Speedo correction

[mishmosh]

Time to spare so Having a play. With my 1200 herald. Sat back tells me that the speedo is way out. Taken the wheels off the Bond Which have oversize tyres165 /80/13 raising the gearing. Previously ithe herald was at least 12 percent out. On 145/80/13 Now it's better but still over reads. In the bond it under reads 9 percent.the bond with 145/ 80 13 is almost spot on. Speedo is not original. Diff and gearbox is standard. Speedo code is 1248 is this the right speedo ?

[Pete Lewis]

have a ply on 

http://www.mintylamb.co.uk/gearspeed/

 

 

to get your speedo TPM  

 

remove cable from speedo  atach a card needle to the cable end

 

measure 52.8FT down the road

 

align car with first marker and carefully move the 52.8ft  while  counting the turns of the cable 

 

multiply the turns by 100  you have the tpm   you need to aim at 

 

speedos can read up to 10% + 4mph over but no under speed  so eg it can read upto 70 at true 60 and be legally accurate   .

 

 

Pete 

[mishmosh]

Thanks. Studied minty lamb. That's why I am puzzled ! Seems speedo is correct. Going to look at the bond one next !

[Mike Crewes]

Mishmosh

 

Remember the SatNav is historic, it's what you've just achieved as an average between a number of satelites, whereas the speedo is in real time.  The two are not a direct comparison, although pretty close.

 

Remember also that your car was built with a +/- 10% speedo inaccuracy, so anything inside this is acceptable by law, although you may, of course, wish to 'tune' this.  Modern cars are only allowed +20%, that is, their speedos can only over read, but by up to 20%.

 

The ACPO speed enforcement guidlines (limit + 10% + 2) is probably to allow for classic cars!

 

Regards

Mike

[Pete Lewis]

Thanks Mike the 10%+4 I mentioned  for SPEEDOS,was what we had to work to when I ran the factory tachograph calibration unit

   we had the first factory approval to do this in house ,  but this was pre 93 , did a lot of work with the police when a variety of cheating devices became a problem

  like using a car alarm plip to operate a crossover to neutralise the driving mode and drive on whilst in sleep  mode then complain about fuel consumption, this introduced armoured  cables   and other deterrents   interesting days 

 

 

Pete

[mishmosh]

Thanks Mike. Good to have you still contributing to the legal details. What puzzles me is the herald with bond wheels is now almost ok. But vice versa bond hasn't corrected much !