Just two weeks into my new job at Motor Trend, I joined testing director Kim Reynolds at a meeting he arranged for members of the Orange County Tesla Owners Club to see the all-new and not yet released (at the time) Chevrolet Bolt EV. After the Tesla owners poked and prodded the Bolt and went for rides with Reynolds behind the wheel, he tossed me the keys and said to take it for a drive. I had no idea what to expect—I was new to EVs.
Turning onto the Pacific Coast Highway, I was immediately impressed with the Bolt’s instant power, quickness, quietness, and surprisingly, its handling. The heavy weight of the battery pack mounted low into the Bolt’s floor gives the hatchback a low center of gravity, resulting in very nimble and fun handling dynamics. This gave me enough confidence to plow through an empty corner at a high rate of speed as if I was driving a sports car. Bad idea! Still green behind the ears, I failed to factor one thing into the equation: tires. Unfamiliar with EVs at the time, I did not know about the low-resistance, hard tires that these vehicles usually come equipped with. In this case, the Bolt EV had Michelin Energy Saver A/S Selfseal Green X tires on. As I turned the wheel entering the corner, I was greeted by not only the unholiest of tire squealing noises but also a frightening amount of understeer.
After I returned the Bolt EV to Reynolds and gave him a PG version of what had just happened, it clicked—what if this car had high-performance summer tires on instead? Not only would grip significantly increase, but that dreaded high-pitch squealing that happens when low resistance tires lose grip should also vanish. When mentioning this to Reynolds, he quickly reminded me that EVs have low resistance tires for a reason, and grippy summer tires would negatively affect the Bolt’s driving range. I wanted to quantify that assertion. Fortunately for me, a few months later Chevrolet gave us the keys to our new long-term Bolt EV. After some convincing, we acquired a set of summer tires for the Bolt EV from Tire Rack—BFGoodrich G-Force Sport Comp-2 ultra-high-performance (UHP) tires—and strapped them on.
Driving Experience
Even before hitting the road with the newly installed BFGoodrich summer tires, I immediately appreciated one thing: the new look of the Bolt EV. The more aggressive-looking tread of the summer tires results in quite a cool look for the tall hatchback. Hitting the road with the newly installed ultra-high-performance tires, I noticed something new: tire noise, and lots of it. Compared to the factory tires, the summer tires are much louder. Once you get going, an obvious whirling sound enters the cabin, only getting louder with speed. If equipped, turn that Bose sound system up. Features editor Scott Evans, who chaperones our long-term Bolt EV, also noticed that “it seems especially noticeable because of how quiet EVs inherently are. I found it bothersome at first because the car was so quiet for the first six months, but I’m getting used to it. The quietness of the interior was a high point of the car for me, and it’s hard to give it up.”
Ride quality also takes a hit, but that’s to be expected because UHP tires have much firmer sidewalls when compared to the factory units. With the Michelin low-resistance tires on, the Bolt is comfortable and rides well, thanks to the cushy sidewalls. Evans also noticed the decreased ride quality. “It’s not brittle or harsh, but it’s much more like a serious sport sedan ride-wise than the everyday commuter it was,” he said. “With the quality of L.A.’s roads, this is a trade-off big enough to give me a bit of pause. Perhaps there’s a summer tire option with a taller sidewall?” A firmer ride might not bother some, but it’s something to consider depending on the quality of your local streets and highways.
With sound and ride quality out of the way, let’s get to the fun stuff. Handling and the overall fun-to-drive factor have increased tenfold. When wanting to drive spiritedly, the Bolt’s factory tires were very limiting in two ways: lack of grip and fear of that dreadful tire squeal that low-resistance tires are known for. If the UHP summer tires were equipped when I took that fast turn on my first drive, there would have probably been zero understeer. When UHP tires lose traction, it is a much quieter and less annoying sound. Additionally, if you find yourself at a stop and turning in either direction in a hurry, expect tire slippage and squealing as soon as you crank the wheel and hit the throttle with the factory tires on (although this will not happen when accelerating quickly in a straight line).The UHP tires shine in the corners. A good example is on the many highway ramps in L.A., as Evans explains: “Just commuting, I notice it every day on the freeway cloverleaves. The stock tires gave up fairly quickly and made a lot of noise, especially when you tried to go to power as you unwind the steering wheel. Now, it turns in sharper, grips much better midcorner, and puts the power down while exiting.” The summer tires also allow the Bolt to enter a corner faster, brake later, and maintain a higher rate of speed through the corner, and it gives you a lot more confidence than you would normally have on the factory set of tires. Additionally, if you want to pass up that slow Prius on the street quickly, flooring the Bolt while switching lanes is much safer because there is much less or no tire slippage when performing this quick maneuver. Honestly, this thing is a blast to drive with UHP summer tires, and it’s much more capable.
That fun does have its limits. Please keep in mind that this is still a tall EV hatchback and not a sports car. You can only push the Bolt so hard before things start getting hairy. The soft suspension and lack of any steering feel will make you hold back before you get into any trouble. You can’t feel much of what’s happening on the road. Additionally, the ESC rears its ugly head when trying to have fun. They might be UHP tires, but that instant torque will still easily break traction when the wheel is cranked to either side. Driving fast through a corner requires careful modulation of the throttle through the turn in order to prevent the system from momentarily sucking power away even when it’s turned off.
Instrumented Testing
Street driving is fun and all, but instrumented testing on the track tells the real story. On factory tires, the Bolt EV does not break traction when flooring it from a stop, so we didn’t expect much improvement in acceleration, and we were correct. With the Michelin factory tires on, the Bolt hit 60 mph in 6.3 seconds and the quarter mile in 15.0 seconds at 92.1 mph. There was basically no improvement with BFGoodrich summer tires. At 6.3 seconds, the 0-60 mph time stayed the same, and the Bolt hit the quarter mile 0.1 second faster at 92.9 mph. However, lateral acceleration increased from 0.78 g to 0.82 g.
When Reynolds flogged the Bolt around Motor Trend’s figure-eight course, the Bolt’s time improved 0.5 second from 27.4 seconds with factory tires to 26.9 seconds. The average g-force around the course increased from 0.63 g to 0.66 g, showing an improvement in overall grip through the corners. This is a nice improvement, but it could have been much better if it wasn’t for the overly aggressive electronic stability control. Even when turned all the way off, the system is very intrusive when wheel slippage is detected. Around the skidpad part of the course (the corners), Reynolds had the Bolt at wide open throttle the entire time, but as soon as the tires slipped, ESC would cut what seemed like most power. This resulted in power being cut then allowed back on about every second or two the entire way around the corner. Killing time, speed, and possibly the maximum grip potential of the tires (g-forces could have possibly been higher). Witnessing this from the outside, it seemed as though Reynolds was hitting the brake pedal (the lights were flashing) every couple of seconds, but he wasn’t. His right foot was pegged against the throttle. The ESC is, of course, aggressively tuned to keep the average driver out of harm’s way and not for the track. If there was a way to detune the ESC, the results would have probably been better. That instant torque is not ESC’s friend.
Driving Range and Charging
Skip this section if you love your Bolt’s long EPA-rated 238-mile driving range because, to no one’s surprise, the driving range took a big hit. The much higher grip and amount of friction of the BFGoodrich Sport Comp-2 tires took a toll on the total driving range, which in turn affected charging time and the amount of electricity used. According to the math that Evans provided, during the 58 days with the high-performance summer tires, the following happened to the Bolt EV’s driving range, charging, and energy usage: the average trip between charges dropped 23.3 miles while using an average of 4.1 kWh more per charging session. In other words, the Bolt’s driving range decreased, and it’s using more energy than before. The predicted charging time has gone up by about an average of half an hour even though we are plugging it in at a higher rate of charge than before (52.7 percent on average compared to 49.4 percent before), and Ideal Range and Predicted Range have of course decreased. Due to our range anxiety, we were plugging in the Bolt sooner, but charging was still taking longer, correlating to the increased energy usage. Based on the EPA-rated 238-mile driving range, our driving range decreased by 10.2 percent.The average ideal range after charging dropped from 248 miles to 224 miles, and the average predicted range dropped from 206 miles to 186 miles.
Fortunately for us at Motor Trend, we have experts in our EQUA Real MPG team that strap on high-dollar testing equipment and calculate real-world fuel economy. The EPA rates the Bolt EV at 119 mpg-e combined city/highway driving with the factory Michelins on, but our Real MPG team calculated a higher 122.2 mpg-e combined driving when tested. When they tested the Bolt again but with the BFGoodrich summer tires, the results were so surprising that our team believed that there might have been an error in the numbers, but there wasn’t. Once they rechecked and recalculated the data, the mpg-e figure dropped by staggering 27 percent, down to 89.2 mpg-e combined driving. That puts it along the lines of one of the most inefficient and recently discontinued EVs on the market: the Mercedes-Benz B250e (84 mpg-e combined and an 87-mile driving range). When Real MPG tested the Bolt EV with the factory low-resistance tires on, they calculated a total driving range of 244 miles (higher than the EPA’s 238-miles range), but with a 27 percent reduction in efficiency, the range drops to about 178 miles with the same charging and driving habits.
Something else to factor in is how we drove the car after installing the UHP summer tires. We didn’t measure it, but there is a good chance that our driving style became a bit more aggressive once installed, therefore using more energy. I know for a fact mine did, and Evans says he found himself driving quicker at times, as well. Reynolds, however, says his driving style did not change.
Why would anyone do this?
Hypermilers would call this blasphemy while some young drivers out there with short commutes might think this is a great idea. In my opinion, UHP summer tires are a bit too extreme for most EVs, especially with the resulting range loss and increased energy use. Considering my short commute to work, I would find a good middle ground with a set of performance all-season tires. Evans shares similar feelings. Regardless, most people who purchase a Bolt EV will be perfectly happy with the factory low-resistance tires and the excellent range they provide. If you want to drive a tall EV hatchback like a Miata or simply want improved braking distance and grip at the expense of some range loss, it’s worth considering a more aggressive tire.
| 2017 Chevrolet Bolt EV Premier | 2017 Chevrolet Bolt EV Premier (with UHP tires) | |
| BASE PRICE | $41,780* | $41,780 |
| PRICE AS TESTED | $43,905* | $43,905 |
| VEHICLE LAYOUT | Front-engine, FWD, 5-pass, 4-door hatchback | Front-engine, FWD, 5-pass, 4-door hatchback |
| MOTOR | 200-hp/266-lb-ft AC permanent magnet | 200-hp/266-lb-ft AC permanent magnet |
| TRANSMISSION | 1-speed automatic | 1-speed automatic |
| CURB WEIGHT (F/R DIST) | 3,555 lb (56/44%) | 3,555 lb (56/44%) |
| WHEELBASE | 102.4 in | 102.4 in |
| LENGTH x WIDTH x HEIGHT | 164.0 x 69.5 x 62.8 in | 164.0 x 69.5 x 62.8 in |
| 0-60 MPH | 6.3 sec | 6.3 sec |
| QUARTER MILE | 14.9 sec @ 92.9 mph | 15.0 sec @ 92.1 mph |
| BRAKING, 60-0 MPH | 128 ft | 112 ft |
| LATERAL ACCELERATION | 0.78 g (avg) | 0.82 g (avg) |
| MT FIGURE EIGHT | 27.4 sec @ 0.63 g (avg) | 26.9 sec @ 0.66 g (avg) |
| EQUA REAL MPG, COMBINED | 122.2 mpg-e | 89.2 mpg-e |
| EPA CITY/HWY/COMB FUEL ECON | 128/110/119 mpg-e | 128/110/119 mpg-e |
| ENERGY CONS, CITY/HWY | 26/31 kW-hrs/100 miles | 26/31 kW-hrs/100 miles |
| CO2 EMISSIONS, COMB | 0.00 lb/mile (at vehicle) | 0.00 lb/mile (at vehicle) |
| *Before applicable tax rebates | ||
The post Chevrolet Bolt EV on Summer Tires: When Electricity Meets Grip appeared first on Motor Trend.
from Motor Trend http://ift.tt/2jtMAjM
Aucun commentaire:
Enregistrer un commentaire