Sunday, October 15, 2017

Today's Odd Question for My Very Smart Readers

Put two rectangular magnets, side by side.  Up is the north pole of each.  Bolt them down to a non-magnetic substrate.  Is there any attraction on their equators?  Past experience tells me no.

We keep getting flats from nails and screws--I am thinking of hanging a magnetic nail catcher in front of each tire suspended on nylon, just above the road surface.


  1. I suppose you assume a natural magnet and not an electro-magnet. There is no dip at the equator, aka aclinic line. However, as the attraction is null the closer to the equator, I believe sensitive instrumentation would register some attraction albeit a weak attraction very close to the equator. The question becomes what is the width (expressed as % of total area) of that null field?

    For practical purposes, the width of null may be defined as where that attraction is weaker than required for the application, such as picking up ferrous nails from the roadbed.

    I also had a recent bout of flat tires from nails and screws. I like the idea of sweeps, whether stiff bristle broom or magnets, preceding the tire. I suspect the problem will become worse given the increase in construction and careless contractors in how they load their trucks.

  2. it may just lift them up enough to let them embed. I used a thorn flicker on my bicycle that would ride on the tire and remove thorns that were picked up before they had a chance to get pushed further in. Putting the magnets just above the descending tire may prevent embedding.
    You might run a magnet up and down your driveway as your recent home construction may be the source.


  3. I don't think I understand the configuration of this gadget you have in mind. Why two magnets? Why not just one magnet? Hang one strong magnet down there.

    I suspect the problem is that the magnet would have to be either extremely strong or extremely close to the road in order to pick up something when you are moving at speed. A magnetic field will apply a force to the ferrous object but that object still has to be accelerated so it moves to the magnet.

    That this isn't common suggests that there are bad problems with the concept, although it might just be that nobody figured out the right trick.

    Also, it wouldn't pick up non-ferrous metal - stainless steel, brass or copper.

  4. Two magnets because I am trying to test with some magnets that I have, but this might do the job in pairs:

  5. We live on gravel and have had more flats than we can count over the 37 years in the country. Nearly all of the flats are the rear tires. Our solution is to never exceed forty mph on the gravel. That speed allows nails to fall down after being flipped by the front tires. I also drive slowly when I can, and pick up nails and bolts that I see.

  6. Are you getting more flats in the rear tires? This is thought to be caused by the front tires standing nails and screws up as they run over the objects, so as to be oriented for puncture.

    I can attest to more flats in rear tires of cars, motorcycles, and light trucks, from being associated with them in various ways for 50+ years.

  7. You didn't mention which tire is getting the (most) nails - front or rear, nor which - F or R - is the driving tire.

    Motorcyclists have, for decades, debated exactly the same thing; rear tires - the drive tire - picks up almost all the nails, not the front (rolling) tire. AFAIK, it's never been resolved as to whether the front tire "lines up" the nail when ti runs over it, that alignment making it easier for the nail to embed in the rear tire, or the stresses involved in applying the motive force to the rear tire are, somehow, assisting in embedding the nail.

    Some anecdotal success has been reported with the installation of "sweepers" immediately in front of the rear tire, but I'm not aware of any data, reliable or otherwise, on it.

    Way back when, Jim Hall built a CanAm racecar with a large Chevy racing engine for motive power (just like everyone else used) and a snowmobile engine driving a ducted fan to produce a vacuum under the car to suck it down to the pavement, in lieu of bodywork aerodynamic structures providing downforce (aero worked best at speed, and Hall was trying to dramatically improve low speed traction as well).

    The car ran only one race before the sanctioning body banned the idea, but it worked. He used - IIRC - teflon as a skirting material (brand new at the time) to create a sliding sealed "air box" between the car and pavement (might have been another very low friction plastic material, but I seem to remember teflon being used). The point here is a sacrificial near-pavement deflector of inexpensive low friction plastic might be more effective than magnetic force that would both have to be rather strong to work on ferrous material at highway speeds and ineffective on non-ferrous material.

  8. Clayton are you planning on suspending the magnets on nylon cord or are you planning to fabricate some piece of hardware to be attached to your car to anchor the magnets? Either way suggests to me that road vibration will render the magnets mostly ineffective, especially so if nylon cord is used.

    Why not just purchase tire repair/replacement guarantees from your tire dealer? I purchased that option and saved myself the cost of a new set of tires when a picture on a tire with some wear would have necessitated the purchase of all new tires.

  9. Your local equipment rental place or someone who sells roofing supplies would have a magnetic bar if you are just concerned with your driveway or some other specific area.

  10. augustrr: Nails on all the highways here. The use of nylon cord is an experiment to see if it works.

    JognG: Cheap to try. I prefer not going to tire repair if I can do so cheaply.