speedo accuracy - Page 2

Mike24 · 6th September 2015, 22:01

I believe the main speedo is electronic rather than mechanical, but all manufacturers calibrate their speedos to over-read so that they can never be accused of being responsible for people breaking the speed limit. The IPK speedo can be enabled by a T4 guru; PhilT4 did mine for me. I'm hoping to make some of the meets this year, so I am looking forward to meeting some of the locals.

Ps3000 · 6th September 2015, 23:16

Loads of speedos (most?) over read, hence why
I pass almost everyone in the 50 sections on the M1 roadworks. I did notice one bloke zooming up behind, as he passed I saw he had foreign plates...

Fred7A · 6th September 2015, 23:28

As others have stated, it is normal for speedos to over-read a little, and mine does too. Incidentally, I believe it is illegal for speedos to under-read. I have noticed that the speed warning on the IPK comes on when the speedo is showing slightly more than the warning is set to, but I'm not sure whether that's deliberate or because the IPK speed is more accurate.

Dragrad · 7th September 2015, 01:49

Quote:

Originally Posted by Fred7A

As others have stated, it is normal for speedos to over-read a little, and mine does too. Incidentally, I believe it is illegal for speedos to under-read. I have noticed that the speed warning on the IPK comes on when the speedo is showing slightly more than the warning is set to, but I'm not sure whether that's deliberate or because the IPK speed is more accurate.

The latter in most cases,

Generally the speedo shows approx 10% greater than actual speed. I have had the Hi-Line IPK update done to show the "actual" speed but this is generally 2-3 mph above the sat nav reading of time over distance.
Certainly it is against the regs for the speedo to read under actual speed. Maybe the 10% over-reading is to compensate for the manufacturer's tyre size range ?

(The car originally had 15" Contours and now I am on 16" Unions)

another_clean_sheet · 7th September 2015, 05:37

From memory,never a good thing, at my age, I think that the regulations say that speedos have to over read by at least 2 mph plus 3%. This would mean at 30 mph, reads 33 mph and at 70 mph reads 74 mph.

BaroqueMoon · 7th September 2015, 05:43

My 75 came with 17 inch tyres from the factory and still reads 10% less than actual speed.
I use my GPS to determine speed.

Kennyeth · 7th September 2015, 05:54

Setting my cruise at 30 in a 30 mph zone, I can tell it`s going less than 30 and so can the people following, what I do is set it at 32, then the IPK was reading 30.
Ken.

stevenicks · 7th September 2015, 06:42

Personally I don't have a problem with this. I have not told the wife aboui it though as she does have a habit of hovering above the limit, especially in a 30 zone.

Dan_Somerset · 7th September 2015, 13:28

I was on the motorway yesterday doing bang on the limit (70mph) and I didn't overtake anyone apart from the odd truck!

stevenicks · 7th September 2015, 13:52

It is called sensible driving Dan. Nothing wrong with that.

7th September 2015, 05:43	#16
BaroqueMoon Gets stuck in Rover 75 Saloon Join Date: Jul 2012 Location: Ballarat Posts: 937 Thanks: 576 Thanked 114 Times in 99 Posts	My 75 came with 17 inch tyres from the factory and still reads 10% less than actual speed. I use my GPS to determine speed. __________________ Love my 75 and it loves me Membership Number 1703 This vehicle was the 82,624th 75 to run off the production line, out of 112,381 This vehicle was the 6,161st 75 2.5 V6 Contemporary to be made out of 8,214 This vehicle was the 9,755th 75 in White Gold Metallic (code: GMN) to be made out of 12,251 White Gold Metallic 75s

6th September 2015, 22:01	#11
Mike24 Loves to post Rover 75 CDTI Auto Saloon Connoisseur SE Join Date: Apr 2015 Location: Coventry Posts: 358 Thanks: 166 Thanked 67 Times in 56 Posts	I believe the main speedo is electronic rather than mechanical, but all manufacturers calibrate their speedos to over-read so that they can never be accused of being responsible for people breaking the speed limit. The IPK speedo can be enabled by a T4 guru; PhilT4 did mine for me. I'm hoping to make some of the meets this year, so I am looking forward to meeting some of the locals.

6th September 2015, 23:16	#12
Ps3000 Gets stuck in None at moment Join Date: May 2013 Location: Loughborough Posts: 899 Thanks: 230 Thanked 125 Times in 113 Posts	Loads of speedos (most?) over read, hence why I pass almost everyone in the 50 sections on the M1 roadworks. I did notice one bloke zooming up behind, as he passed I saw he had foreign plates...

6th September 2015, 23:28	#13
Fred7A Regular poster Rover 75 Saloon Join Date: Aug 2015 Location: Southampton Posts: 73 Thanks: 15 Thanked 9 Times in 9 Posts	As others have stated, it is normal for speedos to over-read a little, and mine does too. Incidentally, I believe it is illegal for speedos to under-read. I have noticed that the speed warning on the IPK comes on when the speedo is showing slightly more than the warning is set to, but I'm not sure whether that's deliberate or because the IPK speed is more accurate.

7th September 2015, 05:37	#15
another_clean_sheet Posted a thing or two Rover 75 CDTI Tourer Join Date: Nov 2014 Location: Great Bardfield, nr Braintree Posts: 1,414 Thanks: 303 Thanked 436 Times in 317 Posts	From memory,never a good thing, at my age, I think that the regulations say that speedos have to over read by at least 2 mph plus 3%. This would mean at 30 mph, reads 33 mph and at 70 mph reads 74 mph.

7th September 2015, 05:54	#17
Kennyeth This is my second home No more Rover Join Date: Apr 2009 Location: Barnsley, South Yorkshire. Posts: 5,881 Thanks: 1,625 Thanked 1,308 Times in 998 Posts	Setting my cruise at 30 in a 30 mph zone, I can tell it`s going less than 30 and so can the people following, what I do is set it at 32, then the IPK was reading 30. Ken.

7th September 2015, 06:42	#18
stevenicks This is my second home MG ZT 180 Auto / Rover 75 2.0 Diesel Join Date: Apr 2013 Location: Brecon. Posts: 7,465 Thanks: 3,297 Thanked 1,666 Times in 1,264 Posts	Personally I don't have a problem with this. I have not told the wife aboui it though as she does have a habit of hovering above the limit, especially in a 30 zone.

7th September 2015, 13:28	#19
Dan_Somerset Avid contributor 75 Saloon, 2.5 V6 Auto Conn Join Date: Mar 2015 Location: Taunton Posts: 106 Thanks: 6 Thanked 11 Times in 9 Posts	I was on the motorway yesterday doing bang on the limit (70mph) and I didn't overtake anyone apart from the odd truck!

7th September 2015, 13:52	#20
stevenicks This is my second home MG ZT 180 Auto / Rover 75 2.0 Diesel Join Date: Apr 2013 Location: Brecon. Posts: 7,465 Thanks: 3,297 Thanked 1,666 Times in 1,264 Posts	It is called sensible driving Dan. Nothing wrong with that.