2012 Jeep Grand Cherokee SRT8: Run-Flat Tires vs. A Spare
October 29, 2012
Those who abandon run-flat tires and switch to standard tires -- like we just did on our 2012 Jeep Grand Cherokee SRT8 -- are typically faced with a problem, and that problem is this: no spare tire.
That's because auto companies typically don't fit run-flats for pure altruistic reasons such as customer saftey and convenience. Instead the decision to use run-flats is usually made in order to ditch the spare altogether in the interest of other goals that fall into two broad categories: packaging and weight reduction.
Mini uses run-flats on the Cooper S because the sytlists wanted center-exit exhaust pipes, but that routing cut straight through the spare tire well. The pre-2008 Dodge Viper used them because there simply wasn't space for what would have been a massive spare indeed.
Others, such as BMW, have gone with run-flats to eliminate the mass of the spare so the vehicle's weight falls into a lower class, which reduces the dyno load on a test car when it's going through the official EPA fuel economy tests, resulting in a tiny MPG improvement on the right-hand side of the decimal point that the customer will likely never notice.
These largely corporate benefits don't do the car owner any favors. Run-flats are very expensive to replace -- on the order of two to three times that of standard tires -- and because their operating range is very limited you may not be able to get the correct replacement quickly if you have you flat outside a major metropolitan area.
But their most obvious liability is ride comfort, which suffers markedly because of the extreme sidewall stiffness that allows them do their thing. I know very few car owners with run-flats who have not complained about their car's ride. I know many that have made the same switch we just did.
Their solution to the no-spare problem is easy, and it cost less than $100. It's called a ContiComfortKit, or Continetal kit for those who like spaces between their words. It's an ironic name because your grandfather's Continental kit had to do with spare tires, too.
His Continental kit was named after the 1939 Lincoln Continental, not the tire company, and consisted of an extended rear bumper and an external spare tire mount that allowed the spare -- usually a white-wall -- to stand up proud behind the trunk in full view. You sometimes see them on questionably-restored '57 Chevys.
This is not that. Continental's Continental kit is compact compressor and tire sealant packed together in one delivery system, and it takes up very little space inside the trunk.
However, having said all that....
...our 2012 Jeep and it's new "get flat" tires doesn't need a Continental ContiComfotKit after all because the Grand Cherokee SRT8 has a spare tire lurking beneath the floor of its hatch area.
Maybe Jeep DID fit run-flats with the customer's convenience in mind after all. It certainly wasn't a nod to ride comfort. Or maybe it made production or certification of this low-volume model that much easier.
Whatever the reason, this state of affairs is a boon to us. No run-flats? No problem.
And we can't help thinking that it also makes life ridiculously easy for the Grand Cherokee SRT8 development should they choose to follow in the footsteps of the 2008 Dodge Viper SRT10 team, who did away with run-flats and retuned the suspension to take advantage of the newfound tire compliance and made the 2008 Dodge Viper a far better riding -- and handling -- car than it had been a year earlier.
The 2012 Jeep Grand Cherokee SRT8 could use some of that thinking. Seriously.
Dan Edmunds, Director of Vehicle Testing @ 11,983 miles