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I want to replace the front derailleur on my 2010 Kona DEW C62cm. Currently it has mounted a Shimano Altus. Unfortunately, I can not find a model number on it, which would made things easier. There seems to be derailleurs for (61)63-66° and 66-69°. I tried to measure the chainstay angle on the bike and get to around 65° - with a large uncertainty. Because the value is so close to 66°, I wont risk to buy the 63-66° and then have the wrong type... However, it looks like 63-66° is the most common angle.

Is there another way of finding this angle or does the Altus should have a model number somewhere? Can I get this angle somewhere out of the geometry table on the Kona website?

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The 63-66° and 66-69° exist because there are two types of bicycles.

Mountain bikes have small diameter 559mm wheels and a high bottom bracket for a lot of ground clearance. The combined effect of the small wheel and the required high ground clearance mean the chainstays are nearly horizontal. Thus, the angle between the seat tube and the chainstays is rather high, about 66-69°.

In contrast, road and hybrid bikes have large diameter 622mm wheels and the bottom bracket is typically put as low as possible for making it easy to stop and making the ride feel of the bicycle stable on roads. Thus, the chainstays angle downwards towards the bottom bracket, meaning the angle between the seat tube and the chainstays is low, about 63-66°.

Your Kona Dew is a hybrid bike with 622mm wheels. Most likely you measured correctly: the angle between the seat tube and the chainstays should fall between 63-66°.

Of course you can calculate it based on seat tube angle, bottom bracket drop or height and chainstay length. Your seat tube is at 72.5° angle. Chainstays are 440mm. Bottom bracket height is 280mm. The rear hub height is about 347mm for those 622-37 tires. Thus the rear hub is 67 mm higher than bottom bracket. asin(67/440)*180°/pi = 8.8°.

That should give 72.5° - 8.8° = 63.7° which falls between the angles 63-66°. So there was quite large uncertainty in your measurement indeed.

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    Definitely living in the 90s or 2000s. Most MTBs have been produced as 29ers for a long time.
    – Vladimir F Героям слава
    Apr 23, 2021 at 18:13
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    @VladimirF This was a good answer that care was put into. We all need a correction on the chronology of things at times, be nice.
    – Nathan Knutson
    Apr 23, 2021 at 22:54
  • @VladimirF the title says 2010 for a model year. One can still buy brand new 26" MTBs today. Here on Bicycles.SE we attempt to help all riders, no matter what age or fanciness their ride is.
    – Criggie ♦
    Apr 24, 2021 at 7:01
  • The answer is quite definitive in proposing a distinction that no-longer exists (and did not exist in 2010). Be aware that I did not vote here in any way.
    – Vladimir F Героям слава
    Apr 24, 2021 at 8:09

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