Tires: Compounds, Tread, and the Foam Inserts Nobody Explains

You can spend a season adjusting shocks, springs, camber and diffs, and none of it will change how your car behaves as much as fitting a different set of tires.

Tires are the only part of the car that touches the ground. Everything else in the setup exists to control how they touch it. That makes them the biggest single handling change available to you, and the one most often ignored because a set of tires looks like a set of tires.

This covers compound, tread, the foam inserts that do more work than the rubber, gluing and venting, and how to tell which of those is actually causing your problem.

The three parts of a tire

Most people think of an RC tire as one thing. It is three, and they can be changed independently.

1. The rubber (carcass) — the tread pattern and the compound it is molded in.
2. The foam insert — the ring of foam inside. This controls how the tire deforms under load, and it matters at least as much as the rubber.
3. The wheel — the plastic rim the tire is glued to. Offset and width change track width and how the tire stands up.

Change one at a time. Changing tire and insert together tells you the car is different but not why.

Compound: how soft the rubber is

Softer rubber grips more and wears out faster. That is the whole trade, and it is not free.

• Soft — most grip on hard, smooth or low-traction surfaces. Wears quickly on abrasive ground. On sharp gravel or hot asphalt a soft compound can be gone in a single pack.
• Medium — the default for most bashing and most surfaces. Where to start if you do not know.
• Hard / firm — long life, works best on high-grip surfaces where you do not need the rubber to do the gripping. Feels vague on anything loose.

⚠️ A soft compound on the wrong surface grips *worse*, not better. On loose dirt the grip comes from the tread digging in, not from the rubber sticking. A soft tire with the wrong tread just flexes and wears.

Manufacturers name compounds differently and there is no shared scale — one brand's "soft" is another's "medium". Compare within a brand; do not compare across brands by the word on the packet.

Tread: what the pattern is for

The pattern is chosen for the surface, and it matters more than compound on anything loose.

A slick tire on grass has almost no grip. A spiked tire on asphalt has almost no grip, and destroys itself doing it. Matching tread to surface is the single cheapest handling improvement available.

Foam inserts — the part nobody explains

Inside the tire is a foam ring. It is not packing material. It is a suspension component, and it does more to determine how a tire behaves than most people realize.

What the insert controls: how much the tire squashes and rolls under cornering load, how it conforms to bumps, and how much of the tread stays flat on the ground.

• Soft insert — the tire conforms to the surface, follows bumps, keeps contact on rough ground. More grip on chop. Too soft and the tire rolls under in corners.
• Firm insert — supports the sidewall, keeps the tread flat, resists rolling. Better on high-grip surfaces and for heavy cars. Too firm and the tire skips across bumps instead of following them.
• Dual-stage inserts — a soft outer ring with a firmer inner ring, aiming for both. Common on 1/8 buggy.
• Closed-cell foam does not soak up water. Open-cell does. This matters enormously if you run in wet or on a watered track — a waterlogged insert changes the tire's weight and behavior completely and stays wet for days.

"Traction rolling" — where the car trips and flips over in a corner instead of sliding — is very often an insert problem, not a suspension one. The tire rolls under, the sidewall folds, the rim edge catches, and over it goes. A firmer insert usually fixes what an afternoon of shock adjustment could not. There is a fuller guide on this site dedicated to traction rolling.

Gluing tires

RC tires are glued to the rim with thin CA (superglue). This is not optional on anything fast.

Why: at speed, the air inside the tire and the centrifugal force on the rubber both push outward. An unglued tire balloons off the rim, usually at the worst possible moment.

How, briefly:

1. Fit the insert and seat the tire fully on the rim. Check the bead is sitting properly all the way round on both sides.
2. Work in small sections. Pull the tire bead back slightly with a finger, run a thin bead of thin CA into the gap, and release. Thin CA wicks along the bead on its own.
3. Rotate and repeat until you have gone all the way round. Then do the other side.
4. Let it cure fully before running.

Wear gloves and work in ventilated air. CA bonds skin instantly and gives off fumes that sting your eyes.

Common mistakes: using medium or thick CA (it sits on the surface instead of wicking into the bead), gluing with the bead not properly seated, and only gluing the outside. Both sides need it.

Venting

Many tires have — or need — a small vent hole, usually pinned through the tread or the sidewall.

Without a vent, the tire becomes a sealed air spring. It balloons at speed, the contact patch shrinks to a narrow strip, and grip falls off exactly when you are going fastest. It can also make the tire behave inconsistently as it heats up and the trapped air expands.

Some tires come vented. Some do not, and are meant to be vented by the user with a needle or a small drill. Check whether yours are — a tire that inflates visibly at speed is telling you the answer.

Ballooning at high speed

Even a vented, glued tire grows at speed. Centrifugal force stretches the rubber outwards, and the faster you go the bigger the tire gets.

Two consequences:

• Your gearing changes as you accelerate. A bigger rolling diameter is taller gearing, so the car keeps pulling further than the numbers suggest.
• The contact patch narrows as the tread crowns, so grip falls off at exactly the point you most want it.

For genuine high-speed running, belted tires exist — a fabric belt inside the carcass restrains the stretch. They are heavier and less compliant, and they are the correct answer above the speeds where normal tires start to distort.

Tire diameter changes your gearing

This is missed constantly. A tire is the last gear in the drivetrain.

A larger-diameter tire is taller gearing — more top speed, less acceleration, more load on the motor and ESC. A smaller one is the opposite. Fit noticeably bigger tires and you have effectively geared up, whether you meant to or not, with all the heat that implies.

If you change tire size significantly, re-check your gearing and your temperatures. The calculator on this site works in rollout, which accounts for tire diameter directly rather than pretending it does not exist.

Crawler tires are a different problem

Rock crawling inverts most of the above.

• Compound is everything, and the softest sticky compounds dominate. Wear barely matters at crawling speeds.
• Inserts matter more, not less. A crawler tire needs to deform around rock and conform to the surface, so soft, light, open-structure foams are the norm.
• Weight and where it sits matters — many crawler builds add weight in or near the wheels deliberately.
• Ballooning and venting are irrelevant. Nothing is happening fast enough.

There is a separate getting-started guide for rock crawling on this site that goes further into this.

Wear, storage and age

• Check wear across the tire, not just in the middle. Wearing on the inside or outside edge is a camber or toe message, not a tire message.
• Keep them out of direct sunlight. UV hardens rubber, and a hardened tire grips like a hard compound whatever it says on the label.
• Compounds age. A soft tire that has sat for a few years is not a soft tire anymore. This is why an old new-old-stock set can be disappointing.
• Store them off concrete and away from solvents and fuel.
• Truing — machining the tire back to a perfectly round, even diameter — is a racing practice that matters on-road and on carpet, and matters very little for bashing.

Traction additives

Chemical compounds painted onto tires to soften the surface and increase grip. Widely used in racing, and banned or restricted at many tracks — some because of the mess, some because of the fumes, some because of what they do to the racing surface.

If you run at a club or track, ask what is allowed before you use any. If you bash, they are mostly an expensive way to pick up dirt.

Diagnosing by symptom

Start with the tires. They are cheaper to change than an afternoon, and they will tell you more than any single suspension adjustment will.