Speedo woes

[snncrv]

Morning all. I have a 1955 split screen and a have a wayward overeading speedo. Its be updated with a 1098 and 4.22 diff fitted. It still has a 80mph bronze? faced speedo fitted. Am I correct in feeling that I need to fit a 1048tpm speedo?

Ta

[Sleeper]

What was the original diff ratio , how accurate was the speedo before?

John

[oliver90owner]

Legal requirement for a speedo reading is +10% of road speed but not less than the true road speed. I suppose sat navs have highlighted the errors. I always took note of the rev counter when I used to ‘stretch’ the rules a tad. Most boy racers over-estimated how fast their cars went.

Back then it was a matter of checking (using motorway count-down markers and a stopwatch) to get an accurate speed assessment. Distance checks to the nearest 1/10th of a mile were also done using the motorway markers, usually over a ten mile stretch (or less).

[don58van]

Am I correct in feeling that I need to fit a 1048tpm speedo?

I think you mean 1248tpm.

If so, I believe that would be suitable. I think that spec only comes with a black face though -- so not original appearance.

Don

[liammonty]

You’ll either need to fit the speedo from a later car - ideally an early 1098 bronze one - or alternatively, have the ‘box apart and fit the Speedo drive gear and matching head from a Series II car to get your existing speedo to read better, though it will still be out due to the diff. The SII speedo will read around 50% fast with 1000 running gear, as the TPM for the SII speedo is much lower than that of the 1000s, at around 1000 TPM.

[Tootall]

Choose the style of speedo you want (if you still have the original in your car, why not stick with that) then send it to Speedy Cables, along with all the details of the engine, gearbox, diff ratio and wheel sizes.

They'll do all the maths and re-calibrate your old speedo to read correctly for your current set-up.

I did that many years ago when my car got a 1275, longer-legged diff and 14-inch minilights with 60-profile tyres.

Checking with my satnav, it's only about 1 mph out at 70... a decent margin of error, I'd say...

[Declan_Burns]

OR,
If all that fails I can make you a custom built speedo corrector gearbox and you can retain your original speedo. This sits on the back of the speedo.
Regards
Declan