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Speedometer adjustment to meet wheel size


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When I have bought my car, it had 185 (80) 15 tyres installed. They look "impressive" on a TR2  but I decided to go back  to the original size .

Actually almost original, as I have decided to go for 185 -70- 15 Dunlops. Still all right for me, as 185-17 do have the same diameter and rolling circumference as the original 165x80.

So, wider but original rolling circumference  (185x0,7 = 130 <-> 165x80=132).

Now I realized, that the speedo is not inidicating correctly. I therfore conclude, that someone has adjusted it to be in line with the 185 (x80 = 148) Diameter fitted earlier

So now finally my question: How can the speedo be adusted to the tire size ? Are there different speddo drive configurations availabe ?

Input welcome

Cheers

Oliver

 

 

 

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You maybe already done this, but before worrying about speedo not reading correct, why not check the reading of your speedometer with an GPS speedo?

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Can you read the "Turns per mile" number printed in small characters under the odomebter readout ? that will tell you if it is an original "standard" speedo.

It would normally read close to 1180 (in miles)  or 740 ( in Km) assuming your axle ratio is 3.7:1

Bob.

 

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Hi All

On my TR3 the speedo recording is close to GPS reading but the distance recorder is not reading right (reads low). standard speedo 1180.

I think my diff is 4.1. Tyres 165s. 

Would the diff make a difference to the distance recorder or would it be something else.

(sorry to hijack this thread)

Brian

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4 hours ago, brian-nz said:

Hi All

On my TR3 the speedo recording is close to GPS reading but the distance recorder is not reading right (reads low). standard speedo 1180.

I think my diff is 4.1. Tyres 165s. 

Would the diff make a difference to the distance recorder or would it be something else.

(sorry to hijack this thread)

Brian

Yes it certainly would make a difference. the fact that your speedo reads close to GPS is either good fortune, or someone has tweaked it.

Bob.

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On another thread running at the moment 

a company jdo offer 2 prices to recalibrate a Speedo one for just speed correction and another to do the odometer as well. 
 

suggesting your Speedo May have just had speed correction carried out. 
 

H

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11 hours ago, Lebro said:

Can you read the "Turns per mile" number printed in small characters under the odomebter readout

 

I wonder if the TPM number on the speedo face is altered if it has been sent away for recalibration at any time in the past.

It would take a very skilled hand and fine paintbrush to produce anything like an acceptable result.

There must be people reading this who have had a recalibration done.

Did they alter the number?

 

Charlie.

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