Topic

By: Gsouth
Posts: 15
Joined: 30/05/10

Tire Size, Please Help.

Posted: May 30 2010 Tags: size, tire, tires, tyre, tyres, wheel, wheels Views: 185

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I have searched the forum for posts on my specific question, but cant find any, sorry if this has been asked before, but here it goes.

I recently bought a 2006 MX5 NC, but to my utter surprise and terror it arrived with 215/40R17 size Tires on the rear and 205/45R17 Runflats on the front, and firstly I just want to discourage, no, WARN anyone even remotely considering putting runflats on an MX5 to JUST DONT DO IT, AT ALL, EVER!!!

It tramlines to the point that it is dangerous to any living creature in its immediate surroundings, even at slow speeds (+- 40km/h).

But getting back to my question, needless to say, I am going to replace all 4 tires this coming week, and was considering maybe going for 215/45R17's all round, for the simple fact that they are slightly cheaper than the standard 205/45R17 normally fitted to the MX5.

Now finally for my question, has anyone got any experience with the above mentioned size I am considering, are there any downsides to going with 215/45 instead of sticking with the 205/45's, and then I would also want to know, specifically about the fuel consuption and performance, is there a noticable difference in performance, especially acceleration, as in my previous vehicle, when deciding to go to slightly bigger tires, there was a huge difference in acceleration, maybe partly because its 0-100 figures should be measured on a calender instead of a stopwatch anyway, but that is another topic alltogether.

Any swift replies would be much appreciated, because I drive about 100km's a day and am very affraid of putting myself into a ditch because of the runflats.

Thanx guys.

Replies

RE: Tire Size, Please Help.

What a weird combination. Point taken on Runflats, I believe they have quite a harsh ride. Your back tyres would gear you down slightly. I have tried different sizes in my NA when I owned it to see what would happen to the gearing. Instead of 185/60 R14 I tried 185/65 R14. Didn't seem to make much difference except give me a smoother ride. At a true 100 kph (62.5 mph) it showed 105 instead of 107 for the original size. I doubt whether 10 mm width difference will make more than 1 mph change to your speedo reading. You can always check it with a Sat. Nav. I assume the tyres have the same speed rating and MOT will not be checking your tyre sizes. Out here a car doesn't get inspected till it is 5 years old. Welcome to the forum anyway. I hope you enjoy our little idiosyncrasies. We do go on sometimes.

Own a 2001 Green Mazda MX5. Have previously owned a 1990 and 1998 model.

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Posted: May 30 2010 By: Brian Posts: 698
RE: Tire Size, Please Help.

First of all, even if the width, profile and load index are the same, it's not a good idea even to mix different brands of tyre on the MX-5, so having different sizes and constructions of tyre must be a nightmare.

As has been raised many times on here, the overall diameter of 215/45 tyres is quite a bit more than that of 205/45 tyres (the 45 being a percentage of the tread width, not a measurement), so your speedometer will under-read. In theory, acceleration would be blunted, but in reality the difference would probably be insignificant.

One point to note is that your insurance company may take a dim view of non-standard tyre sizes.

Edit - Brian's reply wasn't displaying when I replied - typical of this wonderful forum software

Je suis un Scottish Fiver! - The GNU - 07 2.0 Sport, Eibached and Pro-Gripped

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Posted: May 30 2010 By: OchAye Posts: 2598
RE: Tire Size, Please Help.

If the 215/40s you have on the rear are good why not keep them and match the fronts with them? The 40% profile on the greater width actually results in more or less the same size profile as the 205/45 - Hope that makes sense.

Having said that I went for 215/45 and it is surprising the difference the profile makes to the look of the car, it only works out to a few mm (6 I think) but the tyres look much 'fuller' in the arches and I like this compared to the 'elastic band' look of the standard ones, it is a personal preferance though. As these have a slightly larger rolling radius you speedo will read slightly lower than before although I find mine still higher than the GPS speed.

Oh, also worth a mention is that some insurance companies may consider this a change so possibly best to talk to them also. Hope it goes well for you.

EDIT! Neither of the above replies were showing when I posted (this bl**dy useless web site!) so apologies for the repetition.
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Posted: May 30 2010 By: GDCobra Posts: 2911
RE: Tire Size, Please Help.

On my spare/track set i run 215/40/17's with no problems at all.

Only when i go back to my michelin exalto 205/45/17 do i feel a difference.

The main reason being the other tryes are Hankook RS2's & are only slightly less grippy than R888's
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Posted: May 30 2010 By: g40steve Posts: 607
RE: Tire Size, Please Help.

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Je suis un Scottish Fiver! - The GNU - 07 2.0 Sport, Eibached and Pro-Gripped

Posted: May 30 2010 By: OchAye Posts: 2598
RE: Tire Size, Please Help.

30/05/2010 03:47:09, GDCobra said:
"
If the 215/40s you have on the rear are good why not keep them and match the fronts with them? The 40% profile on the greater width actually results in more or less the same size profile as the 205/45 - Hope that makes sense.

Having said that I went for 215/45 and it is surprising the difference the profile makes to the look of the car, it only works out to a few mm (6 I think) but the tyres look much 'fuller' in the arches and I like this compared to the 'elastic band' look of the standard ones, it is a personal preferance though. As these have a slightly larger rolling radius you speedo will read slightly lower than before although I find mine still higher than the GPS speed.

Oh, also worth a mention is that some insurance companies may consider this a change so possibly best to talk to them also. Hope it goes well for you.

EDIT! Neither of the above replies were showing when I posted (this bl**dy useless web site!) so apologies for the repetition.
"

Actually they only have about 1.5mm left, so need to be replaced anyway, also i dont like the look of them at all, they look much too small and lost in the wheel arches.

I also looked at a tire diameter calculator from http://www.tyresave.co.uk/tyresize.html and according to that the 215/40's are 1.95% or 12mm smaller than the 205/45's where as the 215/45's are 1.46% or 9mm larger, so there seems to me a smaller difference.

Did you find any noticable difference in the acceleration or fuel consumption of your car when you changed to the 215/45's?

Oh, and is there any difference in the handeling departement?

Thanks for all your help, any and all replies are much appreciated.
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Posted: May 30 2010 By: Gsouth Posts: 15
RE: Tire Size, Please Help.

O, and ive already spoken to my insurer and they have no problems.

Thanx for all the help from you guys so far.

Posted: May 30 2010 By: Gsouth Posts: 15
RE: Tire Size, Please Help.

I recently had Goodyear F1 215/45/17's fitted to my Zsport, in place of the original 205/45 Michelins.

I too think they look a bit better. Also you get a bit more protection against kerb damage. They're quieter than the Michelins too. And my lowered car is now marginally easier to get out of.

A small disadvantage, as far as I'm concerned, is that they've got a bit too much grip. On a couple of familiar roundabouts where previously there was a nice touch of oversteer, the car now hangs on until I become afraid of a inside wheel leaving the ground!

I can't say I've noticed any change in fuel consumption or performance - too many other variables . .

Overall though I would rate this change as a success.

And a quick plug for Event tyres - great on-the-driveway service, competitive delivered/fitted prices, and no problem with dodgy Thai F1's.

Chris

Posted: May 31 2010 By: slowered Posts: 33
RE: Tire Size, Please Help.

Slowered,

What is the load rating on the Goodyears ? Reason I ask is that I toyed with upping to a 215/45 but found the F1 s being offered by the likes of Blackcircles had a load rating of 91 (OE tyres 84) which I thought might be too stiff for a lightweight car.

Posted: May 31 2010 By: pugwash Posts: 95
RE: Tire Size, Please Help.

31/05/2010 10:09:53, slowered said:
"
I recently had Goodyear F1 215/45/17's fitted to my Zsport, in place of the original 205/45 Michelins.

I too think they look a bit better. Also you get a bit more protection against kerb damage. They're quieter than the Michelins too. And my lowered car is now marginally easier to get out of.

A small disadvantage, as far as I'm concerned, is that they've got a bit too much grip. On a couple of familiar roundabouts where previously there was a nice touch of oversteer, the car now hangs on until I become afraid of a inside wheel leaving the ground!

I can't say I've noticed any change in fuel consumption or performance - too many other variables . .

Overall though I would rate this change as a success.

And a quick plug for Event tyres - great on-the-driveway service, competitive delivered/fitted prices, and no problem with dodgy Thai F1's.

Chris

"

I also considered buying the Eagle F1 Asymmetrics, but found alot of people saying that you dont get great milage out of them, the main reason i thaught of going for Michelins is that they get good milage according to alot of the guys ive spoken to who got them standard on their MX5's when they bought them new.

Posted: May 31 2010 By: Gsouth Posts: 15