Tech Talk: Tires, Tire Warmers and How to Use this Tire "Tool"

28 August 2019

Dave Podolsky from Chicken Hawk Racing Gives SRO America Entrants Extra Insight with This New Tire Tool

Give a carpenter a level and a plane and he’ll know what to do with them. They’re tools of his trade. However, without the proper knowledge, an inexperienced person may not know how to use the tools to their advantage.

Tire warmers are simply tools to manage tire performance and longevity. They also require a base of knowledge to use them effectively. This article will review the basics of what is going with your tires and see how tire warmers can be used as tire-management tools to help you get the most out of your tires.

The Key To Chassis Performance

When discussing tires, grip, traction, tire longevity, chassis and suspension performance are the terms we throw around.

In addition to holding our line through the corner and driving us down the next straight, tires are our first “damper”.   The initial point of contact with a track’s bumps, they act as our initial suspension component. To do this they deform, then quickly return to shape in a process called hysteresis. Carcass construction/flexibility and tire pressure also play important roles in maintaining traction.

To produce grip, a tire must be soft enough that the track’s surface irregularities make an impression in the tread rubber. This permits maximum “mechanical keying”. The tread rubber must also have elasticity, high tensile strength and resist tearing, so that the rubber engaging the track surface doesn’t get torn and scrubbed off.

How Tires Make Grip

Tires make grip in three ways: adhesion, mechanical keying and tear/wear.

Adhesion is an inherent property of rubber that makes it stick to other surfaces. Its coefficient of friction and the momentary molecular bond it creates between two surfaces is adhesion. Imagine a block of rubber on a smooth piece of glass with a 1 lb. weight on it. Now imagine the amount of force needed to push the rubber so it begins to slide on the glass.

The force it takes to initiate movement and overcome inertia is greater than the force needed to keep it moving once it begins to slide.  Drivers on track know this all too well!   

Mechanical keying comes into play because the track surface is not perfectly smooth. Even billiard table-smooth tarmac is quite coarse on a molecular level. It doesn’t take a microscope to discover that every track surface has nooks and crannies. Therefore, contact between tire and track only occurs at the highest points on each.

A tire’s true contact patch varies depending on each material’s properties, their surface profiles and contact pressure, and the vertical load on the tire. Greater vertical loads press tires into a track’s nooks and crannies, increasing their effective contact area and mechanical keying. Softer compounds also allow tires to be more easily pressed into the track surface and lower tire pressures allow for a larger contact patch.

Tear and wear occur when the forces of adhesion and mechanical keying increase as they provide grip to the track surface. The tire grips the track surface, stretching to the limits of its elasticity; at the limit the resulting stress this puts on a tire can be greater than the rubber’s tensile strength. When this happens, the tire stretches beyond recovery.

The force needed to tear the rubber molecules apart is another component of grip. While stretching and tearing, the tire absorbs energy and creates more friction between it and the track surface. This is what creates the balled-up pieces of rubber hanging off the edges of our tires and the little rubber marbles which can be found along the edge of any racetrack.

Tire Science

Modern high-performance tires are made from complex combinations of natural and synthetic rubber, carbon black, silica, metal belting and thread.

Tread rubber is formulated with up to 30 percent oils and waxes. When sold to us, they’re not totally cured or vulcanized. This helps the tire have a soft, pliable and flexible nature. When cold, these compounds are quite viscous and stiff. This is why cold tires have little grip.

In the last 20 years, we’ve seen tire chemistry grow increasingly sophisticated. Long gone are the days when lap records were posted only during the first few laps before their tires’ effectiveness and grip dropped off.

Why? Because today’s race rubber contains chemical activators that create traction. When heated, these new compounds activate, getting the tires to fire. This chemical reaction produces a higher coefficient of friction, making the rubber stickier and grippier.

Once up to temperature, some these chemically active compounds seek to link with one another. Similar to how oxygen molecules are naturally attracted and pair to become O2, these compounds seek to be relinked.

When long chains of molecules in a tire become broken (when weakened by deformation, hysteresis and abrasion), the chains of molecules reconnect, becoming longer and stronger. Just as long fibers make paper towels tough and short fibers make toilet paper weak, long molecule chains in tires provide the strength that help them resist tearing and slow wear.

So, as the laps roll on, these long molecule chains continue to break down, but the chemical activators allow the molecule chains to continually repair themselves. This is why we can now see record-setting times near the end of 20- to 30-lap stints.

How to Use Tire Warmers

Now that we’ve covered the basic concepts of how tires provide grip, let’s explore the most effective methods of utilizing these tire-prep and grip-maintenance tools to manage traction, wear and safety.

It’s better to heat tires up slowly and gently, asking them to begin working once they’re up to temperature--when their carcasses more supple and have greater elasticity.

We want the tire exterior surface to be hot, but internal carcass temperature is more critical. Carcass temperature is a true reflection of how much heat is in the tire. It also affects tire pressure and carcass flexibility.

In the past 25 years, we’ve only seen tires get designed to work at hotter and hotter temperatures. Today many race tires are designed to work best at temperatures from 180F-215F. This past year we see Pirelli World Superbike tires are being heated as high as 248F!

Heat Soaking

Pre-heating the tire surface, carcass and wheel is knows as heat soaking. A high-quality warmer should take about 20 minutes to bring tire-surface temperature up to 185F, but the tire is not yet heat soaked. We recommend pre-heating your tires for an 1.5 hours to get them as hot in the pits as they’ll get on the racetrack.  A good baseline target for heat soaking a race tire would be a tire-surface temperature of 195F, 180F tire-carcass reading and 130F for wheels.  

Race-Day Tire-Warming Procedure

First, set cold tire pressures high enough that after warming the tires they will reach or surpass your desired hot pressure. If you don’t know what hot pressures to run, ask your tire vendor. Tell them what tire you’re running, the car you’re driving and how fast you’re lapping.

With your wheels off the car is best to assist in getting more heat in the wheels and starting about 90 minutes before hitting the track. If you are unsure what temperature to begin with 185F is good place to start. This temperature will not overheat your tire and will be warm enough to put you within its operating window.

With about 10 minutes to go, using the same air gauge, check the pressure in each tire and bleed it down to your desired hot pressure. Good-quality tire warmers have better insulation that helps build more carcass temperature and pressure. It’s common to gain about 20% when going from 75F to 195F.

Obtaining accurate and meaningful tire temperatures is useful but not always easy.  The driver would have to attack the last lap after the checkered flag as hard as the ones before and have a mechanic with a proper probe-type pyrometer waiting on the hot pit lane.  Having a system to the tire in a specified order such as: Right Rear, outer, middle, inner, then move on to Left Rear, outer, middle, inner etc. to try and keep the system as consistent as possible.  The tire surface cools quickly and if temperatures are not obtained in a consistent manner the data can be more confusing than helpful. 

Tire pressure however can be used to help.  After coming off the track, don’t delay but don’t race through the paddock to your pit either! It takes around four or five minutes for tires to lose one pound of pressure. Get the car back to your pits and check tire pressures right away.  Put the Tire Warmers back on right away too!!!!

Did the pressure go up or down? A variation in hot pressure readings are directly related to temperature changes in the tire and rim.  In general, faster drivers work tires harder and build more heat.

Perfect tire heat and pressure management consists of tire and rim temperatures that have little or no fluctuation from pit to track. Over time (and with some good notes) you’ll learn that Track A on a 50-degree, cloudy day might require a temperature of 175F and Track B on a sunny, 90-degree day requires a tire temperature of 210F.

If your right rear tire warmer was set at 175F with a target hot pressure of 25 psi in the pits, but is at 28 when you return, this means you built up more temperature and pressure on track and you’ll need to increase the tire warmer temperature setting and/or get the wheels hotter.

In this case, it would be best to increase the set point to say 195F with an adjustable-temp tire warmer, bleed the pressure down to 25 pounds and repeat the process next time you come off the track.

When you return to your pits with hot tires, install the tire warmers. If your next session is in 90 minutes or less, simply keep them on your hot, track-ready temperature. There’s not enough time to cool and re-heat them.

If you must wait more than two hours before hitting the track, you can lower the setting to say 130F. This keeps tires from traction-robbing heat cycling that also reduces their lifespan. About  45-60 minutes before you go back out, turn the warmers up to your track-ready temperature.

Maximizing Tire Life by Minimizing Heat Cycles

Heat cycles occur when tires are heated and cooled. The cooling side of the process creates changes in the tire, the chemical activators and the tire’s softness. This maintenance temperature between track sessions prevents tires from heat cycling and allow you to get more laps in before their performance drops off.

Proper tire cool-down at the end of the day is an important part of minimizing the heat cycle which will occur when the tire cools off. The most common indicator of improper cool-down is the dreaded blue haze that appears on tires the next day. This discoloration forms because the tire’s oils and chemicals migrate to the surface and oxidize. This needs to be scrubbed off before the tire will develop good grip again.

When you’re done for the day with tires that will be used again, let them cool for about an hour with warmers installed, but not energized. This allows them to cool slowly, minimizing the heat cycle’s effect and keeping more of the tires’ compounds below the surface, where they belong.

Tires are expensive consumables that have limited useful lifespans. Making them last longer with thorough preparation, pressure monitoring and limiting the number of heat cycles they endure is easy with efficient tire warmers.

How to Select Tire Warmers

A tire warmer’s job in your pit is to bring the tire carcass up to the temperatures they’ll see on the track. It’s important to select a tire warmer that spreads heat evenly, drives that heat into the carcass then keeps the heat from escaping.

The differences between competing brands of brake pads, race fuel, helmets and even tire warmers are not often apparent.

A quality tire warmer utilizes job-specific insulation that makes them as efficient as possible, but still thin enough to easily fit between tires and fenders. Among these materials are Nomex, para-aramids and carbon-based insulations.

Get educated and take the time to select the right tire warmer for your use. A good quality tire warmer should last five to seven years even if used often as long as it is cared for properly. Look for a company that offers a great warranty, does repairs and services the product in-house. Compare information on heating elements, insulation quality, temperature-control systems and casing materials.

To save money purchasing tools of inferior quality never pays off in the long run. Unlike tires, tire warmers are not consumables; buying a right tool will pay off with better tire performance, superior reliability and a longer life span.

***Chicken Hawk Racing has been a Technical Sponsor of the Red Bull Honda World Superbike Team.  Although they deal with 2 wheels instead of 4 many of the tire concerns do corelate; we asked Tire Technician Gerrold ten Caat and asked him a few questions about what he sees on track:

Do you see a trend in race tires operating at hotter and hotter temperatures?

For sure! The faster the bikes go, the hotter the tires will get. It’s an effect of more energy being driven into their tread and more movement in the tire carcass. Also, tire pressures are continually lowered to get bigger contact patch on the track. This creates more friction and hotter temperatures.

To deal with this, the race-tire manufacturers keep making tires that work at hotter and hotter temperature ranges. From this it follows that I need hotter tire warmers as well, because I need to be as close as possible to on-track conditions.

How long do you like to preheat a tire with a warmer before sending your rider out?

Never less than 90 minutes, but if possible around two hours. I like to take the first half hour to easily heat them on lower temperature so they do not suffer heat shock. Also, I want the complete carcass hot, therefore the tire needs time to soak all the heat in.

One big issue that affects heating is the wind, so I always make sure no wind is blowing across my rims. Cold rims do have an effect on the temperature of the air inside the tire, making it difficult to get a stable hot-tire pressure.

Are you gauging their ready by their time on the warmers?

My numbers tell the tale. I do many measurements and have tons of data on tread, carcass and rim temperatures, in addition to tire pressure. I compare this with the track and outside temperature to know if the hot tire pressure is good to attack the track.

What about wheel temperature?

In my opinion this is really important. I always tell people to start measuring the rim temperature and compare this with the tire pressure. Do this when the bike goes out and when it comes in so you get good data to work with. If, for example, you note a 18F difference in rim temperature--which equates to 2.1 PSI more or less pressure--it will be really easy to set the right pressure when you go out on track. For lower-budget riders this does not cost a lot of money and will save a lot on tire wear.

Rise in tire pressure?

This is honestly the most important thing to me. I need to get the tires up to a stable hot track pressure before the rider hits the track! If we have the pressure 1.5 PSI out of range, the chassis won’t work like we want it to and the tires will therefore not give 100% of the performance we need. During a race weekend, I am constantly adjusting tire-warmer settings to get the right temperature and tire pressure for the conditions that exist on the track at that time. For this I need accurately calibrated tire warmers with stable temperature control.

How much pressure rise do you typically see on the tire warmers?

Well, I do not focus on cold pressure because this makes no sense to me. I want to see hot pressure because that is what I need! The pressure rise when going from 60F to 200F can easily be up to 10 PSI because I focus a lot of attention on heating the rim. This also depends on how dry the air is inside the tire. In the WSBK championship, we use high quality air dryers on the compressors, but if you do not have access to this the hot pressure will rise even more.

Have you seen any negative effects of leaving tire warmers on too long?

This all depends on the quality of the tire warmers. Basically, you need good insulated blankets and heating elements inside that are closely spaced. During testing I sometimes have tires that are heated all day and we see no difference in performance, this is because we use one of the best products on the market. I’ve tested lots of tire warmers and, believe me, there are warmers that will ruin tires in just one hour.

My advice to club racers would be to invest the time in learning to understand tires, then invest in good quality tire warmers. Tires are the most important parts on any bike. Focusing on this will save money while adding performance.

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To learn more, contact Chicken Hawk Racing at (845) 758.0700 or visit chickenhawkracing.com

Gerrold ten Caat is a mechanic for the Red Bull Honda Racing World Superbike Team who was responsible for managing the tires for the team in 2016, 2017 & 2018.  He’s also a retired SuperMoto Racer and the owner of REV Factory, a race shop in the Netherlands.