You might be going faster than you think if you have a Spartan Chassis

[CJ7365]

Originally Posted by plasma800

hey.. at least you get there sooner..

But with more miles on the odometer than actually.

[Rotten-Red]

Originally Posted by CJ7365

But with more miles on the odometer than actually.

I think you have that backwards. It would be less miles than actual.

[Winepress]

Originally Posted by CJ7365

But with more miles on the odometer than actually.

Yep, and you’ll see better fuel mileage

[JMonroe]

Both of our Spartan chassis coaches were in spot on agreement with the GPS. Like others have already said, a Spartan or Cummins shop should be able to adjust this for you.

[CJ7365]

NVM

[Tizbad]

Originally Posted by duanetf1234

I have a 2018 Newmar DSDP 4369 on a Spartan Chassis.
I noticed that when my speedometer showed a speed – let’s say 60 MPH, my GPS showed a speed 5 MPH faster. Curious as to which was correct I had my wife drive her Lexus alongside when I was going 60 per my speedometer and she reported that I was really going 65 according to the Lexus, which concurred with my GPS.
I called Spartan and asked if there was an adjustment available to correct this and their response was “that difference is within our specifications”. I was surprised at this response to say the least.
So, be careful. You may be driving faster (or who knows) slower than you think if you have a Spartan chassis. I suggest you verify the accuracy of your speed indication.
Duane Frederiksen
2018 DSDP with Spartan Chassis

I think I recall reading that a GPS is accurate within a half of a MPH. Our previous motorhome was on a Spartan chassis, and it was about 2 MPH off. Our Essex is spot on.
I have an old 1999 F-150 and an old Miata and both are exactly 5 MPH higher than actual. Tire sizes are correct in both vehicles. In the Miata, it just adds to the thrill, since I always feel like I am "flying" anyhow!

[Tizbad]

Originally Posted by duanetf1234

I have a 2018 Newmar DSDP 4369 on a Spartan Chassis.
I noticed that when my speedometer showed a speed – let’s say 60 MPH, my GPS showed a speed 5 MPH faster. Curious as to which was correct I had my wife drive her Lexus alongside when I was going 60 per my speedometer and she reported that I was really going 65 according to the Lexus, which concurred with my GPS.
I called Spartan and asked if there was an adjustment available to correct this and their response was “that difference is within our specifications”. I was surprised at this response to say the least.
So, be careful. You may be driving faster (or who knows) slower than you think if you have a Spartan chassis. I suggest you verify the accuracy of your speed indication.
Duane Frederiksen
2018 DSDP with Spartan Chassis

I think I recall reading that a GPS is accurate within a half of a MPH. Our previous motorhome was on a Spartan chassis, and it was about 2 MPH fast. Our Essex is spot on.
I have an old 1999 F-150 and an old Miata and both are exactly 5 MPH higher than actual. Tire sizes are correct in both vehicles. In the Miata, it just ads to the thrill, since I always feel like I am "flying" anyhow!

[Stuart W]

Just drove me 2018 K2 @ 60 MPH matched my phone speed app @60 MPH also tested at 30MPH

[Craig36]

Our 2007 KSDP is the same as my Rand McNally, as best I can tell.

[rewillia]

Originally Posted by NealC

Wow. That's pretty sloppy. Keep that inaccuracy in mind with your tire max speed limit.

Indeed. Actual speed should be something of confidence (i.e. speedometer reading) as it is the primary source for the subject info that most of us rely upon.

A 5-MPH difference does not seem too much unless one thinks he/she is driving 70-MPH and is actually driving at 75-MPH which the majority of RV tires are rated for and further based upon "all things being equal" in terms of vehicle weight and proper tire inflation, along with existing conditions of a tire in the form of age/wear as well as road hazards and weather conditions all of which come into play.

I personally would not want to run at 100% of my rated tire speed for all of the apparent reasons and generally try to keep between 58-65 MPH but on occasion have often exceeded such simply either in passing or traversing downhill slopes.

With the increased speed comes the risk of a tire failure, something none of us ever want to experience particularly at higher speeds. The posted 75-MPH speed limits (or greater on many state and federal highways) today are in my opinion not in the best interest of most RV enthusiasts.

The OP's post (thanks) now has me questioning my own need to do a similar comparison analysis of my speedometer reading vs. GPS, VORAD, or another vehicle and pursuing corrective actions if found to be different.

[wa8yxm]

Have used MM v/s Watch
Michigan State Police Radar (By agreement, not by ticket). (Slowly brought car up to 55 and had Trooper "Flash" me with the spot when I hit it).
And GPS.

Some speedos are not only off, but some are off at low or high speeds and dead on at other speeds.. GPS is the only real way to be sure.

[NealC]

I think the root issue here is an incorrect setting for tire size. These days speedometers are very accurate. Second issue is SP customer service should not have shrugged off the issue but advised how to correct it. I suggest as others stated to take it in to have it checked and verify the tire size setting. Maybe call Cummins or try Spartan again.

[Stuart W]

5MPH @ 100 MPH would be acceptable, 5 @ 60 MPH (8%)seems a little excessive.
6% has been the unwritten limit in the automotive world for many years, and it most always shows higher not slower ([emoji848]indicating more miles driven then actual.......warranty?). This would equate to 3 MPH @ 50 MPH.
One of the major variables is Tire Circumference, new VS worn, New tire tread being close to 5/8 inch or more deep. As already said, heat, pressure vs load are also factors.
GPS speed readings are a calculation of distance driven then speed is calculated using distance and time to come up with speed. GPS measurements very based on Satellite triangulation. Have ever used two GPS units at the same time? Say the onboard and your phone, and one says right turn ahead in 100 feet and the other says at the same exact point right turn in 50 feet? Satellite triangulation can very.
Bottom line none of what we are seeing would be acceptable to NASA.

[rewillia]

Originally Posted by Stuart W

5MPH @ 100 MPH would be acceptable, 5 @ 60 MPH (8%)seems a little excessive.

Bottom line none of what we are seeing would be acceptable to NASA.

Well, I'm certainly no "Rocket Scientist" but I'd really appreciate knowing what my actual is at any given time. I do find that when driving, I adjust my speed using my speedometer then engage the cruise which seems to match my intended speed based on what the VORAD shows me to be set at. Next up will be to pay closer attention between the 3 devices being the Speedometer, VORAD and GPS.