what size tyre?

[deanb90]

So my wheels are nearly here for my NC and the time has come to decide on what tyres to get.

Wheels are BBS RG 17x9 +40. The car will be extremely low via BC coilovers that i have bought.

Question is what size tyres can/should i run? I wont be doing much track work, maybe 2-3 times a year. I am tossing up between 215 45 and 225 45. Reason for the smaller tyres is because of the size/width/offset of the wheels - to prevent scrapage and extensive gaurd rolling.

225 seems to be the minimum to go on a 9" wheel, will there be much difference if i run a 215?

Would a better quility tyre in 215 perform better than a middle range 225 tyre?

I wont be cheaping out on tyres regardless of what size, i will probably end up with KU36 or similar, depending on what price i can find.

Your input is greatly appreciated.

Regards,
Dean

[NitroDann]

Huh, 9 inch wide rims....215 tyres.... Why? Just get 245/45s Which is the minimum those rims should run. People usually buy 9 inch rims to run 275 Hoosiers on them

Dann

[sailaholic]

Come on dann people don't by 9 inch rims to run big hoosier tires for a non track car.

OP, 25.4 * 9 = 228.6 mm. so tires below that size will be stretched. I doubt you would notice the stretch on 225.

The issue of stretch and "fitment" is very much down to personal acceptance.

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[NitroDann]

Ok so there is only 2 reasons people buy them. Ive outlined one. We all know the other.

Dann

[deanb90]

225 is barely a stretch. 225 = 8.85 inches.

I bought the wheels purely for looks, to give the mx5 a better stance. I wasn't planning on getting wheels anytime soon but i got these for $500 landed so i snapped them up.

In a nutshell, will there be a lot of difference in handling/grip between 215 and 225 on my wheels? Tyres will be good quality.

Cheers,
Dean

[pcmx5]

Dean, I had 17x8 et45 with 225x45s on my NC and they fitted pretty snugly(ride height 330mm) so you may have clearance issues with anything bigger given that you are going to come a fair bit more towards the outside than I did.
Another thing to consider is that you are effectively making the gearing taller and the NC is very tall standard.

Peter.

[Bizi]

Dean, that's an exceptional buy.
NC owners like Peter will be able to comment on any issues with 225 tyres and rubbing.

Can you get your preferred tyres in both 215 & 225 widths? I would have thought 225 would be more commonplace at this profile but could be wrong. Ditto what Peter said about rolling diameter - or at least be aware of what difference it might be between the two.

[Charlie Brown]

First up you need to fit 245x40 tyres to a 9" rim. 215 and 225 cross section is too small.
Go here to make your tyre selection http://www.tirerack.com/tires/TireSearc ... iameter=17
You will find it cheaper to import rather than buy here but do some ringing around. Delivery from the US to Sydney is $380USD. Keep the tyre cost below $1,000 and you pay no duty/GST.

Next you really need to look and read this article http://www.mazdatalkforum.com/viewtopic.php?f=12&t=811 that has a 45 offset, 5mm further in than yours.

Next, as we have previously said in an earlier post to you, the lower you go the more rolling of the guards you will need and make no mistake, you need to roll the guards with these wheels.

Next, don't sell your stock rims because if/when you get defected you will need to refit them to clear the defect.

Finally, as PCM has pointed out, your acceleration will now suck, so start looking around for a 4.1 diff, if you can get one before me and Sailor and…..

[sailaholic]

Cb, can you expand on why 225 tires would be too small a section?

Not a challenge, genuine interest in your reasoning / knowledge
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[deanb90]

thanks for the quick replies everyone.

There is so much mixed opinion about this topic, it's very hard to make a choice. Some people say 225/45 is fine, some say to small? With 245/40 i will be faced with extreme fitment issues, i will have to extensively roll the guards and possibly flare them, even then i won't be able to have the car at the height i want.

possibly a good medium is 235/40? Just don't want to get a set of tyres and then realise they don't fit inside the guards etc.

As for gearing, i am now spewing. I just missed out on a 4.444 gear set for NC, bidding was at $160, new it is 160,000yen! If i had of known that the wheels will dramatically affect gearing i would have bought the diff center, i was told 4.444 is to much.

Has anyone experienced 225/45 on a 9" rim?

Cheers
Dean

[pcmx5]

thanks for the quick replies everyone.

possibly a good medium is 235/40? Just don't want to get a set of tyres and then realise they don't fit inside the guards etc.

.

Has anyone experienced 225/45 on a 9" rim?

Cheers
Dean

Sorry to be a wet blanket Dean but i don't think a 235 section will fit under the guard on 17x9 et 40 based on how close mine was one inch narrower and 5 mm et less.

I would be asking the tyre store to do a deal where you mounted one wheel and tried it front and back to test it before commiting yourself.
Maybe a super aggressive alignment may help but if you are compromising everything just to use these wheels then maybe you may need to consider selling them on.

i ended up with 215/45's on 17x8 et 45 and a 4.1 diff and it was a great set up both for handling and performance.

Good luck in whatever you do,

Peter

[deanb90]

225/45 it is.

Cheers everyone

[Charlie Brown]

225/45 it is.

Cheers everyone

225 is optimal on a 9" rim.

225/45 will fit, but isn't "optimal" as it is at the extreme end of the fitting chart.

The rim range for a 225 tyre is 7.5" to 9". A 235 tyre is 8" to 9.5". Obviously the optimal width is half way between the two limits.

Dean, in your case the 225 selection is probably the best you can do with these rims and hopefully you'll not need to big a roll on the guard.

You will be dictated to your minimum height by where the rear tyre hits the guard.

You will find the minimum height for the fronts is 330mm, measured from the centre of hub vertically to the guard. This height will just get you over speed humps at shopping centres, driving very slowly.
Next, set the rake of the car between 5 to 10mm higher at the rear. Measure this from the bottom of the crimped sill seam just behind the front wheel to the same point just in front of the rear wheel.
The rear height for the hub to guard lip will then be in the region of 330 - 335mm but the rake dimension is more important. If the rears hit the guards you will need to raise the car but keep the rake in the same 5 to 10mm range.

For other NC’ers, this is the minimum height for bearable street driving on a 225/45/17 tyre. For a 215/45 it’s 5mm more and a 205/45, 10mm more than the 225 due to the difference in tyre diameter.

[sailaholic]

Cb, thanks for your explanation, but why are you going for the middle of a fitment range being the best?

I know its a neat method for the mind, but have you read anything to indicate this to be correct?

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[Charlie Brown]

225/45 will fit, but isn't "optimal" as it is at the extreme end of the fitting chart.

The rim range for a 225 tyre is 7.5" to 9". A 235 tyre is 8" to 9.5". Obviously the optimal width is half way between the two limits.

225 is optimal on a 9" rim. Plenty of data to prove its faster on a 9" rim vs an 8" rim.

http://www.miataturbo.net/showthread.php?t=60292&page=2

If you read that link it refers to slicks and R Spec tyres, not road tyres.
Emilio talks about a 275 section slick on a 10" rim and tyre design, saying a 11" & 10.5" rim was no advantage. So it comes down to tyre design for certain rim widths.

Cb, thanks for your explanation, but why are you going for the middle of a fitment range being the best?

Again you need to consult the tyre manufacturers tables detailing the correct rim design widths, they are after all the experts, not us.

I know its a neat method for the mind, but have you read anything to indicate this to be correct?

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