I dont think its the diameter as was mentioned before, but was probably more the wheel offset and wheel/tyre width which can also play a factor here..

martymexicoAlso remember that alloy is heavier than rubber..

Spot on Marty! My 15 x 6" steels with 195/45/15 tyres weigh 15kg. Exactly the same as 13 x 7" hotwires with 205/60/13's.

evobda2

Out of curiosity what profile 13's are you running?
185/60/13 were the ones i was using on my previous mk1. Good size i think.
If you compare that to the common 195/50/15 tyres most runs on 15's you get the following..

185/60/13
Rolling Radius 276.1mm
Circumference 1734.79mm
Diameter 552.2mm  

195/50/15 (*note this is about the same as a 175/70/13 tyre)
Rolling Radius 288mm
Circumference 1809.56mm
Diameter 576mm  

 
Been using 205/60R13s on the RS2000 since 1992 on 13x7 rear, 13x6 front - almost identical rolling dia as the original ZR70S13's (165/75R13 in modern parlance)

As someone who runs Escorts with 13, 14 and 15" rims, I can probably add to the discussion.
 
For looks and tire availability - 15's as they "Look" right on an Escort and if used in 195/50/15 are the right size for and Escort.  Now I say this as long as they are "right" for an Escort, as really modern looking rims do not suit my opinion (an a lot of others).  Classic styles like superlights or Bathursts seem to work... I have Performance FX5's and they work, but I do sometimes regret not getting the Superlights despite everyone now having them... Offset should be no more difficult than 13's as you are not actually changing the overall size (despite what some people - including on this forum say - ???)....
 
For period looks and originality - 13's as they were original and if spec'ed with 205/60/13 are the right size too.  Classic styles and original wheels suit, but like most 70's cars standard narrow steelies and standard narrow tires do nothing for the looks.  There are alos plenty of styles and wheels avaiable secondhand too...
 
For 14's you really need to be serious. Tyres are difficult to get is good sizes and the only readily available size to suit an Escort is 185/60/14 which is IMO a little narrow and why would you go to the trouble and expense of going to this size when 13 or 15 are more easily available in good sizes.  Rules for classes can dictate no more than 1" taller, and availability of rally tires can also mean 14" are attractive, but for a road car - I would not bother....
 
 
I use 13's on my motorkhana car, the everyday road car, and the new club car I am building (and all the other cars sitting round)... However I also have some good race rubber in 205/60/13 size for use on the road/race car too as the 15's are getting a little old and bereft of grip..
I use 14" on the autocross car with rally tires (and will o the rally car when finished...)  Occasionally used for Bitumen motorkhanas too with some old sticky but worn A509's...
I use 15" on the road/race car where looks as well as handling are the important (Only wheels I have bought new ever!)
 
 
Just remember that beauty is in the eye of the beholder.  I love the look of my of 13" 5 slots, whereas GDub absolutely hates them...  Ultimately it is your car and whatever floats your boat goes......

PS - for any wheels, the offset is critical to avoid rubbing on the guards or struts or chassis rails... Does not matter about the diameter at all (providing the overall diameter is not different, but the width is also related to the offset.  I have seen 8" rims on a Mk2 Escort with standard arches and no rubbing, but have seen 6: rims with much narrower rubber hitting the guards.... And Cortinas TC-TF have FWD type offsets not too dissimilar to Focus / Mondeo that do not suit Escorts, even though the stud pattern is the same...

On a 155 rim can you fit 175's, or how wide can you go,???
 
Cheers

Sorry, previous post done in a rush.
My Tyres are Bridgestone 155S R1 13, steel rims on a 76 Ghia, 1600  Probably Original.
they just don't have the 1.5mm on the edges for RWC, middle's fine, 4mm.
that doesn't help anyway.!!    there are some cheapies about,  i really want goodies/safeies.!!
i'll find out what tyres are available, in 13", ...  … Cheers Geoff
 
If you are Serious, your seats are Doooable.!!

PM's tried 3 times, what a waste of time.