kx100 vs yz85

i would go for a kx 100 because the power is more spread out than a 85. the bike cant whip like a 85, but is a smoother riding bike by far. my friend is looking at 85s or a kx 100 too. im not the best guy to ask about these two bikes im 5'4'' and ride a kx 125. my brother has a kx 85, and its awesome on tracks and trails! im going to ride a hyped up yz 85 in about a week and a half. ill let you know what i think.

I do not think that the kx100 will be much better in the sand. I have a 2004 kx100 and ride in the sand often. It is not a great, moderate to deep sand bike. There are several guys riding small 4t's that handle the sand much better. The 2t mx bikes just dig in. Perhaps someone call tell you why better than I can but the kids at the pits on the crf230 and the klx 125 seem to do a lot better. Even when riders swap bikes, the small 4t's get all the praise in the sand. The woods and the dirt are a much different story. 2t all the way.

The KX100 with sand oriented tires would be a good choice.

The CRF 230 has 21"/18" tires, the KX 100 has 19/16 tires, and the YZ 85 has 17/14 tires. While the slightly larger tires of the 100 will help, as will the slightly broader power, I doubt the effect will be as significant as you think. If she really needs bigger tires, she may have to deal with the larger, heavier bike. Otherwise, to stay with the smaller lighter bike, you get stuck with the small tires. At 5'6", she could probably handle a full size bike. Perhaps a 125 motocross bike, or a KDX 200 would be better choices. They'll be lighter than the CRF 230, with more power and the same size wheels.

I have had experience on many bikes. I have ridden all the bikes that you have talked about, except a smaller version of the CRF. I owned a KX100 a few years back. I didn't do anything in sand, but I know how it is in other sticky/slippery things like mud, snow, small rocks, gravel, etc.
The KX could or could not be a great bike for her. My stepmom owned a KX100 for a while. She didn't like it too much. She complained about the powerband i.e. she didn't like the speed of it (she prefers going slow). She ended up putting a flywheel weight on it, and it helped a lot. Her riding style was much more suited for a trail bike, though...4 stroke in particular.
I know these aren't the same exact bike, but I recently rode a 2005 CR85R expert. I am guessing it is close enough to that YZ. I didn't like it at all though. It was too slow. I liked the KX much better. The KX picked up right off the bat, whereas the CR wasn't as torquey. Seemed like the throttle response and the convertability to a trail bike was much better for the KX, too. I used to race one, and I always got the holeshot because the KX just picked up and went. The KX doesn't rev as high, either. It may just be the bike for her if she isn't way too slow.
Have you thought about an older and cheaper bike? Perhaps a 2 stroke trail bike, like a KDX? Also, there are many other 4 strokes out there that would fit her, including TTRs and stuff.
I don't know exactly how she rides, so I can only give you my experience. I will guarantee you that she would like the KX100 much better than what she has now by the sounds of things...and that there are many bikes that you aren't considering while determining this decision.
Good Luck, and I'll be sure to keep helping however I can.
Oh!!! I just remembered!!! My stepmom recently bought a gas-gas. I haven't seen it yet, but she seems to love it. They are great for that kind of stuff, so I would look into that. The website is www.gasgas.com just as you would expect.
Hope I helped a little.

:yeehaw: :yeehaw: :yeehaw: kx 100

A flywheel weight, a pipe that is designed to beef up the bottom end, porting if you really want to get serious, will all make the KX 100's power more woods friendly.

You should have no problem finding sand tires for either the YZ or the KX. You simply need to pick your brand and look in the catalog for what their tire designed for sand is. Order them in and mount them up.

I think you should get a KX100, get it ported for low-to-mid, and add a flywheel weight on it. That will make it much easier to ride in the sand and it wont bog down as easy. I rode my CR85 Expert all last season in pretty loamy sand and I could have benefitted from some low end. She'll be fine if the bike just had more low end.

I'd have to say the 125 is probably a little smoother than the 100. The bigger motor, gives it slightly more grunt, and smoothes the hit a tad, but they are still small bore 2 strokes, which hit hard because they have narrower powerbands, and to make power it comes on hard. The KX 100 has what about 24hp, and weighs like 150lbs, the 125 is like 32hp and 200 lbs? That right there will make the 100 seem like it hits just as hard, because it has the same power to weight ratio. At 5'6", she isn't going to need too much to fit the 125, set the suspension up for her, slide the fork tubes up a bit in the clamps, maybe cut the seat foam a bit, and she should be good to go. I'd buy the 125 if it was me. I think the 100 would be a little cramped, I can't imagine she finds the 80 roomy. Have her hop on your bike on the stand, and see what she says about the size of the chassis, if she thinks it's too big, look at the 100, if she thinks it feels better and fits her, get the 125 and tune it for her.

I am 5'10'' and can not fit on a moto 125 and have a 34'' inseem so how is a girl 5'6'' gonna fit on it, even with lowering it 3 inches I can put my feet flat and the 230 weighs a ton for that size I just don't like the thought of some one that cant pick up their own bike when it falls.
STICK with the 2 stroke put a flywheel weight in it. Maybe she has to test all those bike side by side right after each other.

But cant you put bigger suspension and wheels on the 85 for senior class?

Why dont you put paddles on it?

If your riding sand and some dirt I wouldn't see the dirt screwing the paddles up :O