Track Tac

tire roll out vs gear

foreverfaster

foreverfaster

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Just popped in my head. going down on tire size vs going up with gear. if i want to get off the corner faster, naturally I'd go up on gear. (say 67 to a 71) however if i go down on tire size, say 1/4 to 1/2 inch have i made up the difference? can I get the same effect by changing tire size? my only issue there would be ground clearance. anyone got the math for this? guess i'll look over some of Al's old spread sheets.
 
By my calculations, using 12 tooth driver, 6000 rpm, and tire rollout, you would need to go from a 34 inch tire to about a 32 inch tire to make the same distance traveled in 1 minute

Vs 12-67 to 12-71
 
J'-remy said:
https://www.bmikarts.com/Go-Kart-Gear-Ratio-Speed-Calculator
here you are, go nuts! rear sprockets are cheaper than tire/wheels BTW
Click to expand...
That Calculator isnt that accurate according to my RPM, Rear Teeth, Front Teeth input. Saturday night I ran a 14/61, and according to that Calculator Im running a 4.35 ratio, that is accurate. But says top speed of 25.4 MPH. I was over 40 MPH on track according to my Mychron5. Unless of course Im missing something.
 
So you were turning over 5500 rpm?

34 inch tire rollout
4.36 gear

Over 40 mph.

Both on this calculator, and my own.
 
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Running a smaller RR tire might slow you down. If the ratio of engine RPM to axle speed remains unchanged, the distanced the kart travels per axle revolution shrinks when you shrink the tire. If I need to change a gear I change it. IMHO The right controls belong in the right places and that keeps it simple. Maintaining stagger is hard enough even when it’s set right to start. When my daughter ran rookie red plate there was a gear rule and max RR tire size rule. I would run the RR as big as I could and push the limit. If she won I would tell her to take a nice slow victory lap so everyone gets to go across the scales before her and give that tire some time to cool so it does measure 1/16 too big by the tech man’s tape 😬
 
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foreverfaster said:
Just popped in my head. going down on tire size vs going up with gear. if i want to get off the corner faster, naturally I'd go up on gear. (say 67 to a 71) however if i go down on tire size, say 1/4 to 1/2 inch have i made up the difference? can I get the same effect by changing tire size? my only issue there would be ground clearance. anyone got the math for this? guess i'll look over some of Al's old spread sheets.
Click to expand...
There is a downloadable program on our old website that is still available (it is a safe executable file.)
http://www.carlsonmotorsports.com/VectorKartSmart.html
I don't even remember the name of the guy that I got the program from, but it's been safely downloaded and used many times.
It will do the math for you on gearing considering varying tire sizes and has a separate section for scaling.

"Can you get the same effect by changing tire size?" Yes, but...
I would not be changing my right side tire sizes to get my gearing. Changing the right sides from 34" introduces many unintended chassis changes. Keep your right sides at 34" and get the gearing you want with the correct driver/driven gears -- jackshaft if necessary.



-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
33 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
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95 shaw said:
So you were turning over 5500 rpm?

34 inch tire rollout
4.36 gear

Over 40 mph.

Both on this calculator, and my own.
Click to expand...
Im not getting your response as far as what questions your asking. Was I over 5500 rpm, Yes. Right side roll out on my Carlson tires 34", yes.. At a 14/61 gearing , the ratio is 4.35. and was Racing at over 40 MPH. I was in the seat and know I wasnt going 25 MPH. Like I say unless I did something wrong inputing my "stuff" on that calculator.
 
Not sure where you got the 25 mph.

Guessing where it ask for wheel diameter, you put in 6 inches.

Use 10.85 diameter to get 34 inch rollout.

The BMI calculator works correctly.

Just garbage in, garbage out.
 
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