31 replies to this topic

[MSwiss]

The discussion was 64P vs. 72P, but regardless, in your instance, it's hardly a scientific test, when you are switching cars.

Guys bring their RTR Flexi 5's in, with a worn out press-on pinion, the bushings not soldered in, and I solder the bushings in, install a new JK 48P spur, and a ARP angled pinion, and the car is magically dead quiet/gives the impression of being smoother.

[Dave Crevie]

I saw the most use of 72P gears in Eurosport. I used them and 80P gears to get a better mesh with the very small pinions and more

ratio choices for flat track racing. Otherwise, I can't say I saw any advantage, other than 48P and 64P gears tend to last longer.

[old & gray]

The discussion was 64P vs. 72P, but regardless, in your instance, it's hardly a scientific test, when you are switching cars.

Guys bring their RTR Flexi 5's in, with a worn out press-on pinion, the bushings not soldered in, and I solder the bushings in, install a new JK 48P spur, and a ARP angled pinion, and the car is magically dead quiet/gives the impression of being smoother.

 

After the ah ha moment with the borrowed car I did back to back tests on my own car. I seem to remember there were problems (pre ARP) sourcing quality 48 pitch pinions vs 64 pitch Faas pinions. Since the 9:28 ratio was not equal to the 12:38 it was not an exact match so a precise comparison was not possible but trends are observable.

 

In my decades of designing and testing gear pumps, I have found exact comparisons can be difficult but trends can be extrapolated to determine general rules. While I was working with gears which were turning at only 12,000 RPM the rule of thumb was the numerically higher the pitch of a gear the smoother the power transmission and the lower the vibration. The downside of higher pitch gears was the greater precision required to produce the tooth profile.

[Fast Freddie]

Mike, I did this test several years ago when I got back into Gp12 racing.  I was using 64P gears while some of the guys were using 72P metal gears when they first came out.  I believe it was in the early 2000s.  I think I got the thermometer at Sears and I believe it was made by Craftsman.  The late David Stox told me it was something he used to measure the temps of the motors so I had to have one.  I went to use it a few years ago and it was no longer working.  I don't recall the motor temps but they were enough for me to switch over to 72P gears and I have been running them whenever allowed.

As to your question about why manufactures don't expound on 72P gear ratio selections is probably the same reason they don't say anything about 80P gear ratios, who knows.

Like I always say use what works best for you and I'll use what works best for me.

[MSwiss]

The part that confuses me is the claim of less friction, which I don't doubt, but that only leads to smoothness and cooler running.

If it was an appeciable amount of less friction, why isn't the car faster?

Also if reducing the amount of engagement, which would lead to less friction, somehow a performance enhancement, why do quite a few racers, I would say the majority, specifically go with angled pinions, and sometimes spurs, to increase engagement?

[Phil Beukema]

^^^^ Good questions.

 

Are there answers or pitch doesn't matter after all?

[Tim Neja]

The only reason I ran 72 pitch was for a better mesh with SMALL pinions that we use in GT112 and Euro!! And in Euro--I ran 80 pitch!!  Their a PIA and I don't use them in ANY class's except those--anything else is 64 pitch.  Well and in Retro it's 48 pitch!!   And I've always like angled pinions for any of my cars because i wanted the best contact patch possible to avoid stripping gears!!