Mountain Biking - Bike fit

How do you guys decide what is the right size frame for you ?

I understand that this can depend on the kind of riding you are doing.

I am 5'6" tall. My current bike frame is only 16" and I have had a fair amount of knee pain, especially recently when I have been doing more riding.

The LBS suggested a 17" frame which is only an inch bigger than my previous frame.

Sorry for all the questions I am asking here.
This is a great forum. I just want to make sure that I am getting all the info I need to make the right decision on which bike to spend this $1200.00 on.

Justen

I hop on...I ride it...if i like it, it fits. I also take my riding into account and go for a slacker ride than typical xc bikes. It sounds like you have already done this. See if you can take them all out for 1 hour or so and push it a bit. See what happens with your knee. :)

BTW I am 6'5 and currently ride a 19" Kona Roast. My gf is 5'6 and rides a 17" Stuff (that I use for dj's). I like a smaller frame where I can raise the seat for xc and lower it for shore riding :) My gf is xc only so this bike fits her perfectly. But we tested both a lot just to find the right fit :)

The most important aspect of frame fit is top tube length. That will determine how the bike handles. Too small and it's going to handle twitchy, too long and it's going to handle slow.

Like Mael said, you can adjust the seat height for the riding you're doing...the top tube can't really be changed aside from going with a longer/shorter stem or setback post. Even though you can make slight adjustments with those, it's best to get a frame that fits with a "normal" sized stem. (around 100, 110, 120)

Also, what size cranks are you riding. Some manufacturers fit cranks to the application (170mm for road, 175 for off-road), but they should be fitted to the rider. For your size you should probably be riding 170mm for off road, and maybe a tad shorter for road.

You need about 5-6" of clearance to the top tube for safety, but think about where you like your bars to be, and how high or low the head-tube should be to accomodate that position. Different styles of bike may vary in how high the head-tube goes.

Hi Michael,

Well, the Brodie tube is sloped so I assume you take the measurement by standing over the highest part of the slope. I am not sure what size the cranks are at all. I will have to call and ask them.

I only have about 1-1/5 inches of clearance on this bike. It felt comfortable to me when I was riding it but I am still wondering about the actual size of the bike. It is only a 16" frame. My current bike is a 16" frame and I was told by a couple of people that this is too small. The bike shop owner told me that if I want to do any North Shore riding, that I need a smaller frame and yet they were going to sell me the 17" Fury. arrrrrrrrrrgggggggghhhhhhhhh...I like this Bruzza so much. I just don't want to spend such a large amount of money if the bike is too small.

Justen

Bike "size" is a pretty useless figure. It is measured from the bottom bracket to "somewhere" which varies. On a sloping tube bike, it is often to where a horizontal top tube would be, but is it to the centre or to the top edge of that imaginary tube?
The bottom bracket can vary in height off the ground (giving different amounts of pedal and chainring clearance).

Standover height is measured as you standover the bike, so it is to the top tube just below your 'nads.

You need to analyse your current riding position, figure out how you might want to change it, then get a frame which can be adapted to your chosen position. With any bike, you have to take your own tape measure to really get an idea of its dimensions.

http://www.peterwhitecycles.com/fitting.htm

Originally posted by Justen
Hi Michael,

Well, the Brodie tube is sloped so I assume you take the measurement by standing over the highest part of the slope. I am not sure what size the cranks are at all. I will have to call and ask them.

I only have about 1-1/5 inches of clearance on this bike. It felt comfortable to me when I was riding it but I am still wondering about the actual size of the bike. It is only a 16" frame. My current bike is a 16" frame and I was told by a couple of people that this is too small. The bike shop owner told me that if I want to do any North Shore riding, that I need a smaller frame and yet they were going to sell me the 17" Fury. arrrrrrrrrrgggggggghhhhhhhhh...I like this Bruzza so much. I just don't want to spend such a large amount of money if the bike is too small.

Justen

When it comes to shore riding you want the bike a little small. For xc you can always adjust seat height and get a good set of risers. You won't be competing in any xc races with the rig but it will be fine for all round riding :)

Justen, I wouldn't be too concerned with standover clearance issue with a mtn bike. This is more of a concern with road bike sizing. And since you don't have "dangly bits" I wouldn't worry that 1.5" is all the clearance you have.

You need to concentrate on "Cockpit" lenght, or how long the top-tube is. If the bike feels cramped, you can swap to a longer stem or move up to the next size frame. If you feel too stretched out, versa vice. Smaller frame or shorter stem.

If you plan to do mostly road riding, or fast XC off-road riding; you're better off on a bigger frame.

If you're going to ride more aggressive off-road and stuff with drops, jumps or bridges (elevated trails), stick with a smaller frame, AND a shorter stem. A good bike for aggro riding should feel compact. This aides in getting WAY back on the bike and makes it easier to get the front tire up. Plus, a smaller frame is easier to handle through technical trails and in the air. It'll steer faster!

A longer frame responds a bit slower and is more stable in the air and at higher speeds. Thus, better for road riding!

L8R

Regarding the knee pain. I get some of that every now and then, as well. I asked around and was told that for XC riding I should have my seat at a height and cranks of a length such that my knees don't bend more than 90 degrees, which has something to do with the ligaments stretching to far under a load. I was also told that when I lift weights, to apply the same rule (i.e. don't do deap squats). It definitely helped just to make a small adustment in my seat height.
I also noticed some of my knee pain seemed simply to be related to having less muscle support after a ride, as it went away at the same time as that drained feeling after a hard ride.
Anyhow, you might wanna consider what I said, but don't ignore the other posts in the thread as well.