ioTus

iTrader: (5)

Hey guys, i'm looking at getting some 16"x7" rims for my '85 GS.

I want to keep the outside diameter of the tire the same to avoid as many changes as possible.

My friend, who has a GSL SE has 16x7's and is running 205-40-16, mounted by the previous owner (i'm not sure how much the previous owner knows about cars, i know my friend knows NOTHING hehe)

Hey thanks for the help guys!!

Geoff

Manntis

go 205/50R16

205/45 are smaller, making the car slightly quicker but screwing up the speedo calibration. 205/55R16s are more common, therefore cheaper, but 205/50r16S FIT THE BEST.

ioTus

iTrader: (5)

And they are going to be pretty much the same O.D.?

Thanks man!!

Now for any suggestions on tires?

Geoff

REVHED

Are you sure about that? The stock tyres are 13/70's. A 16inch rim would require a 40 series tyre to retain the same outside diameter.

Manntis

I'm positive. the 45s are a bit smaller, the 55s a bit larger. 50 is close to stock in the real world. I looked into it before buying the 205/50R16s I have now.

For my tastes I got the Pirelli P7000s as they have a kevlar bead, they're quite quiet (squealing tires say 'ticket me') and they've got an agressive but rain-friendly tread pattern. I hear other brands as well as the Pirelli Zero Neros are quite good, but the Neros weren't available yet and IMHO would be overkill as they outperform the car's street abilities.

REVHED

If you do the math, a 13/70 has an outside diameter of 22" as does a 16/40. I dunno, maybe the higher profile tyres baloon out more.

rx7gslse

here ya go... the best link ever for these questions...

http://www.miata.net/garage/tirecalc.html

Manntis

If you do the math, bumblebees can't fly. Yet they do.

But the GSL-SE has 14 inch, not 13 inch wheels. The rolling diameter of the 205/60R14 stock wheels works out to 23.68 inches.

A 16 inch rim can use a size 205-14R16 at .42 inches smaller diameter and make the car go a whisker faster, but you're risking the (not cheap) rims (less protection).

A 205/50R16 tire is .39 inches larger, in theory slowing the car slightly, but offers the most cushioning from bumps, etc. that you can expect in a low profile 16" tire.

I've driven a few California Ricemobiles that have such low profile tires that it looks like a black rubber band has been added to the rims in place of tires. They have to slow to a crawl over rail road tracks or even potholes to avoid bending or gouging their rims, which kind of takes away from the whole "go fast" mission.

The 50's do slow the car slightly over the 45's IN THEORY but not so as you'd actually notice, while at the same time allowing you to drive normally without having to baby your rims.

moremazda

iTrader: (4)

Manntis,

I agree with what you are saying but I think your explanation is a little backwards. A larger diameter tire will acctually alow you to travel at a higher rate of speed for a given wheel rpm, due to the fact the a larger diameter will yeild a larger circumferance.

A larger tire WILL take more power to accelerate at the same rate as a smaller diameter tire, in effect slowing the acceleration of the vehical.

Not flam'n', just clarifing.

Ryan

Manntis

the smaller tire gives you more favorable gear ratios which allow more power to the pavement (shorter lever and all that)

it's fulcrum/load physics, not straight out circumference, that makes the difference.

There IS a point of diminishing returns, but at a .42" difference the smaller tire makes for quicker car.

REVHED

Ok I see what your saying. That may have worked for you but the guy who posed the question doesn't have an SE. In his case a 16/40 will give the correct outside diameter.

Manntis

That's my error. I read GS as GSL

knight1976

What size would i need for 15 inch rims?

ioTus

iTrader: (5)

For mine, the tire size calculator and the local shop agree its 205/45/16 for my 16" rims.

For 15x7 Rims, you would need 205/50/15's to closest match the stock O.D. with just a small ammount of difference in spoedometer (sp) change.