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tyre size

Posted by Whimaway36

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tyre size #1
Whimaway36 Bill Coon Melbourne, vic, Australia 1959 MG MGA 1600	Posted: July 07, 2012 05:56AM Registered: 10 months ago Posts: 7

My MGA has 15x6 rims fitted with 195 .60x15 tyres,would like to know the correct tyre size to have the same gearing as original 165.80x15 tyres. thank you

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Re: tyre size #2
bikermga Peter Tilbury Surrey, BC, Canada 1956 MG MGA 1958 MG MGA coupe	Posted: July 07, 2012 04:24PM Registered: 4 years ago Posts: 513

Bill,
The original tires were crossply 5.60-15. So it is difficult to match the tire diameter exactly.
Peter.

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Re: tyre size #3
Gary59MGA Gary H Southern Highlands, Australia 1959 MG MGA 1500 Coupe 1993 Mazda MX-5 NA	Posted: July 07, 2012 06:48PM Registered: 2 years ago Posts: 79

Use a tyre calculator like this one: http://www.miata.net/garage/tirecalc.html

I have the same width tyres as you on my MGA and find they make the car very heavy to steer.

My MX5 had oversized 205 width tyres when I bought it which gave the same effect, putting the correct 185 tyres on the car transformed the handling - felt much more nimble.

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Re: tyre size #4
MGARuss Russ Sharples New Jersey, USA 1960 MG MGA 1600 "Bonnie"	Posted: July 07, 2012 06:48PM Registered: 1 year ago Posts: 603

The OEM tires for an MGA 1600 did 803.7 Turns Per Mile. If you have a 1600 with a 4.3 Diff and 1440 TPM speedo (e.g. the numbers "1440" appear on the front of the speedo under odometer window on the right side), that is what you will want to get as close to as you can. A website like tirerack.com will usually give the TPM ("revs per mile" winking smiley

for a tire. Looking at that site, a typical 195/50R15 tire does 882 TPM, about 10% fast on your speedo. A 195/70R15 is rated at 810, about 1% fast, but that is a light truck tire, probably not appropriate for your MGA. If you have an MGA 1500 then you have a 1450 speedo which wants 809 TPM tires.

Note, the diameter measurement is useless as that is "unloaded". You need to know the "rolling diameter" which will vary with the air pressure in the tire, the weight of the car, etc. To measure it for my car (for speedo calibration) I rolled the car 10 tire rotations down the street and measured the distance.

Russ

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