My car went in to Gatwick for some minor fault correction before Christmas and I was given a loan car for two days. The perfect opportunity to compare the suspension options over a sensible distance on UK roads. These are my thoughts, I hope they might help any of you who are agonising over which set up to order. Black P85 VIN 474XX Registration H15 AWF Coil suspension, 19” wheels, 245/45R19 Goodyear tyres. 42 psi cold Grey S85 loan car VIN 423XX Registration RK64 VAJ Air suspension, 21” wheels, 245/35R21 Continental Tyres. 45psi cold Date: 16[SUP]th[/SUP] December 2014 Weather: 5 to 7 degrees centigrade, damp conditions on day one, light rain on day two Traction: Full power standing start with fast throttle roll on. The 19” Goodyears were fine, only activating the traction control occasionally. The 21” Continentals were very poor, only managing around 1 in 5 clean runs without traction control activating. From cold they were even worse. Applying full power at low speed, around 20 mph, in a straight line. The 19” Goodyears maintained traction every time. The Continentals broke traction around 50% of the time. The Continentals were surprisingly poor in both tests, especially as the S85 has 160 newton metres less torque than the P85. Road noise: The 21” Continentals are considerably noisier than the Goodyears everywhere with the noise varying markedly on different surfaces. It is the dominant noise in the car. Ride: The combination of coil springs and 19” wheels definitely rides better than 21” wheels with air. The air suspension does not have the ride subtlety of the coil set up. It has "sharp edged" responses over small ridges and feels just a bit too stiff everywhere. The end result is closer in feel to a mid sized car than a vehicle in this class. The only difference between the two suspension systems is the replacement of coil spring/damper units with air springs. As a result roll, dive and squat are identical and very good in both cars, largely due to the low centre of gravity in the basic design. The ride heights are different with the coil spring car set at a single compromise height, higher than the standard setting on the air suspended car. As the ride height setting reduces as the car lowers on the air car the front and rear tyres lean in at the tops as the car sinks, creating more negative camber. This transfers the weight more on to the inner portion of the rear tyres and is almost certainly the root cause of the poorer traction on 21” tyres. The full width of the rear tread is not evenly loaded across the tread, so effectively the load is concentrated on the inside edges of the tyre treads. This is born out by the very poor tyre life on air suspended cars with 21” wheels that has been reported on this site. Steering feel: A surprise here, because experience would say that the combination of increased front negative camber on the air suspended car along with the shorter stiffer side walls on the 21” tyres should give better steering feel. I had made sure both cars were on the “normal” steering setting for the test and re-checked I hadn’t made an error after I had gone 10 miles or so. Put simply, the air car’s steering feels more disconnected and artificial. It is precise enough, just devoid of feel about what’s happening between the tyres and the road surface. You do feel the benefit on initial turn in, which is more direct and sharper than the coil car with 19s, primarily as a result of the extra negative camber and stiffer side walls, but does this really matter? At track speeds I have no doubt that the air car on 21s will feel a bit more secure with less understeer when you are hauling towards an apex. The reality is that road driving rarely calls for such a fast rate of application of steering angle, so you don’t notice the benefit. The bit you always notice is the vastly superior steering feel on coils and 19s. Okay, it’s no 911 but you always have a sense of what’s going on and a feel for available traction. Grip At any sane road speed there is no discernible difference in outright grip because both tyres have 245mm tread width. The even front to rear weight distribution ensuring the tail slips out first under power. In fact, classic rear wheel drive handling. This is a big car on UK “B” roads and this is more than anything else the limiting factor to how fast you can go. My conclusions: This is a luxury car and it weighs 2.1 tonnes. The 21” wheels, 35 aspect tyres and low ride height of the air suspension give the appearance of a performance tuned model like an M5, but this isn’t the case. The suspension is set up for comfort and is actually compromised by the adjustable ride height. The increase in negative camber at the rear as the car lowers significantly reduces traction and increases tyre wear rates to near unacceptable levels. Of course the car looks great on big wheels with the low riding stance, most cars do. It’s only perceivable technical advantage over the coil spring set up is the ability to raise to clear steep driveways and self level with a large load in the rear. You have to decide if you want the best appearance and don't mind the increased road noise (plus a bill for £5,500) or the best ride, traction and driving dynamics. Whatever you choose, don’t mistake the Model S for an electric M5, it isn’t. It is great to drive in it’s own right and makes everything with an ICE feel clunky when you go back and drive them. These are my personal opinions, underwritten by 15 years of historic racing experience as a driver and in developing winning competition cars. I have written it to try to help future Tesla owners decide on the suspension specification they might want for UK (as opposed to US) driving conditions. I will be trying some different tyres over the next twelve months, starting with Michelin Pilot Alpin winter tyres, which are on order. Once the winter is gone I plan to go on to Michelin Pilot Sports and I’ll put my impressions of the differences up on the Forum in due course.