Bigger Rims affect Speed gauge??

[Jason99DSM]

ok sorry this is probably a dumb question, but i figure this bored is for dumb questions so here we go. Im getting some 17" rims in the next week or two to upgrade my stock 14 inch POS's. will this affect my speedometer at all since the wheel diameter is bigger?

 

[eclipsegs98911]

As long as you put on the right size tires you will be ok. I f you go to tires.com and put in your car and than your wheel size it will tell you what series tires you need.

 

[Iwantaneclipse]

When you increase the total radius of the wheel the speed being shown on your speedometer may not be as accurate. (your wheels turn at the same speed BUT the circumference is greater so you are actually going faster than what your speedometer shows).

PROOF: (this is in ideal conditions)

Angular Velocity:
v=rw

say you are going 20 meters/sec (72km/h)

WITH 14" RIMS:
--------------------
20=(14/2.5/100)w
w=357.14


WITH 17" RIMS:
------------------
now since the angular speed of a rotating object is the same at any perpendicular distance from the axis, w is constant.
so now we find the speed you are actually going with your 17 inch rims.
v=(17/2.5/100)357.14
v=24.29 meters/sec = 87.44 km/hr

87.44 IS NOT CLOSE TO 72!

this calculation didn't account for any energy losses and doesn't include the extra radius the tires add. As long as there isn't a huge difference between the radius of the 14" rim (including the tire) and the 17" rim (also including the tire) the accuracy of the readings on your speedometer should not be greatly affected. (HAHAHA did u get worried there for a second? )In other words do what eclipsegs98911 said and make sure you check the tires.

 

[DSMSpyder99]

what are the size of your tires?

 

[talontsi01]

For all you americans thats like seeing about 45 mph when actually going 54 mph.

going from 14's to 17's is a big upgrade.

 

[eclipsegs98911]

When you increase the total radius of the wheel the speed being shown on your speedometer may not be as accurate. (your wheels turn at the same speed BUT the circumference is greater so you are actually going faster than what your speedometer shows).

PROOF: (this is in ideal conditions)

Angular Velocity:
v=rw

say you are going 20 meters/sec (72km/h)

WITH 14" RIMS:
--------------------
20=(14/2.5/100)w
w=357.14


WITH 17" RIMS:
------------------
now since the angular speed of a rotating object is the same at any perpendicular distance from the axis, w is constant.
so now we find the speed you are actually going with your 17 inch rims.
v=(17/2.5/100)357.14
v=24.29 meters/sec = 87.44 km/hr

87.44 IS NOT CLOSE TO 72!

this calculation didn't account for any energy losses and doesn't include the extra radius the tires add. As long as there isn't a huge difference between the radius of the 14" rim (including the tire) and the 17" rim (also including the tire) the accuracy of the readings on your speedometer should not be greatly affected. (HAHAHA did u get worried there for a second? )In other words do what eclipsegs98911 said and make sure you check the tires.

As a Mechanical Engineering major in college, nice work! You are correct in saying the angular velocity will be higher on the out side of the 17s than the 14s. Though as long as the overall diamerter including tire is the same there will be no effect as a result, with an acception of a little power loss since your inertia is further from the center of the wheel. In this case an extra 1.5 inches extra on the radius. Ok this has been blow way out of perportion

 

[CowPimp]

http://www.miata.net/garage/tirecalc.html

This will help you figure out the correct tire size to run in conjunction with bigger rims.

 

[dev67]

"As a Mechanical Engineering major in college, nice work! You are correct in saying the angular velocity will be higher on the out side of the 17s than the 14s. Though as long as the overall diamerter including tire is the same there will be no effect as a result, with an acception of a little power loss since your inertia is further from the center of the wheel. In this case an extra 1.5 inches extra on the radius. Ok this has been blow way out of perportion "

While I am not saying you are uneducated, but that last bit about "Perportion"

 

[Sotarts]

ok sorry this is probably a dumb question, but i figure this bored is for dumb questions so here we go. Im getting some 17" rims in the next week or two to upgrade my stock 14 inch POS's. will this affect my speedometer at all since the wheel diameter is bigger?

What's your current tire size?

 

[ac49er]

as the wheels get bigger, as long as you are putting on the right size tire..the tire gets thinner, therefore, your complete wheel/tire radius isn't changing, which in turn will make your speedometer accurate, as it previously was

 

[Dreamchaser]

If you go to this site:http://www.walmart.com/catalog/cata...h=0:91083&redirect_dept=0&redirect_query=TIRE (yeah dont laugh its pretty accurate) and use the find tires by vehicle, it will tell you what size tires and wheels came stock on your car, then go to: http://www.miata.net/garage/tirecalc.html and enter in the tire sizes, you'll notice a lil ways down it will tell you how far off your speedometer will be with the diffrent size tires. You can enter the diffrent sizes on the right to get your speedometer pretty accurate.

 

[Jason99DSM]

my current tires are P195/70/R14 90S

 

[RiceKiller_TSi]

Why are you riding on Mario cart wheels dude? Go 17" immediately and watch your gas mileage go up.

 

[sphillips91]

http://www.eunos.com/tirecalc/

Check that out.

 

[hewhoisknot]

yep i went from 14's to 17's on my old eclipse and my tripometer was all off!!!!! it'd say like 65 miles when i'd gone like 72... so it must mess with the speed too