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Silly question about frame geometry of gravel bikes

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Silly question about frame geometry of gravel bikes

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Old 02-07-19, 05:42 AM
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Aznman
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Silly question about frame geometry of gravel bikes

I've noticed that all of the gravel bikes that I have seen so far have top tubes that are shorter than their respective 'effective top tubes' (i.e. the top tubes are more parallel with the down tubes).


The above mentioned trend is so dominant that I have to ask: in the industry's terms, would a bike still be considered a 'gravel bike' if it has nearly all the same forks, wheels, tyres, and other parts but uses a 'Randonneur type' frame instead (where the top tubes are parallet to the theorectically flat ground; where the top tubes are the 'effective top tubes')?
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Old 02-07-19, 07:55 AM
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Sloping top tubes are an abomination. Long live the horizontal top tube.
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Old 02-07-19, 07:56 AM
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Aznman
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Originally Posted by hmmm View Post
sloping top tubes are an abomination. Long live the horizontal top tube.
Can't say whether I agree or disagree.
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Old 02-07-19, 08:02 AM
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Well, ask a silly question, get a silly answer. My silly answer is that if this "sloping top tube" trend continues unabated, then 20 years from now, us guys will all be riding girl's step-through frames (as well as wearing dresses and playing with dolls).
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Old 02-07-19, 08:48 AM
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Originally Posted by Lemond1985 View Post
Well, ask a silly question, get a silly answer. My silly answer is that if this "sloping top tube" trend continues unabated, then 20 years from now, us guys will all be riding girl's step-through frames (as well as wearing dresses and playing with dolls).
Serious question and hopefully informative answer then.
Why are virtually all gravel specific bikes made and bought with sloping top tubes?
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Old 02-07-19, 10:45 AM
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The trend for shorter reach and maintaining relatively high stack heights
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Old 02-07-19, 10:54 AM
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Higher stack + crotch room. Without the crotch room it's just a rando bike.

Seriously, I think the whole slanted top tube thing is to allow a single frame size to accommodate a wider range of human sizes, so a manufacturer can get by with 5 frame sizes instead of 6. Yet another way to cut costs.

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Old 02-07-19, 11:01 AM
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Originally Posted by Aznman View Post
: in the industry's terms, would a bike still be considered a 'gravel bike' if it has nearly all the same forks, wheels, tyres, and other parts but uses a 'Randonneur type' frame instead (where the top tubes are parallet to the theorectically flat ground; where the top tubes are the 'effective top tubes')?
If the important geometry is the same, then sure it's a gravel bike. Call it that if you want...it isn't a big deal either way.

if a level top tube frame and a sloping top tube frame have identical HTA, STA, trail, bottom bracket drop, tire clearance, chainstay length, stack height, and reach- then yeah they are capable of doing the same things and feel free to call them the same thing.

a decent real world example-
I have a black mountain cycles gravel frame with canti brakes that uses a level top tube. The disc brake frame has almost identical geometey, but uses a sloping top tube to get a higher stack height as that's the one measurement thats different.
both are gravel frames.
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Old 02-07-19, 11:17 AM
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Originally Posted by mstateglfr View Post
If the important geometry is the same, then sure it's a gravel bike. Call it that if you want...it isn't a big deal either way.

if a level top tube frame and a sloping top tube frame have identical HTA, STA, trail, bottom bracket drop, tire clearance, chainstay length, stack height, and reach- then yeah they are capable of doing the same things and feel free to call them the same thing.

a decent real world example-
I have a black mountain cycles gravel frame with canti brakes that uses a level top tube. The disc brake frame has almost identical geometey, but uses a sloping top tube to get a higher stack height as that's the one measurement thats different.
both are gravel frames.
Awesome. Many thanks.
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Old 02-07-19, 11:31 AM
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You probably won't see many level top tube frames MARKETED/SOLD as gravel bikes, but I don't think there are that many level top tube frames on the market anyway. My commuter has a slightly sloping top tube, was sold as a hybrid when new, has cantis, clearance for 38mm tires, gravel/cross geometry, etc. I think I could call it a gravel bike if I wanted to, but I don't do "gravel rides" aside from an occasional 1 mile stretch of a gravel road on my commute, which my bike handles admirably. In other words, if a frame works for a certain purpose, isn't it whatever you make it to be?

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Old 02-07-19, 12:48 PM
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Originally Posted by mstateglfr View Post
If the important geometry is the same, then sure it's a gravel bike. Call it that if you want...it isn't a big deal either way.

if a level top tube frame and a sloping top tube frame have identical HTA, STA, trail, bottom bracket drop, tire clearance, chainstay length, stack height, and reach- then yeah they are capable of doing the same things and feel free to call them the same thing.

a decent real world example-
I have a black mountain cycles gravel frame with canti brakes that uses a level top tube. The disc brake frame has almost identical geometey, but uses a sloping top tube to get a higher stack height as that's the one measurement thats different.
both are gravel frames.
Great example. In fact, I used to own and ride one of the canti version Black Mtn Monster Cross frames and I now have the new disc version MCD. They both gobble up miles of gravel roads like nothing else I've ridden and they have a very similar fit and feel. The only times I notice the sloping tube on the new bike is having more crotch clearance when I stop and straddle the bike and when I have enough exposed seat post to easily clamp the bike in my work stand.

Sloping top tubes has been the industry norm for road bikes for many years. This is not something specific to gravel bikes. There are some exceptions, but not very many that I am aware of.
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Old 02-07-19, 12:48 PM
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A sloping TT might be a small advantage with a gravel bike, as it will better allow a fast and sloppy dismount when the going gets rough. It also allows for more seatpost extended beyond the frame, which might dissipate some shocks and chatter that would otherwise be transmitted to the saddle. But that's not why the manufacturers are putting them on bikes.
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Old 02-07-19, 12:54 PM
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Originally Posted by Aznman View Post
Serious question and hopefully informative answer then.
Why are virtually all gravel specific bikes made and bought with sloping top tubes?
Virtually all bikes made recently utilize compact frames with sloping top tubes. This is not a uniquely "gravel bikes" phenomenon, this has been an industry-wide trend for years.
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Old 02-07-19, 02:21 PM
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Just buy a cyclocross bike, they almost all have horizontal top tubes still for shouldering
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Old 02-07-19, 03:17 PM
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Originally Posted by Aznman View Post
I've noticed that all of the gravel bikes that I have seen so far have top tubes that are shorter than their respective 'effective top tubes' (i.e. the top tubes are more parallel with the down tubes).

The above mentioned trend is so dominant that I have to ask: in the industry's terms, would a bike still be considered a 'gravel bike' if it has nearly all the same forks, wheels, tyres, and other parts but uses a 'Randonneur type' frame instead (where the top tubes are parallet to the theorectically flat ground; where the top tubes are the 'effective top tubes')?
Considering that the paved road bikes also have a sloping top tube, I'd simply call it a feature of modern frame design and not think that it has any serious impact on what type of bike something is.
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Old 02-07-19, 07:26 PM
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I think gravel vs rando, the gravel bike will tend to have less BB drop, and a shorter chainstay. So, slightly higher BB and quicker rear end that a rando bike. That said if you compare geometries on multiple bikes there's overlap all over the place.
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Old 02-08-19, 07:05 PM
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Originally Posted by Lemond1985 View Post
Well, ask a silly question, get a silly answer. My silly answer is that if this "sloping top tube" trend continues unabated, then 20 years from now, us guys will all be riding girl's step-through frames (as well as wearing dresses and playing with dolls).
I never understood why men's bikes had the horizontal top tube. Seems you guys need the clearance more than us ladies do. We don't have dangling bits to worry about smashing.
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Old 02-08-19, 08:32 PM
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Originally Posted by Aznman View Post
I've noticed that all of the gravel bikes that I have seen so far have top tubes that are shorter than their respective 'effective top tubes' (i.e. the top tubes are more parallel with the down tubes).
TT = (ETT)*cos θ
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Old 02-08-19, 08:35 PM
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Originally Posted by Hmmm View Post
Sloping top tubes are an abomination. Long live the horizontal top tube.
If you have short legs and a long torso, it helps if you want the bars at saddle level.

eg: I have to do this with my Bianchi, and the fit is still inferior to that of my gravel bike.




vs.


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Old 02-08-19, 08:46 PM
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Originally Posted by Aznman View Post
Serious question and hopefully informative answer then.
Why are virtually all gravel specific bikes made and bought with sloping top tubes?
I think for gravel people tend to set it up so the tops of the bars are about the same level as the saddle, so it increases the stack relative to the stand-over height.

(Then there are people like me who have short legs, so all our bikes look like this.)
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Old 02-10-19, 10:04 AM
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Me too. 5'11'' with 29" inseam. I'll take a sloping top tube any day
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