Frame sizing and offset seat post.

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Frame sizing and offset seat post.

Postby flamingo » November 8th, 2021, 2:53 pm

Probably a question that was discussed many times.

I am 6ft 0" tall. Have always been using a large frame just like suggested by manufacturers for my height. However I have always found that I like to have an offset seat post which adds about 1" to the top tube length. That distance is roughly what distinguishes large from XL frame on the top tube.
Was wondering if for my next bike should I switch to XL frame? There is only two manufacturers of offset dropper posts. On top of that the stem lenghts are getting shorter as well which would also be compensated by longer top tube.
All opinions are welcome.
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Re: Frame sizing and offset seat post.

Postby c0nsumer » November 8th, 2021, 3:52 pm

Give this a read. I wrote it up after spending a lot of time thinking about exactly how/why I kept wanting for a setback dropper, why modern seatposts are so steep, why modern frames have such a long reach, etc: https://nuxx.net/blog/2020/11/26/though ... -bike-fit/

FWIW, I very happily ride bikes fit as described above on all sorts of stuff. XC, trail, etc. I'm a very full believer in proper modern mountain bike fit; no longer keen focused on ensuring my pedal-saddle fit is identical between all bikes (road and mountain).
Steve Vigneau

Unless otherwise stated the content of my posts are my opinion and should not be taken as the official stance of, nor representative of, CRAMBA-IMBA.
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Re: Frame sizing and offset seat post.

Postby Steve_Balogh » November 13th, 2021, 6:54 pm

In 2012 I confused the Fatbike MFG with my body dimensions and at the last minute he put me into a large frame. Issue was I have a longer than normal torso as compared to my inseam. Made sense, always had issues with stock frames. When Gary Fisher went with Genisis geometry further back in time, he lost me as a customer as none of the frames fit me. Three years earlier I had bought my first Quiring with custom geometry, was the first bike I ever owned that I could put a straight seatpost on. A couple years later when Scott had built a few fat bikes, I sold that large frame fat bike and bought another custom geometry fat bike from him. Just about all of my bikes are the same. I stopped buying from the big name MFG’s. No more set back seatposts for me to try and make a frame work that doesn’t fit right in the first place. Key thing is to find someone who can properly fit you and do the measurements right and make the correct recommendations.

FYI- I’m about the same height as you, and that large Fatbike frame I had was a bit too big, I could not do tight turns at high speed very well. While it felt good, actually riding it under certain conditions was a different story. If I had gone with the medium frame I would have been too cramped. If you can’t get the geometry you need, switch to a different brand that works.
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Re: Frame sizing and offset seat post.

Postby flamingo » November 14th, 2021, 1:21 am

Thanks for the answers (both Steves :) ). I read the blog. I fund it quite interesting. Thank you for taking your time and shearing your thoughts and experiences. Consumer the blog you state the following
With these modern geometry bikes, attempts at copying a classic mountain bike’s fit using the classic saddle setback and saddle-to-bar distance will be frustrating and result in an awkward-steering bike.

I guess this is might be a part of my dilemma. Let share a bit of my experience. One of my bikes is Pivot Mach 4C (Not to be confused with Mach 4SL). It comes in large size as specified by manufacturer for my height, and I ride it with an offset seatpost. A friend of mine has the same bike in XL size without the offset seatpost but the same bar and stem length (80 and 720mm). Last year I had a chance to ride it for for a week in Sedona and Phoenix. I found it to be perfectly fine just like my Pivot with offset post. Then last summer while in Bend Oregon I accidentally ran into a Pivot demo. I got to test the Mach 4 SL in a large size (similar top tube length as Mach 4C). The bike did not have an offset post. The stem was I think 40-50mm and the bars were at least 740 if not 760. Man did I ever fell like I was riding on top of a camel. Because I was not stretched I had to have pretty straight up position which felt somewhat cramped or weird. I understand that once "off the saddle" the top tube length does not matter and what matters is the reach. I do not have problem with the reach on my current large size bikes. But if I get ones of those "modern" geometry bikes in XL size then I will get the reach that might be too long and the top tube that feels right. For a large frame it will be a too short top tube and a correct reach. Unless I am wrong and the more upright positions while riding is the "new/correct" thing. I have been looking at the new Santa Cruz Blur frame and the top tube on a large size is only 24.1". That is the same as my old 26" Blur from 10 years ago! That bike has 100mm stem and 680mm bars. So if I shortend the stem I would still feel cramped even with wider bars. I have also been looking at the newest Ibis Exie. In large size the TT length is 25.4". That is over 1" longer than the Blur. Also I am not the biggest fan of super wide bars since I am pretty narrow in my shoulders and find Michgan trails not the most suitable for anything over 720mm. I have already clipped enough trees. However I definitively do like wider bars for climbing. So going back to the top of my post. Is more upward sitting position the new thing on the modern geometry bikes and I should just "suck up" to it? As for the offset dropper post for those who don't know. Canadian made (no cheap labor used) 9point8 offers offset option on their posts. I have one of those, they are pretty light (unlike offset KS) and customer service is pretty good.
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Re: Frame sizing and offset seat post.

Postby c0nsumer » November 15th, 2021, 7:29 am

flamingo wrote:Also I am not the biggest fan of super wide bars since I am pretty narrow in my shoulders and find Michgan trails not the most suitable for anything over 720mm. I have already clipped enough trees. However I definitively do like wider bars for climbing.


For reference, I like 760mm bars these days with shorter stems. Or 710mm with longer stems. The narrower bars steer faster in tight/twisty stuff and with more body lean, the wider bars require more direct input to steer, but is more stable on rough stuff or when going faster. I don't clip any more trees myself. (Any wider than that is uncomfortable for me.)

flamingo wrote:Is more upward sitting position the new thing on the modern geometry bikes and I should just "suck up" to it?


Yes. With shorter cranks too, so you don't need to have your hip angle closed so far. And you still CAN lean over, but it's not as required, which allows one to handle the bike better because your body remains more centered. And the steeper seat tube (from the more upward sitting position) does sustained climbing better. Because I'm liking to ride outside of SE MI a lot lately, this is a great thing for me.
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Unless otherwise stated the content of my posts are my opinion and should not be taken as the official stance of, nor representative of, CRAMBA-IMBA.
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