Gear ratios, tracks and cutting foams?

[Freddybnj_2004]

Hey guys... does anyone know of a good book, article or website that explains in (Plain English)... all about what spur gear and pinion to use for what size tracks.... cutting foam tires to certain sizes to get the right "Rollout"????
Are there any general rules of thumb ????
I just read an article that explained how to calculate switching from 48 to 64 pitch if you had the right spur/pinion combo to start with.. but how do you find out the right combo.... what would be the benefit of going to a very large pinion gear???????? Help......
Thanks...

 

[Wardo]

What type of racing are you doing and with what car?

 

[werks21]

i dont know of any good books or sites but i can adress the gear ratio and pitch Question. the best rule of thumb is run what the manual that came with your kit says to run for what ever motor but if you want conrtrol you got it;
a larger pinion means more topspeed but less aceleration. a smaller pinion does just the opposite.a larger spur gives more aceleration a smaller spur gives topspeed.
you can determine your final drive ratio with some simple math.

spur/pinion x transmision ratio = final drive ratio ex. 100/25x2.1=8.4
if you do not know your transmision ratio than just divide your diff gear by your top shaft gear.(dont sweat the middle gear)make sure that you keep your your drive ratio reasonabe for your motor wind. for example you may be able to run a stock motor @ 8.22:1 but if you try it with a 10 turn your gonna roast something. as far as roll out goes it can cange the topspeed of you car just like the gears but as long as you keep the same size foams on there you wont notice it. but just like pinions smaller tire equal = acelleration bigger = top speed. a rollout # tells you how far the car will move with one revoulition of the motor. you can figure roll out al follows. (tire diamater X 3.14) / final drive ratio=rollout. althoug at this point in your rc carrer i wouldnt really sweat it unless you will be switching tire sizes. and as far as pinion pich goes; stick with what ya got. off road and on road cars use different pitch for a reason. your intruction manual should provide some gudlines on gear set ups and final drives for different motors. just don stray from them to much and you will be fine. also your bat/motor/esc will let you know when you messed up by getting hot as hell. dont ignore em. if this was not "plain english" enough then dont be shy and ill do my best to help

 

[Diver6127]

The reason why most racers will cut their foams is for "roll out." As werks said, it's the distance a wheel will travel in 1 complete revolution. The reason this is important is because of gear ratio.The larger or taller the wheel, the higher the gear ratio will be. The same goes for vice versa as the foam reduces in size due to wear.Most Foams will come at about 63mm in diameter. People usually cut their foams to about 61mm in order to get the proper roll out.

The reason this is so important is so that your gear final drive gear ratio is at a point where the engine or motor is working with less effort and your holeshot as well as overall engine performance is "dialed-in." One added feature is that your foamswill "cone" easier allowing you to get full traction sooner.

I don't cut my tires even though I do race my car. It's more common for electric guys to do this. The asphalt will "true" my tire enough when practicing the layout of the track. I would only cut one pair of tires that I set aside for when I make one of the "mains" in competition. For qualifiers, I keep the foams at standard height.

 

[Wardo]

You don't true tires for rollout, you set your gear ratio to get the proper rollout with the tires you are using.



Trueing tires shortens the sidewall of the tire, the shorter the sidewall the less flex you get from the tire. The less flex you get from the tire, the better the car handles.


Trueing tires lightens rotating weight on the car.

Trueing tires down makes it much harder to chunk the sidewall of them, that height and flex thing all over again.


After all that, if i have to take a bit off the tires to get rollout then, i don't own enough spur gears. :hammer:

 

[710baby]

Some cars have an manual with gear ratio try to go to the company link & go to the setup guide like hpi has there drivers set up sheet can be helpful
If you are running electric outdoor it is very costly to tru your tires if you are running indoor carpet then truing them is very beneficial for steering response & giving your car a lower cg

 

[Diver6127]

After all that, if I have to take a bit off the tires to get rollout then, i don't own enough spur gears. :hammer:

All said and done, yeah it affects roll out. BUT as 710baby stated, most of the guys that do true their tires, are the indoor carpet racers (electric). Spending the $200+ for a tire truer is something that I would rather spend on something else. If there is as need for me to true a tire, I'll just do it at the LHS I frequent. Besides, it's free for me anyway.

 

[werks21]

Spending the $200+ for a tire truer is something that I would rather spend on something else. If there is as need for me to true a tire, I'll just do it at the LHS I frequent.

i couldnt agree more. tire trueing is not for every one. it has its benifits but so does cutting your comm every few runs. some things can be done without.

 

[Wardo]

All said and done, yeah it affects roll out.

yes it effects rollout but your reasoning of why it's done is incorrect. :shrug:

 

[Diver6127]

ok, I stand corrected ... you learn something new everyday

 

[710baby]

I know you are not referring 200 for a truer where & what brand

Heyfreddy if you are looking for a place to race check out jackson raceway
nice track & if you go don't waste your time truing tires take off 27's work great on that track

 

[Diver6127]

I know you are not referring 200 for a truer where & what brand

Infortunately it is true. Saw it at Bobby's shop in the display case. Don't know the brand, don't wanna know the brand. I'll just use what the shop has in the back if I ever need to true a tire.