Changing from 225-45-18 to 225-40-18
 

I want to know what the effects will be if I change from the stock 225 45 18 to 225 40 18, the problem is that the tire sellers tell me the RX8 has an odd tire size so the original size tires are double the cost, I'm in South Africa so you may not have the same problem in the country you might be in. So the point is i want to get a 40 profile to keep the cost down.

the only downside is the tackometer will be off by like 1 or 2 mile so when it say 50 you really are at 48 . thats it ..... go for the cheap tires!

Wheel one centimeter lower, and 3.5% reduced final drive. I'm installing 225/40r18 Hankook v12 K110 on purpose to get more acceleration and less sidewall flex. I use my scan gauge II for speed anyway so I don't care if the speedo is off.

You can also try and get a 245/40/18 tire to keep the overall diameter close to stock.

235/40-18 works just fine and is closer than 225/40 but a bit smaller than the perfect match 24/40-18

Search "Tire Calculator" on Google. You can see what the differences will be.

Putting 225/40s will also make you car ride a little rougher. I got smaller tires installed on my car and its not much rougher but you will notice

I've got 225/40 Bridgestones on mine. Yes, it's literally half the cost compared to the original size, and no real difference other than ride comfort - it's a slightly harder ride, but there's no other downside. I've noticed a number of 8's with the same profile.

I have used 225/40-18" and 235/40-18" and both dimensions make minimal changes from 225/45-18". The small changes there is is actually (in my mind) to the better.

225/40-18" - Slightly better acceleration, better looks (not so mutch tire sidewall), less sidewall flex, slightly harder ride.

235/40-18" - Same acceleration as stock dim., same comfort as stock dim., slightly better grip.

Im going to stick with 235/40-18" cheaper tires (more auto makers uses this dimension) and the rest is close to stock or better.

thanx for all the advice, def going to help me alot.