 What would cause a speedo to read high?, Reads 90 when I'm really going 65 |
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| matthepcat |
  Apr 21 2016, 09:05 AM
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#1
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Meat Popsicle  Group: Members Posts: 1,462 Joined: 13-December 09 From: Saratoga CA Member No.: 11,125 Region Association: Northern California  |
Like the title of this thread states, what would cause my speedometer to read a higher speed than I am traveling?
Is this a mechanical issue with the factory gauge? (IMG:style_emoticons/default/idea.gif) |
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| Jeffs9146 |
Apr 21 2016, 09:08 AM
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#2
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Ski Bum Group: Members Posts: 4,062 Joined: 10-January 03 From: Discovery Bay, Ca Member No.: 128 |
Smaller diameter than stock tires.
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| tomrev |
Apr 21 2016, 09:34 AM
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#3
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Member Group: Members Posts: 231 Joined: 25-February 14 From: N. Mich. Member No.: 17,037 Region Association: None |
QUOTE(Jeffs9146 @ Apr 21 2016, 07:08 AM)  Smaller diameter than stock tires. REALLY smaller diameter! |
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| era vulgaris |
Apr 21 2016, 10:55 AM
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#4
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J is for Genius Group: Members Posts: 982 Joined: 10-November 13 From: Raleigh, NC Member No.: 16,629 Region Association: South East States |
Wow, that is off by quite a bit. Mine reads about 8-10mph faster than I'm actually going. I'm running 205/55/15's.
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| matthepcat |
Apr 21 2016, 12:16 PM
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#5
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Meat Popsicle Group: Members Posts: 1,462 Joined: 13-December 09 From: Saratoga CA Member No.: 11,125 Region Association: Northern California |
QUOTE(Jeffs9146 @ Apr 21 2016, 08:08 AM) Smaller diameter than stock tires. Duh! For some reason my mind was thinking that the speed was collected at the transmission and is somehow decoupled from the wheel/tire diameter. (IMG:style_emoticons/default/whack_3.gif) (IMG:style_emoticons/default/hitfan[1].gif) Dumb question of the week complete. Yes my new to me car is slammed and running low profile tires. Works well for the rotary motor. (IMG:http://www.914world.com/bbs2/uploads_offsite/s31.postimg.org-11125-1461262698.1.jpg) ^^ First project is to remove the BUBs ^^ |
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| AZ914 |
Apr 21 2016, 01:37 PM
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#6
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914 Dumbass Group: Members Posts: 1,459 Joined: 6-January 03 From: Sunny Tucson Member No.: 98 Region Association: Southwest Region |
That is quite a bit of difference. You can go to Discounttire . com and use their tire size calculator to see what the speed variance would be between stock tires and your tire size.
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| toolguy |
Apr 21 2016, 02:01 PM
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#7
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Senior Member Group: Members Posts: 1,268 Joined: 2-April 11 From: San Diego / El Cajon Member No.: 12,889 Region Association: Southern California 
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That is a 50% error, You'd have to have something like go cart tires to read that far off.
Probably the speedometer magnetic assembly has oil / grease in it. . May be able to take apart and clean but I'd bet someone has a real good deal on a used one. . |
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| porschetub |
Apr 21 2016, 02:09 PM
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#8
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Advanced Member Group: Members Posts: 4,701 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
Only real solution is to have the speedo regeared then you are stuck that profile tyre.
The rims look like 16'' ? I'am guessing the profile is 45 series or thereabouts, from memory my 205/55/16's calculate out at somewhere close to 1% error. |
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| 914Sixer |
Apr 21 2016, 04:06 PM
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#9
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914 Guru Group: Members Posts: 8,886 Joined: 17-January 05 From: San Angelo Texas Member No.: 3,457 Region Association: Southwest Region
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Weight probably came off in the speedometer.
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| matthepcat |
Apr 21 2016, 04:55 PM
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#10
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Meat Popsicle Group: Members Posts: 1,462 Joined: 13-December 09 From: Saratoga CA Member No.: 11,125 Region Association: Northern California |
They are 15" rims. I believe 195/50/15...maybe 195/55/15. Because the previous owner lowered the car as low as it would go, he had to run a small tire.
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| struckn |
Apr 21 2016, 08:25 PM
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#11
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Senior Member Group: Members Posts: 1,069 Joined: 9-November 11 From: South Central York Pennsyvania Member No.: 13,764 Region Association: MidAtlantic Region |
Mine reads about 10MPH faster then actual speed. I decided to not mess with the Speed O Meter and just added a GPS that gives digitally actual speed. There's also an APP you can get for your smart Phone that will work as a GPS Speed-O-Meter..
The need thing about the incorrect SpeedoMeter reading is if you take some one for a ride tell them to watch the speedometer when you're fast into a tight turn or rolling down the Interstate. |
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| 914itis |
Apr 21 2016, 08:54 PM
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#12
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Advanced Member Group: Members Posts: 2,892 Joined: 9-October 10 From: New York City Member No.: 12,256 Region Association: North East States |
QUOTE(era vulgaris @ Apr 21 2016, 12:55 PM) Wow, that is off by quite a bit. Mine reads about 8-10mph faster than I'm actually going. I'm running 205/55/15's. Same tire size , reads 10 mph higher . |
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| PancakePorsche |
Apr 21 2016, 09:45 PM
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#13
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Member Group: Members Posts: 236 Joined: 29-July 11 From: Southern California Member No.: 13,373 Region Association: None |
Have Palo Alto or North Hollywood speedometer calibrate it for your car.
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