do you no how fast one of these gose

[mini_motox]

hay my freind ceeps sayin that his lil bros crf80f is faster then one of these
http://cgi.ebay.com.au/NEW-IMPROVED...7838366QQihZ013QQcategoryZ32074QQcmdZViewItem



is this true

 

[FLICK]

............

 

[noidea]

8.5k/h at 1000rpm in 4th doesnt sound right...

10000 shud b pulling faster than 85

 

[FLICK]

............

 

[sympozium]

heh, your equation is not valid

there are many other factors, torque and friction just to name a couple

 

[FLICK]

............

 

[sympozium]

torque has alot to do with it and friction also has stuff to do with it, your equation may be roughly accurate on a dyno but not valid in the real world.

for starers theres the weight of the rider...please explain how your equation works with a 55kg rider aswell as a 95kg rider

 

[FLICK]

............

 

[No-Fear]

it will just take a little longer to get to it's max speed.

 

[sympozium]

if you havent got enough torque it just wont get there, jump on a little 50cc, you wont get close to the speed ur son or little brother does, it just runs out of puff and wont pull any faster

 

[Redstar]

If a bike does 60kmh at 7000rpm with a 20kg rider it will do 60kmh at 7000rpm with a 120kg rider....

Absolutely correct!

Which is heavier? a kg of cotton balls, or a kg of steel? Same analogy and by the way, I agree with Flicks computation about speed vs. revs/gearing.

 

[Redstar]

if you havent got enough torque it just wont get there, jump on a little 50cc, you wont get close to the speed ur son or little brother does, it just runs out of puff and wont pull any faster

Lemme just paste out Flicks chart again...

in 4th with 14/37 sprockets
1000rpm = 8.5263 km/h
2000rpm = 17.05 km/h
3000rpm = 25.6 km/h
4000rpm = 34.1 km/h
5000rpm = 42.6 km/h
6000rpm = 51.2 km/h
7000rpm = 59.7 km/h
8000rpm = 68.2 km/h
9000rpm = 76.7 km/h
10000rpm = 85.3 km/h

Say, on the same 50cc bike, the son does 6000 rpm, he'd be doing a max of 51.2km. Now for the heavier dude, he struggled to get the bike up to 6,000rpm and no matter how he tries, like you said, he just doesnt have any puff left and stays stagnant at 5,000. Then he'd be doing a mere max of 42.6. Let the kid jump in again and let him drive at 5,000 rpm. you'll see he'd be doing the same max speed as the poor overweight dude.

For the heavier dude, this now becomes the cue to go for even shorter gearing. the chart's example was a 14/37. going 14/38 will get his revs up much easier but the max speed will likewise be affected.

Aah.... now if I can only find that 14/38 chart......... it was here lying somewhere....

Other factors such as tire diameter will affect revs vis-a-vis max speed but basically, all these are all part of gearing computations to suit a particular track/road condition/gearing configuration... all depends what you need.

 

[mini_motox]

yeh but is a crf80f faster

 

[FLICK]

............

 

[sympozium]

Other factors such as tire diameter will affect revs vis-a-vis max speed ....

even more factors which are not taken into the equation rendering it invalid

 

[FLICK]

............

 

[sympozium]

ugh, i say again, equation not applicable to the real world.

fact is if the power cant get to the ground for whatever reason (100% of the power barely reaches the ground in a real world scenario) its not going to do that speed, theres many things holding it back, thats where torque comes in.

put your bike on a roller, the back wheel will go well over 100kph, as soon as you apply a load to an engine its going to lose power, how much simpler do i have to make it?

the more torque you have the less power your going to lose when you apply a load.

then theres variables such as tyres, surface traction which is proportionate to your tyre wear of course, surface slope just to name a few

 

[FLICK]

............

 

[noidea]

lol, sympozium his equation provides speed outcomes based on gearing and rpm. No environmental factors besides traction will affect this.... absolutely none, your wrong.

Flick, just doesnt sound right... and your right, pushing these cheap chinese engines hard isnt the best idea when you have engine life in mind.

 

[sympozium]

your still not factoring in tyre circumfrence