What is the Best Secondary Gear ratio for MX

[Ji Gantor]

I would like to explore what is the best secondary gear ratio for MX bikes.
I know it is determined by the track and the primary gear ratios but there must be a range that better suites MX.
From my research it should be somewhere between 4.0-4.3 to 1.
This ratio should give good pulling power out of turns and off the line.
Most MX bikes have enough gears to make this happen and in fact this may allow the rider to use more of the bikes gears on certain tracks.

Ji

[Ji Gantor]

250 77 Maico's are 56/13=4.3:1
400 73 CZ's are     52/13=4.0:1
125 81 YZ's are     48/12=4.0:1

Ji

[brent j]

Ji,

This ones a bit subjective.

My Suzuki TM125 runs 14/58 (4.14:1) but needs to be geared higher, 15 (3.8:1) or maybe even 16 (3.62:1) front.

My XT500 runs 17/45 (2.64:1) BUT, because of the available torque and flexibility I only need 2nd and 3rd for most tracks. I gear high to get be able to use the bigger gap between the lower gears. I don't need to change gear very often.

It's pretty hopeless for trail riding but on the other hand it will do 100mph!

Brent

[Ji Gantor]

Thanks Brent,
The more I look at this the more I see a pattern.
It does vary between tracks and bikes but it is still within a certain range.

Ji

[jimg1au]

ji
13/52 is std mx gearing for 400 czs
i used 15/52 for my race at nepean (dirttrack)it was too tall so i have just fitted a 14t front
cheers
jim

[Ji Gantor]

Thanks Jim,
When they are to tall you get left behind.

Ji

[brent j]

Actually Ji my original plan was to run gearing so high that I would only need 1st and 2nd for most tracks. That would have given me the biggest gap between gears and greatest flexibility.
I found it is not possible to get a large enough front sprocket fitted without some serious case mods and I'd virtually have to make a new rear hub to be able to fit a small enough rear sprocket.
The ideal ratio would have been close to 1:1 !!!!!!!!!!!!!!!

Brent

[Ji Gantor]

At the Nationals I believe that Glen Bell started in third gear.
If you take a look at images of the start you will see that he was left behind for the first few meters, then as others changed from second to third Glen went past.

Ji

[firko]

250 77 Maico's are 56/13=4.3:1

I change my gearing for different tracks on my Maicos. On the inside of the door on a locker in the shed I've writen the sprocket spread for the various tracks for my 250, 350 and 440 Maicos. For instance..for Nepean dirt track I ran 12/52 on the 250, 12/50 on the 350 and 13/50 on the 440. I'll jot them down later today and post 'em.

[Ji Gantor]

Thanks mate,
52/12 =4.3
50/12=4.16
50/13=3.8

It seems the more torque the closer you can run to 1:1 but still around that 4:1 mark.

Ji

[JC]

Ji,

European bikes tended to run less primary reduction (& smaller clutches) & higher secondary reduction than Jap bikes. Some Euro bikes ran higher than to 5:1 secondary (eg VR 11/59, 4sp Maico 250 11/59) while some Jap bikes run close to 3:1

Too many variables really

[Ji Gantor]

Hi JC,
The more we share and explore the more there is for all of us to take away and try.
What was that quote you once told me.
"As iron sharpens iron so to does one man sharpen another"

Ji

[JC]

Yeh, its true ain't it!

[Ji Gantor]

Yep.

Ji

[Ji Gantor]

When you gassed your engine on the up hills at Conondale you really needed every bit of 4:1 ratio, if you had less in a 125 you were struggling.

Ji