Q&A with a tire engineer: Answering your questions

Sponsored Content Presented by Maxxis Tires.

No matter the make or model, track or series, all of our cars have one thing in common: They run on tires. They're the single, critical link between the car and the ground.

And with those tires come questions. Lots of questions.

Fortunately, we know someone with answers.

John Wu, an engineer by training and now director of product strategy for Maxxis USA, has been working in the tire industry since 2005. He’s been a track day participant for more than 20 years, and he understands the role that tires play in our world.

One of our past Q&A sessions with John generated follow-up queries, so this time we've turned the mic to our forum audience.

DirtyBird222: How much does shaving track tires help performance and heat management?

Maxxis: We’ll need to conduct more testing to provide a scientific answer, but in general, shaving tread rubber off the tire improves performance due to lighter weight (unsprung/rotational mass), reduced tread squirm (better handling and steering responses), and reduced heat generation (as a result of less tread squirm).

 

Patientzero: How similar are the actual compounds between the street and R-comp tires? On a street tire, is the better wet grip 100% due to the tread design or do differences in the compound help, too?

Maxxis: Although the types of chemicals we use in a UTQG 200 street tire and an R-compound may not be too different, the ratios are optimized for different usage conditions.

In some cases, the tread rubber used can also be different depending on the balance we’re trying to achieve between characteristics such as tread wear and dry and wet traction.

In the case of our RC-1, we know it won’t see much street use, so wet traction and tread wear are a lower priority. In the case of our VR-1, we know it still needs to function as a summer street tire, so we do take wet traction/tread wear into consideration when optimizing the compound.

Tread pattern design, profile design and tread compound all contribute to better wet traction. Tread pattern design also plays a major role in hydroplaning resistance, but performance on damp/wet surfaces is more complex. Profile design affects the footprint shape (how much and what part of the tire touches the ground at specific pressures), and compound design affects the friction force between the interface of tread and road surface; different rubbers, chemicals and fillers such as silica are used to enhance wet traction.

 

KentF: What would be the coldest storage temperature you would want to allow for the 200tw and the R-comp tires?

Maxxis: This depends on the compound design, so we can’t speak for other tire manufacturers.

When designing the R2 and S2 compounds, we knew the tires would be exposed to temperatures as high as 270-plus degrees Fahrenheit on a race track, so therefore it is difficult to engineer a compound that can handle both summer as well as winter temperatures.

Our engineers recommend storing our RC-1 and VR-1 indoors in the winter to make sure the ambient temperatures do not fall too close to the temperature at which the compound will freeze (aka glass transition temperature, Tg). Otherwise, the tire can show cold-weather cracking that looks like glass cracks. A more complete write up is on our website.

Vigo: I’m curious about the distribution of how tires shed heat. As in, how much heat goes into the rim, how much goes across the contact patch, how much goes to outside air, etc.? This is just pure curiosity. 

Maxxis: We’d have to conduct a specific experiment to give you a percentage, but in a race setting, heat is mainly generated within the tire cavity (high-stress deformation of rubber compounds) and by the tread surface rubbing against the pavement.

Only a small portion of the internal heat travels from the tread to the sidewall/bead and onto the rim, because rubber is a poor heat conductor. This is the reason that internal tire temperatures and pressures build up so quickly on track, while the tread surface heat is mostly dispersed by the air flowing around the tire.

 

thashane: What is the definition of a heat cycle? For example, if I drive to the autocross in the morning but don't run until the afternoon, how many 200tw “heat cycles” took place that day? One, two, five? Also, if I spray water on tires between runs, will I heat cycle my tires out sooner?

Maxxis: There is really no clear definition of a heat cycle, so it varies from company to company. In general, we view it as a tire going from ambient temp to usage temp and back down to ambient temp.

We would have to conduct a series of experiments to see how much spraying water reduces the heat cycle effect on the tread compound, so unfortunately I can’t give you a scientific answer. A faster cooldown from track temps should help reduce the heat cycle effect somewhat, but there are so many variables to consider that it may not help significantly.

What we do know is that street driving does count as a gentle heat cycle, so unfortunately it still chips away at the tire’s performance. If you want peak performance every time, we highly recommend that you carry the tires in plastic bags and that you do not expose the tires to UV rays or excessive heat.

carpeforza: Up here in the North, we have track days and races early in the season with track temps right around freezing. Even worse, we have sessions only 15 minutes long and sometimes it is raining or snowing. What type of tire would give you the fastest lap times for cold, wet, short race sessions?

Maxxis: We would recommend talking to other manufacturers to see if they have a race tire that can work in the very low temperatures you describe. Maxxis currently doesn’t have anything that would give you race pace under those conditions.

My best guess is probably some sort of ultra-high-performance all-season tire, but you will have to exercise restraint and caution since these types of tires are usually not optimized for track driving.

 

Olemiss540: Was NT01 the target for your RC-1 offering? Where do you see success in dethroning the ultimate HPDE tire and where do you see room left to improve? What causes a tire to better handle braking zones, and why does one tire prefer to have higher angles of slip versus another in the same treadwear segment?

Maxxis: We studied quite a few tires, so we weren’t aiming to beat any one brand per se. We simply addressed our own customer feedback and sought to engineer a solid UTQG 100 R-compound to address drivers’ needs. There is always room to improve, so we will study the market and prioritize certain improvements for our next tire.

Great traction in a tire (braking, acceleration, lateral) is always a combination of compound, construction and pattern working together. There are things we do to optimize for each, but unfortunately I can’t go into that much detail.

Regarding slip angle, what I can say is that we can revise design parameters to reduce slip angle, but usually race tire engineers are seeking improvements in other quantifiable performance metrics such as dry lap times, braking distance, etc. Therefore, slip angle is almost a byproduct of our decisions. The only setting in which slip angles are specifically engineered is probably for OEM automaker business.

 

L5wolvesf: How would these 200tw tires work on a dirt oval that is restricted to DOT tires?

Maxxis: We haven’t tested our VR-1 on dirt ovals, so we don’t yet have that information.

Olemiss540: At what point will we see the 200tw super tires out today be able to hold up to four or five track weekends a year? Give me RC-1 or NT01 grip levels that can handle 32 sessions while driving to/from the track, please–potentially driving to events in the rain.

Maxxis: As cars get heavier and more powerful, this combination of features becomes that much more difficult to achieve. We would love to offer a product that fits your description, but compound technology and materials science may need to advance a bit more before that’s possible.

 

LanEvo: I'm interested in the differences between high-end R-comps (like Hoosier R7s) compared to true slicks (like Hoosier C3000s). Also, R-comps versus asphalt circle-track slicks. 

Maxxis: We are not in the asphalt circle-track business, so we can’t comment on that just yet. Regarding high-end R comps and non-DOT slicks, construction is probably the biggest difference. Most non-DOT slick tires feature semi-radial construction.

DOT tires, even racing models, need to pass FMVSS (federal motor vehicle safety standards) and our own roadworthy testing, so the design approach is totally different and usually results in a much heavier tire. We don’t currently sell a non-DOT slick, but if we did, we would optimize the tire for minimal weight and use higher-grade/higher-strength materials, dry-traction-enhanced compounding, and possibly new manufacturing processes as well.

 

Curtis73: How do the different tire components impact performance? I would love to get deep into tire tech. I would love to know what goes into a tire and what those quantities produce in terms of qualities–like higher plutonium content increases sticktion, increased dilithium crystals helps keep it more stable in wider temps, more dicktonium prevents UV damage, etc.

Maxxis: Great question! Because this is such a wide-ranging and complicated subject, it’s difficult to cover even a few points in this format, but I’ll see if we can do a video series on this topic in the future.

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