13/41!

[Honda TRX250ex]

How much faster would a 13/41 gearing on a 300ex with a pipe and 20 inch tires go compared to stock?

[Blue250X]

Im not sure, but it would accelerate faster, youd prolly have him by about 2-3 lengths when u hit 5th......i think, but he would top out faster w/ stock gearing and tires

[hardkoratvmxr]

that you would make your accelration really fast but your top speed really slow i would reccommend going to 13/36

[Honda TRX250ex]

Don't it go lower sprocket size more acceleration less top speed and bigger sprocket size more top speed less acceleration?

[bwamos]

Making 2 assumptions on this calculation.
1) Stock top speed at rev limit is 55mph
2) Tire diamaters are a perfect 22" and 20" (which isn't the case, but need a standard)

13/38 w/ 22" tires (stock) = (13/38)*(22"*3.14) = 23.63" forward movement per countershaft rotation.

13/41 w/ 20" tires = (13/41)*(20"*3.14) = 19.91" forward movement per countershaft rotation.

Therefore if stock top speed at the rev limit is 55mph. Your new top speed at rev limit will be 46.34 mph.

If you want to match the stock top speed with 20" tires you will need 14/37 gearing.

(14/37)*(20"*3.14) = 23.76" forward movement per countershaft rotation. aka top speed at rev limit of 55.30 mph.

[bwamos]

Originally posted by Honda TRX250ex
Don't it go lower sprocket size more acceleration less top speed and bigger sprocket size more top speed less acceleration?

Smaller in front / Larger in back increased acceleration, decreased top speed

Larger in front Smaller in Back decreased acceleration, increased top speed.

[Honda TRX250ex]

Alright thanks guys. I bought sprockets and chain and i got confused on the gearing. Thank you.

it goes the smaller the sprocket the higher the top speed :)

dont go TO small then it would take it longer to get to the top speed

[prepracing]

stock gearing vs. 13/41 gearing......stock gearing will wear you out in a drag race, that quick acceleration will only hold up for about 50ft. then you will be eating dust

[Honda TRX250ex]

The kind of gearing i got is 13/36 and i had 13/39 on there. Will i see a differnce?

stock is 13/38

im putting 12/37 on mine

[Honda TRX250ex]

Originally posted by 89honda 250x
stock is 13/38

im putting 12/37 on mine
I did't have stock i had 13/39. I can tell a big differnce in top speed but i dont go threw the gears as quickly.

[Sjorge450R]

Originally posted by bwamos
Making 2 assumptions on this calculation.
1) Stock top speed at rev limit is 55mph
2) Tire diamaters are a perfect 22" and 20" (which isn't the case, but need a standard)

13/38 w/ 22" tires (stock) = (13/38)*(22"*3.14) = 23.63" forward movement per countershaft rotation.

13/41 w/ 20" tires = (13/41)*(20"*3.14) = 19.91" forward movement per countershaft rotation.

Therefore if stock top speed at the rev limit is 55mph. Your new top speed at rev limit will be 46.34 mph.

If you want to match the stock top speed with 20" tires you will need 14/37 gearing.

(14/37)*(20"*3.14) = 23.76" forward movement per countershaft rotation. aka top speed at rev limit of 55.30 mph.

Bwamos, I know this is a old thread but I have a question. How do you find the top speed out. Like can you show me all of the math. For an example can you show the entire math needed to do the calculations to figure out the top speed with 14/38 and 20" tires?

[bwamos]

Sure...

A bone stock 300ex with the stock 13/38 gearing, stock rev limit, and stock 22" rear tires has a top speed of 55mph +/-

In stock form the rear tire will roll 23.63" per revolution of the countershaft.

Formula: (Tire circumference) * (Gear Ratio)
(22" * 3.14) * (13/38)
(69.08) * (0.3421) = 23.63" forward movement per rotation of front sprocket.

Now lets say you jsut simply change the rear tire out to a 20" tire and keep the stock gearing.
Same formula:
(20" * 3.14) * (13/38)
(62.80") * (0.3421) = 21.48" forward movement per rotation of front sprocket.

Now to fint the top speed change. you take the ratio of the 2 and multiply it by the top speed of the original gearing.

Formula: (New forward movement / Original forward movement) * (original speed)
(21.48" / 23.63") * (55mph)
(.9090) * (55mph) = 50.00 mph top speed.

Now.. once you ride it you decide that it is geared too low, and you'd like it to feel closer to stock.

Here I usually jsut play with the ratios.
Experience will tell me that simply changing the front sprocket out witha 14 tooth will get me close.. but to check this I'll use the formula.

(20" * 3.14) * (14/38)
(62.80) * (0.3684) = 23.14" forward movement per rotation of front sprocket.

Stock was 23.63" The new gearing is still a tad lower than stock.

Sooo.. lets play with it a little more. Lets try out a 37 tooth rear.

(20 * 3.14) * (14/37)
(62.80) * (0.3784) = 23.76" forward movement per front sprocket rotation.

That's pretty close. Lets compare the top speed between this and the stock top speed using the previous formula of:
(forward movement new / forward movement original) * (original top speed)
(23.76" / 23.63) * (55mph)
(1.006) * (55mph) = 55.33 mph

Close enough.. ;)

Hope that helps.