Minimum insertion
 

Hey guys!

I've been riding my 84 Trek 760 around for a bit and I love it. There's only one little problem. In order to get the same leg extension I have on my cannondale, I need to raise the seatpost a little above the minimum insertion level. I have it right at the mark right now, but I feel the need to have just that little bit more extension.

I weigh 145ish and I was wondering whether I should try to raise the post above the notch by a little bit and what kind of risks I'd be taking if I did this. I don't want to damage the post or the frame. The post will be maybe half an inch over the level.

Thanks a lot for your feedback!

Get a new seatpost?

Don't risk it, yes you are light but the warning is there for good reason. Get a longer post.

sounds like your frame is a bit small

... or merely fashionably small by today's standards.

What kind of saddle is on it? Brookses sit higher than say, Aliases, by about a cm and a half.

Road Fan

Is it the original seatpost? The one on this 1984 catalog photo looks like it may already be raised close to its maximum useable height. Older stems were commonly made with a shaft length of only 180 to 200 mm and for 4" to 5" showing above the seatlug and 2-1/2" below the limit line - which allowed for what was considered a normal bike fit for that era.

Just buy another post. New posts are commonly made to fit modern mini-frames, so they're often available anywhere from 300 to 400 mm long (4" to 8" longer). :)

Could be worse... I have some top end racing bike posts from the 1960s with shafts only 130-150 mm long! :D

http://www.vintage-trek.com/images/trek/84Trek_8_72.jpg

I ride a 54 cannondale with a decent amount of drop but recently flipped the stem up to get a less aggressive (read less painful for my back) position.

The trek is 56 and I need maybe half an inch to an inch more of seatpost. The seatpost is stock from what I know, but I really like the silver fluted seatpost. Anyone know where I can get one for the frame? I don't know what diameter of post I need. Does anyone have one of these bikes and know?

I might swing for a modern silver post if the diameter is the same.

Thanks.

P.S. Lets not start the frame sizing debate. I like my bikes the way they are.

No debate here (55cm C-T is just my size :) ), just an easily verified observation that over the years cyclists have generally moved toward shorter frames. Short seatposts were very common on bikes of the 1960s and early 1970s.

I know :) A lot of people are very adamant that that's the only way to do it and while it's great for some applications (touring commuting etc), it just doesn't fit in with training and racing today.

Any idea what size the seatpost is?

The minimum insertion mark does not mean it is going to break if you have less than than in the seat tube, it means the maker is not responsibe for any problems. I have ridden bikes with the seat post about 1/2 inch beyond the mark, no problem. But like the manufactures, I am not responsible for any problems you have if you try it :D

IIRC, the minimum insertion point is 2-1/2 inches into the seat tube, and it is a arbitrary rather than engineered figure, but I personally would not go less than 2 inchs. If you are a very strong rider you might even want to make your own insertion minimum 3 inchs or so.

I'd look for a setback Thomsom post in silver and in your required diameter. Their lengths are 250 mm, 330 mm, and 440 mm. 440 is RRREEEAAAlly long. I use 250s, and Mrs. Road Fan's Cannondale could benefit from a 330. The setback of a Thomson is not extreme and probably matches the setback of your stock post.

The bike I have right now is the one stronglight linked to. I have no problems with the seatpost on my CAAD9.

I really like the fluted seatpost that the bike comes with though I do feel like I've had to move my saddle forward a bunch to get comfortable. I don't really like the aesthetics of a setback seatpost on this bike though I might go that route if I really need to.

Does anyone know what size seatpost the 84 trek 760 frame uses?

Check near the bottom of the post for any imprints. They often stamped both a date code and the diameter size of the post just below any limit line markings.

According to Trek's online catalog, they used a SR (Sakae Ringyo) "SR-P5" Laprade style alloy seatpost. From my own experience with similar posts they indeed had quite short shafts.

diameter should be 27.2 mm. The length should be around 250 mm or so.

I can see not liking the aesthetics of a Thomson, but it you need setback, your knees pretty much require it, but it doesn't have to be a Thomson of course!

I don't like the SR Laprade my 84 610 came with, but it's no longer than yours, I think, is 27.0, and the saddle angle adjustment is way too coarse for me.

Aren't we talking about a Trek?

Yeah we are, but for some reason I thought someone was referring to my other bike when they started talking about setback seatposts.

I'll take off the post and look around for a new one soon ish.

I wish I could find a decent fluted one for a price that wasn't nuts. Newer posts just don't have the same appeal on this bike.

Thanks.

I don't think I need a setback post. My seat is pushed forward pretty far right now, though I haven't really looked much at KOPS since I haven't ridden the bike long and hard yet.

Well, the converse of what I said is that if you don't need setback you don't need a setback post. I don't measure knee position any more since I'm getting better at feeling what the saddle problem is on myh bikes.

When I did, strangely KOPS turned out to work pretty well for me.

Road Fan

I was riding the bike on a trainer today and I started having knee pain on my right knee. I looked down and asked someone to eyeball it and my knee was behind my pedal spindle. I lowered my seatpost a little and the leg extension is still ok, but the KOPS is still not really on. I think I'm going to hold off on doing anything with this bike and just use it to get around for now...

Thanks for your help though! Vintage trek says that the seatpost should be 27.2mm as people here said.