please help!running different tires ?! madness

here it is. . and remember i'm a broke college-kid

my 05 lgt had a whack alignment, which i took care of. now because the alignment was out the front wore out much quicker and caused uneven wear on those two front and is actually subtly noticeable while driving.

on the car i have stock rims, i have yokohama avid envigors 215/45r17 87w

-two of which wore out uneven, the other two are at about 60% tread

-i moved the two decent %65 tires to the front to make for a less shaking feeling while driving.

now for the part i need help on:

my buddy owns a shop and he got a hold on 2x yokohama avid h4s 215/45r17 91h at about 70-80%, which he offered to give to me for free. i would like to save myself money and send the uneven tires to hell, and take advantage of better rubber. i mean the only diff is the speed rating amiright?

ive heard the rules about deviating from the same size between a set of tires will cause evil witchcraft in our gear,trans,things. my question is can i buy text books this semester and rest easy that the free tires will work with causing minimal to no harm til winter? or do i need to buy all new wheels?

thanks in advance

Envigor

http://t1.gstatic.com/images?q=tbn:ANd9GcQ-89XJgVFxPJ2T1M7Zxk3t6fw3SJ4O5XK4I2CWi6XPGDsb7PXA&t=1

VS

H4S

http://www.qsrproductions.com/store/images/yokoavidh4s1.jpg

They have different speed ratings but as well different treads patterns.

The tires may work in allowing you to drive down the street, but the havoc it would cause on the drivetrain isn't one I would recommend.

(But at the same time, having all 4 wheels the same but varying degrees of wear on them isn't truly better)

My $0.02 on the matter where I probably don't have any expertise.

Good luck

Welcome to THE worst part of having an AWD car. I cringe thinking about one tire getting a real blow out because I know it will mean a pain in the rear or 4 brand new tires to fix.

Running different tread patterns will cause some amount of goofy wear or ride..I would think but so long as they aren't extremely different I don't think that would be so bad.

What you need to be most concerned with right now is potentially having different type and wear amount on each corner making one or more wheels have a larger overall diameter than the others. That's what will goof your diffs up from what I understand. Search around, there's a way to measure them and see how close they are. I THINK the tolerance is like no more than 1/4" in difference per corner or you start to mess things up. You can get tires that are too new/large shaved down to match at some tire shops too.

1/4" is cirmuference difference.

Krzys

PS Would you save enough so you will have money for new tires and new center diff if you get 2 free tires now? Maybe you need to sell GT and buy cheaper car to maintain? Before you fry central diff.