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Upsizing Wheels Fiesta


Zektic
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Hello all. I bought 17 inch OEM ford alloys and I want to fit them onto my 2013 Ford Fiesta. I currently have 15 inch steel wheels with 195/50/R15 Tyres.

I am aware that in order to keep the speedometer accurate I will have to match the same overall diameter of the wheel, although I can't figure out what size of tyre I will need to match the 15 inch wheels, I know it will have to be a lower profile but I can't work it out.

Any help would be appreciated.

 

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I had a look at a speedo error calculator and the closest match would be 205/35 R17 but you won't find a tyre in that size. You are more than likely going to have some degree of error whatever you do.

http://www.willtheyfit.com/index.php?width=195&aspect=50&diameter=15&wheelwidth=6.5&offset=40&width2=205&aspect2=35&wheel_size=17&wheel_width=11&offset2=20


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Can you explain it to me in laymens terms please? If I fit the alloys and reduce the sidewall size of the tyre as close to the original as possible will it really mess up the speedo that much? Also of so can I not get the speed calibrated for the new size and rolling circumference? 

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Or could you suggest a tyre size I can find within about 2 percent? As the speedo on my fiesta already shows about 5MPH above what im actually doing.

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Or could you suggest a tyre size I can find within about 2 percent? As the speedo on my fiesta already shows about 5MPH above what im actually doing.


I'm not great at explaining things, and I don't fully understand the workings of all this. The link that @Frembrit posted has a good explanation without getting technical. I still can't find a tyre that is going to give you a similar diameter.

You say that your speedo reads 5mph over what you are actually doing, what have you based this on, and at what speed? If you are 5mph at 30mph (true speed) then you are nearly 17% out, if it's reading 5mph out at 60mph (true speed) then you are approx 8% out.

Hopefully someone will come along and give you some advice based on personal experience as I have just picked up information from others.


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The rule I've always known is to keep within 3% of the original diameter, I believe this is generally the rule most tyre / wheel places will keep to.

On my last car (ST24) the standard tyre size was 205/50/16 and I used 215/45/17 when I fitted some Focus ST170 alloys. +2.29%

On my current car the standard is 235/40/19 and I use 235/45/18 winter tyres on Focus ST250 18" alloys. - 0.3%

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um, yes. 195/40/17. +2.08%

Probably not going to be an issue as you've got Ford alloy wheels, but to give you something else to think about, what's the width of the 17" alloys that you're bought and the offset? It should be stamped on one of the spokes and will say something like 7Jx17 ET40....7J is the width of the wheel and ET40 will be the offset (distance) the mounting face of the hub is from the centre line. And what is it on the 15" wheels?

Jonro2009's web link will show information about how the 17's will sit on the car compared to the 15" wheels.

 

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7Jx17H2 for the 17 inch wheels and I can't currently see behind my steel wheels as they are already on my car however I've measured the width of the both of them and it looks like the 17 inch alloys are about 1.5 inches wider than my current wheels?

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195 tyres will fit the 7J wheels from what I can see on the web, tyres wont be cheap though for 195/40/17. I think the ST's use 205/40/17 which are cheaper, but this size will make the difference +3.47%, not massively over and will be ok to use I reckon. 

When I went back to 16" wheels on the ST24, I used 205/55/16 tyres instead of 205/50/16 as they were much cheaper, the difference in size was +3.44%. This equates to 62 mph when the speedo read 60mph. Never had any problems with this, and I think speedos generally under read as standard anyway.

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@frembrit I think I will fork out the cash for the 195's if they fit 😀 Can you link me to the info in regards to them fitting please?

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Just fit 205/40/17 like all the other fiestas with 17" wheels, the speed error will be small, it's slightly out anyway.

Fit then go for a drive with a sat nav displaying the speed and see what the speedo indicates when the sat nav is saying 30, 40, 50 etc, then remember it for when you're driving.

All fiestas with 17s from the factory have steering rack limiters which are a few £ from Ford and clip on.

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  • 2 years later...

there are websites out there that you can compare different size wheels, i did the same with mine as i have 205/40r17 alloys and wanted a steel wheel as a spare and turns our the correct size if 195/55r15 with very minimal effect to the speedo (0.03% - 30mph = 30.02mph)

https://www.oponeo.co.uk/advice-and-tips/tyre-size-calculator#replacementsCalculator

follow that link and you can compare multiple sizes to match what you need for your car.

FYI you wanna look at a 215/35r17 to match a 195/50r15

hope that helps

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