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PostPosted: Tue Dec 04, 2012 9:32 pm 
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Joined: Sat Nov 03, 2012 7:08 pm
Posts: 21
Location: London
Hi,

I am about to change from 172.5 cranks to 175. Does anyone have experience with having to change their saddle position as a result of similar change, and if so by how much?

thank you.


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PostPosted: Tue Dec 04, 2012 9:51 pm 
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Joined: Wed Oct 31, 2007 10:32 pm
Posts: 8490
Location: Los Feliz, Los Angeles, California
Why are you changing your crank length?

It isn't a simple matter of raising or lowering your seat height, and if your fit is sensitive (which, as you get older it will be) you may seriously damage your knees.

Why, you ask?
With the increased crank length not only will your legs be extending further, they will also be going up higher at the top of the cycle.
So unless your femur or shins grew to compensate, why are you changing your crank length?

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Posted: Tue Dec 04, 2012 9:51 pm 


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PostPosted: Tue Dec 04, 2012 10:16 pm 
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Joined: Sat Nov 03, 2012 7:08 pm
Posts: 21
Location: London
I am changing since I am upgrading my crankset and I wanted to try a longer crank while at it. I am 6'1 with a ~92cm inseam, and I am also more of a 'gear masher'. Given the above and my reading around the subject I believe it is worth trying 175mm cranks.


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PostPosted: Tue Dec 04, 2012 10:45 pm 
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Joined: Tue Aug 02, 2011 5:54 pm
Posts: 408
This exact subject was covered fairly recently.

viewtopic.php?f=3&t=107646


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PostPosted: Wed Dec 05, 2012 11:03 am 
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Joined: Wed Oct 06, 2004 6:55 pm
Posts: 2577
Location: Vienna, AUT
With those measurements, you should have been on 175s all along.
When raising the saddle down to compensate, remember that you also need to adjust the saddle aft to find the same position you had to the BB you had with the shorter cranks.


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PostPosted: Wed Dec 05, 2012 4:57 pm 
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Joined: Sat Aug 29, 2009 4:30 pm
Posts: 1989
When I change crank length, I do raise/lower the seat the same amount to keep the maximum leg extension the same. I am only 173 cm tall, but have a 84 cm inseam, and I have experimented with cranks as long as 180mm. I was really surprised that it was not a lot more difficult to spin the longer cranks, in fact they felt quite good. But I settled back to 175mm anyway, just because I didn't want to be getting to extreme or exotic with my equipment. I think you may be surprised that much of the "conventional wisdom" about crank length just doesn't hold true when you actually try them. Most studies end up claiming that length doesn't make much difference anyway, so it can't possibly be hurting too much to try them.

On the other hand, when I switched from speedplay pedals to Dura Ace, I should have raised my seat by a couple mm due to stack height differences, but I didn't. They seemed just fine without adjustment. So maybe I am just not all that sensitive to things. :)


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PostPosted: Thu Dec 06, 2012 2:47 pm 
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Joined: Sat Dec 13, 2003 2:25 am
Posts: 4962
Location: Canada
Some guys I know change their crank length from road to TT, which seems to work for them (one won a World Elite ITT championship doing that), but I can't do it. They do not change the saddle position, just the crank length.


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PostPosted: Thu Dec 06, 2012 7:15 pm 
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Joined: Sat Nov 03, 2012 7:08 pm
Posts: 21
Location: London
I've now installed the larger 175mm crank and tested it on the trainer. Position and power feels great and not like I need to change my saddle height. Looking forward to giving a proper (outdoors) test on the weekend.

If it is necessary to adjust saddle position I don't think it will be by much at all. Especially since you have some lateral margin of error to move forwards and back on the saddle.


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Posted: Thu Dec 06, 2012 7:15 pm 


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PostPosted: Thu Dec 13, 2012 11:08 am 
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Joined: Fri Nov 21, 2008 11:23 pm
Posts: 234
Location: Mal Born, Oz.
I have an 88.5cm inseam and use 177.5mm cranks. For me it is relief just like getting in the drivers seat after a short arse drove before me and being all cramped up then shifting the seat back. I'm 179cm and ride a 54.5cm top tube and don't handle saddle setback at all.
The extra crank length also stopped my hamstrings cramping.


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