Durometers

Grip in the corners creates speed that will get you to the front. Fresh tires are the equivalent of bolt on speed.  In order to maximize grip, selecting the best tires will help you to get the corner speed you need to win more races. Since tires are a major investment it pays to spend some time ensuring that the tires you purchase are fresh – equally important is that your tires are consistent. Striving to find a “matched” set will increase overall speed. How often have you dialed your car in on practice tires only to have the set up change when a new set is bolted on? Could tire hardness variations be the culprit? If your series allows multiple compound choices then tracking the Durometer readings is critical if you plan to have speed at the end of the race.
A quality Durometer is a valuable tool that will help you to find more speed in any tire stack. Technology has provided the racing world with new tools that are more accurate and easier to read. Dial Type Durometers may still have their place; the pocket watch dial type utilizes a spring that transfers tire hardness to the face of the gauge.



A Dial Type Durometer can be purchased in a combo kit that includes a Dial Type Tread Depth Gauge. Using a Durometer is more effective if you use a Tread Depth Gauge and a Pyrometer to ensure consistency in your testing procedure.

Digital sensors are designed for accuracy and display giant numbers with resolution that gives you the extra edge. Digital displays provide an actual number taking the guess work out of reading a needle – the resolution is improved through both sophistication and viewing angle. Digital versions provide “relative hardness” that are easy to read even at night. The prominent display gives your team a modern advantage for only a few dollars more. The digital world that makes iPhones and computers available at reasonable prices has created mass produced sensors and chip components that indirectly improve the quality of all digital devices. Digital Durometers are benefactors of the digital world.
Quality analog versions work fine, but noticeable gains are made with new digital technology. The counter debate for the dial type is that they never need batteries and can sit in the tool box for long periods and always be ready to go.

 
Digital Durometers should include a back light helping you to see the accuracy even at night. Digital sensors benefit from the same mass production philosophies that make your smartphone and tablet cost effective.

Measuring tire rubber hardness is less exacting as compared to using dial indicators to measure the thickness of steel. Since you use hand pressure to push your durometer into the tire, it is common that 2 people can come up with different readings. As long as a dedicated crew member performs the task the same way each time then repeatable relative numbers will give you reliable information. The variance in actual accuracy will be limited how different crew members apply pressure. Eliminating variables will provide the best results with both Analog and Digital Durometers. Experience and feel will be enhanced by utilizing a measuring process that eliminates as many variables as possible. With training, all of your crew members should be able to produce the same readings.

Rubber deforms and the best readings are obtained when you take readings quickly – if you allow the Durometer to sit in one spot, the specially sized Shore A measuring probe will sink into the tire surface. The tire rubber deforms around the Durometer measuring probe. If you leave the Durometer in place for 30 seconds on one tire and 3 seconds on the next, your readings will suffer and accuracy is lost.
The best way is to ensure the tire is free of debris - a scraper should be used to remove loose rubber unless you are measuring the hardness of sticker tires.

Place even pressure and take care to hold the Durometer flat on the tire. Flat positioning on the tire creates the best results. It is a myth that rolling the measuring pad on your Durometer over the tire provides better readings, in fact “rolling” introduces un-needed variables. Simply holding your digital Durometer flat, with consistent and light pressure for a consistent time period provides the best results. Just set it on the tire with consistent finger pressure and measure it – simple replaces complicated every time. Doesn’t it make sense that holding a measuring tool flat on an even surface will provide better accuracy than rolling the Durometer over the surface? Why introduce a moving target by rolling a flat surface over the face of the tire?



Using a Durometer is simple – consistency is key to producing repeatable results. Simply place the Durometer flat on the tire surface with moderate finger pressure. Rolling adds a variable so just set the thing on there and take your reading within a second or two – easy.

 Really, measuring tire hardness with a Durometer is a simple process. Marketing hype is replaced by utilizing a simple repeatable process each and every time. Use the finger guide located at the top of the Durometer, provide light and consistent pressure, and verify that the durometer is flat on the clean tire. Then, take readings quickly and take 1 second +/- for the Shore A probe on your Durometer to stabilize – for the best results, be sure to time the measurement so that each measurement is taken with the Durometer foot pad on the tire for the exact same amount of time. Consistency is what will produce “Relative Hardness” that can be recorded to produce real results for future use.

If you set the Durometer into the tire and hold it in one place you will see the hardness number will rise - then as it is held in one spot the reading will start to drop. Hold the Durometer in one place too long and you can be assured that the Durometer measuring probe is sinking into the tire providing you with erratic results. Experiment by holding the Durometer in one spot on the tire for several seconds and you will visually see how the Shore A probe deforms into the tire – the longer you hold the Durometer in one spot – the more you can watch the reading drop as the probe is simply sinking deeper into the rubber. The process is simple – make sure the Durometer is flat on a clean tire surface and with even pressure simply record the reading. You can save rolling around for other more exciting endeavors.

Creating a repeatable process will give you the best relative hardness numbers and give your team the best chance at recording accurate readings. You must start with a clean tire. In the case of testing new tires, you can avoid worrying about debris or rubber build up. New tires are easier to test than used ones. When testing used tires, ample time must be spent cleaning the area to be tested. A flat scrapper easily removes debris off of hot tires that just finished making a few laps. Used cold tires have debris build up that has solidified on the surface. The rough texture will give you erratic results. Be sure to put some muscle on a scrapper on cold used tires. With a little effort you can witness the embedded loose rubber falling to the ground revealing the actual rubber surface that connects your chassis to the contact patch.

Several spots should be checked on the tire as tire rubber is not perfectly homogeneous (some areas of every tire are harder or softer than others). Small areas in the tire can be harder than others and the variation in the rubber surface must be averaged out. The rubber surface can be uneven creating variances. I check an area on the tire in 3 to 5 places. I always throw out the high and the low and then look for a hardness number that comes up to the same reading in several locations. If the tire is hot after a run it will pick up loose bits of rubber on the way into the pits – use a scraper to get down to the “real” tire rubber surface. The same theory applies to checking tread depth – you want to measure the real tire surface and avoid all the loose debris that can skew the readings.

Since rubber becomes softer as it is heated it is critical to measure the temperature of each tire before taking the Durometer reading. If you have two tires with the same compound and one is 100 degrees and the other is at 50 degrees the cooler tire will read significantly harder. You could warm up the same 50 degree tire to 100 degrees and find that the Durometer readings would equalize. To check Durometer readings you must have tires that are equal in temperature. Even one tire measured on the shady side will read harder than the side facing the sun.

 
Pyrometers are a must when measuring Tire Hardness. You can use an IR Pyrometer to check the surface. A probe type with an adjustable probe is really the best tool for checking tire temperatures (see the JOES Knowledge Center on the JOES website for Pyrometer Tech).

Tracking tread depth in conjunction with the tire hardness will allow you to predict when a new set is in order. By measuring the remaining thickness of the rubber on a new tire you will gain insight as to when a tire will lose adhesion. By diligently tracking tread depth and recording Durometer hardness through wear, you will be able to identify when it is time to hit the tire truck and step up for a new set. Over time you will learn the wear patterns and the Durometer will visually show you at what depth your specific tires give up.
Heat cycles need to be factored into the Durometer measurement process as well. Racing tires come out of the factory with a magic mix of chemicals that produce grip. Tire engineers work tirelessly to ensure your tires maintain maximum grip for the maximum time. Chemical engineers mix their recipe of friction producing materials and chemicals into the tire to give long lasting and repeatable grip. Each heat cycle “evaporates” valuable chemicals out of the base rubber. With each run, the tire becomes harder and the chemicals that keep the rubber soft and pliable are lost. Your Durometer can help you find the point in time when performance drops off. Variables such as tread depth wear, heat cycles, number of laps, age, ambient temperature all factor into the tire replacement schedule.

 If you know you have a loose car and have been buzzing the RR all day then you must consider that the RR will have faced more abuse than the other tires. Understanding why tires get hard is a compilation of several variables.

Top teams keep notes on their tire sheets so they can save money by running tires longer (Download Free Tire & Chassis Sheets at http://tinyurl.com/8gu92hj). Detailed tracking of variables provides valuable warning allowing for a purchase of a new set before they quit mid-race. Your rules dictate specific variables and if you run the same set for more than one week you can save some money, without sacrificing performance, by utilizing the results of your Durometer tracking. If you buy a new set each week you can learn which tire serial numbers perform best and cull out any old or bad tires hiding in the at your tire supplier.

Durometers can be used to predict the end of life on tires that are run multiple times. If you run a weekly series and your tires are run for more than one week it can be very valuable to track the tire hardness. Finding a good used matched hardness set from your inventory will help you to have good practice tires.
By understanding the wear characteristics, racers can use science to determine when to purchase a new race set or practice set. Tracking the tire hardness of used tires will give you data that can be used to graph when they are too hard to achieve the best lap times. Often, race tires perform to a lesser degree even when the wear indicators show there is substantial rubber left. While there may be rubber left on the tire the chemical compounds have evaporated due to multiple heat cycles leaving the remaining rubber too hard to create need temperature and friction.

Friction creates heat. More friction – more heat. Using a Pyrometer alongside your Durometer is mandatory. If you have apples to apples wear and you go on a 5 lap run - then all things being equal you should have Pyrometer readings that are reasonably close from the two sessions. If your set suddenly looses temperature as compared to the prior run you can be assured the friction is being lost. The tire is getting harder and the chemicals that create grip have evaporated out of the tire. Tracking tires goes beyond hardness. Paying attention to all of the variables that affect your tires creates the best performance.

Hardness measurements are most valuable when used systematically with pyrometers and tread depth gauges. Lap counting and heat cycles all come into play. Maybe heat cycles are the critical factor for your brand of tires, but maybe simply checking wear depth with let you know when a new set is needed. Durometer readings will back up your concerns and the Durometer will show the relative hardness if readings are taken at equal temperatures.


Careful and consistent measuring utilizing several tools will help you to create a system that produces repeatable results. Shopping is a good idea here.

Digital Durometers are the new revolution and are only a bit more in cost. Soft tires at the end of a race could give you the added grip off of turn 4 taking you to victory lane. You can still type a letter with a typewriter, but with computers the results and time savings are vastly improved. The digital revolution is here to stay. Dial Durometers work fine when used properly and never need batteries. A Digital Durometer used properly will create an easy to read number and the backlight allows you to see your winning resolution even at night.

Tracking tire hardness with a repeatable system will give you the resolution to gain an advantage. Utilizing a Dial or Digital Durometer in conjunction with a Tread Depth Gauge and a Pyrometer will give you all the tools needed to produce consistent and recordable results that will give you the winning advantage as it relates to the theory of relativity.

 Go Forward – Move Ahead.
Jeff Butcher
 05/05/13