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Makotosun

DT1C vs. DT1CM Transmission Gear Comparison: Which is better for street use?

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Comparing tranmission gears on a DT1C vs. DT1CM, it appears the DT1CM has "close ratio" gears like the DT1E.

For a bike that only sees street use, it seems like the close ratio gears would be a better choice, but I haven't ridden a DT with a close ratio gearbox.  Thoughts?

DT1C   /   DT1CM
Primary Drive Gearing:  3.1   /   3.1
Sprockets:  44/14   /   44/14
First Gear:  2.53   /   2.25
Second Gear:  1.79   /   1.65
Third Gear:  1.30   /   1.25
Fourth Gear:  1.0   / 1.0
Fifth Gear:  0.77   /   0.77

 
25 Jan 2023 22:12 #1

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I'd beg to differ . The close ratio box matches the upper gear ratio's , as do the primary drive and sprockets .
So with a close ratio box , first gear would be quite a bit higher than on the wide ratio box ,
so you might have to slip the clutch a bit taking off . You could gear down the secondary ratio's , to get
the close ratio first gear closer to the wide ratio numbers .
Personally I think it's a lot of mucking around trying to fix a problem that doesn't really exist .
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26 Jan 2023 15:24 #2

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===================================================
So with a close ratio box , first gear would be quite a bit higher than on the wide ratio box, so you might have to slip the clutch a bit taking off.
===================================================

Yep.  Close ratio is probably not as desirable for a lot of around town, stop-and-go riding.  But maybe a bit better for open twisty roads.

But yeah, it's a hypothetical argument for most folks as I doubt anybody is going to separate the cases on a well running engine just to switch between close and wide ratio.  But in my case, I'm building up an engine and have both close and wide ratio parts on hand and could go either way.
 
26 Jan 2023 16:11 #3

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...as I doubt anybody is going to separate the cases on a well running engine just to switch between close and wide ratio.


You don't know some of us very well. 

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I've swapped between YZ, MX, IT, and DT transmissions....  and made a couple of "hybrid" versions by swapping gear pairs.

There are a lot of free "Excel sheet" programs online that will allow you to see speed in gears, RPM drop between gears, etc. 

Things that matter (beyond "powerband") is the primary drive ratio and the final drive ratio.  (And yes, I've swapped primary drive ratios too).  Most common is final drive...  if you run a taller final ratio for more top speed, you'll find more need for "close ratio" gears.  But you need the power to pull that top speed.

If you modify the engine for higher RPM, you'll also need close ratio gears more...  not just if you get a narrower "powerband"...  but because the steps between gears are percentage based.  Shifting at 10,000 RPM will result in twice the RPM drop that shifting at 5,000 RPM will...  all else remaining the same. 

 
 
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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26 Jan 2023 18:36 #4

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