Miata Mailing List: October 1998, Message #11

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That's correct now that I think about it. The sapphire is the same as the sapphire sold in UK. Interesting that South Africa now has a Ford Falcon four litre in this country. Makes my miata look like a dwarf !

>>> "Jeff Gehrig" <miata@bigpond.com> 09/30/98 05:12PM >>>
Francois,
             The Ford Orion and Sapphire are Euro Fords I think, Australia
has the Falcon which is designed and built here.

JEFF & KELLY (99 Grace Green, MX5099)
OZTEAM VOODOO
SYDNEY AUSTRALIA
VICE PRESIDENT MX-5 CLUB OF NSW
MCA #42017, MX-5 Club NSW #169
http://www.geko.net.au/~nswmx5/nsw/index.html 

-----Original Message-----
From: FRANCOIS JOUBERT <FJOUBERT@ems.co.za>
To: miata@bigpond.com <miata@bigpond.com>; miata@realbig.com 
<miata@realbig.com>
Date: Wednesday, 30 September 1998 21:22
Subject: Re: This might be a stupid question but...


Agree with everything stated especially :-

"one that manufacturers acknowledge, frankly, I wouldn't vary too
much from their specifications."

It's fun to play with the combinations, but once you deviate too far (and
IMHO 215/40/16 corresponds to too far unless your miata has something
additional under the bonnet) you start to tread on dangerous ground
regarding heat in tires, increased weight and handling. In general you can
pay a small amount for a big benefit (say 195/50/15), and then a large
amount for a relatively small benefit after that.

What people also sometimes forget is that a lower profile tire is great for
performance on a race track, but if you are not racing your car on a regular
basis be careful. If your car is used mainly for normal road driving and
local road conditions are poor, low profiles seriously increase your risk of
punctures and cut tires (and also decrease your confort levels). I learnt
this the hard way, including replacing a rim or two along the way with some
205/40/14 on a modified Ford Saphire (I think you call this a Ford Orion in
Australia IIRC).

Cheers
Francois

>>> "Jeff Gehrig" <miata@bigpond.com> 09/30/98 08:05AM >>>
Francois,
              This is called +1! If you start with the OEM tyre combination
on 14" wheels the tyre size is I believe 185/60/14, to upgrade the wheel
tyre combination, the +1 size is 195/50/15, this effectively allows for a
wider choice of premium grade rubber with a lower profile, the next step and
that offered as an option here on the Mark 2, is 215/40/16, again the
overall diameter of the wheel/tyre is maintained, so the overall gearing is
virtually the same as the OEM 14" setup. Of course, depending on the actual
choice of rubber and wheel, this could be a very negative step, heavy wheels
increase the unsprung weight (not desirable), wide low profile tyres are
much more expensive as are the wheels, and the car, unless modified, might
not generate enough power, to heat the tyres to the point where they
generate the grip that they were designed to generate. The rule of thumb in
+1, is for every 1" increase in wheel diameter, the aspect ratio (height vs
width) should be reduced by 10% 14-15"  60-50%. How many enthusiastic
drivers have vanished backward into the scenery because the huge tyres
fitted to their cars, did not allow the cornering speeds which they were
used to, simply because they didn't get hot enough? I've seen many, some
even on ordinary roads, not in track situations, tyre selection is still a
black art, one that manufacturers acknowledge, frankly, I wouldn't vary too
much from their specifications.

JEFF & KELLY (99 Grace Green, MX5099)
OZTEAM VOODOO
SYDNEY AUSTRALIA
VICE PRESIDENT MX-5 CLUB OF NSW
MCA #42017, MX-5 Club NSW #169
http://www.geko.net.au/~nswmx5/nsw/index.html 

-----Original Message-----
From: FRANCOIS JOUBERT <FJOUBERT@ems.co.za>
To: Multiple recipients of list <miata@list.miata.net>
Date: Wednesday, 30 September 1998 16:07
Subject: Re: This might be a stupid question but...


>Change from 14 " to 16 " tires doesn't necessaarily mean that the overall
diameter will be bigger on the 16 " setup - it depends on what profile tires
you put on.
>
>For example :-
>Stock miata wheels 185/60  14"
>Width = 185 mm
>Aspect ratio = 0.60 (wall height to tire width ratio)
>Tire wall height is    185 x 0.60 = 111 mm
>Convert 14 " to mm = 14 x 25.4 = 355.4 mm
>Overall tire height = 355.4 + 111 + 111 = 577.6 mm
>
>For 205/40  16 "
>2 x (205 x 0.40) + (16 x 25.4) = 570.4 mm
>
>For 205/45  16 "
>2 x (205 x 0.45) + (16 x 25.4) = 590.9 mm
>
>The larger wheel does make the car travel further for each rotation, so for
each rotation of the engine you travel further
>
>Cheers
>Francois
>'91 Classic Red
>Team Stock wheels and rims
>Team waiting to change to 16" - money and low tire wear on existing set
causing delays !!