why do they think that atvs are so much more dangerous?

 

Honda sees the need for making the TRX engine more durable for the long term use of the four wheeler so there are some factors that have been changed within the engine that will make it put out less than the CRF engine on a dyno.
The piston not only is a different size as far as bore size, but also has one more ring and a longer skirt than the CRF
The transmission has a wider gear span for ATV use.
The flywheel is heavier than the CRF
The clutch basket has 8 discs for the heavier demands of an ATV
The exhaust is different than the CRF

These among a few other changes in the engine will cause the TRX to read differently than the CRF on a dyno.
The TRX was engineered with the normal consumer in mind, for the longetivity of the unit, remember, not all consumers by these units to race. And most changes in the engine for the TRX aplication were for a reason. An ATV engine has different demands than a bike.

----- Gimpster -----

 

The bore and stroke read differently, but I think the major change is the cam. take an engine you have, and know. put a cam in it and ride it, then take another cam with different specs, and run that one. I was amazed at how the engine responds, to 2 different Web cams.

 

HONDA TUNED THE TRX450R motor wayyyyyyyyyy down on purpose! U can make ur 450r scream using all honda oem parts

Cam out of crf450r or x
Carb from crf450r or x
Wiring harness from crf450x
cdi from crf450x(more torque than crf450r!)
Now best part use side case and starter from crf450x and u will have electric start for your trx450r!(as long as u use a crf450x wiring harness)

 

Cam, carbs, and just about everything else is different on the atv. Its amazing they kept similar cases. Basically Honda tucked tail and gutted the 450R quad to a mild trail machine. IMO the honda is the better bike, and the yammi is the better atv.

 

I agree with Gimpster. Those changes are correct. They also have a completely different oil distribution system, for when a quad is riding on a angle, it allows oil to reach both sided of the engine/transmission. Yamaha did the same thing. ATV's are heavier and require different power bands. I think they did consciously de-tune the bike for fear of lawsuit. But it also improves reliability thru lowered NVH.

Quads are statistically more dangerous than bikes, as you have four points of contact with the ground vs. two. They are more tipsy........ and better rider weight distribution is needed for cornering. My brother BEATs his CRF450R like it's paid for, but won't dare jump my 400ex for fear of loosing it.

 

Tipsy eh? You are talking about a machine that needs a kickstand to stay upright...

 

I think what he ment by tipsy, was that while riding a bike, the engine is more apt to be in an upright position, other than cornering ETC...
Where an ATV riders engine will be tilted more often from side to side from unleval terrain, hence the term 'tipsy'

riding a side hill on a bike, the rider and bike are still straight up
where a quad on a side hill the engine is tilted

Just an example.

----- Gimp -----

 

The YFZ450 and YZ450F use the same motor, but they have different cams.
AS far as I know, everything else about the motor is the same? (except for Carb jetting)