Do i really need a new bottom bracket?

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BigonaBianchi

BigonaBianchi

Yes I can, Yes I am, Yes I did...Repeat.
So if i switched to 172.5 instead of 175 I could drop by saddle by 2.5cm?

Currently I ride a 61cm frame with a 120mm stem and a lot of seat post showing. Im looking at getting a 62 or 63cm new bike (lottery allowing) but in the meantime shorter cranks may help as I wouldnt need such a lot of seat post. I cant raise the bars as there are no spacers left on the steering tube. im 6'4" btw.
 

BSRU

A Human Being
Location
Swindon
So if i switched to 172.5 instead of 175 I could drop by saddle by 2.5cm?
The crank lengths are in millimetres.
 
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BigonaBianchi

BigonaBianchi

Yes I can, Yes I am, Yes I did...Repeat.
I took a read of sheldon brown:
http://sheldonbrown.com/gain.html

I understand the gain ratio is the thing...so for every kilometre the pedals spin around th ebottom bracket the bike moves forward by whatever the gain ration is in km in this case...erm...??
So looking at the crank lengths on a 700c wheel it seems to me that the 170mm has a higher ratio than the 175mm crank...so would travel further for less effort....er...????

700 X 28 336 2.036 1.976 1.948 1.920 1.867


Blimey ..bit tecky isnt it lol!
 
So if i switched to 172.5 instead of 175 I could drop by saddle by 2.5cm?

Currently I ride a 61cm frame with a 120mm stem and a lot of seat post showing. Im looking at getting a 62 or 63cm new bike (lottery allowing) but in the meantime shorter cranks may help as I wouldnt need such a lot of seat post. I cant raise the bars as there are no spacers left on the steering tube. im 6'4" btw.
if you shorten the cranks, then surely the saddle height would need to be higher to keep the same leg length?
 
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BigonaBianchi

BigonaBianchi

Yes I can, Yes I am, Yes I did...Repeat.
if you shorten the cranks, then surely the saddle height would need to be higher to keep the same leg length?

at the bottom of the pedal cycle yes, but at the top of the cycle no...it's all tooooo confusing lol

sheldons ratios show the 170 cranks as slightly more efficiant for me..but i could have completely ballseditup (tecky term) ...about to hit buy now of a campag 54/34t compact with 175 cranks only because I had them all this time and dunnow how a crank size change will affect anything really, even after the sheldon calculator experience...im more into comfort than speed...i counted my caseete teeth and looks like i have a 12/28 on there...would be nice to have a 11-32 to make those hills easier..basically im just putting the bike back where it was before and not really changing anything on the climbs if i dont change cassette rings...but then i guess a bigger derailer may be needed and ....arrrrgggggggggggggggggggggghhhhhhhhhhhhhhhhh its all a visciuos circle....may buy a Harley and have done with it lol!
 
at the bottom of the pedal cycle yes, but at the top of the cycle no...it's all tooooo confusing lol

sheldons ratios show the 170 cranks as slightly more efficiant for me..but i could have completely ballseditup (tecky term) ...about to hit buy now of a campag 54/34t compact with 175 cranks only because I had them all this time and dunnow how a crank size change will affect anything really, even after the sheldon calculator experience...im more into comfort than speed...i counted my caseete teeth and looks like i have a 12/28 on there...would be nice to have a 11-32 to make those hills easier..basically im just putting the bike back where it was before and not really changing anything on the climbs if i dont change cassette rings...but then i guess a bigger derailer may be needed and ....arrrrgggggggggggggggggggggghhhhhhhhhhhhhhhhh its all a visciuos circle....may buy a Harley and have done with it lol!
but it is the straight leg length that counts isn't it for saddle height and knee injuries/preventing them....
 

boydj

Legendary Member
Location
Paisley
but it is the straight leg length that counts isn't it for saddle height and knee injuries/preventing them....
Correct. The shorter cranks also means that the range of movement for your knees and thighs is reduced, which is helpful if you are built like Ernie Wise (short, fat hairy legs). I have 165 mm cranks.......
 

Sharky

Guru
Location
Kent
What have I started! Short cranks are certainly a hot topic at the moment. Manufacturers have kept us to the same basic lengths since ordinary bikes. It is only now, especially in the tri world where convention is being challenged.
I now have 4 bikes active. Three with 150mm and my latest conversion on 145mm. All feel great and the aero tuck position is much more comfortable.

Cheers Keith
 
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BigonaBianchi

BigonaBianchi

Yes I can, Yes I am, Yes I did...Repeat.
LBS is clueless on the question other than to say tall = long & short = shorter .....all they want is to sell a new bianchi.....off to next LBS.....six in town....lucky me...
 
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BigonaBianchi

BigonaBianchi

Yes I can, Yes I am, Yes I did...Repeat.
cool thanks....looks like the spesh 61cm has a 175 crank...same a sthe one i had origionally.....hang it all i'll stick with 175 and what i know.....thanks all :smile:)))))))
 
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