Why the reverse speedo was used? Anybody know the history or reason?

MaSnaka · #1 (**permalink**) 10-04-2010, 05:47 PM

I was at a car show last weekend and was asked by a guy "why the reverse speedo" and I was dumbfounded for an answer. He just thought that was the coolest thing. Some reasons come to mind like are they that way in all right hand drive cars? Or just AC Cobras? A box of misc. gauges and that is just what was used? Anybody know for sure?

Thanks,
John

Got the Bug · #2 (**permalink**) 10-04-2010, 05:58 PM

Good question. It was touched on in a recent thread, but no specifics about why.

Trivial question: What other cars used reverse speedos?

When people ask, I just tell them that the speedo needle spends so much time over on the left side, it's easier to catch a glimpse of your speed out of the corner of your eye. You'll get some "OKs and head nods" with that one...even though it's BS.

1985 CCX · #3 (**permalink**) 10-04-2010, 06:37 PM

Everything British is backwards......

CHANMADD · #4 (**permalink**) 10-04-2010, 07:09 PM

I think that when you are at racing speeds ..100mph and faster the needle would be visible through the steering wheel,it just means that you have to drive faster.

noblec5 · #5 (**permalink**) 10-04-2010, 08:10 PM

If I remember correctly, the speedo was "reversed" in the AC Ace and other cars due to the right hand drive. When Caroll started using the smith gauges in the Cobra's it was actually extremley expensive or next to impossible to make the gears inside go the other way for left hand drive. So, it was never changed. or something like that.

Chris

Randall Thomas · #6 (**permalink**) 10-04-2010, 08:53 PM

The history of the legendary Smith reverse rotation speedometer installed in the original Cobras has spawned a range of explanations, some near mythical in nature. In an attempt to find out the real answer for an article for the Superformance Owners Association technical library back in 2004, for several months I sought out the real answer through many phone calls and email transactions to anyone that might have lived and worked at the Smiths factory back in the day, and finally received the final answer from the original Smith's employees in Europe.

ANSWERS: Phone interview with Neal Meakin and Ian John of Caerbont Automotive
Instruments Ltd, on 12/7/2004
QUESTIONS: By Randall Thomas
Caerbont Automotive Instruments Ltd
Abercraf, Swansea SA9 1SH
Tel +44 (01639) 732216 Fax +44 (01639) 732201

This is what they had to say...

"...We have pursued a number of ex (retired) SMITHS employees to gain benefit of their knowledge." and they go on to say... "When the car [Cobra] was being designed, the engineers realised that the cable drive from the gearbox to the speedometer was anticlockwise rotation, instead of the more usual clockwise. The normal procedure for an anticlock drive was to fit a reversing gearbox on the rear of the speedo to convert the rotation to drive a conventional clockwise speedo. Between the Cobra engineers and Smiths Industries, it was decided to offer an anticlock speedo as a feature, and obviously cost reduce the speedo installation by not having a cable drive gearbox. None of the Smiths guys from that time are around here these days, so this summary is an educated guess at what happened at the time. Our part number originally fitted to AC Cobra was SN5346-00, first made at the end of 1965. This speedo was updated by us in Nov 1995, we still manufacture it as part no. SN5346-02. Also recently we've developed a full range of Cobra Instruments with black print on white dials."

Randall

tkb289 · #7 (**permalink**) 10-04-2010, 11:56 PM

Randall,

Very interesting … and in an anti clockwise way, it makes sense...

Aside from the speedo face being backwards, were there other changes made to the speedo mechanism such as different springs & things to make it work?

Turning a small 'mistake' into a feature ... now that sounds vaguely familiar

soulman · #8 (**permalink**) 10-05-2010, 02:15 AM

Quote:

Originally Posted by MaSnaka

I was at a car show last weekend and was asked by a guy "why the reverse speedo" and I was dumbfounded for an answer. He just thought that was the coolest thing. Some reasons come to mind like are they that way in all right hand drive cars? Or just AC Cobras? A box of misc. gauges and that is just what was used? Anybody know for sure?

Thanks,
John

Dont believe everything you read.

The truth about the reverse speedo reading on Smiths gauges is as follows....

Graham Benjamin Smith the founder of Smiths instruments was an Australian,
when he first started manufacturing speedos in Australia back in the early 1900s he found there was a bigger market overseas.

By the time he sent all his tooling to the UK and spent his life savings on the move, he found out that the speedo showed in reverse.

Just like when you flush a toilet in the northern hemisphere the water swirls and drains in the opposite direction to the southern hemisphere !

The truth !

Soul.

Richard Hudgins · #9 (**permalink**) 10-05-2010, 01:46 PM

Folks,

The history of Smith and Sons Ltd. (England) can be found here.

http://www.smiths-clocks.co.uk/sm-orign.htm

This does not speak to the reverse action speedo's but it does give an accurate bit of information on the company.

My guess is that the story about not wanting to use the angle box in order to save money is the most likely one.

It is cheap to change a silk screen as compared to a gearbox fitment.

MaSnaka · #10 (**permalink**) 10-05-2010, 03:50 PM

So according to Randall Thomas' research the speedo was designed to accommodate an anticlock speedometer cable and according to Soulman it just happened to work that way so Smith stuck with it because it was cheaper than using a reversing gearbox behind each speedo gauge. Which just brings up more questions than ever.

Do all Smith speedos run counter clockwise?

Why did the Cobra transmissions have a different cable rotation than the mainstream cars?

Is this unique to Cobras or are there other cars with reverse speedos?

My Classic Roadster has a Stewart Warner counter clockwise speedo so it must be catching on. Seems like we all go to extra trouble to either have one or not have one.

John

marcocsx3121 · #11 (**permalink**) 10-05-2010, 04:15 PM

For what it's worth, the street 427s did not have reversed speedos, and they arrived with the same Ford top loader gearboxes that were installed in the SCs and comp. cars. I'm sure that this clears absolutely nothing up.

jay bentley · #12 (**permalink**) 10-06-2010, 07:53 AM

Quote:

Originally Posted by marcocsx3121

For what it's worth, the street 427s did not have reversed speedos, and they arrived with the same Ford top loader gearboxes that were installed in the SCs and comp. cars. I'm sure that this clears absolutely nothing up.

Many of the 427 street cars did indeed come with a reverse speedo. I know of several late 3300 street cars that surely did.

Jay

BT SNAKE · #13 (**permalink**) 10-06-2010, 09:10 AM

According to RT's research the Reverse speedo must not have been on the AC Aces. So this means
it was on Carroll Shelby's watch. I cannot believe he would not know why his COBRAS were using reverse speedos. He had to ask when he noticed it.
Come on Carroll jump in here and straighten this dilemma out.

Hersh

A-Snake · #14 (**permalink**) 10-06-2010, 09:53 AM

Quote:

Originally Posted by jay bentley

Many of the 427 street cars did indeed come with a reverse speedo. I know of several late 3300 street cars that surely did.

Jay

Jay,
Among others, you can add CSX3282 in the 3200 series as having a reverse speedo.

Jim Maxwell · #15 (**permalink**) 10-10-2010, 09:06 AM

CSX 3288 and CSX 3346 as well as many other street 427's that I have photographed have original reverse speedos. I will have to find a 427 with a regular speedo and look to see if it has the extra gear setup described earlier in this thread.

Jim

Cobra Pack · #16 (**permalink**) 10-10-2010, 11:53 AM

289 Cobras prior to CSX 2200 used Smiths 160 speedos as well. These were traditional clockwise speedos.

DanEC · #17 (**permalink**) 10-10-2010, 07:23 PM

Quote:

Originally Posted by MaSnaka

So according to Randall Thomas' research the speedo was designed to accommodate an anticlock speedometer cable and according to Soulman it just happened to work that way so Smith stuck with it because it was cheaper than using a reversing gearbox behind each speedo gauge. Which just brings up more questions than ever.

Do all Smith speedos run counter clockwise?

Why did the Cobra transmissions have a different cable rotation than the mainstream cars?

Is this unique to Cobras or are there other cars with reverse speedos?

My Classic Roadster has a Stewart Warner counter clockwise speedo so it must be catching on. Seems like we all go to extra trouble to either have one or not have one.

John

I'm with you. Didn't the first 289 cars have T-10s? I'm pretty sure the T-10 and the toploader have the same direction speedo cable drive. It sounds like they started out using a drive adaptor to correct the cable drive for the American tansmission to operate the speedo correctly in clockwise motion. For some reason (probably to save some money) they found it cheaper to retool the speedo for counter clockwise motion and drop the cable drive adaptor.

rms427 · #18 (**permalink**) 10-10-2010, 08:53 PM

My car, CSX3225, has a 180 mph reverse speedometer. I don't ever remember seeing a original 427 with regular direction speedometer.

mickmate · #19 (**permalink**) 10-05-2010, 07:06 PM

The street cars indeed had 160 mph clockwise speedometers. I thought the anticlockwise speedometers required the reverser/90 adapter to make them work adding to cost. The other thing about them was a reverse wound cable was required to stop the cable pumping the oil out of the gearbox up the speedo cable.
http://www.prc68.com/I/car_dash.html

joyridin' · #20 (**permalink**) 10-06-2010, 04:37 AM

I thought they used the reverse speedo so you wouldn't get it confused with the tach. During most races, the driver doesn't care how fast they are going, they are more concerned about hitting redline...especially in a big block. If you were running around 100-110, this would be in the running range of the engine as shown on the tach. A quick glance with your eyes and see the wrong gauge could make a huge difference. This won't happen with a reverse speedo.