ttr-125l gearing change

[will pattison]

these ttr posts reminded me of something. one of my wife's complaints racing her ttr-125l in cross country events is lack of top speed in the fast sections. gearing it taller didn't seem like much of an option because of the 1 piece sprocket. so, when somebody suggested that we drop the stock 54t rear sprocket to a 49, i was skeptical...until i rode one. i never would have figured that the thing would pull 5t smaller on the back, but it does it handily. turns out, the smaller ttr-125 comes stock with a 49. i bet that if you worked out the final gear ratios that they would be about the same, which also suggests to me that yamaha purposed geared it not to go very fast. makes sense for a beginner playbike.

anyhow, we switched to a 428 o-ring chain and a 49t rear sprocket, and what a difference. it'll still pull like a champ up the steep stuff, but it has legs now, too.



------------------
will pattison
engineer, racer
ignition
www.ignitioninc.com

 

[Vic]

Stock- 54/13= 4.154

Popular- 54/14= 3.86

Will's- 49/13= 3.77

 

[simimi]

OK, so that is cool. I have recently upgraded to the L chasis so I have both rear sprockets.

I have heard that it can make a difference which sprocket you change even though the final gearing may stay the same, does anyone know about this? (so would it be better to go down 4 in the rear, or up one in the front, or does it matter?)

Thanks,

Mike

 

[HGilliam]

The larger front sprocket is better because the chain doesn't have to turn a small radius thus increasing chain life. It also reduces wear on the swingarm rub blocks. I wonder how it would pull a 14/49?

Howard

 

[theMotoMan]

Originally posted by will pattison:
gearing it taller didn't seem like much of an option because of the 1 piece sprocket. turns out, the smaller ttr-125 comes stock with a 49. i bet that if you worked out the final gear ratios that they would be about the same, which also suggests to me that yamaha purposed geared it not to go very fast. makes sense for a beginner playbike.

What do you mean a one piece sprocket?

To expand on what Will said, Yamaha put a smaller rear sprocket on to compensate for the smaller rear wheel. TTR-125L = 16", TTR-125 = 14". Adding a larger diameter rear wheel effectively increases speed, so they geared the L model down.

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01 YZ250F
00 TTR-125L
00 TTR-90
00 PW-50

 

[will pattison]

uh...i dunno about yours, but ours has a 1-piece rear sprocket.

anyhow, i did the math, and the 3.77/1 ratio gives about a 5 mph advantage at 3600 countershaft rpm on the l-model. i don't know what the stock countershaft on the smaller ttr is, but at 3600 countershaft rpm, the speeds for the stock l-model and a 49/13 combo on the 14"-wheeled model are 41 mph and 39.77 mph, respectively.

wp.

 

[Vic]

Will- I think theMotoMan wants to know why you specifically mentioned the one piece sprocket, when that is what most bikes have.

 

[will pattison]

oh...hello! that's what i get for trying to handle mail at 6am! what i should have said originally was that i believe it's an uncommon sprocket design- not one likely to be made by renthal, sunstar, afam, sidewinder, jt...you get the idea- and that therefore it would be hard to find optional sizes. of course they all have one piece sprockets...

my bad!

wp.

 

[Vic]

I called Sprocket Specialists a while back, and they have some rear sprockets available for the TT-R 125. Sorry, I don't remember the available sizes or the price. I do remember that I thought the price was too high.

 

[will pattison]

i think retail on the oem part is around $45.

wp.