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THE RIDE
In order to be sold as a street-legal sportbike in the U.S., a bike has to pass stringent EPA noise tests — and the fact the HP4’s Akrapovic exhaust has the “meets federal noise emissions standard” writing stamped on its inner portion of a canister that looks more like a race unit is a feat in itself. Granted, the BMW’s bark when firing up is rather muted, so as long as you don’t blip the throttle, you won’t be annoying neighbors on your way to work in the morning.

Although the DDC makes its own damping adjustments to the suspension as you ride, a major plus is that you can adjust the baseline settings that it starts out with. Theoretically this means you can set up the suspension to start out soft while cruising on the highway or city streets before it starts firming things up as your speeds rise and lean angle changes. It doesn’t quite work out that way though, because the four riding modes (as found on the S 1000 RR: Rain, Sport, Race, and Slick) are set up differently. The Race and Slick modes are not only stiffer for the same settings, but they ramp up to a much firmer rate quicker than Rain and Sport modes, ostensibly because the former are meant for the comparatively smooth tarmac of a racetrack.

While you can change rebound and compression damping separately in the rear shock, the front fork damping can only be changed as a single setting unless you get the accessory fork travel sensor, meaning both rebound and compression are changed according to the setting you choose (spring preload changes front or rear require the usual manual tools). As with the DTC, there are 15 possible baseline settings you can choose; seven steps below and seven steps above the zero base setting.

For the street, we found that softening the baseline setting in Sport mode to as much as -4 in both rear rebound and compression and -5 in the front allowed an acceptably smooth ride while cruising over the usual bumps and heaves of public pavement, yet kept everything well under control when the DDC stiffened up the suspension as we headed into the canyons. We couldn’t discern much of a difference going any softer (and even at -7, the HP4 certainly isn’t sport-tourer plush by any means), and starting at too soft of a baseline allowed a bit of wallowing at aggressive riding levels.

The rear suspension reacts instantly to any acceleration, and with the HP4, that’s a good thing. There is a definite increase in midrange power, and when you factor in that the starting point is an S 1000 RR, well, let’s just say that you probably should thank BMW that the wheelie control is there for the sake of your license. Compare the roll-on numbers: the HP4 does the 60 – 80 mph test in 2.44 seconds versus the S 1000 RR’s 2.61 seconds; 80 – 100 mph, the HP4 takes only 2.33 seconds, with the stock BMW requiring a comparatively glacial 2.64 seconds. The HP4 positively launches off corners, yet its throttle response — even in Race and Slick mode — is smoother than the standard S 1000 RR, with less of the belligerence that forces you to stay on your toes when cracking open the throttle.

That additional performance comes with a price: the HP4 is much thirstier than the stock S 1000 RR, even when doing your best to keep from twisting the loud handle. While the stocker would often average up to 36 mpg, we were lucky to average 34 mpg on a good day, with most tankfuls running in the 32 mpg range.

You can also feel the front suspension reacting when getting on the brakes, and when tipping into the corner. While the front fork doesn’t exactly go stiff like some of the alternative front suspensions we’ve tested in the past, there is a perceptible slowing of the front-end dive that allows you to maintain better control while still transmitting excellent traction feel. And when you let off the brakes to begin your turn-in, you can sense a more controlled rebound of the fork that seamlessly transitions into a softer feel as lean angle increases (thus eliminating the compromise that often occurs when trying to keep the spring rebound under control without making the fork action overly stiff).

Speaking of brakes, the Race ABS system has also been refined from the standard S 1000 RR. Although the intervention level was high, the cycling of the previous system was still a bit rough, which could cause some white-knuckle situations as the bike took some time to return braking power (ask Bradley about turn one at Valencia on the S 1000 RR…). The cycling rate now is much quicker and smoother, and braking over rough pavement won’t cause the elevated heart rates like it used to. Power and feel from the new pad compound in the Brembo monobloc calipers is excellent.

THE TRACK
Segueing to the high-speed confines of Chuckwalla Valley Raceway in Desert Center, California, we had hoped to really explore the outer reaches of the HP4’s very heady performance envelope. Unfortunately, blustery high winds and constant sand over the racetrack surface forced us to keep the pace within reason, lest we turn the BMW into a hideously expensive ball of aluminum and carbon fiber. Nonetheless, we were still able to discern many aspects of handling and electronics that would’ve been excessively risky on the street.

The HP4 flicks into corners noticeably easier than the stock S 1000 RR and feels much more agile overall. A good portion of credit here surely goes to the lighter forged aluminum wheels and Pirelli Diablo Supercorsa SP tires; that the HP4 steers lighter even with the monstrous 200/55-17 rear tire is even more of a feat.

The sketchy traction caused by the sand blowing over the track allowed us to do a decent evaluation of the revised DTC in Slick mode, although admittedly we couldn’t make much use of the levels higher than -1 in those conditions. The HP4’s DTC intervention is much more transparent than the S 1000 RR’s, with less of the “pumping” in the higher settings caused by overreaction to changing grip levels, and a much smoother reduction and transition of power in the lower settings.

The HP4 was literally wheelying out of every corner at Chuckwalla, and the wheelie control in Slick mode makes you look like a hero as it keeps the front end from getting too high

That midrange power increase that is so much fun on the street becomes even more of a party on the racetrack — especially with 25 less pounds to haul around compared to the S 1000 RR. The HP4 was literally wheelying out of every corner at Chuckwalla, and the wheelie control in Slick mode makes you look like a hero as it keeps the front end from getting too high while maintaining a solid drive forward. Unfortunately the blustery winds that day cut the party short, as they tried to push the bike’s front end out from underneath it any time the tire was off the ground.

Special mention needs to be given to the HP4’s GSA quickshifter unit. The BMW unit is one of the more well-developed quickshifters made; it not only provides lightning-quick full-power shifts on the track, but it also senses speed and throttle position to provide smooth upshifts on the street as well. Even upshifting from first to second gear at 35 mph, the GSA provides enough delay to allow for a smooth gearchange without jolting the rider.

 

Source: www.sportrider.com
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