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07 Kia Sportage 2WD, V6, EX
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88 Posts
Discussion Starter #1
Currently running 235/60/16 on stock Alloy rim.
In an effort to reduce rpms at cruise (and increase gas mileage) I am looking at going up in tire size to a 235/70/16
comparision:
diameter 27.1 28.9 (there is about 1.25 clearance so this will work)
tread width 8.1 7.1 I lose an inch on the ground. Will I notice?
THe larger tire weighs about 2 lbs more.

Last question, the 70's seem to be more of a truck tire. Is the ride going to be that much rougher

Thanks in advance!
 

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06 Sportage/2012 Navara V6 TD
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304 Posts
I would think the strength of the sidewall would determine if the ride is rougher or not.

Increasing your profile will reduce engine RPM, and the excel calculator I made shows about a 250rpm decrease at 100km/h (62.5mph - hey I am metric). Your speedo will be off though, but if you have a GPS, monitoring speed should be OK.
 

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Cerato
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692 Posts
Ride and handling will be shot. Decrease in engine speed at 60MPH will only be 135RPM.
(2180X27.1/28.9).

Will it be legal? You are talking about a 6% change; most I've done (while it was legal) was 3%, and that made the speedo just about spot-on (odo. was out, however).

Sounds like you need an extra gear, although the differenced will still be small. One of my cars used 8.0 litres/100km in 6th and 8.4 litres/100km in 5th. That was with a ratio difference of 20%, so even with your planned 6%, you will need to be careful to see the difference. Cost? -That's up to you.
 

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07 Kia Sportage 2WD, V6, EX
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88 Posts
Discussion Starter #4
thanks for the replys!
Yes, I figure about 1k drop in rpms.....but I was guessing!!!
Fortunately, in the USA it's not illeagal to raise tire size.
I need to buy at least 2 tires pretty soon so I'm going to give it a shoot w/ a couple of slightly used tires.

I bumped the tire size on my Q45 from 245/45/18 to 245/50/18 and picked up a couple of mpgs.

Cant 'add' a gear.
have another post about the tranny issue.
 

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07 Kia Sportage 2WD, V6, EX
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88 Posts
Discussion Starter #5
tires got in today. Going to have them installed tomorrow!
 

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07 Kia Sportage 2WD, V6, EX
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88 Posts
Discussion Starter #6
installed tires.
here is the clearance:






It rides better. (note these were used so it's not like having a lot of new rubber on the ground)

the odometer is now off about 10%
and the rpms are bout 100rpm lower.
 

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06 Sportage/2012 Navara V6 TD
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304 Posts
You should just stick a blower on the the car, yeah you might use more fuel, but you will get there twice as quick!!
 

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06 Sportage/2012 Navara V6 TD
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304 Posts
Looks like there is still plenty of clearance
 

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07 Kia Sportage 2WD, V6, EX
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88 Posts
Discussion Starter #11
here is were there is possiblity of rubbing.....the tire on the driver side and turned slightly to the right



so, imho, this is the tallest tall possible.
 
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