WR/EXC Trans Ratios



4 replies to this topic
  • PhantomWR

Posted April 27, 2003 - 09:01 AM

#1

I need some advice on the KTM EXC-450 6-Sped Tranny in comparison to the WR-450 Tranny. I have never riden a 6 speed anything. Sounds like knitting to me. Knit one Pearl Two. Kind of like gear grinding a Semi.

The Yamaha and KTM websites are useless in getting good specs.

So the KTM has got a 6th gear. How tall does the 6th gear get you compared to a WR-5th? How short is 1st? Are the ratios the same between the two bikes regarding 1st = 1st ? Is the WR-5th = EXC-6th?? Or does the EXC-6th get you taller than the WR-5th.

Bottom line is will the EXC-450 in 6th give you more top end speed than a WR-450 5th?

  • Hick

Posted April 28, 2003 - 09:32 AM

#2

With stock gearing the EXC should be about 8 or 10 mph faster on top.

EXC Ratios:

Primary: 33/76

34/14
31/17
28/19
26/22
23/24
21/26

WR Ratios:

Primary: 62/22

29/12
26/15
21/16
21/20
21/25


First gear is very low on the EXC as well, just slightly taller than WR first.


Hope this helps.

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  • jschner

Posted April 28, 2003 - 06:00 PM

#3

General question about the primary ratios,

EXC = 2.30
WR450 = 2.81
XR400 = 2.83
DRZ400 = 2.96
KTM SX = 2.70? 30/81 (I think).

So what does a lower or higher primary do for a bike or engine like in the case of the EXC and the SX for example?

  • Hick

Posted April 29, 2003 - 05:08 AM

#4

So what does a lower or higher primary do for a bike or engine like in the case of the EXC and the SX for example?




I'm pretty sure the SX has the same primary as the EXC/MXC...

Anyway if you are comparing gear ratios you really need to take the primary and final ratios into account, particularly the former since the latter can be easily changed and really doesn't vary a whole lot from one bike to the next.

If you want to compare WR first gear w/ EXC first, you could calculate total reduction (primary, gear, final):

62/22 x 29/12 x 50/14 = 24
vs.
76/33 x 34/14 x 50/14 = 20

So EXC first is about 20% taller despite the actual gear ratio being very close and the final gearing being the same (I think), this is due to the different primary ratio.

If you take the reduction numbers, plug in an RPM and tire circumference you can calculate speed (RPM/Reduction x Circ = speed in inches/min).


The Primary Ratio is just the number of teeth on the clutch divided by the number of teeth on the main gear. The higher this number is the slower the transmission is spinning.

I hope this answers your question.

  • jschner

Posted April 29, 2003 - 08:29 AM

#5

Hey thanks, I'm just asking a little "why" to this info after seeing the difference in the primary ratios was vastly different. I'm sure the displacement allows for a taller ratio and maybe it's just manufacturer design in the way they get the power to the ground that makes up for the rest.




 
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