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I have a 2005 MDX Touring with OEM size tires 235/65/R17. I want to change the tires to 245/65/R17.

What is the difference between these tires? I assume the 245 is a bit taller and maybe wider, but they look very close in size. Will it effect my speedometer reading very much? Will it hurt any of the vehicles suspension geometry or sterring?
 

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235 or 245 is the section width in millimeters - the largest width of the tire between the outer and inner sidewalls. Switching from 235/65-17 to 245/65-17 also increases the height of the sidewall, which becomes .65*245 mm instead of .65*235 mm. This increases the overall diameter of the tire by 1.8 percent (from 29.03" to 29.54"), so it would change your speedometer reading by that same percentage. For any given indicated speed on your speedometer, your actual speed will be about 1.8 percent higher with 245 tires than it would with stock-sized tires. It will change the suspension geometry slightly, and that half-inch difference in diameter will also add about a quarter inch to the car's ride height and overall height.

It's not a huge change, but I wonder why you would want to do so, since there aren't any significant advantages in doing so.
 

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And there is the disadvantage of the very slightly lower fuel economy.

G
Realistically, only the MEASURED fuel economy would go down. The actual amount of fuel you'd use would likely not change unless the new tires have a higher rolling resistence than what was on there before. Actually, if the new larger tires had a lower LRR value than the original ones, the fuel economy might actually improve, even though the measured might be different.

I've done a +1 with tires before (done it on my son's '12 Civic going from 195-65R15 to 205-65R15) with negligible change. And in my son's case, going from the stock Conti ProContacts to the almost new Michelin Defenders that came off his traded '05 Accord, he's seeing better mpg's registered than he did with the stock size OEM Conti's. The speedo is hard to tell a difference between "before" and "after". Not a big deal, IMHO.

andy
 

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I've done a +1 with tires before (done it on my son's '12 Civic going from 195-65R15 to 205-65R15)
That's not a "+1" fitment. The term, plus 1, is used to refer to wheels and tires in which the diameter of the wheels is one inch larger than stock. (Similarly, plus 2 is two inch larger diameter wheels, and you can also have a minus 1, with one inch smaller diameter wheels.) Such fitments usually also change the aspect ratio (the middle number, that represents the ratio between the section width and the sidewall height), to maintain the same outer diameter of the tires. If he had gone from 195/65-15 to 205/55-16 (on 16" wheels), that would be a "plus 1" fitment. And 225/45-17 would be a "plus 2" fitment.

You can read more on the Tire Rack website:

The Plus Concept
 

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I don't see what advantage this change would make, unless you are getting free tires in only this size...
 

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That's not a "+1" fitment. The term, plus 1, is used to refer to wheels and tires in which the diameter of the wheels is one inch larger than stock. (Similarly, plus 2 is two inch larger diameter wheels, and you can also have a minus 1, with one inch smaller diameter wheels.) Such fitments usually also change the aspect ratio (the middle number, that represents the ratio between the section width and the sidewall height), to maintain the same outer diameter of the tires. If he had gone from 195/65-15 to 205/55-16 (on 16" wheels), that would be a "plus 1" fitment. And 225/45-17 would be a "plus 2" fitment.

You can read more on the Tire Rack website:

The Plus Concept
Yup - you're right - and I should have known better. When I said "plus 1" what I meant was upsizing the diameter by one size like this typically didn't cause clearance issues, and minimal impact to the speedo. The Plus 1 and Plus 2 keeps diameter the same and messes with the width. You also many times have to adjust the wheel width and offset if you go too crazy.

Sorry for the confusion.

andy
 

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"Realistically, only the MEASURED fuel economy would go down."

You are kidding right.

George
When I say measured, I mean what the car's trip computer says, and what you would calculate by using the odometer reading. Since the tire diameter is larger, it registers less mileage than actual. As such, calculations will show a drop in mpg. When, in actuality, you'd use the same amount of fuel for a given trip than you did before the tire swap.....
 

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That's correct, because your actual fuel economy depends on the actual distance traveled, whereas the gauges don't "know" that you're using a larger diameter tire which travels farther per revolution than the stock size tires upon which they are calibrated.

If you had the ability to measure actual fuel economy at a very high level of precision (based on actual distance traveled rather than the odometer), and the ability to eliminate all the other sources of variability (driving route, traffic, how much the tank is filled each time for calculating gallons used, etc), the larger tire diameter would actually result in a very slight improvement in actual fuel economy. That's because the larger tire diameter has the same effect of putting taller gearing on the car, so it's like being in a slightly higher gear all the time. For the same reason (taller effective gearing), the car's acceleration will be slightly worse with the larger tire diameter.

Keep in mind, though, that the difference in diameter due to the wider tires that we're talking about here is relatively small (1.8 percent). To put that into perspective, that's roughly the same difference in diameter between a new tire and the exact same tire when it is worn and ready for replacement, with less tread depth.
 

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I have a 2005 MDX Touring with OEM size tires 235/65/R17. I want to change the tires to 245/65/R17.

What is the difference between these tires? I assume the 245 is a bit taller and maybe wider, but they look very close in size. Will it effect my speedometer reading very much? Will it hurt any of the vehicles suspension geometry or sterring?


Putting aside all the tire techie talk, if you are looking for a wider tire for better grip, you are better off with the option of going 245/60/17 (or even 245/55/17) where depending on the particular tire/brand you may have almost zero change in the diameter and hence speedometer reading, and mpg, and ...... and it will give you a marginally lower profile.

Edit: I stand behind my comment with the addition of perhaps the better choice 245/60/17. It all depends on the tire/brand. We just did a similar swap on our Highlander using the new Michelin Defender tires.
 

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you are better off with the option of going 245/55/17 where depending on the particular tire/brand you may have almost zero change in the diameter and hence speedometer reading, and mpg
Absolutely NOT true. The outer diameter of 245/55-17 is 4.9 percent (1.4") smaller than the stock 235/65-17. As tire sizes go, a 4.9 percent difference is huge. Furthermore, you'll find very few tires available in that size, with none in the most common performance categories for SUV's.

NOT recommended, unless you're going for a "low rider" show car look, with deliberately undersized but wider tire sizes.

If you want a lower tire profile, the proper way to go about it is with a plus one or plus two fitment (i.e. with larger diameter wheels, keeping the overall outer tire diameter the same). Plus sizes that work on a 2001-2006 MDX include 255/55-18 on 18" wheels, and 255/50-19 on 19" wheels. (Those happen to be the stock tire sizes on the 2007-2013 MDX, but you can't use the stock wheels from those years because the bolt pattern is different from the 2001-2006.)
 

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I appear to have posted this in the wrong model section. But I'd really appreciate some insight on the following:

So after a tonne of research and picking up a set of mint 19" RDX wheels and (****e bald) Michelin Tour HPs for $500, I've got the replacement tire choice down to Continental CrossContact LX20s. This is my wife's car and I grudgingly got her to go along with 19s. Her preferred ride is safe and comfortable, sacrifice is handling. With that in mind, I've got the tire sizes down to:

255/50R19
245/55R19
245/50R19

Those are all of the relevant Plus Two sizes that will meet OEM stock diameter. Let's remove the last one, as Continental doesn't make a 245/50R19 (not many choices, it's apparently an odd tire size). So I've got the 255s and the 245s.

The 245 tire sits more flush on the wheel, but I don't have to worry about curb rash because of sidewall height. With a narrower tire, it has better wet and snow traction, but less responsive handling. With a taller sidewall, it will have a better ride quality and aesthetically, fits the wheel well nicer. On the downside, it's a Standard Load tire and not Low Rolling Resistance, so no potential increases to MPG. They're also about $30 less per tire than the 255.

So the upside of the 255s are that they are XL and LRR. They will handle nicer, but the sidewall is lower, so less ride comfort, I assume? The 255s are also by far the most popular choice.

If anyone has any opinion as to which ones to go for, I'm all ears.
 

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All I can say is WOW - what a difference! The drive south to Oregon and the ride north back to Canada were night and day! Where you felt every bump, were assiled with road and the tires danced and shimmied while cornering with the Michelins, the Conti's were 180 degrees the opposite. Extremely quiet and smooth and just oh so solid and grippy in the corners. I can't wait to plow through puddles and attack snow drifts, when the time comes.

As for the size, they are perfect: a 245/55R19 has a lot of sidewall for ride comfort and the narrower tire is more fuel efficient (so I am told) and handles better than the 255/50R19. It also doesn't have severe impact on the speedo/odo. Aesthetically, they look great, especially on those sexy 19" RDX rims! Very, very happy. I understand that many folks aren't getting the 70,000 miles promised by the treadwear warranty. Well, fine by me: looking forward to a prorated discount on my next set, then.

One last thing: if you're down in the Portland area, I highly recommend America's Tire Co. (which is actually Discount Tire, not sure why the name difference) in Beaverton. Ask for Tony and tell them Vic from Victoria sent you!
 
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