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  #1  
Old 10-24-2022, 10:47 AM
HowardCosellsPR HowardCosellsPR is offline
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Modern Mtb Seat Angles and Fore-Aft???

So... just curious about this... and it might be a total 'noob' question... but:

For folks who split time between road and mtbs, how are you dealing with/setting up your mountain bike fore-aft given the new geometry (eg... ~76d seat tube angles)?

Thanks, HCPR
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  #2  
Old 10-31-2022, 09:11 AM
ah87 ah87 is offline
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On my Esker Japhy (hardtail) I keep my saddle pretty much level, but I also don't ride in an aggressive position on my road/gravel bike.
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  #3  
Old 01-16-2023, 08:38 PM
darkmother darkmother is offline
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Changing from road bike to MTB feels a bit strange if you have been riding one or the other for a longer period of time. For me, I find I adapt to the change fairly quickly, but it takes a few rides to feel at home after a switch.

One thing I find: My hamstrings, which are usually pretty tight, get *super* tight riding upright with steep seat tube angles. If I don't pay attention to that, bad things happen to my lower back muscles, piriformis etc.
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  #4  
Old 01-16-2023, 08:42 PM
darkmother darkmother is offline
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Also, don't set your MTB up like your road bike. Took me a while to figure this one out.

Lots of stem length and decent drop is a good recipe for me on tarmac.

The same offroad just does not work for me.
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  #5  
Old 01-17-2023, 12:11 PM
John H. John H. is offline
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Modern Geo MTB

My short answer is "not ride one".
I know many folks like them, but I am not in that majority. I hit my limit at about 1 hour where I can't pedal them any longer. This is less true if the ride is more up and down than on the pedals. But on the pedals for an hour and my body shuts down.

That said, there are a few bikes that are not as steep. Epic Evo comes to mind.
You can also get (I have this on all of my mountain bikes) a 9point8 dropper with 25mm of saddle setback.

The other thing I have noticed about these steep seat angle long reach bikes is that they don't work well for folks that are "reach challenged". Take a really long bike with low stack, short reach and an already short stem and you have nowhere to go if you if you need to shorten up reach.
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  #6  
Old 01-17-2023, 02:37 PM
Alistair Alistair is offline
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Quote:
Originally Posted by John H. View Post
The other thing I have noticed about these steep seat angle long reach bikes is that they don't work well for folks that are "reach challenged". Take a really long bike with low stack, short reach and an already short stem and you have nowhere to go if you if you need to shorten up reach.
Welcome to my hell. 5'7", >32" inseam, and arms like a t-rex. I'm lucky to get a road bike that fits, let alone a progressive mountain bike.
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  #7  
Old 11-10-2023, 11:27 AM
HowardCosellsPR HowardCosellsPR is offline
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Bringing this back as... it is becoming an issue again...

So... yeah... Im specifically interested in how people are managing fore-aft setback on their setups.

To be 100% specific:
- My road-gravel set ups are all in the 72.5-74d area.. which require either straight or 15mm set back posts to maintain similar for-aft.

I have two mtbs: a fs with 75d seat angle, which when completely maxed out on rails, my seat fore-aft is mostly acceptable (though I start to feel it in my knees after 4hrs). My other mtb, a rigid, which get's double duty as a dirt-tourer and general training bike, is the issue. It has a 76d seat tube angle and I'm a good 20-30mm from where I should be for fore-aft. I know I can ditch the dropper, but I don't want to. And... I'd prefer not to find a new frame.

Adding to the complication, the three fitters I've reached out to have all basically said, 'we don't really do mtb fits, they're just too variable'. Two of these folks I really trust so...

Any other folks dealing with this? Are folks training themselves into more forward-centric fits on their road bikes? I can't be the only one. Thanks
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  #8  
Old 11-10-2023, 12:11 PM
Radius PNW Radius PNW is offline
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Quote:
Originally Posted by HowardCosellsPR View Post
So... just curious about this... and it might be a total 'noob' question... but:

For folks who split time between road and mtbs, how are you dealing with/setting up your mountain bike fore-aft given the new geometry (eg... ~76d seat tube angles)?
I also had this question, and think it makes great sense to explore. Many riders spend significant time dialing in similar fits across road bikes owned, and totally throwing out your seat position simply because you're riding all terrain doesn't always seem the ideal route.

Steep SA are a specific geometry adaptation for steep gradients, as far as I've been informed -- for less aggressive off-road terrain? Not so much.

After riding a 75-deg SA, and finding it awkward and inefficient for my riding, I opted to :
  1. return the steep SA bike
  2. search to find a more moderate seat angle bike

The forum was very helpful in the hunt, in this thread.

Good luck,

R

Last edited by Radius PNW; 11-10-2023 at 12:19 PM.
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  #9  
Old 11-10-2023, 02:26 PM
EB EB is offline
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As long as we're talking about full suspension, it's important to realize that all the angles on the bike are dynamic, not static - and this becomes more and more true the more travel that the bike has.

The basic reason for the steep seat angle, especially on long-travel bikes, is that climbing a hill the bike sinks further into its travel in the rear. With older frames with slacker seat angles taken from road designs, this would put the rider way back on the bike and lead to the infamous wandering front end as well as a non-ideal pedaling position.

Steep seat angles on the other hand end up dynamically as the bike sags at 73.5 or 74 pedaling up a hill, back at a more natural angle.

The more travel the bike has, the steeper the angle generally needs to be to land in the right place, though this depends somewhat on suspension design (e.g. dw-link bikes like Pivots seem to get away with slightly slacker seat angles).

There is an inherent tradeoff here of course - it makes pedaling on flat or gently rolling terrain a little worse. But the riding style that modern bikes are built for trades off that for better performance while climbing - especially since you're going to be standing up once you go downhill. Most places mountain bikes are used these days, this tradeoff makes sense.

If you live in a more flat or rolling place, modern XC bikes are still there for you - they tend to have shorter travel and bias towards more flat/rolling pedaling performance, so their seat tube angles are often closer to 74.5 or 75, where static sag on flat terrain gets you closer to 73.5.

The one thing I don't really understand in the market are long-travel hardtails with steep seat angles, since hardtails sag dynamically in a completely different way.
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  #10  
Old 11-13-2023, 11:16 AM
rothwem rothwem is offline
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Quote:
Originally Posted by darkmother View Post
Also, don't set your MTB up like your road bike. Took me a while to figure this one out.

Lots of stem length and decent drop is a good recipe for me on tarmac.

The same offroad just does not work for me.
So, from a seat position perspective I think your road position a decent starting point. I've found that the steeper the terrain, the steeper I want my seat tube angle, otherwise the front wheel comes up while climbing. So basically the way did mine was to initially set my saddle position in the same spot as my road bike, and bump the seat forward until climbing didn't suck anymore.

Unfortunately, that made me realize I was on a frame that was too small, so I ditched the frame and got one that was the correct size and my saddle is a good ~3cm farther forward on the mtb than my road bike.

Annnd, because I can't leave anything alone, I realized that I made more power with the seat forward a bit, so I started moving my road bike seat forward some until I started to get tingly hands while riding, then I moved it back a bit. My saddle is still father back on the road bike than the mtb, but overall I like the more forward seat position.
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  #11  
Old 11-13-2023, 01:10 PM
HowardCosellsPR HowardCosellsPR is offline
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Thanks for the responses folks.

Perhaps there's a rigid forum where this is a more understood issue.

Or. maybe I just acknowledge that i'm too old to ride the same rigid mtb for trail and extended gnar-gravel rides. Or that this frame, though it's pure magic on the trail, is too steep for me to use as a gravel-spin for 100s of miles bike when I have to actually sit and spin.
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  #12  
Old 11-13-2023, 01:15 PM
HowardCosellsPR HowardCosellsPR is offline
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Rothwem, quick question... how much higher is your saddle on the your mountain bike set up, given the 3cm further forward position?
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  #13  
Old 11-13-2023, 01:27 PM
whatshubdoc whatshubdoc is offline
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Quote:
Originally Posted by HowardCosellsPR View Post
Bringing this back as... it is becoming an issue again...

So... yeah... Im specifically interested in how people are managing fore-aft setback on their setups.

To be 100% specific:
- My road-gravel set ups are all in the 72.5-74d area.. which require either straight or 15mm set back posts to maintain similar for-aft.

I have two mtbs: a fs with 75d seat angle, which when completely maxed out on rails, my seat fore-aft is mostly acceptable (though I start to feel it in my knees after 4hrs). My other mtb, a rigid, which get's double duty as a dirt-tourer and general training bike, is the issue. It has a 76d seat tube angle and I'm a good 20-30mm from where I should be for fore-aft. I know I can ditch the dropper, but I don't want to. And... I'd prefer not to find a new frame.

Adding to the complication, the three fitters I've reached out to have all basically said, 'we don't really do mtb fits, they're just too variable'. Two of these folks I really trust so...

Any other folks dealing with this? Are folks training themselves into more forward-centric fits on their road bikes? I can't be the only one. Thanks
What do you mean by:

1) maxed out on rails? your saddle is slammed back?
2) you are currently 20-30mm too far forward on the rigid?

I think a couple of other questions come to mind:

- what kind of terrain are you riding? XC, flowy, rolling? Enduro, climb and plunge?
- what kind of bikes are these? again, XC <--> enduro/DH, which end of the spectrum
- what's the stem length and bar rise on these bikes?

My FS MTB has a 75.8/76 STA, with a 65.8HTA. I have it set up with a +6mm rise stem and 35mm rise bars, so that the bars are essentially level with the saddle. The grips are probably 5-10mm above the saddle. The post I use is a BikeYoke Revive, and the rails are centered. If you need heaps of rise from the stem, check out the DMR Defy (comes in both bar bores).

My road bike has 73.3 STA, 73.5 HTA. It's set up with ~32mm saddle to bar drop. Post has 20mm setback and rails are centered (maybe -3mm back from center).

What I've found is that the taller stem/bar rise on the MTB helps to load my weight back onto the saddle, much like how the road bike weight distribution "feels" (subjective, I know). If you're going to use the bike for long spins, I'd suggest having the bars higher - yea, not aero, but... comfort > aero. Shoot for that weight distribution and you should get closer to being sorted.

Lastly, are you on a rigid? I had a Surly KM v1 that I rode rigid. Loved it dearly. (read: deeply regret selling) It had a 71 HTA, 73 STA, and found that it fit very well and could handle hours in the saddle. I just picked up a new steel HT that has a 76 STA, and 66 HTA, not unlike the FS. Set it up the same with high rise bars (40mm) and it feels pretty good.


* I wrote this a few days back but then got sidetracked, so some questions might be mentioned already.
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  #14  
Old 11-13-2023, 02:22 PM
rothwem rothwem is offline
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Quote:
Originally Posted by HowardCosellsPR View Post
Rothwem, quick question... how much higher is your saddle on the your mountain bike set up, given the 3cm further forward position?
Its the same saddle to BB measurement as my road bike.
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  #15  
Old 11-14-2023, 09:54 AM
EB EB is offline
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Good article (from Travis Engel, formerly of Beta and BikeMag): https://theradavist.com/measuring-mtb-seat-tube-angles/
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