Changing my speedometer from mph to km... what's wrong?

[3.0CS]

As for me, I live in Mexico and that is why I prefer to have kilomters.

Now... back to measurements... I got two interesting comments but I am not sure I understand well:

Chris: "195/70-14 and 215/60-14 have the same diameter, no need to worry"

Stan: "actually 225/60/14 = stock diameter"

So, sorry for asking but: Do I have in my car now, with 215/60/14, a very close to original diameter, withing 1 or 2% as Stevehose mentions?

If so, I will go ahead remove the speedometer and send it to North Hollywood to calibrate!

Thanks!

 

[Stevehose]

Go here:

https://tiresize.com/calculator/

Choose the "tire comparison" tab

Put in 195/70/14 on one and yours in another and it will show you the differences

As for me, I live in Mexico and that is why I prefer to have kilomters.

Now... back to measurements... I got two interesting comments but I am not sure I understand well:

Chris: "195/70-14 and 215/60-14 have the same diameter, no need to worry"

Stan: "actually 225/60/14 = stock diameter"

So, sorry for asking but: Do I have in my car now, with 215/60/14, a very close to original diameter, withing 1 or 2% as Stevehose mentions?

If so, I will go ahead remove the speedometer and send it to North Hollywood to calibrate!

Thanks!

 

[Bmachine]

As for me, I live in Mexico and that is why I prefer to have kilomters.

OK, that makes sense then. We drove to Mexico a month ago and it was so great being able to switch the digital speedo from MPH to KPH and back!

 

[mulberryworks]

http://www.carbibles.com/tyre_size_calculators.html

You can use the tyre calculator here to determine the actual dimensions of your proposed tire swaps.

In this case the difference is less than half a percent.

Ian

 

[HB Chris]

The Rule of Thumb back in the day was, as width goes up by 20 then drop profile by 10. 175/80-14 = 195/70-14 = 215/60-14. That's my story and I'm sticking to it.

And that 0.48% above results in a slightly smaller diameter.

 

[Honolulu]

As it happens I have a kph speedo that I'm not using. Anyone interested? I'll have to check the number on the back and see what it says. Reply off list to [email protected], thanks.

 

[3.0CS]

Thanks for the links to the tire size calculators... interesting, as is Chris' rule of thumb. Easy enough to understand and learn... though with my early alzheimmers (just a bad joke, I hope, though it would certainly seem that at 50, I have it!) I may forget all about it in a couple of days!

Anyhow, I already removed the dashboard and speedometer, did the tape flag on my cable and it turns 12.4 times in the given distance.... I will be visiting San Diego for a few days and will use the ocassion to mail the speedometer to North Hollywood.

Thanks for all the help
victor

 

[shanon]

Been running KPH speedo in CA for a few years now on 14x7s. Converted to restore original Euro delivery.

With decreasing and shinking 14" tire size options, I've had three consistantly smaller sets: 225s, 205s now 195s. To keep things simple, ive have been just dividing the MPH in half and observing the 'basic speed law'- keep up with traffic.

If the road opens up and i want to get on it, i turn on the free speedo phone app and away we go. The apps have some neat road trip features too. All in all, I haven't noticed much discrepancy between the app and speedo. Tested KHP reading against app and decided the VDO guage was pretty accurate.

It is kinda fun to look down at the speedo and it says your doing 140 and you're not going to go to jail. It was real exciting when I looked down briefly when it was reading 220. ;-)

 

[Gary Knox]

Also, there can be a slight variation in tire sizes (diameters) between manufacturers. Again, probably in the range of 1-2%, but it is there! Similarly, as the tread wears down, the rolling diameter changes as well. Probably ONLY a GPS can be dead on.

 

[Vern]

Steve, you should really get with the times. A bunch of us are converting back to drums too.

Hahaha! Nothing says, "adventure," like losing your drum brakes going down the Sepulveda Pass...

 

[Markos]

Hahaha! Nothing says, "adventure," like losing your drum brakes going down the Sepulveda Pass...

The performance benefits aside, there is nothing I love more than changing the shoes on drum brakes!

 

[hdavis]

And there is a n umber on the back of your speedo with W=x.xx which tells which speedo you have.

So do you know to which ratio those number are matched to:

A speedo that that W 0,68 would work for what diff?

And how can I find out what diff my car has?

Thanks

 

[HB Chris]

I am going to make an educated guess from looking at the parts books:

W=0.679 kmh on CSi and CSL is for the 3.25 differential
W=0.7125 kmh euro CS and CSA is the 3.45
W=1.078 mph euro CS and CSA is the 3.25
W=1.14 mph US/NA CS and CSA is the 3.45
W=1.2164 mph US/NA CS and CSA is the 3.64

The differential ratio is stamped on passenger side of the diff on the large flat spot behind/under the CV joint: 39/12=3.25, 38/11=3.45, 40/11=3.64
A large stamped S above the ratio indicates Limited Slip diff

 

[hdavis]

Thanks, vey useful!

 

[WISE9UY]

I am going to make an educated guess from looking at the parts books:

W=0.679 kmh on CSi and CSL is for the 3.25 differential
W=0.7125 kmh euro CS and CSA is the 3.45
W=1.078 mph euro CS and CSA is the 3.25
W=1.14 mph US/NA CS and CSA is the 3.45
W=1.2164 mph US/NA CS and CSA is the 3.64

The differential ratio is stamped on passenger side of the diff on the large flat spot behind/under the CV joint: 39/12=3.25, 38/11=3.45, 40/11=3.64
A large stamped S above the ratio indicates Limited Slip diff

Great thread as I will be changing speedo as well as differential so at least can keep this in consideration. I have a line on one and they have stated the back to read W969 70-124. This does not fit any you describe. Any thoughts?

 

[hdavis]

This is what the numbers in the back look like

 

[Gary Knox]

W 0.679 rounds to W 0.68. That appears to be the number on the back of your speedometer. Thus, according to Chris's figures, you have the speedo for a 3.25 differential.

 

[hdavis]

W 0.679 rounds to W 0.68. That appears to be the number on the back of your speedometer. Thus, according to Chris's figures, you have the speedo for a 3.25 differential.

That appears to be the case. I will look at my diff later today to confirm what I have, however I don't believe I have a 3.25 since my car is a 1972 CS, and according to the info provided by Chris above a 3.25 was not an option on a CS...

 

[hdavis]

Here is a picture of the passengers side of the flat area of the

diff in my car, but I see no numbers

Where are they supposed to be?

Thanks

 

[HB Chris]

Farther aft. Also, is your coupe a North American VIN?