the Truth, how fast is your KDX

[Kamofly]

Hey Canyncarvr?...........
what were your 0-60 speeds at the 1/4 mile track?.....If calculated.
Just wondering.

 

[kdxjr]

Milquetoast, everyone was told at the riders meeting, with the sheriff
there that we were using paved roads in the enduro. Not for trasfer between trails, but as part of the enduro. Hey, the wind felt real good
it was about 90 degrees and 110 percent humidity last Sunday in Mississippi. I don't abuse my right to ride public property. I think everyone around here takes that pretty seriously..

 

[craig_enid]

LOL, I just got around to checking.... my watchdog idicates that my top speed at the enduro at Scipio, Okla. was 44mph! MAYBE hit 4th gear twice....
http://community.webshots.com/photo/36706994/36707313HkfAQc
1740 acres of brand new riding area, I was wishing for some paved road!
Carver, the 68.69 at 8,000.... was that with stock sprocket gearing, or your lower 12/47? And what would the mph difference be between your gearing and stock gearing at 8,000?

 

[crashburn36]

i've gotten my 200 up to 74.9 mph using trail tech computer, passing cars along the highway.

 

[canyncarvr]

1. Don't recall what the 0-60 time was. Tossed the time tickets, too! Great!

2. Figures above were 'stock' gearing, as per the service manual stated at 9:1.

Note that those numbers are 8000rpm...which the kdx prolly outdoes considerably. It's not a CR125..but it spins over 8k.

re: difference between? Didn't figure that. How about 'some'?? ;)

 

[kdxjr]

changed sprokets today from 13/49 to 14/48 It feels the same, I thought it would give me more pop down low. Was it a mistake putting the 14 on front. I was thinking today ( I know I shouldn't do that ) will
the 14 stall more in the tight woods..

 

[Jonny426]

Brian 2, You forgot about the primary reduction ratio between the crank and cluch hub. Try it again and see what the sheet says

 

[BRush]

154 mph on a KDX? No problem. ;)

First, there's the primary reduction ratio. This is 63/22 or 2.864

Next there's the transmission ratio, which of course depends on which gear you are in:

1st gear = 35/13 = 2.692
2nd gear = 28/14 = 2.000
3rd gear = 23/15 = 1.533
4th gear = 21/17 = 1.235
5th gear = 25/24 = 1.042
6th gear = 20/23 = 0.870

Last but not least, there's the chain ratio, which depends on your sprockets. Stock is:

47/13 = 3.615

The final ratio is calculated as follows:

Final Ratio = Chain Ratio * Trans Ratio * Primary Ratio


If you know the final ratio, your engine rpm, and your rear tire diameter then you can calculate the theoretical speed for that gearing. Say the rear tire diameter is 26 inches:

:confused:

 

[Dazza]

How fast?
I reckon that if you come off at fulltilt you can really screw yourself up.
I think they are fast enough.

 

[Brian2]

Cool, I missed that primary drive ratio, where did you find that?

 

[Brian2]

I'll work on it, cool chart - how can I paste one in?

 

[Jim Crenca]

No way BRush is goingt to make a careless mistake like that. He varies engine RPM to demonstrate gearing diffeences. Anyone venture a guess how far theoretical speed is from mathematical when calculating with "normal" engine RPM and gearing?

 

[Brian2]

Here is the newly corrected info:
Tire Cir. Axle
85.608 10.8

Axle ratio of 10.8 is rounded to one decimal place, and was calculated by: 13/49 gearing x primary drive ratio of 63/22

Trans. gear 40 mph - rpm required for each gear
2.69 1st 14,326- RPM
2.00 2nd 10,651- RPM
1.53 3rd 8,148- RPM
1.24 4th 6,604- RPM
1.04 5th 5,539- RPM
0.87 6th 4,633- RPM

Trans. gear RPM
2.69 1st 8,000
2.00 2nd 30.- MPH
1.53 3rd 39.- MPH
1.24 4th 48.- MPH
1.04 5th 57.- MPH
0.87 6th 69.- MPH

Now change that 10.8 to 3.77 (13/49 gears) and you'll see how i cam up with the first set of numbers.

 

[Dr.Zaius]

Who in the holy be-jesus cares?! Dorks, man. ;)

 

[BRush]

Originally posted by Jim Crenca
No way BRush is going to make a careless mistake like that. He varies engine RPM to demonstrate gearing differences. Anyone venture a guess how far theoretical speed is from mathematical when calculating with "normal" engine RPM and gearing?

Hey, I only want to show what it takes to make a KDX do 154 mph. Just make the engine spin at 17,924 rpm ;) (or drop it out of an airplane). Kind of reminds me of the old Steve Martin Joke "How to be a millionaire and never pay taxes". Step one: get a million dollars....

 

[WoodsRider]

BRush - I don't think there's enough room on Catra's H/S track to hit 154. I bet if we take a KDX, install e Rev pipe, mix a gallon of octane booster with Sunoco pump 94, install the smallest main jet and wire the throttle WFO we might get the motor to spin at 17,000 RPM... for a micro-second. :scream:

 

[canyncarvr]

I don't have any problem with 17k rpm on MY kdx!

Just a minor issue of semantics (and a bit of grammar):

rpm=Revolutions per Minutes.

.....about 2 oughta do it ;)