New rims, MPH off?!?!?
 

Ok so if i were to get 18's, and get ride of my stock 16's my speedo would be off, how exactly do you recalibrate your speedometer to get it correct?

no it won't....get the stock sized 18 inch tires

your car would automatically adjust your speed??? no adjusting???

You must size a wheel/tire set which will equal the Outside Diameter of your current 16" tire if you don't want to deal with calibration issues. If you are accurately increasing wheel diameter while reducing sidewall height, the Outside Diameter does not change.


Go to TireRack and plug in the current tire you have. Find the O.D. on the spec of that tire. Now, match the O.D. as closely as possible with the 18" tire of choice.

even if you upgrade to the 18" wheels as long as the total rolling diameter (with tires) is the same as the 16" you're ok.

so like the above poster said, if you go with the stock 18" tires (225/40R18) you're good to go.

sounds a little confusing... whats the outside diameter of the stock 16's, i dont have time to measure right now...

yeah, so the oem sized tires for the 18's should be fine

i was thinking the Borbet 18's but for Dan its showing on tirerack that the stock 16's are 225/45-18, not going to lie i dont know much about changing tires but could tire rack be wrong?

stock tires are 225/45/18.

get 18s and get 245/40/18. wider tire, really close to stock size.

Select Automatic or Base, etc. on the RX-8 selector guide.

225/45/18 is the OEM 18" tire size for the Sport AT or stock 6-speed.

Go to the actual tire's page and click on SPEC Guide (or whatever it reads) and scroll down the sizing chart to read the tire's Overall or Outside Diameter.


FWIW, you are lazy.

so since im a noob (sigh) im assuming (yes i know what it means) the 245/40-18's are going to be a little off? or do the numbers after the slash have nothing to do with the speedometer? and i apologize South, i didnt look at the website enough, i was more browsing the rims...

Yup.


OP, please let us know what wheel width and offset you are going with.

No worries,

Read the link on the Tire Rack website which deciphers the tire numbers.

225 = width
45 = Sidewall aspect ratio
18 = Diameter wheel it fits on

Overall Diameter needs to be looked up in the tire manufacturer's spec guide.

The speedo runs on sensing axle rotation.

Change in Overall Diameter is what affects the axle rotation, which in turn, uncalibrates the speedo's mph reading.

ok so i was thinking of the Borbet Type XL with the Machined w/Black Accent finish and some Dunlop Direzza Sport Z1 Star Spec 's for 225/40-18, keeping in mind i think it will look pretty good on my Whitewater Pearl color, and since its a 225/40-18 i might need to adjust the speedo or would it matter since its close to stock anyways?

245/40/18 is very close in O.D. to the 225/45/18 tire. Close enough to only throw off the MPH readout slightly, but still within usable range.

No. You need 225/45/18 or 245/40/18, as mentioned above.

aight so getting the rims with 245/40-18 the MPH readout will only be slightly off... well this has helped alot... btw the Borbet tire on tire rack recommends 225/45-18 size tire, will the 245/40-18's be fine? o and someone said the 245/40-18's are close to the stock tire except for being wider etc. but how much of a difference is it really, handling wise? i mean id be willing to go with a wider tire for better handling but if i found a specific rim with uses the 225/45-18 size tire how much performance am i losing? and how much do stock 16's weigh?

No problem.

last question look up lol

cant find how much stock 16's weigh with, and without tire... aight well ill see if anyone knows this tommorow...

that's the key!

unless you get your 18's wrapped in tires with the sidewall as tall as the 16's! :uhh:

the stock 16's are 16.3 lbs.

thats without rubber? so my accel times are gonna go down if i get a 23.0 lb rim without tire... :banghead:

And to re-ask my old question that never got anwsered, aight so getting the rims with 245/40-18 the MPH readout will only be slightly off...btw the Borbet tire on tire rack recommends 225/45-18 size tire, will the 245/40-18's be fine? o and someone said the 245/40-18's are close to the stock tire except for being wider etc. but how much of a difference is it really, handling wise? i mean id be willing to go with a wider tire for better handling but if i found a specific rim with uses the 225/45-18 size tire how much performance am i losing?:uhh:

Thanks

A) You don't deserve a new set of wheels/tires. Fail on the research.

B) Look at the tire sizing charts and you will begin to understand why either the 225/45/18 and/or the 245/40/18 will work. The site is doing a fine job in recommending a 225/45/18 tire.

C) You chose a heavy wheel. Look for something around 20lbs or less if you can.

D) Increased weight in a larger wheel/tire combo has a benefit in increased performance by offering a decrease in sidewall height (increased sidewall stiffness for better lateral control) and several other factors which you simply need to read up on. Yet, if you go too heavy or too large, you are negating the benefits. Going from the 16" to the 18x8, 225 45 18 combo is a proven performance increase if you choose the right wheel and tire (use the stock 18" wheel and tire combo as a basic standard to emulate in weight weight and tire grip -the Star Spec alone will far surpass the OEM tire performance). Read the links on the Tire Rack website which are informative.

I got 20s on my, does that effect the speedometer?