Blundered into a well hidden camera van the other day, and though I think I was a bit over (60 limit) according to the speedo, hope I should be ok as the force concerned operates to the guidelines.

Anyway, it got me thinking about speedo accuracy which I know has been touched on previously.

From what I've read the legal standard is that speedos must not understate actual speed, it may overstate it by up to 10% + 6.25mph, so theoretically you could be doing 40 with the speedo reading 50.25, which seems a heck of a variation.

One of the car mags did some tests on various makes (not Ford, unfortunately) a few years back, and while they found a couple that were virtually 100% spot on (I think they were SEATs), most over read by around 3mph on average.

Just out of interest, wonder if anyone has seen anything similar on the accuracy or otherwise of Ford speedos.

 

Dunno how good gps apps are on smartphones, could always ask a friend family member to hold your phone when at 60/65/70mph etc to see what gps speeds report and extrapolate from there? Especially if you have any long straight roads with minimal obstructions to the gps signals like trees buildings etc?

Yes, that's a good thought. I actually have the mph per 1,000 rpm in each gear figures for the Fiesta 140 somewhere, so I could check my own car that way. I was just wondering whether Ford speedos in general tended to be regarded as accurate.

 

My 2008 Merc C class would show the GPS calculated speed on the satnav display.  I wish my 2019 Focus did the same....

Not sure, but I think that the requirement is that speedos (not the sort you wear in the pool!) should be within 10% at 30 MPH.  Generally, they over-read by this amount (ie +3MPH) on the basis that if speedos under-read, the manufacturers may be liable to legal action if you were prosecuted for exceeding the limit, when the indication was that you were not.

If you do have a stand alone GPS, it is a good idea to compare the GPS and the speedo.  On the M27 in Hampshire, where we currently have a average speed camera enforced 50MPH limit, car speedo reads about 52MPH, when GPS reads 50MPH.

Based on a sample size of a 2007 Mondeo, a 2011 Focus and a 2017 Mondeo, the speedo over-read by 3mph at 70mph when compared to the same Tomtom. So that suggests some consistency at least. 

8 hours ago, erictcleric said:

Based on a sample size of a 2007 Mondeo, a 2011 Focus and a 2017 Mondeo, the speedo over-read by 3mph at 70mph when compared to the same Tomtom. So that suggests some consistency at least. 

Thanks for that. So,that's about the same as the average in the magazine test I mentioned. 

 

 

My Golf over reads by about about 3mph at any speed.  It doesn't get any less accurate the faster you go like old speedo's used to.

Trouble is, now I know that, I generally drive at 3mph over the indicated limit.  

6 hours ago, TomsFocus said:

My Golf over reads by about about 3mph at any speed.  It doesn't get any less accurate the faster you go like old speedo's used to.

Trouble is, now I know that, I generally drive at 3mph over the indicated limit.  

A risky plan!

Found those test results I mentioned above, which I think were originally done by Auto Express. Some of them are pretty near 100% accurate.

 

Model	True speed at indicated 30mph	True speed at indicated 50mph	True speed at indicated 60mph	True speed at indicated 70mph
Kia e-Niro First Edition	27mph	47mph	57mph	67mph
BMW i3s	28mph	48mph	58mph	68mph
SEAT Arona 1.0 TSI 115	29mph	49mph	60mph	69mph
SEAT Tarraco 2.0 TDI 150 manual	29mph	49mph	59mph	68mph
Skoda Kodiaq 2.0 TDI 150 manual	28mph	48mph	57mph	67mph
Peugeot 5008 BlueHDi 130 manual	28mph	48mph	57mph	68mph
Volvo XC40 D4 auto R-Design	30mph	49mph	59mph	69mph
Mazda MX-5 2.0	27mph	48mph	58mph	68mph
Dacia Duster dCi 115	28mph	48mph	58mph	68mph
BMW 330i M Sport	28mph	48mph	57mph	67mph

I wonder if tyre wear affects the reading? As they wear they get smaller, ok only about 5-6mm but is it enough to make a diference?

If tyre size had no impact on the reading then bigger wheels would leave you speeding when you didn't know, and smaller wheels you'd be thinking you were doing a ton in 3rd ... OK I'm exagerating, but you get my point?

1 hour ago, fiestaecoboostman said:

OK I'm exagerating, but you get my point?

Yes, I've read that the difference between brand new tyres and a set worn to the absolute legal minimum can affect the speedo reading by 2-3%. So at, say 70 it would be over-reading by a couple of mph.

On 9/15/2020 at 4:41 PM, Eric Bloodaxe said:

I actually have the mph per 1,000 rpm in each gear figures for the Fiesta 140 somewhere, so I could check my own car that way. 

 

Driving on a long straight traffic free road this morning I thought I'd do a rough check. Held the car spot on 2,000rpm in 6th, and the digital speed readout said 56. According to my info the 140 (having lower overall gearing than other 1.0 Fiestas) is supposed to do 26.16 mph per 1,000 rpm in 6th, so should have read 52 or 53 at 2,000. Not the most scientific test I know, but I repeated the exercise several times with the same result, so it suggests it over-reads by 3mph or more.

I might have a go at downloading an app, having a quick search I didn't realise there were so many available. Anyone used one they would recommend - preferably free and simple!

 

 

 

 

 

Both google maps and waze have digital speed readouts.

I use GPS Test Plus

https://play.google.com/store/apps/details?id=com.chartcross.gpstest&hl=en

Gives you a lot of other informtion like signal/noise ratio etc, and does have a HUD facility

PS Martin I like your image.......

My new Focus's speedo appears to be extremely accurate. V impressed.  My last Focus was about 10% out (the right way) and my car before that, an Audi A3, was hopelessly inaccurate.

47 minutes ago, Paulkp said:

PS Martin I like your image.......

😎 UTA and all that.

3 hours ago, Linds said:

My new Focus's speedo appears to be extremely accurate.

You'll need to take that into account then, less margin for creeping over the limit in error!😀

Done a few more rough checks of rpm versus indicated speed as mentioned earlier in the thread, and it does seem that my speedo under-reads by up to 4mph. Not necessarily a bad thing in helping to keep to the limit. It does confirm my gut feeling though. Ever since I've had the car, it seems to get up to (indicated) speed remarkably quickly, but never feels "fast" and people always seem to want to overtake. Now I know why!

1 hour ago, Eric Bloodaxe said:

You'll need to take that into account then, less margin for creeping over the limit in error!😀

Certainly will!😰

I checked mine today using the GPS test app and the speedo read 2mph fast against the GPS at 30, 35, 40 and 45. That's a 2019 Focus.