Yoko A032's

[youngres]

Does anyone know the revs per mile of Yoko A032's in 165x70x10 size, as I need to calibrate my Halda?

[JC T ONE]

Hi ,

I have the original calibration paperwork from Halda for the Speedpilot & metal case Twinmaster incase you need a copy ?


Jens Christian

[youngres]

Thanks Jens, I do have those but would rather calculate the cogs I need, hence the need for the revs per mile of the A032's.

Robert

[JC T ONE]

Hi,


Thought you might have (given the connections you have )

wouldnt a Yoko tyre dealer have the info you need ? or would that be expecting too much.



Jens Christian

[timmy201]

According to http://tire-size-conversion.com/tire-size-calculator/ the 165/70R10 is 1056.8 revs/mile

[youngres]

I think that figure is a theoretical average, as the different tyre brands do have different rolling radius. The A032 is quite a low profile tyre compared to some and will have, I suspect, a higher revs per mile than say a Falken 165x70x10. But it's a good starting point.

[1071 S]

Uuuuummm - you could calculate it yourself????. And the result will be more accurate as you get to specify the pressures/rim width etc that you intend to use....

Cheers, Ian

[youngres]

The way to calculate the Halda gears is as follows:
Diff ratio x 6/17 (speedo gear ration) x wheel revs per mile x drop gears ratio (if not 1:1)
For example 4.133 diff x 6/17 speedo x 1080 revs per mile = 1575
This usually give a number around 1500 to 1600.
The resulting number is then looked up in the Halda tables which will give you a set of gears needed for that calculated number (or closest to it) In this case 125 and 18 gears.
Incidentally, the speedo gear is fixed on a Mk1 and Mk2 but is different on later cars I believe.
Tyre pressures, will in theory, make a slight difference but the biggest difference is when the tyres wear down, as the revs per mile will change but it is very marginal.

Robert

[rich@minispares.com]

Incidentally, the speedo gear is fixed on a Mk1 and Mk2 but is different on later cars I believe.
Tyre pressures, will in theory, make a slight difference but the biggest difference is when the tyres wear down, as the revs per mile will change but it is very marginal.

rover used a figure called a 'flex rev' when working speedo drives and speedo heads out, as the speedo reading had to take into account the tyre wear and remain a legal reading so a driver could never be done for speeding in a car equipped with 100% standard parts. (i.e a standard car could never show only, say, 30mph on the speedo, but actually be doing 33)

I've got all the equations and calculations written down from when I (sad I know) sat down and cross referenced all the speedo heads and possible drive combinations that where available for later cars - there's loads of confusion as to what's available and people where not taking into account that metro gearboxes had slightly different worm and drive combos than minis due to the tyre sizes, this is before you take into account the minis fitted with the economy a plus primary gear, and even worse, the cars fitted with the French alternative ratio input gear - each of these small changes would have a different worm and drive and each change would have to have the correct amount of +/- as to not affect the relevant speedo by more or less than a certain percentage.



it was one of those jobs I wish I never started, it was nearly as bad as the spread sheet of all the currently available valves for engines!

[surfblue63]

Would it not be possible to measure the rolling circumference of the wheel and tyre that is fitted with the Halda? And then calculate the revs per mile of that specific wheel and tyre.

Mark your tyre and a start point, roll the car forwards for one, two, three revolutions (depends how long your tape measure is and the more revolutions the more accurate the reading should be), and then divide one mile by the rolled distance.

[Lord Croker]

If it's any help, I had to measure the circumference of my A032's to calibrate the electronic speedo & that came out at 1502mm or 59.2" Must be pretty close, as at a constant speed the speedo reads exactly the same as the sat-nav.

[youngres]

Thanks for that, I actually had a reply to my question from Yoko themselves today and your measurements are close. See below:

Hello Robert,

Thank you for your enquiry.

The rolling circumference for 165/70R10 72H A032R = 1491 mm and RPM = 1079.

Best Regards

Simon