DOT approval is user-risk thing. Just don't be at fault in an accident if you run non-approved tires, as this could be used as a basis for liability.
Anyway, I have twice raced against guys in the OBC who ran the Centipedes, whereas I was using 36x12.5x15 Swamper TSL. My observations:
Simex is used in Oz for nearly the same reasons that BFG are used here, they are readily available.
Even those who sell, promote the use of, and are sponsored in some part by Simex will admit that the tires are not good on-road tires. Traction is extremely limited on hard dry surfaces, and they will wear out fast on the road. Look for replacement in 20K miles. However, this rate of wear is not much different from what you will get from a bias Swamper used extensively on road, so it is not offered as a negative, only an observation.
Centipedes and their progeny all have relatively vertical sidewalls (I have not seen the radial, so perhaps it is different). The vertical sidewall has drawbacks, especially if you air down. The tire rolls back and forth across the rim rather than squatting as rounder tires do. So, directional control at the low end of air pressure is worse -- they get squirrelly.
They look better then they perform. Examples: 1) in sand they dig forever, which means that no matter what pressure you use, they sink like a stone. They are not, in my opinon, well suited for sand; 2) in mud, they do not clear as well as they should. It takes a lot of tire speed to clear them, and if the mud is sticky, forget it. Watch some of the OBC videos of guys coming out of mud holes and look at their tires. By comparison, using Swampers we finished 4th overall in 2002 and 4th overall in 2003 in the mud runs. We were frequently able to get going again in mud when forward motion was lost, which I attribute to the tires -- getting stuck was my fault, getting going again was because of the tires; 3) the side lugs look fearsome and stick out farther than almost any tire I have seen in the US. However, I never saw a situation where forward motion was enhanced by side lug traction. Since there is no weight bearing on the side lugs, I feel that all claims of enhanced traction are hooey. They do, however, tend to through really nice roosters of sand when carving a corner. Can't say for sure whether sand launched into the air provides any forward motion.
During really hard and fast outback driving over 100 year old dead brush, Simex tires regularly went flat from punctures. One of the guys on our flight in 2003 repaired 12 flat tires in one day, and stayed up until far past midnight fixing the last of them while the rest of us were trying to sleep. During the week, I believe that same guy fixed no fewer than 2 flats in any day. They were really good at pulling tires at the end of the week. By contrast, in the same 2003 race, the US entires (2 vehicles) were on TSL's. Neither of us fixed any flats during the week. The TJ entry from the US had a slow leak, but not fast enough to warrant the time to repair as we were always airing up and down anyway. On our CJ, we had a quarter inch thick stub of wood stuck in the tread of one of our tires that at first I thought did not penetrate the tire because it was not leaking. Turns out it stuck inside the tire by an inch. I repaired it finally in the summer of 2004 after driving the vehicle for 2,000 more miles. It never went flat until I pulled out the stub of wood. All of the guys in the OBC using Simex were fixing flats, some more than others. My general impression is that they do not suffer punctures well.
Centipedes are incredibly noisy on the road. The Simex dealer, who also races in the OBC on his own brand of tires, told us that for road use he regularly over inflates them so that the outer lugs are off the road. Many of the Oz guys agreed they do the same thing. This is an admittedly dangerous practice, but expresses the extreme to which a guy will go to reduce the darned noise. They also wear out in a flash that way, but the guy sells them, so one assumes he gets a good price on the replacements. The over inflation on the road is not, I would say, responsible for the bad road manners. They are rather like driving on a tractor tire -- high void and not intended for good road performance. There is just not enough rubber on the road for highway use. I have no idea if that inhibits DOT approval, or if Simex just does not see fit to incur the cost of seeking approval to enter a market already flush with great tires.
Overall impression is that they are not worth more and do not work any better than your average TSL, and in many circumstances, the TSL is a better tire. The TSL can also be creatively grooved to create even more traction than the stock pattern, whereas the Centipede leaves little room for creativity. If they were readily available at a competitive price, I would say go ahead and try them if you like. I personally would not pay for them as I regard them inferior in almost every respect to the Swamper.
Parting shot - several of the guys in Oz were using Swampers, even though at the time they had to pay $700 AUS for each of them. These same guys tended to outperform their brethren.
