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Discussion Starter · #1 · (Edited)
It looks like the 2015's and up can. Wondering if the older ones can? I bought some lower profile all season tires for my car. the reason is I had 275x35x20 in the front, and 295x35x20 Nitto Invo summer tires on it. (The car came with Velgen 20" wheels, and the Nitto tires.) Trying to find some all season tires (I live in Seattle area. and summer tires in heavy rains are suicidal.) I found one of the few companies that had all seasons in those sizes was again Nitto. They make a Motivo in those sizes, but in a 30 profile. I went with those, and had my tuner unlocked because I was worried about the rotation throwing off the speedo, and also making the mileage look like it is going by faster, which I really don't want. I plugged in my SCT x4 tuner (Wiped of the Bama tunes), and the thing told me the tire's outside diameter!! I was like WTF??? and it was pretty damn accurate. The Nitto Motivo tires are rated at 27.01 outside diameter. Stock size is 27.7 on 2015 performance pack GT's. The tuner told me the tires were 27.04. only 3/100ths difference from what Nitto says they are. BTW I have only had these tires on for like 200 miles. No way it could have known that unless the car can somehow figure it out. Remember these tires were not on the car when I bought it, and a lower diameter than the Invo's. BTW the 295x35x20 profile Invo's are 28.11" not very close. I was blown away. Thoughts?
 

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It looks like the 2015's and up can. Wondering if the older ones can? I bought some lower profile all season tires for my car. the reason is I had 275x35x20 in the front, and 295x35x20 Nitto Invo summer tires on it. (The car came with Velgen 20" wheels, and the Nitto tires.) Trying to find some all season tires (I live in Seattle area. and summer tires in heavy rains are suicidal.) I found one of the few companies that had all seasons in those sizes was again Nitto. They make a Motivo in those sizes, but in a 30 profile. I went with those, and had my tuner unlocked because I was worried about the rotation throwing off the speedo, and also making the mileage look like it is going by faster, which I really don't want. I plugged in my SCT x4 tuner (Wiped of the Bama tunes), and the thing told me the tire's outside diameter!! I was like WTF??? and it was pretty damn accurate. The Nitto Motivo tires are rated at 27.01 outside diameter. Stock size is 27.7 on 2015 performance pack GT's. The tuner told me the tires were 27.04. only 3/100ths difference from what Nitto says they are. BTW I have only had these tires on for like 200 miles. No way it could have known that unless the car can somehow figure it out. Remember these tires were not on the car when I bought it, and a lower diameter than the Invo's. BTW the 295x35x20 profile Invo's are 28.11" not very close. I was blown away. Thoughts?
Tying to figure this out.
First, I assume you saw that the tune had the tires set for the 28.1tires before you removed it.??
You say you removed the tune (returning it to OEM tune) and when the tuner told you the tires were 27.04, he was talking about the OEM tune? And you feel the stock tune should be reading the 27.7, which would reflect the original OEM tires of a GT Track Pack.

Is there a chance that original OEM tune got lost due to previous transfer of car without the original tuner and was unlocked by a new tune? I would think the current tuner could tell if it wasn't an OEM tune that was saved to the current tuning device.

I doubt very much that the car's computer can learn the dia. of the tires unless it had a GPS system to check the speed of the car against. :facepalm:

EDIT: If what you were suspecting was true, that would mean you could dial in a different tire dia and it would correct itself in time.:eek:
 

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Discussion Starter · #3 · (Edited)
Tying to figure this out.
First, I assume you saw that the tune had the tires set for the 28.1tires before you removed it.??
You say you removed the tune (returning it to OEM tune) and when the tuner told you the tires were 27.04, he was talking about the OEM tune? And you feel the stock tune should be reading the 27.7, which would reflect the original OEM tires of a GT Track Pack.

Is there a chance that original OEM tune got lost due to previous transfer of car without the original tuner and was unlocked by a new tune? I would think the current tuner could tell if it wasn't an OEM tune that was saved to the current tuning device.

I doubt very much that the car's computer can learn the dia. of the tires unless it had a GPS system to check the speed of the car against. :facepalm:

EDIT: If what you were suspecting was true, that would mean you could dial in a different tire dia and it would correct itself in time.:eek:
Well, the car does have GPS. Not just the Navigation, but it has a factory warning sticker saying police can track it if stolen. (Factory security package) The tuner didn't allow me to set tire diameter of the tires previously. My last car on.that tuner was a 2012 gtcs. Tire size was in the pre programmed tunes which I removed.. I will look into their size though. BTW the tuner said the tires were that size. There was no option to.change the size. Not with what's in it now Amway. The GPS angle I didn't think of though. That really would explain it. Looked up the tires. Toyo T1S 275x40x19. Diameter is 27.7. So my tuner was not programmed for 27.04.
 

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If you are saying the the cars computer "senses" what size tires are on the car, I don't think that is possible. As strange as it may seem computers are not magicians and AFAIK there is no sensor in the wheel well that measures your tire and tells the computer what size it is.
 

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I'm not saying I believe that's what happening BUT I think it would be possible for the car to calculate the tire diameter based on knowing the MPH per the GPS system and comparing it to the car's MPH, which includes tire circumference in its calculation.

EDIT: The ABS sensors are used to calculate the odometer reading, which takes into account the tire size. So if the car's speedometer didn't agree with the GPS speed, the computer could theoretically be made to adjust the tire size part of its formula to make the speeds agree.

I think!:D
 

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I'm not saying I believe that's what happening BUT I think it would be possible for the car to calculate the tire diameter based on knowing the MPH per the GPS system and comparing it to the car's MPH, which includes tire circumference in its calculation.
I don't think the computer has the ability to "relearn" a tire size based on GPS. I could be wrong though with the newer cars.

The car's computer leaves the factory with a known tire size, and therefore the calculation for fuel mileage (instant and miles to empty) is calculated based on this fixed computer data.
If you change the tire's size, this would have to be corrected either by a flash change, or by a tuner. Most tuners sold today have the ability to allow an owner to change the tire size so that the computer can calculate the miles per empty and instant miles correctly with the new data.
 

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I don't think the computer has the ability to "relearn" a tire size based on GPS. I could be wrong though with the newer cars.

The car's computer leaves the factory with a known tire size, and therefore the calculation for fuel mileage (instant and miles to empty) is calculated based on this fixed computer data.
If you change the tire's size, this would have to be corrected either by a flash change, or by a tuner. Most tuners sold today have the ability to allow an owner to change the tire size so that the computer can calculate the miles per empty and instant miles correctly with the new data.
Yes I know how it works but the key words are, "I think it would be possible", if they wanted to do it. Maybe not practical!
 

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Yes I know how it works but the key words are, "I think it would be possible", if they wanted to do it. Maybe not practical!
It would theoretically be possible but the added cost to add the GPS data to the rest of the system will probably prevent it from ever happening.
 

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It would theoretically be possible but the added cost to add the GPS data to the rest of the system will probably prevent it from ever happening.
Agree!
Plus, as far as I am concerned, there's already too much automation incorporated into cars.
 

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Agree!
Plus, as far as I am concerned, there's already too much automation incorporated into cars.
Plus they tend to use the same diameter tire from the factory most of the time, and most owners will stick to oem size when replacing them. This feature would essentially never benefit a large majority of cars.
 

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Discussion Starter · #12 ·
So my tuner just told me the right tire size by what, ozmosis? Its never been on that car before, we established that the tire size from my last car doesn't match that. (27.7") The tires I just replaced were 28.11". So how else would it be that accurate unless it figured it out from the GPS? My programmer won't even let me enter a tire size.
 

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Discussion Starter · #13 ·
Agree!
Plus, as far as I am concerned, there's already too much automation incorporated into cars.
Which really doesn't enter into this.
 

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So my tuner just told me the right tire size by what, ozmosis? Its never been on that car before, we established that the tire size from my last car doesn't match that. (27.7") The tires I just replaced were 28.11". So how else would it be that accurate unless it figured it out from the GPS? My programmer won't even let me enter a tire size.
The size difference is probably so small you can't see the speed difference
 

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EDIT: The ABS sensors are used to calculate the odometer reading, which takes into account the tire size. So if the car's speedometer didn't agree with the GPS speed, the computer could theoretically be made to adjust the tire size part of its formula to make the speeds agree.

I think!:D[/QUOTE]

^^^^^This. The rotational speed changes with diameter size. For example If I put 27" slicks on the back while keeping my stock 25.5" tires on the front the ABS will notice it, light on the dash and no ABS.
 

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Discussion Starter · #17 ·
The size difference is probably so small you can't see the speed difference
The difference between 28.11" tires, and 27.01" thats so small? thats a BIG difference. The tires that were on the car were 295x35x20 with a diameter of 28.11" I went to a 295x30x20 with a diameter of 27.01 that just over 1.1 inch difference. That's definately noticable.
 

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Discussion Starter · #18 ·
Plus they tend to use the same diameter tire from the factory most of the time, and most owners will stick to oem size when replacing them. This feature would essentially never benefit a large majority of cars.
That I can't disagree with. But I can't see anything else but the GPS entering into it.
 

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The difference between 28.11" tires, and 27.01" thats so small? thats a BIG difference. The tires that were on the car were 295x35x20 with a diameter of 28.11" I went to a 295x30x20 with a diameter of 27.01 that just over 1.1 inch difference. That's definately noticable.
The post i quoted said 27.7 vs 28.11. That would be a 1mph difference at 50-60 and 2mph at 110

Going from 27.0 to 28.1 would be about 2mph at 50 and 4mph at 100. Still not a huge difference
 

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Discussion Starter · #20 ·
If you are saying the the cars computer "senses" what size tires are on the car, I don't think that is possible. As strange as it may seem computers are not magicians and AFAIK there is no sensor in the wheel well that measures your tire and tells the computer what size it is.
As mentioned in this thread the car has gps so it can litterally tell how fast it's going despite the speedo.
 
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