original tyre size

slimboy66 · Post by **slimboy66** » Wed Feb 04, 2009 9:21 pm

could someone tell me what the new speak on the original 13 x 6.04 tyre is . i'm after the ratio

matches · Post by **matches** » Sat Feb 07, 2009 11:32 pm

i'm actually after the same info slimboy so if someone could help out that'd be great.
i'm also after the original rolling diameter for an fb/ek
L&K&K

blue ute · Post by **blue ute** » Sun Feb 08, 2009 10:45 am

Here's my take on this
The old 6.50 X 13 Goodyears are approximately 625 mm.
The new speak 185/80-13 with a 148mm sidewall , 313mm radius, 626mm diameter & 1967mm circumference, are a little smaller in circumference than the 6.40x13s but as close as you can get in a radial that will still fit on a stock rim, even they are really a bit too wide for stock rims but are ok, a stock rim shouldn't have wider than a 165 tyre.
The 175/75 x 13 are lower profile than the original fitment (6.40 x 13) but may make the car's gearing too short for comfortable freeway with a standard 3.89 diff.

slimboy66 · Post by **slimboy66** » Sun Feb 08, 2009 7:39 pm

thanx blue ute thats exactly wot i was after

FB MAD · Post by **FB MAD** » Sun Feb 08, 2009 8:40 pm

Just measured an Olympic "Air Ride" 6.50 x 13 crossply with 3/4 tread left on it that I have on one of my EK's here and it's diameter is exactly 24 inches ( 610 mm ).

Hope that helps.

matches · Post by **matches** » Sun Feb 08, 2009 9:15 pm

thanks guys, helps heaps.

Cal · Post by **Cal** » Fri Apr 24, 2009 1:56 pm

I'm looking at getting some 185/70x13 whitewalls for mine (similar to EK Dreamer's).

Is the overall diameter of these smaller than what these cars came out with? If so I might go for the 185/80x13, though they are a fair bit dearer than the 70 ratio ryres

At the moment mine has 165/75x13, and the thing is revving it's balls off on the freeway. I'm no too fussed if I lose acceleration coz of the taller tyre.

And thanks EK Dreamer for putting me onto the tyre dude

FB MAD · Post by **FB MAD** » Fri Apr 24, 2009 3:37 pm

Cal,

If you want to stick with the current tyres but don't want your balls to rev on the freeway, stick a red motor 3.36 diff centre in it.

Fits straight into the grey diff housing,axles will even fit and only other thing you have to change is the rear tailshaft uni joint on the grey motor tailshaft needs to be changed to a red motor uni joint ( about $30 for a new uni ).

Just make sure you buy a 3.36 diff with course spline as a fine spline 3.36 ( used in HX Holden onwards ) won't be any good.

This will give you a 0.5 reduction over the grey 3.89 diff and less revs/better fuel economy.

Sorry for getting a bit off track with original post subject matter slimboy66

.

Cal · Post by **Cal** » Fri Apr 24, 2009 4:15 pm

Thanks Terry, I hadn't realised the diff centres were so interchangable.

I might buy the 185/70 tyres as they are 24.6 inch overall diameter. plus I need new tyres anyway. They have good tread, but look like they've been on the car for decades, and are cracked in places

The tyres on it now are barely 22 inch. No wonder it's revving so hard

And looking at a previous post of yours, 24 inches is roughly what these cars came out with.

If that doesn't fix it I'll go the diff route. If I dont blow it in the meantime. Got my take off on a hill all wrong the other day and the thing actually spun the rear wheels for a few metres.

slimboy66 · Post by **slimboy66** » Fri Apr 24, 2009 5:40 pm

hi all i found this on a website it may be helpful to some http://www.miata.net/garage/tirecalc.html

Cal · Post by **Cal** » Fri Apr 24, 2009 7:13 pm

Thanks for that, very good site.

Odd though how it says a 185/70-13 is only 23.2 inch diameter, whislt Khumo claims their tyre (same size) is 24.6

It also tells me there is SFA difference between the tyres I have on it now and the Khumo's

blue ute · Post by **blue ute** » Fri Apr 24, 2009 8:29 pm

This also gives approximate plus/minus speedo readings.
http://members.pcug.org.au/~jdeakins/tyresize.html

fb cruisin · Post by **fb cruisin** » Fri Apr 24, 2009 9:30 pm

Cal,
don't you run a grey

If so with 185/70 x 13 series tyres a 3.55 diff ratio is pretty much spot on with my speedo,
on my grey motor
I tried a 3.36 and found a standard grey didn't have the legs for it,

maybe a hot grey

Cal · Post by **Cal** » Fri Apr 24, 2009 9:38 pm

Yeah, its a stock grey.

I'll get the 185/70 x 13's and see how it goes with the standard 3.89 diff

fb cruisin · Post by **fb cruisin** » Fri Apr 24, 2009 9:55 pm

Cal wrote:Yeah, its a stock grey.

I'll get the 185/70 x 13's and see how it goes with the standard 3.89 diff

I done the same when I got mine on the road,
and I got sick of it revving its head off and going slow

and I have a new grey motor univeral joint thats done under 100km's