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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 03-09-14, 10:26 AM   #1
bombardier
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Frame swap - any red flags in my plan?

Hey folks,

I have a 1990 Giant Allegre with a Suntour GPX groupo... the bike and it's components are in nice shape, but the frame is just too massive (60 cm! I need a 56cm). I am considering swapping out the frame/fork/headset/stem for this generic performance bike aluminum frame, which appears to be compatible with downtube shifters. Based on the information I found in this old Suntour GPX information sheet, it appears as if the bottom bracket sizes will be compatible. I'd buy a fork and headset with the frame, too, so I wouldn't have to worry about head tube compatibility. Is there anything else I should look out for when doing a frame swap like this? Might hub spacing be an issue?

I'm a newbie, so I wouldn't be surprised if I'm totally overlooking something critical here. But I've always operated under the belief that you never learn anything until you try it yourself, and I'd like to get more into the mechanics of maintaining bicycles as a hobby. Thanks for any input, advice, or guidance you can give me! If it'd help to have a picture of the Giant, I can certainly upload one.
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Old 03-09-14, 10:30 AM   #2
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All I'm going to say is Good luck and have fun with it! Post pics when you done.
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Old 03-09-14, 12:12 PM   #3
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Rear dropout spacing, brake reach and tire clearance are other things to consider.
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Old 03-09-14, 12:17 PM   #4
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bombardier, Shouldn't be very difficult. One point could be a drop out spacing mismatch between the two frames. The aluminum frame from Performance will be spaced at 130 mm while the Giant maybe 126 mm. You'll need a longer axle and spacers for the rear wheel if you want to keep your shifters. A new wheelset is an alternative, and an opportunity to update at added cost.

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Old 03-09-14, 12:21 PM   #5
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The things I'd check are the seat post szie (diameter), the front derailleur clamp & is the fork on the old frame 1 1inch or 1 1/8, if was 1 inch you'll need a new stem
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Old 03-09-14, 12:53 PM   #6
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60 cm is a big bike. If you don't think it fits you, I'd definitely make the change regardless of what it entails.

I wouldn't bet your SunTour shifters to fit those shifter bosses but they might. 27.2mm seat post is a common size so there's a good chance your existing seatpost will work. You will need a new fork, headset and stem. Possibly a new handlebar too. How many rear cogs does your present bike have? If it's 7, you may be in luck. 6 or fewer says 126 mm dropouts to me.

I'd suggest costing some of this stuff out before you start spending money. Once you start buying $25.00 parts, it's sometimes hard to stop because you think you need just one more thing to make the whole package work. It might work out to be cheaper to buy a whole bike in a smaller size.
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Old 03-09-14, 01:03 PM   #7
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i've have two of those frames in their singlespeed version. great deal, IME.

if indeed it is like mine, here's what i know.

headset is traditional threadless 1 1/8". i use the Richey Comp. great price and reliable.

i purchased two full carbon forks off ebay. i think one was an Orbea and the other a Litespeed.

those do look like oldschool downtube bosses on the downtube, so that's good.

mine came with 120mm spacing on rear to accomodate a track hub, but i would be surprised if the one shown is not a 130mm.

BB is standard oldschool british theaded, that will work with any old Shimano cartridge BB. or even an old heavy cup and loose ball BB.

seattube is 27.2.

the doodads (like cable stops for brakes and derailleur cables, rear DR hanger) are different on that frame than mine, so i can't comment on them.

i doubt whether this is very informative. i suppose all this is in the "specs" of the frame. and can easily be obtained via PB's "live chat" feature on their website.
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Old 03-10-14, 05:53 AM   #8
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I reckon you're probably better off selling the bike and buying another.

You tend to get a lot more for your money buying complete bikes rather than parts, whether that's new or second-hand, and Suntour was behind the times by 1990; Accushift was never lauded as a fine thing, unlike the Shimano stuff of the era.

You could pick up a ~1990 bike in your size with say 105, for maybe $250-$300 or even as cheap as $150, spend $60 or so on a fresh chain and cassette and maybe one or two other bits, get $200-$250 for your bike, bam.
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Old 03-10-14, 06:06 PM   #9
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As a learning experience it may be worth it. but if you have access to a bike co-op that would help with some instruction and access to tools.
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