17 replies to this topic

[Peter_NottinghamS]

The reason I ask the question is that I'm on my second speedo cable as the first one snapped and both are/were way out.

 

How do I know?

I use a speedo app on an old phone and it [the app] appears to be consistent with the flashing road speed checks, so I know I'm okay.

 

When I'm travelling, say at 25mph, in a 30-zone, the app and road side flashing boards shows 25mph and the speedo shows 20-ish.

 

Two factors to consider.  The Mini is fitted with 12x5in JBW replica Dunlop D1's with wide Yoko A539 tyres and the speedo cable has to negotiate the MED sub-stack filter so doesn't get a straight run to the back of the speedo.

 

I'm happy with this solution as I know I'm legal and safe, but is there anything I can do to improve the accuracy of the analogue speedo?

Thanks in advance.

 

Peter 

 

[bangermadness08]

Thought it was a mini thing. My seiko clock needle bounces around more times than a kid on a bouncy castle full of E numbers. Mine will usually show 4mph more than my initial speed that’s on Google maps & speed check road side.

[Mr Piggy]

The speedo cable won't make any difference to the accuracy of the speedo. You'll need to change the ratio in the gearbox. There are charts on here that will help you or talk to a well known parts supplier for advice on what you need to change the ratio.

[DeadSquare]

I don't need to have mine tested. it's Dead Accurate *

 

Why ?.  Because it was made by Smiths in Gt  Britain.

 

It came from the Centre Binnacle of a 140 MPH Cooper S.

 

 

 

 

 

 

*When I'm stationary.

[absx2]

Mine is bang on thanks to Guessworks speedo ratio calculator.

 

Oddly in an ideal world it should be doing 27 mph at an indicated 30 mph just like every modern car so that way there is less chance of being caught speeding.

 

I have to remember that when going through the countless average speed cameras

[mbolt998]

Mine is very good. I've calibrated it against those roadside matrix display things that show your speed. It reads a bit over but not much (which is what car speedos typically do).

[Ethel]

How sure are you that the gearbox is original? The milometer would be a better starting point as it's directly geared.

[PeterG]

Mine is spot on now. 92 SPi, now 1380 HIF44. Somewhere in an earlier life it got a 3.44 C&P instead of 3.2 and the indicated MPH was higher than reality. I changed the speedo  drive gears in the gearbox to a 3.44 set. Checked with a GPS app and it is spot on accurate now.

[Peter_NottinghamS]

Thanks for all the replies.

The Guessworks speedo ratio calculator is something I need to check out.

@bangermadness08, I'm chuckling like a mad fool!

"....needle bounces around more times than a kid on a bouncy castle full of E numbers"

😂 Peter

[Spider]

They were (if memory serves) within 4 mph at an indicated 60 mph.

 

If I can suggest here before changing gears or playing around with any of it, do some more tests;-

 

Check your tyre pressures as they make quite a difference.

Next check how accurate the Odometer is, even if you don't use it, because this may show if there;s something more serious wrong with the Speedo or if it needs a simple adjustment.

Lastly, check the Speedo at a few different speeds and in particular, take an error reading at a much higher seed than 25 mph, take that at say 60 mph.

[Shooter63]

Try this one for accuracy,

Shooter

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[Peter_NottinghamS]

@Shooter63, that's the one I use!

Just back from a quick blast around the lanes.

The speedo no longer works.

😕 Peter

[DeadSquare]

Odometers were around long before cars.  People needed to know how far they had travelled, not how fast

 

In the late 1700s, hand delivery carts had 11 foot circumference wheels, with a trigger that moved a lead shot from one container to another.  Weighing the shot gave a good indication of how many furlongs or even miles, had been trundled.

 

My mother told me that in the 1920s and even the 30s, moderately priced cars had Odometers, it was only luxury or sporty cars that had speedometers and it wasn't until an Act of parliament introduced speed restrictions in places with street lighting, that all motor vehicles had to be fitted with them.

 

Before that, the government Weights and Measures were responsible for calibrating cars, but obviously they wouldn't be able to cope with every car, and so the Act stipulated that the manufacturer had to fit a speedometer that Had to be accurate at 30MPH.

 

Despite the plethora of 20, 40, 50, 60 and 70 MPH speed limits, Court cases are being argued in Wales, citing only the 30 MPH required accuracy.

 

Good luck to them.

[Steam]

Mini is 10% or 15% low depending on which wheels I fit.
All speedos are factory set at 10% above these days so newer cars will always be under the speed limit.
The large number of different ration speedos and the accompanying speedo drives means there are all sorts possible. The speedos have their tpm or tpk print4d on them, match that with the correct drive and bingo, accurate speedo. Easy to say, not so easy to acheive.

[Spider]

I did use to adjust the gears and speedo head to get them reading spot on, but it's a lot of fiddly work and you only need as much as a change in tyre brand and that's all out the window anyway.

I now run electronic and set them to be spit on, if it reads 60, then I know I am doing 60.

 

 

Mini is 10% or 15% low depending on which wheels I fit.
All speedos are factory set at 10% above these days so newer cars will always be under the speed limit.
The large number of different ration speedos and the accompanying speedo drives means there are all sorts possible. The speedos have their tpm or tpk print4d on them, match that with the correct drive and bingo, accurate speedo. Easy to say, not so easy to acheive.

 

I don't disagree here that that's how new cars are, but, strictly speaking, they don't meet the ADRs as the current ones state " plus or minus 10% ", many are out more than that (Toyota's seem to be about 15% too low) and yet assuming you had a " +10% " Speedo, we can still get booked for speeding in a road legal car.