’ll be explaining to your bank manager why your “adventure companion” is eating into your holiday fund.
What Could Possibly Go Wrong?
In this thrilling installment of “How Not to Ruin Your Truck,” we’ll use my Gen 3 Tacoma to unpack the critical factors that separate a jaw-dropping, high-performance rig from a wheeled catastrophe that spends more time in the shop than on the trails. Buckle up, because this isn’t just about avoiding mistakes—it’s about building a truck that drives like a dream and laughs in the face of rough terrain. Here’s what we’ll cover:
Tire Size, Offset, and Wheels: More than just aesthetics, these choices directly impact your truck’s handling, fuel efficiency, and the lifespan of your components. Get it wrong, and your fuel economy plummets, your handling goes to pot, and your drivetrain starts whispering, "Why do you hate me?"
The Lift Kit Minefield: Ah, the siren song of a higher stance. But beware—choosing a lift kit without accounting for suspension geometry or load capacity is the mechanical equivalent of playing Jenga blindfolded. One wrong move, and it’s all coming down.
Real-World Horror Stories: From cab mount chops that sound harmless but feel like a wallet punch, to suspension rebuilds and drivetrain repairs that could’ve been avoided with a bit of research, we’ll explore the “what happens when you don’t” side of truck building.
By understanding the science—and a touch of the art—behind your build, you’ll sidestep these financial and mechanical sinkholes. The result? A rig that looks spectacular, performs flawlessly, and can handle whatever adventures you throw at it. Let’s dive into the nitty-gritty of making your truck the king of the road and the trails—without the “oops” moments.
Taking a truck on Engineer Pass is like threading a needle while riding a unicycle on the edge of a cliff. The road is narrow, the drops are biblical, and the air is so thin your truck feels like it’s running on a hamster’s last breath. But the views? Utterly staggering—like Mother Nature showing off just how small and insignificant you really are.
Why Are Tacoma’s Cab Mounts Where They Are?
Ah, the humble cab mount. Tucked behind the front wheels, these unassuming bits of engineering might not look like much, but on a Gen 3 Tacoma—and indeed most body-on-frame trucks—they’re a stroke of genius. Placed as if by the hands of a deity with a tape measure, these cab mounts are critical to keeping your truck tough, comfortable, and ready for anything. So why exactly did Toyota's engineers put them there? Let’s dig into the clever rationale behind this seemingly simple decision.
1. Structural Integrity and Crash Safety: Keeping You in One Piece
The placement isn’t random; it’s a calculated move for maximum strength. By locating the mounts behind the front wheels, Toyota boosts the cab and frame’s rigidity. In a crash—whether it’s a fender-bender or something a bit more dramatic—these mounts help absorb and channel the impact through the frame. That means less energy reaching you, the driver, and fewer cracked panels to explain to your insurance company. Plus, their positioning prevents the cab from wobbling like a jelly under heavy loads, keeping the Tacoma steady and confident.
2. Off-Road Prowess and Durability: Built for the Wild
The Tacoma isn’t just a commuter; it’s a go-anywhere, do-anything beast. Off-roading introduces forces that would turn lesser trucks into rattling scrap metal. With the cab mounts strategically positioned to counter torsional stress, your Tacoma shrugs off rocky trails and uneven terrain. These mounts ensure the cab doesn’t twist like a pretzel when you’re crawling over boulders or taking on aggressive inclines at speed. And they keep squeaks and rattles to a minimum, saving your sanity on those long drives back from the trail.
3. Minimizing NVH: The Gold Standard of Comfort
Noise, vibration, and harshness (NVH)—the enemy of smooth driving—are expertly mitigated by the Tacoma’s cab mounts. Positioned close to the front wheels, these mounts act as sound barriers, muting the constant hum of tires, road imperfections, and the odd gravel ping. The result? A truck cabin that’s whisper-quiet (by truck standards, anyway) and doesn’t feel like a drum kit every time you hit a bump. This attention to detail is why the Tacoma remains one of the most refined midsize trucks around.
4. Body-on-Frame Harmony: A Perfectly Aligned Symphony
In body-on-frame trucks, alignment is king. The cab mounts sit forward to create the perfect balance between the frame, cab, and drivetrain. This positioning ensures the transmission and transfer case stay in sync, even under extreme load or off-road articulation. It’s the secret sauce that makes your truck feel bulletproof, even when you’re pushing it to its limits.
5. Space Constraints: Because Suspension Needs Room to Play
The Tacoma’s double-wishbone independent front suspension is a marvel of engineering, but it demands space. Between the control arms, steering rack, and frame, Toyota needed to place the cab mounts in a sweet spot that wouldn’t interfere with suspension travel. By nestling them behind the front wheels, the engineers struck the perfect balance: optimal ride height, ground clearance, and suspension articulation—all while keeping the mounts out of harm’s way.
The Tacoma’s cab mounts might not be the flashiest part of the truck, but their positioning speaks volumes about Toyota’s engineering prowess. They’re there for your safety, comfort, and off-road adventures, ensuring your rig can tackle the toughest challenges while keeping the ride smooth and the repairs minimal. Next time you’re enjoying a rattle-free drive or conquering a gnarly trail, spare a thought for those unsung heroes bolted just behind your front wheels.
For all the brilliance behind Toyota’s cab mount placement on the Gen 3 Tacoma, there’s a catch—and it rears its head the moment you decide to slap on those drool-worthy 33” or 35” tires. While these mounts do an excellent job holding your cab steady, their proximity to the front wheels becomes a bit of a headache when you start thinking big. Literally.
Upgrading to larger tires is practically a rite of passage for truck owners, but on a lifted Tacoma, those cab mounts quickly become an unwelcome obstacle. With larger tires, the clearance between the mounts and the rubber shrinks faster than a puddle in the Mojave. Turning sharply or compressing the suspension during off-road articulation often results in a painful rubbing sound—a not-so-subtle reminder that your dream build is now colliding with cold, hard engineering realities.
Crawling in a truck down Shafer Trail is like descending into the bowels of the Earth on a road carved by madmen. Each switchback taunts you with sheer drops that could swallow a football stadium, while the towering red cliffs loom like ancient gods judging your every move. Terrifying? Absolutely. Worth it? Without a doubt.
Solutions for every budget
1. Lift Kits
Lifting the Tacoma raises the body and frame, creating more clearance between the tire and fender, but it doesn’t directly address cab mount rubbing (especially during full lock or articulation). Lift kits range in height from 2” to 6”.
Types:
Spacer lift: Cheap, but only extends the suspension without improving articulation.
Full suspension lift (coilovers + new rear leafs): Improves articulation and ride quality.
Effect: Reduces fender rubbing but only marginally affects cab mount clearance. For 33s, a 2”-3” lift often works. For 35s, you’ll likely need at least 3”-4”.
Price Range (Parts + Labor):
Spacer lift: $400–$800
3” full suspension lift: $2,000–$3,500
4”-6” lift kits: $3,000–$5,500
Pros: Better approach angles and off-road clearance.
Cons: Expensive, affects driveline angles, and still may require other mods.
2. Adjustable Upper Control Arms (UCAs)
After lifting the truck, adjustable UCAs are often needed to correct alignment (camber and caster). By adjusting caster, you can push the wheel forward, reducing the chance of tire rub against the cab mount at full lock.
Effect: Helps align the front wheels after a lift and slightly improves cab mount clearance by moving the wheel forward in the wheel well.
Price Range (Parts + Labor):
$700–$1,200 installed
Pros: Improved alignment, better suspension travel, reduces rubbing.
Cons: Costly and only marginally affects cab mount clearance on its own.
3. Wheel Offset and Backspacing
The delicate art of wheel backspacing—a game of millimeters that can make or break your off-road dreams. Opting for less backspacing, or in plain English, wheels with a more negative offset, shoves the tires outward like a bodybuilder showing off at the gym. It’s brilliant for keeping the rubber from tangling with your frame and suspension components, offering all the clearance you need for those massive, knobbly tires.
However, too much offset, and your masterpiece of engineering turns into a rolling headache. You’ll mess with suspension geometry, stress the wheel bearings to within an inch of their lives, and find yourself wrestling with handling quirks that make every corner feel like a wrestling match with a bear. So yes, push those tires out—but not so far that your Tacoma starts behaving like a diva with a twisted ankle.
Effect: Reduces rubbing on the cab mount but may introduce fender rubbing, especially with larger tires like 35s.
Recommended Offset for Larger Tires: -10mm to -25mm offset wheels help push the tires outward.
Price Range:
$800–$2,000 for wheels (set of 4), depending on the brand.
Pros: Helps clear the cab mount and suspension.
Cons: Increases strain on bearings and steering, can require fender trimming.
Having some fun at the Canyonlands National Park.
4. Wheel Spacers (Not Recommended)
Wheel spacers, for those not in the know, are a bit like wearing platform shoes to a party—you look wider, flashier, and you’ll probably attract some attention. They shove the wheels outward, creating the illusion of a negative offset, which sounds technical but really just means your car looks a bit meaner. The upside? You get extra clearance from the cab mount, handy if you’re rocking oversized tires.
But here’s the rub: long-term use of these things is about as wise as leaving your pub tab open overnight. They can stress your suspension components like a bad in-law stresses a marriage. Oh, and in some parts of the world, they’re as legal as overtaking a police car in a Ferrari. So, tread carefully—literally.
Effect: Marginal improvement in cab mount clearance, but often introduces other fitment issues.
Price Range:
$100–$300 (parts only)
Pros: Cheap and easy to install.
Cons: Can affect wheel bearings, may require fender trimming, not a long-term solution.
5. Cab Mount Chop (CMC)
Ah, the cab mount chop—a rite of passage for anyone hell-bent on squeezing ludicrously large tires onto their Tacoma. It’s not just a modification; it’s a surgical procedure. Picture this: you take a saw to the cab mount, that chunk of steel Toyota lovingly installed to keep everything sturdy, and lop off a piece like you’re carving a Sunday roast. Then, with all the precision of a master chef, you replace it with a sleek, reshaped steel plate and weld it back in place. Voila!
The result? A mount that no longer throws a tantrum when your suspension articulates or when you decide to yank the wheel into a tight turn. If you're dreaming of running 33-inch tires, this is the key to your oversized aspirations. But for the truly mad—the ones chasing 35-inch monsters—it’s not just an option; it’s the price of admission.
Effect: Significantly improves cab mount clearance without affecting ride quality or suspension geometry.
Price Range (East Coast):
$400–$800 depending on shop labor rates
Pros: Permanent solution, doesn’t compromise ride quality.
Cons: Requires cutting and welding, which might deter some owners.
6. Cab Mount Relocation (CMR)
For those truly unhinged enough to slap 35-inch tires—or larger—onto their rigs, there’s an even wilder option on the table: cab mount relocation (CMR). This isn’t just tweaking or trimming; this is ripping out the cab mount altogether and bolting it back on further down the frame. It’s the motoring equivalent of moving a wall in your house because the sofa you bought is simply too enormous to fit.
Unlike the more modest cab mount chop, which is basically surgery with a scalpel, CMR is full-blown open-heart surgery with a chainsaw. It demands serious fabrication skills, a high tolerance for risk, and an even higher budget. This is not for your casual off-roader; it’s for those bespoke, tailor-made builds where every inch of clearance is sacred, and compromises are left at the trailhead. Extreme? Absolutely. But then again, if you’re chasing 37-inch tires and conquering rock gardens like a lunatic, extreme is kind of your thing, isn’t it?
Effect: Provides even more clearance than a CMC, allowing for full suspension articulation with 35s or larger tires.
Price Range:
$1,500–$3,000 depending on complexity and labor
Pros: Solves cab mount interference entirely.
Cons: Expensive and invasive; not necessary for most builds.
Wharton Forest in the winter—a place where off-roading transforms from a casual jaunt into a full-blown survival test. The snow blankets everything in sight, turning every trail into a slippery guessing game. And there you are, in your lifted Tacoma, carving through the wilderness like some kind of Arctic explorer who traded his sled dogs for chunky tires.
Recommended Approach Based on Tire Size
33” Tires:
2”-3” Lift + Adjustable UCAs
Consider CMC if experiencing rubbing at full lock.
35” Tires:
4”-6” Lift + Adjustable UCAs + CMC
For extreme articulation or aggressive off-roading, consider CMR.
So, you’re dreaming of big tires—33s or 35s—and wondering how to get there without turning your rig into a rubbing, squealing disaster. Let’s break it down. For 33-inch tires, a modest lift in the 2 to 3-inch range, paired with adjustable upper control arms (UCAs), will usually do the trick. Think of it as giving your Tacoma a nice pair of heels—just enough to clear the dance floor. If you still hear the dreaded sound of rubber meeting steel, a cab mount chop (CMC) is your go-to. Cheap, reliable, and gets the job done without breaking the bank.
Now, step into the world of 35-inch tires, where things get serious. You’re looking at a 4 to 6-inch lift, UCAs as standard, and that trusty CMC once again raising its head. At this size, rubbing isn’t just a possibility; it’s a certainty. And for the extremists—the ones who demand full suspension articulation and unimpeded rock-crawling glory with 35s—a cab mount relocation (CMR) is the nuclear option. Sure, it’s expensive, labor-intensive, and about as subtle as a sledgehammer, but when you’re chasing the ultimate off-road build, subtlety isn’t exactly the goal, is it?
Cab Mount Chop (CMC)
Mechanics
A CMC involves trimming the forward-most edge of the cab mount bracket that protrudes into the wheel well.
After cutting the interfering portion, a new steel plate is welded over the trimmed section to reinforce the mount, ensuring that it retains structural integrity.
The cab mount remains in its original position, with only the shape of the front edge altered to allow for increased clearance.
Benefits
Simple and effective: A CMC provides sufficient clearance for 33” and most 35” tires, especially for trucks used primarily for moderate off-roading or overlanding.
Minimal impact: No change to the cab’s structure or position on the frame, maintaining factory suspension geometry and alignment.
Short downtime: A CMC can usually be completed in one day at most experienced off-road shops.
Less invasive: Requires no significant frame or body modifications, making it a safer option for those concerned about long-term structural integrity.
Risks and Considerations
Limited clearance improvement: A CMC only removes a portion of the mount, meaning very large tires (e.g., 35s) with heavy off-road use might still rub during extreme articulation.
Potential welding flaws: If the welds aren’t properly executed, the structural integrity of the cab mount could be compromised. However, reputable shops mitigate this with careful work.
Permanent modification: Once the cab mount is chopped, it can’t be returned to its factory form, which could affect resale value for some buyers.
Frisco Beach, North Carolina—where off-roading feels less like a rugged adventure and more like starring in a postcard. As the sun dips below the horizon, casting the sand and sea in shades of gold and crimson, your Tacoma sits there like a lone sentinel, perfectly at home yet impossibly out of place.
Cab Mount Relocation (CMR)
Mechanics
CMR involves cutting the entire cab mount bracket off the frame and relocating it further back to completely eliminate any possibility of tire interference.
After the original mount is removed, a new bracket is fabricated and welded into a new position, typically an inch or more rearward, depending on the tire size and intended use of the truck.
This process requires precision to ensure that the new mount aligns perfectly with the cab and doesn’t affect the overall alignment of the body with the frame.
Benefits
Maximum clearance: A CMR offers more clearance than a CMC, making it ideal for extreme off-road builds with 35” or larger tires where full articulation is needed.
Future-proof solution: With the cab mount permanently relocated, rubbing is no longer a concern, even with suspension upgrades or further tire size increases.
Better articulation: For trucks used in rock crawling or other heavy articulation scenarios, CMR ensures that larger tires won’t interfere at full lock or under extreme suspension travel.
Risks and Considerations
Highly invasive: Relocating the cab mount requires significant cutting and welding on both the frame and cab, which could compromise the structural integrity if not performed correctly.
Alignment challenges: The new mount must be perfectly positioned to ensure that the cab sits correctly on the frame. Any misalignment could cause fitment issues or body flex.
Impact on warranty and resale: A CMR is a much more extreme modification and may void warranties or deter potential buyers down the road.
More downtime: Due to the complexity of the relocation, the truck may need to be out of service for several days while the new mount is fabricated and installed.
Camping at Sherando Lake
Structural Impact: CMC vs. CMR
Cab Mount Chop (CMC) – Potential Compromises
In a CMC, material is removed from the leading edge of the cab mount, which is part of the frame that provides:
Cab stability – It secures the cab to the frame and helps distribute forces evenly in crashes or during off-road flexing.
Load-bearing support – During turns or suspension articulation, the cab mount resists lateral and torsional forces acting on the cab-body interface.
By trimming the forward part of the mount, you are:
Reducing the surface area that helps distribute stress between the cab and the frame.
Weakening a primary load-bearing point under stress, especially during off-road articulation, which may lead to increased cab movement or body flex over time.
Although the welded steel plate reinforcement restores some strength, the modified mount is still shorter than the original. This means it may no longer distribute forces across the same contact points, especially during side impacts or extreme loads.
Summary of CMC Risks:
Even well-reinforced, the modified mount might not distribute crash or torsional forces as efficiently as the original mount.
Repeated stress could cause cracks to develop around the welds over time, especially under heavy off-road use.
Cab Mount Relocation (CMR) – Strength Through Redesign
In a CMR, the entire cab mount is cut off and repositioned further back along the frame. New steel mounts and brackets are fabricated to maintain the original cab-to-frame connection, and the welding points can be designed to handle stress better than a chopped cab mount.
Improved Load Distribution: By relocating the entire mount, the load is transferred through a properly sized new mount rather than a trimmed one. This maintains the original level of stability between the cab and frame, with no loss of surface area at critical points.
Stronger Welds and Mounts: With CMR, new steel and larger reinforcement plates can be used to make the new mount as strong, or stronger, than the factory design. The new position allows more thoughtful placement of welding points for improved strength.
However, the effectiveness of CMR depends entirely on the precision and quality of the welding and fabrication work. If the new mount isn’t properly aligned or if the welds are poor, it could compromise both the frame integrity and crash performance of the vehicle.
Summary of CMR Benefits:
A properly relocated mount adds steel instead of removing material, potentially creating a stronger connection.
The new placement allows for better alignment of load-bearing points, especially for off-road builds where articulation is critical.
Monongahela National Forest: where your truck transforms from commuter to conqueror. Surrounded by autumn’s finest display and mountains whispering promises of adventure, it sits like a fortress on wheels—ready for anything. Well, anything except explaining the fuel bill when you get home.
Crash Safety and Structural Integrity Considerations
CMC Structural Weakness: The primary argument against CMC is that material is removed from a critical load-bearing point. Even though it’s reinforced with a plate, the modified mount is shorter, which could lead to reduced structural efficiency during a crash. In side or front-end collisions, the trimmed mount may not absorb impact forces as effectively as the original.
CMR as a Potentially Safer Option: Since no material is removed, and instead new steel is added, CMR may result in a stronger cab mount overall, provided the work is done by an expert. The new mount can be placed at a better angle, with welds positioned to improve strength and load transfer. For heavy off-road use, where articulation places significant stress on the frame, CMR offers better long-term durability.
Durability and Long-Term Performance
CMC Durability Concerns: Even with proper welding, the trimmed section of a CMC introduces new stress points where fatigue cracks could form over time, especially if the truck sees heavy off-road use or extreme articulation.
CMR Durability Advantages: CMR, when done properly, replaces and reinforces the cab mount, making it better equipped to handle long-term stress. The new location also eliminates rubbing without requiring further modifications, reducing future wear on components.
Conclusion: When CMR Might Be Superior
Let’s be clear: the cab mount chop (CMC) is the go-to for most people because it’s simpler, cheaper, and doesn’t require a degree in rocket science to pull off. But—and it’s a big “but”—you are cutting into a load-bearing structure. Yes, you can reinforce it afterward, but you’re still removing critical material, which means it’s not quite as strong when it comes to absorbing stress or surviving a crash.
Enter the cab mount relocation (CMR), which doesn’t just chop things away but actually moves the mount entirely, adding new material and potentially ending up stronger than Toyota’s original design. Sounds brilliant, right? Except CMR isn’t something you can do with a sawzall and a six-pack. It requires the precision of a Swiss watchmaker and the expertise of someone who genuinely understands frame dynamics—mess it up, and your truck might drive sideways.
For Tacoma owners planning to slap on 35-inch or larger tires and tackle gnarly off-road trails, CMR is the gold standard. It’s durable, future-proof, and built to handle the worst abuse you can throw at it. But for the rest of us—daily drivers and weekend overlanders running 33s or mild 35s—a well-executed CMC will do the job perfectly without breaking the bank or your nerves.
In the end, CMR is the superior option—if done by a fabricator who knows their craft. But if not? Well, you’ve just spent a lot of money to ruin your truck. Choose wisely.
Doing some easy offroading at the Bald Eagle State Forest in Pennsylvania.
Understanding Tire Sizes
Ah, the rookie mistake of off-roading: obsessing over tire size like it’s a badge of honor. “I’ve just fitted 35s!” they proudly declare, without the faintest clue how wheel diameter, offset, and width are quietly conspiring to ruin their suspension geometry and scrape the arches to oblivion. Tires are more than just numbers on the sidewall—they’re a puzzle of dimensions working together (or against you). So, let’s unravel this mystery, dive into the critical measurements, and figure out how track width, offset, and tire math all play their part. Because bigger isn’t always better—unless, of course, you get it right.
1. Anatomy of a Tire: Key Measurements
Understanding how to size a tire properly requires familiarity with its components. A typical tire size looks like this:
Example: 285/70R17
285 – The tire’s section width in millimeters (mm) (widest point of the tire from sidewall to sidewall).
70 – The aspect ratio, which is the height of the sidewall as a percentage of the section width (in this case, 70% of 285mm).
R17 – The wheel (or rim) diameter in inches (17 inches in this case).
To determine the outer diameter (overall tire height), you need to calculate the sidewall height and account for both sidewalls (since a tire has two sidewalls—one above the wheel and one below).
Calculating Tire Outer Diameter (OD)
The formula for calculating the total outer diameter (OD) of a tire is:
Example Calculation: 285/70R17
Section width: 285 mm
Aspect ratio: 70% (0.70)
Wheel diameter: 17 inches
Step 1: Calculate the sidewall height
Step 2: Convert to inches
Step 3: Account for two sidewalls (above and below the wheel)
Step 4: Add the wheel diameter
So, a 285/70R17 tire has an outer diameter of approximately 32.7 inches, not quite the "33" that some people round it up to. This shows the importance of calculating the real tire size, as slight variations can make a big difference in fitment.
Camping at Bald Eagle State Park in Pennsylvania.
2. Wheel Width and Offset Effect on Tire Fitment and Track Width
Wheel Width
The wheel width (measured in inches) is the distance between the inner edges of the wheel where the tire bead seats.
Wider wheels (e.g., 9-12 inches) stretch the tire sidewalls, slightly reducing the overall tire height.
Narrower wheels cause the sidewalls to bulge more, which can make the tire appear taller and affect clearance.
Offset and Backspacing
Offset and backspacing determine how far in or out the wheel sits in the wheel well.
Offset:
Measured in millimeters, it indicates how far the wheel mounting surface (hub) is from the wheel's centerline.
Positive offset: The hub is toward the front of the wheel, tucking the wheel inward toward the suspension.
Negative offset: The hub is toward the back of the wheel, pushing the wheel outward, increasing track width.
Backspacing:
The distance from the hub mounting surface to the inner lip of the wheel.
More backspacing means the wheel sits deeper inside the wheel well, increasing the risk of rubbing on suspension components or cab mounts.
Impact of Offset on Track Width and Tire Fitment
Track width is the total distance between the left and right tires.
If you switch to wheels with a more negative offset (e.g., from +20mm to -12mm), the wheels push outward, increasing track width. This improves stability but can:
Increase the chance of fender rubbing.
Put more strain on wheel bearings and suspension components.
How Offset Affects Tire Diameter Perception
Wheels with more negative offset push the tire outward, creating a more aggressive stance but making the tire appear larger (because it sits closer to the fender). Conversely, wheels with higher positive offset tuck the tire into the wheel well, reducing clearance and making even moderately sized tires more prone to rubbing.
3. Spacers and Their Impact on Fitment
Wheel spacers serve a similar function to negative offset by pushing the wheels outward, increasing track width. However, they:
Can introduce alignment issues and additional stress on wheel bearings.
May be illegal or restricted in some areas.
Aren’t as structurally sound as choosing wheels with the proper offset in the first place.
4. The True Impact of Diameter on Fitment
While many enthusiasts focus only on the outer diameter of the tire (e.g., "I installed 35s!"), several other factors affect whether a tire fits or rubs, including:
Actual tire size variation: Not all 35” tires measure exactly 35 inches. Brand and tread type (e.g., mud-terrain vs. all-terrain) can result in minor differences.
Wheel width: A wider wheel stretches the tire more, reducing sidewall height and slightly decreasing the overall diameter.
Offset: Wheels with negative offset push the tire outward, increasing clearance from the suspension but decreasing clearance at the fender and cab mount.
Suspension compression and articulation: Even if a tire fits at rest, it may rub during full suspension travel or turns.
Example: 35” Tires on a Tacoma
A 35x12.5R17 tire on a Tacoma with:
17x9 wheels with -12mm offset will push the tire outward, increasing the track width. This setup improves clearance from the suspension but might rub the cab mount or fender liner at full lock or compression.
17x8.5 wheels with +20mm offset will tuck the tire inward, making it more prone to rubbing the upper control arm or suspension components during turns.
Exploring Yellowstone Lake.
5. Practical Tips for Sizing Tires and Wheels Correctly
Calculate true tire diameter: Use the formula outlined earlier instead of relying on the tire's nominal size (like "35s").
Consider wheel width: Ensure the wheel width matches the tire's recommended range (e.g., 12.5” wide tires need 8.5-10” wide wheels).
Check offset and backspacing: Balance clearance needs with track width to avoid rubbing on suspension or cab mounts.
Factor in suspension movement: Test for rubbing by turning the wheels fully and articulating the suspension (e.g., going over a bump or flexing).
Fitting larger tires isn’t just about slapping on some oversized rubber and hoping for the best. Oh no, my friend—it’s a maddening cocktail of wheel diameter, width, offset, backspacing, and the delicate ballet of your suspension. Get it wrong, and you’ll end up with tires rubbing like an overly affectionate dog at the worst possible moment. Get it right, and your Tacoma becomes a symphony of capability and style.
Take 35-inch tires, for example. You don’t just bolt them on and declare victory like some sort of off-road conquistador. No, no, no. You’ve got to think about the wheel width, offset, and suspension setup. And let’s not forget the brutal realities of a cab mount chop (CMC) or, heaven forbid, a cab mount relocation (CMR). Yes, there’s cutting involved—literally. But do it properly, and you’ll have a rig that not only looks the part but dominates on trails and tarmac alike. Magnificent!
