225 40 18 front. 225 45 18 rear?
 

Wondering how this would effect my car and if it would be any harder on the drive train and tire wear?

This will be fine as long as they are the same size on both sides of the car. Front to rear will not really do you any harm. Certainly not enough to justify buying 2 new tires. Just when you replace them get the same size.

For speedo accuracy you have got them the right way round the 225/40 will be a little smaller, if you put them on the back the car will accelerate a little quicker but your speedo will be a few MPH higher than your actual speed.

Curious as to why you would choose to do this? I am assuming you need 2 new tires and found a deal on a set?

Okay thank you ! And yes that is exactly it, one of my tires got ruined, went to order a new one and they don't make that tire anymore. A little low on cash right now and have a chance to get the 40's much cheaper.

As long as both sides are the same it is ok. I have run different sizes front to rear with no problems.
They have to be the same side to side though, if not your LSD constant thinks the car is turning and under heavy acceleration or braking the car will want to push to the right or left.

I put 225/40r18 Hankook Ventus V12 on the front for a few months until my rear 225/45r18 Kumho SPT's wore out.

I drive easy anyway, and 300 miles to the track no problem, but when I found the limit of the tire the DSC was not happy and bucked me off!

Instead of correcting a low speed skid, it forced a 360 spin staying on track, and I understood real quick to turn off the DSC for rest of day.