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Discussion Starter · #1 ·
I purchased and had installed along with Carbotech ceramic pads this past wednesday. I went with everyones suggestion of the 275/30 /19 rear and they fit perfectly! No rubbing and they look great and ride smooth. Also am enjoying not cleaning wheels every 100 miles !
 

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good that ur enjoying it... doesn't the fact that the sidewall is 30 as opposed to 35 make the speedo reading slightly wrong? and how would it be if they were 275/35/19? did you change your front tires?
 

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My 2 cents if I may:
overall diameter of these various tire sizes.

OE: 255/35/19 overall diameter = 26.00 inches

275/30/19 overall diameter = 25.50 inches

275/35/19 overall diameter = 26.50 inches

About a 1/2 inch difference in O.D. either size from factory. Divide that 1/2 by 2 since it's a round tire and you end up with about a 1/4" difference top and bottom from factory spec. Not really enough to make significant difference in the speedo IMO. Probably would be off be 2-4 mph.
 

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That is with the factory rims on correct?
 

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My 2 cents if I may:
overall diameter of these various tire sizes.

OE: 255/35/19 overall diameter = 26.00 inches

275/30/19 overall diameter = 25.50 inches

275/35/19 overall diameter = 26.50 inches

About a 1/2 inch difference in O.D. either size from factory. Divide that 1/2 by 2 since it's a round tire and you end up with about a 1/4" difference top and bottom from factory spec. Not really enough to make significant difference in the speedo IMO. Probably would be off be 2-4 mph.
once again, i say. isnt the speed picked up via wheel speed sensor. aka not in the driveline. so tire size should not matter.
 

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Discussion Starter · #7 ·
I wish someone could verify what Doublexl is saying. I will check with mile markers as soon as possible.
 

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I wish someone could verify what Doublexl is saying. I will check with mile markers as soon as possible.
search the forums for a thread where they put a 4.08 rear differential in the IS F. factory is a 2.93 rear gear. it was a dealership that did it, im not sure who, i cant remember. they said they drove 2 IS F's side by side, one with the new diff, one without, and the speedo's were exactly the same. so if the diff gear change doesnt make a difference, why would tire size.
 

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All you have to do is go to the dealer and they can program the new tire size just like we do when people put big tires on Tahoe's etc.
 

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I've noticed that my IS-F with the stock wheels and tires seems to read about 1-2 mph low. Is that pretty typical?

I'm basing this on the fact that two independent speed trailers that show your speed both showed my indicated speed between 1 and 2 mph too high.

I guess I could pace my wife's car and see if it confirms or denies this. I guess I'd rather have it read low than high :)

Jeff
08 Smoky Granite Mica IS-F
 

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once again, i say. isnt the speed picked up via wheel speed sensor. aka not in the driveline. so tire size should not matter.
If you change the rolling diameter of the tire, that will affect the speedometer. A wheel speed sensor is reading rotation of the wheel. If you change the height of the tire that will change the rotating speed of the wheel. The size chart I presented was to show that we are splittin' hairs with sizes discussed vs. OE.
In this case, size does matter :cool:, but not by much. If you took a sampling of 10 of the same cars from any manufacturer, you would probably find that the mph their speedometers read vary by 1 or 2 mph all things being equal.

The rear end gear swap didn't change the rolling diameter of tires fortunately.
 

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So how about the Ultrac Sessanta tires? Have you noticed it being more slippery on painted surfaces or rolling over road markers? Some people complained about it, and was curious how serious it is.

How about braking?
 

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I have been running the Vredesteins for the last 6-8 months and have found their wet traction to be equal to, or better, than the original Bridgstones.

I have driven them for a track weekend. Saturday of that weekend was wet so wet traction was critical.

I am very happy with the Vredesteins.

Pat
 
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