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confused on the 17" to 19" and tire size

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Discussion Starter · #1 ·
standard 17" wheels have diameter or 26.74" and 19" wheels have diameter of 29.17" do they reprogam these rigs, cause i want 20s with out getting such low profile. Mine came with 17s which i am going to run in the winter then looking for 20's but to get the 20s at the right height i need to order such a low pro tire. but when and if you got the factory 19s the side wall is much taller. soooooo do i need to reprogram this suv to run a taller side wall on 20s??? thanks in advance.
 

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Yes you will have to calibrate your speedo if you change size of the factory wheels.

I suggest you to go with 19" if you don't want thin low profile tires.

You can use that tool to know what tire size you need for different size... But beware... it's not because you find the right size you want that it exist tires in that size...
http://www.miata.net/garage/tirecalc.html



harley1 said:
standard 17" wheels have diameter or 26.74" and 19" wheels have diameter of 29.17" do they reprogam these rigs, cause i want 20s with out getting such low profile. Mine came with 17s which i am going to run in the winter then looking for 20's but to get the 20s at the right height i need to order such a low pro tire. but when and if you got the factory 19s the side wall is much taller. soooooo do i need to reprogram this suv to run a taller side wall on 20s??? thanks in advance.
 

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Yes, if you change tire diameter/height you must change/reprogram oumputer or mileage/speedo will be off. I assume GM does this automatically. Note LARGER height than 19" may NOT clear wells! And 20's will give a stiffer ride for sure. You are wise to go slow..........

MM
 

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Discussion Starter · #4 ·
hey guys thanks for the fast reply. i understand the whole reprogram. But when you read the sidewall height on the 17s to the 19s.... the 17s have 4.87 inch sidawall and the 19s have 5.08 inch sidewall....... and yeah i love the site you guys suggested i use it all the time when i upgrae rim size. but now do you understand what i am saying, the 19s have a taller sidewall so that should give me more room for 20s. i have never road in a 19 inch terrain yet but i heard they are a lot more harsh even with more sidewall???? thanks again everyone.
 
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harley1 said:
hey guys thanks for the fast reply. i understand the whole reprogram. But when you read the sidewall height on the 17s to the 19s.... the 17s have 4.87 inch sidawall and the 19s have 5.08 inch sidewall....... and yeah i love the site you guys suggested i use it all the time when i upgrae rim size. but now do you understand what i am saying, the 19s have a taller sidewall so that should give me more room for 20s. i have never road in a 19 inch terrain yet but i heard they are a lot more harsh even with more sidewall???? thanks again everyone.
Your not understanding how tires are sized I'm afraid...

Aspect ratio effects so much.

17" are 225/65R17

Means section width is 225mm's across, sidewall height (aspect ratio) is 65% of 225, given us a height of 146mm (for sidewall height)

Stock 19" are 235/55R19

Means section width is 235mm's across, sidewall height is 55% of 235, given us a height of 129mm)

So the sidewall is actually smaller than the 17" tires, which is why they ride more harsh than 17's, the smaller the aspect ratio (the smaller the height) which effects how well the tire responds to the road, it stiffens it up. The taller the tire, the more give in the sidewall, it responds better to bumps, and road conditions. This obviously is not considering weights, which heavier tires/wheels will produce harsh ride conditions. Just drive in the 18" vs 19" setup and you will see the difference, and that is a mere 10lbs per wheel, but the same sidewall height. You should not increase much more than the factory setups, or ride quality will worsen (just my rule of thumb)

Btw if you went 20"....255/40R20 would be the ideal size for the LS setup, and require no PCM reprogram
 

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OK I think i can give you some insight. I got the 18s as standard on my car which have a 235/55R18 tire, the 19" one is 235/55R19 so ya theres a difference. When I got my 20s i got tires which have a diameter .5% larger then what the 19s would be the honestly i dont think you could go any larger because as it is when the wheel is cranked the inside turning wheel is nearly touching the panel behind the wheel. The difference between my new ones and my stocks is like 2.9% and i havent had my spedo recalibrated because i dont know where to take it that can do it properly. My new tires are a 255/45RZ20 which like i said is pretty much the largest 20" you can get and the sidewalls look pretty small.
 
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WILSONN said:
OK I think i can give you some insight. I got the 18s as standard on my car which have a 235/55R18 tire, the 19" one is 235/55R19 so ya theres a difference. When I got my 20s i got tires which have a diameter .5% larger then what the 19s would be the honestly i dont think you could go any larger because as it is when the wheel is cranked the inside turning wheel is nearly touching the panel behind the wheel. The difference between my new ones and my stocks is like 2.9% and i havent had my spedo recalibrated because i dont know where to take it that can do it properly. My new tires are a 255/45RZ20 which like i said is pretty much the largest 20" you can get and the sidewalls look pretty small.
Why the 45's vs 40 series? 45's have the speed off 3% while the 40 series would be 28.0 diameter (18's are 28.2stock, which are the smallest diameter available on the nox/terrain)..would give less than 1% speedo error.

235/55-18 5.1in 14.1in 28.2in 88.5in 716 0.0%
235/55-19 5.1in 14.6in 29.2in 91.7in 691 3.5%
255/40-20 4.0in 14.0in 28.0in 88.1in 719 -0.5%[/color]
255/45-20 4.5in 14.5in 29.0in 91.2in 695 3.0%
 

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All 4 wheels with a variance of up to 5% is fine.. Variance between wheels mounted in the car should never exceed 2% (which is the nominal change of a low pressure tire) or you can damage the AWD system.

Good luck! & Post pictures!
 

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2010BlkGraniteNox said:
Why the 45's vs 40 series? 45's have the speed off 3% while the 40 series would be 28.0 diameter (18's are 28.2stock, which are the smallest diameter available on the nox/terrain)..would give less than 1% speedo error.

235/55-18 5.1in 14.1in 28.2in 88.5in 716 0.0%
235/55-19 5.1in 14.6in 29.2in 91.7in 691 3.5%
255/40-20 4.0in 14.0in 28.0in 88.1in 719 -0.5%[/color]
255/45-20 4.5in 14.5in 29.0in 91.2in 695 3.0%
Well basically with the 40s your sidewall is so small that if you hit a pot hole your rims are pretty much trashed. And where i live thats an issue. Aswell i dont know if youve noticed but the wheels on the Terrain tend to look very small, nearly too small for the vehicle with those big fenders and gaps above the wheel (mostly on the back) so I need all the extra size I can get, not to mention the rims are spidery so having slightly bigger wheels makes it look like there is abit more there.
 
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WILSONN said:
Well basically with the 40s your sidewall is so small that if you hit a pot hole your rims are pretty much trashed. And where i live thats an issue. Aswell i dont know if youve noticed but the wheels on the Terrain tend to look very small, nearly too small for the vehicle with those big fenders and gaps above the wheel (mostly on the back) so I need all the extra size I can get, not to mention the rims are spidery so having slightly bigger wheels makes it look like there is abit more there.
I agree, but I would never run 20's either :).....I just try to keep the diameter close to stock because the tire diameter is used in figuring out overall final drive ratio, 3% isnt huge, but just saying option available for less than 1% (whcih is what I try for).

Those that have 18" standard tires, should go to 235/50R19 if they upgraded.....I think even GM sells the aftermarket 19" setup with that setup, and not the 235/55R19 (that comes standard on the 19" upgrade)
 
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