How much seat post exposure is too much

cyclotoine":16ojpwo2 said:

it's pretty long, but the photo doesn't really help. The rampage is pretty light tubing therefore it could be susceptible to cracking. Watch for crack originating from the the end of the slot on the back of the seat tube. Again it matters what is in the frame. measure how much is in the frame and mark it with a piece of tape and take a photo of that. That will be very telling. Most important thing... how much do you weigh?

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I run around 210 lbs and 6 ft 1 in tall - little short in the leg though. Riding an 18 inch Zaskar which feels fairly similar to this one. I have about half an inch more than the minimum marked on the post inserted in the seat tube.

dirttorpedo":20ujry55 said:

I run around 210 lbs and 6 ft 1 in tall - little short in the leg though. Riding an 18 inch Zaskar which feels fairly similar to this one. I have about half an inch more than the minimum marked on the post inserted in the seat tube.

Click to expand...

Tall and short in the leg would suggest a longer body and therefore a bigger (longer reach) frame.

gtRTSdh":31a3gfji said:

dirttorpedo":31a3gfji said:

I run around 210 lbs and 6 ft 1 in tall - little short in the leg though. Riding an 18 inch Zaskar which feels fairly similar to this one. I have about half an inch more than the minimum marked on the post inserted in the seat tube.

Click to expand...

Tall and short in the leg would suggest a longer body and therefore a bigger (longer reach) frame.

Click to expand...

Yep, I agree. 19" would probably be a better suit.

I take it all back, looks like my "rule of thumb" has gone right out of the window :shock:

That is a serious amount of seatpost showing there, and given your size/weight and the lightweight nature of the frame I'd be inclined to trade up to a larger size frame sooner rather than later.

Think about your bodyweight on the saddle and how much leverage that generates with such a long seatpost, even more so when you go over bumps and plonk yourself back down on the saddle. Sounds like the frame would give way before the seatpost did though.

I really think you need a larger frame.

Judging by how much post is showing, and the long riser stem I would say you need a bigger frame - something like 20".

Unfortunately, I agree with the other posters, Given your weight and that the rampage is a pretty light gauge tubing I'd be inclined to size up. If there was a log there I wouldn't worry so much, but there isn't. It might be fine but the chances of something cracking or breaking are much higher given your size and the set-up.

Damn!

Ya, 19.5 to 20.5 was my frame size BITD. When I bought this bike I thought it was a 19.5. Crap, I can't believe my run of luck buying bikes and frames! This is the third frame that's too small. I even measured this one. Serves me right for not doing my research.

Oh well, there are a couple of cheap frames on Craigslist that look like they might be my size. Maybe I can sell the Rampage frame and get a replacement and be no worse the wear.

In my opinion there is no hard and fast rule, buts what is true is that :

• The heavier you are = the more chance of cracking.
• The more post is exposed = the more chance of cracking.

You just can't get away from that ...

Some makes / models / materials / designs are more prone to cracking than others - if yours is one of them, factor that into the above.

Frame ID and post OD (regardless of that the spec says or the post has stamped on it) have a tolerance - a poor fit will alter its fatigue resistance and should be factored in.

Even the bloke / machine that welded it could alter its fatigue resistance on 'identical' bikes made on the same day.

At the end of the day, no one on the net could tell you 100% if it will be ok or not - it's all guesswork that needs consideration / good judgement / good luck ...

Whatever option you go with, the only sure thing is running a post that long has increased the chance of cracks / failure.

Hope that helps

WD

dirttorpedo":247svf2g said:

Damn!

Ya, 19.5 to 20.5 was my frame size BITD. When I bought this bike I thought it was a 19.5. Crap, I can't believe my run of luck buying bikes and frames! This is the third frame that's too small. I even measured this one. Serves me right for not doing my research.

Oh well, there are a couple of cheap frames on Craigslist that look like they might be my size. Maybe I can sell the Rampage frame and get a replacement and be no worse the wear.

Click to expand...

You should go get this one:

http://vancouver.en.craigslist.ca/nvn/b ... 36518.html

I emailed. Original owner but no fork.

If it's any consolation, people won't be able to give bikes away in Vancouver soon (if that's where you are). It happens every year. I remember trying to sell my Rocky Mountain Fusion around December time a few years back. Granted it was a fairly lowly model but it looked almost new, and I'd upgraded to XT V brakes, new commuting tyres, a complete overhaul, bearings....everything....the bike ran like a dream (it was my commuter) and I finally had to let it go for 100 bucks as I was broke :roll:

Something will come up!