speedo calibration

[big e]

Hello people. I am new to the world of stag ownership.I have discovered that the speedo on my 1975 built stag is currently under reading by approx 10 mph. Before I acquire too many points to be able to enjoy my new toy , could anyone suggest a place to get it rectified. If it makes any difference I am in Essex. I don't really want to swap speedos as mine is showing the original 63000 miles. Any help would be greatly appreciated

[GDPR]

If you are under reading by that amount, you may have wrong diff ratio - I had the same, so I swapped to the speedo from a 2500S which used the same diff (3.45:1) and wheels - clocking the mileage recorded up to the same as you have now is very easy....

Speedo cost me £25 from Wins, so a cheap fix

[Andrew S]

Welcome to the Forum Big E

[jasper]

Welcome to Stag ownership Big E
I had the same trouble as you . it turned out tyres were the wrong size
Hope you get it sorted
John

[GDPR]

Or the right tyres on the wrong car?

[big e]

Thank you for the welcome. I believe the tyres fitted to my car are correct in being Michel mxv 185 R 14s , so maybe it does have the wrong diff. Thanks for your help

[flying farmer]

When you say it is under reading by 10 mph, is this right across the speed range?
I have had this once before on one of my Triumphs (can't remember which), and solved the problem by dismantling the speedo and turning the needle on the spindle by the required amount.
I have also used this as a bodge on my Stag powered estate that is under reading by about 10% due to the 195/65x15 tyres fitted. I twiddled the needle so it now over reads at 30mph, is about right at 70mph, and under reads above that (less of a problem)
Most modern car speedos I have come across seem to read 10% high, probably fear of litigation!
Neil

[jasper]

Unjust the same size Tyers as mine except they had a 90 stuck on the end

[norstag]

Tyes and diff ratios only make small differences to the speedo reading(around 10%) so if you are 10mph out at low speed it probobly means the speedo is faulty, my flickered badly for years, and nothing would cure it. I finally sent it to Speedy Cables to be reconditioned and calibrated, and now its perfect, around £50 well spent. Go to www.speedycables.com for further info.
Alan

[tony750cc]

Modern car speedo's are allowed to be out by no more than 10% over the indicated speed. If you want to check how accurate it is find a roadside speed indicator and drive through it at a constant speed. These are generally accurate. The ones on sat-navs are fairly accurate but dont rely on them as they are only receiving signals at a set time. There are set speed check points which are used to check the calibration on speedo's fitted to police cars these are normally small blue and white marker posts at the side of a dual carriageway and are set at half a mile apart, you need a stopwatch and a steady foot to check using these!

[big e]

I haven't worked out the speed difference over the entire range yet. I think i will compare notes between speedo and twat nav so i can use it without collecting points thru the summer and send the head off to speedy cables during its winter hibernation.

[Stag About Town]

I'm a bit wary of size 185r14. My Stag is a 77 vintage and the original handbook says 175R14. Did Triumph really fit two different sizes? If so which model years had which or was the manual different to the auto? As an ex tyre industry oik I know a small difference in diameter, or rolling radius to be precise, makes a difference to the speedo and the ratios. Try a decent sat nav. They usually give a fairly accurate speed over the ground which can be compared with the speedo. Might give a clue. Out of interest I checked the road speeds corresponding to r.p.m. as shown in the handbook and these were spot on. John

[DJT]

I'm a bit wary of size 185r14. My Stag is a 77 vintage and the original handbook says 175R14. Did Triumph really fit two different sizes? If so which model years had which or was the manual different to the auto?

Hi John,

185HR14 Michelin XAS was the standard tyre fitted to all Stags other than a small batch of approx 30 cars that were fitted with Goodyear G800 Grand Prix 185/70HR14 tyores in March 1973 due to a shortfall in the correct tyres.

Towards the end of production 175HR14 tyres were fitted, possibly as a cost-cutting venture to standardise deliveries of wheels/tyres for both Stag and saloons.

Autos and manuals all had the same tyres.

Nowadays 185HR14 tyres are hard to source, but 175HR14 tyres are still available from 'quality' manufacturers.

Dave

[john 4d]

Maybe we should swap diffs, at top speed mine registers 10MPH over, on 185/80R14 Falken's. I was wondering why at the speed 'limit', the broken down old white van was disappearing into the distance, I was actually only going 60, honest, m'lord!
Again, this is checked against a sat nav app, which matched my Passat's speedo perfectly.
John4D.

[flying farmer]

Don't know what tyres my stag was fitted with originally, but the mileometer was only one mile out over a 200 mile journey with a 3.45 diff and 185/70x14 tyres, I have now got 195/60x15 fitted which are very close in diameter to the 185/70 x14
Neil