Sfchung Neutral Newbie July 9, 2003 Share July 9, 2003 I am currently using 215/55/16 tyres. I was using a "tire size calculator" to compare different sizes in case tyres don't comes in the size I want. When I compare 215/55/16 with 225/55/16 ,the calculation shows that the diameter difference shows 1.68%. According to the calculator, it is safe to use the alternative size. In addition, the calculator also says as it is safe as logn as it stays within 3% of the original. Question is, is this true? If the 3% rule is true, I would be able to use 205/55/16, 205/60/16, 225/50/16 tyres. It opens up many possibilities. http://www.1010tires.com/TireSizeCalculator.asp ↡ Advertisement Link to post Share on other sites More sharing options...
E36UDM Neutral Newbie July 9, 2003 Share July 9, 2003 Hope this helps....... Point to note: 1 inch = 25.4mm. You need to know that because tyre/wheel manufacturers insist on mixing mm and inches in their ratings. Also note that a certain amount of artistic licence is required when calculating these values. The tyre's rolling radius will change the instant you put load on it, and calculating values to fractions of a millimetre just isn't worth it - tyre tread wear will more than see off that sort of accuracy. Lets take an average example: a car with factory fitted 6x14 wheels and 185/65 R14's on them. Radius of wheel = 7 inches (half the diameter) = 177.8mm Section height = 65% of 185mm = 120.25mm So the rolling radius for this car to maintain is 177.8+120.25=298.05mm With me so far? Good. Now lets assume I want 15 inch rims which are slightly wider to give me that nice fat look. I'm after a set of 7x15's First we need to determine the ideal width of tyre for my new wider wheels. 7 inches = 177.8mm. The closest standard tyre width to that is actually 205mm so that's what we'll use. (remember the tyre width is larger than the width of the bead fitting.) Radius of wheel = 7.5 inches (half of 15) = 190.5mm We know that the overall rolling radius must be as close to 298.05mm as possible So the section height must be 298.05mm-190.5mm = 107.55mm Figure out what percentage of 205mm is 107.55mm. In this case it's 52.5% So combine the figures - the new tyre must be 205/50 R15 ....giving a new rolling radius of 293mm - more than close enough. Check out this website for more indepth bro. http://www.chris-longhurst.com/carbibles/i...tyre_bible.html Link to post Share on other sites More sharing options...
Saaber Neutral Newbie July 9, 2003 Share July 9, 2003 yep, it is true, but best is to stay with the original size so that the speedo calibration stay true....unless you do a +1 or +2 change.... Link to post Share on other sites More sharing options...
Soya Supersonic July 9, 2003 Share July 9, 2003 3% deviation is still considered acceptable but that's usually applicable for +1 or +2 upgrades. juz remember; larger rolling circumfrance deviation = more 'drag' (esp if u start increasing tyre width) Link to post Share on other sites More sharing options...
Nanoman Neutral Newbie July 10, 2003 Share July 10, 2003 Anyone care to enlighten me on what do you mean by +1 or +2 upgrades sort of thing ? Link to post Share on other sites More sharing options...
Virus 2nd Gear July 10, 2003 Share July 10, 2003 Read this for more info. http://www.chris-longhurst.com/carbibles/i...tyre_bible.html Simple explanation: When increase the size of rim, eg 15" to 16", the tyre wall height U get must be lower to maintain overall turning radius. Slight different in turning radius is acceptable, just need to take note of the Speedo & Odometer will run out. Link to post Share on other sites More sharing options...
Soya Supersonic July 10, 2003 Share July 10, 2003 +1 means upsizing your rims by 1 inch compared to stock size, i.e 205/50/16 to 215/40/17, while still maintaining the 3% rolling circumfrance deviation. Link to post Share on other sites More sharing options...
Zrun Neutral Newbie July 19, 2003 Share July 19, 2003 (edited) If i want to get 225/45/17 I must get 17x8 wheels? 25.4mm x 8 = 203.2, which is quite abit less than 225. Or I should search for 17 x 8.5. I am considering 225 40 17 by forcing it abit to -2.5%. Is the performance increase worth it? Going from 45 to 40 profile. Searching for lightweight rims, can anyone recommend? So far, cheap and light is Konig Helium, and Racing Hart CP-035 http://www.wheelspecs.com/specs/wheelmodels/312 My nissan used to be 225/16/50, now my toyota is 205/16/55 and 1 foot taller, cannot stand the handling. Edited July 19, 2003 by Zrun Link to post Share on other sites More sharing options...
Virus 2nd Gear July 20, 2003 Share July 20, 2003 I'm using 17x7.5 rims for 225/45/17 tires. Frankly speaking, I still confuse on this rims width. Why different rim width can support same tires width?? Or reverse way, why same rim width can support different tire width?? Anyone like to enlighten me ?? Link to post Share on other sites More sharing options...
Zrun Neutral Newbie July 20, 2003 Share July 20, 2003 Just found out a cheap imitation set of the Racing Hart CP-035 ($700 SGD EACH, 17x7.5 13 lbs) It is called Rota Subzero, looks the same, weight 16.5lbs, cost only $200 SGD each. http://www.wheelspecs.com/specs/wheelmodels/350 Link to post Share on other sites More sharing options...
Eyke Supercharged July 21, 2003 Share July 21, 2003 (edited) coz rubber can stretch. when rim width ~= tire width --> side wall of tire will be straighter |__| when rim width < tire width ---> side wall of tire will be slanted __/ Edited July 21, 2003 by Eyke Link to post Share on other sites More sharing options...
Virus 2nd Gear July 21, 2003 Share July 21, 2003 OIC ! Thanks !! But in this case won't it affect the tire construction, thus affect safety/performance?? Link to post Share on other sites More sharing options...
Eyke Supercharged July 22, 2003 Share July 22, 2003 (edited) there's an acceptable range of rim width for each tire, check with tire manufacturer for the range. check this out: www.dunloptire.com/tiretech_101/tire_width/index.htm Edited July 22, 2003 by Eyke Link to post Share on other sites More sharing options...
Zolidlim Neutral Newbie August 30, 2003 Share August 30, 2003 Saw from the site, it stated the +1 concept. Ok, now my current tire run at 175/65R14. I am upgrading to 15", so it should be 195/55R15, am I right? And based on the caculator, the diff is -1.22% if I use 195/50R15, as the mechanic said its better, and wont feel the drag and pinch in wallet. But again, based on the concept, it should be 195/55R15, and it is +2.22%. So which is more suitable?? Link to post Share on other sites More sharing options...
Saaber Neutral Newbie August 30, 2003 Share August 30, 2003 Either 185/55 r15 (-0.2%) or 195/50 r15 (+1.2%) ....195/55r15 no good (+2.1%) Link to post Share on other sites More sharing options...
Zolidlim Neutral Newbie August 30, 2003 Share August 30, 2003 Different calculation?? funny le... Nm, i will take 50, instead of 55. Link to post Share on other sites More sharing options...
Saaber Neutral Newbie August 30, 2003 Share August 30, 2003 195/50 would be good enough lah...since it is a more common size and thus can get better price... ↡ Advertisement Link to post Share on other sites More sharing options...
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