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The fall 2006 meeting of the General Motors Law Enforcement Product Council (LEPC) was held in Scottsdale, AZ. The meeting site was selected for its closeness to the GM Desert Proving Grounds in Mesa and to the numerous off-road 4x4 trails in the nearby desert. The entire point of the meeting, after all, was the first drive of the new 2007 pursuit-capable Tahoe PPV.
The LEPC meeting began with service information presented by the legendary Earl Gautsche. Nobody knows Chevy police cars better. In service since 2000, the police Impala has no chronic and recurring service problems and only a few minor service issues.
Of these, the most important is premature brake pad wear on the 2006 and 2007 models. The 2000 to 2005 police Impala used Akebono semi-metallic pads. While pad wear differs greatly from department to department, most of these police Impalas got between 15,000 and 20,000 miles preset of front pads.
The new-for-2006 model was upgraded to TMD Friction semi-metallic pads. This was done specifically to pass the Los Angeles County Sheriff’s tests. The TMD pads offered better high-speed performance and were more resistant to brake fade under the extreme pursuit situations simulated by the LASD tests. The performance needed to pass the harsh LASD tests came at the expense of pad life. As a result, the 2006 and 2007 Impalas may achieve only 6,000 to 10,000 miles between front pad changes...but the brakes ARE better.
Keep in mind that brake pad materials are a compromise. GM Fleet continues to investigate the optimal brake material, i.e., the best compromise of performance and pad life. In the meantime, GM officials intend to stand behind their Impala brakes.
While they are NOT guaranteeing pad life, they are offering a case-by-case, goodwill warranty for up to 12,000 miles on the 2006 and 2007 brake pads. Again, this is not an official policy, and it must be individually approved by GM’s regional service reps. But so far, all requests have been approved. Get to know your regional rep! This is not a dealer service issue; it must go through the regional rep.
On the topic of warranty, Gautsche made it clear that GM’s new powertrain warranty specifically includes police vehicles. The extended powertrain warranty covers up to five years or up to 100,000 miles, even of severe-duty patrol use.
E85 Flex Fuel Vehicles
With the continued emphasis on flexible fuel and E85-compatible vehicles, Gautsche also cautioned against two very specific E85 service issues.
First, only use E85 in E85-compatible vehicles. The police Tahoe is E85-capable. The police Impala is NOT. Alcohol is very corrosive, and E85 is 85% alcohol, 15% gasoline. The non-E85 vehicle may run for a while on E85 fuel. However, it will almost certainly set off the oxygen sensor code, and it will certainly cause internal corrosion from the gas tank to the fuel injectors.
Second, do NOT install the quickie, aftermarket E85 conversion kits in non-E85 vehicles. Some aftermarket gizmos are advertised to convert the car to run on E85. While these wizbang devices may feed the correct oxygen content reading to the vehicle’s powertrain control module, they do not resolve the corrosive nature of alcohol. Engine components will eventually corrode.
GM has announced that the 2008 police Impala with the 3.9L V-6 will be E85-compatible. The retail-only Impala with the 3.5L V-6 is already capable of running on E85.
Oil Life System
GM Fleet continued to emphasize its new oil change policy, the Oil Life System (OLS). This system uses only the engine oil temperature and engine rpm to calculate when the oil should be changed. The OLS does not measure oil viscosity, and it is not based on miles. The system does, however, absolutely depend on the right grade and viscosity of the oil being used. Those agencies that are using reformulated oil and a different viscosity of oil, beware! The 2007 Impala should get “API Service Grade SM” 5W-30 weight oil…then the driver should literally wait for the “Change Oil” light to come on in the driver information center.
Under high engine temps and high rpm operation, this may be 3,000 or 4,000 miles. The same goes for low engine temps typical of short, urban and suburban trips. For normal engine speeds and normal engine temperatures, the oil change interval can be 5,000 to 7,000 miles, and even 10,000 to 12,000 miles. If the dash light doesn’t come on at all, change the oil every year or every 15,000 miles. See the July-August 2006 issue of Police Fleet Manager for a detailed review of GM’s Oil Life System.
Here is how confident GM is about OLS...it extended the basic powertrain warranty to 100,000 miles after a decade of experience with the algorithm-based change interval system. And police departments across the country are using this system. When the light comes on, change the oil, and not before.
The 2006 and 2007 Impala do not have a trunk key cylinder lock. You open the trunk by the key fob or by the dash switch. The problem comes when the battery is run completely dead. With poor upfits and heavy loads, dead batteries are all too common in police vehicles. With a dead battery, the trunk cannot be opened. A key lock on the Impala trunk will be available in mid-2007 as a running change. Kerr Industries, the GM factory-authorized upfitter, will do the install.
Gautsche also reviewed the Active Fuel Management system, i.e., cylinder deactivation, used on both the Impala’s 3.9L V-6 and the Tahoe’s 5.3L V-8. Under ideal conditions of very light loads on the engine, the engine control module will shut off some of the injectors and valve lifters in the engines. The V-6 will become a V-3 and the V-8 will become a V-4 to conserve fuel.
This cylinder shutdown really only takes place under steady-cruise conditions. The engines operate as normal V-6 and V-8 engine at idle and under medium to heavy throttle. That means nearly all of the time in police use, all of the cylinder are working.
The point for police fleet managers is two-fold. First, don’t expect much better mileage because, in police use, the system is rarely activated. Second, this cylinder deactivation system, while very complex, has also proved to be very reliable. It has not caused a maintenance issue.
Another very complex aspect of both the 3.9L V-6 Impala engine and the 5.3L V-8 Tahoe engine is the camshaft position activator system, i.e., variable valve timing. Depending on engine load, the camshaft will be advanced or retarded to change the valve timing from 17 degrees before top dead center (BTDC) to 45 degrees after top dead center (ATDC). This capability improves both low-end torque and high-end horsepower.
Like cylinder deactivation, changing the camshaft timing with respect to the crankshaft timing is extremely complex. And like cylinder deactivation, after being in service for a couple of years, the system has proved to be free of maintenance issues.
Pirelli National Tire Program
The final service information relates to the Pirelli P6 Four Seasons tires used on the police Impala. GM Fleet again stated its recommendation to replace worn out police tires with exactly what came on the vehicle the first time. This is especially true for the Pirelli P6 in size P225/60R16. This is one of the few tires specifically developed for police use or modified as extensively from the normal retail tire for police use. Pricing, of course, is the issue.
Pirelli has set up a national police tire program, which is essentially state bid pricing without the state bid process. Police-spec tires for the Impala run $75 (delivered) on this program. The department must first sign up for the program by contacting Hiskia van der Ley at either (800) PIRELLI, ext. 5842 or via e-mail at email@example.com.
Pirelli offers similar pricing for Ford CVPI tires. Both the P Zero Nero M+S and the severe snow-rated Winter 240 Sottozero. This Pirelli contract pricing may be the solution to the numerous fleets facing police tire shortages.
The rest of the morning was spent in discussion on future vehicles. All aspects of future vehicles are considered business confidential by all automakers. More to the point, production plans and specs and dimensions change all the time. If you have input on what you would like to see in future Chevy police vehicles, contact your regional sales rep or any LEPC board member. You may also contact Ed Sanow, editorial director of Police Fleet Manager, who is also an LEPC member, at firstname.lastname@example.org.
Desert Proving Grounds
The afternoon was spent driving at GM’s Desert Proving Grounds near Mesa. We were on five different courses with the 2007 pursuit-capable Tahoe PPV (2-wheel drive). And we had a previous generation (2005) Tahoe PPV along with us as a benchmark. GM’s goal, of course, was to have the totally new, re-engineered Tahoe perform better in all areas than the older generation Tahoe. And it does.
The first event was a good ol’ fashioned, quarter-mile drag race between the old 295-hp Tahoe and the new 320-hp Tahoe. The new 2WD Tahoe, however, is also 287 pounds heavier.
At the lower speeds, both the Tahoe SUVs were equally matched. The Michigan State Police tests show zero to 60 mph times of 8.69 seconds for the old and 8.66 seconds for the new. During the last half of the quarter mile, things change. The older Tahoe reached 100 mph in 25.7 seconds while the new one got there in 24.5 seconds.
While we didn’t reach top speeds, the older Tahoe reaches about 124 mph. The new Tahoe continues to pull hard up to 136 mph, as measured during the MSP tests, however, when released for production, it was speed-limited to 130 mph.
The second driving event was braking from 60 mph. This is important because the brakes on the new Tahoe are significantly different from the 2005 and 2006 models. Those two years used hydro-assist brakes, pulling hydraulic pressure from the power steering system. This was an improvement over the earlier vacuum-assist brakes, which uses engine vacuum to power assist the brake pedal. For 2007, the new Tahoe uses vacuum-assist brakes again. And this is an improvement over the hydro-boost not only in brake performance, but also in pedal feel.
When run side-by-side and braked from 60 mph, the new Tahoe stopped about a half of a car length shorter than the older model. The MSP confirmed this with carefully measured stopping distances of 145.4 feet (2006) and 138.2 feet (2007).
The third event was a standard EVOC cone course about 60 seconds in duration. Set up on the dynamics pad, the course includes emergency lane changes, high-speed sweeping turns, full wheel-lock hairpin turns and a deceptive, decreasing radius turn.
The 2007 Tahoe PPV has a new rack and pinion steering (replacing the recirculating ball), new Short-Long A-arms and coil spring suspension, new Goodyear Eagle RS-A tires and new brakes. It handled very well on the cone course. Yes, there is still some body roll. No, it does not handle like a sedan. Yes, this is still an SUV.
However, with a lower center of gravity than the rest of the SUVs, a lower profile, and high-performance tires, the Tahoe PPV does well. It was predictable, it didn’t have any bad habits, and it was easy to drive aggressively without loosing control of the vehicle. This is as good as an SUV gets. It is what it is.
The fourth event was on the 1-mile vehicle dynamics road course. This was a more open, higher-speed course with banked turns. We found the Tahoe PPV very easy to set up for a long, throttle controlled drift. The Tahoe turned-in predictably, stabilized in the modest degree of body roll and then let the driver easily increase or decrease the speed. No oversteer. No understeer. Just right. This course actually made the Tahoe look better than the EVOC course. And, again, it was easy to drive hard.
The fifth driving event represented GM’s growing interest in the use of StabiliTrak (stability control) on pursuit-capable vehicles. Stability control is a safety device, but some retail versions of stability control may limit vehicle performance. GM is currently defining the control parameters of StabiliTrak for police use. “We are balancing the StabiliTrak technology with the perceptions and performance expectations in the law enforcement community,” said Bruce Wiley, product and marketing manager, Law Enforcement Programs.
The driving event involved two passes through the EVOC course in a Z06 Corvette. One pass was with the StabiliTrak set to the competition setting. The next pass was with StabiliTrak turned completely off. The LEPC members were unanimous in the need for some form of electronic stability control, and the consensus was that the competition setting is a good starting point for police use. And a lot more work has to be done before the police Tahoe and police Impala get a police-spec StabiliTrak.
The trip back from the Desert Proving Grounds gave LEPC members the first chance to drive the 2WD Tahoe PPV or 4x4 Tahoe SSV on public roads in regular traffic. I picked the 4x4 Tahoe for this 28-mile trip on interstates, state roads and city traffic.
The on-center feel from the new-for-2007 rack and pinion steering was greatly improved over the old recirculating ball steering. The front coil spring suspension was also an improvement in ride over the old torsion bars. Fortunately, we did not have a chance to test the StabiliTrak with rollover sensor, standard on the 4x4 Tahoe.
The quietness of the ride (low NHV) and the ease of driving (rack and pinion) were immediately apparent even with the fairly aggressive Goodyear Wrangler AT/S tires. The Tahoe did, indeed, seem to turn in quicker and have more lateral traction. That is, the 17-inch Goodyear RS-A tires are an immediate and significant improvement over the 16-inch General AmeriTrac tires.
4x4 Desert Trail
After giving the 2WD Tahoe PPV a workout on the first day, the second day was all about 4-wheel trail driving in the Special Service 2007 Tahoe 4x4 SSV. The Ride & Drive was 150 miles of interstate, state roads and finally Forest Service roads. This gave us the total ride and handling experience…everything from ride comfort (noise, vibration and harshness) driving down the interstate to back-jarring, chassis-scraping, 4-wheeling on some very difficult roads.
The off-roading was the Four Peaks Trail inside the Tonto National Forest northeast of Phoenix. Veteran off-roaders such as Arizona Highway Patrol’s fleet manager and LEPC member, Mike Fuson, rate the trails from 1 (easy) to 5 (difficult). A 2-wheel drive SUV or pickup can negotiate a level 2 off-road trail. A level 3 trail calls for a 4-wheel drive vehicle. Trails more difficult than that require modified vehicles, i.e., lift kits and locked differentials.
The Four Peaks Trail, Forest Service 422, is about a 2.5 out of 5. After all, the rules for selecting the course were no dents, no scratches. A 2WD pickup or SUV could do it as long as the road was dry. Ground clearance and wheel travel were more important than four-wheel traction. We took the trail in the 4x4 Tahoe SSV and only put it in 4-wheel low on one occasion. The rest of the 26 miles were spent in either 2WD or 4x4 high.
The trail had plenty of twists and turns, ruts, washboard and gullies. Even going slowly, we solidly bottomed out the suspension a dozen times and scraped the standard equipment skid plate a couple of times, and grounded the front air dam at least 50 times.
The Four Peaks Trail starts off at an altitude of 1,260 feet. By the time we completed it, the altitude was 5,750 feet. We started off with the desert foliage of prickly pear, saguaro, jumping cholla and staghorn. These cactus plants ended at about 4,000 feet and were replaced with pine trees and southwest shrubs like manzanita, AKA mountain mahogany. The travel speeds ranged from 5 to 25 mph, but the vast amount of time was 10 mph.
Running 80 mph on the interstate or 8 mph across washboard service roads, the new-for-2007 Tahoe was quieter and more comfortable than a 4x4 SUV deserves to be. The suspension was neither so soft that the body roll made you sea sick nor so stiff that you were jarred over every rock in the road. It was right in the middle, and perhaps slightly softer and more yielding than the average 4x4 SUV.
Ed Sanow is the editorial director of LAW and ORDER magazine. He can be reached at email@example.com.
Photos by J. Averill Townsend.
Published in Public Safety IT, Nov/Dec 2006
Rating : 10.0