"Optimistic speedometers"

Brian said:

midniteson said:

In reply to stanger_missle :

honda's definitley had high hopes lol. 

I think my accord had the same 120 speedo. My best was an indicated 108. A week later I had a police confirmed 98. 

Hmmm... Sounds like I should do a little more testing.

For science, of course 

Speedo in the Jeep is as un-optimistic as they come.  Within 1% compared to GPS for accuracy.  Speedo goes to 130.  Stock speed limiter was 115, but with it removed, they're known to top out right around 130 when stock.  So I think they got that one right. 

Every modern Toyota I've driven seems to read at least 5% fast, however.  I've seen some that are almost 10% off...

My Boxster, actually all 986's are optimistic in what they read, not necessarily what they read too.  It reads approx. 5mph fast throughout the range, not a % fast, but a solid 5mph fast as verified by GPS and WAZE.  I can say this happens up to at least 130 mph, allegedly on a private airstrip of course.

In reply to stanger_missle :

In a CRX with 90 horsepower, 120 MPH is the right speedometer maximum, because the true maximum speed is 113 MPH, which shows up as 117 MPH on the speedometer.

My 2005 Phaeton had a 200 mph speedo.  In europe they are limited to 155 but here stateside with our dawdling speed limits it's choked all the way down to 130.  I'd suspect that with a reflash and removal of said governor it might top out somewhere in the 170-180 range (according to Clarkson the W12 version actually did 202 mph so maybe the speedo was justified)

In the other direction, my '88 TurboCoupe laughed at it's 85 mph speedo.  When new they were clocked at 145 bone stock.

My courier Speedo went to 100.. with a 4 speed trans, 4.10s, and 75 horsepower 70mph was pretty scary

Seems no coincidence that the margin of error trends on the high side.  5-8% less warranty coverage really adds up.

IIRC, there was class action against Honda for this 10-15 years ago. 

this brings up a point. Comparing GPS speeds to Speedo speeds on the disco, my speedo reads about three to four mph FAST at 50mph, I wonder if I could correct with a slightly taller tyre

Tyler H said:

Seems no coincidence that the margin of error trends on the high side.  5-8% less warranty coverage really adds up.

IIRC, there was class action against Honda for this 10-15 years ago. 

One big reason for it is this: it's illegal to sell a new vehicle with a speedo that reads low, but not if it reads a little high.  So they err on the high side so that it'll never read low, even if all the tolerances line up to make it read lower (slightly tall tires, etc.).  

Brian said:

midniteson said:

In reply to stanger_missle :

honda's definitley had high hopes lol. 

I think my accord had the same 120 speedo. My best was an indicated 108. A week later I had a police confirmed 98. 

That reminds me of one of my favorites quotes from my brother. We both met at a place for lunch one day and I had seen a cleverly hidden officer shooting radar on the way. When we got there I asked if he saw the officer and he replied “Saw him, hell, I talked to him!” 

I'll tell you one that is surprisingly not optimistic. 1985 Toyota Camry.

I had one up to an indicated 125mph on a long straight stretch of private road. As a vehicle would pass me, on said private road, I would match speeds with them. Until at 125 mph the car was very floaty and scary and I was passed. I had to say uncle and let up. The coolant was brown and smelled like burnt popcorn, but it used every inch of that speedometer.

NGTD said:

I thought you meant something else, but VW's are infamous for not being calibrated right.

My wife's former 2010 Golf Wagon was actually doing 102 km/h when it indicated 110 km/h. Nothing like 8% error.

My 2006 MCS does that too.  After buying the car I'd get on the hwy and set the CC at a bit over 70... and cars would pass me like I'm stopped.  Then I started noticing construction zone radar was often about 5 MPH less than the speedometer. 

Oddly enough, compared against the radar signs, the speedometers in my two Triumphs (and even my old Mini) are surprisingly accurate.

I'm looking at buying a E350 van with a 7.3L non-turbo diesel. Even if it has an 85 MPH speedometer, I'd say that is optimistic.

My uncle had a 1969 c60 grain truck with a 350. If it were properly tuned it would have probably ran out of breath at 60. Since it was never properly tuned it topped at around 40, which it was kind of terrifying at that speed with the brakes and steering being what they were.

wlkelley3 said:

Just this afternoon someone told me he had a European version in the states that had a 1.1L and 5-speed and got a ticket for 143 mph.

I would bet it was KPH and even that is optimistic. 

I just remembered another one. When I was growing up we had a 67 Newport 4 door in my driveway with a 120 mph speedo.

I bet it would be terrifying with the squishy bench and pogo stick suspension and old truck tires as snow tires out back, but the 383 with open headers would probably make your death sound really good.


Not Optimistic was the 100 mph one in my dads 79 Magnum XE, even with the garbo lean burn 318 in it.

My '69 F100 had a 390 (redline about 4000 rpm) a 3 speed trans, and a 4.10 rear gear. It also had a 140mph speedometer. Of course, I put the cluster in, it was out af a 65 or 66 Mustang. The truck would barely hit 80 wound out downhill with a tailwind.

OTOH, the '96 Too Fiddy I have now has peg just past the top listed 85mph. I have actually BOUNCED the needle off the pin (like it was climbing fast enough it rebounded, then stuck) just to see what it had. Once I confirmed I could top the gauge I backed off, but the diesel with 3.55s out back was almost done anyway.