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Old 10-03-02, 09:30 AM   #1
robzr
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Mountain bike sizing

I have a question about mountain bike sizing. I have gone through the whole bike sizing process with a road bike and been to enough shops to think I have it down OK. Maybe 2" from ground to a little pressure on the crotch via lifting frame; leg slightly bent at bottom of stroke; handlebar blocking out front hub when in comfortable riding position with arms slightly bent.

I'm curious how this translates to mountain bike sizing? I'm not sure that the salespersons are not just telling me a bike fits because that is all they have in stock. How can I tell if a mountain bike is the proper height? Does the same rule apply for top tube length sizing (blocking hub)?

Also nobody responded to my Bad Boy thread! Any comments on using a Bad Boy or Bad Boy Ultra for a mountain bike? Good geometry? Bad Geometry?

Thanks!

Rob
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Old 10-03-02, 09:38 AM   #2
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Mtn bike sizing is a little more vague than road bikes.

It depends a lot on the rider, and the type of riding.

General rule of thumb. @2" clearance over the top tube of traditional frame designs.

It's all about comfort. You've really got to test ride a bunch of bikes to see what you like.

For example. On a XC race bike, you want to be in a very forward (bent over) position with seat height set for optimum pedalling effiecency.

For DH and Freeriding, you don't want the seat in your way at all, and basically have it as low as you can get it.

For technical trails, lower seat, shorter cockpit, and taller handlebars.

BTW, the Bad Boy is the build of a mtn bike with 26x1" tires. You can essentially turn any mtn. bike into a "Bad Boy". Don't know about the exact geometries. I'd have to trust Cannondale's info.

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Old 10-03-02, 10:03 AM   #3
robzr
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Thanks for the response. My use for the bike would be for putting some narrow light treads on it and using it on Limestone trails/light dirt, and then getting a second wheelset to try out mountain biking on slightly more serious trails (like a trip to Kettle Moraine) and who knows if I like it then I would take it from there.

I spoke with Cannondales tech support about their frame geometries, and they swore that it's "a mountain bike frame". But when I compare the geometries listed with one of their mountain bikes (f600), it seems that the top tube:seat tube ratio is higher (ie longer top tube).

One cool thing about the Bad Boy Ultra is that it comes with 700c wheels and disc brakes, so you can easily swap the wheels out for 26". But it is clearanced so that 700c's work as well. And it has a lockout fork so you can go from solid to rigid at the turn of a knob.

Rob
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Old 10-03-02, 10:06 AM   #4
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This whole sizing thing is, to some degree, a lot of nonsense. Like a2psyklnut says, you have to ride to see what is comfortable for you, and you alone. Most bikes have (fairly obvious) at least three frame sizes: S, M, and L. The geometry of the frame is usually identical, and in the most part the only difference is to be found in the tube lengths and the angles are the same. In that case, bike A will be ideal for only a % of people, bike B for another %, and so on. That's why you need to ride some different types. Sure, you can make some adjustments, like seat height, seat angle, how far forward or back the seat is, bar width, bar angle, bar height, and other things. Some bikes have different head tube angles, and that can make a difference, but whether the average rider can deduce that, or even care about it, is another matter.

Don't overlook brand loyalty either. Most folk are polarised and will only buy from one manufacturer or by suggestion, reason, or emotion, will exclude some brands so you will select from the choices remaining. Nothing wrong with that. What you are prepared to pay, prepared to listen to, prepared to read about, prepared to talk about will ultimately point you in the direction of that you can select from. At that point, sizing will be secondary.
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Old 10-03-02, 10:12 AM   #5
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You can base an aggressive CX riding position on the points of contact from a road bike, but note a few differences.
MTBs commonly use longer cranks.
MTBs have a higher bottom bracket.
The flat bars should be in a position equivelent to the brake tops.

The rule of thumb about bars blocking the hub is not something to worry about, it depends on the type of bars, your style of riding, and the steering geometry. (If you ride a road bike with flat bars placed to mimick the brake hoods, they wont block the hubs.)

For comparing bike positions you need a reference frame, or an origin[0,0]. The ground is not suitable. You can use the BB or the crank 6:00 or the crank 9:00 position. Measure from pedals to saddle on x and y, then from saddle to bars in x and y. Thats all you need for your riding position.

There are some differences in frame angles between the two styles, but as long as you can set up the points of contact using sensible seatpost and stem combinations, it should work.
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Old 10-03-02, 10:26 AM   #6
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At least on my bike, if you make the handlebars hide the hub while comfortable, yes it's great while going in a straight line, but when you get into steep hills and stand up, the handlebars are so close to your gut that you feel extremely unstable. I try to keep my seat adjusted to where it's a good compromise between the best efficiency and good clearance. Even if you're XC racing, you're still going to want to crouch down on hills and hop over logs, neither of which is very fun if you've got your seat cranked up like a road bike.
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Old 10-03-02, 10:36 AM   #7
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Dont forget than when a road/drop bar blocks the hub, the handholds are a good 4" ahead of that bar. Thats one reason you cant just swap out a curly bar for a flat one, you need to change the stem length as well.
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Old 10-03-02, 06:15 PM   #8
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Quote:
Also nobody responded to my Bad Boy thread! Any comments on using a Bad Boy or Bad Boy Ultra for a mountain bike? Good geometry? Bad Geometry?
Robzr-
If you are looking for a very versatile ride... the BadBoy is a good ride to put under ya... You already know of the ability to swap wheel sizes. This can really enhance any on road riding you do with the larger wheels. Off-road the CAAD3(unsuspended) or CAAD4 FRAME(Headshok) will do you well, also.
I would only say, if you are looking to spend more time offroad, then look at an f800. Tends to have a slightly better Geometry for offroad.
Either way. The BadBoy has a Geometry that compliments Road riding and is very capable offroad as well.
Sizing: You will want a frame slightly smaller than you would ride as a strictly road bike, cuz it affords better maneuvering off road.
and if you are in the Kettles (wi?) and need a guide drop a line, we may have a ride goin' out.
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