Chip adjustment due to tire size ?

[mungce]

I am considering larger tires on my 300A. I have D.R.s stage I chip, 4:10's. From what little I understand, tire size, unless its a major change won't require a chip re burn or adjustment. any help ?

[RF Overlord]

By "larger", do you mean bigger around or wider? As long the as diameter of the mounted tire doesn't change, then no reburn is necessary. If it changes by more than a few percent, then your shift points and speedo will be off.

[magindat]

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

[Rider90]

I changed to the larger 255/55/18 KDW2s and from what I recall my speedo was off 10 MPH @ 60 MPH.

[RoyLPita]

I changed to the larger 255/55/18 KDW2s and from what I recall my speedo was off 10 MPH @ 60 MPH.

according to the site above, the speedo should be off by 1 MPH.

[Rider90]

according to the site above, the speedo should be off by 1 MPH.
Oh right, i did the gears and the tires at the same time. Disregard.

[SergntMac]

I changed to the larger 255/55/18 KDW2s and from what I recall my speedo was off 10 MPH @ 60 MPH. Jason, typo, right? You mean 1 MPH? Or, are you including your gear swap to 4:10s? I peeked at the differences in these two sizes, OEM rear tire and your 255/55 here...

http://www.discounttire.com/dtcs/infoTireMath.dos

______________245/55-18____255/55-18________Difference
Sidewall________5.31"________5.52"____________.21"
Sectional Width__9.65"________10.04___________.39"
OD____________28.61"_______29.04"___________.43"
Circumfrence____89.88"_______91.24"___________1.36"
RPM___________727.02_______716 .25__________-10.77

Speedo________65 MPH_______65.98 MPH

The differences should not disrupt any systems on board, so, I'd say Jason has found us a new tire size to consider in the search for rear tires. Bravo!

[Rider90]

Jason, typo, right? You mean 1 MPH? Or, are you including your gear swap to 4:10s? I peeked at the differences in these two sizes, OEM rear tire and your 255/55 here...

http://www.discounttire.com/dtcs/infoTireMath.dos

______________245/55-18____255/55-18________Difference
Sidewall________5.31"________5.52"____________.21"
Sectional Width__9.65"________10.04___________.39"
OD____________28.61"_______29.04"___________.43"
Circumfrence____89.88"_______91.24"___________1.36"
RPM___________727.02_______716 .25__________-10.77

Speedo________65 MPH_______65.98 MPH

The differences should not disrupt any systems on board, so, I'd say Jason has found us a new tire size to consider in the search for rear tires. Bravo!
There isn't that much 255/55 unless you own an SUV, or want that look. Ever since the S/C my rear tires are well.....being very well distributed across the streets in my area. I need new rear tires soon, don't know if I should go widened - I'm not too impressed with that tire selection either.