SUVs

LDTs and SUVs exhibit much higher emissions levels than do automobiles (roughly 30 percent more lie and CO, and 85 percent more NO. per mile traveled). Light-duty trucks also have a significantly longer lifespan in the fleet than do automobiles, compounding the emissions impact over time. 

The difference between the two instruments is the inside diameter (ID) of the outlet flow tube. The SUV uses a 0.176 centimeter ID and the SFV u.ses a 0.315 centimeter ID. The SFV is used for samples that have a flowing time greater than 600 seconds. For most conventional gas oils, the flowing time is short enough that the Universal Visco meter is frequently used. The tube dimensions in the two procedures... 

Fifteen tire brand-vehicle combinations were collected from Phoenix, AZ Los Angeles, CA Detroit, MI and Hartford, CT. Six different vehicle types and three different tire manufacturers were studied as detailed in Table 34.1. Vehicle-brand combinations are denoted by the vehicle type followed by the letter denoting the specific manufacturer, e.g., SUV/Minivan-A. The geographic locations were chosen based on ambient temperature and ozone level. Both on-road and full-size spare tires were collected ranging in age from two weeks to six years old. In total, over 1500 tires were analyzed in this study. A small number of tires from Miami, FI and Denver, CO were collected to evaluate the effects for road roughness on aging. No significant effect was observed and these tires were not included in the analysis. 

In addition to the Ford field-retrieval study, NHTSA has carried out further studies of aging from tires retrieved from Phoenix [8]. Analysis in this chapter will be Umited to tires SUV/Minivan-A, -B, and -C and Large Car-C from the Ford study. Tire sizes and maximum inflation pressures for these tires are reported in Table 34.2. The analysis will focus on extracting accurate rate data from the field data. Of key importance is developing an understanding regarding the sources of variability in field aging. 

Tires were mounted and inflated to the maximum pressure listed on the sidewall prior to oven aging using either air or a 50/50 blend of N2/O2. In the case of tires inflated with the 50/50 blend of N2/O2, the atmospheric air present was not purged the blend was added on top of it yielding a tire cavity concentration of approximately 41%-44% O2. Two of the tires in this study (SUV/Minivan-A and SUV/Minivan-C) were aged at 50°C, 60°C, and 70°C for up to eight weeks, while the tires and... 

FIGURE 34.S Elongation to break of wedge rubber versus weeks in Phoenix for SUV/Minivan-A tire. 

FI GU RE 34.10 Peel strength retention for skim rubber (center) versus week in Phoenix for SUV/Minivan-B tire. 

FIGURE 34.13 Monte Carlo simulation of Peel strength retention for SUV/Minivan-A tire. See Figure 34.10... 

FIGURE 34.18 Peel strength of skim rubber (center) versus time in oven at 70°C, air for the SUV/ Minivan-A tire. 

Based on the above arguments, with peel strength measurements for the three SUV/Minivan tires. We will also include the elongation to break data for the Large Car-C tire even though the difference in wedge rubber modulus between the held and oven sets makes the comparison between these data sets somewhat questionable. 

FIGURE 34.22 Log (strain ratio) versus log (modulus) for field and oven-aged SUV/Minivan-A tires. Both sets are linear indicating oxidative aging, but the slopes are different indicating a change in composition of the wedge rubber. 

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