Lotus Elan and Lotus Elan Plus 2 Forums

The comments above are interesting and helpful, including the historical notes.

I’d done it before, but I decided to go through Colin Chapman’s explanation in Lotus Engineering again. The cap or tape move as predicted. What I don’t understand is why cap (in the case of the RW example) is moved not rotated. The cap represents the wheel, which rotates. Is that because the point of contact with the spinner remains at the same place (I.e, at t12:00) even if the actual surfaces change? My brain hurts. I will appreciate an explanation please.

Many thanks, Andy

Andy,

Its tough to visualise, and although the Chapman tape and lid example clearly demonstrates that there is something going on, and that a male and female taper behave differently, its not immediately obvious (at least to me) which way around it all is. The other name for 'mechanical precession' (according to Wikipedia) is 'epicyclic fretting precession' which I find much easier to visualise.

Pretend the tape is the wheel and the paint lid the spinner, so looking at the wheel as a clock, the weight of the car will be supported by the spinner resting on the wheel at the 6 o'clock position.

Assume your roll of tape and paint lid work just like an epicyclic gear. Mentally roll the 'car' forward - on the right hand side wheels, forward is clockwise, so turn the tape clockwise keeping the paint lid contact point at 6 o'clock.

As you turn the tape, the lid will also turn, but at a slightly faster speed than the tape - just like an epicyclic gear. From the perspective of the tape, the lid is moving faster and therefore clockwise relative to it, so if this was the wheel / spinner combination the spinner would move clockwise relative to the wheel - and on a right hand thread would tighten itself up.

Applying the same argument, but reversing the direction of the tape (the left hand side of the car) means the lid moves faster anticlockwise than the tape, so the spinner would move anticlockwise relative to the wheel and needs a left hand thread to tighten itself up.

If the spinner were the tape and the lid the wheel, the the above argument works in reverse (as is the case with a Rudge-Whitworth spinner.

Hope this is of some help.

Andy.

Andy, many, many thanks for taking the time to write that. I’ll sit down and do what you suggest.

Best regards, and keep safe.

Andy

This is an article in a Bugatti replica build site with good illustrations that helped me understand the phenomenon a little better and Andy’s good explanation above (I hope, correctly).

http://trumpetb.net/57SC/knockoff.html

I think the conclusions are wrong though in that : (1) In a RW wheel, the weight of the car is carried at 12:00, not at 6;00, as the writer states, and (2) in the Dayton wheel, which uses a male taper, the smaller circle is the spinner (which he calls “cap”), not the larger circle.

If I think simply of two circles, one within the other, both spinning in the same direction (let’s say clockwise, as in a RH wheel), precession seems to state the smaller circle will move faster relative to the larger circle. The result will be that the smaller circle (the spinner in our case) will have moved clockwise relative to its original position vis-a-vis the larger circle (the center part of the wheel against which the taper presses). See illustration So Chapman seems right here

Andy, I think this is consistent with your explanation.

That’s assuming I understood correctly.

Best,

Andy

Yep, that's how I understand it. The diagram is great, they say a picture is worth a thousand words. Its the two different size circles that cause the problem. In our case, the diagram represents a left hand wheel, the spinner is the smaller circle in the middle, the wheel the bigger outer circle. When the car goes forward, the wheel turns anticlockwise, the spinner turns slightly faster than the wheel, and needs a left hand thread to self tighten.

The Bugatti guy describes the effect, then falls at the final fence. He is assuming that the 'epicyclic fretting' occurs between the spinner and the thread, and then reaches the incorrect conclusion that male and female tapers should be tightened the same way.

While there probably is fretting between the spinner and thread, I believe it is the fretting between the wheel and the spinner that dominates. The spinner to thread diameter difference is small and constant, the wheel to spinner diameter difference gets bigger as the spinner loosens and the contact point moves along the taper.

I am still of the opinion that the 26R type written sheet earlier in the thread is wrong.

Just a question regarding which side of the car do the Right handed or Left handed threads go when installing the hubs. If I remember correctly the hubs are color coded like aircraft lights. That is Red on the left and Green on the right. So wouldn't that answer the question regarding which hub/handed thread goes on which side?

Regardless of colour-read this thread and you will know which way to fit them.
The "Handling and Maintenance Notes" provided by Lotus in 1964 and '65 are wrong.

Hello, Joe. I don’t recall any color coding on the hubs when I began restoring my Series 4 in 1980. Perhaps the colors had disappeared by then.

In any case, I painted the spaces between the webs of the hubs red or green. For good measure, even though one can’t install them on the wrong hubs, I also painted the inside of the spinners and, when I switched to aluminum spinners (which have no centers), placed a coloured sticker, as shown. This might have helped Shelby and his pit crew.

Andy

Yes, David, it does seem from the accounts here and the instructions from Lotus Components that Lotus had gotten it “wrong” in the early days.

Bruce Ward, who may be a member here, wrote on the Facebook page of the Manila Sports Car Club that his 26R came front the factory with hubs installed the “wrong” way around. He and his dad have had the car since new. He wrote, “I believe it to be the only original owner 26R in existence. There has been no indication the hubs were ever swapped.”

Bruce sent this photo of one of the early 26R wheels original to his car. The damage is courtesy of the turn 9 wall at Riverside in 1966 (not due to a wheel coming off!).

Bruce advises the spinners were never wired They raced the car in the 200-mile LA Times GP, a 6-hour enduro, and several shorter races. No wheel ever came off.

Which leads to another question - does it really matter? Perhaps the fact that the spinners are tapered prevents precession, as with tapered lug nuts. But then, why do Rudge-Whitworth wheels fly off of the hubs are installed wrong-way around? Female vs make makes a difference?

Andy

abstamaria wrote:

70094C9B-280E-4597-8C92-123ECC6185D3.jpeg

Bruce Ward, who may be a member here, wrote on the Facebook page of the Manila Sports Car Club that his 26R came front the factory with hubs installed the “wrong” way around. He and his dad have had the car since new. He wrote, “I believe it to be the only original owner 26R in existence. There has been no indication the hubs were ever swapped.”

t

Andy

It has been discussed here before, there is a 26r in Japan that was raced one time, then placed in a museum. Maybe viewing that car would be further corroboration

Regarding the color on the hubs check out the recent video about "locking wire on rear hubs}. First pic red on left, later green on right and nicely painted as such. That said I don't know what handed the treads are on the hubs.

joe7 wrote:Regarding the color on the hubs check out the recent video about "locking wire on rear hubs}. First pic red on left, later green on right and nicely painted as such. That said I don't know what handed the treads are on the hubs.

Green is right hand thread on RH Side. Red is left hand thread on LH Side of car. In convention of RHD UK, LHD US.

Yes, the traditional nautical convention, adopted by aircraft. Red on the port side, green on the starboard side. When i started to sail as a kid, the memory tool was “there is no more red port left.”

Let me just close the thread - for the meantime - with a photo I just took of two cars whose KO nuts screw in differently but follow the same principle.

We’re on strict lockdown still, but restrictions may ease a little after the 15th. Non-essential travel will still be prohibited, so neither car will go out in the near future.

Andy

abstamaria wrote:Let me just close the thread - for the meantime - with a photo I just took of two cars whose KO nuts screw in differently but follow the same principle.

We’re on strict lockdown still, but restrictions may ease a little after the 15th. Non-essential travel will still be prohibited, so neither car will go out in the near future.

Andy

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I like the cam cover wall furniture