Final Drive + 18" Wheels?
 

Tax refund coming in, plan on getting FD and some new wheels/tires. Not sure if this question has been asked before SO here goes nothing.


Ideally 4.67 seems to be the FD most suited for my needs. Weir only sells 4.56 & 4.88, and I refuse to pay 2.5-3x the price for MFactory gears. If I were to get 18" wheels and the 4.88 FD, would that put me around 4.67 because of the wheels making the gear ratio longer? Or would the difference in diameter drop me below the 4.56?

will depend on the profile and width of the tyres you put on the wheels ie the amount of rolling diameter change over stock tyres, as well as final drive ration selected.

4.88 with 235/40/18 or 225/40/18

Look on tire rack they give you the diameter. I have 245/35r18's all around and they are the same diameter as stock. Which is the primary reason I went with that size. :thumbsup:

So what outer diameter should I be aiming for to drop the overall gearing of the car to a 4.67 range?

Something narrow and like 16" wheels. Not really feasible or cosmetic. Most tires decrease the final drive.

If you were one of those kids in high school math thinking to yourself, "I'll never use this, why do I need this, this is so stupid!" I bet you're kicking yourself now.

Why not 16s or 17s?

Warning! MATHS inside
 

The difference between 4.88 and 4.67 is about 4.3%. Using the tire size calculator at http://www.1010tires.com/Tools/Tire-Size-Calculator I found, strangely enough, that 215/45/18 is the closest, (the exact same profile as stock, only 18" instead of 17"). It comes in at 4.06%. Putting you at 4.68, rather than 4.67. Does that answer your question?

Haha, ironically I am an engineer and graduated 1-2 courses short of a mathematics degree as well. EE's don't know anything about gearing is all!

Numbers are still numbers.

What wheel size are you planning on running? widths/offsets?
How low do you plan to go?
And how much power/grip do you have and want?

245/40-18 is a pretty good size, but would be slightly shorter(bigger number) than 4.67 gears. Just beware if you go too low, since you are planning to get a bigger diameter tire, there will be less room in the wheel wells.

And how did you come to the conclusion that 4.67(or 4.88 with taller tires) is the setup you are after?

18x8.75 +35
1" drop (Eibach Pros)
Stg 2 OFT beta tune (~200whp 93oct)

I looked at the RPMs I would be hitting in 70 on the highway at 4.56 and 4.88, and somewhere in the middle is a happy medium.

So you want to get the 4.88 and a bigger diameter tire to emulate the gearing of a 4.67.
As mentioned above, 4.88 to 4.67 is about 4.3%
215/45-17 compared to 245/40-18 is about 4.3% also. (Reconfirm yourself)
So that IS the tire size you need. 245/40-18.
Good luck and thank me. :party0030:

Interesting thread. I'm about to do the same exact thing but never really thought about how much the wider wheel/tire diameter would effect the aftermarket final drive.