18 replies to this topic

[Elliskwleisk]

1984
998cc
13x7 wheels
3.44 final drive

What speedo is correct for my car?

[petey81]

try this mate http://www.guess-wor.../Tech/ratio.htm

[Elliskwleisk]

Thanks but I don't know my drop gear ratio, or the worm and pinion ratios or the gear box type?

[Elliskwleisk]

Or the TPM..

[dklawson]

Not knowing all that stuff you may want to consider measuring/counting.

Remove the speedo temporarily leaving the end of the speedo cable exposed. Put a piece of tape on the end of the cable to act as a flag. Drive the car SLOWLY through a known distance of 1/10th mile while an assistant counts the number of cable revolutions. Multiply by 10 and you will have the TPM number. If 1/10th of a mile is too long to be practical for you, use a shorter known distance and make several runs so you can add up the results.

An alternative measuring method is described at the Speedy Cables web site. See the link below.
http://www.speedycab...alibration.html

[petey81]

or try this? http://www.guess-wor...Tech/speedo.htm

[Elliskwleisk]

Okay thanks, but how much more will I be able to work out by knowing the TPM?

[dklawson]

The TPM number is typically printed somewhere on the gauge face. On center speedos it is easily found as a 3 or 4 digit number on the gauge face. I believe that John has some pictures on the Guessworks site that show where the number is found on the later gauge clusters.

Once you know the TPM number for your car, you look for a matching/close number speedometer. There is a fairly wide tolerance though so the numbers don't have to be a 100% perfect match. For example, on the early center speedos for "regular" Minis there were 90 MPH speedos calibrated for 1408 and 1376 TPM. That sounds like a huge difference but it isn't. If the speedos were perfectly calibrated and you used one in place of the other you would have... 60 MPH x (1408/1376) = 61.4 MPH or... 60 MPH x (1376/1408) = 58.6 MPH. In both cases, using the wrong speedo gives you an error of less than 2 MPH. Tire wear and running a "different than stock" tire size can cause more error than that.

In short, determine the TPM number for your car's combination of tires, gearbox, etc. then find a speedo with the matching (or close) TPM number and you will have a working setup.

[Elliskwleisk]

Is there a written guide as to what years and models of minis had what TPM's?

[62S]

Yes there is but it won't help if you have a non standard set up.

[DannyTip]

It all depends on the speedo drive in the gearbox. Run whatever speedo you like and adjust the speedo drive to suit.

[Noris8322]

It all depends on the speedo drive in the gearbox. Run whatever speedo you like and adjust the speedo drive to suit.

+1

Or if you dont fancy pulling your gearbox apart etc etc, you could do what I've been doing for the past 2 years. Work out what your speedo reads at 30,40,50 & 60, then remember them. lol
I know its not the correct way of doing it but certainly easier

Edited by Noris8322, 20 February 2013 - 06:09 PM.

[Elliskwleisk]

How can I work out my pinion and worm drive ratio?

[DannyTip]

You don't need to. http://www.guess-wor.../Tech/ratio.htm will tell you the recommended for your speedo.

[Elliskwleisk]

No I need to to work out what gauge to purchase that has the right TPM to work with my set up as my engine was only put in about 2 weeks ago and I really don't want to take it out again anytime soon..

I know:

Tyre size - 175/50/13
Diff ratio - 3.444:1
Gearbox type - Standard

So I need to work out me worm and pinion ratio in order to know war gauges will work with all my current setup?