View Full Version : TR2/3/3A Original Dunlop 5.50X15 Bias Ply Tire Data

04-20-2019, 08:41 PM
I'm trying to find any information on the original manufacture tires that came on the TR3. Specifically, I'd like to find the actual diameter and width of the Dunlop 5.50 X 15 bias ply tires. I know that when Radials came out, the 155R15 was the factory replacement for the bias ply tire and that's what was on my 60 TR3 when I bought it in 73. I later put the larger 165R15 and really liked the improvement in handling, but I think most of that was more from changing to Michelin from Pirelli. With the 165s the speedometer seemed to read just a bit slow. I know the difference between the 165 and 155 isn't much (25.4" dia. Vs 24.8" dia), but I did notice it.

So I trying to find out what size the original bias ply tire actually was. I can find information on the 5.90x15 but nothing on the 5.50x15. I've tried calling Dunlop, but they've been bought by Goodyear, who had very little information.

Does anyone out there have any of original documents from the 60's that came with the bias ply tires?

04-20-2019, 08:58 PM
My TR3A (built May, 1960 but registered as a '61) is listed on its BMIHT "birth certificate" as having been shipped with 5.90 x 15 whitewall tires. No indication of manufacturer. That size, according to the latest Coker Tire catalog, equates to a 165R15 80-series radial. You may also already know that Coker (and others) sell "bias-look" radial tires in Triumph sizes, but they're somewhat pricey.

04-20-2019, 09:54 PM
Mine was built in Nov 59, but all the BMIHT certificate had listed was "Whitewall tyres". What is your Speedometer calibration number?

04-20-2019, 09:54 PM
There is a chart in the owners manual that gives engine revolutions per mile (or something like that) for each gear and tire combination. From that, you can work out the effective diameter of each tire.
By 1960, radial tires were a factory option, and they were slightly shorter than the bias-ply (as shown in the table).
You can compare the speedometer calibration number to find out which your car was likely supplied with (assuming someone hasn't changed the speedo).

04-20-2019, 10:06 PM
Thanks, I've done that, so I'm now trying to confirm the calculations. (just a little anal-I know). In the end, it probably won't matter much with GPS to confirm the speedometer. But, now I'm on a quest--I'd really like to know what the real 5.50X15 diameter was?