Seat Tube Angle

[padams10003]

Seat tube angle (specifically making them steeper) seems to be the one of the manufacturers big selling point on bikes now. Is the whole basis of this a bit misleading?

Assuming that the saddle fore/aft position is set how it has traditionally been set (ie. Sitting on the bike, position one foot forwards so the crank is parallel to the floor at 3 o'clock. Hold a length of string with a weight on the end at the front of your knee. The string should drop down in line with the pedal axle.), then surely once the STA angle becomes too steep, then doesn't it reach a point where the saddle needs to be slammed back as far as possible?

Also, another thing that I think is often overlooked is that by moving the saddle back or forward you can effectively change the STA by a degree or two (depending on the bike). As an example, I have calculated on my bike (STA 73.5), by moving the saddle forward or back 20mm i can change the STA to between 72 and 75.

Looking forward to hearing what others think about this.

 

[ozzybmx]

Nowadays when nearly everyone has droppers... even the top end XC bikes, depending on the STA, unless your seat tube has a kink at the bottom of your seat tube, the STA wont change as you drop the seat, but the ETT will.

Slamming your saddle back or using a setback post is probably ok if your body is a different proportion, but it may also indicate you have bought the wrong sized bike.

The saddle position just changes your position on the bike, the STA remains unaffected... the ETT changes as you lift or drop your post either with a dropper or a manual change.

The STA really only affects climbing stability and putting your seat further back can only make it worse. It changes the foot/BB position to your body/ass/saddle

 

[Mywifesirrational]

STA have always been shit house on MTB bikes for tall folks, its only recently that the bike designer 'experts' have got their shit together.

My above hyperbolic statement mostly refers to effective vs actual STA's. Actual is the only measurement I am interested in, as the effective angle may seem good on paper, but when you have 400mm of post sticking out of a frame, the effective angel which is generally measured as a horizontal line from the top headset cup, gets very slack indeed. Then add in 140-170mm of rear travel, up an incline, with 30+ % sag, and no your effective STA is 62 degrees.

Steeper STA's are fantastic, and as reach numbers and by default ETT numbers have gotten longer, there is no disadvantage to a steeper STA. much better climbing position, much better for power transfer. Only issue I have heard is knee's moving to far forward of the toes, but that is a load of shit that some dickhead made up decades ago.

Each consectutive bike I buy has a steeper STA and still I am pushing my saddle as far forward as possible, so running somewhere around 76 degrees on the flat, would like to try 77-78 degrees, a few new bikes are starting to head this way. I imagine the limit is somewhere around this.

Played around in the lab a few years ago on someone elses fandangled 100k exercise bike out of hours (science man gets angry when people fuck with their equipment), adjusting the STA to make it steeper made the power output improve a little bit, or more so at the same speed heart rate was a little lower. Wonder what the STA are on track bikes? probably 73 still as the UCI probably has a rule...

 

[LPG]

I always wonder what sort of effect different foot placement on the pedals effects effective geometry. When you ride clipped in the ball of your foot typically is over the pedal spindle. When you ride flats your arch is over the spindle. This is probably a difference of 30mm or more making the effective ST angle slacker when riding flats.

What I'm not sure of is what the different spindle location on the foot does to the body geometry and the muscles used. I know that if you are doing a squat you put all your weight on your heels to engage the glutes and prevent sore knees. Is the foot placement doing a sikilar thing? Pedalling efficiency studies ive seen seem to be based on road biking and xc and clipped in is expected.

 

[mas2]

I reckon it's a tiny incremental improvement in an industry that's getting pretty stagnant.

 

[caad9]

I'm riding a Kona Satori with a 78.3 STA. It's pretty radical looking.
It felt a bit odd for a week or so, but I haven't looked back since. The riding position feels really centred and the climbing, in particular front end, feels quite good for a 140mm bike. There are some quirks with the bike for sure, but despite what everyone says, the perfect bike does not exist.

 

[ashes_mtb]

Based on the speed a recumbent whipped past me this morning, I'm guessing the ideal STA is somewhere around 0.

 

[beeb]

Personally I'm a massive fan of the steeper seat angles. Being over 6ft I reckon @Mywifesirrational comments hit the nail on the head. It puts the taller folk into a way more efficient and balanced position on the bike. And yes, I have slammed my seat forward as far as it allows. IMO, it's not quite the same as a steeper seat tube because (A) you're limited how much 'virtual' seat angle you can gain, and (B) having the seat clamp right at the back of the rails takes away a lot of the compliance in the seat and can make for a pretty harsh ride when seated.

 

[PJO]

The only compromise I've noticed from riding a steeper seat tube (~75 unsagged, even steeper sagged because hardtail) is that on flatter terrain I can feel more weight on my hands when pedalling.
This negative is totally overshadowed by the better position for climbing, don't feel the need to shuffle forward on really steep terrain.

My knees haven't noticed the change but I have also started riding flats. Riding flats has shifted my foot forward slightly on the pedals but because I have been riding clipped-in for the last 8 years I still prefer to pedal closer to the balls of my feet.

 

[caad9]

I feel like flatter terrain with roots/rocks can be a bit more sluggish due to the centred position, it feels like you get hung up a little more.
That could be just as much to do with the bike as the position itself.

 

[The Reverend]

As stated by @Mywifesirrational I've hated slack STA on bikes. I'm 1.93m and all legs so my first experience with this was on a Scott Genius with about 72° and then sagged it felt like my ass was behind the rear axle. I hated that damned thing and avoided slack bikes ever since.

Anything I buy now has to be north of 76° and then that has to be taken in consideration with rear centre bias too. At under 35% it's too short for my tastes and most brands either can't be arsed to make different length rears. So only medium and large get a decent ride experience.

Brands seem to be drunk on shorter is better.

Steep STA within reason rock for tall folks!

 

[Zaf]

Removed by user

 

[Cardy George]

What I'm not sure of is what the different spindle location on the foot does to the body geometry and the muscles used. I know that if you are doing a squat you put all your weight on your heels to engage the glutes and prevent sore knees. Is the foot placement doing a sikilar thing? Pedalling efficiency studies ive seen seem to be based on road biking and xc and clipped in is expected.

Spindle under the ball is good for outright power as it's at the end of the calf/ankle/foot lever, but shite for endurance as the pedal also has the same effect going back through the foot, making you engage the calf muscle more.

Therefore spindle back towards the arch is best for long endurance rides where speed isn't so important.

But the actual difference in power/endurance is tiny, and easily negated by training and conditioning.

 

[Ultra Lord]

Spindle under the ball is good for outright power as it's at the end of the calf/ankle/foot lever, but shite for endurance as the pedal also has the same effect going back through the foot, making you engage the calf muscle more.

Therefore spindle back towards the arch is best for long endurance rides where speed isn't so important.

But the actual difference in power/endurance is tiny, and easily negated by training and conditioning.

it also acts as a lever when landing jumps and can hyperextend your ankle which hurts like a bitch. Don’t overjump or collapse into the bike sending too big a drop if your pedals are too far forward, probably a non-issue for most but believe me it hurts. Don’t even need to stack.

 

[Zaf]

Removed by user

 

[padams10003]

So at what point does the position of the knee in front of the pedal axle become a negative? Is something like the Kona Satori above hitting that point?

 

[beeb]

I think about 77-78deg would be about the limit for me.

One thing to consider with these steeper seat tube angles is it's mostly starting to appear on enduro and trail bikes (so far) where you tend to be doing steep climbs then descending in a standing attack position (or at least that's where they make sense to me...). IMO - I don't think they'd need to go quite as steep on an XC or road style bike.

 

[Mywifesirrational]

So at what point does the position of the knee in front of the pedal axle become a negative? Is something like the Kona Satori above hitting that point?

It is probably never going to be an issue, as the STA gets steeper, the pelvis is moving more forward in relation to the pedal axle, so while in a static sense the knee looks well in front of the axle, its more so your whole body is leaning into the pedal stroke.

I think about 77-78deg would be about the limit for me.

One thing to consider with these steeper seat tube angles is it's mostly starting to appear on enduro and trail bikes (so far) where you tend to be doing steep climbs then descending in a standing attack position (or at least that's where they make sense to me...). IMO - I don't think they'd need to go quite as steep on an XC or road style bike.

I am thinking they need to be steeper, a 160-170mm bike once its going up something relatively steep, when the front wheel wants to lift, is going to have the entire mass of the rider on the rear wheel, creating even more sag. A really steep STA is going to remedy this, where as a 100-120mm bike this is more of a non-issue.

 

[beeb]

Yeah, that's fair. I prefer short travel bikes, so that's probably why my preference is where it is.

 

[Ezkaton]

Riding a Pole Evolink with a STA of 77.5 degrees.
At 6'3 with a 150mm dropper, I have to say it's the best climber I've been on yet... and certainly the most comfortable in terms of lower back pain.

I'd be pretty keen to give the Pole Stamina a shot... the STA is nearly vertical!