Wheel/tyre Size

[enforcer]

Hi everyone

 

The wheels from my doner (1988 2.0l carb saloon) were nasty 13" steel with 165/80 R13 tyres. I bought a set of Sierra pepperpot alloys with brand new tyres for a bargain off ebay which look a lot better. They are 14" alloys with 185/60 R14 tyres.

 

I think I'm right in saying that the 14" wheels and tyres will come out slightly smaller in diameter (about 17mm). Am I right in thinking that when it comes to the SVA my speedo will read higher than I am actually going? In which case this should be ok??

 

I've been trying to get my head around this for days and it's just too confusing! Someone please put me out of my misery!

[Joel]

I think the speedo works on revolutions, so if your new wheels have a smaller circumference than the old ones, you'll be covering less distance with each revolution.

 

So if the revs are the same, but you're covering less distance, then speedo must be reading higher than your actual speed?

 

But don't quote me on that

[Guest TerryBarry]

Hi,

That appears to be correct.

From info I have diameters are:

165.80R13 = 598mm

185.65R14 = 596mm - these were fitted to my '89 2.0l donor

185.60R14 = 578mm

Speedo will over-read by 3.4% - over reading is not normally a problem for SVA (under reading IS )

According to the SVA book at an indicated 70mph the true speed must be greater than 57mph

HTH

Terry

[Mitch]

try this link for calculating the diferance between wheel/ tyre combinations

 

http://www.chris-longhurst.com/carbibles/t...tyre_bible.html

 

HTH

Mitch

[Guest Battery Bill]

Mitch

That looks a good site Plenty of info on it.

See u