[grentarc]

OK.. . a couple of questions...
My spedo reads about 10% faster than i am actually doing... atm running 185/65 R15's on it (very narrow to the previous 205/55's i bought it with.. the 185s came off my old almost dead 900.. a complete brand new set just before i bought the 9000). anyway.. i found that the spedo reading isnt because of the tyre size because both sets have had almost the same percentage out, and they are both recommended sizes. The speed alarm in my Co-driver computer though, is correctly monitoring the speed. Does the computer pick up the speed signal from the same sensor, and if so, why is my speedo out of synch with everything else by a percentage, ie the needle cant be shifted back a bit to compensate.

 

[grentarc]

oh yeah.. 2nd question was - is there an easy way to remove the glove compartment door of an '87 model 9000??? i need to get to the relays and it is a pain to undo the screws with the door on.. the is an easy way isnt there????

 

[NedLudd]

I actually thought that all car [and bike] speedos typically overestimated speed by about 10%. It's very common, certainly. I've always assumed it was a blend of manufacturers' boasting - indicated top speeds looking higher then they are - and safety - as I seem to remember that the legal fine for a speedo which _under_estimates speed is very high indeed.

I hope someone will tell us if that's a wrong assumption on Saabs, as I commonly assume that when I'm doing e.g. an indicated 80, it's nearer 70...

 

[grentarc]

My old 900 was correct with the 185/65 tyres to around 1 kph off the radar units. I also tested the 9000 against my parents Landrover Discovery (MY03) which said i was doing about 100 kph when the speedo read 110.. i also converted RPM to speed in 5th gear being 40 kph/1000 rpm with this tyre size and thats how i calculated the 10% error (as well as the speed alarm)

 

[NedLudd]

Very interesting, thanks Grentarc. I should obviously be more cautious...!

 

[gassy]

A few months back several of us were on a rolling road and did a speedo calibration check. ISTR that none of us were more than 1% (one percent) out. So believe your Saab speedo!

 

[Mark B]

On 205/60-15 tyres, my speedo was about 5% out, compared to a GPS speed reading. After changing to 205/55-16 tyres, it is now about 2.5% out, which agrees with the theoretical radius change.

 

[NedLudd]

Wow - very illuminating, thanks all. I really did blithely assume that an indicated 37ish was 30, an indicated 80 was nearer 70, etc. I'm glad to be corrected!

 

[DaveS]

I don't know about the newer models but on 1989 ones, the speedo accuracy is marked on the face of the speedo. Mine (a VDO unit) reads W = 1.026, "w" standing for "Wichtigkeit" ("accuracy"), if I remember my German correctly.

Presumably, this applies on the tyres supplied with the car only.

 

[Mark B]

Originally posted by DaveS:
[qb]I don't know about the newer models but on 1989 ones, the speedo accuracy is marked on the face of the speedo. Mine (a VDO unit) reads W = 1.026, "w" standing for "Wichtigkeit" ("accuracy"), if I remember my German correctly.

Presumably, this applies on the tyres supplied with the car only. [/qb][/b]

I think you will find that the number on the front of the speedo is the number of turns of the speedo cable per 1000m travelled. Obviously with the newer speedos it will be an electrical impulse equivalent to the number of turns, but you get the idea.