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YBR 125 - bigger front sprocket pros and cons

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Hi to all,

I had a search of the forum but couldn't find a specific answer - so thought i'd post and see if anyone had experience of adding a toth the the front sprocket of the YBR 125. This is my first post.

I've an 07 YBR 125 and am considering getting 1 tooth extra front sprocket. This is to try to increase the top end (hoping for 5mph extra - where wind isn't against me). I'm also hoping that it will allow me to go a bit faster in the lower gears. for example, at 40mph i'm very comfortably in the top gear. With an extra tooth on the front I'd like to be able to use 4th instead. The same applies for most of the lower gears.

So, here are my questions. Does anyone agree that this change would be beneficial? anyone think of any pitfalls? i expect to lose some acceleration, but it can't be that much as i commute through london so accelerating ahead of cars at lights is quite important!

Also, a technical question - can I just swap out the sprocket, or do I need a new chain as well? I've had different answers from friends on this. I need to know what to ask for when (if) i take it to my local dealer to get the work done.

Thanks for any advice that you can offer.

Jay

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I don't have experience with the YBR but i doubt it has an excess of power. Back in the days of blue smoke and fumes one up on the front could give you around 10% extra in terms of available mph/RPM. If that is to be turned into speed you have to have the power to pull it.

You have already commented on the effects of wind with the bigger cog it will be funnily enough around 10% worse. You will get a bit more in each gear too but you could affect the way the gears overlap so you could drop completely out of the available power changing up from 4 th to 5 th. Used to happen to a GP100 i had regular if i didn't cane it in 4th :icon_mad:.

I am talking worse case and in all likelyhood you will get some gains, don't forget though you may need a longer chain and don't get suckerd into messing with the sprocket at the rear unless you are changing both sprockets for a specific ratio change as the difference is tiny.

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ok 1 tooth isnt going to make any noticeable improvement ur better off going up or down by 3 teeth,

ok if you get more teeth you get more speed with lower rpm (that is if you have the torque to pull it) and less teeth gives you more pulling power which = acceleration but at higher rpm.

if you get 3 less teeth and put a bigger main jet in the carb to give you more torque, that way you would be able to get to a good speed, fast but ur over all top speed will suffer for it.

but if you put 3 extra teeth and put a bigger main jet in the carb then you should get the same pulling power but more top end speed at a slightly lower rpm (works out better for the engine)

if it was me id put 3 extra teeth on and jet the carb then if i wasnt happy i could put the original sprocket on but still keep the added torque produced by the bigger jet.

with regards to chain, it depends on how much slack you have when you put the back wheel as far forward as you can but you should put some cash aside for a longer chain.

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ok 1 tooth isnt going to make any noticeable improvement ur better off going up or down by 3 teeth,

ok if you get more teeth you get more speed with lower rpm (that is if you have the torque to pull it) and less teeth gives you more pulling power which = acceleration but at higher rpm.

if you get 3 less teeth and put a bigger main jet in the carb to give you more torque, that way you would be able to get to a good speed, fast but ur over all top speed will suffer for it.

but if you put 3 extra teeth and put a bigger main jet in the carb then you should get the same pulling power but more top end speed at a slightly lower rpm (works out better for the engine)

if it was me id put 3 extra teeth on and jet the carb then if i wasnt happy i could put the original sprocket on but still keep the added torque produced by the bigger jet.

with regards to chain, it depends on how much slack you have when you put the back wheel as far forward as you can but you should put some cash aside for a longer chain.

But, re-jetting the carb wont do anything (only upset the enging) unless you give it more air on the intake and more room for the said air to excape, (free flowing exhaust)

Me thinks 3 teeth up is alot for the front sproket, i would only go 1 tooth or max 2 teeth. 3 teeth up is like taking 1/3rd away from the power of the engine.

Thats just me thaughts on it.

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+1, 2 wheels, changing the carb jet will do nowt bar make things worse. And 3 teeth off the front? crikey, thats huge.

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Aint YBR's fuel injected anyway?

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Aint YBR's fuel injected anyway?

Dunno, its one of those engines that has its fuel without ANY oil in it, can you imagine? :D

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Dunno, its one of those engines that has its fuel without ANY oil in it, can you imagine? :D

No oil, But..but...but   i've been premixing my rental YBR for weeks!!!! what madness will they come up with next,   :crylaugh:

Suck > Squeeze > Bang > Blow!!!    :unsure:  WITH oil 

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Suck > Squeeze > Bang > Blow!!!    :unsure:  WITH oil 

Vez this is the MOTORCYCLE forum....... :D

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I've an 07 YBR 125 and am considering getting 1 tooth extra front sprocket.

Jay

I think theres a thread in workshop titled Sprockets " goes into great detail . i think u"l find 1 tooth up on front is a big jump, i did put a 17 tooth [ +2] on the DT400 , big mistake, no real power-band, and if a headwind, dropping gears all the time, as for +3 , i doubt if they"l be room in the front casing,:unsure: . Also yamaha spent a lot of time getting the gearing correct for the BHP. output. . B)

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Vez this is the MOTORCYCLE forum....... :D

Thats what you think, its just a front i tell ya  :whistle:

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It may give you some gains in the lower gears but on the 08 and 09 models (injection) it's almost impossible to get the bike up anywhere near the red line rpm wise anyway so I doubt an extra tooth would improve the overall top speed.

Typically I'll get 60-65mph in top gear on the flat with a little tail wind and have had 72mph on a hill, still not touching the red line.

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The benefit of 1 tooth will be:

Naximum torque at higher speed. I have to write it in km/h. Usually ('05 YBR) approx. 8500 to 9000 rpm at ~100 km/h, 8000-8500 rpm at ~85 km/h.

Trying to overtake a lorry with 85 km/h while the peak of torque was at about 70-75 km/h -> kind of an andventure.

So 1 tooth more -> more torque when you need it.

I do not care about the maximum speed. So it does not bother me if it would bei 100 or 104 km/h. ;)

_____

I have read that more than 1 tooth (15 instead of 14) ist not possible without carving some metal of the box.

Someone with a 16 teeth sprocket here to verify or falsify that statement?

Greetings, Martin

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Ok. I know this is waaaay after this topic got started, but I'd like to throw in my 2 cents.

I had a +1 tooth sprocket installed on my 2007 YBR and it makes a heluva difference. For example, each gear increased 5km/h to 10km/h and in the end my 4th gear's max speed does what my 5th gear did before the upgrade. That means I effectively have an extra gear. Yes, you loose a bit of power (no more than 5%) but I quickly fixed that by upgrading to a Cowley free flow exhaust, bigger jets and a new air filter/intake (Yamaha can help you with all of this and it's cheap). A bit overkill for a 125cc, but worth it when you can't have a bigger bike. Pull away is also well enough to beat 99% of bikes below 220cc.

Fuel consumption went down from 38km/l to 32km/l AND considering I have 28992km on the dial.

My top speed on average is above 140km/h and uphills are about 115km/h.

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I've been looking to purchase a smaller rear (1 or 2 teeth less) for my '09 fuel injected YBR since carrying out a few subtle modifications which has left the engine revving into the red and hitting over 10,000rpm in fifth gear on occasion.

Could anyone please advise where I might actually purchase one from or if there is another Yamaha model using a sprocket of identical dimensions but has less teeth?

ric.

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I've been looking to purchase a smaller rear (1 or 2 teeth less) for my '09 fuel injected YBR since carrying out a few subtle modifications which has left the engine revving into the red and hitting over 10,000rpm in fifth gear on occasion.

Could anyone please advise where I might actually purchase one from or if there is another Yamaha model using a sprocket of identical dimensions but has less teeth?

ric.

Don't bother with smaller rear sprockets its a waste of time, you will also be screwing with the sprocket to wheel ratio which although static affects the amount of power needed to actually turn the wheel.

Stay with the front cog go up a tooth there or maybe 2. Don't get dragged into the hype like the previous post, 90mph on a naked 125 4 stroke don't make me laugh, the YZF needs to be fit and lucky to break 80.

And as a final note, start your own thread, a lot more people will read it.

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