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Old 11-09-2017   #1
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17" Alloys too big for a 1.2 8v GP?

Hi there and thanks to anyone that decides to respond! Basically I have heard that 17" alloys are too big for the power of the 1.2 Active 8v which is understandable. Is this the same case with 16"s also? IMO 17"s look great but I'd rather not have to replace my gear box in the future for the sake of them.
Thank you!
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Old 12-09-2017   #2
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Re: 17" Alloys too big for a 1.2 8v GP?

Hi Mitch (I guess) and welcome on board !

How on earth would wheels be too big for an engine / gearbox ?
If you install reasonable size tyres on them with the correct height/width ratio, the development (distance by turn) will be the same, or very similar so there will not be any extra load on engine / GB...

Little reminder:

Tyre circumference = (2x (width x ratio) + Rim eight) x 3.14
Exemple 185/70/15= (2x (185 x 0.70) + (15 x 25.4)) x 3.14 = 2 010 mm
Equival. 185/55/17= (2x (185 x 0.55) + (17 x 25.4)) x 3.14 = 1 995 mm

Do the reverse math with your current tyre size and you'll find what you need, but keep in mind than USUALLY, the big alloy are often LARGER than smaller ones ! This is given by the second number of the rim, ex: 17 x J6,5 would be 165mm width (internal) and you cannot mount any tyre on any rim !

BRs, Bernie

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Old 12-09-2017   #3
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Re: 17" Alloys too big for a 1.2 8v GP?

Isn't it more the case of the wheel weight?

i.e. trying to spin up a wheel several kgs heavier than standard puts undo strain on the box leading to failure, worse when coupled with aggressive driving?
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Old 12-09-2017   #4
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Re: 17" Alloys too big for a 1.2 8v GP?

There are several theories and discussions on this
so no doubt will rage on
Probably biggest cause of issue with fitting larger wheels is also the other mods which are used which then can cause a detrimental affect on the accelerated wear and tear of other parts, lower stiffer suspension,hub spacers,etc.
The way i see it if Fiat and the dealers sell the wheels and fit them to various models then there cant be a huge issue
A lot of the components of the cars are the same throughout the range any way
I have also even seen the 900cc twin air with the 17"two tone wheels on (the same style as my wheels) as a factory option
I have a 1.2 8v not noticed anything untoward other than the steering is slightly heavier due to the wider wheel/tyre and mpg is very slightly less again wider wheel/tyre.
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Old 12-09-2017   #5
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Re: 17" Alloys too big for a 1.2 8v GP?

Makes sense that the steering will be heavyer and the mpg less attractive if one INCREASE the tyre width; in my exemple the width are equal ...
More metal but less rubber, the moment of inertia should be almost the same; and BTW how about moving the 1.2 tons of the car, THIS is a big inertia !

Installing 17" alloy rims will not over-stress the powertrain if the tyre width is kept the same and the w/h ratio is adapted to get the same development.
The look will improve, the car will be more 'direct' on steering (less flex of rubber), but the comfort will deteriorate proportionnaly ...

BRs, Bernie

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Old 12-09-2017   #6
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Re: 17" Alloys too big for a 1.2 8v GP?

Quote Originally Posted by Bernievarian View Post
Makes sense that the steering will be heavyer and the mpg less attractive if one INCREASE the tyre width; in my exemple the width are equal ...
More metal but less rubber, the moment of inertia should be almost the same; and BTW how about moving the 1.2 tons of the car, THIS is a big inertia !

Installing 17" alloy rims will not over-stress the powertrain if the tyre width is kept the same and the w/h ratio is adapted to get the same development.
The look will improve, the car will be more 'direct' on steering (less flex of rubber), but the comfort will deteriorate proportionnaly ...

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)
Thanks a lot for the detailed reply, Bernie.

The only 17s i have seen are 205/45/17? never really heard of 185/55/17.
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Old 12-09-2017   #7
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Re: 17" Alloys too big for a 1.2 8v GP?

Quote Originally Posted by derbyshire gp View Post
There are several theories and discussions on this
so no doubt will rage on
Probably biggest cause of issue with fitting larger wheels is also the other mods which are used which then can cause a detrimental affect on the accelerated wear and tear of other parts, lower stiffer suspension,hub spacers,etc.
The way i see it if Fiat and the dealers sell the wheels and fit them to various models then there cant be a huge issue
A lot of the components of the cars are the same throughout the range any way
I have also even seen the 900cc twin air with the 17"two tone wheels on (the same style as my wheels) as a factory option
I have a 1.2 8v not noticed anything untoward other than the steering is slightly heavier due to the wider wheel/tyre and mpg is very slightly less again wider wheel/tyre.
So do you have 205/45/17s on your 1.2 8v? How long have you had them? I've just heard some horror stories and don't fancy fitting a new gear box anytime soon...
Cheers.
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Old 12-09-2017   #8
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Re: 17" Alloys too big for a 1.2 8v GP?

205/45/17 tyres
been running them for just over 18 months now
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Old 13-09-2017   #9
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Re: 17" Alloys too big for a 1.2 8v GP?

Quote Originally Posted by MitchGP View Post
Thanks a lot for the detailed reply, Bernie.

The only 17s i have seen are 205/45/17? never really heard of 185/55/17.
Maybe they simply don't exist with this particular combination (though I think that's what they were on my Tipo 16V, but on 16").
Anyway, that was more for demonstration purpose, one may even find tyre vendors with corresponding tables for various size/ratio...

BRs, Bernie

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