Tyre Size Question (Advice Please)

[DannyH]

Hi All,

 

I was just looking for some advice, i have the standard Rays wheels on my 350z and the tyres on them are 245 45 18's, i have the opertunity to buy some 255 45 18's, my question is will these be ok???

 

Will have any problems as thats the last thing i want.

 

Thanks

 

Danny

[H5]

Standard rears are 245

 

http://www.350z-uk.com/forum/viewtopic.php?t=4361

 

Going wider than the rim would look wierd, not sure about any safety implications though.

[Trev-the-Rev]

They would also alter your gearing and speedomer readings due to the rolling radius being greater.

[Cool Hand Luke]

Maybe i'm missing something but how would adding a wider tyre alter the rolling radius?

 

I was under the impression the rolling radius would only be altered if you changed the profile of the tyre (and/or the size of rim) i.e going down to a 40 series tyre or up to a 50 series tyre.

[Trev-the-Rev]

The the height of the tyre will alter as you change the overall width. Thats why a 205 45 looks lower in profile than a 225 45.

[Ekona]

Yup, the second number is the height of the sidewall expressed as a percentage of the width, which is in mm.

[Cool Hand Luke]

Yeah i know that but if you look at his first post he is going from a 245 45 18 to a 255 45 18 - thats not going to affect the rolling radius in my opinion.

[Ekona]

Not by much perhaps, but it will alter it for the worse. 45% of 255mm is more than 45% of 245mm.

 

 

*EDIT* using this handy site, with 255 tyres on the speedo will read 1.3% too slow.

[Trev-the-Rev]

Not by much perhaps, but it will alter it for the worse. 45% of 255mm is more than 45% of 245mm.

 

That's quite correct. The end result in this instance will be a slight lengthening of the gearing and a speedometer that reads under.

[Cool Hand Luke]

Yeah - it does only seem like a small change cant see it being that noticeable but take the point if it was say an increase from 205 to 245 or something. I'd always stick with the standard sizings anyway

[z-man]

There is a difference. 245 x 45 x 18 has an overall diameter of 26.68 inches (678 mm) whereas 255 x 45 x 18 has an overall diameter of 27.04 inches (687 mm) so the difference is 9 mm (1.33%).

[SAFC99]

Stick with the 245's!

[DannyH]

Thanks for all the replys people, thought i had a good deal aswell. oh well lokks like im still on the hunt lol

 

Thanks again

 

Danny

[Chris`I]

A 1% difference in the rolling radius should not effect the TC or anything like that and 255 should be fine for an 8.5" wheel (which Rays are on the rear iirc). All you will find is with wider tyres is a buldging look as it is the widest that the wheel will take.

 

Check with Phil@ESR, Adam@Z1, Kev@Envy for their views, but as far as I can see the tyres will fit. Personally I still wouldnt use them as they just "feel" too wide to me.

[jonathan73]

Depends if you like fat rears - I do. But not on my women!

 

I went with 265 40 18s when my Potenzas becamse slicks. I Had the GT4 wheels though which I believe were 8.5J on the rear; 8J on the front.

[rmmackfc]

Doesn't just effect rolling radius does it? The friction coefficient would be higher as there is extra rubber footprint being put on the road. Tyre calculators are the best judge though, as long as the rim will take it.

[DannyH]

so let me get this riight, i can use 255 45 18 tyres, and also stay safe? and the only effect i will have is my speedo will read 1% slower?

 

Thanks

 

Danny

[jonathan73]

Danny, what REALLY matters is whether your rim width will take a wider tyre.

 

After extensive research I found that my 8.5J rims could take up to 285 but 265 would be more comfortable and not be at risk of popping off the rim when high speed cornering (on a track of course). I believe regular Rays are 8J so you should be fine with 265 and definitely 255.

 

As for the rolling radius..... :yawn:

[DannyH]

thanks for putting it clear mate, guess ill make an offer on them, thanks again for all comments and advice

[Senya]

here is tire calculator with rim width advice http://www.1010tires.com/TireSizeCalculator.asp