Favor to Ask of Gravity Bike Owners
I'm trying to get to the bottom of the frame size discrepancy issue with the Efective Top Tube length (ETT) on Gravity 29er bikes, because I'd like to buy one. There have been multiple people that have actually measured their ETT and find it to be MUCH shorter than advertised. Would you be willing to measure the ETT on YOUR Gravity G29 or 29point1-5 and report the ETT length? Also post the model and size.
Attached is how Trek measures their ETT which is who Gravity openly shares they are mimicking in their geometry:
Last edited by Ufdah; 10-31-2012 at 02:47 PM.
I'll post the results of this thread here as they come in.
23.75" (G29 SS - mazey)
23.5" (G29 SS - Sasquatch1413)
And just so we know what things are suppposed to look like, here is the current advertised Gravity bike geometry chart. This is supposedly the same for both the G29 single speed and 29point1 - 29point 5 bikes.
Last edited by Ufdah; 10-30-2012 at 06:12 PM.
Here is a reply from mazey on the G29 SS thread:
Originally Posted by mazey
Last edited by Ufdah; 10-30-2012 at 06:03 PM.
Gravity G29 SS XL, measured my ETT at about 23.5 inches.
Just to clarify, that's a G29 SS right?
Originally Posted by Ufdah
I will measure my 17.5" G29P1 tonight..
I just measured a 21" Trek Marlin at the bike shop and it measured correctly at 25.3" ETT
I also just received an email from the BikesDirect service center stating that the 21" frame size is the same as mazey measured 23.75" not 25.3" as advertised.
I would really like for someone to measure a 29point1-5 bike to see if they are the same or if it's only the single speed bikes that are off...
Cassoulet forever !
ETT lenght is useless on a gravity bike, you should compare frame by REACH and STACK.
I'm not trying to be mean but are you serious? Why is it ETT the most important measurement according to virtually every bike manufacturer and fitter but useless on Gravity bikes?
Originally Posted by 20.100 FR
I understand that knowing these two measurements would help understand the actual differences between the Trek and Gravity frames but the simplest competent way to size a bike is by the ETT measurement. Which, whether you measure from the middle of the stem attachment (like Trek) or the top of the head tube will be virtually the same distance.
I think 20.100 FR may have been thinking gravity bike rather than a Gravity brand bike.
That said, I do agree that reach/stack is more useful for predicting how a frame will fit you. ETT also depends on the seat tube angle, whereas reach doesn't. My hardtail has a ETT that's 12mm (0.5") longer than the ETT on my full suspension frame. But the reach is 8mm shorter, and the cockpit feels shorter as a result. That 8mm is what I notice.
People are more used to thinking about ETT, and it works to a degree as a quick-and-dirty estimate. It's not necessarily the most useful measurement any more, though. When STAs vary from frame to frame as they commonly do now, it's less useful. It's similar to the way consumers and manufacturers both fixated on megapixels for digital cameras, when it really wasn't the best predictor of photo quality.
"Back off, man. I'm a scientist." - Dr. Peter Venkman
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