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Discussion Starter · #1 · (Edited by Moderator)
Hi everyone,

I did a bit of a dodgy thing late last year and now want to repair it.

Tyre size: 205/55/16

I put 205/60/16s on the front and left the not-so-good 205/55/16s on the back as a temporary measure. Had no money but needed front tyres, so got some second-hand just to get us through. Due to confinement here in France, we haven't been driving very far anyway, and they were the only size the dude had in at the time, so I took them.

But I have noticed a very interesting thing. With the 60s, the speedo is correct. As in, the speed on the speedo matches the speed on the GPS. I've always felt like my car was going slower than it should be when I had the 55s on the front, and now it feels much more normal. The GPS confirmed this - with the 55s, my speedo was showing 80kph but the GPS said 73kph. With the 60s, it's dead on.

Now we have money and I want to replace all the tyres and fix her up. She's an epic car and deserves the love, and she'll be going for rego renewal in a few weeks too (Controle Technique here in France).

So I looked it up online but it states that the tyres need to be the 55s (or other sizes - wider and even lower profile), but that size puts my speedo out.

Question is: is it illegal to put 60s all-round? Or should I just use the 55s and add it up in my head? Or should I go for the 55s and pay to get the speedo adjusted, if that's still a 'thing'?

Of course I'd rather have the lower profile for more stability, but an accurate speedo is also very important to me when trying to navigate speed cameras and whatnot. In France they are stupidly strict, so accuracy is VIP.

Cheers luvs.
 

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Discussion Starter · #2 · (Edited by Moderator)
I'd also like to know if and why Ford calibrated the speedo to be lower than the actual speed. i.e. my speedo says 80kph, but the GPS says 73kph. Or is there something else going on?
 

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GPS may not that accurate, unless its a calibrated unit. The number of satellites can vary

and that can alter the accuracy.

Also a cars speedo must never under read. If your were doing 70mph and the speedo

showed 69mph it would fail testing.

Alter your tyre pressures and the speedo will also vary, manufacturers have to cater

for the car with different overall wheel/tyre heights. Your speedo accuracy will vary

depending on a new or used tyre and even down to the brand/build.
 

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All manufacturers calibrate their Speedos to read slightly higher than the actual speed of the veh. Average is usuall for Speedo to say 80kph when true speed is 75kph (approx 3 miles per hour difference at that speed)
Also as Purple says, a Speedo should never under read hence why manufacturers do what they do.
Also GPS is not always 100% accurate
 

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Does CT actually measure the displayed speed vs the actual speed of the tyres? Otherwise I wouldn't worry about it. You probably have slightly less margin for error when you drive past a speed camera. We have people driving consistently at 50kph indicated on my speedo (usually less, around 45 or even 40) it is absolutely frustrating when I have to downshift to 3rd gear to keep it in the rev. We have a radar with speed display which is supposed to tell you how fast you are going (and no, it doesn't read higher than 50kph, over 50, it tells you to slow down), it reads minimum of 5kph higher than my speedo. This is the government installed machines, so I would expect them to read slightly under as well, but at least there is consistency across different makes and models of cars so people can drive accordingly.
 

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Discussion Starter · #6 · (Edited by Moderator)
Does CT actually measure the displayed speed vs the actual speed of the tyres? Otherwise I wouldn't worry about it. You probably have slightly less margin for error when you drive past a speed camera. We have people driving consistently at 50kph indicated on my speedo (usually less, around 45 or even 40) it is absolutely frustrating when I have to downshift to 3rd gear to keep it in the rev. We have a radar with speed display which is supposed to tell you how fast you are going (and no, it doesn't read higher than 50kph, over 50, it tells you to slow down), it reads minimum of 5kph higher than my speedo. This is the government installed machines, so I would expect them to read slightly under as well, but at least there is consistency across different makes and models of cars so people can drive accordingly.
I don't think the CT measures the speedo or anything, but I am concerned that if I put 60s on it, when the tyre size should be 55s, that I'm breaking the law and it won't pass the CT!

That's why I asked the question.

And yes, as for the government installed machines, they tell you how fast you're going and with the 55s on, the speedo is showing 50kph but the machine is saying 47kph or so.
 

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Discussion Starter · #7 ·
After reading all your comments, I will go with the 'legal' size of 55s and do some calculations. It's just been nice with the 60s on to have a more accurate speedo is all. :)

Thank you for your responses!

As an aside, what should the pressure be in 205/55/16s (cold)?
 

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It's printed on the petrol flap (as well as the handbook) 30psi/210kpa for light load.

What is the threshold for speed camera ticket in France? I think it's 7kph here (unless long weekend holidays, then it drops down to 4kph - just got pinged last Easter)

Why don't you go for CT with the tyres you have on then if they fail, you can go back to 55. Otherwise you can buy 60 all around.
 

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Discussion Starter · #9 ·
It's printed on the petrol flap (as well as the handbook) 30psi/210kpa for light load.

What is the threshold for speed camera ticket in France? I think it's 7kph here (unless long weekend holidays, then it drops down to 4kph - just got pinged last Easter)

Why don't you go for CT with the tyres you have on then if they fail, you can go back to 55. Otherwise you can buy 60 all around.
I think the threshold is only something like 2kph. (!!!) The cops are barely ever around on French roads but when they do turn up, they're harsh. I have a friend who got done with a speed camera doing 82kph in an 80 zone...

Hmmm, not much printed on the petrol flap. I usually do 32 in cold tyres so I was pretty close. (Groan - I'm so special that I didn't think of that handbook, apologies for the stupid question.)
 

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I must have been super lucky - I was speeding for 5000km when I was there in 2019.

Here is the stuff.

lcB4dFl.jpg
 

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Discussion Starter · #11 ·
I must have been super lucky - I was speeding for 5000km when I was there in 2019.
Well, there are never any cops on the roads here anyway, and speed cameras are well-marked, but when they DO get you, they get you good. :)

I'm used to driving in Australia, where in the space of 1000km (driving from our house to my mum's house - 11.5 hours on the road) one day, there were 23 cop cars with cameras, cameras on the overhead bridges, many fixed speed cameras, and a private firm that the NSW government hire to check your speed on the side of the road with tiny signs warning you way too late that they're checking your speed.

Here there is next to nothing.

And thanks for the pic, mate. :) Helpful! I'll check out my car for that.
 

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I understand Aussies never got Mk 3 Mondeo, which is a great shame.

It's a brilliant car (ok probably a tad small for Oz)

I wouldn't mind an AU XR6 but they are either all trashed or rusted and falling into pieces here...
 

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Okay, quick question while I've got everyone's attention! :)

I am trying to find the name for this piece in French.

I think in English it's called a rear suspension track control tie bar trailing arm. Please correct me if I'm wrong!

Mine's effed. That explains why there is a sagging in the back left! I know exactly how and why this happened: a friend jacked up my car and didn't have the car in gear. It rolled forward off the jacks and whatnot and everything got jammed under the back wheel. Hence the serious bend.

I need to replace it ASAP. The first pic is the rear right. All goodly. The next photos are of the stuffed one on the left.

01.jpg

02.jpg

03.jpg

04.jpg
 

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