Any rim that can take one 700C tire will take any other 700C tire, after a fashion. But just because the tire will fit the rim doesn't guarantee that the tire will fit in the frame or fork.
23C to 28C isn't much of a difference, but if you go crazy wide there's a risk that the wider tire won't sit that well on a narrow rim.
No. A 700 C rim has a bead seat diameter of 622 mm, while a 27" rim has a bead seat diameter of 630 mm. If you use excessive force it might be possible to mount the tire, but it won't sit well. On www.sheldonbrown.com there's a nice section about tire sizes.
It's best not to use tire sizes in inches, as there are often several different sizes in the same inch designation. Safest is the ETRTO size in millimeters, where 700C = ETRTO 622 mm. If you insist, 700C will usually be a 28" - but there are at least two sizes starting with 28".
700 C refers to a wheel size, so there are several different frame sizes that use that size of wheel.
700 x 14
3.5 all around with stock tires
Hi tire size on vt 700 1986 is front 110/90-19 Rear size is 140/90-15
well it can be worth 500-700 dollars it depends on how the condition is
According to statistics there are nearly 700 people died from bicycle-related accidents every year.
It's not that easy to tell. Generally, a thinner tire will be more aerodynamic than a wider tire, but there's more to speed than aerodynamics - rolling resistance for instance. A wider tire with less rolling resistance can be a faster choice than a narrower tire with higher rolling resistance. And there's tire pressure too. With a narrower tire, you'll need to run higher pressure to avoid pinch flats. With higher pressure the ride gets bouncier. And each bounce will turn some of your speed into an upward motion, losing you both speed and traction for the moment.
The dimensions of the tire is written on the sidewall of the tire. Make a note of these, then just buy an inner tube with the same dimension. You can go a bit narrower than recommended but the wheel diameter needs to be of the right size.
The with of a bike tire wheel in mm would be 622-20. This is math.
The standard rear tire size for this bike is 140/90-15 70H. You may be able to find another 15 inch tire that fits, for example 150/90-15 but the bike will not ride as smoothly on that.