Dirt Rider Magazine

smellmyexhaust

Im going to buy a used late model (one of the big4) bike for the easy trails. I started looking at the 250f, 4 strokes first. Than I heard that the 125 2 strokes are lighter,faster and much more economical than a compareable 4 stroke. Is this true?
Which should I buy? :?

NZrider

lighter yes, faster no, more economical? perhaps in overall maintenance budget but certainly not in fuel usage. for easy trails i suggest a 250f enduro like WR or CRF250X or perhaps and enudro 2 stroke like ktm exc models. dont buy a race bike for trail riding

rockrider

The 2-Stroke is Faster. 2-Stroke's usually have a better power to weight ratio.

2010 YZ125
Horsepower: 34.01
Wet Weight: 208 lbs
Power to Weight: 1 horsepower for every 6.11 lbs

2010 YZ250f
Horsepower: 35.88
Wet Weight: 224.8
Power to Weight: 1 horsepower for every 6.26 lbs

On a pavement drag race, the 2-Stroke will win. On a dirt track with twists and turns, the 4-stroke's traction and torque out of corners would make it the winner.

NZrider

that math is for a bike riding itself. if you factor in a rider of 150lbs on both bikes then the ratio will actually swing in the favour of the 250f

yz125
208+150 =358lbs/34.01hp=10.526 lbs/hp

yzf250
224.8+150=374.8lbs/35.88hp=10.452lbs/hp

either way its a negligible difference and the additional torque of a 4 stroke will only benefit.

smellmyexhaust

Thanks, both of you for your thoughts! I believe that I'll go with the 4 stroke Honda/Kawi 250f.

rockrider

@NZrider

There is no torque advantage, thats a myth, both are 19 lbs from what I can find online; also I am using the more conservative yz125 hp estimate, in reality I think it has more horsepower.

What I am saying is that on pavement where both bikes can put down the power with no traction worries, the 2-Stroke is faster, it revs and makes its power faster and you can hold it in the powerband range through all gears.

From personal experience on the street, an 04 RMZ250 and 04 RM125 are not even comparable, but I can't comment on the Yamaha's other than the numbers are almost identical and the 2-Stroke will make that power much quicker and hold it in the powerband through the gears.

[bold]The poster asked: "Is a 2-Stroke Lighter and Faster [than a 4-Stroke with double the engine size!]" [/bold]
[bold]Answer: Yes and Yes[/bold]

[bold]Lets compare apples to apples and see what happens when the 4-Stroke doesn't have double the engine size.. [/bold]Same engine displacement comparison.

2010 YZ250f
Horsepower: 35.88
Wet Weight: 224.8
Power to Weight: 1 horsepower for every 6.26 lbs

2010 YZ250
Horsepower: 46.80
Wet Weight: 229
Power to Weight: 1 horsepower for every 4.89 lbs - [bold]Absolute and utter destruction of the 4-Stroke![/bold]

usrockband

personally i think you'll have more fun on a 2 stroke then a 4 (i've ridden both, i own a 2) i personally advise you ride both before you make quick judgment in a scenario like this. whatever you pick is what you like tho i guess :D

wwjdftw2

smellmyexhaustThanks, both of you for your thoughts! I believe that I'll go with the 4 stroke Honda/Kawi 250f.

DO. NOT. GET. A. RACING 4 STROKE. FOR TRAIL RIDING.

You do realise you have you have to do valve checks AT LEAST every 15 hours of riding? That a rebuild (racing 4 strokes need them often) is almost 4 times as much as a 2 stroke? If you want a 4 stroke for your sake don't buy a race bike just get double the displacement...

rockrider

Heres a quick rule of thumb..

1. Do you consider yourself to be a lazy rider? if so buy a 4-Stroke. if not buy a 2-Stroke.
2. Are you upper middle class to rich? If so buy a racing 4-Stroke. if not buy a 2-Stroke OR big displacement 4-Stroke like wwjdftw2 said, think XR400.

Kiwi450x

Settle down rockrider.

NZrider

no torque advantage?

have you seen dyno curves of 125s and 250fs?

im not talking about peak numbers, which is what is nearly always quoted. the torque curve of a 4 stroke is much smoother and stronger from a lower RPM.

try lining the 2 bikes up and doing a 4th gear roll on from low end to top end then tell me whos out front.

im not saying the 125 is slower. i think they are pretty much identical in acceleration on ideal surfaces with equal riders.

dont get me wrong, i'm all for 2 strokes, i race one, they just arent the answer to everything.

Dirt Dont Hurt

trails you will need a trail model such as a TTR/CRF 230F or CRF250X or XR100-600.
don't buy a crf/r model for the trails, no kick stand and frequent valve adjustments are a major pain. the torque of the 4 stroke will also help and if you just happen to run out of gas you can siphon straight gas into your tank without worrying about the premix ratio

rockrider

@NZrider Yes out of corners or in an actual motocross situation the low end 4-stroke torque can be put to the ground easier, but in a drag race you can keep a 2-stroke maxed out and in the sweet spot through all gears, so you will have that max torque figure. And again, Im still talking about a 4-Stroke with double the displacement. Also on the new YZ125, I am pretty sure it has a very very flat torque curve from down low.

I like 4-Strokes and 2-Strokes, I have always owned both as they serve different purposes. I own 2-Strokes for fast trail riding, motocross and jumping, and 4-Strokes for running trails when I feel lazy, and long distance trail riding; but I have owned big thumper XR and DR 4-Strokes. I rode a borrowed RMZ250 extensively for over a year and blew the engine several times, not impressive.

NZrider

just out of curiosity, what failed on the RMZ for each engine blow? I raced 70 hours on a CRF 250 in 9 months and never had 1 mechanical failure. granted i replaced parts when they needed replacing but it never let me down.

rockrider

Scorched piston and loss of most compression, and then 2nd time engine seized. I never did the repairs so this is just what the mechanic told the owner.

I can tell you the reason it went out was that I rode it very hard because I was riding with 450's and had to keep up, but the thing to remember is that I rode for years and years 2-Stroke's, XR's, DR's, etc., and I have never been stranded on 2-Strokes or my well-maintained 4-Stroke Air Cooled bikes, and I rode them all much harder than that RMZ.

Btw, I like 4-Strokes for taking it easy and long distance riding, so I am not totally bashing the RMZ, though I think my next one I will buy a 600'ish KTM or something big so I don't stress the engine so much; or actually that BMW 450 is calling my name too!

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