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Old 08-27-2003, 18:12   #1 (permalink)
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confused Can someone explain tyre sizes to me?

Hi,

I have standard 15 inch ELXR6 mags (the ugly spoked ones) and I have some badly badly BADLY worn yokos on them atm. They are 215/60/15s apparently. I have a spare in my boot (a michy) that is a 205. My question is.. what do these numbers mean? Is it a wider tyre? Are wider tyres better? I want good grip in the wet... I hate driving the XR in the wet, she does 360s.

I'm looking for a cheap way out of getting tyres, I was thinking of buying a nice set for the front (some 215s) for around $160-$180 and some second handy 205s for the back. ($35 each :)

Is that odd? Will it make the car look wierd? What about handling? Legal?

I don't care about back tyres, I don't do burnouts but my back tyres do wear fast from quick takeoffs and cornering.

Any advice would be appreciated :)
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Old 08-27-2003, 18:56   #2 (permalink)
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Re: Can someone explain tyre sizes to me?

the first numbers of the tyre refer to the width in millimetres eg, 225/60R15 is 225mm wise, the next number refers to the height of the side wall, its a percentage of the width ( anyone know exact formula? )
There isnt much price difference between a set of 205 - 215' or even 225's, You can get some decent tyres ( 225/60R15 ) for arounf $150 each but there are cheaper options out there, no name brands etc
It would also be better to have the wider tyres on the back rather than the front

Wet weather:

Wider tyres are generally thought of as WORSE in the wet, however, theres some major factors that play a part in it, tyre compound for one, but most of all, tread design. You want something with nice thick channels to spray the water out back/sides, skinny tyres with "tight" tread will perform hopelessly in the wet when compared to wider tyres with wide channels etc
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Old 08-27-2003, 19:32   #3 (permalink)
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Re: Re: Can someone explain tyre sizes to me?

Quote:
Originally Posted by SiX_iN_a_RoW
the first numbers of the tyre refer to the width in millimetres eg, 225/60R15 is 225mm wise, the next number refers to the height of the side wall, its a percentage of the width ( anyone know exact formula? )
There is no formula. The number '60' as in this case, is just 60% of the width.
It represents, 'Aspect ratio'.

A 235/45/17 is 235mm wide, with the sidewall height being 45% of the width.

BTW, the last number is always the rim diameter (you forgot to mention that).

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Old 08-27-2003, 21:14   #4 (permalink)
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Re: Can someone explain tyre sizes to me?

you forgot to mention, that if you change the width of your tyres, and dont change your aspect ratio, then you will affect the rolling diameter of the tyre, therefore messing up your gearing, speedo accuracy and oddometer readings.
For instance if you have a 205/60 that means you have a sidewall of 123mm, however if you go to 215/60 then you have a sidewall of 129 mm, and 225/60 makes 135mm sidewall. Therefore a 225/ 60 has apporximately 24mm extra in diameter, therefore making your overwheels larger. All speedos will be out. So Consider this when you are selecting a wider tyre with the same aspect ratio.

I remeber when i got my Datsun 1600, it had 78 aspect tyres on it, now my TS has 40 aspect. What a difference.
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Old 08-27-2003, 22:51   #5 (permalink)
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Re: Can someone explain tyre sizes to me?

Also the Z, or H that is usually in between the numbers, like on my wheels it's 255/40ZR17, where the ZR means the speed rating, usually you don't need to worry too much about this, unless you are on H rated tyres and plan on doing over 180 on regular occasions. Probably not a good idea! I think HR is up to 180 Kp/H, ZR is over 260 I think, but I'm pretty sure I am wrong, but you get the idea.
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Old 08-27-2003, 22:55   #6 (permalink)
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Thanks for the replies guys, always helpful as usual. Another question.. so if I get 215 or 225s, can I get a smaller wall size? Does that mean the 60 part of 215/60/15 can go down to 45? Would that stop the speedo from going out, but have wider, lower profile tyres?
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Old 08-27-2003, 23:12   #7 (permalink)
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Re: Can someone explain tyre sizes to me?

For a car like a falcon, tyre fitters dont usually recommend going lower in a side wall size than 60. You can get tyres such as a 225/50/15 but fitters only recommend those for medium to small cars.

If you are that worried about the speedo being out, check your vehicle manual on what tyre size your car came out factory. I assume a 215/60/15??? not sure but if you decide on that size, get that size all round.

I've had a 245/60/15 on my 15x7in rim before but my speedo was out by about 4kph so I had to adjust my speed accordingly.

If your not sure look up your manual in your glove box or inside drivers door for factory tyre size and go by that.

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Old 08-27-2003, 23:15   #8 (permalink)
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Re: Re: Re: Can someone explain tyre sizes to me?

Quote:
Originally Posted by Soxx
BTW, the last number is always the rim diameter (you forgot to mention that).
Hehe, I assumed he already knew that

As for choosing which size to go for, go to http://forums.fordmods.com/phpBB2/documents.php?doc=30 theres a pretty decent tyre calculator on there
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Old 08-27-2003, 23:23   #9 (permalink)
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Re: Can someone explain tyre sizes to me?

dcliff1,

Your standard size unless I'm mistaken would have been 205/65/15.

Thus a 215/60/15 is only 1.3% smaller on diameter,
and a 225/60/15 is only 0.5% larger.

Your tread wear is probably more than that now. Both of these sizes are common replacements on 15" rims.

All you ever needed to know and more here;
http://www.chris-longhurst.com/carbi...yre_bible.html

Even a comparative calculator.
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Old 08-28-2003, 00:18   #10 (permalink)
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I'm reasonably sure that smaller tyres on the rear is illegal - but check with a tyre retailer or rta for sure . . .

In tyres, its a general case of "you get what you pay for" ... Generally, the more the money, the better tyre and better peformance in wet and dry . . .

Small tyres on the back do look pathetic (imo) - and if you buy cheapies, forget about those quick launches, cause all you'll be getting is quick smoke :)

I'd ask for bottom end of the performance tyre range, and specifically aim for wet weather performance . . .

Oh - and what the guys have been saying about the tyres is spot on ( markings etc). But - remember - grip is totally dependent on compound and tread design - not width - altho, as you go wider, you generally get better tyres ( softer compound and better tread pattern and more $$$$ )

Last edited by XR8 Lamah; 08-28-2003 at 00:22.
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