Increased efficiency with 255/45 20 Hankook Ion on my GT (updated OP)

[mkhuffman]

Some of you may be considering putting slightly wider tires on your GT, and I thought this post might help you decide. The OEM size is 245/45 20. I installed 255/45 20 Hankook ion EVO AS SUV tires.

I was hoping slightly larger tires would improve the quality of the ride, maybe even reducing some of the bounciness. Unfortunately, it did not reduce the bounciness, but ride quality is better.

I should qualify that: it has not so far at the same tire pressure I was running before, 41 psi. Because these tires have a higher load rating, I understand you can safely lower the pressure to 38 psi. I will try that after running them at 41 for a while, and post my impressions. (See below and other posts in the thread.)

I selected the new Hankook Ion tires because I was hoping for better efficiency, better handling, and a quieter ride. I have early impressions of the tires, but I'm going to hold off on those until I have more miles. I will say they are definitely quieter. The OEM tires had 39,000 miles on them so it might not be a fair comparison.

<<Real world efficiency results added further down.>>

245 OEM (front):

255 Hankook:

245 OEM (rear):

255 Hankook:

245 OEM:

255 Hankook:

I didnt take an equivalent OEM version of this Hankook picture:

As expected, the tire sidewall sticks out a little more than the OEMs, which looks better. However, the shorter sidewall on the 245 OEMs looks better, IMO. Oh well.

Also, the tread patten on the Hankook is like a touring tire, and isn't aggressive looking. I guess that is to be expected since that is really what the tire is.

Let me know if you have any questions.

Edit: adding additional info into the OP.

The speed difference between the two tire sizes was more than I expected. With the OEM tires the speed was actually 79 mph when the speedometer showed 80. Now the speed per my phone GPS sometimes shows 79 mph when the speedometer shows 78, and sometimes it matches. Which means it isn't a full 1 mph faster than the speedometer. It is closer to 0.5 mph, because it flips back and forth between being exactly right and 1 mph faster. Using this method, the size difference is 1.5/80 or 1.88%.

Using OBD data, the average speed per the car and GPS speed tracked by the phone, I get a more accurate estimate. According to that, the difference between the OEM and Ions with this size is 2.61%. Approximately.

The size difference also impacts efficiency readings, because now the car is traveling 2.61% more miles than it knows. So, the trip efficiency shown in the car is lower than it is in reality.

Efficiency:

To figure out if these tires are actually more efficient or not, I obviously could not rely on the trip computer. I think it is wrong anyway. In fact, the data I have proves it is wrong. It is a good measure relatively so you can compare between trips, but not as an absolute measurement. The trip display is significantly lower than reality, which could be by design. Maybe Ford engineers figured we would use it to calculate range, and they wanted it to be lower than reality. Who knows?

Anyway, I compared ten 80-mile drives over the exact same road, with very similar traffic, battery temperatures and speed. The trips are about as identical as you can get. Five of the trips are with the OEM tires, five with the slightly larger Ions.

I used OBD data, which IMO is the only way you can really figure out if a tire is more efficient or not.

Here are the results:

	Miles Traveled	EtE Start	EtE End	Energy Used	Average HVB Temp	mi/kWh	Average Speed per OBD	Average Speed per GPS	Efficiency Improvement
OEM Tires	399.9729172	403.812	252.63	151.182	74.66	2.653	69.208	69.55
Hankook	410.4664319	393.318	249.37	143.948	73.04	2.854793723	69.85070517	72.02	7.62%

There are more miles on the OEM tires because I had to adjust for the incorrect odometer readings. I used 80 miles on the odometer, start to finish, and then adjusted the distance for the 2.61% size difference.

You can see that even though the average speed was higher in the Ion trips, and the average battery temp was lower, they still used less energy over a slightly longer distance. The calculated efficiency improvement based on this real data is 7.62%. That improvement is real, and it is significant.

By the way, for one of the Ion trips the tires were at 34 psi. And even that trip was more efficient than the four of the five OEM tire trips. I may do some more 34 psi testing to see the real impact, but I probably won't. I am happy with the comfort at 41 psi, and I plan to put the Eibach spring on anyway, which will eliminate the need to lower tire pressure.

Not only is range improved by 7.62% with these tires, they are more comfortable and quieter. These are the perfect tires for my use case - lots of highway driving.

Highly recommended!

A couple final thoughts:

I think it is possible the larger tires size has contributed to the efficiency improvement. It is a very small difference, but a taller sidewall means the rotational resistance of the wheel has probably decreased at the same GPS speed. So if you replace your OEM tires with the same size tire, you might not see the same improvement I have.

Also, this is a highway trip test at highway speeds. The results for city driving could be totally different. But I only care about highway efficiency, and it is very difficult to measure city efficiency in the real world anyway. There are way too many variables in stop and go traffic that impact efficiency.

And this comparison is only valid with the GT OEM tires. The Premium models (and others) will have totally different results. I think that is obvious, but just wanted to make it clear.

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[Chainspell]

Looking forward to your impressions. I have been eyeing these, but out of the handful I am considering they are by far the most expensive.

 

[mkhuffman]

Looking forward to your impressions. I have been eyeing these, but out of the handful I am considering they are by far the most expensive.

I have a strong feeling they are going to be more efficient. I can't tell just driving around town, but next week I will be putting a lot of highway miles on the car, and if the difference is measurable, I will see it.

In about two weeks I will have enough experience with them to post my impressions.

 

[AliRafiee]

Why didn’t you go with a shorter sidewall? Like a 40?

 

[HuntingPudel]

Looks cool, Mike. How do they handle? I went with wider wheels and tires. The tire shop set them at 41psi (give or take a few tenths). The steering was super light and the ride was rough so I knew they were over-inflated. I dropped them to 36.5 this morning and went out to beat on the tires. Too much traffic to do a good job but I got my pyrometer out and found that the rears might want a little more. This will probably change if I can do some hard launches while hitting the corners. ?‍?

 

[Chainspell]

How accurate is something like this calculator to determine the new optimal psi?

 

[HuntingPudel]

How accurate is something like this calculator to determine the new optimal psi?

Depends on your purpose. For just tooling around, it's probably not bad. It seems to be missing a vital variable though: rim width. A wider rim places the tread edges more firmly on the road, thus requiring a slightly higher pressure in order to wear the tires correctly (all else being equal). This is why my Blazer needs to run higher pressure than a couple of friends' trucks that weigh more (no A/C, no insulation in my K/5) but have narrower rims (8.5" vs 10") with the same tire. ??

If you're going after max performance, you need to utilize a pyrometer and adjust pressures so that you get correct readings across the surface of the tire (also useful for determining where your camber needs to be set, given the corners you're running and driving style). I've also used chalk in a pinch to at least get myself into the ballpark, then go out and practice the car in order to get the pressure dialed-in. ??

 

[Chainspell]

Depends on your purpose. For just tooling around, it's probably not bad. It seems to be missing a vital variable though: rim width. A wider rim places the tread edges more firmly on the road, thus requiring a slightly higher pressure in order to wear the tires correctly (all else being equal). This is why my Blazer needs to run higher pressure than a couple of friends' trucks that weigh more (no A/C, no insulation in my K/5) but have narrower rims (8.5" vs 10") with the same tire. ??

If you're going after max performance, you need to utilize a pyrometer and adjust pressures so that you get correct readings across the surface of the tire (also useful for determining where your camber needs to be set, given the corners you're running and driving style). I've also used chalk in a pinch to at least get myself into the ballpark, then go out and practice the car in order to get the pressure dialed-in. ??

Good info, thanks. I really want to get this dialed in. "Correct" readings meaning equal temperatures across the width?

 

[tuminatr]

Depends on your purpose. For just tooling around, it's probably not bad. It seems to be missing a vital variable though: rim width. A wider rim places the tread edges more firmly on the road, thus requiring a slightly higher pressure in order to wear the tires correctly (all else being equal). This is why my Blazer needs to run higher pressure than a couple of friends' trucks that weigh more (no A/C, no insulation in my K/5) but have narrower rims (8.5" vs 10") with the same tire. ??

If you're going after max performance, you need to utilize a pyrometer and adjust pressures so that you get correct readings across the surface of the tire (also useful for determining where your camber needs to be set, given the corners you're running and driving style). I've also used chalk in a pinch to at least get myself into the ballpark, then go out and practice the car in order to get the pressure dialed-in. ??

You can and should lower your tire pressure to 37psi. Without doing this there is no advantage to going with the larger size.

The high tire pressure is one of the reasons the MME has a harsh ride. So tires with a higher load rating allow you to lower pressure the result is a softer ride.

 

[Mach-Lee]

Mike those tires have a higher load rating (which means less PSI needed), so you can go all the way down to 34 psi if you're not loaded. I would try 36 psi.

Ford spec'ed the tire pressure for max load (GVWR) going 100+ MPH. If it's just a couple people in the car and you're not going over 100 MPH for minutes at a time, you can lower the tire pressure quite a bit and still have plenty of safety margin.

 

[HuntingPudel]

Good info, thanks. I really want to get this dialed in. "Correct" readings meaning equal temperatures across the width?

Yeah, more or less. In a lot of circumstances, you're going to generate more heat on the inboard edge of the tread because of negative camber on driving straight after beating on the tires. It kind of depends on how soon after you are doing hard cornering you can get to a safe place to stop in order to take your readings. In a perfect world, you stop right at the exit. There's a little guesstimating involved when you have to drive to somewhere safe. And, of course, you will end up having to change static pressure when there's a change in barometric pressure or temperature if you're trying to keep it dialed in all the time. ??

 

[azerik]

Why didn’t you go with a shorter sidewall? Like a 40?

Rally the sidewall is only about 3 or 4 mm taller. 45% of 245 is 110.25, 45% of 255 is 114.75 that higher sidewall is mostly an illusion. Same tire brand to same tire would be hardly noticed, most of it is probably perspective of the sidewall profile appearing thicker because it’s more squared.

How accurate is something like this calculator to determine the new optimal psi?

It doesn’t work well for us because what we’re relying on is the sidewall pressure to help hold the tire in the car from wobbling. One could get better ride at an optimum, load and pressure, but side to side movement of the car might be too much due to the weight of the battery.
I’m really curious if you were to air down if the sidewall still holds the car well. My RX’s at 36 are like a bounce house on the stock ER springs. Now that I have the Eibach on there, they may actually be able to go down a few psi.

 

[mkhuffman]

Mike those tires have a higher load rating (which means less PSI needed), so you can go all the way down to 34 psi if you're not loaded. I would try 36 psi.

Ford spec'ed the tire pressure for max load (GVWR) going 100+ MPH. If it's just a couple people in the car and you're not going over 100 MPH for minutes at a time, you can lower the tire pressure quite a bit and still have plenty of safety margin.

Great advice.

I am going to leave it at 41 until I can see how efficient the tire is at the same pressure I was running the OEMs. Then I will lower the pressure and see how it impacts comfort and efficiency. Ideally, efficiency will be similar at the lower pressure but I doubt it. As you know, tire pressure has a significant impact on rolling resistance.

 

[mkhuffman]

Looks cool, Mike. How do they handle? I went with wider wheels and tires. The tire shop set them at 41psi (give or take a few tenths). The steering was super light and the ride was rough so I knew they were over-inflated. I dropped them to 36.5 this morning and went out to beat on the tires. Too much traffic to do a good job but I got my pyrometer out and found that the rears might want a little more. This will probably change if I can do some hard launches while hitting the corners. ?‍?

Before I give handling impressions, I want to be sure to be fair and have some time on them first. I don't want to give an impression that isn't fully informed.

Soon! TM

 

[mkhuffman]

Why didn’t you go with a shorter sidewall? Like a 40?

The main reason I did not go to 255/40 is because I wanted the extra sidewall for potential comfort improvement. I didnt think a 40 would be able to be as comfortable.

A secondary reason is the load rating. The 40 Hankooks have a load rating that is 100 lbs less than the OEM tires. It might be fine, but definitely I would not have been able to safely lower tire pressure for more comfort. Refer to Lee's post. I can lower the tire pressure safely on the 255/45 tires because they have a higher load rating than the OEM tires.

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