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Discussion Starter · #1 ·
Just out of curiosity, what would be the possible negaitves of buiding a bike with a long top tube, let's say 25.5". Currently I ride a 24.5 TT with a 100mm stem. Why not take the length out of the stem and put it into the frame, that is 1" longer bike and a 1" shorter stem.

More or less just really puching the Genesis geometry principle. Push the head tube all the way to the bars and run the shortest stem possible.

Any thoughts?
 

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XL Fisher are 25.5" ETT I think?
Especially due to many 29"ers still having a steeper-than-with-26" head tube angle, a bit less length goes to the front center measurement.

For the future, I'd like to try a very short top tube, with a second headtube placed in front of it. Fork in the mor rearward head tube, stem on the forward one. The 2 connected by some linkage (chain, whatever). Normal length or short stem, really slack head tube angle, loads of fork offset, preferable front center. I wonder how that would ride. Obviously much different from a Genesis style bike with 39mm offset and the same (perhaps preferable) front center.
 

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desert kid said:
Any thoughts?
I normally ride a 23.75" ETT and a 120 mm stem, but this weekend I swapped bikes with a friend of mine, mid ride, and he runs a 24.5" ETT w/90 mm stem. I rather liked this setup a bit more, I felt like I was able to keep my weight back for the flowing downhills, steering was responsive and precise (ie. not twitchy like I thought it might be), and my COG seemed to feel lower, which helped out in the techy twisty stuff. The bike I own has a 71 deg HTA and 73 deg STA, and please don't flame me, is a 26er. The bike I borrowed has a 72.5 deg HTA and 73 deg STA BUT uses 29er wheels. My test was conducted to blow me over the fence into 29er land. :D
 

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Discussion Starter · #5 ·
What do you guys think is too long? Will the bike start to feel srange as far as a wheel base that is too long?

So lets say you keep you bars in your happly place and basically make the front triangle as long as possible. Keep the head tube angle the same but just strecth the effective tip tube. Say for example a 50mm stem that puts you in a comfortable cross country position.

At my height i am starting to push the length of XL bikes. What about really tall guys wo would need a 27"TT to make this priciple work?

Basically how long is to long?
 

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Gary Fisher once reminded me of how perfectly fine city bikes ride, and those just have back swept bars mounted directly to the steerer, no stem length, thus negative handlebar reach over the steerer. They do steer just fine. Front Center (front axle - BB) is the main thing affecting handling here. as said, on 29"ers the HTA is often a bit steeper than with 26", so you get away (require) a longer top tube. Once forks all get 29"-specific offset, these steep hed tube angles won't be needed anymore (to spice up handling/fork trail figure) and we'll see more shorter(normal for 26") head tubes.
 

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How tall are you?...

Meat Foot said:
I normally ride a 23.75" ETT and a 120 mm stem, but this weekend I swapped bikes with a friend of mine, mid ride, and he runs a 24.5" ETT w/90 mm stem. I rather liked this setup a bit more, I felt like I was able to keep my weight back for the flowing downhills, steering was responsive and precise (ie. not twitchy like I thought it might be), and my COG seemed to feel lower, which helped out in the techy twisty stuff. The bike I own has a 71 deg HTA and 73 deg STA, and please don't flame me, is a 26er. The bike I borrowed has a 72.5 deg HTA and 73 deg STA BUT uses 29er wheels. My test was conducted to blow me over the fence into 29er land. :D
because I ride 2 29ers, both 20in frames, one with a 23.75" TT and a 120mm stem and the other with a 24.4" TT and a 100mm stem. The One with the shorter TT is the more nimble and agile of the 2 and they have identical head and seat tube angles. Im 6ft 2in w/a 34in inseam.
In my experience the bikes with longer TT's have not out performed the ones with moderate TT's. Infact, the shorter ones are noticeably better handling here in the tight and twisty east coast. By shorter I mean 23.5 - 24in on a 19-20in frame. This is just my experience, Im sure it will differ from one rider to another.
 

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edouble said:
because I ride 2 29ers, one with a 23.75" TT and a 120mm stem and the other with a 24.4" TT and a 100mm stem. The One with the shorter TT is the more nimble and agile of the 2 and they have identical head and seat tube angles. Im 6ft 2in w/a 34in inseam.
5-11 on a good day ;) I have about a 32 inch inseam. I do not doubt your findings. The bikes I rode were differrent enough to notice ETT and even though my 26er has shorter wheelbase, I felt the 29er and its attributes made for a more controlled ride without sacraficing comfort. It was a good blend. Oh, and it was rigid with a Rohlhoff. :D
 

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Ohhh...

desert kid said:
I am 5'11" with a 34.5" inseam
And I thought my 6' w/ 3.425" inseam was bad. You are mostly leg and need a bike with a lot of seat tube and a relatively short TT to fit you correctly. Something like a Spot or Soma Juice (both of which I own).

Long TTs and short stems makes for a nice straight DH oriented rig but that's about it, IMO. Not enough weight on the front wheel to make it stick hard, fast turns, ie, prevent washout. It lengthens the wheel base. Longer stems help to "stabalize" steering very much like a "poor man's Hopey steering damper". It's true. Go from a long 120mm to a 100mm and feel the difference. On slower, curvey, technical trails the shorter 100mm stem will feel choppy like it wants to turn the front wheel too far too fast; and it allows for more front end deflection because of less leverage. These affects are noticed more on slower curvey trails, typical of East coast riding where I'm at. Wider, fast open trails would more easily allow you to get away with a shorter stem, and it may even be prefered by some (see MTBA's last month's issue on stem length-which they foolishly left out the bike and rider size).

After 15 years of trying all types of sizes and geometries and setups I've settled on about a 23.6 to 23.8" effective TT and either a 110mm or 120mm stem (I wish Thomson made a 115mm). I'd bet you'd feel pretty good on a similar geometry. One caveat... the 71.5 to 72 degree HA is too steep IMO, especially for a tall, leggy guy. It tucks the wheel too far under the front of the bike and makes you a bit endo prone. I jacked up the front of my Soma Juice a bit with a taller headset and got the HA a bit slacker. For my Spot (which I'm going to build up this weekend) I had the stock geo tweaked by shortening the TT a bit and bumping the HA out to 71 from 71.5 on a large frame.

Keep in mind the vast majority of my riding has been on 26" bikes, but now with a fair amount of miles on 29ers I'm finding bike set up isn't that much different with either size.

Hopefully this will help.

Mike
 

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I like short stems and a fairly upright position with my bar height generally no lower than my seat height. I was afraid of the 24.5 TT on my large SIR9, but ever since swapping from a 90 mm stem to a 70 mm stem, it has been great.

Dave Turner says (I think) that you should get the same size bike in 29 than you use in 26 and run a shorter stem. I have a large 5-Spot with a 90mm stem. Thus, I would need a large Sultan with a 70 mm stem. I think the Niner and Sultan have the same TT.
 

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For 20+ years I rode Cannondales with 23.5" top tubes and 150mm stems. For the past 2 years I've been on 29ers with 25.2" top tubes and 100 to 120mm stems and there is no comparison. With the longer top tubes the bikes are much more stable even when climbing. I'm not going back. Give me G2 geometry anyday!:thumbsup:
 

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Meat Foot said:
My test was conducted to blow me over the fence into 29er land. :D
ha HA! ;) That bike went off to AZ today for more testing, but it's yours again as soon as it gets back here.
 

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Cloxxki said:
For the future, I'd like to try a very short top tube, with a second headtube placed in front of it. Fork in the mor rearward head tube, stem on the forward one. The 2 connected by some linkage (chain, whatever). Normal length or short stem, really slack head tube angle, loads of fork offset, preferable front center. I wonder how that would ride. Obviously much different from a Genesis style bike with 39mm offset and the same (perhaps preferable) front center.
Just like the bike pictured as my avatar...
 
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I personally shoot for a 100mm stem because XC stems shorter than 80mm are rare and stems longer than 120mm are awkward. That way I have an inch or two to play with to tweak comfort and handling. The trade-off of the top-tube is that a longer wheelbase feels more stable, a shorter one, more maneuverable. A couple inches in wheelbase make a noticeable difference. Too short and you've got a twitchy bike, too long and it rides like a boat.

bm
 
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