Fastest Speed by Scooter 70

When the scoot isn't gaining speed (accelerating) it means that all the power that the engine is making is used to fight airdrag and roll frictions.
Because of this, there is no power left to increase the kinetic energy (=speed) of the bike.
If the gearing is too short, the variator comes to the end of its range. At this point the engine tries to increase revs, and so it does, but unfortunately after the maximum HP rpm, the power falls rapidly (bad cylinder scavenging). 2000-3000 rpm over the maximum power rpm, an 20hp racing setup will make only ex.:10hp. A scoot with 10hp isn't very fast.
So we try to keep the rpm at maximum power, this way it will stop gaining speed when the opposing "power" of the airdrag matches the engine power. Well, would be more correct talking about forces, but it will do...

The airdrag goes up by square (^2). This is why a scoot does not have a constant acceleration until top speed (if it would have an constant acceleration this means that the drag force would be constant or none, so it would constantly accelerate until near speed of light).
If a scoot with 20hp makes 150km/h, to go 300km/h it would need 80hp.
 
roost said:
When the scoot isn't gaining speed (accelerating) it means that all the power that the engine is making is used to fight airdrag and roll frictions.
Because of this, there is no power left to increase the kinetic energy (=speed) of the bike.
If the gearing is too short, the variator comes to the end of its range. At this point the engine tries to increase revs, and so it does,....

What if the bike with the short geairing has it's rollers/variator set in such a way, that the engine will stay in its powerband RPM.

I mean I could have a full Evo/MHR setup that makes max. BHP 2 say 13.500rpm.

Now long or short gearing, if it stays @ 13.500 RPM, wouldn't it just make peak BHP, regardless of final gear ratio.

And you say "if wants to increase revs, and so it does" I don't get that. What if the scooter can't make any more? Since the variotor is at its end...how would it gain any more RPM's? (yeah I guess if you go downhill, but what if you're on a flat piece of road)

My guess is: that the gearing allows the scooter to still go faster, but since the variator is at its end, it can't "soke up" the revs, so will directly transfer it to the cranks and thus engine speed (RPM) would increase beyond the powerband. (sounds logic when typing it)
My only "but" would be that this would only happen if the gearing would allow higher speed. If variator is at its end and the gearing also can't generate more speed, because it's also at its "end". Then RPM can't increase anymore I would say.
Unless like I said, you would go downhill. Then the scooter will go faster (or wants to) since gravity now also gets a pull on it.

So a scooter with a long(er) gearing will not go into overrev?
What if that scooter also comes at the end of its variator range? wouldn't it also go into overrev? If not, why? (and for this example, both scooters are @ Top BHP RPM when at the end of their variator's range)

I can't see how this would relate to the final gearing. Only that it would take longer for the best geared scooter before it reaches that point where it would go possibly into overrev.
 
And you say "if wants to increase revs, and so it does" I don't get that. What if the scooter can't make any more? Since the variotor is at its end...how would it gain any more RPM's? (yeah I guess if you go downhill, but what if you're on a flat piece of road)

The variator is there to keep the engine rpm at a more or less fixed number.

When the variator comes to the end of the range, the transmission becomes fixed, its no more automatically variable. At that point, if the force on the rear wheel generated by the engine, is higher than the drag forces, the bike can still gain speed. But since the transmission overall ratio is fixed it can only rise the speed by rising the rpm. And so it does. But not for long since the power will fall rapidly.
My guess is: that the gearing allows the scooter to still go faster, but since the variator is at its end,
This is an paradox saying. If the variator is at its end, then the gearings are too short!:)

I think you don't exactly know how the scooter transimssion works.

An example:
On a short final geared scoot the variator working range is from 5km/h to 80Km/h
On a long final geared scoot the variator working range is from 15km/h to 130Km/h

The fact is that on a longer geared scoot the operating range (in Km/h) of the variator is large. The longer the final ratio, the slower the belt will change position, for the same km/h change.
 
roost said:
...

I think you don't exactly know how the scooter transimssion works.

An example:
On a short final geared scoot the variator working range is from 5km/h to 80Km/h
On a long final geared scoot the variator working range is from 15km/h to 130Km/h

The fact is that on a longer geared scoot the operating range (in Km/h) of the variator is large. The longer the final ratio, the slower the belt will change position, for the same km/h change.

okay, that is what I wanted to know. I wasn't sure about that part (if or not the variator would work in the same speedrange with different final gears.

So it's not. Okay, that explains a lot.
 
this thread is a handful to read with all that tech talk, it was informative but it gave me a headache. :D

yes the scooter with shorter gears will accelerate quicker off the line than a taller geared scooter but runs out of gear sooner so it stops accelerating but the scooter with taller gearing will still be accelerating so if the track is long enough he'll pass the shorter geared scooter at the "big end" of the track. now i'll tell something based on my experience, for 3 years i have been using the tallest gear available for my Yamaha Jog scooter (6,73:1 gear ratio) and my best time i have got with that is a 13.2 second 1/4 mile run (unofficial) so we tried gearing the scooter lower (7,15:1) & it gave an astounding 12.8 second 1/4 mile run again it's unofficial.

we took a step further and reduced the rear tire size from a 90/90-10 to an 80/90-10 and after a few more adjustments to the rollers we got our best et of 12.6 seconds, my engine has been heavily tuned for very high rpm power so wisdom dictates that the shorter gear benefits scooters with top heavy powerbands but there is way to get a higher top speed from a shorter gearing & that is with modifying the variomatic transmission itself, my MHR OR kit received heavy mods to give more overdrive to compensate for the shorter gears drawback when it reaches 300m, a standard MHR OR kit will run out of gear at around 250 to 300m then after that the engines' "overrev" takes over but then hp & torque output at "overrev" is significantly lower than before peak hp rpm so the extra overdrive of the tuned vario & rear pulley system extends the time your scooter stays at the sweetspot, the quicker you reach the powerband & the longer you stay there makes for a quicker accelerating scooter.

the more time the engine spends on "overev" the slower your et's become so it may surprise you that we ended up with heavier rollers than what you'er all accustomed to but then again our scooters a significantly lighter in weight & have less bulk or mass which also reduces frontal area & aerodynamic drag. our scooters may look like "brakke" but they are fast & not to be underestimated.

have a nice day & Folkert congrats for making it the 2nd time on the front cover you deserve it.:)
 
tiba_karotsu said:
this thread is a handful to read with all that tech talk, it was informative but it gave me a headache. :D

Yeah I can believe that!

yes the scooter with shorter gears will accelerate quicker off the line than a taller geared scooter but runs out of gear sooner so it stops accelerating but the scooter with taller gearing will still be accelerating so if the track is long enough he'll pass the shorter geared scooter at the "big end" of the track.

Thank you. That is EXACTLY what I was saying The Whole Time!!
I'm NOT saying that everything I said was correct. Some things about the tranny working was still not totally clear to be, I found out in this topic.

But that part you (also) said, the above lines, that was exactly what I said. So there IS a difference in acceleration. Two scooters with different gearing just can't have same acceleration.

now i'll tell something based on my experience, for 3 years i have been using the tallest gear available for my Yamaha Jog scooter (6,73:1 gear ratio) and my best time i have got with that is a 13.2 second 1/4 mile run (unofficial) so we tried gearing the scooter lower (7,15:1) & it gave an astounding 12.8 second 1/4 mile run again it's unofficial.

we took a step further and reduced the rear tire size from a 90/90-10 to an 80/90-10 and after a few more adjustments to the rollers we got our best et of 12.6 seconds, my engine has been heavily tuned for very high rpm power so wisdom dictates that the shorter gear benefits scooters with top heavy powerbands but there is way to get a higher top speed from a shorter gearing & that is with modifying the variomatic transmission itself, my MHR OR kit received heavy mods to give more overdrive to compensate for the shorter gears drawback when it reaches 300m, a standard MHR OR kit will run out of gear at around 250 to 300m then after that the engines' "overrev" takes over but then hp & torque output at "overrev" is significantly lower than before peak hp rpm so the extra overdrive of the tuned vario & rear pulley system extends the time your scooter stays at the sweetspot, the quicker you reach the powerband & the longer you stay there makes for a quicker accelerating scooter.

Nice findings, that's for sure.

the more time the engine spends on "overev" the slower your et's become so it may surprise you that we ended up with heavier rollers than what you'er all accustomed to but then again our scooters a significantly lighter in weight & have less bulk or mass which also reduces frontal area & aerodynamic drag. our scooters may look like "brakke" but they are fast & not to be underestimated.

You guys have been drag racing for years and definitely more experience than over here.
Still, looks dominate the game
[/quote]

have a nice day & Folkert congrats for making it the 2nd time on the front cover you deserve it.:)

Thank Francis, same to you.
And a minor correction: I made it 2nd time in the mag yes, but 1st time on the cover (and poster) :).
 
Joël said:
Duh :|

So I guess everything is clear now?

Duh?

Joël, I didn't try to tell any different, you and Roost were.

Because of the CVT, no matter if the gearing was short or long(er) both had equal acceleration accoring to Roost (and you)

Right from the start, I said something else and now you're gonna "duh" me?

Francis just confirmed what I was trying to tell the whole time. But Roost and you came up with all scientific stuff etc, which wasn't what I was aiming for.

Roost even said the two bicycles has same acceleration (the world hour record example)

Now don't try and turn the tables and tell me "now it's al clear right?"

I even admitted some things about the working if the CVT/gearing weren't known to me. I learned a few new things, which is good.

But read back from the beginning. All I ever said was that the shorter geared bike had quicker acceleration and that LATER on the longer geared bike would pass the shorter geared one. So when one arrives at a certain place sooner, someone's acceleration is faster.

That's all I said. And (too bad) someone like Francis has to come and confirm.
 
Folkert. First you have to distinguish "faster" and "acceleration"
But of course the scooter with the short gear is faster (on a drag race)! Where did I deined that?
But it accelerates the same no matter the gearing. But not all the time of a race. I explained that why.

There is one rule that goes to the gearings: they have to be as short as possible, but not to short to go overrev (for example in a middle of a dragrace)! I sayd this also somewhere back.
 
p.s. Tiba's experience is perfectly in order with what Joel and I said. Joel also made a drawing to show you where the short gearings will gain.

An other point of wiev: the variator's function is to make the overall transmission ratio always the same. But it can't help if it is under or over his working range.
So you have to find the right gearing that will keep the variator in his function most of the time possible needed. For example for a 1/4 mile drag run.
 
roost said:
Folkert. First you have to distinguish "faster" and "acceleration"
But of course the scooter with the short gear is faster (on a drag race)! Where did I deined that?
But it accelerates the same no matter the gearing. But not all the time of a race. I explained that why.

There is one rule that goes to the gearings: they have to be as short as possible, but not to short to go overrev (for example in a middle of a dragrace)! I sayd this also somewhere back.

Again my final try. Scooter with shorter gearing will beat longer geared scooter the first 200m (just an example) the shorter geared scooter acclerates faster. But stops sooner with accelerating and then the longer geared scooter will pass him.

That's what I said the first couple of times and is exactly what Tiba also said.

But (even in this post) you still say the scooter with the shorter gear will win on drag and at same time you say: accelerates the same.

So sorry if I get you wrong. But it's totally condradicting. And now don't say I confuse "acceleration" and "faster".

Even Tiba says it. If the shorter geared scooter wins a 200m dragrace, it gained more speed in a shorter amount of time (if time was longer (than it took to go the 200m distance) the longer geared scooter would gain higher speed in longer time)
So the shorter gains a certain speed in a shorter amount of time, so its acceleration is faster.
So even when the longer gearing takes more time to get to that speed (and eventually to a higher speed than the short geared one) how could the acceleration ever be the same?


But when I said it, I was wrong and didn't know how the tranny works, now Tiba comes in and says the exact same thing and now all of a sudden, it is true.

So can I be a bit confused or what?

And for that: "where did I denied that?" Well about after every post I made. You even claim that the good bicycle example, where these bikes take like 400m to come up to speed, accelerates equally to a bicycle that is in "mountain climbing" gearing.

Only thing I can come up with, is when a scooter would have such a rediculous low gearing (which would be highly unrealistic) that it would not accelerate at all; yeah the first 10cm it would go like a jetfighter, but it's terminal velocity would be like 5km/h.
And at the other end of the spectrum: a scooter with such a unrealistic high gearing, would just stall right away when the clutch engages. (like trying to get your car of the line in 6th gear).
 
Seems like you have learned nothing. That is why you didn't understand where Tiba gained that time. (hint: in the first meters, because with shorter gearing allowed an faster end of clutch consumption of power).
In his case (drag racing) the best thing to do is to increase the variator working range. This way he will get a very fast launch (little clutch work), and the engine will be able to work in powerband all the time of the race.

The scooter with ridiculously short gears wont accelerate much faster. You should calculate that easily now.
 
but with a shorter gearing, you need an exhaust with a wide powerband which still gives a lot of power with overrevs... only that way you can continue accelerating and win from the longer geared scooter.
 
An exhaust with wider powerband will loose the maximum power (the amplitude of exhaust pulse is lower, but is longer).
That is no good. We have the variator to do the job of keeping the engine in powerband. So let's use it as much as possible.
 
Question with respect to gearing.....

When comparing two different gear ratio's on a scooter which has a constant power output no matter which ratio ... for example 20hp .... what can you expect the difference in speed to be.

Lets say the starting ratio was 13/44 ~ 13/50 = 13.02
Then we change the ratio to 13/44 ~ 14/41 = 9.91

What change would you see in the topend speed of the scooter and after what distance would the scooter start to reach peak rpms after the transmission has fully opened and the scooter has then started using the gear wheels?
 
last weekend hit 150kph (93mph) and got to it really fast. the low end power was amazing even with the 7 to 1 gear set. next i will be installing a 6 to 1 set and i think i can get to 160kph (100mph) and still be running the 70cc evo kit ;)
 
Back
Top