How to Disonnect Speedo for Track

[Caterham Track Days]

Hi All,

I use my car on road and track.  Is there an easy way to disconnect the speedo / milometer when on track and reengage it when back on the road?

[Jonathan Kay]

Yes.

What type is it? Mechanical or electronic? And if electronic driven from the gearbox, wheel or driveshaft?

Jonathan

[jody391]

Why would you do this?

Isn't it cheating when you come to sell the car!

[CAT170]

Unless the car is having regular 24hr races I can't see that disconnecting the speedo makes much difference to mileage and value. I am intrigued as to why it should be disconnected - too distracting?

[Caterham Track Days]

Hi Jonathan, I have this speedo - 

https://caterhamparts.co.uk/gauges/6067-speedo-mph-s-pack-instrumentation.html?search_query=speedo&results=36

Thanks.

[Golf Juliet Tango]

What is the legal position regarding the actual mileage if you sell the car?  Wouldn't it be defined as "clocking"?

[Jonathan Kay]

That's an electronic speedometer. You can disconnect it at the instrument or at the sender.

Before disconnecting at the instrument I'd check the wiring diagram to see what else is connected there. Let me know if you'd like a copy.

Jonathan

[Caterham Track Days]

Hi Jonathan, thank you. A wiring diagram would be useful.  Kind regards, Ben.

[Jonathan Kay]

Private Message sent.

Jonathan

[ScottR400D]

Seems a pointless exercise and I suspect the OP knows that but for some reason is ignoring it. 

[aerobod - near CYYC]

I like to know the mileage (kilometres) I do on track to keep track of engine usage, change in oil and fuel consumption and distance to wear out tyres and brakes, that may indicate an impending problem and just the number of laps I did on a given day.

[opplock]

A pointless exercise or a wheeze for staying within mileage limitation on an insurance policy? 

[SLR No.77]

Can I ask why? Each trackday only totals around 150 miles.

[Andy135]

I seem to remember that on the Academy cars they disconnect the speed sender at the rear wheel. This is because if the sender or cable gets hit or damaged on track it can cause a fuse to blow (not sure which one) that cuts power to the ECU, meaning loss of power on track and a recovery back to the pits.

Thus, speedo disconnection is considered a preventative way to avoid early retirement from racing. The same would also be true when on a track day.

[Guy Lowe]

As above, why would you?

My average track day mileage (sessions) is less that 150 miles per day so pretty pointless and unethical in my opinion.

[Wrightpayne]

I wonder where you stand with insurance if you have a limited mileage policy and trackday cover?

[Spuddy Supersport]

The speedo is on the same fuse as the fuel pump and instruments, if if trips the car stops, I had this trip on mine whilst out for a drive.

[ScottR400D]

#14. Not heard that before and seems extremely unlikely. In fact I can't imagine how that sort of damage could be done on track without the car being in a state which would need recovery in any case.

 

[Jonathan Kay]

There have been several reports of problems with the speedometer wiring stopping the engine. I've never been totally convinced that it was only blowing fuses.

There is a Factory Notice about modification to the wiring.

Jonathan

[Andy135]

#18, picking up incident debris on track and spinning off track into the litter are a couple of situations that I could think of that could catch the speedo sensor wiring without also meaning structural damage to the rest of the car.

[ScottR400D]

#20. You'd still need recovery back to the pits if in the gravel to that extent. 

As for the debris damaging the speedo cable/sensor, "what are the chances of that?" as Harry Hill might say. 

After 9 years with regular TDs, it's never crossed my mind  

Anyway, maybe the OP will enlighten us? 
 

[David JLM]

Yes, that was the reason given when I was in the Academy.

I think we all disconnected our speedos, so I don't know whether it would have been a problem or not!  However, bouncing over curbs and picking up gravel etc. *could* have fouled the cabling/sensor and at best stopped one's race, and at worst, caused an accident through losing drive in close quarters racing.  

[aerobod - near CYYC]

The speed sensor as opposed to the speedo itself would have to be disconnected to alleviate shorts from damage to the sensor wiring. The sensor has it's own power feed that doesn't come from the speedo, but is combined into the general power feed to the instruments before connecting to the fuse.

Also, I think the problem with blowing the instrument fuse and the car then stops running is likely due to the immobiliser losing power, as the ECU power is supplied on a different fuse. This is perhaps backed up by the fact there is a "mystery" wire in the instrument power pigtail that doesn't have a device on the other end, likely the undocumented immobiliser power feed.

[K7 VCT]

I had my speedo sensor blow a fuse.

The car runs perfectly fine. 

However the instruments are dead and the indicators except  hazard lights are dead as they go via tell tale in the rev counter.

Nothing to do with fuel pump,  I drove over 100 miles back from.the Taffia run .

[Roger Ford]

I was told it was the fuel pump that shares a fuse with the speedo sensor (makes sense as they're in similar locations). So a short in the speedo sensor wiring - which is quite exposed - leads to loss of fuel pump and thus the race.

The connector is under the wing near the sensor. It's fairly obvious.

This is on a Sigma Ti-VCT car. Others no doubt vary.