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Nuro has just posted this Gear Ratio Chart in our SF Resources section.

We hope this will prove helpful to scratch builders and those who like to adapt their RTR cars.
The RED figures are to give a point of reference to the common 9:27 or 3 to 1 ratio fitted to most cars as bought.
 

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Cheers for the head's up Tropi


Now if I could only get my printer to print the full table rather than cutting a row out when it goes over to the next page. It only does this when printing from web pages....

Mark.
 

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Discussion Starter · #3 ·
Diff


Two possible solutions:
1. Take a screenshot [ALT + PRINT SCREEN] of the page and then shrink it to a suitable size in a photo editor.
2. If you are stuck, I can Email you the original Excel spreadsheet
 

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Brian Ferguson
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Just to be really picky (and anal), the word "spur" at the top of the chart should say "pinion". Said I was picky!
 

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thats brill!

Could there be an extra bit saying wot the standar crown and pinion is on various makes (if they have standards) like scalex, fly, carrera etc etc - so we dont have to count all those teeth b4 ordering new bits?

I know that info is prob already on the forum, but i think it would be cool
 

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Discussion Starter · #6 ·
You are right Fergy and I like picky if it corrects things - so thanks.

Also 'contrate' might more universally read 'crown'
I'll see if they can be changed.
I was a bit brain-dead earlier on - am totally brain-dead now and will wish you all good night.
Last race of our official season tomorrow and I need my beauty sleep!
 

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Brian Ferguson
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Useful stuff, Tropi!


You say "contrate", I say "crown"... kinda like "tomato" and "tomato"....


To be honest, I had never heard the term "contrate" until I joined a UK board. Didn't have a clue what the term meant! But if I could figure it out, I think you can leave that as is.


QUOTE I need my beauty sleep

Sleep in... okay?
 

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Jan Groosmuller
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QUOTE (Tropi @ 4 Apr 2004, 00:34)Diff


Two possible solutions:
1. Take a screenshot [ALT + PRINT SCREEN] of the page and then shrink it to a suitable size in a photo editor.
2. If you are stuck, I can Email you the original Excel spreadsheet
Then ther is the "nerd" option I used....
:D

select the text, [ctrl-c], open excel, [ctrl-v]

and hey presto, the gear chart is in
:D

only thing I had to do was correct the spur (pinion?) gear numbers, they were misaligned...


works like a charm


Jan
 

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Discussion Starter · #10 ·
How's that for quick service from the ever-obliging boss!


Suggestions for extensions are always VERY welcome.
Astro's request for 'standard' RTR gear sets is well on the way - I've had it around 90% complete for months - I will try to complete it 'soon'.
 

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DT
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Who wants to do a table with tyre / tire & rim sizes?

A list of cars with their standard tyre & rim size plus a selection of tyres and rims that fit.
 

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Allready got that started for my stuff,and will add other brands as I get info.

BWA Wheel n Tire sizes

Tropi,I borrowed your last 12 sizes,I allready had 24 - 48 posted hope that's OK,you are welcome to any of my info.

I will also have Axle sizes,and specific car conversions soon too,ie,what wheels fit what cars.
 

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..what I'm offering since years on my hp
gear ratio chart
...but - including tire diameter and distance you make - extreme helpful.
Reifen = tire
Motorritzel = pinion
Achszahnrad = spur gear
Ergibt die zurückgelegte Strecke je Motorumdrehung in mm = distance travelling per round in mm
Motordrehzahl = rpm
If necessary I'll do an english version of this table - which is mainly used for 1/24 and just got some extensions for 1/32...
 

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Just for a little discussion.....

let's say you have 9/27 set, ratio of 3.

you change it to 12/36, also a ratio of 3

or 8/24, still a ratio of 3.......

now let's see, would the car perfomance be the same?

Would one set up be better for a track with lots of long straight?

Would one be better for twisty, tight corners, short straights?

How 'bout if we really change it to say, 14/28, ratio of 2?

or, 6/24, ratio of 4?

how would going from 3 to 4, or 3 to 2 effect the car on straight vs twisty tracks?

ok, i know you got tire circumference, motor revolutions and other factors, but some basic tenants re: gear ratio and its effects on the car, and applications for tuning for a specific track, would be interesting and useful.

what's tall gearing...and short gearing..within the perspective of using this chart?
 

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Matt Tucker
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basically for each track you'll find a mm/rev fig that gives you best lap times - find it and stick to it knowing that varying wheel size wil mean you have to change gear ratio to get the same number.

Bascially - smaller mm/rev = good acceleration and suit twisty will little straight and vice versa

I've found that on my GS test track a mm/rev of about 20 is good for me and on my club so far a mm/rev of 22.5 seems best. Once I found it I intedn to stick to it.

I have yet to throw motors into the equation other than choosing a motor thats decent
 

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Brian Ferguson
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VOA, any combination that yields the same ratio will perform the same. In your examples of 3:1 gearing (8/24, 9/27, 12/36), there will be no performance difference, although 12/36 might give you a smoother mesh if you can cram a 36 tooth gear in there!

Tall gearing is the term given to lower numeric ratios. IE, 2:1 is taller than 3:1.

Tall gearing, in theory, gives you great top end but less acceleration. Short gearing does the opposite.

When changing ratios, don't make massive changes unless you are certain you need it. Smaller changes (from 3:1 to 3.2:1, for example, will often change performance very noticeably).

If you need more low end power, go to a higher numerical ratio. If you need more top end, go to a lower numerical ratio. Only the ratio matters, not the actual number of teeth on each gear.

Yes, tire diameter (and therefore circumference) is in fact another element in the overall ratio of a drive system, and changing tire diameters DOES change the effective gear ratio. This is a very convenient way to make fine adjustments in drive ratio, assuming that you can afford to make the resulting change in ride height! This is often not feasible with mag cars because you will also be altering the downforce level.
 

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Discussion Starter · #19 ·
The next development in the gear ratio chart was always going to be a version that took tyre diameter into account to give the mm/rev figure. It's very easy to produce the numbers but I have never crystallised the ideal format in which to present it to other users. If anyone has thoughts on this, please don't hesitate to post or contact me direct - or produce your own of course!

Just a little thought for Fergy on identical ratios, but using bigger numbers.
Although 9:27 is the same as 10:30, 11:33, 12:36, 13:39 etc, the mass of the larger toothed gears is also increasing, thus increasing both dead weight and rotational inertia.
Any thoughts on how significant these factors might be?
Perhaps insignificant?
 

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QUOTE smaller mm/rev = good acceleration and suit twisty ...a mm/rev of about 20 is good for me

Sounds like you are talking about the distace it takes for the tire to make one complete revolution? ergo smaller or larger tires.

That won't change with the gear ratio. Now, the number of motor revolutions for the tire to complete one revolution will change with the gear ratio, which is what we are talking about, right?

Or are you talking about something else, and I just don't seem to get it?

edit:
ok tropi..you mean like distance traveled for one armeture revolution? which of coarse, gear ratio would effect.

QUOTE rotational inertia

Like maybe breaking effect?
 
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