# Thread: Modern geometry question

1. ## Modern geometry question

Question about modern bike geometry:

My understanding is that seattube angles are getting steeper, but at the same time I see most (dropper) seatposts have zero offset heads.

I ride an (older) geometry bike with a slightly slacker seatpost, and dropper post with offset.

If I would switch to a new bike, I would imagine I would like to maintain the same horizontal distance between BB and saddle, so would I have to put the saddle "too far back" on a zero offset post ? (considering steeper seattube angle will bring the top of the seatpost closer to the front of the bike ?)

2. Which bikes are you looking at? Interpretation of modern can be anywhere from 73-79deg seat tube angle. Your steeper STA is offset by a longer reach, so you'll feel a similar cockpit fit.

The pedaling position and saddle to BB horizantal offset will be closer, but that is the intent, so you are in a better pedaling position on the climbs. It's not super ideal on the flats, but goal of modern bikes is to optimize for the ups and downs...while expecting you not to spend a huge amount of time on the flat terrain.

3. Curious about this as well. So what is less ideal about relatively steep sta and flats sections? Why does steeper feel/work better assuming reach is corrected for by longer front / reach?

4. The steeper seat angle puts you in a better position (relative to the crank) for seated climbing on relatively steep uphills as compared to a "normal" STA. The down side is it puts you in kind of a crappy position for pedaling on flat(ish) sections.

E: The more forward position improves weight balance and keep the pedals in a more efficient position when climbing. You can kind of think of an "instantaneous seat tube angle" that is slacker when climbing than on the flats (and the geo chart). Making it steeper compensates for that, but then on the flat you are a bit too far forward and the pedaling position is a bit more awkward.

5. Originally Posted by smoothmoose
The pedaling position and saddle to BB horizantal offset will be closer, but that is the intent, so you are in a better pedaling position on the climbs. It's not super ideal on the flats, but goal of modern bikes is to optimize for the ups and downs...while expecting you not to spend a huge amount of time on the flat terrain.
Aha, that is an interesting assumption the bike industry is making.
Probably also means I will have more weight on my arms/wrists.

6. My latest bike has a 76° actual STA and it's the best I've ever had. Fast and comfortable on flat sections or climbing, my experience has been very positive, and my next bike will have a similar STA. Saying it's not ideal on flats is just a personal fit issue and doesn't apply to all. If you don't gel with the steep STA there are some great droppers with setback. I say it's about time that STAs got steeper after 30 years of riding bike with too slack STAs and no way to get the saddle in my correct position. If you don't want a steep STA there are plenty of companies making old school geometry bikes.

7. Originally Posted by pirati
Aha, that is an interesting assumption the bike industry is making.
Probably also means I will have more weight on my arms/wrists.
Everything shifts forward. So you shouldn't have anymore weight on your wrists. You will just be more centered on the bike.

8. Originally Posted by pirati
I would imagine I would like to maintain the same horizontal distance between BB and saddle

Don't presume anything. Test ride a few bikes to get a feel -- there are a lot more changes than what you've listed, with the overall end result that things are just...

...different. Usually, different is better, unless your old bike was way ahead of it's time.

9. Originally Posted by Travis Bickle
My latest bike has a 76° actual STA and it's the best I've ever had. Fast and comfortable on flat sections or climbing, my experience has been very positive, and my next bike will have a similar STA. Saying it's not ideal on flats is just a personal fit issue and doesn't apply to all. If you don't gel with the steep STA there are some great droppers with setback. I say it's about time that STAs got steeper after 30 years of riding bike with too slack STAs and no way to get the saddle in my correct position. If you don't want a steep STA there are plenty of companies making old school geometry bikes.
So, who is likely to gel, and who is not? I have old school STA-- something like 73° and have most often had seats slammed backward (seatpost all the way to the front of rails). I'm 6'2" with 35in inseam and long femur. I'm curious if a relatively steep 76° STA would work for someone like me, or if it is something more suited for someone who has experienced "no way to get the saddle in correct position" which I assume means you have historically had to slam your saddles forward (back of the rails) to try and achieve a good fit.
With changes in geo -- im interested in the better climbing of a steep STA, but curious about how it effects rider with long femur especially. Concern is would have to raise seat height to get same distance from pedals, which then requires higher stack height, etc. etc.

10. I have stumpy legs, or so Ibis told me on the phone.

Sent from my SM-G935S using Tapatalk

11. Originally Posted by pirati
Aha, that is an interesting assumption the bike industry is making.
Probably also means I will have more weight on my arms/wrists.

Yeah. You can't get something for nothing.

A viscous cycle???

Riders think they need more travel. More travel means bad geo changes for the climbs. Bike makers go to steeper STAs. It helps the climbing on longer travel bikes. But, shorter travel bikes climb just fine with say, a 74 degree STA on the climbs. I hear steeper STAs put too much weight on the hands on the flats. Not sure if that is true but seems like that would be the case. As I have very long levers my seat is high, and maybe that makes a difference. Time will tell.

12. I think it really is depend on the bikes. It's mainly enduro and trail bikes that are get the steep seat/slack head/longer reach treatment. And these have a more upright position to start.

End of the day, you gotta test ride a few bikes to see if the feel the benefits on the ups and downs, and determine if there is any noticeable deteriments on the flats or other areas.

Also people riding flat pedals can also better adjust their foot position to further adjust their effective STA whether they are on ups or flat.

13. Originally Posted by pirati
Question about modern bike geometry:

My understanding is that seattube angles are getting steeper, but at the same time I see most (dropper) seatposts have zero offset heads.

I ride an (older) geometry bike with a slightly slacker seatpost, and dropper post with offset.

If I would switch to a new bike, I would imagine I would like to maintain the same horizontal distance between BB and saddle, so would I have to put the saddle "too far back" on a zero offset post ? (considering steeper seattube angle will bring the top of the seatpost closer to the front of the bike ?)
I use a 1" set back dropper on my "modern geo" bikes. If not I couldn't ride them. 9.8 makes and 1" setback dropper.

14. I jokingly call modern geometry "tri-bike geometry" since the seat tube angles and saddle position to BB distances are getting pretty close to those on tri-bikes. I hate it, there's a lot of mostly flat riding in my area and the forward position of the saddle puts me in a poor position for 80% of my riding. With my hips so far forward, it's hard to stay seated when putting down power, if I want to stay seated I need to use my arms & body to hold my butt in the seat and that uses up a ton of energy which I'm trying to save by staying seated. On flatter sections, I need to either stand when pedaling harder or spin the cranks at 120rpm, I can't put down a decently hard effort at my preferred cadence while staying seated.

The modern trend of steep STA doesn't work for me given the kind of riding I deal with in my area. 73-74° is about as steep as I can go before my pedaling mechanics get all screwed up. I have the same saddle on everything from a 100mm travel XC hardtail to a long travel enduro bike, on every bike the saddle has ended up being the same distance behind the BB. I didn't initially set them up that way, but over the course of time they all migrated to within a few millimetres. Apparently that's where my body wants the saddle to be.

15. My pedaling position is pretty much the same on all my bikes...regardless of the STA. The STA doesn't really matter as long as I can get my saddle to where I want it to be. Just because the STA is steeper...doesn't mean that I'm going to run my saddle that much farther up. I mean you can adjust your effective STA by moving the saddle back and forth on its rails...no?

16. Originally Posted by RS VR6
I mean you can adjust your effective STA by moving the saddle back and forth on its rails...no?
If you run a saddle slammed all the way back on its rails you will break saddles. I know from experience. So you are limited to how much adjustment you have at a given STA. I use 1" setback droppers to tame really steep STAs and that works for the most part.

My current bike has a steep enough STA that even with the 1" setback dropper I am maxed out with how far forward my saddle is.

Funny thing [to me] is moving the saddle forward on its rails to make a slacker STA feel steep doesn't break saddles because it puts your body weight right over the dropper clamp. So I would prefer more moderate STA bikes with long enough TTs so people that wanted steep STAs could slide their saddle forward and still have enough TT room to pedal comfortably.

17. Originally Posted by attaboy
I have old school STA-- something like 73° and have most often had seats slammed backward (seatpost all the way to the front of rails). I'm 6'2" with 35in inseam and long femur.
If the rest of your bike is as oldschool as your STA you might find on a newer bike with a longer front-centre you might be able to achieve a similar seated position relative to the bars without a setback post or slamming your saddle back. Old geo was pretty short [thus the long stems and setback posts] and IME it was worse if you're on the taller end of the spectrum. Do you know what the ETT and reach are on your existing bike, what length stem are you running?

18. Originally Posted by David R
If the rest of your bike is as oldschool as your STA you might find on a newer bike with a longer front-centre you might be able to achieve a similar seated position relative to the bars without a setback post or slamming your saddle back. Old geo was pretty short [thus the long stems and setback posts] and IME it was worse if you're on the taller end of the spectrum. Do you know what the ETT and reach are on your existing bike, what length stem are you running?
So I have XL as means to achieve longer front. ETT is 25.4, reach is 17.3, 60mm stem. after installing angleset that raised stack and made front too light on steep ups, moved seat forward (first for me) and raised it a bit, also lowered handlebars. I like the result.

19. Your XL has 439mm reach, my L has 465mm (and a 74* theoretical STA) and I run a 50mm stem.

20. Originally Posted by aerius
I jokingly call modern geometry "tri-bike geometry" since the seat tube angles and saddle position to BB distances are getting pretty close to those on tri-bikes. I hate it, there's a lot of mostly flat riding in my area and the forward position of the saddle puts me in a poor position for 80% of my riding. With my hips so far forward, it's hard to stay seated when putting down power, if I want to stay seated I need to use my arms & body to hold my butt in the seat and that uses up a ton of energy which I'm trying to save by staying seated. On flatter sections, I need to either stand when pedaling harder or spin the cranks at 120rpm, I can't put down a decently hard effort at my preferred cadence while staying seated.

The modern trend of steep STA doesn't work for me given the kind of riding I deal with in my area. 73-74° is about as steep as I can go before my pedaling mechanics get all screwed up. I have the same saddle on everything from a 100mm travel XC hardtail to a long travel enduro bike, on every bike the saddle has ended up being the same distance behind the BB. I didn't initially set them up that way, but over the course of time they all migrated to within a few millimetres. Apparently that's where my body wants the saddle to be.
whilst I appreciate you have stated that a steep STA doesn't work for you, you also acknowledge that tri bikes, who's sole purpose is to be as efficient as possible on the flat employ Steep STA's.

I'm always a little surprised when I read someone suggesting a steep seat tube will be inefficient on flat terrain when the bikes that are specifically designed to be as efficient as possible employ steep STA's.

Am I missing something here?

I will concede that not everyone is the same so there may always be a few exceptions but based on the above would it not be more likely that steep STA's will benefit the vast majority of riders and be not suited to a few???

21. The steep STA on TT/tri bikes is a necessary concession to the aggressively aero riding position. If you tried to get a similarly flat back with the saddle further rearward of the BB like in a 72ish STA, you'd eventually start hitting yourself in the chest with your knees. I don't have any articles on it at the moment, but I am pretty sure that power production is less efficient in an aero TT position than in a more normal-ish road riding position, but the reduction in drag means that it is still faster. If riding conditions are such that speeds are slower (slower riding surface, uphill, whatever), then the aero benefit is less significant and the power production penalty will take over.

22. Originally Posted by fissiontofallout
The steep STA on TT/tri bikes is a necessary concession to the aggressively aero riding position. If you tried to get a similarly flat back with the saddle further rearward of the BB like in a 72ish STA, you'd eventually start hitting yourself in the chest with your knees. I don't have any articles on it at the moment, but I am pretty sure that power production is less efficient in an aero TT position than in a more normal-ish road riding position, but the reduction in drag means that it is still faster. If riding conditions are such that speeds are slower (slower riding surface, uphill, whatever), then the aero benefit is less significant and the power production penalty will take over.
Interesting. I've found on my typical 5 hour rides with lots of flat moorland riding, long reach coupled with a 77 degree actual STA has resulted in significantly increased comfort and performance once my body got used to the new position and far less instances of lower back pain and leg cramps when at the limit of endurance.

I suppose you've got to try it to see if it works for you.

23. Originally Posted by pigglet13
i suppose you've got to try it to see if it works for you.
yes!

24. Originally Posted by Pigglet13
whilst I appreciate you have stated that a steep STA doesn't work for you, you also acknowledge that tri bikes, who's sole purpose is to be as efficient as possible on the flat employ Steep STA's.

I'm always a little surprised when I read someone suggesting a steep seat tube will be inefficient on flat terrain when the bikes that are specifically designed to be as efficient as possible employ steep STA's.

Am I missing something here?
Mountain bikes don't have tri-bars, and I'm not riding a mountain bike from a tri-bike position. We use tri-bars on tri-bikes because we want an aero riding position, and this requires moving the seat forward with respect to the BB to open up the hip angle a bit so that the knees don't bang into the chest on every pedal stroke.

What manufacturers are doing with mountain bikes is steepening the STA which moves the seat forward while lengthening the front end which keeps the seat to handlebar distance the same, but it also opens up the hip angle and moves your centre of mass forward with respect to the BB. With an older style bike on flat ground, your centre of mass is directly above or slightly behind the pedal spindle when you're pushing down on the pedals, this keeps your butt on the seat until you're pedalling really hard or choose to stand up. With new geometry bikes your centre of mass is forward of the pedal spindle, pushing down even moderately hard will lift your butt up & forward from the seat unless you use your arms & upper body to hold it down.

25. Originally Posted by aerius
With new geometry bikes your centre of mass is forward of the pedal spindle, pushing down even moderately hard will lift your butt up & forward from the seat unless you use your arms & upper body to hold it down.

This absolutely goes against my own experience, you are making generalizations that aren't true.

26. Originally Posted by aerius
With new geometry bikes your centre of mass is forward of the pedal spindle, pushing down even moderately hard will lift your butt up & forward from the seat unless you use your arms & upper body to hold it down.
The statement above contradicts just about every profesional review of a modern bike sporting modern contemporary geometry.

Over the last 2 years I have bought three bikes with what may be described as modern geo, firstly a pivot switchblade. Infinitely better in terms of comfort, fit and efficiency compared to the 429 it replaced. This made me think, what happens if I go longer and steeper. Bought a mondraker.
Significantly more radical geometry than the switchblade. Different style of bike but the geometry resulted in more rider comfort on the flat and better climbing performance.
With that in mind I booked a demo day with MOJO bikes to try a Geometron for the day.
The geometry of that bike is as radical as it gets.

At no point on any of these bikes have I though whilst riding on the flat "this is worse than my cramped old school bikes"
At no point whilst riding any of these bikes have I thought "hang on, my arse is lifting off the seat here as I press on the peddle"

What I have thought is that despite the Geometron being a relatively heavy lump, running 27.5 wheels as opposed to my preference for 29ers and sporting fox 40's and 170mm of rear travel " frickin hell, this thing is pretty damm quick cross country all things considered"
Tight corners, narrow singletrack and uphill switchbacks are despatched with ease.

Now I'm no XC racer BUT until about 5 years ago my preference was for XC based hard tails as the bulk of my typical 5 hour ride is flat terrain and climbing. I do not ride man made or trail centre trails with any frequency.

So my actual experiance of "modern" geometry, bought and paid for out of my own pocket is that it is a revelation. Particularly on flat terrain and when climbing.
My geometron will outclimb my switchblade despite being bigger, heavier and running more travel. In 30 years of mountain biking that has included racing XC and enduro the Geometron has been the biggest revelation.

What I would like to try is a lightweight 130mm 29er shod with light hoops and sporting the same geometry as the Geometron as I believe that would be a real trail weapon. Travis's moxie looks pretty sweet too.

As said above, I will admit that it may not work for everyone due to personal preferances and body shape BUT I would suggest that it will work for the vast majority of riders who want to ride regular trails, go farther faster and increase their confidence.

Do not knock it until you have tried it.

27. Originally Posted by Pigglet13
Do not knock it until you have tried it.
I'll add, 'try it for a while'. It was 3 months of twice weekly rides before I jelled with my new bike. After I developed the muscle memory to move the bike under me in a new and different way, I started improving lap times over my old XC bike.

28. Originally Posted by Pigglet13
What I would like to try is a lightweight 130mm 29er shod with light hoops and sporting the same geometry as the Geometron as I believe that would be a real trail weapon.
This seems like the New Hotness trend - modern geo, short travel (e.g. Yeti SB 100, 2018 Stumpjumper ST). Soon the marketing machine is going to tell you to ditch all that extra travel and go with the new betterer short travel, modern geo do-it-all super duper extra special trail bike.

Actually I kind of like the trend, but maybe I'm an easy mark.

After that, it's going to be sub-boost, 145mm instead of 148mm rear spacing, shaving off those milimeters to save you weight and make you even fasterer! Of course, not all the way down to that weak, flimsy 142mm spacing because sub-boost will give you the best of both worlds, boost strength and light weight!

Wait, what were we talking about again?

29. Originally Posted by jim c
I'll add, 'try it for a while'. It was 3 months of twice weekly rides before I jelled with my new bike. After I developed the muscle memory to move the bike under me in a new and different way, I started improving lap times over my old XC bike.
Yes definitely agree that it takes a while to allow your body to adapt. I found that for the first hour radically different geometry feels slightly strange. Then you get used to it but after a few hours aches and pains may manifest themselves for a few weeks until muscles adapt.

30. Originally Posted by kpdemello
This seems like the New Hotness trend - modern geo, short travel (e.g. Yeti SB 100, 2018 Stumpjumper ST). Soon the marketing machine is going to tell you to ditch all that extra travel and go with the new betterer short travel, modern geo do-it-all super duper extra special trail bike.

Actually I kind of like the trend, but maybe I'm an easy mark.

After that, it's going to be sub-boost, 145mm instead of 148mm rear spacing, shaving off those milimeters to save you weight and make you even fasterer! Of course, not all the way down to that weak, flimsy 142mm spacing because sub-boost will give you the best of both worlds, boost strength and light weight!

Wait, what were we talking about again?
Don't get me started on the whole boost thing. Why any 29ers designed in the last 5 years that do not utilise a 157mm back end is beyond me.................

31. I noticed that some modern bikes force me to get my weight back, compared to some of my older bikes, when out of the saddle. Not sure if I'd call it a plus or not, but I feel no need to lean/slide forward in the saddle to pedal, on flat or uphills.

On an older model, say like a 26 SJ FSR Evo, I'd feel centered in a comfortable upright standing position. On a new "upsized bike" with shorter seat tube, I feel that I need to have my hips approximately where the saddle would be if it were raised, to feel centered. Considering the longer reach, I'm having to extend my hips back more. Well, at least having my hips in such a pushed back position doesn't risk the rear tire buzzing it on a forward geo bike, like it would on a non-forward geo bike.

On the other had, some modern bikes, like the newer Intense ones (e.g. Primer), still have a nice centered feeling that I'm used to. I'm able to corner out of the saddle way more comfortably on them, without feeling I need to hold a certain unnatural position to feel centered. Based on familiarity, I think I'd choose a Primer, but I think I'll keep giving the new style a try. Might just need to shorten the stem a bit more, but it already feels rather upright, cause the ETT is almost the same. Another plus for forward geo is that my knee pads no longer smack the controls hanging under the bars when I'm putting extra pedal power down.

All I know is that half my preconceptions about modern longer reach geo was wrong. If I had tried to set up fit to compensate, based on old principles, I bet it would've made things no better. For example, since I feel that I have a bit too much weight being propped up by my arms compared to before where I could hold all my weight in my back, I'm thinking that I could compensate for it by raising my bar and bringing it closer. With this change, the distance from the grips to the saddle will be a good deal closer than it was on my old style bikes. Would seem to be wrong, but in this case it'd be a common sense solution to improving fit.

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