924Board.org

stumo72 · Joined: 22 Oct 2024 Posts: 4 Location: Angus, Scotland.

Hi All

My 924 speedometer reads exactly 10% slow

20 Speedo - GPS says 22
50 - 55
70 - 77 and so on.

The speedo runs perfectly, no wobble or noise. Tyres are original size fitment for the car.

Does anyone have any thoughts on where I should be looking?

Could someone have changed something in the past? (I am aware of different gears for the odometer, but not sure how the speedometer can be changed for speed?)

Could the gauge just be faulty?

Thanks!

morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

What tire size are you running?
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stumo72 · Joined: 22 Oct 2024 Posts: 4 Location: Angus, Scotland.

185 x 70 x 14 on the stock rims. I believe that is stock tyre size.

Kenodog · Joined: 25 Jun 2003 Posts: 2669 Location: Vancouver,B.C.

Just drive 10% faster...
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1979 Euro 931, Olive
1981 931, Sabine
1991 Ford Ranger XLT 4x4, Ricky
1996 Ford E-350 ex-FedEx Van
2014 Mazda CX-5 (Kinderwagon)
2019 KTM 790 Adventure
2024 KLX300
2024 KLX140

stumo72 · Joined: 22 Oct 2024 Posts: 4 Location: Angus, Scotland.

morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

The 10% rule is more or less the same for most cars.
Speedo will always show a bit more than it actually is.
_________________
Supercharger and EFI kits
https://www.the924.com

stumo72 · Joined: 22 Oct 2024 Posts: 4 Location: Angus, Scotland.

This is less by exactly 10%.

scm924s · Joined: 22 Oct 2010 Posts: 296 Location: Gloucester UK

Check that the LH front hub grease cap is tight on the hub, the speedo cable is driven by this and can affect the speedo reading if it slips
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1984 n/a Ruby Red Metallic
1988 924S Guards red- sold
1986 924S Guards Red - sold
1984 n/a Black - sold
1980 n/a Le Mans#1 - sold
1980 n/a Le Mans#2- sold
1977 Martini - sold

Beartooth · Joined: 05 Apr 2022 Posts: 314 Location: Roberts, MT

I monkeyed with the needle on mine when I had it apart to fix the odometer gear slipping on the shaft, aiming to have it read accurately at 60. I got it pretty close at highway speed, but it's off at significantly slower or faster speeds. This is with 195/65/15 tires. 185/70/14 seems to have been originally spec'd, according to the 924.org tech section. But there are a few other sizes. How does the odometer read? If it's high too, dropping to 185/65 or maybe even 195/60 tires might be worth a try (and have the same effect as gearing down - not sure if you'd want that or not). Ultimately though, I doubt you have a mechanical problem: mechanical speedometers have more error (and can get worse over time), and they're skewed to read high by design because driving slower than you think you are is the safer choice for a manufacturer.
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1980 931 diamond in the rough