18 minute read
T e skinny on tall
from Modern Tire Dealer - August 2013
by EndeavorBusinessMedia-VehicleRepairGroup
feature T e skinny on tall, thin tires
Is this the tire of the future? Or just an electric vehicle trait?
By Bob Bissler
They were on the Ford Model T a century ago. T ey were on the Citroën 2CV in the 1950s. Today they’re on hybrid and electric concept cars. T ey’re also used in racing.
Are tall, thin tires going to be the next big trend in the tire industry?
T at’s what we asked the f ve largest tire manufacturers in the world: Bridgestone Corp., Continental AG, Goodyear Tire & Rubber Co., Groupe Michelin and Pirelli & Cie SpA.
Some were forthcoming with details and information; others, not so much.
“We are constantly working on many technical projects, but we don’t always want to talk publicly about them,” a Goodyear spokesperson told Modern Tire Dealer.
Two other tire companies also declined to participate in this story at f rst, then later agreed to. Two of the tire makers would not comment on the details of manufacturing tall, thin tires. Two would not discuss the tall, thin tires their companies of er.
T ere appears to be a great deal of secrecy surrounding the design of tall, thin tires. One thing is certain: T ere is a trend for bet er fuel economy in vehicles, and tires play a signif cant role in the equation. Less rubber on the road means bet er rolling resistance, less noise and less wasted energy.
Several OEMs have designed concept cars that feature tall, thin tires. T e BMW i3 Concept Coupe, unveiled at the 2012 LA Auto Show in November, has tires size 155/60R20 up front and 175/55R20 in the rear. T e Audi Urban Concept car has 125/60R21 tires in front and 145/50R21 in the rear. T e Volkswagen XL1, a production vehicle that is available in Europe, has Michelin Energy tires size 115/80R15 on the front and size 145/55R16 on the rear.
As OEMs develop more electric vehicles and hybrids, tire makers continue to develop taller, thinner tires to go on them.
Continental AG says that the Conti.eContact, introduced in 2012, is pioneering tire dimensions for the growing electric vehicle market. T e company estimates that 2.8 million electric vehicles will be registered worldwide by 2020.
T e Conti.eContact’s dimensions include a larger outer diameter, and the size is 195/55R20 instead of a traditional 205/55R16, resulting in reduced rolling resistance. A more f exible sidewall helps conserve energy loss when def ecting or rebounding.
“T e height is because the increased outer diameter of the tire improves rolling resistance signif cantly due to reduction of tire deformation,” explains Dr. Christian Strübel, head of Continental AG’s Expert Field Rolling Resistance PLT Tires Business Unit in Hannover, Germany.
Bridgestone Corp.’s Ecopia ologic tire, size 155/55R19, has a larger vertical diameter and increased air pressure to limit changes in the contact patch. Introduced as the Large and Narrow concept tire, it is now in production, the company reports.
Strübel says Continental’s tall, narrow size concept focuses on reducing the section width by 10 mm to improve the aerodynamics of the tire while keeping the aspect ratio constant to conserve handling. Next, the rim size is increased by four inches. T e result is that the new size for a 205/55R16 is 195/55R20.
“Very simplistically, the skinnier the tire, the less material that’s
The Volkswagen XL1, a production vehicle available in Europe, has Michelin Energy tires size 115/80R15 on the front and size 145/55R16 on the rear. Volkswagen Group of America says it can get up to 262 mpg.
going to be in that tire to generate heat and rolling resistance,” says Steve Carpino, vice president, R&D, North America for Pirelli Tire North America.
What is a tall, thin tire?
“It’s a higher pressure, skinnier tire,” says Pirelli’s Carpino.
Continental’s tire engineers had to start with a new approach to the Conti.eContact while still ensuring that the tire excelled at wet braking. Wide circumferential grooves, optimized tread depth, a f at contour and smooth offshoulder design result in an eff cient and durable tire for the electric vehicle market.
“Even if it has the same diameter or is taller, there are just certain match-related ef ects that will generate less heat and rolling resistance.”
Carpino says that one of the challenges in designing tall, thin tires is maintaining load-carrying capacity.
“Say you have a Ford Fusion that has a 225/55R17 tire today. If you try to replace that tire with a tall, skinny tire, it still has to be able to carry the same load as that conventional tire. You can get that load-carrying capacity by keeping the same air volume. Air is what carries the load in a pneumatic
Hank Hara, Bridgestone Americas
tire. You need to have a certain volume of air to inf ate, to carry that same load. You can get that by going to a taller sidewall and a narrower tire.”
Carpino says that one of the biggest benef ts of tall and thin is bet er fuel economy if they are designed to of er comparatively lower rolling resistance. Depending on the tread pat ern and compound, a skinny tire also will perform bet er in aquaplaning conditions.
Unlike in the days of the Ford Model T, tall, thin tires today are generally designed to replace a specif c shorter, wider tire.
“T e size range for tall, thin tires depends on what your starting point is,” says Carpino.
As far as speed ratings go, Carpino says the kinds of vehicles that would be riding on these tires generally are not the unlimited speed range vehicles.
“I would expect they would still have to be in the H and V category at the higher end, and probably you could get away with S and T on some of the lower-level vehicles. On most vehicles today, if you’re talking car tires, H and V are not uncommon at all. If you’re doing this on conventional vehicles, you’d have to maintain that kind of performance.”
T e tall and thin driving force
“Everyone’s looking for (energy) ef ciency right now, and taller and skinnier is a way to be more ef cient,” says Rafael Navarro, vice president of communications, media relations and motorsports, Pirelli Tire North America.
While it still remains uncertain whether or not tall and thin
Europe, noise reduction and tall, thin tires
Part of the movement toward tall, thin tires is being driven by the European Union, where regulations on exterior noise are in effect. The EU says that a tire’s exterior noise grading is expressed in decibels, with one, two or three sound waves for the label.
One black wave indicates the best noise level performance. It means that the noise output level of the tire is at least 3dB below the future legal limit.
Two black waves indicate sound levels that are in the moderate range.
Three black waves indicate the weakest performance in terms of tire noise output. It represents a noise output level between the current maximum and the new lower limit that will be introduced in Regulation 661, coming into force by 2016.
The European Union requires tires to display the European Commission’s exterior noise grading. Two black waves means the noise output is moderate.
tires will become an industry trend, it is clear that vehicles are Europe where the European Union’s regulations on exterior get ing lighter and more fuel ef cient. noise are in ef ect.
“I think the trend toward lighter vehicle weight is grow“Energy ef ciency is enhanced thanks to the tire’s lower ing,” says Hank Hara, chief technology of cer, Bridgestone rolling resistance and bet er aerodynamics,” says Knowles. Americas Inc. “T e vehicles equipped with large and narrow “Continental has been promoting the tall and narrow concept tires are the next generation in this process, following the for some time now,” explains Strübel. “T is was part of the lighter-weight vehicles.” new tire line project, the Conti.eContact. T e tall and narrow
Hara says he sees many concept was also shown in more lighter-weight vethe company eCar and it was hicles on U.S. roads today ‘To take full advantage of the performance presented to several OEMs than several years ago. in the last several years. In the Those vehicles include benef t of tall and narrow tires, vehicle meantime, we see a movemodels such as Versa, Soul, Sonic, Accent, Fit, Fiesta, manufacturers must adapt their designs ment to this new tire size segment in the market.” Mazda2, Yaris, Rio, Juke, to accommodate the larger diameter tires.’ Rouge, CR-V, CX-5, R V4, Where is the tall, thin Forester and Escape. Jim Knowles, Michelin North America market heading?
“T ere are two key drivers “T e market will start f rst behind the trend in tall and with niche vehicles that will narrow tires — style and ef ciency,” says Michelin’s Knowles. help consumers begin to accept these new types of car and “In terms of style, automakers are looking for new ideas to help tire designs,” says Michelin’s Knowles. “T at is why we will dif erentiate their vehicles. Larger rims and outside tire diameters likely see them on hybrid or electric vehicles f rst.” have an appealing look while allowing manufacturers to revisit He says we are then going to see tall and narrow tires start how they distribute the space inside the vehicle.” to appear on European city cars and then European city utility
Fuel ef ciency and function are even more important than vehicles. In this category of European city utility vehicles, tall a vehicle’s appearance. Automakers want to reduce the fuel and narrow tires are interesting because of increased vehicle consumption of their vehicles and they also want to reduce ground clearance. the external noise of their vehicles on the road, especially in “Tall and narrow tires are gaining interest among several
Two very big advantages Bridgestone’s tall, thin technology saves fuel and lives
1. Environmental performance: By giving tires a larger vertical diameter and increasing their internal air pressure, it is possible to limit changes in the shape of the contact patch.
By optimizing the structure of tires and using the most appropriate materials, Bridgestone achieved a rolling resistance coefficient 30% lower than conventional tire sizes such as 175/65R15.
Making the tread area narrower reduces air resistance, a major factor that needs to be considered when working to improve fuel efficiency. Due to these features, tires that have this new technology have levels of fuel eff ciency exceeding those of the fuel-eff cient tires Bridgestone has already put on the market. 2. Safety: The narrower size of tall, thin tires helps reduce wet road water pressure placed on the tires. In addition, the tires have been specially designed to have a longer contact patch and higher contact pressure, which helps these tires prevent water
from accumulating between the tire and the road. These features combined with the benef ts of the tires’ newly developed, specialized patterns and compounds enable the tires to achieve an improvement in wet grip performance of 8% in comparison to conventional tires, thereby enhancing safety.
The BMW i3 Concept Coupe has tires size 155/60R20 up front and 175/55R20 in the rear.
OEMs as they explore technologies to improve safety and to meet the new 2016 and beyond CAFE and CO 2 emission regulations.”
“If I had to guess — and this is based on what we hear from our OE customers — I don’t see it in the next f ve or six years for sure,” says Pirelli’s Carpino. “It’s both technical and cosmetic at this point, more for the appearance of the vehicle.” Carpino says Pirelli has heard from at least one of its OEM customers that for style, a popular look is to see the wheel well fully f lled by its tire. T at, at least today, requires a tire that is similar dimensionally to tires that are currently common. “For a while, it will just be more in the concept and electric and hybrid vehicles.” Even if they did become more popular, manufacturing them would not require a major change in the existing infraThe Pirelli Cinturato structure. Tire engineers told us that in P1 Special Edition addition to new molds, manufacturing concept tire was plants would only require some equipdesigned for Audi. It ment adjustments to produce the tires has 21-inch rims. en masse.
What are the drawbacks?
T ere are disadvantages to using taller, thinner tires on cars.
“T e main disadvantage for the tall and narrow concept is the building space in the car, where of en the wheel house must be changed,” says Strübel. “T at is more likely to happen in cases of the new architecture of electric and hybrid vehicles, where the car planning is starting from the beginning.”
T ere are no issues with traction when they are used on electric cars and hybrids, says Bridgestone’s Hara. “Highperformance cars like today’s Corvet e are not in the scope of applications.”
Hara says he does not anticipate any wear issues with tall, thin tires, either.
“One of the challenges, but not necessarily disadvantages, of tall and narrow tires is that the overall diameter of the tire is larger,” says Michelin’s Knowles.
Knowles says that in order to maintain the tire load capacity required for current vehicles, the overall diameter of a narrow tire must be slightly larger, thus the term “tall and narrow.”
“To take full advantage of the performance benef t of tall and narrow tires, vehicle manufacturers must adapt their designs to accommodate the larger diameter tires,” he explains.
Continental’s Strübel says the outer diameter of the tire is an important consideration in the beginning of the concept phase of a new car and must, therefore, be discussed early in the vehicle’s development. A longer lead time is necessary for this new size concept. “For electric vehicles, the rolling resistance of a tire is even more important than for combustion engines due to the limitation of the bat ery capacity,” says Strübel.
He adds, however, that a European OEM “is developing a vehicle with a combustion engine with such a tire size for market entrance soon.”
“We anticipate that these tires will be equipped on a widevariety of environmentally friendly vehicles,” says Bridgestone’s Hara. “T ese tires are ideal for EVs (electric vehicles) and HEVs (hybrid electric vehicles), as the lower rolling resistance is a signif cant benef t. However, we do not feel that their use should be limited to these EVs or HEVs.”
“T at’s going to be more for the OE to drive the market,” says Pirelli’s Navarro. “If a premium OEM partner comes to us and says we’d like your support in doing this, we believe in it and as a company that prides itself on innovation and research, we’re going to go through with it.
“Until you get the OE to agree to bolt that up as part of their strategy for their cars, I don’t think it’s anything we can impose on them.” ■
Tall, thin, FAST tires
T e DeltaWing project has resulted in the design of ef cient, slim tires
By Bob Bissler
DeltaWing Project 56 LLC, which does business as DeltaWing Racing, says it is transforming the motorsports and automotive industries with radical innovation. A big part of that innovation is in the DeltaWing’s tires.
“For the dimensions of the tires, we wanted: 4.0/23/R15 for the front and 12.0/24.5/R15 for the rear,” says Simon Marshall, DeltaWing Racing lead engineer. “We determined those sizes through simulation using a couple of vehicle dynamics simulation sof ware programs where we could test-drive everything about the car and we knew it was going to turn and handle well before we ever designed or built the car.”
T e rear of the DeltaWing car was designed to do all the work. Marshall says that is where most of the aerodynamic downforce and weight is located. T e rear tires have 15-inch diameter rims, which is typical of something like an IndyCar rim, in order to accommodate a larger size brake disc.
“The front also has 15-inch rims for brake discs,” says Marshall. “Rim size is all about get ing brake discs in. Clearly with race cars, it’s not like road cars, where the bigger the rim, the bet er for some people. It carries a lot of inertia with it. Big rims aren’t necessarily good for performance. You get the rim big enough to f t your brake package.”
T e DeltaWing’s testing took place in front of the world, at the 24 Hours of Le Mans, June 16-17, 2012, in Le Mans, France. T e f rst set of tires taken of the car during an early pit stop showed lit le wear.
The lightweight DeltaWing race car was designed with 75% of the car’s weight in the rear of the chassis, and combined with an eff cient engine, the car burns half the fuel and reduces tire wear by half of that of a conventional race car, notes DeltaWing Racing Cars.
“T e fuel economy concept of the vehicle allowed us to use very light, slim, small tires at the front,” says Marshall. “At the Le Mans race in 2012, we were get ing just under 200 mph, and the lateral forces were 3G-plus in the turns and the tires were just bomb-proof.”
The lighter front end of the DeltaWing car allowed for smaller front tires, and engineers from both Bridgestone and Michelin worked with the DeltaWing team to create four-inch front tires. The DeltaWing’s tire sizes are 4.0/23/ R15 for the front and 12.0/24.5/R15 for the rear.
Marshall says because the front tires are small, there isn’t much demand placed on the front brakes: T e front tires can’t support a lot of demand laterally and longitudinally. Bridgestone, Michelin, Bridgestone
When the DeltaWing was f rst proposed as an IndyCar in 2008, it was going to be f t ed with Bridgestone tires.
“T ey actually commit ed back then to making molds for the tires because they could make some show tires to present,” says Marshall. “It turned out they didn’t pursue the DeltaWing because of their other commitments in IndyCar. T at’s when we went with Michelin. But now we’re back with Bridgestone and it was quite handy because they already had molds made.”
Marshall says both Michelin and Bridgestone had to put a lot of work into the construction, geometry and compounds involved in these tires because they were doing a job not seen before. He says both companies overestimated how stif the construction needed to be on the front tires.
DeltaWing Racing says that going forward, it will be working with Bridgestone. T e tire maker is now using the same molds with a dif erent compound and construction to try to improve the current tires. Sizes will remain the same.
“Def nitely there’s nothing worse for fuel economy than a heavy, wide tire,” says Marshall. “So the fuel-ef cient cars like the original Honda Insight, the original hybrid Honda, they need to have skinny tires. If you take fuel economy seriously, you can’t do it with a regular tire.” ■
