Reasons: Why dirt bikes are slow compared to others.

[warejohn]

Why are 2-stroke dirt bikes so slow compared to sport bikes, like the CR500 has a slower top speed than an RS125? However dirt bikes contain super acceleration.

[DEATH_INC.]

Gearing and aerodynamics. Have you ever stood beside a RS125? They're tiny. Also the RS and most sport bikes have mostly top end power, where that would be useless in the dirt.

Back in the day they weren't too bad compared to roadies, I remember back in the early 80's Australasian Dirt Bike magazine geared a KX500 and took it to the local drag strip where it held it's own against most of the road bikes of the day down the 1/4.

Around a tighter track a supermotard with a decent rider is damn hard to beat on a ZX10, and almost impossible when it's wet.

Top speed isn't everything.

Edited September 30, 2019 by DEATH_INC.

[crypto666]

For the same reason the fastest motorcycles on the planet usually need a push start. 

[pat22043]

Dirt bikes don't care about top speed. Its useless in the dirt. I don't know the top speed of either of my two dirt-oriented bikes. I've done about 50 on the KTM, and that is plenty fast on dirt for me.

[ohiodrz400sm]

Why are 2-stroke dirt bikes so slow compared to sport bikes, like the CR500 has a slower top speed than an RS125? However dirt bikes contain super acceleration.

You answered your owned question and don't even know it. MX bikes have gear ratios matched to racing on MX tracks. Sport bikes are ratios best suited to road racing.

[Truman Sparks]

Why not compare to a 50cc?

 

 

 

Edited September 30, 2019 by Truman Sparks

[TC686B]

Why not compare to a 50cc?
 

 
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Just try to imagine what speeds he could of hit with a properly set up 685cc.

[Truman Sparks]

Seeing that a stock Maico 700 will do about a 110 mph in offroad trim

In a streamliner the 685cc that powers the Maico it would do about 250-275 no problem.

[Chris Russell]

Just now, Truman Sparks said:

Why not compare to a 50cc?

 

 

 

hows about 110?

 

[Drop-Bear]

Honda CT90 is Australia's best selling bike.

[Sspeedfreak]

Yup aero n gearing folks !

Raced an 88 CR500 (with a heavily ported cylinder and the usual pipe n carb upgrades ) in AM250GP (RS250s n TZ250s)and even Heavyweight Twins (TL1000s,RC51s!!)

Obviously this was on asphalt 

 Bike had a Gixxer750 frontend with clip-ons as well as a Gixxer rear rim

Ran hard against those guys

Snatched a podium on a cpl occasions !

Top speed was around 200km/h (125mph)

Rear sprocket was custom at 36 teeth !!

 

[Sspeedfreak]

[Piney Woods]

Obvious answer. The tool fits the job.

[donwann]

7 hours ago, TC686B said:

Just try to imagine what speeds he could of hit with a properly set up 685cc.

Is that frame backbone made from Unistrut?  Where's his carburetor and fuel tank?  All he would need for aero is a luge helmet and suit with somewhere to hang his feet behind the rear wheel.

[Chris Russell]

Just now, Drop-Bear said:

Honda CT90 is Australia's best selling bike.

nah, thats the ct110. the postie. millions of em. gone all chinese and EFI now...

ct90 was an old postie, sometimes with a dual range gearbox. not common.

c90 is the cub. has the leading link forks vs teles. maybe thats what the t stands for.

there was a ct125 but its basically an xl.

 

 

 

done more damage to myself on one of them than anything else...

[Drop-Bear]

1 minute ago, Chris Russell said:

nah, thats the ct110. the postie. millions of em. gone all chinese and EFI now...

ct90 was an old postie, sometimes with a dual range gearbox. not common.

c90 is the cub. has the leading link forks vs teles. maybe thats what the t stands for.

there was a ct125 but its basically an xl.

 

 

 

done more damage to myself on one of them than anything else...

I used to service all the posty bikes when i was 17/18. All over Vic.

Only ever saw one CT125 being used.

Should have seen some of the prototype posty scooters they had at the Oakleigh depot.

[TC686B]

Is that frame backbone made from Unistrut?  Where's his carburetor and fuel tank?  All he would need for aero is a luge helmet and suit with somewhere to hang his feet behind the rear wheel.

I’m a electrician. Unistrut was the first thing that I thought also.

[TC686B]

Seeing that a stock Maico 700 will do about a 110 mph in offroad trim
In a streamliner the 685cc that powers the Maico it would do about 250-275 no problem.

Ha. Good sport.

[Drop-Bear]

Same bike after revisions?