shikbas

Hi ,I have rx330 04,I want to upgrade tires from 235/55/18 to 255/55/18.What do you think about the navigation system accuracy here?
thanks

The G Man

You are just changing the width of the tire, should be no difference at all. Besides, the Nav. works with satellites not tire speed or rotation.

Ritzyblue

As G-man says you are only changing tire width, The 235 is the width. The 55 is the sidewall height. The 18 is the rim diameter. Changing the 55 would be more of a concern on the speedometer not the navigation as that tracks your speed and position from various satellites. Changing from 235 to 255 is just a bit wider but just be careful not to go to wide as the tire will rub inside the fender well on tight turns.

This should help:

http://www.tirerack.com/tires/tirete...e.jsp?techid=7

kpblade

Actually. the overall diameter of the tire and its circumferance would change. The "55" is actually the size of the sidewall as a percentage of the tread width, in this case 55%. So if you go from a 235/55 to a 255/55 the sidewall size will increase and chage the overall diameter. To keep it a +1 size (same tire diameter) you would need to go 235/55 to a 255/45, or there abouts.

CK6Speed

iTrader: (1)

Even though you are increasing the over all diameter by a small margin, it is nothing to worry about. Speedometer accuracy tolerance from vehicle to vehicle is probably greater than your change in tire diameter. I went from the stock 17" 65 series tires to 255/50/20 over sized tires and according to my GPS my speedometer was only off by about 2 MPH at 60. Heck, my states law allow up top a + or - 7% change in over all tire diameter from original. It is rare to find a speedometer that is 100% accurate anyway, so the slight change in speedometer accuracy is well within the industry tolerance.

jfelbab

I considered the Bridgestone Alenzas in the 255/55/18 size but decided I didn't want to deal with the speedometer/odometer error and weight issues. The Bridgestone 235/55/18 tire has 1.2" wider tread than the Goodyear RSA of the same size so it looks and handles much better and no speedo/odo errors or fiitment issues.

The Bridgestone Dueler Alenaza 255/55/18 is only an "H" rated tire as opposed to the 235/55/18 "V" rating. V rated tires flex less and run cooler.

Also the tire weight for the 255 is 38 lbs. The 235 is 33 lb., 5 lbs. a tire lighter. The OEM Goodyear weighed only 29 lbs. I didn't want to add 9 lbs. of unsprung weight to each wheel as this would likely affect the road feel in a bad way. I did this to one car and it felt like the wheels were slow to respond and heavy over any bumps or tar strips. It really made the car I did this to ride much worse due to the added unsprung weight.

FWIW, the speedo/odo error for the 255's would be about 3% which is reasonable.

For every 100 miles traveled the odometer will read 103 miles.
At 65 miles/hour the speedometer will read 67 MPH.

I don't believe this would cause any major issue with the NAV.

The Bridgestone Dueler Alenza 235/55/18

Lil4X

Your nav system does use wheel speed to calculate distance traveled UNTIL it can lock up a series of two or three satellites and triangulate a fix. This ordinarily takes as much as 45 seconds from engine start, but could vary somewhat depending on how much of the sky and how many satellites are in view. Don't count on this happening in a parking garage.

The "Dead Reckoning" function is what keeps your position when incoming data is lost, too - such as passing through a tunnel, heavy overhead vegetation, or driving on a narrow street with tall buildings on either side. Fortunately these intervals are fairly short, and a few tiny percentage points' error over a matter of seconds, should not produce any observable error in your plot.

The G Man

You are right, thanks for clearing that up. Going up to 255/55 will increase the diameter by about 7.5%, but going down to 255/45 will decrease it by about 11%. Too bad they dont make a 50 series tire

jfelbab

Here is a site that will tell you everything you need to know about plus or minus sizing.

http://www.rims-n-tires.com/info_specs.jsp

Really an excellent site.

shikbas

thank you all gys

AM1

iTrader: (6)

i have 255/55 on my car and the nav still works the same

mandyfig

Is it me or this Photo is so great looking, looks like an ad for the Alenza! Great shot!

jfelbab

Blush! Thanks, maybe I should send it to Bridgestone,

mandyfig

You should, they will send you a talent fee!