Jellybean Posted January 21, 2011 Share Posted January 21, 2011 Stock sizes are Front - 235/45R17 Rear - 255/40R17 I currently run a 35/275 tyre; using a 30 profile will get me closer to the Stock Rolling Radius I dont know if this is a stupid question but what is the advantage of having your car closer to the rolling Radius? I am just a bit concerned using a 30 profile; heard some horror stories about the new BMW's; tyres popping all the time Quote Link to comment Share on other sites More sharing options...
johnny g Posted January 21, 2011 Share Posted January 21, 2011 Moved out of tech to Supra Chat. Your speedo is calibrated to the Rolling Radius. Keeping it closer keeps your speed more accurate. Quote Link to comment Share on other sites More sharing options...
TTRickeh Posted January 21, 2011 Share Posted January 21, 2011 The closer you are to the stock rolling radius the more accurate your speedo should be and the closer you will be to the standard gearing. I wouldn't bother with a 30 profile on a 275 tyre personally, I have 30 on a 285 (not on stock wheels) and wish i'd gone 35. Quote Link to comment Share on other sites More sharing options...
dr_jekyll Posted January 21, 2011 Share Posted January 21, 2011 bigger wall = more grip Quote Link to comment Share on other sites More sharing options...
johnny g Posted January 21, 2011 Share Posted January 21, 2011 bigger wall = more grip Not neccessarily, it means it's more predictable at the limit, but not always more grip. Quote Link to comment Share on other sites More sharing options...
dr_jekyll Posted January 21, 2011 Share Posted January 21, 2011 iv allways found that when i test the same model tyre a 265-40-18 felt much better than a 265/35/18 came in quicker and held on in the constant circle alot better same test, different model tyre 285/35 vs 285/30 , same result, so i go by that Quote Link to comment Share on other sites More sharing options...
Jellybean Posted January 21, 2011 Author Share Posted January 21, 2011 I was going to go with the 35/285 tyre next just to get better rim protection (Filthy -- sounded better in my head) but will have my car on the 30 profile closer to the stock rolling radius improve handeling is probably my main question; can somebody explain the standard gearing too please Quote Link to comment Share on other sites More sharing options...
Scott Posted January 21, 2011 Share Posted January 21, 2011 http://www.mkivsupra.net/vbb/showthread.php?237553-Understanding-the-Rolling-Radius-and-the-tyre-Profile It's not THAT old Quote Link to comment Share on other sites More sharing options...
Jellybean Posted January 21, 2011 Author Share Posted January 21, 2011 (edited) http://www.mkivsupra.net/vbb/showthread.php?237553-Understanding-the-Rolling-Radius-and-the-tyre-Profile It's not THAT old I seen that alright but was just more interested in Advatages / disadvatages of having my car setup close to the rolling radius plus how people find the 30 profile due to the BMW horror stories if I go to a 30 profile I will be closer to stock but my ride height will drop; on the rear is ok but not the front ; if going to a 30 profile will no improve handling/ run a higher risk of tyre issues and allow me to have a more accurate spedo then pants to that I am staying with a 35 profile Edited January 21, 2011 by Jellybean (see edit history) Quote Link to comment Share on other sites More sharing options...
Scott Posted January 21, 2011 Share Posted January 21, 2011 In order to have the exact same rolling radius as the stock wheel/tyre combo the profile would have to be 31.3333%. Clearly you cannot have an exact profile so you then decide which of the closest profiles would suit you best. In this instance 30 would be the closest to stock choice. Some people may favour 35 in order to bring more comfort, this would throw out the speedometer further though Near the end, it throws out the speedo. You run the risk of blowouts due to hitting potholes and the likes. That's just the risk you take with big wheels and low profile tyres. THey don't have as much give in the sidewall. Quote Link to comment Share on other sites More sharing options...
Jellybean Posted January 21, 2011 Author Share Posted January 21, 2011 So in short 30 profile versus a 35 profile Advantage more accurate speedo Disadvantage Not as comfortable Higher risk of a blow out Lower ride height (in my case) Quote Link to comment Share on other sites More sharing options...
TTRickeh Posted January 21, 2011 Share Posted January 21, 2011 can somebody explain the standard gearing too please Changing the radius of your wheels is a bit like changing the final drive (diff), think of it like the last gear cog in your drivetrain, it alters your gearing, so it can change your acceleration/top speed. Bigger wheels = taller gearing = slower acceleration but higher top speed. If you're just talking about a change in profile of 5 on near enough stock sizes I wouldn't be too concerned about the gearing effects though. Quote Link to comment Share on other sites More sharing options...
Jellybean Posted January 21, 2011 Author Share Posted January 21, 2011 Changing the radius of your wheels is a bit like changing the final drive (diff), think of it like the last gear cog in your drivetrain, it alters your gearing, so it can change your acceleration/top speed. Bigger wheels = taller gearing = slower acceleration but higher top speed. If you're just talking about a change in profile of 5 on near enough stock sizes I wouldn't be too concerned about the gearing effects though. cool thanks Quote Link to comment Share on other sites More sharing options...
Scott Posted January 21, 2011 Share Posted January 21, 2011 What size are your wheels? I can't comment on the size difference without knowing them Are you still on 17s? Quote Link to comment Share on other sites More sharing options...
Dnk Posted January 21, 2011 Share Posted January 21, 2011 (edited) There is quite a differance going from 30 - 35 profile on a 275 width tyre on a 17" diameter wheel, its 27 mm in diameter or 13.5 mm radius !!! On an 18" wheel with 275 width tyre the differance between 30 - 35 profile is 28 mm diameter or 14 mm radius Edited January 21, 2011 by Dnk (see edit history) Quote Link to comment Share on other sites More sharing options...
Jellybean Posted January 21, 2011 Author Share Posted January 21, 2011 What size are your wheels? I can't comment on the size difference without knowing them Are you still on 17s? Volk Racing GT-C Face 2 Wheels Size:5X114.3 19X10.5J (REAR) Volk Racing GT-C Face 2 Wheels Size:5X114.3 19X9.5J (FRONT) Quote Link to comment Share on other sites More sharing options...
Scott Posted January 21, 2011 Share Posted January 21, 2011 If it's 17" alloys then the 35 profile is closer to stock. Stock = 635.8 Diameter or 317.9 Radius 275/30 = 596.8 Diameter or 298.4 Radius 275/35 = 624.3 Diameter or 298.4 Radius Quote Link to comment Share on other sites More sharing options...
Scott Posted January 21, 2011 Share Posted January 21, 2011 (edited) Volk Racing GT-C Face 2 Wheels Size:5X114.3 19X10.5J (REAR) Volk Racing GT-C Face 2 Wheels Size:5X114.3 19X9.5J (FRONT) Ahh, 19s are a totally different kettle of fish. Stock = 635.8 Diameter or 317.9 Radius or 1996.4 Circumference 275/35/19 = 675.1 Diameter or 337.55 Radius or 2119.814 Circumference (Speedo will read 6% higher) 275/30/19 = 647.6 Diameter or 323.8 Radius or 2033.464 Circumference (Speedo will read just under 2% higher) To be honest you could go with either. The speedo reading 6% higher will probably just make it spot on as they tend to read a fair bit lower, as per Jake's comment in my thread. Take your pick Edited January 21, 2011 by Scott (see edit history) Quote Link to comment Share on other sites More sharing options...
Dnk Posted January 21, 2011 Share Posted January 21, 2011 A 275 tyre on a 19" wheel using 30 profile is 1.89% bigger than stock or 6 mm in radius using 35 profile it's 6.13% bigger than stock or 19.5 mm radius Quote Link to comment Share on other sites More sharing options...
Jellybean Posted January 21, 2011 Author Share Posted January 21, 2011 they are the same Measurements I got but I am more interested in the Adv/ and Dis-advs of having my wheel as close the the rolling radius? I would rather run the 35 due to a lower risk of tyre blow outs but will using a 30 improve handeling Quote Link to comment Share on other sites More sharing options...
Scott Posted January 21, 2011 Share Posted January 21, 2011 they are the same Measurements I got but I am more interested in the Adv/ and Dis-advs of having my wheel as close the the rolling radius? I would rather run the 35 due to a lower risk of tyre blow outs but will using a 30 improve handeling 35 will improve the corner grip, will be quieter, will have more flexibility and will protect the wheel better. The downfall is that it will put the speedo out from stock by around 6% and will probably be more expensive. Just as a sidenote, the difference in risk between 30s and 35s with regards to blowouts will be next to nothing. If you hit something hard enough to pop a 30 profile tyre the 35 won't take much more punishment and you will probably have a bust wheel anyway. Quote Link to comment Share on other sites More sharing options...
Jellybean Posted January 21, 2011 Author Share Posted January 21, 2011 35 will improve the corner grip, will be quieter, will have more flexibility and will protect the wheel better. The downfall is that it will put the speedo out from stock by around 6% and will probably be more expensive. Thanks that all I need 35 it is so I taught it was a more determental effect Quote Link to comment Share on other sites More sharing options...
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