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 Post subject: Non standard tyres
PostPosted: Wed May 17, 2017 4:00 pm 
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I have just had some skinnier non standard 145/65/15 front tyres fitted to my Smart car which previously had 155/60/15. I believe skinnier tyres give better fuel economy but wider ones are better for grip.

I see some of you have fitted 195/45/R15 to you bugs, this is quite a big difference to the standard 14" ones fitted as standard. Why do you do it? Is it for looks or for performance reasons.

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 Post subject: Re: Non standard tyres
PostPosted: Wed May 17, 2017 4:39 pm 
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There are a lot of misconceptions about tyre and wheel sizes. I'd go in to it but I don't proclaim to understand much more than half of it. Instead I'll link to the guy that does know.

http://www.carbibles.com/tyre_bible_pg3.html

Worth a read.

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 Post subject: Re: Non standard tyres
PostPosted: Wed May 17, 2017 5:46 pm 
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Skinnier tyres will also give less contact patch for braking, so potentially the wheels will lock earlier. Its not just about section width, but pressures and vehicle weight, tyre compound etc. A higher weight per unit area of a tyre could cause the tyre pattern to deform, so creating extra drag than a trye wider and not deforming. In general there is a good reason why a tyre is fitted as standard and I personally would not fit narrower tyres. I do run my EVs at higher pressures (well within the load ratings) On the C1s I run at about 34psi, and they cope with the extra weight on the front end perfectly OK.
Often putting a wider tyre on a car can give you unexpected results, we all assume wider tyre = greater grip, but a wider tyre will have a larger area so load per given area will be reduced. On hard compound tyres that could mean less actual grip, and depending upon the tread pattern, could actually mean less rubber on the road. Many high performance tyres have huge channels in the tread, to clear water , but actually have less rubber in contact with the road. Good for soft ground though.
All the above is why makers specify a certain tyre, as thats what they have beased their specification on. Strictly speaking , if you couldnt stop in the makers specified distance on a specific tyre, because you have fitted a non standard tyre, you could ultimately be considered as having some liability. Thats also why Insurance companies ask if you have modified the vehicle, and why they somtimes refuse to pay out.
If a tyre is a factory option then its not an issue. The smart Pulse has wider tyres than the passion.


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 Post subject: Re: Non standard tyres
PostPosted: Thu May 18, 2017 8:59 am 
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I presume therefore that you wouldn't fit larger wider tyres for the same reasons?

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 Post subject: Re: Non standard tyres
PostPosted: Thu May 18, 2017 9:10 am 
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I would suggest you advise your insurance company that you have non-standard tyres fitted, even if your wheels are stock. Technically you've modified the car from the Smart spec, unless that size tyre was available as a factory option.

Did you consult anyone before fitting narrower tyres?


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 Post subject: Re: Non standard tyres
PostPosted: Thu May 18, 2017 9:23 am 
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ade33 wrote:
Did you consult anyone before fitting narrower tyres?


All I said to the tyre fitters was that my car had narrower tyres on the front and that I wanted the same size. They then went ahead and fitted 145/65/15 because I guess 155/60/15 weren't available in that size.

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 Post subject: Re: Non standard tyres
PostPosted: Thu May 18, 2017 1:11 pm 
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Yes I have fitted larger tyres in the past, in the 80s I built street rods for a living. Mostly people were after an image, a bit like over stretching tyres on over wide banded steel wheels. Most wide tyres were from the US and were far from technically advanced. Many still Bias ply (half way between a radial and a crossply)
Most people have no idea about the implications of fitting a different wheel / tyre. And assume that just putting bigger tyres and wheels will give a getter handling vehicle. Far from it. If you go to seriously short sidewalls, with no give then the ride will be substantially harsher, and the shock life will be reduced . Also hit a pothole and you will almost certainly get rim damage. Out here in the sticks our roads are totally rubbish and a 60mm pot hole is not unusual.
Often larger rims are chosen to allow larger brakes. So a tyre appropriate to the opening and use is important.
On my electric smart, I have the larger 195 tyres (rear) as against the 175, only because they look better , and being wider they probably handle better, especially with the extra weight.
Personally I would not put narrower tyres (145)on the front of my Smart which already has the 175 option, and frankly works well, and rarely locks up. Im certain the ABS would have to do greater service with the narrower tyres and the roads I use.
Looking at the Smart handbook, the 145 was not an option , so strictly speaking you should inform your insurance company you are using non standard tyres.


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 Post subject: Re: Non standard tyres
PostPosted: Thu May 18, 2017 1:21 pm 
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nlel wrote:
ade33 wrote:
Did you consult anyone before fitting narrower tyres?


All I said to the tyre fitters was that my car had narrower tyres on the front and that I wanted the same size.


I still can't get why, seeing as you are so particular about your car being by the book, that you would arbitrarily change tyre size, apparently on a whim.

Still, it's your car. I would still inform my insurance though.


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 Post subject: Re: Non standard tyres
PostPosted: Thu May 18, 2017 1:34 pm 
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ade33 wrote:

I still can't get why, seeing as you are so particular about your car being by the book, that you would arbitrarily change tyre size, apparently on a whim.

Still, it's your car. I would still inform my insurance though.



I would prefer to have the proper sized tyres fitted but its too late now they have fitted these 145/65/15 so not much I can do about it.

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Electric Windows
Air Conditioning
Smart Radio 9
Panoramic Sunroof
Luggage Compartment Cover
Softouch Automatic Gear Programme
Bodypanels & Tridion Cell in Silver Metallic
15" Alloy Wheels


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 Post subject: Re: Non standard tyres
PostPosted: Thu May 18, 2017 3:06 pm 
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You can go back and complain....

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