anyone know if the factory mags of the TH sports ( 16's i think they are) will fit onto a 1992 tr and if they bolt straight on or are changes involved?

Will bolt straight on, no modifications needed. Check the rolling diameter of the tyres though, stock tyre for stock tyre they will throw the speedo out.

how much out do you think it may throw it? is their any way to fix that or just keep a mental note of it?

how much out do you think it may throw it? is their any way to fix that or just keep a mental note of it?

The OD of 215/60R16 is 664.21mm ------ 100km/hr
The OD of 205/65R15 is 647.44mm ------ 102km/hr
The OD of 185/75R14 is 632.96mm ------ 104km/hr

You'll need to fit 215/55R16 (642.87mm) tyres to be compatible with either of the 14 or 15 OEM wheels as you did'nt specify what you have at the moment.

I'm running 215/60 R16 on stock KJ EI 16" alloys (check profile pic), according to the info I could garner it should actually make the speedo more accurate, as apparently the stock 15" size reports 100km/h at an actual speed of about 96-97. So with that info, I calculated that the 215/60 R16 actually brings it to pretty-much smack on the money.
Don't have a GPS or similar to test with, but have been past plenty of radars / speed cameras without the slightest hint of a reaction.

Well it depends on what your speedo is like at the moment, our TR has 215/60R16's on it from my Verada and it adjusted the speedo about 4% from the original wheels and tyres, but its actually made it pretty well spot on.

I'm presuming you have an Astron 2.6 given its a 92, so find out what your actual speed is at indicated 100km/h (using either a GPS on a flat road, or a speed gantry on the highway if you have one nearby), then visit this site (http://www.miata.net/garage/tirecalc.html), enter your current tyres and rim size, and 215/60R16 for the new size (presuming the TH Sports wheels have the factory size tyre on them), set the results to metric and add the percentage difference it states, and see how that compares to your indicated 100km/h on the speedo.

For example, in my case, our TR had 215/65R14's on it, which read ~95km/h @ Indicated 100km/h under the speed gantry and on GPS. The difference between the 215/65R14's and 215/60R16's on it now is 4.6%, so added it to our old figure, your looking at 99.37km/h. Tested under the gantry/GPS, Indicated 100km/h now equals 99-100km/h actual speed. Mathmatically what I'm suggesting may not be 100% spot on, but its close enough to give you an idea what the outcome will be.

This site may help
http://www.miata.net/garage/tirecalc.html

thanks guys, yeah had one of those mobile speed signs down the road and drove past it, and the site lugo posted worked a treat :D

This site (http://www.1010tires.com/tiresizecalculator.asp) allows you to compare up to 4 tyre/wheel sizes with your stock one.