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Old 03-09-04, 03:50 PM   #1
math2p14
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FR/DH/Trail sizing in comparison with XC

Hi all,

Beeing stuck for some time in old skool xc bikes, i am slowly realise some stuff about modern trail/fr/dh bikes. They all seem much smaller in comparison with an xc bike and even smaller in comparison with an old skool xc/dh bike (1992).

Given my old (stuck) ideas , i bought a year ago a 110mm stem (RF Deus). I had a rockhopper large frame (tt 590mm) and the bike felt large to me, with no standover clearance at all.

Recently i got an SX (med, 585mm tt but seems longer since the seattube angle is much slacker). The bike feels perfect as far as standover goes. It is ok with the current (110mm) stem, but usually i feel like i am about to go over the bars, ie i cant move backwards a lot. Some people told me to try an 80 or 70mm stem and 2" risers so that i ll have more manouverability on the bike on steep/technical terrain. Initially this sounded absurd to me since i was used to xc sizes (silly me), but now i come closer to realising that one needs a relatively smaller bike in order to tackle technical DH.

My impression is that a shorter stem will just get me on a more upright position, and not cramped (since my knees are far from my bent elbows). So far i tried to hold the bars with my fingertips, trying to imitate a shorter stem, and it felt fine. (Having the option of trying a shorter stem on loan is not easy here).

Anyhow, i am 185cm tall with a normal build (torso.legs.arms) that is 6.1".

Cheers.

BTW i am ditching the thomson seatpost for a titec


(sorry if the long post causes any inconvenience)
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Old 03-09-04, 06:31 PM   #2
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Is it possible that you cant get back on the bike because you ride with the seat really high? The bike isnt meant to be ridden like an XC bike like that.
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Old 03-09-04, 11:23 PM   #3
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Yannis, Klein may have a good point. The more agressive you ride, the lower you want your seat. When descending, you want to be able to easily hang your as(rear end) way off the back. If your seat is too high, you'll have trouble doing that.

So why are you ditching the Thomson post in lieu of a Titec. I would consider that a downgrade. I would definately recommend a quick release for your seatpost. That way when you ride the road to the trails your seat can be in a more XC position. Then when you hit the trails you can quickly drop you saddle 2" and have it in a lower "technical" position.

I would definately recommend a shorter stem. I run a 50 mm stem on my bike. That may be too much of a jump coming from a 110, I'd recommend a RaceFace Diabolous in the 70mm size.

What type of bars are you currently using? They are risers, just not big risers right? Like a 1" rise.

That should work for the time being. I wouldn't start changing too much at once, take it slow and change one adjustment at a time. Start with a lower seat height and see how that affects your riding. Then go for the shorter stem and realize how the front end comes up easier and you can shift your weight back even further. A riser bar will do the same just to a further degree.

Realize though that these changes will improve your DH sections and you handling on jumps/drops/technical sections, but at the sacrifice of climbing prowess. Your front end will want to "Walk" on you when you start heading up.

You need to find the balance point, the equilibrium, the ying and yang between going down manueverability and climbing skill.

L8R
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Old 03-10-04, 12:12 AM   #4
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First of all, you would be crazy to ditch the Thomson for a Titec. The Thomson is with the best of seatposts when it comes to strength and low weight. If there is anything you should consider as far as a seatpost, it should be a telescopic post so you can easily get it short for aggro riding, and then back up into a climbing/classic xc position.
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Old 03-10-04, 02:47 AM   #5
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Originally Posted by Pharcyde
First of all, you would be crazy to ditch the Thomson for a Titec. The Thomson is with the best of seatposts when it comes to strength and low weight. If there is anything you should consider as far as a seatpost, it should be a telescopic post so you can easily get it short for aggro riding, and then back up into a climbing/classic xc position.
That is exactly the reason that i want to ditch the Thomson. It is the best post i have ever had. But, it is 410mm, and i can cut a maximum of 2" off it in order not to have minimum insertion problems, i havent done it so far, but i have this feeling that 2" arent going to be enough for the cases that i want to put the seat all the way down.

That is why i was thinking about a Titec Knock Scoper, telescopic one, 270mm-410mm range.
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Old 03-10-04, 02:51 AM   #6
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A2,

I am using 1" risers. The 110mm stem come from my previous hardtail. The plan is to get exactly what you suggested, a 70mm diabolus 31.8 with the respective bars. I really hope that given my TT & height , the 70mm stem will make things better.

The lack of DH ability given my seatpost/stem/risers is what i want to improve. As for climbing....i can either walk or take it easy, flat land and DH stuff is what i need the bike good to be for.

the plan is,

Change from RF Deus 110mm to RF Diabolus 70mmX10deg

Change from stock 1" risers to 1.5" or 2" Diabolus risers

Change or Cut (if it fits) my Thomson post.

I would be obliged for further advice.
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Old 03-10-04, 10:23 AM   #7
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Like everybody else has stated, drop your seat and maybe move it back some...not so much as to stress the rails, but enough to change the cockpit.

Definitely change the stem. Other than actual top tube length, the stem and the seat position/height can affect your riding the most.

Just as an afterthought, check/maintain your air pressures or spring pressures in the front and rear...a weak front end will want to pitch you over (I know this from experience)...too much/quick rebound in the rear will tend to bounce you around/over/up...
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Old 03-10-04, 10:27 AM   #8
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Originally Posted by math2p14
That is exactly the reason that i want to ditch the Thomson. It is the best post i have ever had. But, it is 410mm, and i can cut a maximum of 2" off it in order not to have minimum insertion problems, i havent done it so far, but i have this feeling that 2" arent going to be enough for the cases that i want to put the seat all the way down.

That is why i was thinking about a Titec Knock Scoper, telescopic one, 270mm-410mm range.

No no no no no no dude. You can cut the seatpost as far as you want, the marking on the post is just for how far it should be inserted into a frame when the post is uncut. You can cut it as far as you want.
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Old 03-10-04, 11:36 AM   #9
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So klein, you reckon that my guide should be the hole on the seattube of the frame as far as min insertion goes?
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Old 03-10-04, 12:02 PM   #10
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Keep the Thompson and opt for a quick release clamp. I've seen 2 telescopic seat post fail. One was simple, the other was catastrophic.
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Old 03-10-04, 12:03 PM   #11
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YES! Also apply some of your basic physics. The longer the post, the deeper the insertion to counteract the lever arm. If you cut your post and don't have as long a lever arm, you can theoretically (slightly) reduce the insertion amount.

IOW, if you are above that hole by 1/2" I wouldn't sweat it!

L8R
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Old 03-10-04, 12:12 PM   #12
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Quote:
Originally Posted by a2psyklnut
YES! Also apply some of your basic physics. The longer the post, the deeper the insertion to counteract the lever arm. If you cut your post and don't have as long a lever arm, you can theoretically (slightly) reduce the insertion amount.

IOW, if you are above that hole by 1/2" I would sweat it!

L8R

Ok maybe i wasnt so explanatory. I have the full 410mm length now. I can now lower it only for 2" in order to avoid hitting the shock on a bottom out compression. If i chop 2" i will basically be able to lower it effectively by 4". The plan is to be BELOW that hole for about 1". I guess this is 100% safe for both frame and post (220lbs rider). The seatpost is out of the seattube by 23cm for perfect XC height.
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Old 03-10-04, 12:18 PM   #13
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Correct, and what I'm saying, is you can cut your post even further to the point just above the inspection hole.

That would allow you to lower the seat another 1" or 1-1/2"

L8R
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Old 03-10-04, 12:19 PM   #14
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hmm i guess you mean just below the hole, coz specialized says that the post should be visible at all times through this hole.
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Old 03-11-04, 10:07 AM   #15
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Originally Posted by math2p14
So klein, you reckon that my guide should be the hole on the seattube of the frame as far as min insertion goes?

Yes, your exactly right.
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Old 03-14-04, 03:31 AM   #16
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Ok i went to the lbs (since i dont have a hacksaw...) and the guys there said to me to chop only an inch off (which they did). They also told me that they recommend that the seatpost should be well below the guiding hole on the seatube and basically to be entirely inside the tube. ie i should get is as high as i was as long as the bottom end of the post is flush with the bottom end of the seattube. go figure....
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