Frame Sizing

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Postby Jon H » Fri Jun 01, 2007 11:33 am

If your forks are going rusty, you could just replace them with some nice carbon ones. :wink:

These days with semi-compact and compact frames the seat tube length is largely irrelevent. It's the top tube (or effective top tube equivalent to a horizontal frame) you need to look at. I'd have thought that 3cm shorter is going to mean it's too small for you, unless your current bike has a short stem and/or the saddle is right back on it's rails.
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Postby Andrew G » Fri Jun 01, 2007 12:05 pm

Yeah it's all a bit confusing these days. My GB's seat tube c-c is something silly like 45cm because it's a compact frame.

I think you should be okay with only a 3cm difference. My fixie has a top tube that is technically a bit big for me but by shoving the seat forward a bit on a straight seatpin and using a 75mm rather than 100mm stem I've "shortened" it to fit me. Maybe not perfect but I've done 60 mile club runs on it without problems or discomfort.

If the new frame is the smaller top tube it'll be even easier. Use a 10mm longer stem than before (won't affect the handling or your position over the front wheel noticably) and use a seat pin with a bit of lay back / offset on it. An extra 10mm due to layback of seatpin and 10mm of slidding saddle back on the rails and there shouldn't be any real problem as no one element or position has changed more than 1cm.

Look forward to seeing this fine stead on the road soon Marco.
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Postby Elliot M » Fri Jun 01, 2007 1:16 pm

what is it? steel?
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Postby Mike I » Fri Jun 01, 2007 1:59 pm

[quote]Its only 19 years old


That's pathetic! I've bought bikes older than that. And kept them for longer! :)

I think I was once told (but don't quote me) that a stem between 9cm and 13 cm should be ok. Any longer and the front gets a bit twitchy, any shorter and the bars become a bit like a rudder (or was it the other way round?). Bike shop man then said something about geometry, head tube angles and fork rake, my eyes glazed over, I made my excuses and left.
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Postby Andrew G » Fri Jun 01, 2007 2:34 pm

My fixie frame with the 75mm stem is circa 1968-1970 (Marco you'd be proud :wink: ) so has steel forks with the more old fashioned curlier rake. I wouldn't want to race on it like this, but for general riding / TTing it's fine, not overly twitchy. You can still ride no hands on a reasonable road surface for example.

Re the layback seatpost I think most main manufacturers do a staight and layback version. The one I have (again on the fixie - it was a budget build up) is a basic Alu one from Evans (Selcof "Team" I think) and only cost about £15. I think Selcof do some reasonable budget posts.

I had a Selcof post in my older bike originally which had a bit of layback on it, I'll have a route around the garage and see if I've still got it. Being short of leg it isn't very long but it might do. I'm guessing your frame will be a standard diamond frame anyway so won't have any of this more modern long exposed seatpost malarkey. :D
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Postby SimonJOsborne » Fri Jun 01, 2007 3:02 pm

In my limited experience you need to factor in your proportions. I am 6'4" so when I bought my first road bike about two years ago online I went for the largest frame available. But my 63cm Trek is a bit on the large side for me. I have it setup just about right with a 90mm stem.

After doing some bike sizing and test rides it seems that I have a proportionately shorter torso/back for someone of my size. So top tube length tends to be key for me anyway. The frame i ended up looking at was a 58cm S-Works Roubaix, which I will pair with a 120mm stem and more seat post than I have used in the past.

Aside from that I reckon that bike fitting, unless you are going for a custom frame or build, is a little over the top. If you get someone with a tape measure, a skilled eye and maybe some different bikes to try out you will probably have more success.

Not sure how much use that is but theres my 2p anyway.
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Postby Andrew G » Wed Jun 06, 2007 1:42 pm

Marco I found the slight layback seatpost if you need it / want to have a look. It does only have a short shaft though (stop sniggering at the back) so couldn't be used it you needed to have a fair bit exposed, probably about 6 inches sticking out (stop it!)

Cheers,

Finbar.
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Postby Sylv » Fri Jun 08, 2007 12:51 pm

Well done!

What are the cranks then in the end?
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Postby Andrew G » Fri Jun 08, 2007 1:07 pm

Blimey, that does sound a cracking deal.
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Postby Jon H » Fri Jun 08, 2007 1:11 pm

Sounds like a Bobby Dazzler, you bargain hunter.
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