Stepping up one aspect ratio

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Rochester, MI, US, World
My Focus has the optional 16" rim package, which get wrapped in 205/50 R16 tires. The stock 15" option comes with 195/60 R15 tires. Now, although the 205/50 16's are the closest match to the 195/60 15's, they are still slightly smaller in diameter. I was considering using 205/55 16's for several reasons. 1) MUCH more popular tire size (GM, Toyota, Honda, etc), giving me more/better tire options. 2) 0.8" bigger diameter, meaning 0.4" thicker sidewall, meaning smoother, quieter ride. My Focus doesn't exactly have soft suspension or much soundproofing, so I'm all for a smoother ride. Now, the 205/55 16's are slightly bigger that the 195/60 15's, than the 205/50 16's are smaller. Does that make sense? My speedometer already reads slightly fast (based on all of the speed sensors around town) so the 205/55 16's could help make my speedo more accurate, too. No fitment issues with the bigger tire either. I've only seen one other Focus with the 205/55's fitted. Opinions? I just wanna make sure that the bigger tires won't throw off my odometer or speedo by some crazy amount, based on something I've failed to consider.
 
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As long as there is room in the wheel wells, which it sounds like there is, I'd say go for it. I followed the same logic when I got winter tires for my 530i.
 
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It's not as much the size of the tire that makes the ride more comfortable than the way the tire was built and the compound they used. The extra meat wouldn't do much, but if you can find them more easily for cheaper prices, that's a very tempting reason to move and you should do it.
 

Klutch9

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Originally Posted By: Promo
It's not as much the size of the tire that makes the ride more comfortable than the way the tire was built and the compound they used. The extra meat wouldn't do much, but if you can find them more easily for cheaper prices, that's a very tempting reason to move and you should do it.
I agree that the compound and build of the tire can also make a big difference. But in my case, the 205/50 16 tire only has a ~4" sidewall, so an increase of 0.4" in the sidewall height is 10%. To me, that is substantial, especially considering that the "measured" sidewall also includes some rubber that is not exposed outside of the diameter of the rim. So my "actual" or realized % sidewall increase is more than 10%. Looking at my current tires, there is no way that sidewall is 4", so I'm guessing that any given sidewall measurement also includes the seating lip of the tire, which is not seen. So, let's say that the "exposed" sidewall is only 3.5" currently. With an extra 0.4", that's 3.9", which is an 11.4% increase.
 
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In theory you're right the higher aspect ratio will give a better ride all other factors being equal. If your speedo is already reading fast (as they almost always do) it sounds like you've made a good choice.
 

Klutch9

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Correct me if I'm wrong: the odometer is directly affected by the reading of the speedometer, right? So if the speedo is reading high (which, as noted, they nearly always do), then getting slightly bigger tires will give me a more accurate speedo AND odometer reading, and give a smoother ride. Win, win, win?
 
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Klutch9

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Originally Posted By: kkreit01
You might also notice a minor negative affect on acceleration and braking, but other than that, you should be fine.
Good point. On the other hand, it could also help MPGs out a little bit, considering that I'll be at a slightly lower RPM at any given speed (although the engine may have to work a tad bit harder to get to those speeds, considering the bigger tires). All-in-all, I think those factors kind of cancel each other out, and are a wash in some sense. I just want a smoother ride smile
 
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In real life you wont notice any difference. Its such a small factor any other factor pretty much drowns it out. Just changing tires(brand or model) will have more effect than the .4" sidewall. you would have to purchase new tires in both sizes to even notice what the actual difference (from just the size change) is. oh and +1 I think its a good idea.
 
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Originally Posted By: Klutch9
Correct me if I'm wrong: the odometer is directly affected by the reading of the speedometer, right? So if the speedo is reading high (which, as noted, they nearly always do), then getting slightly bigger tires will give me a more accurate speedo AND odometer reading, and give a smoother ride. Win, win, win?
Although both speedo and odo take their signal from the wheel, it's very likely that your odo is fairly accurate while your speedo isn't. In many cars these days, the speed value read from the sensor is then increased by the car's computer by x% or by a couple of MPH before it is sent to the speedometer display. This is by design - the speedo must never read low, even if you were to install somewhat larger tires, but it is allowed to read high (up to about 10% I think). The same "correction" is typically not applied to the odo. Otherwise, your odo may have shown 50K miles while in reality the car only traveled 45K actual miles. Think of the potential "50K mile" warranty implications. Honda or some other car mfg got sued over this at one point, so that's why odos are now fairly accurate, but speedos still read high. At any rate, the difference in your case will be so small, you'll probably not even notice it, as others have already pointed out.
 
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Klutch9, I have done this(changed aspect ratios') in the past with good results as long as there is enough room in the wheel well and strut area. I don't think you'll have any issues. A friend of mine does this often as well. My daughters '06 Mazda3 2.0 (similar to your '07 Focus) has 205-55-16 OE. I don't know how many parts these two cars share but, many items on her car are labeled "FoMoCo" smile Her speedometer is the only one in the family that is dead on with all of those speed sensors around town and her GPS! If the shoe fits, wear it!
 

Klutch9

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Originally Posted By: Char Baby
Klutch9, I have done this(changed aspect ratios') in the past with good results as long as there is enough room in the wheel well and strut area. I don't think you'll have any issues. A friend of mine does this often as well. My daughters '06 Mazda3 2.0 (similar to your '07 Focus) has 205-55-16 OE. I don't know how many parts these two cars share but, many items on her car are labeled "FoMoCo" smile Her speedometer is the only one in the family that is dead on with all of those speed sensors around town and her GPS! If the shoe fits, wear it!
A friend of mine also has a late model Mazda 3, and I noted that it had the 205/55 16s. In fact, seeing her car was one of the things that made me consider getting the bigger tires. And I see that you also have speed sensors around your town... Must be a "thing" in cities named "Rochester" LOL
 
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Messages
13,378
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ROCHESTER, NY
Originally Posted By: Klutch9
Originally Posted By: Char Baby
Klutch9, I have done this(changed aspect ratios') in the past with good results as long as there is enough room in the wheel well and strut area. I don't think you'll have any issues. A friend of mine does this often as well. My daughters '06 Mazda3 2.0 (similar to your '07 Focus) has 205-55-16 OE. I don't know how many parts these two cars share but, many items on her car are labeled "FoMoCo" smile Her speedometer is the only one in the family that is dead on with all of those speed sensors around town and her GPS! If the shoe fits, wear it!
A friend of mine also has a late model Mazda 3, and I noted that it had the 205/55 16s. In fact, seeing her car was one of the things that made me consider getting the bigger tires. And I see that you also have speed sensors around your town... Must be a "thing" in cities named "Rochester" LOL
Yeah really! smile
 

pbm

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New York
Here's a formula to determine the outer diameter of a tire: (I'll use 195/70/14s as the example) 195 X 70% = 136.5...convert to inches by dividing by 25.4 (constant) = 5.374...multiply by 2 = 10.748 + 14 (the diameter) = 24.748. Any upgrade should equal this + or - 1/2". Using this formula we see that a 195/65/15 = 24.980 and can be used in place of 195/70/14. I found this formula years ago and it has come in handy....
 
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Perhaps you have already checked; the pages at TireRack include rev/mile under 'specifications'. This is where I check when changing aspect ratio. This gives you accurate info as to speedo change.FWIW--Oldtommy
 

JHZR2

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New Jersey
I went from one H-rated tire in 195/65 (Falken ziex) to another H-rated in 195/60 (Michelin pilot), and felt like the sidewall stiffness was reduced and ride comfort improved!
 
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Lake Forest, CA
You're comparing two different brands. If you went from Michelin Pilot 195/65 to 195/60 you will feel that sidewall stiffness increases and ride is firmer.
 
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