18 7.5 rims with 225/40/18 tires 42++ offset ?

[The UnseeN]

Just got 18s with 225/40 tires 42 ++ offset just wondering if this will fitt correctly and if anyone here has this setup ?? I got a 5th gen (1996)

[vasponger]

wow 225's thats pushing it. good luck, not sure how it fits though, post some pics when its done.

[matts]

crunch some numbers
your stock 195/60/15's have an overall diameter of 24.21"
the 225/40/18's have an overall diameter of 25.08"

your car thinks that one revolution is 6.338 feet
with the different diameter it will actually be 6.566 feet

i gotta go, but 225/35's would be almost exactly the same as stock.
i have this program that will tell how much the speedo is off, i'll do it later

[matts]

using 4.06 final drive ration off a prelude (not sure if thats what we have, but it's close enough)
the stock tires, at 3000 rpms have you going 53 mph, which is what the speedo will read no matter what size wheel/tire you have on there
at the same rpm you will actually be going 55 mph

at 6000 rpms the new tires have you going 110, while the speed will read 106.

i guess thats not too far off. might warrant a few speeding tickets, but it's not that bad.

ok, it might be worth the 2 or 4 mph off to gain a little ride quality.

[myGrub]

I've just gone through this - I'm actually waiting for my rims to turn up. I was told that 225 tyres will fit, but your offset is wrong. A 225 tyre will fit, providing the offset is soemthing like 35 - this relates to the width of the rim or how far it sticks out apparently. Is the rim 18" x 8" or 18' x 7.5"?

And the rolling diameter is too big as matts said. A 225/35/18 is like exactly the same diameter by a millimetre. I actually went for 215/35/18 (smaller by 8mm - but still within tolerances) because I was also worried about scrubbing, as well as the load index.

Best of luck with it - but think about changing the offset if you can, just to be safe

[takezo]

using 4.06 final drive ration off a prelude (not sure if thats what we have, but it's close enough)
the stock tires, at 3000 rpms have you going 53 mph, which is what the speedo will read no matter what size wheel/tire you have on there
at the same rpm you will actually be going 55 mph

at 6000 rpms the new tires have you going 110, while the speed will read 106.

i guess thats not too far off. might warrant a few speeding tickets, but it's not that bad.

ok, it might be worth the 2 or 4 mph off to gain a little ride quality.

Maybe you're right matts.
But did you calculate the weight (rims and tires) too?
I feel my 18s wayyy lighter than my old 15s.

[matts]

your stock 15's were around 15lbs. unless you spent a healthy 2G on your wheels, they are probably somewhere around 20lbs. you do loose a little weight of the tire but, in general bigger wheels are heavier. also, there is something that is called rotating inertia, which effects how much torque you need to turn the wheel. the farther the mass is out from the center, the harder it is to spin. so, not only are bigger wheels heavier, but they have a greater rotational inertia (again, in general) but along with that comes the better handling of the wider tires, the more stiff sidewall give you better handling, and more room for bigger brakes.
so you may not be able to feel a difference in the acceleration of your car, but if anything, it's gotten worse.