smooth gearbox?
 

How smooth do other members find the XTX gearbox is, I ask as I have owned 4 Yamaha bikes over the years, and they have all had superbly smooth gear changes,not so the Xts.

The bike in question is a 2009 model with just under 4000km ,when i engage first gear there is a small clunk and the bike moves forward slightly,changing between 1&2 is good,between 2&3 usually results in a very loud clunk, not smooth at all, but not always. The rest of the gears are all fine, as is changing down the gears.

I have taken it back to the shop and they rode it and said all was fine,that all bikes jump when put into 1st gear ,xts something to do with larger clutch plates engaging,all my other bikes have been 250cc bikes and the gear boxes have all been super smooth, never clunked into gear or lurched forward when first gear engaged.

Its not been a problem, never misses a gear or finds a false nuetral,just feels a bit agricultural compared to past bikes.

Yamaha are usually known for there smooth gear boxes,but the XTX is definately not smooth.

However well designed it is, the gearbox on a big engine, particularly a single, will never be as smooth as a small engine.

When the bike's ticking over at a standstill with the clutch engaged, both sides of the clutch and approximately half the gearbox is connected to the engine, and thus spinning at some speed. The other half of the gearbox is connected to the rear wheel, and thus is not spinning.

When you pull the clutch in and knock it into gear, you've got to connect those two halves of the gearbox together, which means the first half has to stop spinning. Since it has mass it also has rotational inertia, which means it wants to keep spinning.

The more torque a bike makes, the bigger the clutch and gears will be to cope with that torque, so the more inertia they will have. The bike itself also has inertia, which is why if you push it around it's hard to get it moving, but once it's moving it's hard to stop it (without pulling the brakes).

Imagine you have three marbles, a big one, a medium-sized one, and a small one. The big one represents the bike. If you sit that one on a table, and roll the small one towards it, when they collide the big one will hardly move - the inertia of the bike is much greater than the inertia of the gearbox internals. Roll the medium-sized marble at the big one at the same speed, and the big one will move a bit more - the bike with a heavier clutch and gearbox is more able to jolt the bike forwards when you engage gear suddenly.


Apologies if I've over-simplified this to insulting levels. It's a bit tricky to guess someone's knowledge of physics over the internet!

Thank you ,excellent reply ,believe me you could never over simplify it for me,so why is 2nd to 3rd so bad and the others smooth.

The same physics applies for gear changes once you are on the move, except in this case both 'marbles' are moving, but at different speeds.

In general, the gear ratios get closer together the further you go up the gearbox, so you'd expect to get less of a jolt shifting from (say) 4th to 5th than 2nd to 3rd.

However it's complicated by the fact the gear ratios may be a bit irregular, and that some gear shifts involve moving multiple gears on different shafts in the gearbox. So short of taking your gearbox apart and measuring it, I can't really say why some shifts are better than others!

thanks again,thats put my mind at rest.

The XTX is not Yamaha, it's a Minarelli engine into an italian chasis. Japaneses bikes are a lot smoother, I have owned several jap thumpers, and they are smooth. however I have to agree wit h u berthumper, bikes with a wider gear ratio are less smooth.

have fun,

j.

So, uberthumper, why does my bike drop out of gear when accelerating hard/under load? The gears it drops out of are from 2nd to neutral, and from 4th to 3rd. I've never had any bike drop out of gear like this before.

I'm going with operator error :p

Can I have that fixed under warranty?
It was a serious question, it's bloody annoying.

Different engine oils also effects the XT gearboxes, make sure you are using 10/40W if you want a smooth gearbox. I use Motul 5100.