tyre sizes

Post by **ColinChandler** » Sat May 29, 2004 11:09 am

Hello everyone,
Does anyone know the circumference of a standard 520x14 morris tyre? I'm fitting some radials to my unfinished restoration and I wondered how they compare in size. I'd like to know if the speedo will need recalibrating etc.
Thanks, Colin.

Post by **Willie** » Sat May 29, 2004 11:51 am

Lo, the difference in revs per mile between a 5.20 cross ply
and a 145 radial is only an extra 27 revs. Not worth bothering with
I think,even with all these speed cameras about !
Do not fit any wider than 155X14 radials. The ideal with
standard wheels is 145X14 which is WIDER than the tyres fitted by
the factory to the wide van wheels.

Post by **ColinChandler** » Sat May 29, 2004 7:43 pm

Hello again,
Thanks for that but I'm not sure if I made too good a job of explaining what I'm after. I'm fitting a 13" rims and slightly lower profile tyres so I'd like to know how different these are from the original crossplies or indeed 14" wheels with 145 radials on. If someone could run a tape measure round the circumference of one, I can see how much different my tyres are and by how much it affects the speedo. It may also cause the car to run out of steam at the top end and so perhaps need a higher diff to drop the revs back down.
Hope someone can help give me an actual measurement around the circumference of the tyre.
Thanks again, Colin.

Post by **rayofleamington** » Sun May 30, 2004 12:41 am

ColinChandler,
You don't need to go as far as tape measures - it's not hard to calculate how one radial compares to another.

The rim dia is 14" (355mm) and using a 145 tyre width (145mm) with approx 80 profile (ie the tyre height is 80% of the width) gives a diameter approx 587mm.
(I'm guessing the original crossplies were a tad bigger diameter)

Using a 13" rime you want to match the diameter so...
155 - you wont get there
165/80/13 = 594mm dia (80 profile is standard ie. not low profile)
185/70/13 = 589mm dia
195/65/13 = 583mm dia
and I'm not going to mention anything wider, as if you want to go that wide you're need to do a lot more than worry about the tryre diameter ;-)

Post by **ColinChandler** » Sun May 30, 2004 9:22 am

Much obliged for that. Thanks, Colin.