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Old 02-03-12, 08:57 AM   #1
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Longer seat post and risers for a slightly too small frame? any problems with this.

I have an old Specialized Rockhopper Comp that is just a tad too small for me, I ride a 21 inch mountain bike generally and on the low end I can pull off a 19 inch with the seat post extended as far out as it can go but just stick to buying 21 inch bikes because, well, it only makes sense!

BUT

that old Rockhopper is an 18 inch frame, I am attached to the bike for whatever reason and have considered just selling it but every time I do I end up putting it back in the pile, I think that it has something to do with its the first bike that I "refurbed" since getting back into riding.

My question is, are there any issues with putting a longer seat post and some short riser bars onto it and riding it? the riser bars may not even be necessary honestly, I have ridden this bike as far as about 7 miles as it sits and is really a third bike so doesn't get ridden too often by me.

and because pictures are always fun.


Thanks for any help guys and gals.
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Old 02-03-12, 09:48 AM   #2
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If the seatpost is long enough that the minimum insertion mark is below the top of the seat tube you should be fine. There are seatposts 400 mm long or even more available and the minimum insertion marks are typically 75 mm or so from the end so you have a lot of extension available.
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Old 02-03-12, 10:41 AM   #3
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steel tube stem riser will let you use the existing stem,
you can combine a quill to threadless adapter, instead, if you wish

sloping top tube mountain bikes have a market segment now
so there are quality, strong seat posts and,
if 27.2, the Thudbuster suspension seat posts Too..
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Old 02-03-12, 03:15 PM   #4
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I've been riding a tiny MTB since 1997. Love it. I knee the stem more often than on bigger bikes but still pretty rare.

I agree that the hi-rise stem on the Rockhopper would make riser bars an option, not a necessity.


DSCN1785 by Lester Of Puppets, on Flickr
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Old 02-03-12, 03:41 PM   #5
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Originally Posted by fietsbob View Post
steel tube stem riser will let you use the existing stem,
you can combine a quill to threadless adapter, instead, if you wish

sloping top tube mountain bikes have a market segment now
so there are quality, strong seat posts and,
if 27.2, the Thudbuster suspension seat posts Too..
something like this? http://www.ebay.com/itm/290663926466...84.m1423.l2649


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I've been riding a tiny MTB since 1997. Love it. I knee the stem more often than on bigger bikes but still pretty rare.

I agree that the hi-rise stem on the Rockhopper would make riser bars an option, not a necessity.


DSCN1785 by Lester Of Puppets, on Flickr
what seat post is that? I am thinking that any old seatpost that is long enough should work? I found a 26.8 x 400mm post on ebay for about $30 delivered, I don't think that's bad but it would be more than I have into the entire bike so far nice looking Mongoose by the way.
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Old 02-03-12, 03:49 PM   #6
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Quote:
something like this? [ebay picture]
yah, you can get one thru any bike shop,
3 sizes, .833" [bmx]
22.2mm/7/8" that is what you need,
and 9/8"

I got a long Chromo 25.4/1" seatpost thru Redline, cheap, strong . chromed.
needs a clip on top for the saddle. and shim to fit the seat tube ID on the bike ,
but pretty darn strong ..
you can find those as 1" is a common shim ID to work from..

Last edited by fietsbob; 02-03-12 at 03:56 PM.
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Old 02-03-12, 04:11 PM   #7
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There's about a dozen (or more?) different seat post diameters in .2MM (.008") increments!
You MUST get the proper diameter!!!!!

Rock Hoppers seat posts varied from year to year, so you can't assume they have a generic size for that model.
You MIGHT be able to find the proper diameter on bikepedia.com

I installed a 400MM post on my bike last summer for the same reason as you.
I found a NEW one for $30 on the net and the bike shop matched the price.
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Old 02-03-12, 06:12 PM   #8
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Originally Posted by Bill Kapaun View Post
There's about a dozen (or more?) different seat post diameters in .2MM (.008") increments!
You MUST get the proper diameter!!!!!

Rock Hoppers seat posts varied from year to year, so you can't assume they have a generic size for that model.
You MIGHT be able to find the proper diameter on bikepedia.com

I installed a 400MM post on my bike last summer for the same reason as you.
I found a NEW one for $30 on the net and the bike shop matched the price.
Measured with a Digital Caliper 26.8 is what the seat post that is in there right now is and I have been riding on it and it hasn't moved yet (and I am a clyde) so I gotta assume its the correct diameter for the frame.
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Old 02-03-12, 06:53 PM   #9
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Not that it matters, but I think that may actually be a 17" frame. According to a 1989 Specialized catalog I found online, that bike was available in 15, 17, 19.5, 21.5 and 22.5.

I think my Rockhopper is a 19.5.



Ironically, I'm generally happy with 17" mountain bikes. For some reason this one feels smaller. I guess because they were still experimenting with MTB geometry back then.

You can probably get a Kalloy seatpost in the size you need for around $20 if your LBS doesn't charge you shipping.
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Old 02-03-12, 07:56 PM   #10
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MTB geometry/fit is way different than road fit. In my experience, a MTB feels best when the seatpost (300mm) is almost to the minimum insertion point which puts me on 18" frames (BUT these are "newer" MTBs with sloping top tubes from the 1990s). I ride 22-23" road frames. If the photo of your bike is setup for you now, I would say the fit is fine.

I once tried riding a 16" MTB with a 400mm post and decided that I didn't like the fit and sold it.
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Old 02-03-12, 10:05 PM   #11
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Originally Posted by Push View Post
Measured with a Digital Caliper 26.8 is what the seat post that is in there right now is and I have been riding on it and it hasn't moved yet (and I am a clyde) so I gotta assume its the correct diameter for the frame.
Well, I wouldn't have posted if the link you posted wasn't for a STEM, while you were discussing seat posts.
I thought you were going to stick that into the seat tube!
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Old 02-03-12, 10:50 PM   #12
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Originally Posted by Andy_K View Post
Not that it matters, but I think that may actually be a 17" frame. According to a 1989 Specialized catalog I found online, that bike was available in 15, 17, 19.5, 21.5 and 22.5.

I think my Rockhopper is a 19.5.



Ironically, I'm generally happy with 17" mountain bikes. For some reason this one feels smaller. I guess because they were still experimenting with MTB geometry back then.

You can probably get a Kalloy seatpost in the size you need for around $20 if your LBS doesn't charge you shipping.
Mine is an 88 (note the U brake) but it would appear that you are correct in the size either way as there was no 18 inch in 88 either http://www.retrobike.co.uk/forum/viewtopic.php?t=164394 , I got 18 inches from measuring the center of the crank to the top of the seat tube (and was going off of memory ) Your bike is NICE! was it re done? and I mean completely, not just cleaned up like I did to mine


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Originally Posted by FastJake View Post
MTB geometry/fit is way different than road fit. In my experience, a MTB feels best when the seatpost (300mm) is almost to the minimum insertion point which puts me on 18" frames (BUT these are "newer" MTBs with sloping top tubes from the 1990s). I ride 22-23" road frames. If the photo of your bike is setup for you now, I would say the fit is fine.

I once tried riding a 16" MTB with a 400mm post and decided that I didn't like the fit and sold it.
The bike in the image is as close to set up for me as it can be with that seat post on it, it is right at the limit and I could use a tad bit more room to be perfectly comfortable enough for a long ride.


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Well, I wouldn't have posted if the link you posted wasn't for a STEM, while you were discussing seat posts.
I thought you were going to stick that into the seat tube!
Nah, wasn't gonna stick that in the seat tube, my original post I asked about riser bars and fietsbob mentioned the stem riser (thats what the link was)
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Old 02-04-12, 12:22 AM   #13
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Mine is an 88 (note the U brake)...
Ah, I missed that. I thought the color scheme was sufficient to determine year.

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Your bike is NICE! was it re done? and I mean completely, not just cleaned up like I did to mine
As pictured above, it just had new tires and was otherwise as I bought it (used but in near-mint condition). I've since changed out everything but the seat post, saddle, crank arms and headset.

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Old 02-04-12, 12:55 AM   #14
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Originally Posted by Bill Kapaun View Post
There's about a dozen (or more?) different seat post diameters in .2MM (.008") increments!
You MUST get the proper diameter!!!!!

Rock Hoppers seat posts varied from year to year, so you can't assume they have a generic size for that model.
You MIGHT be able to find the proper diameter on bikepedia.com

I installed a 400MM post on my bike last summer for the same reason as you.
I found a NEW one for $30 on the net and the bike shop matched the price.
That's the preferred way to do it, but I've had success with shims. This has the advantage of lower likelihood of scratching the seatpost. An undersized seatpost with a properly-sized shim can leave the seatpost relatively unscratched.
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Old 02-04-12, 01:49 AM   #15
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When I got back into biking in 2008 or so, I didn't realize that the $180 mountain bike I'd purchased from Target was actually a "youth size" until I held it up to the one my roommate had gotten. It worked for the most part, but when I pondered the fact that I only had about 1" of seat tube in the seat post, I realized it was time for a larger bike.

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