By Becky Lewis
October. Time to take off the summer tires and put on the winter ones, even though the summer tires aren’t very worn.
April. Time to take off the winter tires and put on the summer ones, and a good thing too, because the winter tires have been more than well-worn since March. But where are the tires that came off in October? Are they in storage at this site, or some other one? Are these the same tires that went on this Dodge Charger, or did they come off that Tahoe? Or did they get thrown away? And wait, the storage fees came to how much?
If that sounds like a system guaranteed to keep a fleet manager up at night, a new report from the Michigan State Police (MSP) Precision Driving Unit, 2015 Pursuit Rated Winter Tire Performance Evaluation (PDF), might help with that problem. The 39-page PDF details test results for various all-season and winter tires under severe weather conditions in January 2015, and these results indicate that the all-season tires currently on the market provide year-round quality performance and may eliminate the need for agencies in the Snow Belt to perform the semiannual switching with all its associated headaches.
“Winter tires don’t last as long because winter tire compounds are a lot softer than the summer ones, and they tend to wear out faster than all-season or summer tires. Our all-season tires last more than year, and all of this results in a tremendous cost savings,” says MSP Sgt. Michael McCarthy. “For a moderate-sized department with 20 or 30 cars, the savings will be significant. And even for a small department with just a few cars, there will be some savings they can roll back to their employees and into other equipment.”
The Michigan State Police maintains a patrol fleet of more than 1,000 cars, and research and the results of tire testing under summer conditions in 2011 (2011 Police Vehicle Tire Evaluation, 2 mb PDF) led to a switch to all-season tires in May 2013. However, during winter 2013-2014, troopers driving rear wheel Dodge Chargers complained about traction issues, leading to the winter tire testing covered in the new evaluation report.
MSP used the Charger (in both rear-wheel and all-wheel versions), rather than the Chevrolet Tahoe, as the test platform. Because the Charger can reach speeds of 152 mph, MSP tested snow and all-season tires with a W speed rating (capable of speeds from 150 to 168 mph) that came in the sizes used by the patrol fleet. The three tires that met these qualifications were:
A fourth tire, the Firehawk PVS, had a V speed rating (capable of speeds up to 149 mph), but was tested due to its very aggressive tread pattern.
The Firehawk PVS proved to be a lesser-rated tire on receipt, but was still tested due to its very aggressive tread pattern. The Precision Driving Unit developed tests for acceleration, braking, steady state turn and hill starts. The report includes detailed test results as well as a thorough description of the test methodologies.
“We didn’t use the factory-equipped tires that come on the Chargers, because their performance is not up to what we need. That is why we had already switched to a different all-season tire, and we didn’t see any reason to test a tire when our officers had already complained about its poor performance,” McCarthy says. “We also learned during testing that the drive platform is even more important than the tire. Our troopers were complaining about the lack of acceleration ability in the rear-wheel drive Charger, and the all-wheel drive cars definitely performed better.”
The overall good results for the all-season tire selected by MSP seem to indicate an improvement in all-season performance in the past decade. In 2004, the then-NLECTC-Northwest Center conducted winter driving tire tests in conjunction with the Royal Canadian Mounted Police, and came to the conclusion that winter tires provided superior performance to all-season tires (See Winter Tire Testing). McCarthy says that since those tests took place, the compounds used in tires have changed, the rubber compounds have improved and tires in general perform better.
“Also, 10 years ago cars didn’t have traction control. Without traction control, the driver has to modulate the power to the wheels when they start to slip, but with it, the traction control shuts off power to the rear wheels when they start slipping. This will change performance results,” he says.
Weather conditions can also change performance results, and while the temperature during the MSP testing was not far above zero in the morning hours, it did warm up into the 20s by afternoon.
“It was ironic that we picked late January in hopes of seeing morning temperatures of 20 below, and it was the warmest week of the winter. The weeks immediately before and immediately after were much colder,” he says. “The rigidity of a tire changes during extreme temperatures and it might have affected all of the tires performance if it had been colder.” Note that during the 2004 testing, temperatures fell to 40 below zero.)
The detailed results published in 2015 Pursuit Rated Winter Tire Performance Evaluation allow for side-by-side direct comparisons of the various tires tested, which can help agencies make informed decisions.
You can download the report from this website, where you can also find other information about testing results for equipment such as ballistic- and stab-resistant body armor, restraints, patrol vehicles and more in JTIC's Find Compliant Products section.
Download the reports mentioned in this article :