[kaiserkaiser]

Hi there, need some help, i have a 2005 CRF450X and i think is strange how low is the top speed of the bike.
She does the same top speed with 14-51(enduro wheels) and 13-42 (17' SM wheels), is this normal?
The bike have stock exhaust and 170 main jet and cutted airbox.
Any idea why the bike is so flat at top end?
Here is a video of the bike accelarating to the top speed.
https://www.youtube.com/watch?v=e1jafiSWuwo
Thank You

[JimDirt]

The gear ratios (excluding total tire diameter) is somewhat close , so that would explain the similar top speeds , the 14/51 is a 3.643 ratio (off-road wheels) , the 13/42 is a 3.231 (super moto wheels) , i would think that because of the 17" wheels , this is bringing the ratio back to about where it is with the off-road wheels on it , also very important , are you resetting the calibration of the speedometer to compensate for the different wheel size , , i am betting if you put a mark on the enduro wheel tire sidewall and a corresponding mark on the ground and go 1 rotation forward and place a mark on the ground , then switch to the super moto wheels , and make a mark , that they will be significantly different where they end up , if the speedometer is not re-calibrated to this difference it will throw your speedo off significantly

The manufacturer of the speedo (even if its Honda) will have a calculator/formula to adjust/re-set the speedo to various wheel sizes , i think this is where your top speed is being calculated incorrectly


Here is a gearing calculator to help you figure out what is off



INSTRUCTIONS:

http://www.crfsonly.com/forum/viewtopic.php?t=37723

CALCULATOR:

http://crfsonly.com/howto/gearing/motor ... ulator.php

[kaiserkaiser]

The gear ratios (excluding total tire diameter) is somewhat close , so that would explain the similar top speeds , the 14/51 is a 3.643 ratio (off-road wheels) , the 13/42 is a 3.231 (super moto wheels) , i would think that because of the 17" wheels , this is bringing the ratio back to about where it is with the off-road wheels on it , also very important , are you resetting the calibration of the speedometer to compensate for the different wheel size , , i am betting if you put a mark on the enduro wheel tire sidewall and a corresponding mark on the ground and go 1 rotation forward and place a mark on the ground , then switch to the super moto wheels , and make a mark , that they will be significantly different where they end up , if the speedometer is not re-calibrated to this difference it will throw your speedo off significantly

The manufacturer of the speedo (even if its Honda) will have a calculator/formula to adjust/re-set the speedo to various wheel sizes , i think this is where your top speed is being calculated incorrectly


Here is a gearing calculator to help you figure out what is off



INSTRUCTIONS:

http://www.crfsonly.com/forum/viewtopic.php?t=37723

CALCULATOR:

http://crfsonly.com/howto/gearing/motor ... ulator.php

Hi JimDirt, thank you for the deep explanation. The speed calculations where done by GPS of the mobile phone (Motorola Moto G), what i know is that the GPS is the most precise thing to get the speed(am i wrong?).
Normally i use the sigma sports bicycle computer and works really nicely but i lost the sensor when i changed to SM wheels and now i only have the smartphone. To set the Sigma i measure the wheel in the ground and then compare to a GPS to try to get the more precise speed.
I buyed the sprockets by doing the calculations in the gear commander and it was supposed to have 170kms of top speed (106miles).
I think is more something in terms of jets, the top end of the bike is very flat, i need to get a RPM gauge to know what is the RPM the bike does.

[JimDirt]

I am not sure your gear calculator is accurate , i can not see you getting 106 mph with that gearing , i would think you would need a 14/48 to be closer to the speed your looking for , not a 14/51 , stock (here in the U.S.) is 13/51 with a top speed of about 85 mph , 1 tooth on the front is equal to about 3 teeth on the rear , i think you need to drop 3 more on the rear (from the 51)

Try the calculator i posted the link to , i think it will differ from the one your currently using , and be closer to what i suggested for the ratio , especially when using super moto wheels , since they are gearing down the bike , since its rotating faster , but not going the same distance per revolution as the off road wheels are because they are physically smaller in diameter , so if you were to use the 14/51 with the off road tires , i believe your top speed would be higher than with the super moto wheels , so i would go 14/48 or even 14/46 to make up for the smaller wheels

[kaiserkaiser]

I am not sure your gear calculator is accurate , i can not see you getting 106 mph with that gearing , i would think you would need a 14/48 to be closer to the speed your looking for , not a 14/51 , stock (here in the U.S.) is 13/51 with a top speed of about 85 mph , 1 tooth on the front is equal to about 3 teeth on the rear , i think you need to drop 3 more on the rear (from the 51)

Try the calculator i posted the link to , i think it will differ from the one your currently using , and be closer to what i suggested for the ratio , especially when using super moto wheels , since they are gearing down the bike , since its rotating faster , but not going the same distance per revolution as the off road wheels are because they are physically smaller in diameter , so if you were to use the 14/51 with the off road tires , i believe your top speed would be higher than with the super moto wheels , so i would go 14/48 or even 14/46 to make up for the smaller wheels

JimDirt the calculator i used was that . The bike is with 13/42 at the moment doing 94miles(151kms) of top speed like i show in the video. The stock gearing is 13-51 here too but i changed for 14-51 when i was still waiting for the rear sprocket and supermoto wheels.
I know the 17 decrease the top speed and i needed to compensate with the sprockets but i didnt tought that i will stay with the same top speed.

[JimDirt]

Swap out that 13 for a 14 and see how it works , i bet you will be a lot happier !!

[kaiserkaiser]

Swap out that 13 for a 14 and see how it works , i bet you will be a lot happier !!

With the 14 i got less top speed and less wheelie power .

[JimDirt]

How can that be ??? , your gearing UP with a 14 not down

[kaiserkaiser]

How can that be ??? , your gearing UP with a 14 not down

That is something that i dont understand too but i lost two miles of top speed with the 14. People say that 14 is too much for the bike but i dont believe because she feels still short geared.

[JimDirt]

In checking around i am finding that the Honda Baja guys were gearing 15/47 and topping out at 108 in the dirt , ans 115 on pavement

[kaiserkaiser]

In checking around i am finding that the Honda Baja guys were gearing 15/47 and topping out at 108 in the dirt , ans 115 on pavement

The 17's wheels takes a lot of top speed and that baja bikes are not stock . I need to change the exhaust for the CRF450R of 2005 and change the air filter and remove the backfire protection. More air flow maybe will help.

[JimDirt]

That is what i have on mine is the 05 muffler and airbox cut out , with a Pro Moto Billet Spark Arrestor , along with the Pink Wire Mod , and a HotCams Stage 1 (you would like a Stage 2 , or a R cam for your application)

And maybe on the gearing go 14/43 , that should give you some top end speed back that the SM wheels take away

[kaiserkaiser]

That is what i have on mine is the 05 muffler and airbox cut out , with a Pro Moto Billet Spark Arrestor , along with the Pink Wire Mod , and a HotCams Stage 1 (you would like a Stage 2 , or a R cam for your application)

And maybe on the gearing go 14/43 , that should give you some top end speed back that the SM wheels take away

I dont have idea wich hotcam i have, you have the full exhaust or just the exhaust slip-on ?

[JimDirt]

I have just the slip on , stock X header , if you have a HotCams , then it will be very RPM/Power selective

Stage 1 is for Bottom End and Mid-Range only , it has no top end power at all , it is designed for single track riding where your needs are bottom end power/torque

Stage 2 has less bottom than Stage 1 , but has more Mid-Range and more Top End , it is designed to be a "all around" cam , it has decent power everywhere in the RPM ranges , most guys that ride/race desert prefer this cam

Stage 3 is decent Mid-Range and the best Top End , with no Bottom End , and best suits a heavily modded engine , it is best suited for racing Baja , etc , where mainly speed/top end is desired with about stock power on bottom end , again , it only shines with a heavily modded engine

The stock X cam is OK bottom , Mid and some top , but is not as strong as any of the HotCams in any given RPM range , it "works" everywhere in the RPM ranges , but is not great anywhere in the RPM ranges , its quite mellow all around

Then you have the different year R cams , (stock Honda cams 02-08 ) that each have their own benefits depending on your needs

[kaiserkaiser]

I have just the slip on , stock X header , if you have a HotCams , then it will be very RPM/Power selective

Stage 1 is for Bottom End and Mid-Range only , it has no top end power at all , it is designed for single track riding where your needs are bottom end power/torque

Stage 2 has less bottom than Stage 1 , but has more Mid-Range and more Top End , it is designed to be a "all around" cam , it has decent power everywhere in the RPM ranges , most guys that ride/race desert prefer this cam

Stage 3 is decent Mid-Range and the best Top End , with no Bottom End , and best suits a heavily modded engine , it is best suited for racing Baja , etc , where mainly speed/top end is desired with about stock power on bottom end , again , it only shines with a heavily modded engine

The stock X cam is OK bottom , Mid and some top , but is not as strong as any of the HotCams in any given RPM range , it "works" everywhere in the RPM ranges , but is not great anywhere in the RPM ranges , its quite mellow all around

Then you have the different year R cams , (stock Honda cams 02-08 ) that each have their own benefits depending on your needs

I mainly use the bike for twisties and wheelies, having fun ...
The best for me would be a CRF450R cam, i know they are different from year to year, but for now i will only want to change the exhaust because the header is all bent and the R exhaust give me better throttle response and i prefer the design.

Thank you for the time spent explaining