Q&A With a Tire Engineer: R-Comp Race Tires vs. 200-Treadwear Extreme Street Tires

Staff
By Staff Writer
Jun 11, 2021 | Tire Test, Sponsored Content, 200 TW, R-comp, Maxxis Tires | Posted in Tires & Wheels , Features | Never miss an article

Sponsored article presented by Maxxis Tires.

 

Today’s 200-treadwear tires have gotten fast–really fast–and have become a staple in autocross, time trials and endurance racing. But don’t forget their true purpose: At the end of the day, they’re designed for the street.

How about running a true race-ready, R-comp tire in these events instead? Yes, they’re also street-legal and carry a DOT stamp, but they’re engineered more for the track than the road. That means less comfort but more speed. 

One look immediately reveals their different missions: Where the 200-treadwear tires feature some tread, R-comps practically resemble full slicks. 

We’ve tested 200-treadwear tires against R-comps before–same car, same size, same tire manufacturer–and the lap times revealed the performance advantage: 28.114-second autocross laps for the street tires and 27.703-second laps for the race tires. 

The in-car data, though, showed even bigger advantages for the race rubber: higher average g-force readings through the turns, much quicker transitions, higher throttle load capacity, and more grip in straight-line situations–meaning quicker acceleration. 

What if we could peek inside the two tires to see how the magic happens? 

We asked someone who could take us there: Meet John Wu, an engineer by training and now director of product strategy for Maxxis USA. He’s been working in the tire industry since 2005 and has been a track day participant for 20 years. 

Maxxis has one foot in each of these tire camps, too. The brand’s Victra VR-1 is a 200-treadwear model designed for today’s extreme summer tire market. It features a full tread for daily use yet is still suitable for motorsports events. A GRM tire test showed that it should do well in endurance races that require tires carrying the 200-treadwear stamp of approval.


The Maxxis Victra VR-1 is a 200-treadwear model designed for today’s extreme summer tire market.

For those looking for more speed, Maxxis offers the Victra RC-1, a 100-treadwear, R-comp model tuned for track use. It features the minimum two grooves required for DOT approval and is tuned solely for the track. Its mission statement is posted right there on the Maxxis website: Recommended for DRY COMPETITION EVENTS ONLY.

 
The Maxxis Victra RC-1 is a 100-treadwear, R-comp model tuned for track use.

GRM: What specifically makes R-comp tires faster than true street tires?
Maxxis: R-comp tires are engineered with much shallower tread depth plus a specific pattern, profile, construction and compound design for track use. 

Shallower tread depth means a shorter tread block height. Shorter tread blocks do not move or flex as much as taller tread blocks and therefore don’t generate as much heat when the tire is driven to the limit. 

The downside is you have less void for water evacuation. Therefore, most companies usually recommend R-comps for dry use only due to their limited wet-weather performance.

The pattern design will usually employ large tread blocks or continuous ribs to maximize road contact and tread block rigidity. Engineers analyze the contact patch shape–aka footprint–and optimize a tread design to work well with footprint changes under load. 

Engineers also have to make sure the tread will wear somewhat evenly under racing conditions, so this is where expertise and technology come in. 

Tire profile design is another tool we have to optimize the footprint shape for wear and performance. Typically, R-compounds will have very large-radius profile designs, whereas street tires will be more reserved. Large-radius profile designs make the tire sidewall/shoulder area look “beefy” and “square.” That larger radius gives us the footprint we want and need in an R-compound.

Most materials start to lose their strength/rigidity with heat, so our engineers pick materials that can handle the heat generated under racing conditions. Construction of R-compounds usually utilizes high-tensile-strength materials that are more resistant to heat. This tensile strength provides a stable, rigid casing, which helps with overall dry performance but is not so great for ride comfort or noise. 

Casing strength is vital for fast steering/vehicle response as well as cornering traction. We sometimes will use additional sidewall steel belts to further improve steering/vehicle response. This feature is rarer on a street tire. 

Other parts of the tire, such as bead and sidewall design, can also differ on an R-compound due to the anticipated race use, so we forgo ride comfort and rolling resistance in order to optimize heat dissipation, rim contact and increased response.

Compound design is more complex and is a highly guarded secret within most tire companies, so I can’t say too much. All I can say is that R-comps intended for dry use will be engineered to warm up quickly, resist high temps, and provide great traction at the expense of tread wear. 

The compound will be engineered to work within a specific temperature window, so performance drops off greatly when the temperatures get closer to freezing or get too hot. We have usage and storage guidelines for winter conditions because race compound tires will crack when the temperature drops too low. Another caveat is race compounds typically don’t work well on wet and slippery surfaces.

GRM: Why do R-comps run cooler than true street tires, and how does this translate into longer tire life and better track manners? 
Maxxis: Large tread blocks and a shallower tread depth generate less heat and also dissipate heat better.

Heat is usually the number-one enemy for tires. We haven’t done specific studies on tire life versus running temperature, but in general we know heat ages a tire faster and durability goes down as the tire is exposed to extended periods of heat. 

Regarding track manners, the mechanical properties of different tire components start to degrade with increasing heat, hence the performance drop-off you experience when the tires gets hotter and hotter. 

Due to the inherent design advantages–shallow tread depth, large blocks, construction materials–R-comps tend to run cooler than street tires on track, so even though they have shallower tread, they may actually last longer than street tires. The bigger/shorter tread blocks on R-comps also have higher rigidity, so they can withstand the abuse more and not chunk or wear rapidly.

Why? Because the 200-treadwear tires should run hotter on track, so the tire wears faster at these elevated temperatures. Although R-comps have slightly less tread depth, if you maintain a cooler running temperature, they should wear slower than the 200-treadwear tires.

We probably need to do a back-to-back study on this, but I’d say for cars that are heavier–3000 pounds or more–R-compounds should last a bit longer than the fastest 200-treadwear street tires.

GRM: Is there a line or a point where you as a tire engineer say that it’s time to move to an R-comp tire? 
Maxxis: It really depends on the individual, because some people want the fastest street tires available so they don’t have to swap tires for track days–that customer will most likely purchase the fastest 200-treadwear tires and doesn’t mind that the tires only last two track days.

GRM: What compromises are being made when running a 200-treadwear tire on track? 
Maxxis: We haven’t dissected them all, but the fastest 200-treadwear tires wear out pretty quickly. Some 200-treadwear tires may be heavier due to the deeper tread therefore you can sometimes improve your unsprung mass by switching to R compounds. Yes, tread wear seems to be an issue that tire companies haven’t been able to overcome.

GRM: Is there a downside to running R-comps?
Maxxis: Besides the obvious wet weather performance sacrifice, they don’t work very well when street driven: bad traction at low temps, bad traction on slippery surfaces, uncomfortable ride, significant pattern noise, poor rolling resistance. I can’t think of any downsides of running R-comps on track.

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Comments
David S. Wallens
David S. Wallens Editorial Director
5/13/20 12:55 p.m.

I have a question to the question: What other tire questions does the group have? Experts are standing by.

Thanks. 

DirtyBird222
DirtyBird222 UberDork
5/13/20 2:43 p.m.

Very interesting and entertaining Q&A. We've been running Maxxis VR-1s on our 94 Accord Champcar for the last two years and the Q&A segment about heat got the gears moving in my noggin about issues we've run into with the VR-1 in a hot setting. Sebring in September for a 14 hour race, I can't think of a more brutal venue for a tire when you factor in all variables such as heat, track surfaces, speeds, and so on. Once the track got hot in mid-day we started losing corner exit grip on the VR-1s, they would bite in great on entry; but, as the car apexed it would start to plow. At night when things started to cool off they went back to the same driving characteristics we had in the early hours of the race and eventually to a class victory. As mentioned, the heat also caused much more wear on the tires than our previous race in a much cooler setting. 

David S. Wallens
David S. Wallens Editorial Director
5/13/20 3:36 p.m.

I wonder, would shaving the VR-1 tires help? 

Patientzero
Patientzero Reader
5/13/20 4:04 p.m.

How similar is the actual compound between the street and r-comp?   On a street tire is the better wet grip 100% due to the tread design or does differences in the compound help too?

KentF (Forum Supporter)
KentF (Forum Supporter) Reader
5/13/20 4:28 p.m.

What would be the coldest storage temperature you would want to allow for the 200 treadware and the R Comp tires?

David S. Wallens
David S. Wallens Editorial Director
5/13/20 6:35 p.m.

Good question and keep them coming. Spoiler alert: There's a part 2 in the works. 

Emilio700
Emilio700 GRM+ Memberand New Reader
5/13/20 7:32 p.m.

In reply to David S. Wallens :

In our experience, yes. We were one of the race team asked to participate in early testing durin the development of the VR1 and RC1. Heat cycling is just heat x time. The longer the tread is exposed to heat, the harder it gets. The deeper the tread, the more it deforms, which generates more heat. The extra rubber mass also holds more heat. So a shorter tread has the double benefit of generating less heat and shedding whatever thermal load much faster than a full tread. Wehave shaved VR1's and RC1's for various events. Quicker than full tread and they actually last nearly as long. Proble is few shops still shave tires, fewer still know how to do it right and it ain't free. 

Emilio700
Emilio700 GRM+ Memberand New Reader
5/13/20 7:37 p.m.

In reply to Patientzero :

Surprisingly, we have seen some of the latest 200tw EHP (extreme high performance) tires have lower durometer and faster wear rates than some older 100tw race tires. The softest wet specific race tires like a Hoosier H2O are actually designed to generate casing heat in the rain. They are fast in the rain even when cold but surreal once they heat up. Normal to come off track on full rainy day on H2O's and they're steaming, too hot to leave your hand on. The lack of sipe(tread grooves) and casing design are major factors in performance. EHP's ride like crap and are noisy. That's not tread design, that's casing design. The best current EHP's (A052, RE71R are far more sophisticated than the 100tw race tires of 15 years ago, like the NT01 for example.

adam525i (Forum Supporter)
adam525i (Forum Supporter) GRM+ Memberand HalfDork
5/13/20 8:47 p.m.

I liked this line "Yes, tread wear seems to be an issue that tire companies haven’t been able to overcome."

Jeez, I wonder why that is? lol

Anyways, very interesting and I'm looking forward to part 2 (also looking forward to eventually upgrading from 200 TW to R).

Vigo (Forum Supporter)
Vigo (Forum Supporter) MegaDork
5/13/20 10:56 p.m.

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

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