I did quite a bit of internet and other research before buying new tires for my 93 Nighthawk 750. The stock 505's lasted 11k, but the back was squared off and the front cupped and had some dry rot cracks. I really like the ME33 for the front: great all around tire and famous for being good in the rain. The back tire choice was tougher. Decided against the Dunlop 591 due to persistent reports of low miles before wearing out. Elimated 505s due to lack of performance and hard to get. Eliminated Bridgestone BT35 as an old design without good wet design. Eliminated BT17 for similar reasons. Eliminated ME 55 due to cost and tendency to square off. Elimated ME 99 due to cost and old design. Eliminated Chen Shen due to various reports. Elimated radials in general due to numerous shop experts saying they would not be safe on the rims. So it came down to Michelin Macadam 50s or Bridgestone BT45. Both are newer designs which are supposed to not square off as bad as most. Finally (reluctantly) Elimated Macadam 50 due to cost and mixed reviews (the front especially has had problem reviews on the net). Bought the new Bridgestone BT45 as a new design which appears to have a good design for commuting and rain. It is designed to warm up quickly and contains silica like the new radials. It also has the dual tread design for longer life and resisting square off. It is hard to find out much about this new (1897) Bridgestone tire. I finally called Bridgestone factory reps. The BT45 appears a bit flat compared to radical sporty tires, but how many of us drag knees a lot on 750 nighthawks? If you want to lean to the max, you might want to pick a 591 or Michelin 50? I like how the ME33/Bridgestone BT45 combo handles in town and on curvy Colorado Mountain roads. So far I really like the ME33 in front and the Bridgestone 45 in the back (140/70/17). It is not as flat after inflation, but the BT45 is slightly shorter than the 505 back. At 3000 rpm in high gear, the speed of the bike went down 1 mph with the Bridgestone compared to the stock 505 rear. So it would give one a tiny bit more acceleration at the expense of a very small increase in engine speed at a given rpm. The 140/80/17 tires would do the opposite, slow the engine down a bit at cruise. Very stable combination, smooth transitions, and overall much better handling than the warn 505s. Can't really tell you how long they will last yet.
Here is my experience with the Metzeler Me Z4 on my Nighthawk. This is a Z rated tire with steel belts front and rear.
On their web site, Metzeler recommends their Z2 tire for the Nighthawk. I preferred the tread design of the Z4 and while the Z4 is not listed by Metzeler for the Nighthawk, the Z4 is listed for the European version of the CB750- the "CB Seven Fifty". I guess the weight and steering geometry is similar for both bikes so I went with the Z4.
Interestingly, Metzeler recommends a 150/70 rear rather than the 140/70 that is stock. I thought this might be a mistake, but I noticed that Michelin also shows a 150/70 radial tire recomendation. Somewhere I saw that a 4" rim (which the Nighthawk has) is the optimum size for a 150 tire and the European CB750 comes with a 150/70 rear. The 150/70 is about 1/2 inch taller radius than the 140/70 which may be of concern to some.
Ride Report:
The Z4 makes the Nighthawk handle much differently than the stock K505 and it did take a while to adjust.
In sport cornering, I had to sort of Pull the K505 shod bike over. The Z4 just rolls right over with light pressure. I attribute this to the K505 being designed for Commuter use and is relatively flat shouldered, while the Z4 is a "single radius" tire with a steep shoulder. The good news is that the Z4 will respond to any rider input; the bad news is that it will respond to any rider input.
It requires much more attention to holding a line as opposed to the set it and forget it of the K505. However, if you need to hook a hairpin or reset a line in a corner the Z4 is easier.
Mileage:
I got 6,000 miles out of the K505 rear. I got 4,500 out of the Z4 rear in similar use (the front Z4 shows no major wear at 4,500). Note: A high percentage of my riding is "sport mode" in the Blue Ridge and Smokies :)
MPG:
I have recorded all my gasoline use. I got 53.6mpg average over the life of the K505 (I'm 150lbs). The Z4 saw an immediate drop in mpg and yielded lifetime 51.0mpg. The mpg loss is probably due to the more agressive tread design and higher rolling resistance of the Z4.
Notes: Recommended Tire pressures for the Metzelers are high. See their web site.
The Z4's are pricey- $123 front, $141 rear at MAW