Do I Need Crossbars? Understanding Car Rack Compatibility Basics

So, you’re thinking about strapping something to the top of your car. Maybe it’s a kayak. Maybe a bike. Could be a rooftop cargo box for that epic road trip you’ve got planned. But before you start dreaming about the wind in your hair and your gear riding high above, let’s pump the brakes for a sec. Do you even have crossbars? Do you need them? And what the heck are all these different rack systems people keep talking about?

If you’ve ever felt overwhelmed standing in the automotive section of a big box store or doom-scrolling car rack forums at 1 a.m., you’re not alone. Crossbars, towers, rails, fit kits, roof types—it can get confusing fast. So let’s break it all down in plain English, minus the marketing mumbo-jumbo.

First Things First: What Are Crossbars, Really?

Crossbars are exactly what they sound like: bars that run across the roof of your car from side to side. They form the foundation of most roof rack systems, and they’re the key to hauling anything from skis to surfboards.

Now, a lot of people think their car already has a “rack” because it has those two rails running front to back. Not so fast. Those are side rails. They’re just part of the puzzle—and whether or not you can use them depends on the rest of your setup.

There are two main types of side rails:

• Raised side rails – These are the ones with a gap between the rail and the roof. You can slip your fingers under them. They’re super common on SUVs and wagons.
• Flush side rails – These sit tight against the roof, with no gap underneath. They look sleek but can be trickier when it comes to adding a rack system.

Some cars don’t have side rails at all. In that case, we’re talking about bare roofs. And yep, that’s still workable—it just usually means you’ll need a complete rack system, towers and all.

Do You Actually Need Crossbars?

Here’s the real question, right? Because not everyone does. The need for crossbars depends on:

• What you’re hauling
• What your car already has
• What kind of mounting system your gear requires

Let’s go through a few scenarios.

Scenario 1: “I just want to throw a cargo box on top for my family road trip.”

You’ll need crossbars. Almost all cargo boxes require crossbars because they clamp or attach across them for stability. No crossbars = nowhere to mount the box. Some companies make systems that integrate crossbars and boxes, but they’re not common.

Scenario 2: “I’m hauling bikes, but I already have a hitch rack.”

You’re good! No need for crossbars. Hitch racks don’t rely on the roof at all, so if you’ve got a solid hitch mount, carry on.

Scenario 3: “I want to carry a kayak.”

Now you’re getting into definitely-crossbar territory. Kayak carriers—whether they’re J-style, saddles, or stackers—all require a stable foundation, and that means crossbars.

Scenario 4: “I have factory-installed side rails. That’s all I need, right?”

Not quite. You still need to bridge the gap between the side rails with—you guessed it—crossbars. Some vehicles come with factory crossbars already installed between those side rails, in which case you’re golden. But if it’s just rails and nothing crossing them, you’ll still need an aftermarket solution.

Scenario 5: “My car has a bare roof.”

This is where things get real. If your roof is completely bare—no side rails, no factory mounting points—you’ll need a full system:

• Towers or feet that attach to your roof (usually via door clamps or a fit kit)
• Crossbars to run across
• Possibly a specific kit designed for your car’s make and model

It’s doable, but definitely more involved. And honestly? It’ll cost more too.

Crossbar Compatibility: Why It Matters

Not all crossbars are created equal. And not all accessories will fit on every crossbar. There are a few shapes you’ll see out there:

• Square bars: Classic, boxy, and strong. Not very aerodynamic though, and some accessories need adapters.
• Round bars: Think old-school Yakima. Similar issues with wind noise and fit.
• Aero bars: These are oval or wing-shaped and designed to reduce wind noise and drag. Most newer accessories are made to fit these.
• Factory bars: Sometimes these are… fine. Other times, they’re oddly shaped and don’t work well with aftermarket gear.

Pro tip: If you’re starting from scratch, go aero. It might cost a bit more, but the reduced wind noise alone is worth it. Plus, you’ll have way more options when it comes to accessories.

Don’t Forget About Load Limits

Even if your setup seems good to go, there’s another piece of the puzzle you can’t ignore: weight limits. There are actually three load limits you need to keep in mind:

1. The dynamic load limit of your rack system – This is how much weight the rack can hold while driving.
2. The roof load limit of your car – This is how much your vehicle’s roof can handle.
3. The dynamic load limit of your crossbars – Some bars have lower limits than your towers or rails, so check them all.

Most passenger vehicles can handle somewhere between 100 and 165 lbs on the roof while moving. That includes the weight of the rack plus your gear. You’d be surprised how fast it adds up.

Pro tip: Want to throw a rooftop tent up there? Check your static load limit too (how much the roof can handle when the car’s parked). Some setups can handle people sleeping up top, some definitely can’t.

A Word on Rack Brands

There are a few big names in the game: Yakima, Thule, and Rhino-Rack are probably the most recognizable. Each has its loyal fans, and honestly, most of the gear is solid.

But compatibility? That’s where it gets tricky. Not every Yakima bar works with a Thule tower, and vice versa. Some systems are modular, some are proprietary. Before you buy, make sure all the components you’re piecing together actually talk to each other.

And while we’re at it, don’t just buy whatever’s cheapest on Amazon. That random no-name set of bars might not fit your car properly—or worse, it could fail on the highway.

Don’t Forget the Little Things

It’s easy to focus on the big stuff—bars, towers, mounts. But don’t forget the accessories that make life easier (and safer):

• Locks: Good racks aren’t cheap. Don’t skip the locking cores.
• Wind fairings: If you’ve got noisy bars, these can help reduce the whooshing sound.
• Tie-down straps: If you’re carrying boats or boards, make sure you’ve got bow and stern tie-downs too. It’s not just about stability—it’s also about keeping other drivers safe.

Installation: DIY or Shop Time?

A lot of crossbar systems are DIY-friendly, especially if you’re just attaching to raised side rails. It’s usually a matter of measuring, tightening bolts, and checking your spacing. But bare roof systems or anything involving door jambs and fit kits? That’s next level.

If you’re even a little unsure, have a shop do it. Some stores will install for free if you buy the rack system from them, and it saves you the stress of wondering whether that creaking sound is just the wind or your kayak about to become a projectile.

The Bottom Line: Crossbars Are (Usually) a Must

Here’s the deal: if you’re putting anything on your roof, there’s a good chance you need crossbars. They’re the middleman between your vehicle and whatever gear you’re hauling.

And while it might feel like a lot of homework upfront—figuring out what type of roof you have, what fits your car, what works with your gear—it pays off when your stuff stays securely in place, even at 75 mph on the interstate.

So do you need crossbars? Probably. But now, at least, you know what you’re looking for—and what to avoid. And trust me, your future self (the one on that road trip or hauling that SUP to the lake) will thank you for getting it right the first time.