Kumho tires aren't consistently better or worse than any other manufacturer's. That's because almost every tire manufacturer makes a wide variety of tires - everything from super-sticky track tires, to top-of-the-line street tires with excellent performance, to budget performance tires with decent performance at a bargain price, to all-season tires that will do okay in all weather conditions, etc. And there is no single manufacturer that has the best product offering (for the money) in every one of these segments. Different manufacturers are better at different things.
Kumho applies the "Ecsta" name to a lot of its products (just as Bridgestone does with the "Potenza" name, Michelin with "Pilot", etc). It really doesn't distinguish one tire from another. But we can look at each of its offerings and see how they compare with others on the market.
The Kumho track tires - the
Kumho Ecsta V700, the
Kumho Ecsta V710, and the
Kumho V700 Victoracer - are all highly regarded, although I wouldn't claim that any one tire in this segment is the "best you can get". The track tire segment is very competitive, and word gets around quickly if one tire is significantly worse (or better) than the... er... competition.
The
Kumho Ecsta MX is Kumho's top-of-the-line street tire. It's a good street tire on dry pavement and wet pavement. But it's not as good as the very best top-of-the-line street tires from other brands, such as the Goodyear F1 GS-D3 or the Bridgestone Potenza S-03. What it offers is good performance at a bargain price, because it's significantly less expensive than the very best street tires out there. This is exactly the same situation as Toyo with its T1-R top-of-the-line street tire; it's clearly not as good as the best out there, but if you're willing to sacrifice some performance for a lower price, it might be a good choice for you.
If you're interested in reading more about how various top-of-the-line street tires compare with each other, check out the current (December) Car and Driver, which txtony mentioned and which contains a side-by-side test of eleven such tires. The Goodyear was ranked first. The Kumho MX was ranked dead last. The Toyo was ranked eighth, but they really didn't like it and attributed its better-than-last-place showing primarily to its low price. Keep in mind that none of these tires are BAD tires; it's just that when you try them side by side, it's easier see just how they differ, and how one is clearly better than another. This explains why someone might be happy with the MX or the T1-R, without realizing that another tire like the Goodyear could perform significantly better.
The "budget performance tire" segment has seen quite a lot of activity in the past few years among most of the manufacturers. In 2002, Yokohama introduced their ES100 tire, and it was a big leap in performance over others in this bargain price category. To give an idea how much of a leap, the Tire Rack conducted a
side-by-side comparison test that included the ES100 and the
Kumho Ecsta Supra 712, and the ES100 beat the 712 in all 23 out of 23 characteristics tested. This sent designers at Kumho, Dunlop, and other manufacturers back to the drawing board, to develop new tires that could compete with the ES100. It is just within the past year that these new tires have started hitting the market. The
Kumho Ecsta SPT is now much more competitive in this segment than its 712 predecessor. In
another Tire Rack comparison test, the SPT was tested alongside the ES100. The SPT was significantly superior on wet pavement (which was already a strong attribute of the ES100), while the two tires were similar on dry pavement, with an ever-so-slight advantage to the ES100 in important categories like handling and lap times.
As for the
Kumho Ecsta 711... let's just say that most manufacturers also make tires that are cheap and crappy, and this tire is less expensive (and lower in price) than the no-longer-competitive 712.
Another tire that
is worth mentioning is the
Kumho Ecsta ASX, which is their all-season tire. It is competitive with the best all-season tires on the market in performance, and comes at a bargain price. I often recommend it for those who need an all-season tire, i.e. a single tire to use year-round, in moderate winter conditions as well as summer conditions. Still better, though, for those who drive in winter weather, is to have a separate set of winter tires (a second set of wheels will add convenience), which will give your car superior performance to all-season tires in the winter, and will let you use summer tires for superior performance to all-season tires the rest of the year.
As for suitability for the NSX, it all comes down to your personal preference, and particularly your willingness to trade off performance for a lower purchase price on your tires. If you're looking for the very best performance from a street tire, then get one of the very best street tires out there, like the Goodyear F1 GS-D3 (an attractive price is a bonus), the Bridgestone S-03, or one of the OEM tires (Yokohama A022H or Bridgestone RE010 for the '91-01 NSX, Bridgestone RE040 for the '02-05). Another option is the Falken Azenis RT-615, which is intended to fall in between a top street tire and an R compound track tire, although keep in mind that means rapid treadwear and so-so wet traction along with its great dry traction.
If you are willing to accept some degradation in performance for a lower tire price, then the Kumho Ecsta MX or the Toyo T1-R might fit your needs; if you're willing to go even further in this direction, then the Kumho Ecsta SPT or the Yokohama ES100 might be suitable. However, keep in mind that you will be sacrificing performance, including capabilities in cornering, acceleration, and braking, as well as that "crispness" in handling that the NSX is capable of (and which the OEM tires do so well). If you bought your NSX for its handling and performance, and you really want to maximize it, then one of the tires mentioned in the previous paragraph will be more suitable... even more so if you take your car to the track or autocross, and/or if you modify your car. Tires are perhaps the most important performance variable of any part of the car, and if you're
spending money on performance modifications, simultaneously trying to
save money on tires by degrading performance won't make a lot of sense.
To give you an idea of how all of the above-mentioned tires compare in price, here are prices (from the Tire Rack, except where indicated) for the 245/40-17 size (stock '94-01 NSX rear size) (again, except where indicated), organized by segment:
Track tires:
Kumho Ecsta V700 $161
Kumho Ecsta V710 $182 (for 245/45-17)
Kumho V700 Victoracer $164 (for 255/40-17)
Best top-of-the-line street tires:
Goodyear F1 GS-D3 $196
Bridgestone Potenza S-03 $224
Yokohama A022H $246
Bridgestone Potenza RE010 $227
Falken Azenis RT-615 $152 (for 255/40-17, from
Vulcan)
"Value" top-of-the-line street tires:
Kumho Ecsta MX $128
Toyo T1-R $142 (from
onlinetires.com)
Budget performance tires:
Kumho Ecsta SPT $100
Yokohama AVS ES100 $113
Kumho Ecsta Supra 712 $95
All-season tires:
Kumho Ecsta ASX $99
