**Unofficial Tyre Thread**

[TW]Fox;24328475 said:
Presumably though the manufacturer has chosen that tyre size for a reason. You are increasing the size of the sidewall, after all.
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Only other option is to fit different alloys, but that's false economy.

I don't think a 1.5% increase in tyre profile is going to affect the car at all. I once changed the alloys on my Ford Focus 1.6 from 15" (195/60/15) to 17" (215/45/17) and it didn't make the car explode into a ball of flames...

Car's come with many different sizes and options of alloys when the car is initially sold. I doubt the manufacturer changes the set up of the car based on what alloys the customer chooses...
 
They do keep the rolling radius close though – which is why as the tyre size increases or the width increases the profile is reduced so that the overall diameter of wheel and tyre remains broadly constant.

Where manufacturers do have tyres fitted of different width but the same size, the profile is adjusted to counter this – which is why the rear tyre profile on say a 3 Series Sport is 35 compared to 40 at the front despite both being 18” wheels. The profile isn’t a fixed measurement – it’s a percentage of the width of the tyre.

You are not changing the profile of the tyre at all despite increasing the width, manufacturers avoid this where possible.

My point is that they presumably didn’t pull this tyre size out of the air for the lulz. There is presumably a reason why they picked it. Your car won catch fire if you fit randomly sized tyres to it but for the sake of just over a tenner a tyre saving why even bother? Ok its 40 quid over a complete set of tyres but it’s not as if you buy a new set of tyres every month is it, it hardly adds up to a large amount of money over your ownership period.

If the saving was 50 quid a tyre it’s probably worth thinking about further but I just can’t see the point in this example?
 
But what's the disadvantage?

Because the manufacturer didn't spec 215 instead of 205, so there must be a reason? What is the reason?

Better MPG? Will be marginal...

If I can save £15 a corner for no real disadvantage, then I don't see the harm.
 
rossk26 said:
But what's the disadvantage?

Because the manufacturer didn't spec 215 instead of 205, so there must be a reason? What is the reason?

Better MPG? Will be marginal...

If I can save £15 a corner for no real disadvantage, then I don't see the harm.
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Do you not trust the people who made your car?
 
panthro said:
For 19's thats a good price so I wouldn't be sad. Where did you buy them from?
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Black Circles - that is a fitted price too I guess (sent to a garage and fitted). I also got over 8,000 Tesco Clubcard points, which would be £80 at Tesco.

Camskill was cheapest, but was a faff to get delivery and get them fitted (not even sure if 4 tyres would fit in an M3).
 
hurfdurf said:
Do you not trust the people who made your car?
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There's probably a compromise somewhere, presumably manufacturers spec tyre size according to a combination of performance, cost and comfort, depending on the perceived target market/style of car.

My particular car rolled out of the factory with 16" with a larger profile and slightly wider 17"s with a lower profile depending on what model, and the 'more sporty' 17s were not just fitted to the slightly more powerful models and vice versa.

I don't see any issue at all with a slight change in size if your compromise is not quite in line with the manufactures vision for what's best.

Sure if I had a specialist or ultra high performance car I would more than likely stick to standard spec, but for the vast majority of average size, average power cars it much more personal preference really, and if that preference is to save £10 a corner, fine IMO.
 
hurfdurf said:
Do you not trust the people who made your car?
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Trust them for what?

They offered alloys in the following sizes:

195/65/15
205/55/16
205/45/17

The difference between 195/65/15 compared with 205/45/17 is 2.9% less on the speedo reading and a 2cm increase in diameter, and a reduction in sidewall height of 2.4cm...

Someone could spec the 17" tyres when the car can also be fitted with the 15" tyres...
 
rossk26 said:
Trust them for what?

They offered alloys in the following sizes:

195/65/15
205/55/16
205/45/17

The difference between 195/65/15 compared with 205/45/17 is 2.9% less on the speedo reading and a 2cm increase in diameter, and a reduction in sidewall height of 2.4cm...

Someone could spec the 17" tyres when the car can also be fitted with the 15" tyres...
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How do you know Mazda simply boshed other sized wheels on without changing the speedo calibration?
 
Firestar_3x said:
How do you know Mazda simply boshed other sized wheels on without changing the speedo calibration?
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I'm fairly sure they did adjust the calibration. But as I said above I'm not bothered about a .9 difference in reading at 60mph...

People said Mazda put that tyre size on for a reason. But what is that reason? How is fitting 215/45/17 instead of 205/45/17 going to ruin the car?
 
The MX5 NC tyres are 205/45/R17 standard, but apparently it's quite common to increase that size to 215/45/R17.

They are slightly cheaper, there are more tyres available and the increased profile may help ride quality slightly. Aesthetically the tyre looks better as well, giving a 'squarer' profile, and helping to protect the rim a little more.

Granted, the speedo will under read (by 0.9mph @ 60MPH). I am considering swapping to 215/45 at my next tyre change, as it seems this is the only negative effect.
 
[TW]Fox;24329836 said:
Then the standard size on 17 inch wheels is 205 50 17 not 45?

Which makes the whole thing different as your intended new size DOES now include a profile reduction to counter the increased width.
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Where did you find that information from? That tyre size applies to cars post 2008 I think

My budget would only allow for pre 2008, therefore the tyre size is 205/45/17 according to blackcircles anyway...
 
[TW]Fox;24329958 said:
My sister has a 3 so I will check it later for you :p
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I just put the registration plate into blackcircles and it gave the size.

There was a facelift which seems to be around 2007 (56) which changed the alloy style. And 205/50/17 were fitted. But before that the alloy style was fitted with 205/45/17.

Pre-facelift:
http://www4.autotrader.co.uk/classified/advert/201305116703963

Facelift:
http://www4.autotrader.co.uk/classified/advert/201305196837655

So would be it better to change 205/50/17 to 215/45/17? Rather than changing 205/45/17 to 215/45/17?
 
I just drove home on the AD08's and it started spitting with rain, I survived. How many miles do they say to bed in tyres from new, I forgot to ask?
 
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