cant make out the tire discussions

The car doesn't know which tyre is fitted. It just assumes the diameter. If you look it up, the 195/55 R16 is almost the same diameter as the 185/65 R15 (both stock sizes). As long as you stay that diameter, and your tyre has the same or higher load rating and fits on the car (doesn't rub the springs etc) you can change the tyre size as you please.

The speedometer gets the same reading as long as the tyre diameter is the same (same revs per km).

(I'm driving the US spell checker crazy using proper English spelling. )

What you WILL notice is the larger tyres will decrease mileage a bit. They have higher rolling resistance. A good general rule is the more traction, the higher the rolling resistance. I'm sure this will change once the tyre manufacturers figure out how to get low rolling resistance with good traction. I think Nokian is on the right track with the WR.

 

<div class='quotetop'>QUOTE(prius2go @ Aug 19 2007, 12:43 PM) [snapback]498744[/snapback]</div>

As was posted by David Beale, as long as you stay within the standard diameter, you won't have speedometer or odometer problems. Personally, I would tend to go with the revs/mile specification, as you can have slight variations in diameter (+/- .1-.2 inches) yet still be within 2-3 revs/mile. If you have a candidate tire, check the specification for Measured Rim Width as your fitting guide. The Measured Rim Width is the wheel width that was used to take the measurement of Rotations/Mile. If the tire's Rim Width Range will accommodate the wheel width that you are contemplating installing the the tire on, then you can fit the tire to that wheel. There may be some variation in speedometer and odometer accuracy if you fit a wheel that is at the margin of the Rim Width Range vs. one that is right at the Measured Rim Width, but it should not be too great.

One thing that I have found when going to the larger diameter (17+ inches) wheels & tires is an increase in ride harshness. If ride harshness is an issue for you, you will want to stay under 17 inches in wheel & tire diameter. And avoid runflat tires like the plague - the sidewall hardness of the runflats makes for a very harsh ride.

Also, you need to consider the total weight of the wheel and tire combination for any impact on gas mileage (presumably that is a consideration, since you have a Prius). Everything being the same between the stock tire and wheel weight and the larger/wider wheel and tire combination, the larger/wider wheel and tire will reduce gas mileage due to the greater friction of the larger/wider wheel and tire. However, there is a way to offset the gas mileage loss - go with lighter wheels (presuming they are available). If you can get the total overall weight of your proposed replacement wheels and tires to be less than the total overall weight of the OEM wheels and tires, then the weight reduction will offset the increased friction.

Lastly, you need to stay close to the stock offset specification for the wheel. If you vary too much from the stock offset, you may run into clearance issues for the wheel with suspension or brake components. One of the nice things about ordering from Tirerack is that they give a fit guarantee for wheel/tire combinations that will work for your car.

Hope this helps.

 

<div class='quotetop'>QUOTE(prius2go @ Aug 19 2007, 01:45 PM) [snapback]498781[/snapback]</div>

Definitely getting technical. The site that I inevitably seem to go to first is Tirerack.com. Go to the page for the specific tire and there will be a link to specifications for the tire. The wheels have a 5-100 requirement. If the wheel vendor says that the 4-100 wheels will fit the Prius, you have a problem. If it were me, I would pass on that vendor, since they missed the first requirement for proper wheel fit - the correct number of mounting points. Bore typically refers to the depth of the bolt hole that is cut into the wheel. Bore can usually be addressed with deeper sockets. Tirerack also supplies deeper sockets if needed. (I am not an employee of (or otherwise affiliated with) Tirerack; it is just that I have had good results with them.)

 

<div class='quotetop'>QUOTE(prius2go @ Aug 19 2007, 02:12 PM) [snapback]498790[/snapback]</div>

Could be. It depends in the context in which it is used. Since I don't know which wheel you are considering, my first thought was depth of bolt hole. Middle hole diameter can vary by wheel manufacturer; also, the aftermarket wheel manufacturers generally supply a cap for the center hole. 54.1 mm (presumably) is definitely a large hole.