tire sizes
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hey im looking at getting some new tires i desperatly need and found an extremly cheap set on ebay that ends in 2 hours so looking for some help in 2 hours because i have called everyone i know with no answers
so the size of the tires on my care right now are 245/45/17 and the one i am looking at are 235/45/17 now i have been told you can vary the width of most tires on rims by about 20 mm or so does anyone know if this is true or not or if these tires would even work? -
my spedo is already off so no worried
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weshole;180133 wrote:
A 245's are 25.7 inches in diameter and the 235's are 25.3 inches in diameter. It's about a 1.4% difference. In terms you'll understand... at 61mph, you'll actually be going 60mph. But the faster you go, the further of it is.....wow....thanks for that lol
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lol where? i sell tires all day and i dont figure that kinda stuff out. but i guess i just sell them the same size they had
here a psht, there psht, everywhere a psht psht
PVC SQUAD MEMBER #2- 95 CIVIC EX- DD 320whp on a mustang dyno
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well right now when im going 80 im going roughly 76-77 so that really dosent worry me if it saves me 150 bucks or more on tires, i still dont understand how the width would factor but i will take your word for it
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bubba;180148 wrote:
it's not width it's circumference and how many rotations it makes.
thats exactly what i was thinking^^^^ can some explain whay exactly the width would matter if the tire is making the rotations at exactly the same amount as a tire that is slightly skinnier then it? -
copied from a website:
Tire sizing tends to be a bit confusing to most. That is probably because the numbers aren't really accurate. A P205/50 VR15 tire size is translated as follows:
The "P" designates it as a passenger car tire. Many tires assuming this and do not show the letter. A "T" here would mean it is a temporary-use tire (your spare tire). This tire has a 205mm nominal sidewall-to-sidewall width, with a profile (or aspect ratio) of 50%, which is the height of the sidewall measured as a percentage of the tread width (102.5mm in this case). The "nominal" width means that this is an estimated number. The actual width will vary somewhat. The "V" is the speed rating of the tire, which is the maximum constant speed that the tire can handle. By exceeding this speed, you are at risk for tire failure due to heat build up and centripetal force. Below is a chart describing the speed ratings and their meanings.
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bubba;180148 wrote:
it's not width it's circumference and how many rotations it makes.WRONG! They will all make revolutions. It's diameter and how much area is covered per each revolution. A bigger diameter will cover more distance per revolution than a smaller diameter. Which means a taller tire will effectively lengthen your gear ratio and a shorter one does the opposite. That's just in the diameter part. Theres also the width which shouldn't have too much impact in this senario.
Tire sizes typically break down as follows. EXAMPLE P205/55R16 89H
P= Passenger vehicle
205= section width in millimeters (hardly ever exact but close)
55= Aspect ratio or profile. 55% of the width is the height of sidewall from bead area to outer edge of the tire. The lower the number, the lower the profile
R= radial construction. Most tires used by passenger cars and light trucks on the road today use a radial tire.
16= wheel diameter.
89H= load index and speed rating.
There's alot more to tires than just this. But with this little bit of info, you should be able to stumble your way through what you need.
For more info read this.
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35 -
The formula to figure the rolling radius of the tire is stupid because it mixes standard and metric units. Basically, the sidewall height is the AR * the nominal width. This figure is in millimeters. Then you add the radius of the wheel (half the diameter). This figure is in inches.
For the case above: 205/55R16
55% of 205 == .55 * 205 == 112.75mm
half of a 16" rim is 8". 1in = 25.4mm, so 8in is 203.2mm.
The radius of the tire is then 112.75 + 203.2 == 315.95mm
The diameter of the tire is 2x the radius, or 631.9mm.
The rolling distance (rd) of the tire is pi*d, where pi is however many digits you want to use, starting with 3.141592653
rd = 3.141592653 * 631.9 == 1985.17mm
for silly US units, that's a tire+wheel radius of 12.43", or a tire diameter of 24.8", and a rolling distance of 78 inches (6'6")
This level of "accuracy" is irrelevant, since inflation pressure will affect the amount of deformation during rolling. Additionally, speedometers have inaccuracy built in, usually between 3 and 10% @ 60mph. Finally, the wear of your tire will contirubte -- a new tire may have an 11/32nds tread depth, which is 8mm, while a worn tire could be be down to essentially 0mm. This constitutes a 16mm reduction in diameter, and thus a ~50mm reduction in rolling distance, which is just about 2 inches. A reduction 2 inches on a stated rolling distance of 72 inches constittues a 2% difference...just from tire wear.
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