2012 Jeep Grand Cherokee SRT8: New Shoes
October 25, 2012
Our 2012 Jeep Grand Cherokee SRT8 has new shoes. Scott already told you why: we've grown tired of the stiff ride; we didn't much like the idea of running the tires 5 psi below the recommended pressure (and it didn't work anyway); winter is coming and folks will want to take it skiing in the local mountains.
On the other hand, winter tires won't do because it'll be relatively warm here in the LA basin during the winter months.
So we went looking for all-season tires that would give us reasonable cold-weather performance that were not run-flats. But 295/45R20 is an uncommon size. We were left with two choices: The Sumitomo HTR Sport H/P tires we bought or the Yokohama Parada Spec-X tires we didn't.
Sumitomo is the parent company of Dunlop, and they design and build the Goodyear tires that are made in Japan and installed on Asian cars built overseas -- they are by no means small potatoes. Besides, we had good luck with another one of their tires on an earlier iteration of project Miata. Also, the well-regarded Yokohamas were back-ordered.
Because we were curious, we weighed the mounted wheel and tire assemblies before and after we made the swap.
The OE Pirelli run-flats are weighed 79.2 when mounted on the rims. Because we've dismounted these tires we know the wheels weigh 39 pounds and the P-Zero run-flats weigh 40.2 pounds.
It turns out that the new Sumitomos are heavier even though they're not run-flat tires. They tip the scales at 43.8 pounds apiece when loose and 82.8 pounds when mounted. What the heck? Well, the Pirellis do have a bit more than half their tread worn off -- that might account for a pound or three.
Still, you might think run-flats would be clearly heavier. And you'd be right except for one thing: the Sumitomos (and the Yokohamas) are "extra load" tires. Their size is P295/45R20 and the load rating is 114 points. The Pirellis are a standard load 295/45R20 tire with a 110 load rating.
The extra 4 points of load rating comes from a stronger carcass. But it's more of a general robustness -- XL tires still don't have the kind of heavily reinforced sidewalls found in run-flats. They need air to support any weight, so they should still give us what we want: sidewalls that have some "give" to take the edge off some of the sharper stuff and maybe a little less head toss.
As for the speed rating, the Sumitomos are, in fact, H-rated. The Yokohamas we didn't buy are V-rated. We'll just have to remember to keep it below 130 mph, is all.
We don't expect miracles. After all, the springs are still the springs, the shocks are still the shocks. And it'll take a little time to hear back from everyone that complained before.
But the early returns show promise. The last time my wife rode shotgun she complained bitterly, said the Jeep made her sick, asked me to never bring it home again. Last night we took it on an errand on the new tires and she didn't say a word. Sure, it's firm, it's sporty, but the constant busy movement and head toss seems more muted.
We need more miles, though. And once we get a few hundred or so we'll head straight for the track. Because we didn't stick with summer tires we fully expect to lose a little something in the ultimate grip department. The question is, how much?
Dan Edmunds, Director of Vehicle Testing @ 11,905 miles