going through gears so fast

[markrolls88]

i have bought this new bike its a import bike 125 i can get 50 mph out of it 60 down hill what the problem is, i go through the gears so quick its unbeleivable so when im in 5th gear i am screaming the hell out of it but it wants to do more if i change the rear sprocket and front sprocket will this fix my problem as the rear sprocket looks tiny but what are the sizes i can get cos i dont have a chain tool so i dunno how to go about getting the right size chain for the sprockets
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sparky

[Frost]

Smaller rear sprocket = higher top speed

[snowdude2004]

Could go for a bigger front sprocket which will add more top end and reduce your acceleration too though
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CBT passed: 26/09/09, Theory Passed: 18/08/10, Mod 1 passed: 20/10/10, Mod 2 passed: 26/10/10.
Current Bike: Honda CBR 400 Nc23

[markrolls88]

yea but if i change the size of the sprocket getting the right size chain will be difficult
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sparky

[Ariel Badger]

You just buy standard chain and chop it to length.
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Bikers make great organ donors, get 115 on your licence today.

[DrDonnyBrago]

[dextersaurus]

Treat it to a new chain when you replace the sprockets.

To be honest, that's a 125 for you. you can't really mess about with the gearing too much, as they're built to work best standard.

You'd probably be better just getting a smaller rear sprocket - That'll give you more top end, but you'll lose a bit of acceleration. So you'll not get through the gears too fast.

Say... 2 teeth less in the rear, should give you about 10mph?

Dunc

[Teflon-Mike]

Depending on what it is, and the gearing it has, and the power it has, 55ish may be all it will do whatever the gearing.

From the fundemental defanitions of physics, Power = Force x Speed, so Speed = Power / Force

We then need to look at the forces in action, from either end.

Engine is making force; comes from the bang inside the engine, where the petrol and air burning make a pressure, which multiplied by the area of the piston gives a force, then the leverage of teh crabk-shaft, makes it a torque, that then gets multiplied by the reduction gearing through the transmission to the back wheel, where it becomes the 'motive force' pushing the bike along the road, over coming the restistive force of drag, mostly wind resistance.

Important thing about wind resistance, is it increases with speed, more importantly, it increases exponentially. Wind resistance at 60mph is something like four times what it is at 30mph, not twice.

Right. See-saw principle. On one end of the see-saw we have the engine, making force, on the other end we have drag resisting it. When the engine makes more force than drag, bike accelerates. When drag is greater than force the engine makes, bike slows down, when the force the engine makes EXACTLY balences the drag, bike travels at constant speed.

Now, the gearing on a bike controls the ratio of engine speed to road-speed.

Engine may rev from idle, say 500rpm, to the red line of say 10,000rpm.

Typical 172 rear wheel will have a rolling diameter of about 500mm, so a circumference or about 1.7m, which means that it will turn roughly 1000 revolutions per mile.

So to do 30mph, you need the back wheel to turn 30x1000 revolutions, per hour, or 500rpm.

Engine can spin up to 10,000rpm, back wheel needs to turn 500rpm, so you need an overall gearing 'reduction' ratio of 20:1 between crank and wheel, right?

Do the same maths to max out at 60, and you need half the reduction, or 10:1 between crank and wheel, so that the back wheel spins at 1000rpm. To do 100, just under 1/3 the reduction, or about 6:1

HOWEVER, the FORCE you get at the back wheel, is inversely proportional to the gearing.

Back to the see-saw, and the gearing ratio is like moving the pivot.

Low gears are like having the pivot closer to the end with the wheel on. You dont get much speed, but you get a lot of force.

High gears are like having the pivot closer to the engine. You can get a lot of speed, but not a lot of force.

NOW we have the problem; Raising the gearing will turn the back wheel faster, BUT the engine is still delivering the same amount of force.... but becouse the gearing is taller, you get less of it at the back wheel.

However, for the same speed, the drag that force is needed to over come, hasn't changed, worse, the drag at the higher speed you WANT to go at, is even greater.

SO, if the bike in question is geared correctly for top speed, raising the gearing will NOT make it go faster, becouse raising the gearing, will reduce the motive force. So more LIKELY it will actually make it SLOWER, as with the higher gearing, it will ONLY be able to go as fast as the drag it can over-come, and with less motove force at the wheel, you will only be able to over come the lower drag at a lower speed.

THAT is the 'fundemental' truth of the matter.

You could gear a moped up to go faster than the speed of sound, if you really wanted to, but without the POWER to back it up, and shove the bike through the air at that speed.... never going to happen.

Getting 'practical' though, bikes are rarely geared optimally for top speed, and when I described the fundementals, I presumed that the engine ws making a constant force at the piston top regardless of how fast it was turning.

In practice, engines have a power-curve. Force they make varies accross the rev range. At lower speeds they tend not to make much power, as the crank-speed increases it ramps up to a peak, and then it starts to trail off a bit as the engine aproaches max revs.

So when you decide on the gear ratio to use, for top speed, you would want to select the reduction ratio that turns the back wheel at the speed you expect to go, at the speed the engine makes max power, not max revs, but the story would pretty much still be the same; Speed = Power / Force, so upping the gearing wouldn't get you going any faster.

BUT, second presumption, most bikes aren't geared for max speed. MOST are actually geared HIGHER.

Reason for this is that the force the engine makes is variable. Its not JUST dependant on the crank-speed, increasing as the engine turns faster, but it also varies on the throttle opening.

Close the throttle, and you choke the flow of air into the engine, you limit how much gets burned in each bang, you restrict the force the motor makes.

In practice then, 'max' power is a very particular set of conditions, a particular engine speed, under a certain load, with the throttle wide open.

But at something LESS than 'max-power', which on a 125 lests say is 10bhp, you can get say 8bhp from any number of different perameters; the engine turning a lot faster or slower than max power rpm, or running closer to max power, but on a part throttle.

AND, as said most bikes TEND to be quite significantly over-geared. Bike might only have the power to over come the drag at 60mph, but if they geared it so that it was at max power rpm at that speed, then come a hill, and a little gravity assistance, big risk of easily over reving the engine, and mashing valve gear or stuff driving the motor a lot faster than it can tolerate. So they over gear it, so that even of you got it up to about 80, still wouldn't rev the engine TOO far beyond 'safe' limits.

Other reason they over-gear, is reliability and economy. Reving the nuts of the motor under full load, will wear it out faster, and will be burning a lot of fuel. Gear it up, a 'bit' and in that 'tolerence zone' where you get 80-90% of max power, you'll still get enough force to go 'almost' 60mph, but be able to do it with a lot less revs, and more throttle.

So, NOW you understand gearing....... lets look at this ere Chinky-bike and think about whats going on!

First off, is it a cruiser, dirt-bike, commuter or 'sports-bike'?

Cruisers often have much bigger and heavier frames around thier little motors, and then have high wide bars. High wide bars spread the rider out like a parachute, increasing drag, so they wont go as fast to begin with, so they need lower gearing, but also, the heavier frame means that they take more shove to get them moving, so benefit fromlower cogs there too, so tend NOT to be geared higher. So for any given speed they will normally be reving higher.

Dirt-bikes tend to be lighter, but they still have wide bars, so again more drag, but dirt-bikes are expected to wheelie, and throttle response, and acceleration are more important in dirt-riding than top speed, so again, they tend to be geared lower.

Commuters, are the general purpose machine. Tend ot to be so heavy, wont have such high or wide bars, and will normallty be slightly over-geared, becouse ecconomy is the more significant criteria, and over-gearing, reduces acceleration, and if over done enough, top speed, and that makes the MPG figures look good.

Sports-bikes, you would expect would be geared for top-speed, thats what they sell on. BUT, on a 125 sports-bike, chances are they have taken on quite a bit of weight and bulk to give them the full-faired 'sports' styling, and if whats lurking underneathm is essentially your standard commuter model, possibly that they have been given a lower gear-set to move the added mass, brisken up the acceleration, and give that added notch or two of top speed, RATHER than any more power! Yes the fairing may inprove aerodynamics a tad, but, err not a lot!

SO... most bikes are over-geared, BUT on all but a commuter, Learner-Legal, chances are they are not AS over-geared as bigger bikes, and on a Chinese Import, NOT made to the standards of western bikes, and without as much power, probably geared a bit lower still.

Lets look at what you wrote:

[danjameswhitt]

[pa_broon74]

[markrolls88]

its a chineese import its a kinroad xt 125-18 see before i had this i had a cg 125 and i could get 75 and 50 was no problem this is the same cc and it screams at 50
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sparky

[0ddball]

[Blue_SV650S]

if you get 1t larger front,the current chain will probably be ok. ... you will just have to move the adjusters in a bit.
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The purpose of life is to fight maturity.

[N cee thirty]

wow that was one hell of a write out
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'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[flumpy7]

[Teflon-Mike]

[Frost]

Dammit, i always start to read your posts, scroll down and realise its a foot long then have to abandon it. Which is a shame as that one started off so well.

[markrolls88]

i got it second hand with less than a thousand miles on the clock for 400 quid
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sparky

[Teflon-Mike]

[markrolls88]

i cant wait to get a big bike but when i pass my test do you think i should get a 400 or get the bike really want a gsxr 600 do you think going straight for a 600 will be too big of a jump if i did get a 400 i was thinking like a vfr 400 or a CBR 400
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sparky

[Frost]

The 400's are all old, abused, expensive for what they are and in high demand. People (usually young ones) want sports bikes as they look cool and go faster, so they have got to be good in every way, right? Not always. Truth is they aren't what most people expect, they are unfomfortable, a pain in the arse to ride at times, difficult to work on, a target for theaves, a good way to attract police attention, fast enough to cost you your licence in a heartbeat, and cost a fortune when dropped.
I'm not saying don't get one, i'm just saying there are other bikes out there that won't cost a fortune to insure, might be a better choice for your only mode of transport. Getting a non sports can still be cool and fun (cruiser, supermoto, naked, retro, whatever), have fewer draw backs, more beginner friendly power wise and give you more choice.
So if your hearts set on a sports bike, go for it. If not, have a look around and try not to base it 100% off looks like most people seem to. Try sitting on a few bikes at a dealers and see what you think about the size, weight, seating position etc.
In terms of specific bikes: Bandit, CB500, diversion, er6, hornet are all great all rounders that will be sure to please until you decide what exactly you want out of your next bike.

[Teflon-Mike]

Pretty much of a mind with Frosty on that question.
I'm NOT a sports-bike fan, to begin with, and I DONT think that they are a great tool for a newly qualified rider, in any capacity.
they are just to compromised for speed & style.
The 'conventional' bikes work a lot better, as a road-bike and every-day machine, and TENT to be an AWFUL lot less hassle and expense to run.
My 'eldest' is the typical 'wont-listen' hot-head, and after I got him a C50 at 16, has gone through a succession of bikes between 125 cc and now 900, that suit his sense of 'style' and aspirations of 'performance', but unfortunately NOT his bank-balence or ability, that he has variousely, blown up, thrashed to oblivion, crashed or simply had laid up waiting his Student loan to come through so he can either get it fixed, MOT'd or Insured, or as often as not, all three!
As a young rider, on a budget, as your sole and every-day means of transport....
I HAVE to say, that being BORING pays!
Something like a CB500 is NOT glamourouse; it is NOT fast, and it is about as exiting as a wet weekend in Grimsby, with your best mates glamourouse girlfrends Fat ugly sister for company!
BUT, a wet week-end in Grimsby, with a real life, wet, willing woman, no matter HOW fat and ugly, is a LOT more entertaining than a sunny bank-holiday in Skegness, with a wallet emptied by a fit-blonde who has just dumped you, becouse you cant afford another drink..... let alone the petrol to get home!
Also, fat ugly girl that goes all the way, tends to be more satisfying than fit-blond that wont.....
Which is a pretty reasonable analogy of what riding a 33bhp restricted sports 600 is like..... you just KNOW it has SOOOO much more to offer, but you aren't allowed to do more than fiddle with the bra-straps!
somewhere in the middle though lies a compromise; and its called a GPz500S, or an SV650.
Both 'sporty' twins; GPz has already been lauded, and I have to say they are a good little bike, with teh attraction fo a lower price tag than an SV, and lower tax and insurance, being smaller capacity. BUT older, and oft abused by LOTS of post learner loons; they CAN give grief. But then can ANY older and cheaper bike.
But that would be my starting point, & a GPz was the only time Hot-Head eldest kept things together for any length of time!
four years of hot-headed-ness, he eventually listened to reason and got rid of the nail of a CBR6 he had completely failed to get on the road, but STILL managed to crash, and 'encouraged' to get a 'sensible' bike, got a GPz5S from a dealer, on 12months finance!
fourteen months later, it was incredibly still alive, despite his best efforts to kill it through neglect and abuse, though a timely MOT half way through helped! when the restriction lapsed on his licence and he lost his head again and traded it in for a 'cheap' RF900, that only needed 'a bit of tarting up'... it never got, being ridden into the ground, and crashed (frequently!), layed up whenever the direct Debit for the insurance bounced, or something critical, like the exhaust fell off or a spark-plug popped out the head..... and he was back to his 'usual' self, moping about grumbling he had to CYCLE to Uni on a push-bike or WALK to the train station to go see his girl-freind, and moaning that he'd be in the bad-books with HER becouse he was broke and couldn't take her out as promiced......
ANYWAY...... thats all pretty much irrelevent, other than to illustrate the ideas, about being a BIT concervative in your first 'big' bike.... and why playing it safe and boring CAN be more fun!
MEANWHILE, you have a test to get passed, before you need worry about such things! So put your attensions into that one, for now. See what the state of things is after you have the licence in your back pocket. To save the pennies for a 'decent' enough Big-Bike, you MAY have to suffer it a while longer after you have lost the L's...
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Teflon-Mike]

thought just crossed my mind; thinking big-bikes / small bikes, costs and practicality & 'stuff'.
THIS is my 'little baby':-
https://i178.photobucket.com/albums/w269/teflons-torque/XX-Forum%20Posts/DT125.jpg
Thirty something years old, and looking like a nail, its waiting for a little attension to get it streetable. But when done, it will probably not LOOK a lot better, but it will be very mechanically sound and a very useful little tool for hooning about town and down the tracks and trails and back-lanes; and it will have cost me under £500 to put it there, and be cheap as chips to keep it there!

On a restricted licence, dirt bikes make a lot of sense, and CAN be a LOT more fun than a 'boring' commuter or 'sporty' twin.... ANd a lot cheaper to run, especially if you go for a smaller one.

Designed to be thrashed and crashed, they tend to be a lot more rugged than road-bikes, and can take a LOT of abuse.

And steeping OUT of the fast lane, or by-passing it all together; you can get some pretty big adrenaline kicks knocking about on the loose-stuff..... 30mph on the road, is seriousely pedestrian, but 30mph on the rough, the bike bucking beneath you, FEELS so much more exiting, like the sort of thrill you wouldn't get trying to get your knee down on a twisty lane tackled at WELL over the national speed limit!

Old Honda 650 'dominator' is a pretty useful and under rated dirt-donk.
https://images03.olx.ca/ui/1/34/52/8143252_1.jpg
Unloved these days as its 'old hat', and the XR is 'so much better', BUT as an every day bike? Has a LOT going for it, most especially the price tags; you can get a pretty good one for around £750, ready to ride.
650cc it IS a 'big-bike'. doesn't need much restricting to make 33bhp complient, and you can pretty much exploit what performance it has, on road or on dirt, where you CAN get the sort of thrills a restricted road-bike wont deliver.
On road, big enough and comfortable enough to tackle longer hauls, great round town, really manouverable, and easy to manage.
But seriousely cheap to run, and keep on the road, curtecy of low-tech, low stress single pot motor, and designed to be dropped, would take a pretty seriouse desaaster to see it really dent your wallet should you come a cropper.

I know sports-bikes are what ring your bell..... BUT thought I'd just chuck up some food for thought.

If, on a restricted licence and budget, you would struggle to get all you hope for out of a 'big-bike', and sitting it out on a compromise, frustrating, THIS kind of thing (dont HAVE to be an old DT or Domminator) can give you all the benefits of the 'compromise bike' and some 'thrills' to at least vent your frustrations in substitute for a pure sprots-bike until you are off restriction and beyone that, have the budget to achieve your aspirations, rather than fuel your frustrations!
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Digitalize]

Struggling to reach 50mph?

Jesus thats a shit 125, thats the kinda performance i expect from a 50 2 stroker.
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1998 CB600F Hornet

[markrolls88]