zei20l Posted August 11, 2011 Share Posted August 11, 2011 stretching the tyre doesnt affect its rolling diameter Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5961063 Share on other sites More sharing options...
iamhe77 Posted August 11, 2011 Share Posted August 11, 2011 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 Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5961140 Share on other sites More sharing options...
pipster11 Posted August 11, 2011 Share Posted August 11, 2011 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 Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5962094 Share on other sites More sharing options...
Raysboostin Posted August 11, 2011 Share Posted August 11, 2011 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. Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5962498 Share on other sites More sharing options...
slippylotion Posted August 12, 2011 Share Posted August 12, 2011 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. Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5963391 Share on other sites More sharing options...
zei20l Posted August 12, 2011 Share Posted August 12, 2011 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?? Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5964167 Share on other sites More sharing options...
capturedcreation Posted August 13, 2011 Author Share Posted August 13, 2011 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? Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5964264 Share on other sites More sharing options...
zei20l Posted August 13, 2011 Share Posted August 13, 2011 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 Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5964294 Share on other sites More sharing options...
The Bogan Posted August 13, 2011 Share Posted August 13, 2011 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. Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5964377 Share on other sites More sharing options...
pipster11 Posted August 13, 2011 Share Posted August 13, 2011 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) Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5964491 Share on other sites More sharing options...
Sunkist Posted August 15, 2011 Share Posted August 15, 2011 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! Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5967072 Share on other sites More sharing options...
zei20l Posted August 15, 2011 Share Posted August 15, 2011 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. Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5967116 Share on other sites More sharing options...
Sunkist Posted August 15, 2011 Share Posted August 15, 2011 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 Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5967128 Share on other sites More sharing options...
zei20l Posted August 15, 2011 Share Posted August 15, 2011 dude, SAME tyre specs. you have shown a 195 and 185 there, of course they will be different. Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5967136 Share on other sites More sharing options...
Sunkist Posted August 15, 2011 Share Posted August 15, 2011 how else would you change the angle of the wall? oh wider wheel - yeh according to the sight iains right which is strange lol Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5967141 Share on other sites More sharing options...
zei20l Posted August 15, 2011 Share Posted August 15, 2011 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 Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5967145 Share on other sites More sharing options...
zei20l Posted August 15, 2011 Share Posted August 15, 2011 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 Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5967155 Share on other sites More sharing options...
Sunkist Posted August 15, 2011 Share Posted August 15, 2011 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. Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5967158 Share on other sites More sharing options...
zei20l Posted August 15, 2011 Share Posted August 15, 2011 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 Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5967173 Share on other sites More sharing options...
Sunkist Posted August 15, 2011 Share Posted August 15, 2011 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 Link to comment https://www.sau.com.au/forums/topic/373541-tyres/page/2/#findComment-5967195 Share on other sites More sharing options...
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