freckles

Just discovered my beloved Omais not 49cm but actually 52cm frame! I bought her secondhand over 2 years ago and the seller said she was 49cm.

In the process of getting a new custom BikeFriday NWT so learning all about frame size, crank size etc so I measured Oma's seat tube length and its 52cm! My 3 speed Robin Hood is 49cm.

I ride for local errands/commuting, do get knee pain sometimes but chalked it up to getting older... but maybe its because the frame and/or crank size is too big?

Can't change her frame size, seat is in the lowest position and crank size is 170mm. Inseam is 28.5" Could changing the crank size help?

Carbonfiberboy 

Yes, you could profitably go all the way down to 160mm. That's a whole cm. Would make a difference. Where's the knee pain?

They may not be that easy to find, but they do exist. Ask at a very good bike shop.

Leisesturm

So ... I just had a look at an Oma since I had never heard of them. Unfortunately the picture isn't big enough to give me the detail I need and I am only partially sighted to boot but it does not look as if that is a standard crankset in use. Finding cranks in any other length than the supplied 170mm may be difficult, if not impossible. In any case, IF the 52cm frame is 'too big' the areas of difficulty where that might become apparent would not be the leg length one. Why? Because there is an easy remedy for that: lower the seat. A larger frame should (but may not) have a greater 'reach' to the handlebar but the Dutch bike geometry already has the rider sitting so upright that its probably beneficial to have the frame a little more stretched out. Sitting bolt upright is great for short distances but American commute distances are typically longer than the mile or two common in The Netherlands.

The Oma does not have a top tube. Where exactly to measure the seat tube then? Do you measure right to the top of what seat tube is there or to the center of the (non-existent) top tube? On a 'normal' bike that would be at the top of the head tube. As you can see that strategy just won't work with the Oma. This may or not be the reason for the discrepancy issue with the seller? You already have the bike and clearly ̶l̶i̶k̶e̶ love it, so ... knee pain ... I personally just can't agree that a 10mm change in crank length could do anything substantive for a knee issue. The resulting change in knee flexion would be minimal. Just throwing stuff out there ... knees can hurt because seats are too low as well as because they are too high. How was the seat height determined? Since your seat is already slammed (as the kids say) one way to lower it further (if that were necessary) would be a different, lower profile, saddle. The OEM saddle is quite tall, there is room there to go lower. But the saddle height should be determined in some objective way. There are formulas and such to use as a starting point.

freckles

Hi Leisesturm,
Yes, I do have to reach just a little forward to reach the handlebar shifter/bell/brake levers. Luckily, they are wonderful swept back handlebars so the reach isn't as much as it could be.
I measured the seat tube length from the seat post to the center of bottom bracket to get 52cm.

With the seat to its lowest, by feet have the slightest bend (depending on the shoe) at 6 o'clock but I feel like my knees are being stressed when pushing down the pedal at 12 o'clock which let me to think about shortening the crank....

freckles

I emailed Workcyles about the type and feasibility of changing the crank. I get knee pain sometimes when pushing down the pedal from 12 o'clock....I think it may depend on the shoe's padding/sole thickness. Platforms are comfy at 6 o'clock but more stress at 12 o'clock if that makes sense.

CliffordK

Why don't you start with posting a photo of your current bike.

How tall are you?

Shorter cranks usually require raising the seat slightly.

But, once riding, the amount of seat post sticking up doesn't make much difference.

170/172.5/175 cranks are really for the "average" cyclist.

Personally I like cranks a bit long for my height, but will ride anything, and hardly notice the difference in lengths.

But, if you are short... say < 5'4, then absolutely consider shorter cranks. 155mm? 160mm? 165mm? I think the mid 150's have a few sizes if you're searching 154? 156? 157?