The Beginner’s Guide To Grooving And Siping Your Tires

One of the most often overlooked pieces of equipment on any racing vehicle has to be the tires. Out of every handling adjustment that is made available to us on our vehicle of choice, they all work to help increase or decrease one thing – traction. Traction is what we fight for in every corner! The search for this grip will lead teams to do some wild things to their tires. We’ve all heard the war stories of teams getting caught using some ancient chemical recipe to soften tires. Hell, it wasn’t to long ago Bloomquist himself was caught and banned for half a year from the World of Outlaw Late Model Series.

“Reducing the number of sipes will reduce your trips to the tire truck… Did I just say that?” – Shanon Rush of Hoosier Racing Tire

Walk through the pit area at your local dirt track and your bound to see people performing all types of tire “adjustments.” These extend beyond the normal air pressure or stagger change, rather you’ll see teams literally cutting into a brand new tire with razor blades, or cutting chunks of the tire out. The teams are performing what is known as grooving and siping. If you have ever seen a professional like Bloomquist, or Moyer with a brand new tire you’ll admit that it is like an art form. But just like any artist, these guys have the knowledge that only comes from years of experience of racing on the dirt and knowing what they are trying to accomplish with each cut into the tire.

The goal of this story is to lessen the learning curve when it comes to grooving and siping your tires. To do this, we went to the experts – Product Manager, Shanon Rush of Hoosier Racing Tire, and Marketing Manager Justin Fantozzi of Goodyear. Both companies are widely used throughout the dirt world, and each expert works closely with the biggest names in dirt track racing today. These are the guys that really understand the benefits of grooving and siping, because they not only design the tire, but they are also at numerous tracks throughout the year.

What Is Siping and Grooving?

To better understand the advantages of each, we first have to define just what is grooving and siping. Hoosier’s website offers us the best explanation for the two tire altering methods:

SIPING: Siping is a technique first patented in the 1920’s by a man named John Sipe who came up with the idea of putting razor cuts in his shoes to give him better traction. A sipe is simply a razor thin cut or slit in the rubber tread block. When applying this technique to a dirt tire, siping will do many things. First, this will help the tire build heat quicker which will help the tire “fire” better. Siping will also dissipate heat when the tire gets to operating temperature and the sipes open up. If you are using a fairly hard tire, siping will help create a “graining” effect which will help keep the tire from “sealing” over.

GROOVING:  Grooving is deeper and wider cuts in the tread block. Grooving serves many purposes like helping to channel the dirt out the tire to help maintain a good contact patch between the tire and track surface–just like the grooves in your street tire which help keep your car from hydroplaning. Grooving also creates more edges for better traction or grip. Just as with siping, how much you elect to groove your tires depends on what you have experienced in the past along with watching what the top finishing drivers are doing as well.

So how do you decide then to groove or sipe a tire? “The decision to groove or sipe, to me, depends on what I’m trying to accomplish from a specific tire and track combination,” explained Rush. “Whether I want my tire to heat up faster, wear more, run cooler, or clean better has more effect on when I choose to groove and sipe.”

“We always tell racers to not do anything until you see what the track is going to give you that particular night,” Fantozzi explained to us. “Every track presents different challenges, even the same track varies greatly night to night.”

So for the rookies out there, is there ever a situation where you might not want to groove or sipe a tire at all? “Absolutely. We most often use grooving and siping to maximize the performance of a compound in track conditions or race distances that it may not be specifically designed for,” Rush explained. “Therefore, if you are racing softer compound tires on easy tracks, you probably don’t need to groove and sipe.”

You can see the differences between siping and grooving pretty easily in these two photos from Hoosier

The Tools:

Just like the techniques that teams use, each driver or team will prefer a different tool to groove or sipe their tires. But you don’t need to spend a fortune on the correct tools, the one pictured above is AFCO’s Heated Tire Groover that is available through Speedway Motors. The groover retails for $85.99 and can be turned upside down to sipe the tires also.

How To Properly Sipe A Tire

The thing to remember when siping or grooving a tire is, everyone has their own way of doing it, and each is probably right. The best way to learn is to go to the experts of your tire manufacture and ask their opinion, or talk to other (trustworthy) drivers at the track to help you with your technique. Shannon summed it up well by saying,  “If you look at 10 different tires, you will find 12 different ideas. The equipment has made the job easier, but the techniques are still the same.”

Like we stated before, Siping is quite simply razor thin cuts into the tire tread block. Both Goodyear and Hoosier explained to us, that Proper siping will result in a nice texture or grain to the surface of the tire. Generally, to sipe a tire, the grooving blade is reversed to result in two independent cutting blades. The depth should be set no deeper than 1/2 the depth of the tread blocks. Deeper than 1/2 the depth may cause individual tread blocks to rip or “chunk” out. When setting the depth of the blades for siping, place the siping head on the tread block and visually adjust the depth to 1/2 the thickness of the block. “How much you sipe a tire will come through experience and trial and error,” Explained Rush.

How To Properly Groove A Tire

Unlike siping in which you should go no deeper than 1/2 the depth of the tread block, grooving is a much thicker cut that can, and generally is, the full depth of the tread block. While both grooving and siping can be used as tuning devices, grooving will usually produce the most noticeable difference.

The grooves can be cut in a multitude of ways:

  • Horizontally
  • Vertically
  • Diagonally
  • In the shoulder of the tire
  • Both horizontally and vertically in the same tread block
  • tread blocks can be grooved and siped together or separate
  • Widths, shapes, and depths can be changed for tunability

Goodyear and Hoosier both expressed to us, that the decision to groove, sipe or both, is dependent on a ton of variables. These include, how hard or soft the tire is, how many laps you are planning on running on the set of tires, and how much the track is going to dry or rubber up are just a few that you have to consider.

A Day At The Average Dirt Track

A dirt track will go through a ton of changes throughout an evening, and just as you would make chassis or shock adjustments to keep up with the track, you also need to be keeping up on the tire grooving or siping based on the track conditions.

Early in the day when the track is heavy and wet, Hoosier recommends grooving a tire. Grooving will help channel the mud and debris out the tire to help maintain a good contact patch between the tire and track surface. During this time when the track is lacking “bite”, the grooving will also create edges on the tire to help find that grip. However according to their website, “on tracks where you are not moving or throwing any dirt, but the surface is still relatively soft, a soft tire can often be run effectively with little or no grooving at all.”

The softer tires are very susceptible to tearing or “chunking” once you groove or sipe them. “When you groove or sipe a tire it not only increases grip, but it also increases wear on the tire,” Explained Fantozzi. Infact, Hoosier actually recommends that you don’t sipe their soft D10 compound because of how soft the compound is.

“More is not always better when it comes to sipes. Often if you sipe too deep or put too many cuts in opposing directions, it can prematurely wear your tire, cause the compound to fade, or chunk out sections of the tread,” Rush explained. “Reducing the number of sipes will reduce your trips to the tire truck… Did I just say that?”

Both companies also explained to us that if track conditions deteriorate and get rough, the need for grooves increases. Grooving a tire makes the tread-blocks more flexible to the surface, and in these rough conditions the grooves really prove their worth.

Tracks like this with a bunch of debris and dust need to have grooves to sweep the debris away and maintain a good contact patch between the tire and track.

Once The Track Starts To Harden and Dry Up

If the track starts to dry out, then your variables increase. We all understand that no two tracks will dry out the same, some will rubber up, some will get crazy dusty and not take any rubber, and some will rubber up and get black and shiny with no dust. Each one of these scenarios can require different approaches when it comes to grooving or siping.

“On dry tracks, we normally use medium-width grooves with minimal sipes,” Rush explained to us. “You need some groove width in order to clean the loose debris from the contact patch but we reduce the sipes because the wheel spin will generate heat and wear on its own. Generally, you will still be on relatively soft tires on dusty, dry tracks so they don’t require as many sipes to perform well.”

Notice however, the complete focus of the tire changes once a track rubbers up, Rush went on to say, “Now, when a track truly rubber’s up, not just gets shiny and black, we shift our focus to tire conservation, not tire performance. I generally use narrow grooves and minimal sipes circumferentially around the tire. These sipes and grooves help cool the tire without increasing wear.”

But what about when a track gets very slick and black from a night of racing? Rush would give us his approach, “In black, slick conditions, we generally get pretty aggressive with both grooving and siping. We generally use narrow grooves in both directions to reduce block size significantly and sipe medium depth numerous times across the tire. I avoid siping both directions as I think this leads to tires chunking on black, slick tracks.”

Conclusion:

Some people view the grooving and siping of tires as a black art, but ultimately it is something that can’t be learned over night. It is a ever changing study of how tires react to what that particular track is doing that night. Both Shanon and Justin explained that keeping a “track” or notebook is a really good idea. If you have a notebook, you can write down what the track conditions were that night and provide detailed notes on what you did to your tires that night. That is the real way drivers become good at grooving or siping.

If you have questions about grooving and siping your tires, feel free to call our friends at Goodyear and Hoosier, they were more than willing to give us the information in this story. This is just a tip of the iceberg, ultimately at the end of the day, the way you become good at grooving and siping your tires is by doing your research and performing some trial and error. Fantozzi summed it up the best, “I think the hardest part of grooving and siping is predicting what the track is going to do next. The teams that have the most success grooving and siping study, and study, and STUDY the track before making a single cut or sipe.”

About the author

John Gibson

John has been around dirt track racing his entire life. In fact, he was almost born at Monett Speedway in Monett, Missouri. He has raced everything on dirt and asphalt from karts, to Indy cars, to 650 horsepower stock cars in the USAR Pro Cup where he currently races.
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