What Is Tyre Degradation in IndyCar? A Beginner-Friendly Guide
Why do IndyCars get slower as a stint goes on, why are some tyres red, and why do teams obsess over “deg”? This guide explains tyre degradation in plain English: what causes it, how Firestone’s tyres differ, the new 2026 rules, and how it shapes race strategy.
What Is Tyre Degradation in IndyCar?
What causes it, how IndyCar’s tyres differ, and why it decides races.
Watch any IndyCar race and you’ll hear commentators talk about “deg”. A driver is “struggling with the rears”, another’s alternates have “fallen off a cliff”, a third is “saving his tyres”. All of it comes back to one idea: tyre degradation, the way a tyre loses grip, and therefore speed, the longer it’s used.
It sounds technical, but the basics are simple, and once you understand them you’ll see why teams make the pit-stop calls they do. This guide explains what tyre degradation is, what causes it, how Firestone’s IndyCar tyres work, what changed for 2026, and how degradation shapes strategy. If you’re new to race strategy, our explainer on fuel strategy covers the other half of the puzzle.
What Is Tyre Degradation?
Tyre degradation is the gradual loss of grip a racing tyre suffers as it’s used. A brand-new tyre, once it’s up to temperature, gives the most grip it ever will. Every lap after that, it wears a little, heats and cools, and gradually loses performance. Less grip means the driver has to brake earlier, carry less speed through corners and be gentler on the throttle, so lap times get slower.
How quickly that happens is what teams call the “degradation rate”. A tyre with low degradation might lose only a few hundredths of a second per lap. One with high degradation might lose several tenths, and at some point the drop-off becomes so steep that it’s faster to stop for new tyres than to carry on. That moment is often what decides when a team calls its driver into the pits.
Tyre degradation is how much speed a tyre loses as it’s used, and managing it is one of the biggest factors in IndyCar race strategy.
It’s worth separating degradation from simple wear. Wear is the physical loss of rubber. Degradation is the loss of performance, which can come from wear but also from heat, from the rubber’s chemical changes, or from damage to the tyre’s surface. A tyre can have plenty of rubber left and still be “degraded” if it’s overheated.
What Causes Tyre Degradation?
1. Mechanical wear
Every time a tyre slides, brakes or accelerates, a little rubber is scraped away. Abrasive surfaces, like older street circuits with bumpy, patched tarmac, speed this up. Less rubber means less grip and, eventually, a tyre that simply can’t do its job.
2. Thermal degradation
Racing tyres work best within a specific temperature window. Push too hard, slide too much or follow another car closely in dirty air, and the tyre overheats. An overheated tyre becomes greasy and loses grip, and repeated overheating can permanently change the rubber, so it never quite recovers. Hot weather makes this worse.
3. Fuel load
An IndyCar starts each stint with more fuel on board than it finishes with, and a heavier car puts more load through its tyres. That’s one reason drivers often have to be gentle at the start of a stint and can push harder as fuel burns off. Our fuel strategy explainer covers how fuel and tyres work together.
4. The track surface
Tracks change during a weekend. As more cars run, rubber is laid down on the racing line and grip generally improves, which is called “track evolution”. Off the line, bits of worn rubber collect as “marbles”, which are like driving on ball bearings. Street circuits, used as public roads most of the year, often start the weekend dusty and slippery and improve a lot by race day.
5. Driving style and set-up
Two drivers in identical cars can get very different life out of the same tyres. A smooth driver who avoids sliding will usually suffer less degradation than one who throws the car around. Set-up matters too: a car that slides its rear tyres out of slow corners, for example, will wear them faster. IndyCar’s hybrid system and push-to-pass button add extra power, which helps overtaking but can also put more strain on the rear tyres when used heavily.
IndyCar’s Tyres: Blacks, Reds and Rain Tyres
Every car in the NTT IndyCar Series runs on Firestone tyres. Firestone makes around 32,000 race tyres for a season, including more than 5,000 for the Indianapolis 500 alone, and produces more than 60 different specifications to suit the series’ circuits. There are three types you’ll see on track, each identified by the colour of its sidewall.
| Tyre | Sidewall | Character | Where used |
|---|---|---|---|
| Primary | Black | Harder; balance of speed and durability; lower degradation | All tracks |
| Alternate SOFT | Red | Softer; faster over a lap; wears and degrades quicker | Road and street courses |
| Rain | Grey | Grooved tread to clear water and prevent aquaplaning | Road and street courses |
The contrast between the black primaries and red alternates is at the heart of IndyCar tyre strategy. The reds are quicker, especially over one lap, which is why drivers use them in qualifying. But they degrade faster in a race, so a stint on reds is usually shorter or involves a bigger drop in lap time towards the end. The blacks are slower at first but more consistent over a long run.
Ovals are different
On ovals, teams normally run a single oval-specific tyre rather than reds and blacks. Oval tyres are built for sustained high speed and heavy loads in one direction, and teams run “stagger”, with slightly larger tyres on the right side, to help the car turn left. Degradation on ovals is mostly about the right-side tyres, which carry more load, and about how the car’s handling changes as they wear.
IndyCar has experimented here. At Gateway in 2023, the series brought an alternate tyre to an oval for the first time, using a compound made with guayule, a desert shrub that Firestone has developed as a more sustainable source of natural rubber. The idea was to create different strategies and more passing as cars cycled through tyres that degraded at different rates.
IndyCar first used an alternate tyre at the 2004 Long Beach race, and the two-compound system became standard on road and street courses by 2009. It was introduced for exactly the reason covered in this guide: two tyres with different degradation create strategy choices and make races less predictable.
The 2026 Rule Change: Two Stints on Reds
For 2026, IndyCar changed its tyre rules for street races to put degradation back at the centre of strategy. At all six street races on the 2026 calendar (St. Petersburg, Arlington, Long Beach, Detroit, Markham and Washington, D.C.), drivers must complete two stints on the alternate tyres, as well as at least one stint on the primaries. Previously, only a single stint on each compound was required.
The reason was simple. Teams had become very good at minimising their exposure to the faster-degrading reds. At Long Beach in 2025, 21 of the 27 drivers ran only the minimum required on alternates and switched to primaries by lap 3. That made strategy predictable. IndyCar president Doug Boles said Firestone’s “higher degradation alternate tire has given strategists plenty to think about,” and the new rule forces teams to deal with it.
The change also affects qualifying. Teams now need more fresh sets of reds for the race, so using too many in qualifying can leave a driver short on Sunday. That trade-off, between qualifying speed and race tyres, is exactly the kind of decision that makes a weekend interesting. Road courses and ovals kept their existing tyre rules.
IndyCar didn’t make the tyres degrade faster. It made teams face the degradation they’d been working hard to avoid.
How Degradation Shapes Race Strategy
Because tyres lose speed, every stint has an ideal length. Stop too early, and you waste tyre life and may need an extra stop later. Stop too late, and you lose time on worn tyres. Teams model this constantly, using data from practice to predict how fast each compound will degrade on race day.
The undercut and the overcut
Degradation creates two classic tactics. The undercut is pitting before a rival: fresh tyres are so much quicker than worn ones that a driver can gain enough time in a few laps to come out ahead when the rival stops. It works best when degradation is high. The overcut is the opposite: staying out longer, usually when degradation is low or the car ahead gets stuck in traffic after its stop.
Which tyre first?
On road and street courses, teams must choose when to use the reds. Starting on reds gives a fast opening stint and a chance to gain places, but it means a shorter stint and possibly an earlier stop. Starting on blacks is steadier and may allow a longer first stint. With the 2026 street-race rule requiring two red stints, the choice is less about whether to use them and more about when.
Cautions change everything
Caution periods, when the field slows behind the pace car, are a huge part of IndyCar strategy. A caution lets teams pit and lose far less time than under green-flag racing, and it also gives the tyres a chance to cool. A well-timed caution can rescue a driver on badly degraded tyres, or ruin the plan of one who has just pitted. That’s why strategists always have one eye on the likelihood of a yellow flag. Our guide to what causes crashes in motor racing explains why cautions are so common on street circuits.
How to spot degradation while watching
You don’t need team data to see degradation happening. Watch the lap times on the timing screen: a driver whose laps are getting steadily slower late in a stint is feeling the tyres go. Look at onboard footage for small slides out of slow corners, or a driver taking a wider line to avoid the marbles. Listen to team radio for phrases like “the rears are gone” or “managing the fronts”. And watch the gaps: when a car behind on newer tyres is suddenly catching several tenths a lap, degradation is usually the reason.
Degradation also varies by track type. Street circuits are often bumpy and abrasive, with lots of slow corners that punish the rear tyres under acceleration. Permanent road courses tend to have smoother surfaces but faster corners that put more energy into the tyres. Ovals load the right-side tyres heavily for long periods. Knowing the track helps predict whether a race will be decided by tyre management or by outright speed.
Tyre saving versus pushing
Drivers can influence degradation during a stint. Smoother inputs, managing wheelspin and avoiding following another car too closely all help the tyres last. The trade-off is lap time: a driver who saves tyres early may be slower for a while but faster later in the stint. The best IndyCar drivers are known for knowing exactly when to push and when to save.
Tyre Jargon, Decoded
| Term | What it means |
|---|---|
| Deg | Short for degradation: how much lap time a tyre loses as it’s used |
| Fall-off / the cliff | A sudden, steep drop in grip when a tyre is near the end of its life |
| Reds / blacks | Alternate (softer) and primary (harder) tyres, named after their sidewall colour |
| Stint | A run between pit stops on one set of tyres |
| Graining | Small rolls of rubber forming on the tyre surface, reducing grip until they wear away |
| Blistering | Bubbles or chunks lifting from an overheated tyre |
| Marbles | Small bits of worn rubber that collect off the racing line |
| Stagger | On ovals, the size difference between right- and left-side tyres |
| Undercut | Pitting before a rival to gain time on fresh tyres |
| Overcut | Staying out longer than a rival to gain time |
Once you know these terms, broadcasts become much easier to follow. When a commentator says a driver is “on the reds and starting to grain”, you’ll know it means a faster but softer tyre that is losing grip and may be close to a stop. For more on how races are timed and gaps measured, see our explainer on how race timing works.
Tyre degradation is the reason IndyCar races aren’t simply won by the fastest car. Choosing compounds, timing stops and managing grip through a stint are what turn raw speed into results, and the 2026 street-race rule has made those decisions more important than ever.
Tyre Degradation in IndyCar — FAQ
Grip is temporary, strategy is everything
Every IndyCar stint is a race against the tyres. From the moment a new set goes on, it starts to lose performance, and the teams that understand and manage that best usually come out on top. Reds or blacks, push or save, stop now or stay out: these are the decisions tyre degradation forces on every team, every race.
Next time you watch, keep an eye on lap times late in a stint and on which tyres each driver is using. You’ll start to see the strategy unfold before the commentators explain it.
