Questions Re: Effective Top-tube, Head-tube Angle, and Stem Length
KYHikerBiker
Posts: 9
Hi all!
I'm looking for a new bike after 6 months away from riding, and finding a bike I can work with has been quite a challenge.
I'm a mere 5' 8.5", but I've found only one size M bike ever (an 18.5 Trek Superfly) that allowed me to ride without back discomfort/strain, which usu. sets in the night after a ride and lasts for a couple days.
I've owned two size M bikes, and I've ridden a half-dozen or more at shops around my region; all of them cause back strain that worsens the longer/more frequently I ride. I've become perceptive enough that I can usu. predict if this back discomfort will occur, based on how the bike feels when I ride in the standing position.
Recently, I rode a size L Salsa Timberjack, and voila! The bike felt great in the standing position, and I had zero post-ride back strain.
I did, however, have achy and snappy elbows and shoulders, I'm sure due to the bars being too far away.
So I'm trying to figure out whether I have a comprehensive enough understanding of effective top-tube (ETT) to make some reasonable predictions about my range of possible adjustments on the Salsa Timberjack.
Here goes: first, my old Trek Superfly had an ETT + stem length of 685. If I make the ETT + stem length of the T-jack identical to the ETT + stem length of the old Trek Superfly, can I expect the reach-to-the-bars (notwithstanding stack height) to be the same, in the seated position, on BOTH bikes?
My understanding is that ETT takes into account seat-tube angle, but I wonder if the tighter seat-tube angle on the T-jack might necessitate moving the seat farther back than I did on the Superfly, in order to get the right position over the pedals.
Secondly, assuming I can bring the bars back enough on the T-jack to get a good, seated, reach-to-the-bars, can I predict that the T-jack's range of adjustment will "tolerate" the specific stem-length reduction I'll need to make?
In order to get the T-jack in line with my old Trek, by my estimation, I'll need to reduce the stem from 70mm to 45mm, possibly even down to 40mm. I know that mountain bikers hail short stems these days, and I'm not a bit hesitant to use one; I'm just not sure if the T-jack in particular would "tolerate" a stem this short. The head-tube angle = 68.7, whereas my Trek had a head-tube angle of 69.6. The Trek did well down to about 70mm of stem length, but it got a little wacky around 65mm or less.
Cheers, and many thanks to any bikers who might help me with some input.
I'm looking for a new bike after 6 months away from riding, and finding a bike I can work with has been quite a challenge.
I'm a mere 5' 8.5", but I've found only one size M bike ever (an 18.5 Trek Superfly) that allowed me to ride without back discomfort/strain, which usu. sets in the night after a ride and lasts for a couple days.
I've owned two size M bikes, and I've ridden a half-dozen or more at shops around my region; all of them cause back strain that worsens the longer/more frequently I ride. I've become perceptive enough that I can usu. predict if this back discomfort will occur, based on how the bike feels when I ride in the standing position.
Recently, I rode a size L Salsa Timberjack, and voila! The bike felt great in the standing position, and I had zero post-ride back strain.
I did, however, have achy and snappy elbows and shoulders, I'm sure due to the bars being too far away.
So I'm trying to figure out whether I have a comprehensive enough understanding of effective top-tube (ETT) to make some reasonable predictions about my range of possible adjustments on the Salsa Timberjack.
Here goes: first, my old Trek Superfly had an ETT + stem length of 685. If I make the ETT + stem length of the T-jack identical to the ETT + stem length of the old Trek Superfly, can I expect the reach-to-the-bars (notwithstanding stack height) to be the same, in the seated position, on BOTH bikes?
My understanding is that ETT takes into account seat-tube angle, but I wonder if the tighter seat-tube angle on the T-jack might necessitate moving the seat farther back than I did on the Superfly, in order to get the right position over the pedals.
Secondly, assuming I can bring the bars back enough on the T-jack to get a good, seated, reach-to-the-bars, can I predict that the T-jack's range of adjustment will "tolerate" the specific stem-length reduction I'll need to make?
In order to get the T-jack in line with my old Trek, by my estimation, I'll need to reduce the stem from 70mm to 45mm, possibly even down to 40mm. I know that mountain bikers hail short stems these days, and I'm not a bit hesitant to use one; I'm just not sure if the T-jack in particular would "tolerate" a stem this short. The head-tube angle = 68.7, whereas my Trek had a head-tube angle of 69.6. The Trek did well down to about 70mm of stem length, but it got a little wacky around 65mm or less.
Cheers, and many thanks to any bikers who might help me with some input.
0
Posts
Get that right and you can adjust most bikes to suit provided you start with the right frame size.
I feel like my back problems originate from inadequate standing position on the various bikes.
According to the Salsa size guide you should, going by your height, be on a small or, at a push, a medium Timberjack.
Unless you have abnormally long arms and/or legs a large is way too big for you.
Maybe your bad back is because you are riding a bike that is too big and you are continually over-stretching?
You need to go to a decent bike shop and get advice on what size bike you really need.
As a comparison I am 6’ tall with a 31” inside leg. I ride a Medium Giant Trance with a reach of 425mm. The Large Timberjack has a reach of 463mm. There is no way I could ride that and remain comfortable.
And it all promised so so much”
Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
Bike James disagrees:
https://www.bikejames.com/strength/why- ... -pedaling/
And it all promised so so much”
Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
Indeed. And I won't pretend I developed a riding style based on Bike James!
I just tend to ride in that position a lot (much less so on the road), and I thought it was pretty typical to ride standing when on trails.
Doesn't matter what that says, a bike has a saddle so is meant for sitting, as above. Sure it is OK to get out of the saddle to accelerate or climb up hills but that is a tiny amount of the riding time.
You don't need to read nonsense like that but use your noggin and try for youre.
Do a short 1 mile ride. Youll do it fine sitting but I'll bet you would not be able to do it sanding the whole way.
Do you have an underlying health issue? I'm very tall and can tolerate my much shorter girlfriends bike for about an hour before I get seriously uncomfortable.
Standing position is fairly much irrelevant.
This is quite a good video about bike fitting, it's road bike focused but the same principles apply to mountain bikes unless you want to do the red Bull rampage, it's a good general guideline..
https://youtu.be/oxNznrlRXGU
That bike james site sounds like absolute guff to me.
You only stand off the saddle when you want a short burst of power, it's not a normal riding position.
I'm 5'9.5" but have short legs and arms, from experience I know I need a bigger frame to match my torso. I'm taller sitting down than a mate who is 6'1" and nearly as tall as another mate who is 6'4", but he has freaky long legs.
retired 9.6kg Carrera Kraken
The Carrera Hardtail combined thread - come on all you Carrera's!
The Sons Scott Genius RC20 build
Not to my knowledge, though certainly a reasonable question.
I can throw two+, 18-hole rounds of disc golf at a sustained, sweat-dripping, water-guzzling pace any day I get a chance.
Last weekend, I backpacked 14 or more miles over three days with a 45 lb pack (I pack too much. Something I gotta work on).
No back discomfort whatsoever.
This appears to be the case. A shop owner took some measurements and brought this apparent fact to my attention. He said I have short legs with a longer-than-average (for my height) torso. Unfortunately, he didn't have any bikes on hand that would serve well for a test-ride.
He did say he'd put me on a size L frame without hesitation and work from there.
I appreciate that and understand that frame length is usually more important than height in an MTB frame but if you look at the geometry of the Timberjack there is quite a difference in the stand-over heights between a small and large frame (over 3 inches) and that has to come in to play as well doesn't it?
And it all promised so so much”
Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
Yup I frequantly have minimal or negative standover on bikes that fit me perfectly.
retired 9.6kg Carrera Kraken
The Carrera Hardtail combined thread - come on all you Carrera's!
The Sons Scott Genius RC20 build
[