Hey all...

I've finally kicked my aerobar addiction and have gone back to being a roadie again...blame the Tour for that! Here is my question...I've been riding a custom Javelin Aero that was made for my long torso and short legs (56.5cm TT, 52cm ST, 120mm stem). The bike fits great and I have plenty of power with no pain. The seat tube is a 76 degree angle and I am wondering if I need to get a bike with a more traditional 73 degree ST. Am I losing power in this set up? What would I gain by changing?

Thanks in advance....
Scott

ST angle makes no difference to power output, it does however affect handling. A 73 degree STA will provide far more balanced weight distribution.

Hey all...

I've finally kicked my aerobar addiction and have gone back to being a roadie again...blame the Tour for that! Here is my question...I've been riding a custom Javelin Aero that was made for my long torso and short legs (56.5cm TT, 52cm ST, 120mm stem). The bike fits great and I have plenty of power with no pain. The seat tube is a 76 degree angle and I am wondering if I need to get a bike with a more traditional 73 degree ST. Am I losing power in this set up? What would I gain by changing?

Thanks in advance....
Scott

Power output can certainly be affected by the rider's position relative to the BB. If you have a steep STA and use it to move your position forward, it will affect both torque and cadence (generally more cadence and less torque).

If a post with a lot of setback is used to move the saddle back to a normal road position, the effective TT length will become longer, requiring a shorter stem. 3 degrees of STA is equivalent to about 3.5cm of TT length.

Power output can certainly be affected by the rider's position relative to the BB. If you have a steep STA and use it to move your position forward, it will affect both torque and cadence (generally more cadence and less torque).

If a post with a lot of setback is used to move the saddle back to a normal road position, the effective TT length will become longer, requiring a shorter stem. 3 degrees of STA is equivalent to about 3.5cm of TT length.


I've found that when I use the right size cranks(170mm), my cadence is higher with a steeper ST angle. Something about the crank not being ahead of me helps me get through the bottom deadspot easier. My seat nose is even with the BB, but I think it is behind on most 73 degree bikes. If I moved my seat back, I think I would have to lower it to be able to reach the pedals in a full circle. Do you think that I'm losing serious power by being too far forward?

SB

It will affect your efficiency (i.e. power output) as your ability to cycle efficiently depends on the positioning of your body's mass in such a manner that you efficiently use your energy to make the bike go forward. Traditional tri position assumes you are lower in the front end and more aero. Being further forward and lower would mean your thighs would smash into your abdomen compromising your pedal stroke and breathing if you didn't do anything about your position. Moving forward opens up your abdomen, improves the efficiency of your pedal stroke, and doesn't compromise pedalling efficiency as you get to use your aero bars as a point of leverage for effective cycling.

Sitting in a traditional manner (drop bars) while staying forward in position (76 degree seat angle) puts your center of gravity forward meaning you don't get to use it as an efficient leverage object when cycling on the flats. Also, with your arms fully extendended you use more arm muscles to 1) support your body's mass and 2) pull on the bars to transfer energy to the pedals. It shouldn't, as it was mentioned it would, mess up your weight distribution too much as most tri specific bikes (if sized and built properly) should have a longer top tube to compensate for the more forward position (being forward is about aerodynamics while maintaining an efficient pedal stroke, bike balance is still an issue and the bike should be designed accordingly)

To use a tri bike for effective road riding you should get a seatpost with as much setback as possible, keep the nose of the saddle at least 5cm behind the BB (will be a UCI regulation in the US within a couple of years) and get a shorter stem to maintain proper reach. This will actually put more weight on the back wheel and make the bike feel really light in the front. The bike will handle a bit strange and your weight won't shift off center when corning as it should with a shorter stem but for the majority of riding (straight lines, climbing) it will feel pretty much as good as a road specific bike.

All that being said, frames can be pretty darn cheap these days. A couple of hundred bucks offset by the sale of your old frame could get you on a bike that makes you very happy without compromise.

Recumbants must have a lot of torque then and force riders into a very low cadence... whats the effective STA, 0deg?

If there is a decernable difference between a 76 and 73 deg STA then the difference between 73 and 0 deg must be HUGE!!!

Power output can certainly be affected by the rider's position relative to the BB. If you have a steep STA and use it to move your position forward, it will affect both torque and cadence (generally more cadence and less torque).

I don't think I could get a seat post with that much room to move it back that far. Any recommendations? If I could get it 3cm behind, that might be it as I could probably get away with a 10cm stem and still be OK. I think that would give me around a 73 degree if the formula from C-40 is correct.

This is starting to look like a new frame issue. Generally, only compact frames seem to fit me well because of my long torso, short legs. In my last fit kit, my femur length is barely on the chart, and I'm 5'11"!

Sprinters move way up forward on the nose of their saddles for the final effort. From right over the crank, you can just stomp on the pedals, straight down, using your whole upper body weight, and work up a really fast cadence, too, because your legs are working more like running or walking than from more of a "rowing" position behind the crank, where the back and arms come into play. Track bikes all have steep seat tubes for these reasons.

If your rear wheel is hugging that steep seat tube, and you're not draped way over the front wheel, fore-aft balance could be acheived. I sure wouldn't try to duplicate a 73 degree set-back, especially if you have short legs. Those short levers can develope alot of power spinning very fast.

Sprinters move way up forward on the nose of their saddles for the final effort. From right over the crank, you can just stomp on the pedals, straight down, using your whole upper body weight, and work up a really fast cadence, too, because your legs are working more like running or walking than from more of a "rowing" position behind the crank, where the back and arms come into play. Track bikes all have steep seat tubes for these reasons.

If your rear wheel is hugging that steep seat tube, and you're not draped way over the front wheel, fore-aft balance could be acheived. I sure wouldn't try to duplicate a 73 degree set-back, especially if you have short legs. Those short levers can develope alot of power spinning very fast.


My rear wheel is tucked right into the seat tube, which actually has a cutout for it. I've always been a good sprinter, but on this bike, the position seems to give me a bit more speed when I hammer. I still keep good cadence(94+), which I couldn't do on a standard bike. I think the short legs is a the major factor here. My 30" inseam just doesn't want to reach that far in front of me, and when I am in that position, my reach to the bars is pretty far, because....I have short arms too!

SB

My rear wheel is tucked right into the seat tube, which actually has a cutout for it. I've always been a good sprinter, but on this bike, the position seems to give me a bit more speed when I hammer. I still keep good cadence(94+), which I couldn't do on a standard bike. I think the short legs is a the major factor here. My 30" inseam just doesn't want to reach that far in front of me, and when I am in that position, my reach to the bars is pretty far, because....I have short arms too!

SB

That's fine. If the rear wheel is in a cut-out on the seat tube, there's plenty of weight over it for great traction when accelerating. I bet the bike has a pretty short wheelbase. Very responsive, fast, maneuverable, even with a 73 degree or so, relatively laid back head tube, which would be typical of a TT or tri-bike, to keep the short wheelbase from becoming squirrely.

I have short legs, too, and two bikes, one with 73 degree seat tube, another with 74 or 75, I haven't been able to exactly measure, but it handles differently. I can pedal fast up over the crank all day long, effortlessly. The 73 degree bike encourages pushing, leveraging the crank at slower cadences, and using more of the fast twitch fibers in the quads.

A new 52 cm. frame would likely have a 74 or 75 degree seat tube, anyway, so your mount is only slightly exaggerated from normal road geometry.

The relationship of the knee to the BB varies tremendously among the many recumbent designs. Comparing a recumbent riders position relative to the BB could still be done, but obviously you can't use a plumb bob for any measurement, since the bottom of the stroke does not position the crankarm anywhere near a vertical position.

Recumbents are often much less efficient and one of the resaons may be that the designer neglected to properly position the crank relative to the rider.

so if I am sitting on my bike on a trainer are you suggesting that raising the front of the bike and therefore changing the seat tube angle will have an effect on efficiency?

I can see how changing the seat height would have this effect as it changes muscle involvement, but as the foot, pedal, crank etc... are a series of levers their rotation in relation to each other given no change in distances should have no effect on power.

The relationship of the knee to the BB varies tremendously among the many recumbent designs. Comparing a recumbent riders position relative to the BB could still be done, but obviously you can't use a plumb bob for any measurement, since the bottom of the stroke does not position the crankarm anywhere near a vertical position.

Recumbents are often much less efficient and one of the resaons may be that the designer neglected to properly position the crank relative to the rider.

so if I am sitting on my bike on a trainer are you suggesting that raising the front of the bike and therefore changing the seat tube angle will have an effect on efficiency?

I can see how changing the seat height would have this effect as it changes muscle involvement, but as the foot, pedal, crank etc... are a series of levers their rotation in relation to each other given no change in distances should have no effect on power.

Raising the front of the bike would not change the relationship of the rider to the crank arms. Moving the saddle forward or backward (or up or down) does. It's not a coincidence that you see pro riders slammed all the way back on the saddle when climbing at lower cadence and higher torque levels and positioned more forward ("riding the rivet" as Phil Ligget says) when riding in a breakaway on the flats (higher cadence and less torque). If you've never experimented with this, try it. Moving the saddle back abour 2cm can increase the ability to apply torque that's similar to having 1-cog lower gearing. When the saddle is moved back, it should also be moved down about 1/3 the amount of the fore/aft adjustment.

To compare a recumbent to a road bike, you'd measure the crank angle at maximum leg extension (bottom of the stroke) and then rotate the crank back about 70-75 degrees to approximate the horizontal crank position on a road bike. Some sort of large square would be needed to project a 90 degree angle from the crank to the knee. That's all a plumb bob does is create a 90 degree angle, IF the crankarm is horizontal and IF the bike is sitting level.

Moving the saddle backwards and forwards on the rails changes the distance from the saddle to the pedals. This is NOT the same as a change in seat angle or a combined saddle/height adjustment which keeps the distance from the saddle to the pedal the same.

That is exactly my point, a change in STA has NO effect on power output. Changing the seat height DOES. By sliding the saddle backwards or forwards without a corrective height change is simply changing the seat height.

Therefore a 76deg STA is no different form a 73deg STA in terms of efficency or power output. Those are merely a factor of seat height (or distance from saddle to pedal)

Raising the front of the bike would not change the relationship of the rider to the crank arms. Moving the saddle forward or backward (or up or down) does. It's not a coincidence that you see pro riders slammed all the way back on the saddle when climbing at lower cadence and higher torque levels and positioned more forward ("riding the rivet" as Phil Ligget says) when riding in a breakaway on the flats (higher cadence and less torque). If you've never experimented with this, try it. Moving the saddle back abour 2cm can increase the ability to apply torque that's similar to having 1-cog lower gearing. When the saddle is moved back, it should also be moved down about 1/3 the amount of the fore/aft adjustment.

If you move the saddle back 2cm and move it down about .6cm to maintain the same maximum leg extension and there will be an improvement in the ability to apply torque to the cranks, with the SAME "saddle height". A substantial fore/aft adjustment should never be made without the proper saddle height adjustment.

Just about any experienced bike fitter starts with the knee to pedal relationship and saddle height. They do not place the bike on a pair of scales and adjust the front/rear weight balance to some perfect ratio using the saddle adjustment and ignore the relation of the knee to the pedal (which is what you propose).

If you move the saddle back 2cm and move it down about .6cm to maintain the same maximum leg extension and there will be an improvement in the ability to apply torque to the cranks, with the SAME "saddle height". A substantial fore/aft adjustment should never be made without the proper saddle height adjustment.

Just about any experienced bike fitter starts with the knee to pedal relationship and saddle height. They do not place the bike on a pair of scales and adjust the front/rear weight balance to some perfect ratio using the saddle adjustment and ignore the relation of the knee to the pedal (which is what you propose).


My thought now is this....with my femur length being so short, I don't believe I can move my saddle too far back because it cause my knees to go to far behind the pedal axles. Right now, the very top of my tibia is directly over the axles with my cleats centered under the balls of my feet where my saddle currently is and the crank arms parallel to the ground. I believe with a 73 ST angle, the BB will be positioned farther forward, causing my legs to have to stretch forward when maintaining the same saddle to head tube distance. I believe the relationship of the saddle to the BB to be a constant when your legs and cleats are properly aligned. Does this sound plausible? The distance from the TT/ST intersection plumb line drop to the BB is 12cm on my 76 degree bike, and 16+ on a 73 degree bike of the same TT length. So keeping the saddle the same distance back would cause my feet to be 4cm forward on the same size bike with the 73 ST. Now in order to adjust to get my legs back in line, my saddle would end up way forward on the 73 degree bike, which it always has in the past. On my current bike it is just even with the BB, and I have a loooongg Fizik Arione saddle.

So my thought is, in order for me to fit a bike correctly, the relationship of BB to Saddle is the crucial factor given that the cleats are in the correct position and knees are over pedals. The saddle can really be in only one place to achieve this, and for me, it results in a well forward saddle and short TT on a 73 ST bike, or a normal TT and a 76 ST. This leads to my next question, given that your legs are a certain length and cleat and knee positions are a given, why is 73 degrees the standard? While there is some adjustment with the saddle, if you have short legs, the result is that you need the BB brought back to you in order to fit.

Any thoughts?

SB

why is 73 degrees the standard? SB

It isn't standard for seat tubes. Smaller frames have steeper seat tubes for shorter femurs, typically 74, 74.5, 75 degrees. Larger frames go with 73 or even 72.5, 72 degree set-back, to accomodate long femurs. Here are the specs on Colnagos, for example:

http://www.competitivecyclist.com/za/CCY?PAGE=BRAND_GEOMETRY&BRAND.ID=10

Maybe you're thinking about headtubes, but that's steering geometry. 71 or 72 degrees angles the front wheel furthur out in front, making the bike understeer but giving the bike great directional stability. 74 degrees, and 75 which you don't see much anymore, makes the steering sensitive, "twicthy," oversteer. 73 degrees is just right, "neutral," neither twitchy nor unresponsive.

If you move the saddle back 2cm and move it down about .6cm to maintain the same maximum leg extension and there will be an improvement in the ability to apply torque to the cranks, with the SAME "saddle height". A substantial fore/aft adjustment should never be made without the proper saddle height adjustment.

If the saddle to pedal distance is still the same after you move the saddle back and lower it then all you have achieved is moving the riders CG rearward. The rider is effectively rotated around the BB a few degrees. Their legs have not changed length, nor has the crank arm etc... That would have the same effect as placing a bike in a trainer, and rasing the front of it with books and seeing a wattage power increase. (Which you won't)

]Just about any experienced bike fitter starts with the knee to pedal relationship and saddle height. They do not place the bike on a pair of scales and adjust the front/rear weight balance to some perfect ratio using the saddle adjustment and ignore the relation of the knee to the pedal (which is what you propose).

I was wondering when KOPs was going to come it this....

Here is some more reading: http://sheldonbrown.com/kops.html

perhaps more frame builders should work off CG not KOPs.

Don't believe the old idea that there is only one "ideal" position of your knee to the pedal.

You never know if a new position will work unless you try it. If bostonkiwi is correct, then you can move your saddle back 3cm and down about 1cm to maintain the same maximum leg extension and it will have NO effect on your pedaling action. I don't believe that this is what you'll expereince. After many years of riding with my knee directly over the pedal spindle, I moved my saddle back about 2cm and (and down to maintain the same maximum leg extension) when I moved to the mountains. I'm thoroughly convinced that the new position improves my ability to climb by applying more torque at 80-85 rpm (compared to my normal 90-110 rpm on flatter terrain).

Maybe on my next ride, I'll move the saddle forward 2cm (and) up and see if the difference is as obvious as I think it will be. According to bostonkiwi, there will be no difference.

Perhaps the real disagreement with bostonkiwi is about maximum power versus how the power is delivered. I never contended that there would be an increase in maximum power due to a change in saddle fore/aft position, only maximum TORQUE. Since power = torque x cadence, anytime torque is increased, cadence is reduced at a given power output. I've always found that a lower cadence if more effective for climbing, so my experience backs up my contention that moving the saddle back improves the ability to apply torque. I have noticed riders who can effectively climb at 60 rpm when seated, but my muscles burn quickly at this low cadence/high torque. I've also found that trying to run 90-100 rpm with less torque produces an excessively high heart rate.

The key for every rider is to find the cadence/torque combination that works best for the given terrain. I'm convinced that saddle fore/aft position does have an impact on acheiving this. If it doesn't, then setting up your bike is simple. Unless you have too much weight on the front end that adversely affects cornering, all you do is adjust the saddle height in fine increments until you find the perfect height. If you want a more "normal" road bike weight distribution, move the saddle back 2cm, down .6cm and get a 2cm shorter stem.