Max front tire size
 

I've got a project goin on, and I'm liable to end up with some 19" wheels about 8-8.5 wide that are more or less surplus. Question is on a 19" rim what can I get bye with for large tire size, and please, skip all the debate about offset.(it's adjustable) Just trying to give the thing a chance of cornering like like it will accelerate..:)

Have you tried a tire size calculator? 19" is going to push you into the "oversize" category with tires unless someone makes a 30 or 25 sidewall series tire.
http://www.miata.net/garage/tirecalc.html
Stock tire size is 205/60-15. You can fit a 245 width in front. That's about max with the correct offset.
245/30-19 would be about right, if that size of tire is even made.

Doesn't look like many have messed with 19" fronts, and the more I think about it, the less I like the idea.(would have to look, and be stupid) How about this, what's the biggest tire the stock 14" wheels(or maybe the z31 15x7"s) will tolerate?

what do you mean by big? Are you going for the widest tread possible? Wide tread will be the same max no matter how much wheel diameter you have.

By big I mean the tallest and widest I can get in there without modification,(or interference) got a feeling the back is going to require all that I want to mess with on that score!:)

Going taller than stock will look stupid and throw off your speedometer reading.
Stick with 245 in front and use the calculator to figure out the proper size. Go slightly smaller diameter if you must.

The rear can hold a really wide tire. I'm not sure how wide though.

?? Not sure which end your talking about?? The subject is the front. Haven't had it apart, but I believe the speedo is driven off the driveline, so front tire size should not affect that. I thought only VW's drove speedo off front. Far as the back goes, the only way I know to put any power to the ground is with a big tire, and the back tire has already been selected, it's 29"x12.5".(yes, it WILL fit, only question is how much time it will take to make it) I doubt seriously anything that will fit on the front will be that big.

What I was trying to find is people that had experienced just what exactly what to big was.