Friday, February 29, 2008

Bike Fitting

In order to get a good bike fit you need to ensure you have the proper frame size for your body. I selected the 17" frame and it looks like it fits perfectly. Below is the link for the Motobecane website geometry for the Fantom 29:

My leg inseam is 33.75". This is measured by placing a 1" thick book up tight between your legs and measuring the distance between the floor an the book spine. The 17" frame has a standover height of 31.7". Therefore I have about 2" of clearance. It is recommended to have 2 to 4" of clearance for mountain biking. The 19" frame would have only given me 1" of clearance so that is why I purchased the 17" frame. Note that you usually need to be one size down for a 29er vs a 26er. I would normally fit a 19 to 20" frame for a 26er.

The next step is to adjust the seat height. You can get a rough idea of where to set the seat height. The distance between the center of the pedal crank and the top of the seat is approximately 0.883 X leg inseam measurement. For me this would be about 29.8". Make sure the seat is level. Now that I have a longer seat post I can make this adjustment. When sitting on the seat the fully extended leg should be slightly bent at the knee.

The next step is to adjust the front to back seat position. The seat should be moved front or back so that the tip of your knee is directly vertical over the center of the pedal when in the horizontal position. This is called the neutral knee position.

Next I check my reach to see if my stem length is proper. When I sit on the bike I do not feel cramped or too far forward. I will see how this feels in future rides. Here are some links on bike fit that found helpful:

At this time I also adjusted the front derailleur to fix the problem of not shifting into the large crank sprocket. I also noticed that the end of the cable for the front derailleur was too long so I trimmed it and crimped on a new end. Here are instructions:

I also lubed the chain. I installed a rear fender that I had on my old Mongoose Pro.

Finally I installed the Cateye Enduro 8 Computer. Here are the instructions:
These instructions do not include the tire setting for the 29x2.1 tire. On the cateye website it says to use 229 cm.


Anonymous said...

Hi Mike,

I just purchased a 19inch Moto Fantom 29 from Bikes Direct. I believe my bike was shipped today. However, Im having some serious concern over the frame size I chose. When comparing the standover height(32.8) with my inseam length(34.8), I took my measurements while wearing athletic shoes. My actual inseam when bare foot is just 33.9. Am I heading for trouble ? Did you check your clearance after you assembled your bike ? Is there anyway I can get an additional 1" clearance if my frame size is indeed big for me ?

Sorry if this sounds silly, but I felt its better to hear it from you than get sniped at by the guys at the LBS where I intent to get my bike tuned.

Do let me know

Mike said...

Sorry for a late reply, but I was just looking at past comments.

I have 2 inches of clearance and the fit is fine. You also have 2 inces of clearance since it should be measured with the shoes you will be using on the bike. You should be fine.


mccarthyink said...

I appreciate your notes on the fit as we're identically sized and I was wondering which Fantom 29er to order. Sadly, the 17" is out for the moment and I'm waiting for them to restock. I noted that you replaced the seat post and I suppose I will have to also. You also replaced the handle-bar stem didn't you? Was the first OEM stem a problem?

Alan said...


Thanks so much for taking the time to create and keep this blog up to date. I too am contemplating a 29er and the Motobecane is near the top of my list. I'm 6'5" with a 36" inseam, so I'm thinking the 21" will be best, but I want to try out some other brands at LBS first.

I appreciate your running commentary. Most folks post just one time, so it's hard to know the long-term reliability.

Thanks too for the pictures...looks like you have some cool places to ride. Have you ever looked into Rails-to-Trails? I joined last year, even though railtrails are virtually nonexistent here in So. Cal. They publish a magazine with some nice reviews of trails, many of which are in the northeast.