is it time to mention tonearm's length again?

Hi folks,
I looked over quite a few posts related to the subject, tons of intricacies again which is great!
But one thing slipped my understanding, sorry, I am a little slow last ten years.
What I can not figure is - why longer arm helps traction (between the tip and the record). Or more to the point - I would think that the traction will be minimal when the tip's axis (provided such exists) is perpendicular to the line going from the tip to the spindle. I probably should know more about how the tip is built - in other words whether it does matter or not how the cartridge (and the tip) is positioned. But I thought the groove should go "along the cartridge". Now if as in my case the distance between the center of the arm base and the center of the disk is 9 inch and the tonearm is 12 inch long then the angle between the tonearm line and the line going to the center of the record becomes less then 90 degrees.
In the above example then with 12 inch arm - does it make sense to rotate the cartridge clockwise a little on the tonearm to get that angle back to 90 degrees? If above makes sense at all.
Sorry for the lengthy email. And thanks for your time.

Maybe one of the technically smarter members can better untangle your post than me, but let me give it a try.

My tonearm is 10.5 inches long. My recollection from reading something somewhere is that the longer arm, if properly set up, tracks in a larger arc (i.e., "flatter" because the radius from pivot to stylus is longer) across the record than a shorter arm. Big circle versus little circle. As a consequence, the cartridge offset angle is lower than a shorter arm. Geometrically, what I'm try to say is that the stylus will track the record grooves closer to a perpendicular angle, approaching the geometry of a tangential tracking arm.

The bottom line result is less distortion, especially in the inner tracks. Having said that, I believe the cartridge and arm are still set up in the usual way using your favorite geometry, e.g., Baerwold (sp?), Loengren B (sp?), Stevenson or some other proprietary method. Same as regards VTA. You may still have to raise the carty's butt to achieve optimal SRA if that sounds better to your ears.

OTOH, I've read that 12 inch arms present other problems, e.g., the arm may be less stable and be subject to resonances. But having said that, there are a lot of fine 12 inch arms out there, so I assume the manufacturers are able to make the necessary compensating adjustments.

I don't recall reading anything about stylus traction as you mention in your OP. I would surmise that traction or friction is more a function of VTF and stylus shape.

That's my 2 cents worth reaction. I'm sure the smarter vinyl-heads will do a better job explaining this than me.
Avs9, It sounds like you think a 12 inch arm mounts in the same location as a 9 inch arm. A 12 inch arm needs to mount farther away from the spindle than a 9 inch to accommodate its extra length. A longer arm will scribe a flatter arc so there will be less tracking error. The headshell offset will actually be around 17 degrees as opposed to around 23 degrees for a 9 incher.

Sorry, meant to say less tracing error.

Thank you thank you - yes, you got it right, that's what I thought. All right, now it falls in picture more nicely.


When you say "traction", do you mean "tracking" (the ability of the cartridge to stay in the groove during difficult musical moments) or "friction" (force generated by stylus tip traveling in the groove that is counter to the rotation of the platter)?

Meantime, what the other guys say is correct. Mounting position (tonearm pivot to spindle) is much greater for a 12-inch arm than for a 10.5- or 9-incher. Each designer specifies how to mount his tonearm, usually, and usually provides some sort of template to assist you in correct mounting of tonearm and cartridge. In general a longer tonearm will produce less skating force, because the angle of the headshell with respect to a line drawn from the stylus tip through the tonearm pivot center gets smaller as effective length gets bigger. Skating force is also a function of the friction generated by the stylus tip, so I would think that longer tonearms produce also less frictional force. (Have to think about that a bit.)
Lew, everything makes a lot of sense. Btw, I thought I read somewhere that the 12" arm, at one time, presented some stability and resonance design issues. I assume whatever may have been an issue a while ago has been worked out by now. Any thoughts on that point?
I thought I read somewhere that the 12" arm, at one time, presented some stability and resonance design issues.
All other things being equal, a longer arm will be less stable (internally) than a shorter one. When flexed, it will also resonate at a proportionally lower frequency. These things will affect the sound.

Of course all other things are not necessarily, or even very often, equal...