Speed limit?

[B J G]

Yes GPS is a good way to check speed but it's also useful to know what your speedo error is as well. Factory calibration will be on OEM tyres of course but then even a small change in tyres size will make a significant difference to speedo.

Eg by switching from say a 55 to a 65 profile on 235 tyres would change speedo from reading 2% over, to something approaching 5% under.

Gets even more complicated as it now seems that different manufacturers use different new tread depths, giving varied speedo readings.
eg my new Michelins have 7.1mm, Nokian were 8mm and All Terrain tyres can be as much as 12mm.
8mm is generally quoted as the standard depth but may be more of an average in practice.

 

[Velma's Dad]

Yes if you want to get very accurate you have to take into account lots of things, including tread depth as you say, and also tyre pressure.

(In 'regularity' rallying which involves hitting a string of un-mapped time controls to the second, a high precision tripmeter is used with recalibration 'on the fly'. For best performance several things have to be factored in, including temperature - which affects tyre pressures - and estimated amount of wheel spin. End of geek-thread-drift.)

 

[B J G]

Yes if you want to get very accurate you have to take into account lots of things, including tread depth as you say, and also tyre pressure.

(In 'regularity' rallying which involves hitting a string of un-mapped time controls to the second, a high precision tripmeter is used with recalibration 'on the fly'. For best performance several things have to be factored in, including temperature - which affects tyre pressures - and estimated amount of wheel spin. End of geek-thread-drift.)

Personal example of speedo reading against Sat Nav indication at 70MPH

235/55/17 Summer Tyres Speedo 72MPH

235/55/17 All Season Tyres Speedo 73MPH

235/60/17 All Season Tyres Speedo 70MPH

 

[Velma's Dad]

Personal example of speedo reading against Sat Nav indication at 70MPH

235/55/17 Summer Tyres Speedo 72MPH

235/55/17 All Season Tyres Speedo 73MPH

235/60/17 All Season Tyres Speedo 70MPH

Quite. Although for general motoring and speed limit compliance I fear we may be dancing on head of a pin at this point.

 

[ShmBK]

Question is who will be the first to run at 70MPH on the A90 Dundee - Perth Average Speed Camera Zone?

Hey folks, I assume by the lack of complaints about speeding tickets, that we are ok driving at 70 on dual carriageway?

just did 70mph cruise in GC600 on a90 from Stonehaven and then onto Perth, so I guess I’ll find out soon!

 

[B J G]

Hey folks, I assume by the lack of complaints about speeding tickets, that we are ok driving at 70 on dual carriageway?

just did 70mph cruise in GC600 on a90 from Stonehaven and then onto Perth, so I guess I’ll find out soon!

during my recent run up/down on there I did notice that Commercial Vans were doing 60MPH.

Had a few cars not liking being passed (slowly) then shooting past before they saw another Camera then brake light panic set in.

 

[c4s2rs6]

I’ve been up and down the road between Stonehaven and Dundee a few times.Normally I’m only doing 60 -65ish as van feels happier a bit slower, especially when it’s windy when it’s hard quite work. No tickets so far.


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