Wheels, Rims, and Tires

[JoeS]

If you Google 'NHTSA Tire Rolling Resistance' you'll see a huge PDF showing the results of Phase 2 of their testing and it will give you way more data on the subject than you ever wanted to know :shock:

Don, thank you so much for this, and I look forward to reading it.

One other thing I learned which is completely contrary to what I thought I knew is that for a given vehicle weight and tire pressure, wider tires have a lower rolling resistance than narrower tires do - This is due to the fact that since the cars weigh the same and are both supported by tires of equal pressure, the tire contact patch will be the same square area for both the wider and narrower tires. Therefore the wider tire will have a shorter longitudinal flat spot than the narrower tire, so the wider tire flexes less than the narrower tire when you roll it and less flexing means a lower rolling resistance.

You're right - it seems counter-intuitive. If I take a bicycle with narrow tires on a 50-mile bikeride and then take my other bike with balloon tires (both weighing the same) and same tire pressure and take it on a 50-mile bikeride, my perception is radically different ... :roll:

 

[jray3]

BOOM- there goes my previous understanding of tires... :roll:
So, if the wide and short contact patch yields less RR than a narrow and long contact patch due to less sidewall flex, and I presume, a harsher ride because not only do you get less yield in the tire, but you hit more road imperfections with a wider tire (or does contact area flex offset sidewall flex).
Then the aero comes into play. Our skinny tires add less drag than fatties do. So, this could mean that a wide tire will give more range in a city driving cycle, and narrow tires give more range on the highway?

 

[alohart]

One of the really interesting conclusions of their testing (found near the end) was that lowering the rolling resistance of the tires on a vehicle by 10% gave an improvement in fuel economy of only 1.1%.

I'm guessing that this applies to normal ICE cars only. I say that because of the experience of Honda Insight hypermilers who reportedly increase their fuel efficiency noticeably by increasing their tire inflation pressure. The Insight has a lean burn mode that increases fuel efficiency considerably but that is very sensitive to engine load. Higher rolling resistance at lower inflation pressures would reduce the percentage of time their engines can spend in lean burn mode.

I don't know whether lowering the tire's rolling resistance would affect an EV in the same way as a standard ICE vehicle. The fuel efficiency of an ICE varies with engine RPM and other factors that aren't the same in an EV.

 

[Don]

The 10% to 1.1% ratio *is* skewed because they were talking about ICE cars and not electrics. I don't recall the exact numbers, but something like 20% of the fuel burned in the ICE is what is moving the car, so when you improve it's MPG by lowering the rolling resistance, you're only talking about that 20%

Yes, the wider tires do suffer from greater wind resistance than the narrower tires, so they are not as much better at highway speeds as they are at city speeds . . . . but the narrower tire suffers even more in city driving because it's longer contact patch makes it harder to get rolling from a standing stop than the wider tire

As to overinflation and reduced rolling resistance, if you read long enough, there are numbers all over the place. There is a decrease in rolling resistance when you overinflate, but the lions share of that decrease is gained by overinflating by only 10% (3 to 4 psi) and higher pressures than that gain very little more. But, almost everyone cautions that you shouldn't overinflate because the car's engineers designed the cars suspension system based on a tire inflated to the pressure on the doorjamb placard and overinflating gives up both traction and tire wear as per the 'Magic Triangle'. I've always inflated my tires just a little over the manufacturers recommendation because I notice a more crisp steering response and because I always figured the car manufacturer wanted you to be impressed with the cars smooth ride, so I *thought* maybe they were recommending slightly lower than optimal pressures and my adding 2 or 3 psi helped all around. These days though with the mandated CAFE fuel economy standards, the manufacturer is probably already fudging their recommended pressures a bit higher to help them meet those standards, so going much about the doorjamb number probably yields less improvement than it did on older cars

I used to run my iMiEV's tires at 45 psi - I've since backed that number down to 40 psi to get me closer to the 10% which gives most of the benefit without giving away too much traction and treadwear. 40 psi is at least 6 or 8 psi more than I have ever run in tires on any other car . . . . but Mitsu's recommended 36 psi is also at least 6 more than recommended on any other car I've owned. As a comparison, my very well handling Mazda Miata has a doorjamb sticker recommending 26 psi - I've always run 30 but with what I've learned this week, I'm seriously rethinking that

But, as they say on the Miata forum, YMMV . . . . Your Miata May Vary - Or, in this case, YiMiEVMV

Don

 

[JoeS]

Don, I now don't know whether to thank you or not, as one has to read this 138-page NHTSA report and keep notes at the same time… this is the kind of stuff one needs to be focused on for six hours while locked in an airplane seat and not be a happy dabbling retiree. Too reminiscent of work. :roll:

One general observation so far is that they seem to have an inordinate emphasis on tire underinflation.

I just erased a number of points I'd gleaned so far, and (if I get ambitious) will try to go back and reference specific pages/paragraphs before mentioning them, especially the differences between wet and dry traction. It occurred to me, since I haven't seen much rain in ages, that my personal perspective is skewed when it comes to emphasis (or lack of it) when it comes to traction as I simply never experienced any problem with traction with my iMiEV, even with those worn-out tires.

A minor point: I'm perplexed as to why the NHTSA abstract would provide numbers without a baseline. Specifically, "Reducing the inflation pressure by 25 percent resulted in a small but statistically significant decrease of approximately 0.3 to 0.5 miles per gallon for four of the five fuel economy cycles, excluding the high-speed, high-acceleration US06 cycle". Not providing a context in the same sentence is perhaps the result of excessive editing?

The excellent observation alohart made about lean burn in the Honda Insight is IMO very significant: at the same speed, the difference between being in or out of lean-burn is on the order of 20mpg at 60mph. Even a slight reduction in rolling resistance which results in keeping the car in lean-burn gives a fantastic gain. Just as a reminder, my own lifetime average in that Insight is over 77mpg (here's a link to a photo of the instrument panel showing 77.7mpg when I crossed 77,777miles: http://www.insightcentral.net/forums/mpg-issues/20620-sevens-bragging-rights.html). That's certainly (inordinately?) skewing my perspective on tire pressures.

Finally,

The 10% to 1.1% ratio *is* skewed because they were talking about ICE cars and not electrics. I don't recall the exact numbers, but something like 20% of the fuel burned in the ICE is what is moving the car, so when you improve it's MPG by lowering the rolling resistance, you're only talking about that 20%

Point well made, and I need to head-scratch over this one.

 

[alohart]

But, almost everyone cautions that you shouldn't over inflate because the car's engineers designed the cars suspension system based on a tire inflated to the pressure on the doorjamb placard and overinflating gives up both traction and tire wear as per the 'Magic Triangle'.

I believe it was you who pointed out in an earlier post that the considerably lighter ICE version of the i runs the same size tires as the i-MiEV. If this is true, then our tires are running closer to their load limits than the ICE version and are thus squished down (scientific term) more with a resulting larger contact patch. Increasing the inflation pressure would reduce the contact patch back to that of the ICE version for which our tire size was designed. A higher inflation pressure would also increase the tires' load limits. However, traction almost certainly suffers a bit due to the decreased contact patch. I guess that's a trade-off I'm willing to accept.

I have never overinflated above the maximum inflation pressure on the tire sidewall on my Insight or i-MiEV. Honolulu roads are just too rough. Also, I'm not comfortable inflating above the maximum inflation pressure although many have done so without tire failure on the Insight's OEM Bridgestone tires.

 

[Don]

I believe it was you who pointed out in an earlier post that the considerably lighter ICE version of the i runs the same size tires as the i-MiEV. If this is true, then our tires are running closer to their load limits than the ICE version and are thus squished down (scientific term) more with a resulting larger contact patch. Increasing the inflation pressure would reduce the contact patch back to that of the ICE version for which our tire size was designed. A higher inflation pressure would also increase the tires' load limits. However, traction almost certainly suffers a bit due to the decreased contact patch. I guess that's a trade-off I'm willing to accept.

Same wheels/tires, but I doubt the lighter, smaller ICE version specifies 36 psi in it's tires like they do for our car, so the contact patch may actually be similar with both cars using the recommended pressures. Should we really be happy with the same sized contact patch on our 800 pound heavier car?

Yes, our tires are dramatically close to their maximum rating when the car is loaded to the gross vehicle weight rating - Maybe even a little above if you had four 200 pound passengers in the car. From my earlier post:

It appears the 3329 max weight rating is limited by the tires, specifically the tiny front tires. The car has an actual weight distribution of 45/55, F/R which means 45% of that 3329 pounds (1498 lbs) is resting on the tiny front tires, which are rated for a max weight load of 783 lbs each, or 1566 pounds - No reserve margin of safety left there at all :shock:

By comparison, the rear tires are carrying 55% of that 3329 lbs which is 1830 pounds, or 915 lbs per tire. The stock 175/60-15 tires are rated for a maximum of 1019 lbs each

I'm not familiar with any other vehicle which cuts so closely to the absolute maximum ratings of it's rubber. More than ever, this convinces me that the suspension and tires were not really designed for this car, but for the 1960 pound I kei car they originally came on - This *really* makes me wonder how the Feds allowed this car to be sold in the USA!

The wheel/tire situation still concerns me and one day I hope to find something better

Don

 

[JoeS]

Ok, here are my impressions after two weeks with the Yokohama AVID ENVigors:

Noise - there definitely is a thrumming sound emanating from the tires on smooth surfaces. Noticeable, but not obtrusive, and even my non-critical wife noticed it.

Handling - I tried three tire pressures: 36psi (specified by Mitsu), 50psi (max sidewall is 51psi), and 60psi. Having driven on highly-inflated tires for the last two years in the iMiEV and ten years in the Insight, I consider the stock 36psi mushy. Probably my imagination and I'm having difficulty describing it, but the minute difference between 50psi and 60psi is that the car feels lighter and the tires groan less going hard around corners at 60psi... probably because they have less traction :roll: ... but she still holds the road wonderfully! Like the tires so far!

Wet roadholding and handling - We got our first significant rain for about three hours yesterday morning (YAY, first noticeable rain since late last Spring ), and I used that opportunity to try out the tires at two different pressures (36psi and 60psi) on the fairly-slick curvy roads around here. Result: all the same to me in terms of roadholding (she slipped a little at both pressures, but very controllable), but at 36psi the handling crispness is missing.

Fuel Economy - this morning did a round-trip 45-mile run to the dealer to have my Clipper Creek recall done. Temperatures around 55degF (13degC) and tires at 60psi. Used only the seat heater. May be my imagination, but it seemed I had to work harder than before to keep the consumption down.

Conclusion: way too much subjectivity and perception on my part and no supporting data. I like the Yokohamas so far. Far be it for me to recommend anything other than Mitsu-specified tire pressures of 36psi.

Future: since my wife drives the car most of the time, I'll drop the tires back down to 40psi; however, whenever we take long trips that will be testing the car's range, I'll be back up at 60psi. Everyone's advice duly noted, thank you.

I've unsuccessfully looked on the Internet, but cannot find any comparative Rolling Resistance data for the Yokohama AVID ENVigors vs. the OEM Dunlop Enasaves. Anyone?

 

[alohart]

I've unsuccessfully looked on the Internet, but cannot find any comparative Rolling Resistance data for the Yokohama AVID ENVigors vs. the OEM Dunlop Enasaves. Anyone?

If these tires are sold in Europe, they would have the A-G fuel efficiency ratings, A being best. In a brief effort, I was unable to find the Yokohama AVID ENVigor in Europe, but maybe I didn't look in the right place.

Otherwise, there doesn't seem to be much rolling resistance information on tires sold in the U.S.

 

[sandange]

Thanks for the tire review Joe
They sound like they are what I'll be looking for this spring.
I ran the original tires at 50 lbs for a while but due to our poor roads here, I dropped them down to 42lbs. It help to soften the bumps some what.
I guess time will tell how well they wear.

 

[Barbagris]

I've unsuccessfully looked on the Internet, but cannot find any comparative Rolling Resistance data for the Yokohama AVID ENVigors vs. the OEM Dunlop Enasaves. Anyone?

If these tires are sold in Europe, they would have the A-G fuel efficiency ratings, A being best. In a brief effort, I was unable to find the Yokohama AVID ENVigor in Europe, but maybe I didn't look in the right place.

Seems than in Europe Yokohama sells the Bluearth AE01. Labeled "C"

http://www.tyres-pneus-online.co.uk/car-tyres/yokohama/bluearth-%28ae01%29/175-60-r15-tl-81-h.html

 

[JoeS]

One-month (exactly 1000 miles) update using the Yokohama AVID ENVigors.

Something has gone wrong with our mileage: easily a 20% drop in range!

I've kept my mouth shut, but my wife has noticed it too, and her driving habits are consistently featherfoot.

Used to be a full charge would get us somewhere about RR=75 miles. Nowadays, it's around 60.

Driving locally, 8 bars would usually give RR=35-40 miles. Nowadays it's closer to 25 miles.

Air temperatures are in the 60's (degF). We finally have some much-needed rain, but for most of our driving it's been dry. Negligible heater use.

There were three changes that I made in mid-January:

1. Put on four new Yokohama AVID ENVigors
2. Reduced tire pressure from my previous 60psi to 40psi
3. Had the Clipper Creek recall performed

The rolling noise of the ENVigors is a definite and significant thrumming sound (I don't recall the Ensaves' making any noise), and I don't think it's just my sensitivity to it. Roadholding is excellent, but I preferred the handling at 60psi.

I still have not yet taken a LONG trip on one charge since getting the new tires, nor have I discharged the battery down to two bars and performed a clean full-up charge, so these are still all initial perceptions.

Jury is still out, but sure would like some objective third-party test data comparing the rolling resistance of the Yokohama AVID ENVigor vs. the OEM Dunlop Enasave.

 

[PV1]

I noticed a slight drop in range after the Clipper Creek update, but I think it was due to a reset of the car. It was temporary. I doubt after a month you're still seeing remnants of the update.

 

[Don]

One thing for sure - It's not the tires costing you 20%. A Daily Green test shows about a 5% improvement going from ordinary tires to LRR tires . . . . and you went from one brand of LRR tire to another - Couldn't be more than a couple percentage points at the most . . . . could it?

http://www.thedailygreen.com/living-green/blogs/cars-transportation/low-rolling-resistance-tires-461009

Don

 

[ndm]

I know it's not inline with the current thread but has anyone found a source for stock sized steel rims, I'd like my stock tires back on the factory mags come spring and then mount the winter tires on steel rims as backup for a blowout

 

[FiddlerJohn]

... has anyone found a source for stock sized steel rims ...

Many of the older Japanese 15" SPACESAVER tires had wheels of 15", 100mm 4 bolt, 4", 4.5" and 5" wide. I bought several of these real cheap ($6) at a junk yard. These spacesaver wheels are difficult for the recycle yards to sell. Most of the acceptable spacesaver tires seem to have the same outside tire diameter of as our beloved car.

I tried a few of these spacesaver tires and wheels of the front of the i-MiEV. They worked. The center hole in the wheel seemed to fit. This spacesaver tire test showed very high rolling resistance (though reduced RR ) and sometimes triggered the TPMS warning on the dashboard because of the difference in diameter.

Please us know what you do.

 

[jray3]

I tried a few of these spacesaver tires and wheels of the front of the i-MiEV. They worked.

And what John didn't mention is that pert' near anything with the 4x100 pattern will work on our rear axle. I've rolled with 13" Honda Civic rims back there (since they had snow tires mounted). Of course the idiot lights went beserk, but it was all for the sake of science.
:ugeek:

 

[JoeS]

One thing for sure - It's not the tires costing you 20%. A Daily Green test shows about a 5% improvement going from ordinary tires to LRR tires . . . . and you went from one brand of LRR tire to another - Couldn't be more than a couple percentage points at the most . . . . could it?
http://www.thedailygreen.com/living...portation/low-rolling-resistance-tires-461009

Here are the Tire Rack tests of LRR: http://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=121, which I believe was the source for the above article (which I can't find again and in my case results in a weird link to Good Housekeeping)

It shows a "mileage" variation between 53.8mpg and 50.0mpg, or a difference of 7.6%

 

[JoeS]

Ever since I mounted the Yokohama AVID ENVigor tires we've noticed a very significant drop in our Mitsi's range. I've been quite bothered by this (as discussed in preceding posts).

Background

There were three variables simultaneously at play here:

- New tires
- Clipper Creek charger update by Mitsubishi
- Tire pressure dropped from 60psi (4.14bars) to 40psi (2.76bars)

I had previously detected no loss in mileage due to any possible battery degradation despite the car having been driven 23,000miles (37,000km) prior to installing the new tires. My frame of reference for the car on the original worn Dunlop Enasave tires had been a number of my usual long trips in December which showed "normal" mileage performance; also, we did a 160-mile New Year's Day trip which showed a slight drop in mileage but which I attributed to an additional 250lb (113kg) load in addition to our weight [185+125= 310lb(141kg)] - and that trip entailed a couple of 1800ft (549m) climbs.

It was a nice day yesterday (temperature ~65degF (18.3degC)) so we decided to take one of our usual 55-mile round-trips to the coast (Half Moon Bay) for lunch, and to use this as an opportunity to assess the car's mileage. Prior to leaving, I fully charged the car and, to eliminate one variable, I pumped up the tires to 60psi. Prior to charging, the car had been used in its usual mixture of city/highway driving with no particular attention paid to efficiency.

This was a mileage range test, so I did my usual hypermiling: featherfooting, highway speeds rarely over 55mph, a lot of coasting in Neutral, and negligible brake use. After returning, I fully charged the car overnight using the Clipper Creek L1 EVSE (12A).

I have a separate GPS that I use as a trip mileage recorder. I elected not to use CaniOn during this trip because I still have not played with it enough to assess it's consumption measurement accuracy.

Here's the data -

Prior to departure, 16 bars and Canion shows the battery nicely balanced and 360v at 100% SoC
RR at departure = 56miles (90km) Note: that's well below what we're used to.
Air temperature: 65degF (18.3degC)
Zero use of heater or aircon
Trip Length = 54.9miles (88.4km)
Trip's end RR = 9miles (14.5km)
Trip's end Fuel Gauge shows 2 bars (dropped from 3 bars to 2 bars as we went up our steep driveway)
Trip's end CaniOn SoC = 22% and 328v
Recharge = 13.91kWh (Kill-A-Watt) or 14.209kWh (TED). Average = 14.06kWh
RR after Recharge = 65miles (104.6km)

Consumption calculation (take your pick):

3.9miles/kWh
256Wh/mi
6.29km/kWh
159Wh/km

Part of this trip's profile can be seen in this posting: http://myimiev.com/forum/viewtopic.php?f=28&t=442

Discussion -

As discussed here, I had seriously measured my energy consumption for over 8000miles (12,900km) with my overall average being 4.2miles/kWh (148Wh/km). I would have expected this trip to have resulted in a number close to 5miles/kWh (124Wh/km).

After fully charging the car, one of the fun ways I monitor our energy consumption is to sum the GPS trip recorder reading plus RR. This number had actually climbed up to 72miles (116km) by the time we reached the coast (altitude drop of 600ft (183m)), but had decreased to 55 + 9 = 64 miles (103km) by the time we got home. I would normally have expected this number to be at least 75miles (121km) after such a trip.

This trip we normally return with 4 bars showing. After a full recharge I would have expected to show a RR of around 80miles (129km) after such a carefully-controlled trip.

The Clipper Creek charger update should have had no effect on the car's mileage, and I'm discounting this as a variable.

An unsolicited subjective anecdote from my wife:

"While driving, when I put the car into Neutral it now immediately feels like it's slowing down. It didn't do that before."

Recall my saying that these new tires have a noticeable thrumming sound on certain smooth road surfaces.

Conclusions -

Pumping up the tires from 40psi to 60psi did not noticeably improve mileage (Don is right, again).

Something has changed to make things worse. Only way to tell if it's the tires is to go back to the Dunlop Enasaves.


My Verdict:

The Yokohama AVID ENVigor tires are inferior to the OEM Dunlop Enasave tires in terms of Rolling Resistance.

Anyone have any hard data comparing thes two specific tires?

 

[sandange]

Interesting observation Joe

New tires have fresh thread = more traction = more drag.

The only way to be sure is to swap wheels with a local fellow Miev member for original tires and rims, for a week, to compare or replace your old tires if you still have them.
With out changing anything else.