Tyre measurements

[tezarity]

Hey guys,
Have been looking at getting a new pair of 17inch tyres.
However, with so many to choose from i was hoping someone could explain to me the differences with width, aspect ratio and offset. (i.e wider tyres mean better grip?)
I've got no idea when it comes to these things, just looking for better performance for track and also everyday.

Thanks

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[sooty]

So you're after the differences in the effect that they have?
Width, you're not going to be going too wide anyway, i think the stock 17"s on the SRi run 225/45/R17 or similar. That should be fine for track work, is the width most of the guys run on their 18"s on the vxr's etc for track days (rory's burg)
Aspect ratio about 40-45 is good. Anything lower than that leaves you pretty much no flex in the sidewall so if you hit some curbing you can buckle the wheel, and generally the extra sidewall height gives you some flex in the sidewall to slightly (very slightly) reduce wheelspin (think dragster's massive tyres, you actually load up the sidewall to release the energy without wheelspinning, don't know how prominant this effect is in normal tyres though)
Offset is just how far the wheels sit out, lower offset = further out. So i guess if you went for +35, you're technically increasing your track width by 2cm all round on the same car with wheels that are +45. I doubt you'd be able to feel too much difference though. (i don't know if you could get away with +35 without some plastics modification to the inner guard, depends on the camber you're running)

[tezarity]

Okay, maybe i should have asked for a simplified answer.

Keeping in mind my very limited knowledge and the fact i take almost everything on board,

The reason i'm getting 17's is that i've been told i'm getting too much sidewall flex on my stock 16's and that getting 17's would solve the problem.
However going to 18's would actually slow the car down and be illegal.

So your saying that 225/45/R17 would be ideal?

Just browsing Ebay and looking around the $150 mark max each.
Trying to figure out what's best
235 45 17 NEXEN Performance Tyres N5000

235-40-17 PIRELLI DRAGON TYRES

NEW 235-45-17 TYRES Federal 595 SS

NEW 215-45-17 TYRES Federal 595 SS

NEW 205-40-17 TYRES FEDERAL 595 SS

[tezarity]

or the 235/45/17 94V BRAND NEW NANKANG NS2

[guy 27]

However going to 18's would actually slow the car down and be illegal.

won't slow the car down but you just need to make sure you have a good solid suspension setup and 40 - 45 profile tyres on them
those tyres you have recommend. the only ones i would consider at the Pirelli's but they are more suited as a road tyre than a track tyre.

here are some to consider in the 17's in the size ain has recommended.

http://cgi.ebay.com.au/4-X-NEW-225-4...ts_Accessories Great track tyre but dont expect a long life out of them

http://cgi.ebay.com.au/225-45-17-94W...ts_Accessories Excellent tyre in the dry, can get a little slippery in the wet

http://cgi.ebay.com.au/Kumho-225-45-...ts_Accessories Good track and road tyre. My pick for price vs value and well worth it if your going to get the car on the track more than once a year.


Just read your price limit. To be honest, save up a bit more. Tyres are the only thing between you and the road. Having had 3 different sets of tyres on my car in the last week, each set has very different characteristics. I don't think i would ever purchase low or mid range tyres. They just don't feel safe. I.e. braking distance tripled with mid range tyres and my high end tyres, major tenancy to understeer with low end tyres.
do yourself a favour even if it takes a bit longer and save for something nicer. You will thank yourself should you ever need to get out of an emergency situation.

[sooty]

Ah sorry mate. Ok, so on the 16's you have a 55 aspect tyre (205/55/16) which means the sidewall height is 55% of the width of the tyre.
As you increase the rim size, you decrease sidewall size (aspect) and as such there's less give in the sidewall. This is good to a point. 225/40/18 is the wheels that the stock sri-t comes with, and are perfectly legal. I'm not completely sure on the sri 17's but I'm pretty sure it's 225/45/17. Either will be fine for track, but the tyres and wheels themselves will be cheaper for 17's, so you can stick with them if you don't mind the looks.
With tyres, you need extra load tyres, that is tyres with a load rating greater than 91. You'll see on most tyres have like 93Y or something, the number is weight rating (you need higher than 91) and the letter relates to the speed rating, unless you're going over 200km/h it shouldn't be much of an issue.
If it's predominantly track work you're looking for, and don't mind about a shorter lifetime, search for semi-slicks. They're more a grip directed tyre as opposed to fuel economy or road noise.

Edit: confirmed 225/45/17 is the SRI size, on a 17*7" rim and the stock tyres are 91V load/speed

any questions just say

[tezarity]

Thanks Ain.
Think i've got it now.

If stock is 225(Width)/45(Sidewall aspect)/17(Diameter)
Ideally i would want the same as changing the sidewall aspect would be putting my speedo off?

Also, would it be possible to put a 235 tyre on or will it be too wide for the wheel?

[sooty]

Thanks Ain.
Think i've got it now.

If stock is 225(Width)/45(Sidewall aspect)/17(Diameter)
Ideally i would want the same as changing the sidewall aspect would be putting my speedo off?

Also, would it be possible to put a 235 tyre on or will it be too wide for the wheel?

Yeah 225/45/17 should keep your speedo pretty right. You can use a tyre calc to see the diff, but will be less than 1%.
I believe you'd probably need at least a 7.5" wheel for a 235 tyre, but unless you can get them considerably cheaper as a more common size than 225, it's probably not worth it

[tezarity]

Thanks again mate.
Picking up a set of SRi 17's on Saturday.
Then off to the tyre shop we go.

[J]

Sorry I only read this now, tezarity, but to be totally honest (and I do apologise if I seem really direct, but I need to say this for your sake): if after planning to get new 17's, I only have $150 to spend per corner on new 225/45R17's, I would scrap the idea of getting the new rims while I still can (you can always go that option when you have more money), and spend, say, at least $200 each on new 225/50R16's. They should go on your standard rims no problems, and, as a bonus, they will also provide extra kerbside protection for your existing 16's!

Just read your price limit. To be honest, save up a bit more. Tyres are the only thing between you and the road. Having had 3 different sets of tyres on my car in the last week, each set has very different characteristics. I don't think i would ever purchase low or mid range tyres. They just don't feel safe. I.e. braking distance tripled with mid range tyres and my high end tyres, major tenancy to understeer with low end tyres.
do yourself a favour even if it takes a bit longer and save for something nicer. You will thank yourself should you ever need to get out of an emergency situation.

Sadly, I have to agree with guy 27. There is a *world* of difference between even the low and mid range tyres, let alone the high range ones. Enough of a difference for me to believe that, if you are only spending $150 on a 225/45R17, besides a *slightly* better steering response (especially when you are only going up by 1 inch), everything else will likely to be *inferior* to your standard 205/55R16 (they are Bridgestone Turanza ER300's right?), including grip. Which means it largely defeats the point of doing the upgrade for better performance...?

Look, put it this way: at any given time, 4 postcard-sized patches that are channelling all the accelerating, braking, and cornering forces, are *all* you have from losing control and hitting something. Even if the $150 225/45R17 is ok for normal driving, they are unlikely to offer the extra safety margin you need when you least expect it eg. a sudden need to tighten your cornering line in order to avoid a collision. I won't even talk about using them on a track...unless you prefer to do it very slowly!

Ever wonder why there are so many sets of not 4, but *3* near-new rims with low end tyres on sale on Ebay? There is a reason for that...and it doesn't take a rocket scientist to work it out!

So, provided you can still get reasonably decent tyres, and you only do tracks occasionally, I would strongly recommend the Bridgestone Potenza RE001 Adrenalin. Personally, they perform noticeably better than the Toyo Proxes 4 I used to have (this is 215/40R17 on a Astra G SRi T). Even on low tread now, it still grips fine (i.e. no need for traction aids/stability control intervention) when cornering with reasonably good speed in the wet, so long as you have a careful right foot. I can't say the same about the Silverstone FTZ Sport in the Corsa C (195/50R15) though, which almost killed me in the wet. For not much more $ than the FTZ Sport's, I replaced them with the Adrenalin's: it was a *world* of difference! In fact, so impressed am I with the Adrenalin's, that I am running them in my Mum's Mazda6 as well (215/45R17). They actually grip when Mum tries to start going up a hill, unlike the old squabbling made-in-Japan Turanza ER30. Even Mum notices the improvement, which gives her a lot more confidence. In fact, she loves it! Which means come replacement time for the SRi-T, the Adrenalin's will again be at the top of the list.

Anyway, I digress. So, to wrap up: I'd seriously consider to not get the rims, and just get higher-end 225/50R16's. You may even find the improvement to be more than enough for your needs for quite a while!

P.S.: In case you have not already done this, instead of going straight for a tyre shop, try ringing up many different tyre shops, specify what tyre and size you want, and ask for the best price they can do. You will be amazed at all the different quotes you get for essentially the same thing, and can save you heaps!