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Discussion Starter #1
Can any one of you confirm this for me?

Evora S with 19/20" Diamond Wheels. My Speedo is reading 5-7% faster than the GPS speed. Wondering if TADTS or whether it's something I should bring up to the dealer.

Thx.
 

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Don't rely on the GPS readings, they aren't too accurate..

If your car's speedo is slightly fast, you are incurring more miles on your car than actual, so technically your running your warrantied mileage down faster. I'd calculate an exact distance and drive it to confirm if the mileage incurred on the odo matches.
 

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The GPS is more accurate than the speedo. Most speedos overestimate your speed by a safety factor so that even if your tires' diameter is larger than OEM, you will not read a slower speed than actual. Well documented in the Elise/Exige.

I've done extensive studies of GPS vs. actual vehicle speed and most GPS devices are quite accurate when you have good visibility of the sky.
 

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Speed accuracy of my speedometer, plus 7 percent, linear. Accuracy of my GPS, better than 1 percent at highway speed, determined by stopwatch time between mile markers.
 

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My speedo is only showing about 1 mph faster than the GPS at about 80 MPH. That's just fine for my needs.

When you guys say 5% error, does that mean that your speedo is reading 84 MPH, rather than 80? That is a lot. That would be right up there with most Elises and Exiges.
 

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By law the speedo must not show a too low value, so all car manufacturers adjust it to be a few percent higher. 5% is well within the range set by most manufacturers and certainly not an issue, the exact value will, asyou asumed, depend on wheelsize, tires, inflation, etc.

The GPS speed is certainly more accurate, however there is a software damper in it, so you will only get valid readings at steady speed (don't believe me, just accelerate from 0 to see how slow the GPS will be).

Oh, and my Evora S with 18/19"-wheels is actually very close, much more so than any of my former cars.
 

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Discussion Starter #7
If my Alpine GPS unit reads 100km/h, my dash will read around 105km/h to 107km/h. And I've used my iPhone's navigation software (Waze) to confirm the Alpine GPS speed, so the speedo is over by a significant margin.

I've mentioned the rim size as I'm wondering if the tire/rim combo can make that big of a difference?

Was there ever a resolution to the Eliges or was it :tadts:?

It's quite annoying as when I was driving my friend's Pilot yesterday, I found myself constantly in the speeding-ticket territory now that I'm used to the Evora speedo.
 

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Taking the car to the shop last week I noticed going thru construction zones that my speed was a constant 6 mph slow on the (your speed is ...) radar sign than what was reading on the dash. I mentioned it to the service manager and that the clock would not hold the correct time. I was told that there is a known problem with some dash clusters and it would need to be replaced.
 

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Yor in best shape. The same measurement with a Porsche or Audi will likely show 110 km/h! If you stick to the speedo figure you'll be on the safe side of ticket territory. Or, aas we say over here, just add 10%.
That's why people keep telling you their cars are so much faster than the manufacturer stated.
 

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Was there ever a resolution to the Eliges or was it :tadts:?
If by resolution, you mean verification of the speedo's error, then yes.

The ECU also calculates an OBD-II parameter called VSS (Vehicle Speed Sensor) that is supposed to be an accurate and unadjusted measurement of wheel speed based on the sensors in the wheel hubs. I've read that parameter and compared it to GPS speed over dozens of track sessions, and they are within 1% of each other.

So the ECU knows the car's speed accurately (assuming OEM tires sizes and inflation). It then intentionally adjusts it upward for display on the speedo.

As far as non-OEM (or optional) wheel and tire packages go, the important measurement is the rolling diameter of the rear tire (some manufacturers spec the "rotations per mile" instead). If the diameter is larger than OEM, the speedo (and the ECU) will show lower values for speed than they would with the OEM tires.
 

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18/19 combo on my 2010 NA model was only off ~1mph with new tires. But if I am correct the OD on the 19/20 tires is a bit smaller. (.2-.3?) That could account for the speedo being 2+mph off and worn tires can add another mph so that would be ~3mph off.

No resolution ever occured with the Eliges. I just know speedo at 80 =actual 74mph. Makes it easy for highway driving.
 

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If by resolution, you mean verification of the speedo's error, then yes.

The ECU also calculates an OBD-II parameter called VSS (Vehicle Speed Sensor) that is supposed to be an accurate and unadjusted measurement of wheel speed based on the sensors in the wheel hubs. I've read that parameter and compared it to GPS speed over dozens of track sessions, and they are within 1% of each other.

So the ECU knows the car's speed accurately (assuming OEM tires sizes and inflation). It then intentionally adjusts it upward for display on the speedo.

As far as non-OEM (or optional) wheel and tire packages go, the important measurement is the rolling diameter of the rear tire (some manufacturers spec the "rotations per mile" instead). If the diameter is larger than OEM, the speedo (and the ECU) will show lower values for speed than they would with the OEM tires.
Is there a way to reprogram the ECU to take out or adjust the correction factor? :shrug:
 

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We tried that for years with Elige. No luck not even Charlie X did that one.
 

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I was told that there is a known problem with some dash clusters and it would need to be replaced.
Been there, done that...twice.
 

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You can buy this device that has been in the market for years and has a lot of good feedback. For our cars, select model: U1
https://www.motomummy.com/store/product.php?productid=18212&cat=255&page=1

On the Elise (may not be the same location on the Evora), the center console seems to be a good location to splice into the post-ABS speed signal (rear-left wheel signal). LotusSport.org • View topic - Datalogger systems

I plan on doing this, later this fall. If you decide on this or alternative, keep us posted.
 

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Taking the car to the shop last week I noticed going thru construction zones that my speed was a constant 6 mph slow on the (your speed is ...) radar sign than what was reading on the dash. I mentioned it to the service manager and that the clock would not hold the correct time. I was told that there is a known problem with some dash clusters and it would need to be replaced.
I had mine replaced as well. It would not hold the correct time. It is now fine.
Ron
 

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My dash cluster is starting to act up. Went blank ~2ks ago for 5 minutes, restart didn't help. Was driving home from work and it just came back to life. Second time it stayed off for ~15 seconds. But since that time can't reset clock and yes, I do know how. Sorry for the side.
Along the SC issue though, my dealer has both NA and SC cars available to drive, and both the sales reps and test drivers more often are liking the linear power band of the NA cars much to my surprise hearing this. The overall impression has been that the SC's additional cost isn't worth it. That's a new car perspective. For you , RAMTIN, adding power is what you want because you are used to the vehicle. Just try to keep the power band as linear as possible.
 

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The Evora's RPM gauge is also not very accurate; it shows less than actual RPM. Limiter in sport mode is at around 6900RPM; ECU readout however shows me 7200-7300RPM.
A plan of mine is to remove the instrument unit and create new scales, perhaps in a new design with brushed aluminium or something else have to think about it, and more accurate. IMO the OEM unit looks a bit cheap.
 

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Lotus speedometer? I do not think that the two have ever met. My Elise has something that looks like a speedometer, and it is accurate +/- 20 mph. It's about as accurate as the weather guessers.
 

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Lotus speedometer? I do not think that the two have ever met. My Elise has something that looks like a speedometer, and it is accurate +/- 20 mph. It's about as accurate as the weather guessers.
That's not actually true IMHO It is off by a constant percentage ~7.5%+/= .5%
 
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