Original Dunlop RoadSpeed 5 whitewall width

[bopperd]

My car was originally sold with Dunlop RS5 whitewalls. I cannot find the width of the whitewall anywhere. Do any of you fine folks have an original kicking around and could measure it?

[Heuer]

White wall tyres have a 2.5" white band which does not extend over the bead. Longstone Tyres offer a service to convert new tyres to white wall but it is not cheap - ?130/tyre +VAT plus the cost of the new tyre. It cannot be done on used tyres. The people who do the work will only do it on quality radial tyres such as Michelin and Pirelli. It involves machining off the side wall rubber and vulcanising white rubber in its place. So far they have not tried it on RS5 cross-plies but that is pretty academic as Dunlop is no longer making them and there is uncertainty if they will ever be available again. All 185 Dunlop's are out of stock including SP Sports.

[manyc]

I am running with 2 1/4 WW American Classic tires that I bought from Coker Tires. Paid $230 each. The correct size for a 3.8L series I is:

P195/75R15 AMERICAN CLASSIC 2 1/4" WW


-Chris

[christopher storey]

The diameter of a 195/75 is a little small even by comparison with 185/80, and it is considerably smaller than that of an RS5 ; however, provided you are satisfied with a slightly lower ride height, and a small speedo overread, they would do. The correct size radial, however, is 185/80, and in period it may even have been an 82% profile

[manyc]

My car is a 1962. As I understand it from 61-64 the standard tire size was 6.40-15, which has a width of 162mm and an aspect ratio of 90. This is the calculation I did a few years ago based on that info:

This results in a wheel diameter of: (162mm / 25.4mm/in * 0.90)*2 + 15 inches = 26.48"

for a 195/75R15 the diameter is:
(195/25.4 * .75)*2 + 15 = 26.516"

The difference in ride height is 26.516-26.48 = 0.035"
So my car is higher than it would be with the original tires by about 1/32".

As far as speed inaccuracy, starting with the assumption the my speedo was calibrated for the original 6.40-15 tires:

63360"/mile / 26.48"*3.1459 (aka PI) = 760.584 tire revolutions per mile

760.584 tire revolutions * 26.516"*3.1459 = 63444.8" traveled for same speedo reading

Actual error in speed = 100% -100 * 63444.8"/ 63360" = 0.134%

So at a 100 MPH speedo reading I would actually be traveling at 100.134MPH

Of course my math falls all to crap if I used the wrong source for the original dunlop tire dimensions......

If someone has a proven accurate source for the Dunlop tire specs, do you mind passing them along so that I don't keep believing the wrong thing?

thanks Chris

[Heuer]

According to Longstone Tyres RS5 640H15 - Diameter(mm) = 683; Section Width(mm) = 174

[christopher storey]

Your value for pi unfortunately has lost one crucial digit : it should be 3.14158 not 3.1459. However, the difference is fairly minimal at about 1/7 of 1 percent

[gsv]

And ride height calculations in reference to the differences in tires should be made using the radius not the diameter. Hub to ground. Using diameter would double the difference would it not?

[christopher storey]

Yes, ride height is affected to the extent of the difference in radius only . Incidentally, one source I looked at yesterday showed RS5 diameter as 711mm ! This actually is more in accord with my recollection of the diametric difference