Can New Sumitomo Tires Cut Fuel Mileage??....& UPDATE - Human Error!

[saflyer]

Just installed a new set of Sumitomo ST719s on my coach in place of my Michelins.I haven’t done a rigorous check yet but they appear to be delivering about half the fuel mileage as the old tires. Maybe 3-3.5 mpg vs. my former 6.5-7, which was nothing to write home about. I can almost see the fuel gauge move as I drive. It’s so bad I checked for a fuel leak. Is this possible?

The installers put 115 psi in all tires. I gat the Sumitomo numbers and the table ssid 95 psi so I lowered all 6 to 105 psi for this trip.

Will update st my next fill up.

Ed             
‘05 HR Ambassador 

[BradHend]

Hold up.  You’re only getting 3-3.5 MPG with the new tires and your normal usage is 6.5-7MPG???😳

[saflyer]

Fairly inaccurate but when gauge was on half mark, about 50 gallons used I had only gone 150 miles since fill-up.

[nvrtoofast]

Tires are an important part of the mileage game. I would double check pressures as that will make a difference too. that drastic of a change is astounding though. Please report back if you find anything. Very curious to put this on a do not buy list if in fact they are an issue. What a shame. New tires should bring happiness and stress relief.

[vito.a]

Tires and tire pressures can change fuel mileage by very small amounts (.1 mpg or so), but not by the amount you're seeing.  Either the math is wrong or something serious is happening.  

Hope you figure it out.  

[jacwjames]

How many miles was the test, I'd do a long trip and collect the info to compare.

I drove across Kansas on Thursday battling a wind from the NW.  My steering wheel was between 1 & 2 Oclock the whole time.  I still managed to get +6 mpg and I weigh much more and pull a jeep. 

If your mileage is that low you definitely need to investigate. 

[DavidL]

No way are the tires contributing towards a fuel mileage change like that.  Especially if they are inflated anywhere near what they are supposed to be.

Sounds like inaccurate mileage calculation.

 

[saflyer]

29 minutes ago, DavidL said:

No way are the tires contributing towards a fuel mileage change like that.  Especially if they are inflated anywhere near what they are supposed to be.

Sounds like inaccurate mileage calculation.

If the halfway mark on my fuel gauge is 50 gallons the mileage indicated is 3.2 (160/50). If it’s only indicating 40 gallons used that’s still no better than 4 mpg. The gauge has always been accurate. We’ll see at the next fill-up. I hope you’re right.

[Guest Ray Davis]

It's gotta be because of relying on the gauge.  I wouldn't panic yet, more than likely you'll find the mileage is the same.

[timaz996]

1 hour ago, saflyer said:

If the halfway mark on my fuel gauge is 50 gallons the mileage indicated is 3.2 (160/50). If it’s only indicating 40 gallons used that’s still no better than 4 mpg. The gauge has always been accurate. We’ll see at the next fill-up. I hope you’re right.

I put the same tires on my coats last March. And I still get the same mileage as anywhere from 7 1/2 to 9 miles per gallon at 60 miles an hour. I would wait and do a true mileage check by topping off the tank to start with, and topping it off again to finish.

[cbr046]

That much energy, the difference between 3-3.5 mpg and your former 6.5-7, consumed by the tires would cause them to explode. 

Something else is going on . . . .

- bob

[Frank Bergamo]

The tire pressure should be set after weighing coach. Four corners is preferable. Then set pressure accordingly. As far as fuel mileage, is your cooling fan running wide open? It takes an awful lot of HP to turn that fan at full speed. At start up, with engine cold, it should be barely turning. As the engine warms, speed of fan should increase. Hope this helps.

[Dr4Film]

Your problem is that you are relying on an analog fuel gauge which is the most INACCURATE gauge on your dash.

Fill the tank, drive 500 miles, fill the tank, then calculate your MPG.

[jacwjames]

1 hour ago, Dr4Film said:

Your problem is that you are relying on an analog fuel gauge which is the most INACCURATE gauge on your dash.

Fill the tank, drive 500 miles, fill the tank, then calculate your MPG.

Agree with Richard, the fuel gauge at best is a dash ornament. 

I used a Silverleaf VMSPC and it is pretty darn accurate.  Last time I filled up it said I needed 78 gallons based on the 128 tank capacity that I use and I pumped 83.  The 5 gallons can be attributed to if the rig is leaning a little.  It is usually within 1-2% on the long haul.  It displays trip gpm but also instantaneous which can be stressing, I was averaging 3.1 mph has I was climbing the Rockies toward Eisenhower Tunnel.  But at times I was getting 256 mpg as I was descending the other side.

 

[Raymond]

Not that I would ever consider switching from Michelin tires, this is an interesting topic—would really like to know the final conclusion on your mpg dilemma. 
 

Ray W

[Tom Cherry]

18 hours ago, saflyer said:

Just installed a new set of Sumitomo ST719s on my coach in place of my Michelins.I haven’t done a rigorous check yet but they appear to be delivering about half the fuel mileage as the old tires. Maybe 3-3.5 mpg vs. my former 6.5-7, which was nothing to write home about. I can almost see the fuel gauge move as I drive. It’s so bad I checked for a fuel leak. Is this possible?

The installers put 115 psi in all tires. I gat the Sumitomo numbers and the table ssid 95 psi so I lowered all 6 to 105 psi for this trip.

Will update st my next fill up.

Ed             
‘05 HR Ambassador 

Back to basics….if you are 100% sure on your corner weights and the inflation.  I pulled your sales brochure.  The 275/70R22.5 is correct.  Your frint axle is 13,000 pounds.  Rear is 20,000.  The OEM Goodyear’s was what came on it and their inflation table would show  115 (psi) Front and 95 Rear.  You have a plate or decal, probably on the drivers console or the side part where the shifter is.  Look on the vertical wall of that or in a cabinet.

Now the Sumitomo S719’s values are a bit different.  If you look at the table…..then the rear’s would be OK at 90.  Our “old timers that know tires and are well informed” say never to go below 90 and some say 95 (psi).  The S series tires are a bit different in inflation pressures from GY…so, yo go with what their tables say.

Front….@ 115 psi, they are a couple of hundred pounds SHY for a 13K axle.  Monaco always rounded up.  So, you would have to go to 120.  OUCH!.  From a “engineering” or calculation….if you went 117 psi with the Sumitomo….that will get you the correct inflation for the front.  Then, invoking the rule of thumb….95 in the rear.

If you are grossly under loaded…., unless you have individual front corner weights….then you are probably UNDERINFLATED.  Don’t guess. If NO WEIGHT INFO…put 117 in the front.  Rears don’t matter…except if you go crazy and decide that an additional 10 PSI is better….your ride deteriorates.  YES…i thought more was better…but after a 20 or so miles…..back to the correct or plate pressure.

I would adjust, cold in the early AM, the tires….run them….forget using the fuel gauge..…  I don’t know if your rig has a fuel computer or not.  Mine does.  Pull into a level truck stop.  Fill up until the pump shuts off…..drive several hundred miles….then repeat.  Level the MH before filling as you may be canted as you come in, that is the Only way to get consistent information. Here is a thread I found….

https://www.irv2.com/forums/f258/sumitomo-st719-453968.html

 

 

[frankogrly]

I am on my second set of Sumitomo's and fuel milage is not effected.

Frank o

01 Endeavor

[saflyer]

3 hours ago, Dr4Film said:

Your problem is that you are relying on an analog fuel gauge which is the most INACCURATE gauge on your dash.

Fill the tank, drive 500 miles, fill the tank, then calculate your MPG.

Before my first post of this thread I fueled up at 390 miles with 72.25 gallons. This gives 5.4 mpg. But I had 124 miles of that tank on the old tires. Applying a conservative adjustment for that returns about 5 mpg.

I’m fully aware of the inaccuracy of the dash gauge and a drivers inability to read it to a fine point but even allowing for 20% error gives 4 mpg. My gauge has been accurate enough over the years to have cause for concern of my current mileage. I plan to fuel up Friday at the same station which will take any difference in coach tilt out of consideration. As most know any tilt of the motorhome can make a significant difference in the amount of fuel you can squeeze in the tank. But I don’t think there is any way I’ll get near the 500 miles you suggest.

[saflyer]

2 hours ago, Tom Cherry said:

Back to basics….if you are 100% sure on your corner weights and the inflation.  I pulled your sales brochure.  The 275/70R22.5 is correct.  Your frint axle is 13,000 pounds.  Rear is 20,000.  The OEM Goodyear’s was what came on it and their inflation table would show  115 (psi) Front and 95 Rear.  You have a plate or decal, probably on the drivers console or the side part where the shifter is.  Look on the vertical wall of that or in a cabinet.

Now the Sumitomo S719’s values are a bit different.  If you look at the table…..then the rear’s would be OK at 90.  Our “old timers that know tires and are well informed” say never to go below 90 and some say 95 (psi).  The S series tires are a bit different in inflation pressures from GY…so, yo go with what their tables say.

Front….@ 115 psi, they are a couple of hundred pounds SHY for a 13K axle.  Monaco always rounded up.  So, you would have to go to 120.  OUCH!.  From a “engineering” or calculation….if you went 117 psi with the Sumitomo….that will get you the correct inflation for the front.  Then, invoking the rule of thumb….95 in the rear.

If you are grossly under loaded…., unless you have individual front corner weights….then you are probably UNDERINFLATED.  Don’t guess. If NO WEIGHT INFO…put 117 in the front.  Rears don’t matter…except if you go crazy and decide that an additional 10 PSI is better….your ride deteriorates.  YES…i thought more was better…but after a 20 or so miles…..back to the correct or plate pressure.

I would adjust, cold in the early AM, the tires….run them….forget using the fuel gauge..…  I don’t know if your rig has a fuel computer or not.  Mine does.  Pull into a level truck stop.  Fill up until the pump shuts off…..drive several hundred miles….then repeat.  Level the MH before filling as you may be canted as you come in, that is the Only way to get consistent information. Here is a thread I found….

https://www.irv2.com/forums/f258/sumitomo-st719-453968.html

 

 

Tom,         
I had my coach weighed at the four points years ago but can’t find that anymore but as I recall the difference left to right wasn’t enough to make a difference in pressure. And yes, we weighed at travel weight. All of our gear, passengers, supplies, full fuel and 20 gallons of potable water. On a Cat scale it’s 10,000# front, 20,000# rear. Your table is different from the one Sumitomo gave me. The table I have has no pressures below 95 psi. At that the single weight is 5400# whereas mine imply 5000#. So steer and drive pressures would be 95 psi per my table. And, yes I checked the pressure in the shade at 75°. So, my 105 should be more correct than 115, or am I confused. BTW, the tire guru who writes for one of the RV travel email newsletters advises to add either 10psi or 10%, I don’t recall which, to the tables to allow for lower temperatures. He also does not adjust for temperatures different from 75° but I believe you should.

Would it be possible to have a fuel leak while driving but not while stopped and idling?

Thanks,        
Ed

 

Edited October 9, 2023 by saflyer
Punctuation

[Tom Cherry]

51 minutes ago, saflyer said:

Tom,         
I had my coach weighed at the four points years ago but can’t find that anymore but as I recall the difference left to right wasn’t enough to make a difference in pressure. And yes, we weighed at travel weight. All of our gear passengers supplies, full fuel and 20 gallons of potable water. On a Cat scale it’s 10,000# front, 20,000# rear. Your table is different from the one Sumitomo gave me. The table I have has no pressures below 95 psi. At that the single weight is 5400# whereas mine imply 5000#. So steer and drive pressures would be 95 psi per my table. And, yes I checked the pressure in the shade at 75°. So, my 105 should be more correct than 115, or am I confused. BTW, the tire guru who writes for one of the RV travel email newsletters advises to add either 10psi or 10%, I don’t recall which, to the tables to allow for lower temperatures. He also does not adjust for temperatures different from 75° but I believe you should.

Would it be possible to have a fuel leak while driving but not while stopped and idling?

Thanks,        
Ed

 

Here is the link for the table that I used.

http://rvweigh.com/wp-content/uploads/2019/01/Sumitomo-Truck-Tire-Load-Inflation-Table.pdf

YES…the ST719 is NOT listed. If Sumitomo gave you a different table, then they are the “source”….but why do they publish this technical bulletin that may be different….it was NOT something I grabbed off a site…we try to be accurate and thorough here and, we the staff, often check out posts for that…

Next….in REVERSE ORDER.  No offense to the “general” sites where folks are paid or not paid…but I had a few lengthy phone   calls with the Engineering Manager for Bridgestone Commercial Truck tires…and he “wrote” his on newsletters…in their site.  He says NEVER, especially on the steers, run MORE PSI than what you need for your “correct”, measured weight.  A long time ago, an “Engineer” from GY, fielded questions on the rivering or premature side rib wear on the GY670(?) OEM Monaco tires.  “Inflate then maybe 8 PSI”. Lots of folks like me read  that here.  Turns out…no real impact….except to shorten the life and put the MH at risk.  The Bridgestone guy was also a MH owner. He said bumping them up caused more POTENTIAL internal damage to the belts and rubber…he advised me to not run them until they wore out…or FAILED. That is from a real expert in the field…..

OK…don’t know where your fresh tank is.  Mine and the fuel are up front.  Don’t know and don’t still have your brichure up.  If, say, your fresh tank is 70 Gal….then 70 - 20 = 50   Times 8.33 is 416 pounds…do the math.  Ads that or split it up to one axle or the other.  If your chart says 95…then I really would call Sumitomo AGAIN.  That is spooky.  I KNOW, from doing the same drill….that Monaco should have had your plate data like I posted….look at yours….

OK….I THINK I FOUND IT. You have a SUPER DUTY Load Range J tire….  

http://www.sumitomotrucktires.com/Tires?linename=ST719

NOW…if you out in YOUR SIZE in the drop down…you get this….see photo below….so, this tire was not exactly rated or recommended for a MH…more of a really heavy or high load.  Thus, for ride comfort….you need to drop the pressures to whatever the table says…..

HERE is where it baffles me.  The spec photo says …and Sumitomo needs to answer this…..the spec says DUAL MAX is 6495 @ 130 PSI.  BBBBUUUUTTTT….the chart I got out of Sumitomo technical document says 6355 @ 115 psi. To me….that does NOT compute…..  maybe i messed up inreading the spec sheet…

MAYBE they meant that 6395 is the MAX Weight….and 130 is the MAX PSI….but what good does it to go from 115 to 130 and get “no weight gain”.

FWIW, many folks have been advised or chose a “18 ply” tire and there was some discussion and perhaps “buyers remorse”.  All we know is that Monaco used Load Range H and that was on the tire decal….or maybe I am mistaken….but that was the load range that was used for the OEM tires…that is why it is recommended to go back with the SAME size & load range.

I haven't a clue about a “ghost or intermittent leak”.  My advice….and others might not agree. Set the correct pressure for your weights or axles.  Drive and measure and verify the calculations…..and it will vary all over the map.  Many of us have a record of the date and at least 10 columns for mileage, the fuel computer’s results and some, even the temp and winds….YES….NOT KIDDING.  Our individual fillups vary.  I’m recording Genny Hours.  Another not only does that, but Aquahot hours….

BUT…we look at where we filled up….the terrain….as in hilly and the average speed for that segment…..

I can NOT believe that tires would halve or such.  My FOCUS….get the pressure correct…then calculate….

 

 

.  

 

[Specialk]

I’ve been running these same tires for 3 years now without a problem.  I have not experienced this negative fuel mileage as stated in the post.  

[saflyer]

6 hours ago, Dr4Film said:

Your problem is that you are relying on an analog fuel gauge which is the most INACCURATE gauge on your dash.

Fill the tank, drive 500 miles, fill the tank, then calculate your MPG.

I’m not relying on the dash gauge. It’s just a heads up, first estimate.

This is where I was led to the ST719:

http://www.sumitomotrucktires.com/tires/find
It says “steer tire” but the diagrams show them in all positions. The ST709 is stated as an “all position” tire. BTW they web page says ST 719 SE. I don’t know what difference the SE makes.

Edited October 9, 2023 by saflyer

[cbr046]

24 minutes ago, saflyer said:

BTW they web page says ST 719 SE. I don’t know what difference that makes.

The SE is 16 ply and 75 mph rated and touted as a regional steer, the ST719 is 18 ply and 81 mph rated and touted as an all position.  But I couldn't match apples & apples on tire sizes.  The closest SE was a 285/75 where the ST719 was a 275/70 tire.  Odd they don't match sizes . . . .

The SE also features Sumitomo's "S-Tech" features, which sounded more like marketing hype than actual features (to me).

- bob

[Tom Cherry]

1 hour ago, saflyer said:

I’m not relying on the dash gauge. It’s just a heads up, first estimate.

This is where I was led to the ST719:

http://www.sumitomotrucktires.com/tires/find
It says “steer tire” but the diagrams show them in all positions. The ST709 is stated as an “all position” tire. BTW they web page says ST 719 SE. I don’t know what difference the SE makes.

If you go to your link.  There are TWO ST719's.  The E is NOT available in your size.  Click on the PLAIN ST719.  Then go to the bottom of the page.  In the FIND A size drop down, there is where your size is.  Click on that.  That takes you to the same page that I did a screen print of.  
 

That is the one that is, not exactly, clear...at least to me.

If Sumitomo sent you a link to an inflation chart, then post that.  That might help us to understand....

 

[saflyer]

5 hours ago, Tom Cherry said:

If you go to your link.  There are TWO ST719's.  The E is NOT available in your size.  Click on the PLAIN ST719.  Then go to the bottom of the page.  In the FIND A size drop down, there is where your size is.  Click on that.  That takes you to the same page that I did a screen print of.  
 

That is the one that is, not exactly, clear...at least to me.

If Sumitomo sent you a link to an inflation chart, then post that.  That might help us to understand....

 

I sent a request for info to Sumitomo via their website. Evidently they forwarded it to a U.S. distributor, TBC Corp. who responded as follows:

Mr. Fogle,

We are in receipt of your inquiry.  We are a wholesale tire distributor of multiple brands of tires, not a tire manufacturer, and we create dedicated websites for each of the brands of tires we distribute; we distribute the Sumitomo brand of tires in North America.  Most tire manufacturers only provide us with the maximum psi and maximum load a particular tire can hold, as they cannot foresee where the tire will be installed on; however, Sumitomo has provided a load inflation table which you can find by clicking on the link below:

https://tbc.scene7.com/is/content/TBCCorporation/TBC%20Brands/Commercial/Sumitomo%20MRT/Catalog/2022/Medium-Truck-Technical-Data_0322.pdf

 This information can be found if you return to the website, go to the DEALER RESOURCES section, and under the 2023 MEDIUM TRUCK TIRES catalog, clicking on the third link that reads Medium Truck Technical Data; the information you are looking for is on page 4 of this document.

Thank you,

 Olga Fraga

Consumer Relations

Tel. (800) 238-6469

Fax. (800) 467-4638

Email: ofraga@tbccorp.com