> I now want to replace these and was set on getting a set of 205/70s
> until I read on the VTR maintenance page an article on TR6 tyres which
> says:
>
> "I would stay away from the 205/70-15 or shorter profiles (like 60
> series) unless you don't care about how accurate your speedometer is.
> If you're into autox you might want the 205/70 because they are
> roughly 2% smaller diameter."
>
> This person promoted the 215/70. Now I'm totally confused.
>
> If the original tyres were 185/80 then the tyre width was 148mm.
> 205/70s are 143.5 while 215/70s are 150.5. It would seem 215s are
> closer to original. However. they border on overtyring the rim and
> look big. What advice can listers give me?
>
A small problem here. The '80' in 185/80 does not make the width 148mm.
The '80' is the ratio (as a percentage) of sidewall height to the tread
width. So the width of a 185/80/15 is ABOUT 185 mm and the sidewall height
is ABOUT 148 mm.
And a couple of things about speedo error. I don't know the original
tire (tyre) size for the TR-6 but if it was a 185/80/15 the following
shows the speedo errors for some other sizes. These are aproximates, but
they should be close.
The formula for this is:
(Original Tire Diameter/Replacement Tire Diameter) x Indicated Speed
Speed at
Indicated Approximate
55 MPH. Tire Diameter (inches)
55 185/80/15 26.6
60 185/65/15 24.5
56 205/70/15 26.3
59 205/60/15 24.7
54 215/70/15 26.9
57 215/65/15 26.0
Now keep in mind that all of these numbers will vary from manufacturer to
manufacturer, as few '60's are exactly 60% of the tread width, and few
'185's have exactly 185 mm tread width.
The way I see it 205/70/15 tires and 215/70/15 tires enduce about the same
error, just in different directions.
Anyone see any blatant errors?
So Long,
Darrell Leach, KD6LRC DM-15, Ridgecrest, Ca
email: Triumph_TR4@ridgecrest.ca.us
http://www.ridgecrest.ca.us/~token/PAGE1.html
1962 TR-4 (CT5368LO) Everyday
1962 TR-4 (CT13108L)
1965 Spitfire Mk 2
1967 Spitfire Mk 3 In work, lots of 1500 stuff
Keeper of the TR-4 List, Version 2.0 availible.
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