11:36 SW and 9:27 IL

[Audi1]

Often times when you race 1/32 scale slot cars in a class where both sidewinders amd inlines are allowed, there are spec gearing ratios and they’re usually 11:36 SW and 9:27 IL. Where did these ratios come from?

Is it simply that manufacturers put these gear ratios in their cars and when we race similar SW and IL cars together that’s what we end up with? Was there some testing done a long time ago that equated the performance of 11:36 SW with 9:27 IL for one type of car/one type of motor?

9:27 is one of the possible 3.00 ratios whereas 11:36 is 3.27; giving, roughly, a 1.1:1.0 ratio between SW and IL. Does that mean that sidewinders are approx. 10% more efficient in transferring power to the rear wheels?

What’s the current understanding on this topic?

Allan

[Audi1]

133 views and no replies........? Someone must know how those gear ratios became linked....

Allan

[Rleog]

I guess that I’m getting old. I thought that I had read a reply by Harry.

[HomeRacingWorld]

Well I did. Dang it. Might have deleted it during the database clean up. Sometimes if that is done right after a post, it does that. I’ll reply again.

[HomeRacingWorld]

Let me try and reword/repeat. I'm long winded though so...

Try and forget ratios for this part. Think physical size. Like outer diameter, etc.

Sometimes it is not the ratio. It is what will FIT inside the car/chassis. Such as gears in some models like SCX F1 that use smaller than 27 tooth because the crown is simply smaller in diameter and fits.

Or a spur gear in sidewinder/anglewinder. You just cannot have too large a diameter given the pitch we are working with. Think Monogram NASCAR. The spur gear almost drags the track in stock form, so don't sand the tires too much. The tire/wheel basically says: "That is far enough".

On pitch. Might be a few protestors on this one, but our common RTR gears are right around 50. In between 48 to 52. We say pitch, but these gears are actually a metric standard. And you can only stretch/shrink the gap so far while restricting diameters before you get a "mesh" that sounds like nails in a blender. REMEMBER...I'm talking our Euro RTR models here. Not the commercial/vintage offerings ok?

And when face with a "fixed" inline, where the motor shaft rests between the teeth and the "boss" or flange...you are limited even more.

Now with this in place, what about HOW the cars act/perform in SETS. Not all of us have Walmart sized, 8 lane Euro tracks. The cars have to run well in the smaller sets they are placed in.

And there are some ratios than can cause our little China/Japanese automotive/industrial born motors to over heat. Might seem trivial...but it's not.

And one final tidbit...how does the car SOUND? Is it quiet and smooth? Or that bag of nails in a blender? What would YOU prefer your end product to sound like to customers?

So a standard ratio was started as a baseline that fit most restrictions and parameters. Maybe it was because of performance. MAYBE it was because the gears already existed thanks to automakers/industry already investing in the tooling? Because...so we are clear...our motors (Mabuchi, etc) are directly from them. Those little square holes in some of our cans are NOT for cooling ok? They are for the adapters that snap to them for side mirrors, wipers, etc.

One must admit that a 9/27 ratio works well for many small to medium tracks with low excess heat. Even my 5x16 oval proves that. Still the hot setup. 11/36? Yep. Spur gear almost small enough in diameter to fit a very wide variety of cars. Given the distance the motor is placed in the chassis and is not easily adjustable.

Compatibility. You need to know, if not already...they don't care. If compatibility were priority, NINCO would not have changed motors every other release. One of the reasons they are a dead player today because the people that keep changing things never raced.

Today is a different. We have all the parts and availability to create compatibility, to some degree.

Now don't get too mad....but in my opinion any club/track/race organizer who mandates STOCK ratio only, well...only has themselves to blame. Not the manufacturer. Why do this and then expect the cars to be equal? Won't happen. What WILL and DOES happen is racers gravitate to the car/setup that is dominant...and thus you lose the variety you were striving for.

Mixing configurations without the "permission" to tune is simply a waste of time. It cannot be about money. We spend oodles on parts and tuning. Especially the advanced racers around these parts.

Rules are made by the people. So I would open things up a bit and allow the racers to experiment with ratios. I mean, don't we all want to mimic 1:1 racing these days? Increased scale accuracy...better lane and track design flow...etc? If that were the case, then allowing gear ratio changes should be the norm...not the exception?

Ok your turn!

[Austin]

OK, OK, OK

Way way way way back before HRW was even a forum and before Allan took over SCI, The SCI Administrator, a member call Sweet and me started proxy racing, 1st it was just one track with the scalextric black window nascars with magnets, thinking about 5 times. I have no idea what the rules were if any. Then we came up with the first Carrera RAA with magnets, Then open classes without magnets, at this time still using the hard stock tires back in the day. With the open class the cars were all over the place, some were rockets and wouldn't handle at all. Stock rubber tires without magnets were a hand full. So the slow them down rules were set for motor RPM and gears, tires, Magnetic downforce if magnet class, and so on. Now if this is were it all started from I don't know.

[chappyman66]

Ratio is all about acceleration vs top speed. Lower ratio (2:1) is higher top speed but longer to get there. Higher ratio (4.5:1) is less top speed but getting there faster ("squirting" down a short straight) and also can give better braking depending on the motor.
At the large commercial track, we used and 8:31 combo (3.8:1) on the basic cars because it slowed the cars down and made it easier for the new racers to drive.
Remember that this all presumes that the motors are consistent which is not the case...

3:1 is a fair compromise ratio...most home tracks are short. As Harry has pointed out, SW gears have sizing issues. I have run an 8:26 combo on a scratch build using the gray 48p gears but that's a pretty small SW gear. Small gears = more manufacturing problems too. They are necessary for some car designs though. Inline ratios are much easier to change that SW, especially with motor location fixed by the pod/chassis mount. So with a given location/spacing, certain ratios are almost defined....and as Harry says, further constrained by wheel and tire size. So 11:36 gives a smooth mesh and fits common tire sizes......

Changing ratios can really affect performance...think of it as keeping the motor in the "power band" (the concept, not actually applicable to DC motors). I have seen cars "come alive" with a change of 1 tooth on the pinion just because the motor is happier at that ratio. It probably has more to do with changing the mesh just enough to get everything spinning freely....but that's another topic.

[chappyman66]

And btw.....the whole "efficiency" argument is at least 50 years old. I doubt it will be resolved here.

There is some beautiful engineering in slot cars....and some of it is far more theory than real measurable improvement. I will go out on a limb and say that the driver variability far outweighs the marginal improvement in power transfer efficiency.

[Xr4ti]

To me, what Harry wrote defines the parameters all manufacturers are forced to adhere to in achieving parody and proper fit.
Dollar costs are minimal when you produce the same parts for every car.
Having to inventory gears is much simpler when they're all the same ratio like 9/27.
That's how I see those ratio's coming into being. Good business decisions.

We always raced the stock gears against equal configurations IL/IL & SW/SW in the PSSRA early on.
It was fair because it was simple. Scalextric NASCAR's we're very, very close without having to spend more $$$.
Tuning is for those of us searching for that edge, but that's a whole other topic.

[Audi1]

Thanks for the feedback everyone; particularly Harry. I think I've got the picture and I'm now seeing open gearing as a better alternative to defined gear ratios.

Allan

[Audi1]

Chris (chrisguyw) gave me another perspective on the 11:36 and 9:27 ratios and it was a practical one that makes a lot of sense. Harry alluded to it, too, but I missed it first time around.

When you look at the diameter of the gears that are used in stock SW and IL gearing, for the most part they follow the mode: [(diameter x 2 )- 2] = optimum tooth count for a given pitch. Most of our 1/32 gears are 50 pitch, or thereabouts.

So, with a SW the pinion is generally 6.5mm in diameter: (6.5 x 2) - 2 = 11. Spurs are generally 19mm in diameter: (19 x 2) - 2 = 36. There's your common 11:36 SW ratio.

With IL's, the pinion is generally 5.5mm in diameter: (5.5 x 2) -2 = 9. Crowns are generally 14.5mm in diameter: (14.5 x 2) - 2 - 27. And there's your 9:27 IL ratio.

So, performance matching in the often used "equator" SW at 11:36 and IL at 9:27 really doesn't exit. It's a manufacturer's choice, based on the optimal number of teeth for a given gear diameter, keeping pitch in mind.

Apparently, experience over time racing SW's and IL's together has come to support that concept that optimally geared cars; SW 11:36 and IL 9:27, are also roughly compatible racing ratios; and that may well be the case. But, the physical basis for choosing these ratios is now a lot clearer to me and it makes a lot of sense; both from the performance and the manufacturing standpoint.

As Harry said; fixing the gear ratios to equate SW and IL performance doesn't make a lot of sense and I, for one, won't be doing it anymore.

Chris can add a lot more detail to this topic.

Allan

[chrisguyw]

[Audi1]

Thanks Chris. Yes, in my rush to find a generalization, I overlooked the fact that crown gears are structured at 90 degrees to the pinion gear and that the difference in tooth count is primarily made up in increasing the diameter of the crown. I had measured a crown from a Scaley F1 Ferrari and it did, indeed, measure out to be 14.5mm; probably dictated by the fact that the crown on most modern Scaley F1 cars needs to have a relatively small diameter in order to fit under the rear axle housing on the body and to clear the indent on the chassis.

Allan

[Changing-Gearz]

From a manufacturing side - I can't see having that kind of tooling on hand to make gears. You need two cutting tools to make that tooth range of SW gears..... unless they change pitch. Then You probably need a dozen - and they don't make a .47 module cutter off the shelf.... (I suppose if your a Chinese machine shop - and you had 3-4 customers it could be done).....

My handy dandy gear designer tells me that a 31t spur should be 16.5 outer diameter (at the Euro .5 module (pitch)). Is the 31t not 16.5mm?

[chrisguyw]