Tyres

[zei20l]

stretching the tyre doesnt affect its rolling diameter

[iamhe77]

I've used the tyre calculators before to check rolling diameter, trouble is there is no allowance for wheel size and therefore potential stretch. That one did have the info on recommended size though which was useful, looks like I should be going for 255s.

Any other thoughts or experiences are useful though!

I'd agree that 245 is way too narrow for a 9.5" rim.

I am somewhat biased though as I do not like the stretched look at all.

Try this rim/tyre calculator.

http://www.rimsntires.com/specs.jsp

[pipster11]

stretching the tyre doesnt affect its rolling diameter

i'd beg to differ

pythagorus yo!

also, www.willtheyfit.com is one of the best tire size calculator i've found

[Raysboostin]

i know im goin to get flamed to death for saying it, but IMHO the federal 595 is highly over rated on a daily drive car. they are great for a weekend warrior or if u do ALOT of hard cornering. but for the daily commute i'd suggest something thats a little better in the wet and maybe wears better. i also agree with the other guys a 245 is pretty narrow on a 9.5 inch rim. id be goin a 265 to protect the rim a little better.

[slippylotion]

I like a slight stretched look and to help fit in the guards a little better. On my 180sx the rear runs a 9.5 with a 235-45. On the M35 the new rims are 9" so I will run a 245-45-18 but would really prefer a 235 but the diameter isnt as nice as the 245. I would never run a 265 on a 9.5" rim.

[zei20l]

i'd beg to differ

pythagorus yo!

also, www.willtheyfit.com is one of the best tire size calculator i've found

it cant affect the rolling diameter. all youre doing is changing the angle of the sidewall. isnt pythagorus' theorum for triangles??

[capturedcreation]

it cant affect the rolling diameter. all youre doing is changing the angle of the sidewall. isnt pythagorus' theorum for triangles??

But wouldn't changing the angle of the sidewall change how the tread sits and therefore the rolling diameter? Or is that a really dumb question?

[zei20l]

it cant change the tread, the size is the size. to make a circle smaller, you need to cut a piece of it, or put a crease in it. good luck doing that to a tyre.

the rolling diameter is the rolling diameter

[The Bogan]

It would change the dia by a small amount only, didn't you guys do geometry at school, think of a tree that is 10 mtrs high, standing upright it is 10 but when on a lean it is slightly less high, the length though doesn't change but the height does, the ground is the fixed point as in the rim being the fixed point.

Dia may be changed by a mil or two maybe, post up the height of the side wall and the size of the gap from vertical.

[pipster11]

it cant affect the rolling diameter. all youre doing is changing the angle of the sidewall. isnt pythagorus' theorum for triangles??

changing the angle of the sidewall would change the height from the bead to the tread

immagine house, the wall height is 2m, the length of the roof could be 2 meters too but the height of the wall is 2m because its vertical but because the roof is on an angle the heigh of the roof may only be 1m

i think what would happen in real life would be that the circumference of the tyre would be under a little bit of compression and the sidewall would be put in tension (otherwise the tyre would wrinkle like you said, this is also neglecting the internal pressure of the air and the load from the car's weight)

[Sunkist]

i'd beg to differ

pythagorus yo!

also, www.willtheyfit.com is one of the best tire size calculator i've found

how right you are!

[zei20l]

well, using this website is the perfect example. the circumference cant be changed.

www.willtheyfit.com

put in the EXACT same tyre size into the boxes, just change the rim width and tell me what you get with rolling diameters for both sets of values.

[Sunkist]

195 185

Diameter 559.1mm 570.1mm

Circumference 1756.5mm 1791mm

Poke 81.6mm 81.6mm

Inset 121.6mm 121.6mm

Speedo error 0% -1.93%

Reading at 30mph 30mph 29.42mph

Reading at 60mph 60mph 58.84mph

Ride height gain 0mm 5.5mm

Arch gap loss 0mm 5.5mm

diameter changed? not by much but it did. everything else is the same except width

[zei20l]

dude, SAME tyre specs. you have shown a 195 and 185 there, of course they will be different.

[Sunkist]

how else would you change the angle of the wall?

oh wider wheel - yeh according to the sight iains right which is strange lol

[zei20l]

we are talking about stretching a tyre. so using the same tyre specs and only adjusting the rim width is how to prove that you cant affect rolling diameter

[zei20l]

how else would you change the angle of the wall?

oh wider wheel - yeh according to the sight iains right which is strange lol

lol strange huh? smart ass

[Sunkist]

something still isnt right about it.

if you were to measure the side wall between the two (stretched/not so stretched) the wall length would HAVE to be different for the rolling circumference to change. you can see that in the image. which means that instead of being 195/45, it may be 195/47(for argument sake) im pretty sure the rubber wont physically stretch to meet the exact circumference.

you may be very right. just doesnt make sense to me.

lol not strange that your right. strange by the law of physics. it simply doesnt agree with the pythagoras theorem which actually can be used. the hypotenuse would actually be larger with the larger width wheel, for the circumference to be exactly the same.

[zei20l]

how can you use pythagorus when youre talking about a circumference?

i know you mean the cross section of the wheel/tyre, but you have to remember you cant make a circle smaller or larger unless you add or subtract to it, thus affecting the tyre size, then it would change the size of the sidewall to accomodate the larger/smaller rolling diameter

[Sunkist]

i think i know what your trying to get at with the amount of rubber being the same around the circumference. and it does make sense.

but unfortunately rubber works differently. you are actually subracting from the circle(circumference) by adding a wider wheel, back to hypotenuse, for a wider wheel to = the same rolling circumference as thinner wheel, there has to be a larger hypotenuse(wall). the only way that can happen with the same spec tires, is by physically stretching the rubber material in the wall, which would make it go from a 45 -> 47 theoretically.

I think mythbusters is needed lol