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Gear Conversion?
#1
Have a pristine '85 Fuji Allegro w/ 12spd gears. Can this bike be converted
to a 18spd by changing the front cog from 2 to 3 gears? Or would the conversion cost more than the bike was worth?

Front cogs=42,52 w/ 170mm chain
Rear spindle= 14,16,19,22,26,30

Thought adding a 32 cog to the front would help with climbs.
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#2
(01-03-2014, 02:54 AM)oldfoxb Wrote:  Have a pristine '85 Fuji Allegro w/ 12spd gears. Can this bike be converted
to a 18spd by changing the front cog from 2 to 3 gears? Or would the conversion cost more than the bike was worth?

Front cogs=42,52 w/ 170mm chain
Rear spindle= 14,16,19,22,26,30

Thought adding a 32 cog to the front would help with climbs.
Bottom line only you can decide if it is worth it or not. Many people put money into bikes merely because they just love the bike and want to modify it to suit themselves better. I often will take new bikes straight from the box and gut them and rebuild to suit for various reasons.
Going from a double to a triple can most always be done but requires perhaps a triple crankset, bottom bracket, front derailleur, could even involve replacing the rear derailleur also.
If you can, post some pics of your system that you have now, i.e. shifters, rear/front derailluers, model numbers/names if possible. clear close-up shots of your bottom bracket area and we can better guide from there. but expect anywhere from $100 to even as much as $200 or more depending on the components you choose for this mod
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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#3
A new front derailleur and crank set can be inexpensive, but as Painkiller said, you will have difficulty calculating where the new chain rings will line up with your existing bottom bracket.
Do you use the 52 tooth front chain ring?
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#4
As Jef alluded to; I would seriously consider a 50-34 compact double instead of a triple, as a more economical route.
http://www.amazon.com/Shimano-FC-A070-Road-Crankset-Cog/dp/B007Q4P490/
and suitable BB with the bolts (110.5mm)
http://www.amazon.com/dp/B00B58QJCY/
Nigel
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#5
(01-03-2014, 04:49 AM)1FJEF Wrote:  A new front derailleur and crank set can be inexpensive, but as Painkiller said, you will have difficulty calculating where the new chain rings will line up with your existing bottom bracket.
Do you use the 52 tooth front chain ring?
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#6
Yes, I do use the 52 tooth front ring, that's what makes this bike fly. The other thought that has come into play is the front derailleur controls which are now on the stem. Not enough movement in the existing lever to make 3spds work; would have to convert that also. Oh well it was just a thought.
Just purchased another Fuji, this one a hybrid Sunfire, but it's is geared lower.
(01-03-2014, 09:17 AM)nfmisso Wrote:  As Jef alluded to; I would seriously consider a 50-34 compact double instead of a triple, as a more economical route.
http://www.amazon.com/Shimano-FC-A070-Road-Crankset-Cog/dp/B007Q4P490/
and suitable BB with the bolts (110.5mm)
http://www.amazon.com/dp/B00B58QJCY/

I understand your concept of splitting the gear ratio, but why would I have to replace the BB if I was only using 2 front cogs? Chain would have to be shortened to 160-164 mm also.
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#7
(01-03-2014, 09:17 AM)nfmisso Wrote:  As Jef alluded to; I would seriously consider a 50-34 compact double instead of a triple, as a more economical route.
http://www.amazon.com/Shimano-FC-A070-Road-Crankset-Cog/dp/B007Q4P490/
and suitable BB with the bolts (110.5mm)
http://www.amazon.com/dp/B00B58QJCY/

Browsing on Amazon saw this Shimano FC-M131 Tourney Crankset with Chain Guard 170mm 48/38/28 Silver ; compatible with 8/7/6 spindles; $27.00 Then the issues would be width of this Crankset vs the OEM Shimano Dble on the Fuji. Would have to replace lower BB to get additional width at crank, then still have the issue of the controls for the triple crank.........hummmm, interesting.
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#8
(01-03-2014, 08:10 PM)oldfoxb Wrote:  Yes, I do use the 52 tooth front ring, that's what makes this bike fly. The other thought that has come into play is the front derailleur controls which are now on the stem. Not enough movement in the existing lever to make 3spds work; would have to convert that also. Oh well it was just a thought.
Just purchased another Fuji, this one a hybrid Sunfire, but it's is geared lower.
(01-03-2014, 09:17 AM)nfmisso Wrote:  As Jef alluded to; I would seriously consider a 50-34 compact double instead of a triple, as a more economical route.
http://www.amazon.com/Shimano-FC-A070-Road-Crankset-Cog/dp/B007Q4P490/
and suitable BB with the bolts (110.5mm)
http://www.amazon.com/dp/B00B58QJCY/

I understand your concept of splitting the gear ratio, but why would I have to replace the BB if I was only using 2 front cogs? Chain would have to be shortened to 160-164 mm also.

Different cranksets (even doubles) can take different BB spindle lengths. You would have to do some research and some measurements to see if your current spindle would be compatible, but it's unlikely - probably too long. For that reason folks usually purchase a crankset that includes a BB or at least buy the BB at the same time. Most every seller will specify or at least know what BB is required.

The chain would not necessarily have to be shortened - depends on the rear derailleur wrap capacity. Besides, if it's properly sized now you can only safely remove one complete link (inner/outer) for the 2 tooth large chainwheel difference. Otherwise you run the risk of damage if you shift to the large-large combo.

You will not lose any significant speed going to a 50 tooth. Your high gear of 50-14 should be good for 35 mph. After that you're going downhill anyway - tuck and coast!
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#9
(01-03-2014, 08:10 PM)oldfoxb Wrote:  .......... but why would I have to replace the BB if I was only using 2 front cogs? ......

Because all cranks are different; even in Shimano's line up, some triples are supposed to be used with 122.5mm BB, some with 113mm and other lengths. Doubles are the same. Also note, that often Shimano's recommendations are not the best solution.
Nigel
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#10
(01-03-2014, 09:23 PM)nfmisso Wrote:  
(01-03-2014, 08:10 PM)oldfoxb Wrote:  .......... but why would I have to replace the BB if I was only using 2 front cogs? ......

Because all cranks are different; even in Shimano's line up, some triples are supposed to be used with 122.5mm BB, some with 113mm and other lengths. Doubles are the same. Also note, that often Shimano's recommendations are not the best solution.

Things became slightly more interesting here. Checked the detail for the suggested Cog set, those will not fit the OEM Sugino VT Crankset. Check manufactures, (2) Cogs would cost $70-80, aluminum crank bolts are $25. An XCD compact crank on Ebay was selling for $135......still waiting for word from supplier as to compatibility. Re-read all the links on compact cranks, now I fully understand your original suggestion. Thank you.
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