Tire Sizes Between Manufacturers?

[Propflux01]

I have a question on tire sizes. I recently swapped out my 17" Elantra wheels for a set of 16" elantra wheels. I did it because I could no longer stand rolling on rocks ( or that's what it felt like). The 16" solved my ride issues but I did notice some oddities: First, both wheels are OEM for the Elantra. 2nd, the 16" are definitely taller than the 17's. Where I used to run 2250 RPM @70mph, I am Now running about 2000 at he same speed. Now knowing the same car can take two different rims, one a limited with the 17's, and the SE with the 16"s, I am curious as to why the big difference in RPM's ( I can feel it in the butt-dyno as well, it is sluggish more so. So off the calculator I go, putting in the two different sizes, and I come up with this: Original Tire Size: 215/45R17 New Tire Size: 205/55R16 Diameter inches (mm) 24.07 (611.4) 24.62 (625.3) 0.55 (13.9) 2.3% Width inches (mm) 8.07 (205) 8.46 (215) 0.39 (10) 4.9% Circum. inches (mm) 75.62 (1920.77) 77.34 (1964.44) 1.72 (43.67) 2.3% Sidewall Height inches (mm) 4.04 (102.5) 3.81 (96.75) -0.23 (-5.75) -5.6% Revolutions per mile (km) 837.86 (520.62) 819.24 (509.05) -18.63 (-11.57) -2.2% Now for my question.... Are there different sizes for the same tire size, and could this be causing the discrepancy in sizes? IOW, If I bought at 205-55R16 from tire company "A" and bought another 205/55R16 from tire "B" would there be a difference in actual size, even by a few mm? It just seems awfully strange that the same alternately installed wheels could have so much height difference on basically the same car. Meaning, I drop the sunroof, leather seating, and 300W stereo (yeah), and My car turns into a SE model with 16" rims. Nothing else is done to the cars engine. tranny, suspension, etc. Now if I drop my next new tire purchase from the 205/55R16 to a 205/50R16, It will be much closer in size to the original 215/45R17. I have time to get the tires, as the wheels I have are direct takeoffs from a new Elantra. So should I go down a size, to the 50 series, or maybe if the sizes are different between manufacturers, to find another set of tires, just keeping the 55's and deal with the speedo error and power loss?, or go down to the 50's?

 

[RooflessVW]

Run the OEM size. It is the closest you can get in a 16" size. If you go to 205/50R16 the tire will look too small and you'll be back to crashing over bumps.

 

[TinyVoices]

There is absolutely tire size variation between manufacturers. The federal 595ss on my mr2 are almost a full size wider than marketed. Well known for this online.

 

[eljefino]

Yup. My wife rented a new Dodge ram and the 235s looked like 215s. Sometimes the tire maker publishes revs per mile which could be more actual than theoretical And remember s tire squishes a little on the bottom making it slightly less tall.

 

[Carmudgeon]

The 205 refers to the section width of a tire, not (the common misconception of) tread width. Even the actual section width can vary, if a tire is mounted on a rim this is not the same width as the designed standard measuring rim for a specific size. Capri can probably provide an explanation as to how that standard is arrived at, but the short answer is that yes, there are variables involved.

 

[CR94]

Originally Posted By: Propflux01

... Where I used to run 2250 RPM @70mph, I am Now running about 2000 at he same speed. ...

How did you determine those numbers? There shouldn't be that much difference.

 

[Quattro Pete]

Originally Posted By: CR94

Originally Posted By: Propflux01

... Where I used to run 2250 RPM @70mph, I am Now running about 2000 at he same speed. ...

How did you determine those numbers? There shouldn't be that much difference.

As a matter of fact, tire and wheel size does not affect the relationship between the tachometer and speedometer. https://www.deseretnews.com/article/412545/WHEEL-SIZE-WONT-AFFECT-TACHOMETER.html So, if the OP is really seeing this much difference in RPM at 70 mph, then something else is causing this. Unless the OP is talking about actual speed (measured by GPS), but even then, the difference should not be this significant.

 

[CapriRacer]

Long Version: Barry's Tire Tech: Tire Dimensions Short version: While there are standards concerning what dimensions a tire of a certain size should be, there are no regulations. So tire manufacturer may or may not build a certain tire size to the standard dimensions. A tire manufacturer would be risky not to do so, but there are advantages to making a tire "Off Size". For example, a tire that is large can pass most tests more easily. A tire that is small uses less material. If you spend some time at Tire Rack's website looking at tire dimensions, you'll find some variation - and every so often, one that is kind of odd. But the 10% listed in the OP sounds a bit large. For a 205/55R16, that's 2 1/2 inches. That just doesn't sound right. If I were the OP, I would look up the specs for both the tire taken off and the new tire and see what it says.

 

[Propflux01]

I determined it by looking at the RPM gauge. The tire is a Kuhmo TA 31. It replaced a general rt43 in a 17” size. Physically, side by side the 16” is taller by about 1/2-3/4 Minch (by eye). I determined the Speedo is off about 2 mph at 75 indicated, via Garmin. Quattro: I tend to disagree with the tire size not having an effect on speed indicated vs actual. Your telling me I can stick on a set of monster truck tires and not have any change in speedo error? IIRC, thevVSS, driven by RPM, it what determines indicated speed, and knowing bigger tires will be a lower Voss sensed, it would tell the ECM I’m going slower than actual. I have that issue with my Harley right now, as it shows lower than actual speed, and I can adjust the VSS math to get it right. Capri: I don’t know where your getting thev2 1/2 inches from, I provided the tech specs of both wheels/tires, and I don’t see 2 1/2 inches. There is a difference in rpm per size of tire. I just didn’t want to stick another pair of tires on (different brand, of course) and still have such a large discrepancy. The ride is satisfactory, that problem solved, but scratching head on what so much different for wheels that go on basically the same car, sans something in the ECM adjusted for it.

 

[Quattro Pete]

Originally Posted By: Propflux01

Quattro: I tend to disagree with the tire size not having an effect on speed indicated vs actual. Your telling me I can stick on a set of monster truck tires and not have any change in speedo error?

That's not what I was saying. What I am saying is that using a tire/wheel with a different overall diameter will not affect the relationship between indicated RPM and indicated speed on your speedometer. The actual speed will be off, obviously. So, you should be seeing the same RPM at 70 mph (on your speedo) with either tire. But in reality you will be going slightly faster with the taller tire.

 

[Propflux01]

I understand where your coming from, however what I’m describing is taking the car at what I believe is a certain speed, but since the tire size is taller, I’m getting lower indicated rpm. In order to reach where the rpm was before the tire swap, I must exceed the speed I am going in order for it to “match up”. If that makes sense.

 

[CapriRacer]

Originally Posted By: Propflux01

…… Capri: I don’t know where your getting thev2 1/2 inches from, I provided the tech specs of both wheels/tires, and I don’t see 2 1/2 inches. There is a difference in rpm per size of tire. I just didn’t want to stick another pair of tires on (different brand, of course) and still have such a large discrepancy. The ride is satisfactory, that problem solved, but scratching head on what so much different for wheels that go on basically the same car, sans something in the ECM adjusted for it.

2250rpm/2000rpm = ~110%. The tire diameter is about 25", so 10% difference is about 2 1/2 inches. That is what ought to be showing up in the diameter specs - but it's not. So there is a problem in there somewhere. I would suggest before you go further, you figure out where this discrepancy is coming from. My best guess is your memory about the rpm differences - and that you shouldn't be planning any tire size changes.

 

[thescreensavers]

Originally Posted By: Propflux01

Now for my question.... Are there different sizes for the same tire size, and could this be causing the discrepancy in sizes? IOW, If I bought at 205-55R16 from tire company "A" and bought another 205/55R16 from tire "B" would there be a difference in actual size, even by a few mm?

Yep! But Minor, Every tire is sized to a standard "205/55R16" but their actual size may vary for example two random tires I picked Tire Name SECT. WIDTH TREAD WIDTH OVERALL DIAM. Pilot Sport A/S3+ 8.4" 6.8" 24.9" FIREHAWK INDY 500 8.4" 7" 24.9" In this case the firehawk is .2" wider but overall Dia is the same for your case it wouldn't change anything.