[Tamar]

Hello Gents
Most interesting post in this topic. Nice initiative Alan, good contributions Mark and good questions Jeremy.
If I may add my 2ct's here.

As Mark mentioned and explains the pitch diameter is the most correct one to calculate if a gear/pinion combo will mesh.
But as manufacturers hardly ever mention these, Alan's rule of thumb  of comparing Gear/pinion outer diameters gives you a good starting point.
And whenever you're desired combination is out of OEM range...you can always make small changes to the motor position by enlarging the holes for the motor screws.
(As I described is this post on the Ford GTLM)

However, come theory and or semantics, in practice there are two main parameters to judge a proper gearing/Mesh on your car

• Your ears
  
• Your eyes..on the timing screen
  

Mind you, the latter doesn't have to mean that a faster laptime means this is the best gearing for a race.
Might be over a single lap, but if it also makes your car less reliable, m racers are still won on maximum number of laps.

DiSCA Digital Gearing
So Mark, make that two persons that run on a track with absurd long straights ;)
I must agree that DiSCA is something most unusual, and I'm not just referring to the tall ratio's preferred for the 1/32 Le Mans circuit.
Even on much shorter tracks like Rock bull Rockingham, Suzuka Eindhoven and Catalunya Igualada and Manchester were DiSCA spec cars have raced...
...a taller gear ratio (compared to analoge racing) gave the best average laptime.

Now I might trip over some technical semantics here as I'm not a pure technical guy. But in trying to understand why...I could come up with but one explanation:

In analoge racing you alter the power of your lane to alter the speed of your motor (via your controller wired in between the power supply and the track)
In Oxygen (wireless digital racing) the power (voltage) on each lane is constant with more amp available than your motor will ever need.
Here it is the in car O2 chip that regulates the speed of your motor (via commands given by your wireless controller)
As the chip uses PWM to control the motorspeed (basically) by switching the full track power on and off in high frequent cycli...
...this means that the motor will pull with full torque on each cycle...and as such can pull a taller gear ratio.

With kind regards
Tamar

[munter]

However, come theory and or semantics, in practice there are two main parameters to judge a proper gearing/Mesh on your car

• Your ears
  
  
• Your eyes..on the timing screen
  

Good to read this as I agree.....you only need to know what you need to know.

[BAracer]

I'm slowly realising I love gears!

Bought one of these last week...tis a thing of beauty!

   

[chrisguyw]

I'm slowly realising I love gears!

I realized I loved gears quite a while ago !!

Cheers
Chris Walker

[BAracer]

Gear porn!

[Nonfractal]

Gear porn!

Hardcore  

[BAracer]

Bottom row

Third bay from the left

Top left... 

I spy my slot.it 36t crown gear





Too easy





Next!

[BAracer]

Chrisguyw, apologies if this is a well known fact, are you a serious car racer to have such a collection of gears? Are the gears in the picture a 'graveyard' of redundant parts, or is it a 'live' collection that you take to each meeting to tweak cars to suit tracks? 

Is there a strategy I should follow for putting together a set of gears that will form the basis of a car tuners basic kit?

[Nonfractal]

Jeremy, 

I would make a guess that Chris's porn-box of gears is a retail box from which parts are for sale, maybe at a shop or a club.
C'mon Chris, fess up!

You asked about a "kit" of gears that maybe you should have to hand.
This is a matter of opinion, but this is how I go about it:

Just buy what you need as you need it. 
A box full of crowns is expensive.
Typically, I never buy the crown sizes that come with the cars or kits (Eg slot it yellow SIGI28 or SIGA1628 ) because you accumulate these quickly as you upgrade cars.

As you do upgrades and optimisation on your fleet, you will start to accumulate spare crowns. 

At some point, you will find a need for one of those crowns when  working on another car so the cycle of use and reuse begins.
Some crowns are worth ordering and keeping to hand because they can be used in many cars (eg slot.it inline crowns will fit most inline configurations)
I try to keep one inline slot.it 24,25,26 to hand.

Keeping sidewinder and anglewinder crowns to hand is difficult because the sizing is proprietary and they do not fit all cars.
I keep a few NSR anglewinder and sidewinders to hand but most of these are from cars where I have upgraded the gears. 

Gearing is interesting and challenging but I suggest that you don't jump straight down that rabbit hole with big spending.

Something that has not yet been mentioned is the pinions.
Beware of fitting, pulling, refitting again and again. The friction fit loosens with every refit.
Rough up the motor spindle and use a smear of super glue when refitting old pinions.
When a pinion is so loose that it no longer requires a pusher tool, throw it away.

Again, inline-9 is supplied on most inline cars so I never need to buy one.
(Inline-10 is the factory fit on the NSR 86/89 car, untypical)
Most of my spare pinions are old ones because I only every buy a pinion for a specific job.

Try to be pragmatic.
Gearing is not a golden ticket to the podium.

Seeing as we are in "I'll show you mine" mode ...
It's been a useful excercise to figure out what I have. 

Clearly I have more (factory fit) NSR AW 31 than I will ever need. 
I'll probably never find a use for the "NSR for Ninco" crowns now that our club doesn't race Ninco anymore. 

   

[BAracer]

Well you know where to send your spare ones...

I welcome the organic growth option rather than a collectors approach. But with a bit of time on my hands, I might look at the 7 cars I own and assess where there is commonality and differences, and perhaps select I few pinions and crowns to build up a bit of stock.