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aevans692

bike gearing , sprockets ??'s

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Hi all , so I picked up my bike this weekend, am very pleased ..  

 

I have noticed that the previous owner is running 38 on the back and 9 on the front sprockets ...  Im sure that standard for the TRS RR that its 40 and 10 ..   

I understand a little about gearing, but not 100% sure what is happening with this , I'm guessing that its lowered the top end and increased the low end response  ??  is this correct, what would be the reasoning behind it be, what's achieved  ??  

 

Any info would be great ..    Cheers .  .  

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I don’t know the standard TRS gearing but if you’re right you are geared down about 5%. It will be easier to get through the awkward bits without slipping the clutch but will run out of revs a bit sooner. I would be inclined to go back to standard. Chains don’t like going around small sprockets so a change from 9 teeth to 10 will significantly improve chain and sprocket life.

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In effect they have changed the gearing the same as if they had fitted a 42tooth rear sprocket, not sure I would have done it the way the have.

As said before the 9tooth front sprocket wears the chain quicker & has a shorter lifespan due to the tighter radius the chain goes around

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Ok sure , its easy enough to swap bk to standard .. 

What purpose has it served by gearing the bike down , is it beneficial in any way ?   bit of a newbie question ..   ;) 

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Gearing is virtually identical, just achieved in a different combination. Run it till it needs replaced, then go for standard as is easier on chain as stated above.

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sure , ...   

Im guessing its been done to make the bike a little more responsive in lower revs and maybe slower moving for stuff..  or maybe the shop didn't have any other sizes .. lol ...  

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When I bought my 15 Sherco, I found it nervous and I felt the first gear '' too long ''. I change the rear sprocket from 40 to 42t. I'm now more confortable in slower section and I feel more control with the throttle. You might think the opposite since the gearing in shorter, but it did the job for me.

Guy

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Think of it as a change of gear speeds, so instead of 1st, 2nd, 3rd, 4th etc.  You now have..

3/4,  1 3/4,  2 3/4, 3 3/4 etc....    Much the same as old motor cars had an overdrive, which added half a gear.

In agriculture, some tractors have three gearboxes, Rabbit and Snail, then 1,2,3,4th, and then Hi / Lo.

.

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I chatted with Steve Saunders today about the gearing , he said that its a fairly normal thing done , he said that it should tame the bike down a tad ..  said as I get used the bike and my riding improves to move back up to standard ..   but the difference are fairly small , so im told...   

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It took a while to get my head around too as the lower gearing should make the bike feel more powerful but in reality in trials, it slows things down so you can react to things more easily and the bike speed increases at a slower rate relative to the engine speed so you can get away with less throttle control. Trials is a funny old game. 

I'm a newb and I'm fairly comfortable with a 9/40 setup although I've not really ridden with 10/40 properly to compare.

Edited by al_orange

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 Actually 10 and 42 is a very nice compromise. I had told my son to do this as soon as he got his 2018RR. Of course he did not listen. He finally did this a few months ago. He did it to make second more usable  for large splatters as we ride at high elevation.

 I am guessing the previous owner first did the 9 tooth and realized it was too low.

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Im going to be swapping back to the standard 10-40 as soon as I need a new chain and sprocket , also the bike is fitted with a slow throttle tube, so it must be slow in comparison to a standard bike , I haven't had chance to ride a standard one yet

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You know, car racers laugh at motorcycle racers saying we can't even change the overall gear ratio without changing the wheelbase too.  Unfortunately, I have to agree with them.

If the wheelbase changes as a result of the gearing change, this can have a cascading effect on other tuning variables.  Moving the rear wheel rearward lengthens the lever arm acting on the shock.  This in turn makes the shock spring feel softer to the rider.  Without a change in preload, a softer rear spring increases rear sag which changes the bike's fore/aft weight distribution (and therefore traction).  These are subtle, but noticeable, changes and often a rider will subconsciously compensate with a change in body position.

Speaking from personal experience, my OSSA TR250i "works better" in 3rd gear with a 9T front sprocket than in 2nd with the standard 11T.  The overall gearing difference is an almost insignificant 1 percent.

And, yes, a 9T front sprocket is horrible from a chain-life standpoint -- but only slightly more horrible than a 10T or 11T.   Industrial designers generally consider 17T as the smallest sprocket that should ever be used.

Edited by konrad

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