Why isn't it SOP to run the speedometer off a non-driven wheel like on a VW Beetle? Isn't it better to know how fast you're going than how fast your wheels are spinning?

Sixto
95 S420
87 300SDL

My guess, and remember, it is only a guess.

Many front engine/rear drive cars drive the speedo from the transmission, since it is a short distance from there to the instrument cluster, and the trans was a handy source to measure driveshaft/wheel speed.

In the VW Beetle, the transaxle was in the rear, and a front wheel readily was closer.

As I said, that's my guess...

It also enhanced the sales of front wheel bearings due to water ingress .


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And a good guess it is!

It was a LOT of fun trying to figure out gearing required to fabricate a custom speedo cable to work with an AutoMeter speedo unit to replace the OEM speedo in my Beetle.

Fortunately, AutoMeter provided specs on speed versus tranny pinion gear revolutions, so I knew what the speedo would be seeing. Then I had to factor in front wheel revs coupled with the aftermarket wheel/tire diameters to determine what step up/step down gearing I needed to make it work. Got a speedo shop in Cali make it for me.

Then there was the issue with calculating high/low resistance conversion to get the AutoMeter fuel gauge to work with the VW tank float....but that's another story...

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I'll guess also, but, isn't there some value in having the speedo tell you (or at least confirm) when your wheels are spinning?

I had two bugs and wheel spin was never an issue.

Back in the sixties, my wife and I were into sportscar rallies. It became apparent after a while that the cars that were doing the best were Porsches and they measured off the left front wheel. (Coincidently, many rallies used Porsches to make the official mileage measurements.) We swapped our British sports cars for a Porsche and went on to win quite a few rallies over the next ten years or so. I guess it wasn't that critical. If you used a rear-wheel measuring car and didn't push it too hard, your accuracy would be close. Maybe not enough to win, but in the ballpark.

After leaving the rally scene (and when Porsches priced themselves out of our budget), we went back to older British sportscars and, of course, M-Bs.

I did change a few wheel bearings through the years, but I don't recall that any were caused by water ingress. The cable housing, at least on the Porsches, was pretty water-tight where it entered the spindle on the inside.

Wes