We are in a golden age of tires for motorcycles. Let’s get that straight first and foremost.
I am so tired of hearing at track events that “….these tires are/were terrible!”. That is not only disrespectful to all the engineers and testers that developed them but also uninformed with a very poor POV/perspective underscored by a very limited amount of knowledge.
This is a complicated topic and fortunately, it can be broken down into simple components of knowledge that you will use for the rest of your motorcycling life. Read and study the building blocks, create a one page cheat sheet and get to the nearest store that has a good stock of motorcycle tires so you can do some homework on diameter and carcass.
There are no guards, infrared safety lasers nor ticket admissions only to the tire area. I never cease to be amazed that this area is always silent, no one goes to it nor pulls down tires to compare and contrast diameter, profile and carcass. Thankfully, this article will reverse that “stay away” mantra.
Procedural notes:
No tire testing can take place until you have a chassis geometry baseline established and your suspension is correctly calibrated for spring rate, preload and damping with optimal travel used. Your suspension fluid is ideally fresh for the forks and shock(s) or it is relatively new oil, that being less than 2 hours of track time.
Aging fork oil gives variable viscosity and flow rates based on temperature so you can quickly take the wrong direction to be misled and waste a significant amount of money and time chasing set up, let alone adverse wear. That variance will be apparent after 5 track days and will exponentially deteriorate by the 12th track day.
Tire Gauge
Use the tire gauge you have always used and every 2-3 months have it tested against a calibrated port. Carrying the tire gauge in a tool box will by default, throw it around during transportation unless you have it securely stored in a case. Do not compare to other gauges – trust your own. If you cannot get it checked/calibrated, use a tire pyrometer to give you the carcass temperature, then capture the temperature and hot pressure.
Second set of wheels
Have a second set of identical wheels (front and rear) available. If you do not, you are testing wheels, not tires due to the difference in weight and reciprocating mass. An identical pair of wheels ensures that you can immediately install one or both to avoid significant downtime with time lost waiting for wheels to be stripped and the next set of tires mounted. That means two sets of warmers and a portable wheel tree if you can afford one. This tree allows additional sets to be off the ground avoiding asphalt damage to the exterior of the warmers or to the rotor(s).
All wheels must have the same brand, model and diameter brake rotors on them. They must have the correct cush drive and the same rear sprocket by manfacture. Note that a common practice is to balance the wheel without a tire mounted to reduce the number of exterior weights used. This simple practice will expedite tire changes potentially minimizing time spent balancing wheels post tire install.
Tire construction:
Before you test any set of tires, you need to go to the manufacturers website to see how they are made and what materials are used. That helps you understand the carcass, cap, sidewalls and bead. This educates you on tire flexibility and rigidity, two absolutely critical factors to know and understand prior to evaluating each set of tires.
- Tire construction technical information
– https://www.dunlop-moto.com/en_gb/safety-and-technology/
– https://www.pirelli.com/tires/en-us/motorcycle/tech-and-knowledge
– https://www.metzeler.com/en-us/tech-and-tips/tire-construction-and-technologies
– https://www.continental-tires.com/tire-knowledge/tire-construction/
Peeling the onion layer by layer in regards to tire construction is great knowledge to have especially in regards to carcass flexibility and/or rigidity. R&D constantly evolves and as such the data, diagrams and explanations we can access via Manufacturer websites can constantly increase our knowledge base. A carcass will always give you feedback, and understanding the how and why you receive feedback can lead to much faster lap times by leveraging this specific information.
When discussing “What tire should I buy?” with clients, I always start with a question:- “Are you ADHD or even keel to mellow?” A stiff carcass will give you a never-ending stream of feedback at all times whereas a soft carcass will take away feedback and let you focus on decisions and timing. Conceptually, that makes great sense and it takes a minute for riders to unravel and understand that concept. The requirement is that you are honest about yourself as that will give you a huge ROI from your tire purchase via the carcass that you need.
NOTE:
– as a rule of thumb, a soft carcass will need more pressure, a hard carcass less pressure. Therefore, review what the manufacturer recommends for cold and hot pressure ranges with each model/compound so you have a known starting point.
– As an example, the hot pressure for my Dunlop R4 rear was 20psi at Buttonwillow whereas the Pirelli SC1 rear was 24.5psi for the same track.
- Tire circumference/diameter
As noted earlier that is no universal circumference between manufacturers, the balance point of your chassis can move noticeably depending on the diameter of the tires you install. As such, we MUST acquire the difference via data or do some measuring (tape or Vernier calipers) to understand what happened to the balance point.
– if the front tire is larger, the balance point moves back.
– if the rear tire is bigger, the balance point moves forward.
– if both tires are bigger, the bike is raised up.
– if both tires are smaller, bike is closer to the ground (is your ground clearance impaired?).
This concept is by far, the most neglected, misunderstood or simply ignored data point for the vast majority of street and track riders. This is also true of racers at the local level. The handling of your motorcycle that you think was great can be devastated with a tire swap between manufacturers or sizes and very few think of changing geometry immediately to put the balance point back to where it belongs for YOUR motorcycle.
Measure between the top dead center of the cap and the center of the front and rear fender/mudguard with every new tire you install. If there is no rear fender, measure to the center/inside of the swing arm. This will give you the clearance that you have with this brand and model.
– if the brand and model have a new version, measure again.
– if you change brand and model, then you MUST measure again.
The balance point shift can cause a plethora of handling issues if you do not correct the geometry of your motorcycle to compensate! Here are a few examples.
– front chatter trail braking when the brake lever is released (larger front tire).
– bike will not turn without considerably more effort (larger front tire).
– braking stability is dramatically reduced (smaller front tire and/or larger rear tire).
– motorcycle runs wide on exit (smaller rear tire)
- Control your air source
– Humidity is a nightmare to manage for cold to hot pressure gain.
– Water vapor turns to steam at 212F/100C.
– Compressors store water so empty and dry them out before every use*.
– Electric pumps just move air so no need to worry about a stored reservoir of rusty water.
– If there is any doubt, point the air nozzle 6” from the concrete or asphalt and assess the water content from the air released.
*In one often to referred to incident, racers went out on new tires at the start of a practice session at a California track. Within 3 laps, all riders were coming back in with complaints of zero grip and the bike riding as though it was on ice. Cold to hot pressure variance was 10-12psi and should be 2-3psi over hot temperatures in the warmers. Therefore, the air going into the tires was full of water vapor from air compressors. Tires were deflated in the hot pit, refilled and practice resumed. A very short time after this occurred, a considerable swath of rusty water was released across the paddock when the compressors were emptied.
For those living in hot and dry climates, you do not fight humidity. For those in humid climates, having a water separator in the air line is essential to minimize water vapor effect. An alternate strategy for humid climates is to use nitrogen gas as it is “dry”. It is an expensive option and for motorcycles, you need to find hot pressures to match ideal carcass temperatures based on compound and track aggregate. That takes a lot of testing.
- Track aggregate/surface.
Some surfaces are very low grip, whereas others are highly aggressive and wear tires out ridiculously fast. Some aggregates give a literal 1,000 grit finish to the cap which visually seems like they are not wearing at all until you examine the core holes or wear markers. Some tracks will devastate certain compounds in just a few laps (ask riders at Jennings and Carolina Motorsport Park) whereas other tracks are forgiving allowing 2-4 compounds with no adverse wear.
We all have heard and seen of stories from MotoGP down to Club racing where a new track surface has required a unique compound or has mandated a mandatory wheel and tire change based on the fact that the tire will not make it to the end of the race. An appropriate example is The Podium Club in Arizona as tire wear was a huge problem for months with new pavement.
If you are testing and want to maximize the opportunity, what local knowledge can you source from racers and vendors? They know what brand and compounds work best based on lap times and bike engine size via experience. This research can save you hours and $$ and get you to the compound(s) you need very efficiently.
If budget allows, you should have 3 compounds from the same manufacturer available to test.
- Tire warmers and warm up periods?
There are so many options and price points for warmers. You can have the basic single temp, dual or triple temperatures, adjustable temperature by degree, warmers that cover the upper surface only, those that have additional material to shield wheels from the wind and some that offer wheel rim warming.
The mandatory details for tire warmers are:
– You test them regularly to make sure they are 100% functional.
– You retire them if there is any discrepancy with surface heat variations.
– You know what the single temperature warmer reaches via 5mm probe.
– You test any multiple setting warmer to document the heat produced.
– You honor the warm up time and temperature that the manufacturer recommends.
The other major area of concern is power. Are you in a garage that is shared by 5, 8, 12 bikes? How much does that affect the power you are getting to your warmers? Do you find a significant reduction in temperature for the high setting between a generator and a shared garage? Perhaps you should use your own generator to guarantee consistent stable power to your warmers? Going out on “cold” tires will create bad information and yet again, you divert down the wrong road for an extended time period, chasing the wrong data.
- Carcass temperatures vs surface temperatures?
You will see at all National and World levels of competition, tire staff using a device similar to the Longacre pyrometer with a 5mm needle. They are recording the temperature of the carcass, not the surface of the cap. This data point is absolutely critical to tire testing and a mandatory item to use.
For a meaningful analogy, we use a temperature sensor when cooking meat in the oven or on the BBQ to make sure the meat is at temperature. Same principle applies to the tires as the data point is the carcass temperature.
For those that cannot afford a device like this, see if you can work with someone that has it and compare carcass temperatures to your laser for surface temperatures. It is not apples to apples and never can be, but you have something to work with for comparative data.
Manufacturers offer data on what carcass temperatures should be for optimal operation. This is for grip and longevity as the tire has to last a race for top level riders. For us as track day riders and Club racers, we need grip and longevity as we do not have $3,000 for a track weekend in tire expenses, so we must optimize temperature to optimize wear in this regard. Trapping this data can save you enormous amounts of money.
- Compounds vs track temperatures vs surface aggregate?
I will always ask a rider that is starting to race at the Club level to build a data table with track temperature, hot pressure and compounds used. I will also guide them to research what the manufacturer recommends for compound to ambient temperature, so they are using the correct compound and therefore, getting the most out of their investment.
Some tracks favor certain compounds per brand, so again complete your due diligence by talking with local racers and vendors!
Here in Northern California we can go from a track temperature of 50F/10C to 120F/49C in just a few hours in March and April. As such, we may need one compound for the morning and one for the afternoon. If you are serious about your tire budget, having a second set of wheels ready to go with the compound needed makes a great deal of practical and financial sense. The added bonus is optimal grip irrespective of the track temperature range.
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