saflyer

3 hours ago, Ivan K said:

If you changed tire size and use odometer for calculation, it would make some difference but not that significant. I would check hub temps, brake drag, assuming no ECM parm updates.

Same tire size.

10 minutes ago, DavidL said:

Because you are saying that you are trying to squeeze every drop into the tank, indicates you aren't calculating mileage correctly.

You should be long term tracking how much fuel goes into the tank, independent on the capacity of the tank or fullness.  Across time, the errors with each fill will normalize.

If your calculations are indeed correct (after monitoring for several more fuel fills / documenting how many gallons across miles), and you are getting consistently low mileage, then you have a motor problem.  If it's running well, then you probably aren't having motor problems.

But no way is changing tires going to affect mileage to the degree you are saying.

I fully understand the concept of calculating mileage. But two points. One, it was my first opportunity to update. Two, as I said it’s not likely I made a difference in filling of anywhere near 5 gallons but factoring that my mileage is still horrible. 

Re: previous post about lowered mileage with new tires.              

Just did a fill up with the new Sumitomo ST719s. The last one had 124 miles on the old tires so this one is more representative. My last fillip on the Michelins gave 7.6 mpg. The last six fillups gave an average of 6.8 mpg. This fill up was after driving 309.8 miles mostly at 65 mph. Fuel used was 69.651 so about 4.5 mpg! Ouch! My mileage dropped by fully 1/3! I filled at the same station and pump so the coach level the same on both fills. I did squeeze more fuel in the second time so that dropped my mileage. But even applying a huge fudge factor of 5 gallons the mileage is still less than 4.8 mpg.

Next week I’ll take the motorhome to a shop to find out if there could be any drive train problem causing the change.

Ed           
‘05 HR Ambassador

13 hours ago, Tom Cherry said:

OK.....This gets confusing.  First of all, the table above shows that the ST719 is a Load Range J (18 ply) tire.  GO TO THE LAST PAGE or so and scroll down.  That is what the spec sheet say on it.

BUT, look at the "Secret" as I called it....inflation table says for the 275/70R22.5 ROW.  It is a load range H or the Alpha after the Weight.  SO, Sumitomo publishes a Load or Inflation table that lists ONLY the 275/70R22.5 in load range H...but does NOT have a row for the Load Range J....which is what the ST719 is.  That is interesting.  Perhaps Olga could explain this.

BUT, curiosity is a horrible vice....so I put together an Excel file with the Published....or what comes from the commonly found table, the link that I posted and the screen shot.  Then the SECRET that Olga sent you ....  JUST TO COMPARE....here it is...

OK....I had to COPY this from an EXCEL file and paste it here and the formatting went crazy.  SO, I used THIS for illustration.

My CONCLUSION.  The Sumitomo tires, regardless of the load range...are DIFFERENT from the Original Goodyear 670 tires.  That is TOTALLY weird...based on doing comparisons for many members over the years.  The same size tire & Load Range in a Michelin, Goodyear, Toyo, and several different other brands were all in the SAME range or ballpark.  BUT, your Somitomo's are "DIFFERENT"....so again, you rely on the Manufacturer....and NOT on what is posted on some random site.

Bottom line....if it were ME, I would run 95 PSI in the FRONT....and 100 PSI in the rear.  The additional 5 pounds should NOT cause any issues...but IF it does...then, from an interpolation standpoint....you could run probably 97 in the rear and be just fine....the front is OK at 95.  BUT, I would NOT run 90 in the front....the Olga SECRET chart does NOT even list a value for 90 PSI....so run 95 up front....and 97 if you want the smoothest ride in the rear.  That is WAY too precise...but we Engineers tend to be a little OCD...

That's it.  I think you are fine here...but as to the Fuel....I think you need more data.  If it continues to be an issue....then talk to the folks.  The Rev's per MILE would be a minor issue...but very minor.  The tires are close to the same....unless the load range J ST719 looks like it is totally underinflated and looks like a "FLAT"...but, seriously....that is a physical impossibility.  NOW....the lower the pressure...the LOWER the tire will be pumped up....and the wider the tread patch or surface contacting the road.  That DOES provide more resistance.  I could see the difference, maybe 0.1 MPG between towing a lighter H3 Hummer with fatter tires as compared to a heavier Yukon with somewhat "less aggressive tread".  BUT that was based on a few years of data for each to compare.  CERTAINLY not halving...

That's it.  Let us know when you have more data.  OR you can have the engine scanned....to see if there are any codes....it would take a tremendous blockage of the air filter to reduce your mileage by half.....

 

ST719	PSI	65	70	75	80	85	90	95	100	105	110	115	120		125	130		135
Publish	Single	NA	NA	NA	NA	4920	5160	5400	5645	5880	6130	6355	----	7000 (H)
	Dual	NA	NA	NA	NA	4590	4815	5040	5270	5490	5720	5940	----	6395 (H)
Secret	Single	NA	NA	NA	NA	NA	NA	5400	5630	5850	6070	6290		6510	6730	--NA--	----	6940 (H)
	Dual	NA	NA	NA	NA	NA	NA	4980	5180	5390	5590	5800		6000	6200	--NA--	----	6395 (H)

 

 

Call Michelin.  Ask their tire gurus or send them an Email....

Interesting side note about lower inflation. When I purchased this coach 12 years ago Ibelieve it had Michelins but not absolutely sure. Driving it home from Michigan I thought I had made a big mistake. It drove terribly. Wandered all over the road. I was constant turning the wheel left and right wearing myself out. I was driving 60-65 and when trucks passed it scared the begeebers out of me.

Got it home and had the alignment checked. It was good. Then I looked up the inflation tables. The dealer had the tires at something over 120 psi, exactly how much I don’t recall. The inflation tables were more like 95 rear and 100 or so steer. I was leary of lowering the pressure as I thought that could only worsen the drifting problem since the sidewalls would be less stiff. To my surprise that wasn’t the case. The new pressures improved the driving of the coach immensely. Still didn’t drive like a car but far better than before. I realize some of the improvement may have been muscle memory but I’m sure the inflation was a big part.

To get better steering I switched from the Shephard steering box to a TRW one but didn’t notice any improvement with that.

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

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.

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

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.

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.

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

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 

On 9/24/2023 at 10:14 AM, saflyer said:

There are several different models based on wheel type. Hope they have good customer support for helping me order the right ones.

One person said it’s best to buy Centramatics where they have all models in stock and do a lot of motorhomes so they can select the best ones. I don’t have that luxury but the tire shop that is installing my tires installs a lot of Centramatics on semis so I figured he could tell if they sent the right one from the local Centramatics dealer. So far so good.

4 hours ago, miacasa_2000 said:

I have Centramatics all around they are great, But a word of caution . On my last set of tires they did not spin balance because of them and I had a terrible wobble went back and they put them on the spin balancer and found a tire out of round a factory defect which nothing will overcome. So I know I will from now on always have them balanced along with my Centramatics so I know I'm starting out good and who knows later down the road if a weight falls off the balancers will keep up with it.

Roy   2003 Dynasty

Interesting. Just today someone posted on ramblinpushers.com the same thing. Seems like “belt and suspendes” idea but makes sense.

There are several different models based on wheel type. Hope they have good customer support for helping me order the right ones.

2 hours ago, Ivan K said:

Balance masters up front. Centramatics on all rears. Same function, different material. One time expense and done.

OK, I need to know more about Balance Masters. What’s the difference between them and Centramatic?

2 hours ago, Ivan K said:

Balance masters up front. Centramatics on all rears. Same function, different material. One time expense and done.

Anyone use Centramatics for balancing your steer wheels? I’m getting new tires all around and a friend advised me to go with them versus beads or spin balancing.

Ed            
‘05 HR Ambassador 

On 9/19/2023 at 8:02 AM, dl_racing427 said:

My next tire change I'm going with Centramatics or similar balancers.
I have tire equipment and I rebalance the tires on my cars once a year or so, but these things are just too heavy to be doing that myself. LOL

What are others thoughts on the Centramatics? One friend was of the opinion bead balancing for motorhomes is not ideal since they sit so much of the time and the beads will migrate while sitting.

Well, since Toyo doesn’t make the 275/70R 22.5 anymore I checked locally and could only find Hercules and Sumitomo in my load and speed range. Current Michelins show 148/145M for these ranges. The Hercules and Sumitomo run close to each other in price, low $3000 range out the door. Any suggestions?

Also, bead or spin balancing? If I go with online tires where they come to me to install I guess it will only be the bead option. 

I need six new tires for my HR Ambassador, 275/70R 22.5. Running Michelins now but they’re too expensive this time around. A friend put Toyos on a few years ago for a good price.He’s happy with them. Another thread poster put Hercules on but had a harsher ride than his old ones. Nothing was said about other brands like Goodyear, Goodrich, Firestone, etc. Any sugestiona.

Also, things like M144 and 11A were mentioned. Are these models or specs?

11 minutes ago, Ivan K said:

You can just add if you have to but that would mean that you have a leak (unless it was low from the get go) and you don't want it to leak at the back on brakes, if it did. Personally, if I did not trust that they used full synthetic, I would drain them and refill. It doesn't look like yours have a drain plug so you would have to suck it out. Tilting the axle helps as there is oil behind the outer bearing. I use the same synthetic gear oil as for the differential for simplicity. Once you refill, check again in a bit because it will take some time to level out.

Thanks

On 9/5/2023 at 1:23 PM, K9 Exec said:

Hi Ed, good advice on the forum- you won't go wrong. 🙂

I will add this to the post: I would use full synthetic (any brand) 75w90 gear oil and call it a day. I have a friend in the lubrication analysis business that I trust and have seen the data. Pop the cap, add the oil to the add/full line right below the lip, replace the cap and you are good. You will be good until you have to add it again, which unless you have a leak should be never. Drain then refill  every 300,000-500,000 miles for commercial use or 3-5 years. I would not use dino in this application due to high heat and breakdown, the synthetic is the same cost so it is a win-win. You can buy a quart bottle with the cut top and will be good for both sides typically with a bit to spare. 🙂

Best of luck!

I have no idea what lube they were originally filled with. When I need to add lube can I mix the synthetic with whatever is in it now or should I drain and start over.

Found it: Knight. Is that correct?

Ed

Looked for a wiring diagram for my ‘05 HR Ambassador. The ones in files are for Monacos so I need to know the Monaco equivalent of the Ambassador.

Thanks

On the advice of some on one of the forums i use I changed my front wheel hub grease fittings to the type in the picture. I don’t know what they are called so if anyone can help me with that please do.

I was given the briefest insulation on checking and replenishing the fluid and have now forgotten what little I knew. Can anyone tell me how to check the level and fill if necessary and with what type of lubricant?

Ed         
‘05 HR Ambassador 

Found out what the lower lights are. Fog lights with a separate switch. They work.