Slack geometry and gear inches

[SkipdiverJohn]

I'm taking a chance posting this in here as I doubt that many roadies riding modern steep-angled stuff frequenting the main forums would grasp what I'm getting at - which is does the slackness of your geometry (specifically the seat tube angle) affect how high a gear inch you can push for a given level of perceived effort or fatigue?
As some on here will know, I have several old steel bikes with some geometry variations, and one thing I have noticed is that pushing the same or very similar gears on two bikes with different geometries results in a noticeably different perceived effort level. For example I have a Raleigh Pioneer and a Raleigh Gemini, very similar flat bar hybrids with absolutely identical gearing and tyres fitted, yet the Gemini is slightly faster (according to my Cateye computers) and feels slightly easier to push in a given gear on the same road. The Pioneer has a 73 deg seat angle and the Gemini is "touring" geometry which I believe was 72 deg on Raleighs of that era. The only other difference is the Gemini is one pound lighter, but given I'm nearly 200 lbs, that only equates to less than 0.5% of the total rider & bike weight.
If I compare my 21 speed Raleigh Highlander MTB with my old Puch Touring 3 speed roadster, the difference is even more noticeable. So long as I'm on the flat and not riding into the wind, the 88 inch High gear on the Puch's Styria hub is manageable, if a bit on the high side. It has a frame geometry of about 70 degrees, visually quite slack. The Highlander has a 73 deg seat angle, and if I try pushing the same gearing on that as on the Puch I very quickly get fed up with it and drop down at least one ratio, which probably equates to about ten gear inches less. It's the same up hills, the Low gear on the 3-speed is 53 inches yet it feels no harder than the 45 inch gear I use to climb the same gradient on the MTB. The MTB is the lighter bike by about 4-5 lbs as well!
In theory gear inches are gear inches no matter what, but in reality the same gear feels different when propelling different bikes. I wonder if this is why you would often (at one time, not so common now), see an old chap going along at a reasonable speed on an ancient 3-speed rod-braked roadster with a super-slack frame, in High gear on the SA hub, ultra-slow cadence, and not seeming to really break a sweat? It's almost like the more pedals-forward frame geometry on the old-school bikes allowed the rider to get more of a push on the pedals than when sitting more over the cranks pushing down as on modern bikes.

 

[Edgy Dee]

Your query had me reaching for my usual bibles on these matters; Bicycling Science by David Gordon Wilson, and High-Tech Cycling by Edmund R Burke. Bicycling Science doesn't even have geometry in the index! But I do recall something about increased power from increasing seat height from the traditional formula. High-Tech Cycling has a section on seat-tube angle, but refers more to correct fitting than energy transfer. I think the usual logic is that a steeper seat-tube allows better power transfer, but is less comfortable, hence more likely to be seen on a sprint bike than on a tourer. Interesting observation you have there about different perceived rate of exertion for same gear inch. Probably needs more research .

 

[Smokin Joe]

In theory gear inches are gear inches no matter what, but in reality the same gear feels different when propelling different bikes. I wonder if this is why you would often (at one time, not so common now), see an old chap going along at a reasonable speed on an ancient 3-speed rod-braked roadster with a super-slack frame, in High gear on the SA hub, ultra-slow cadence, and not seeming to really break a sweat? It's almost like the more pedals-forward frame geometry on the old-school bikes allowed the rider to get more of a push on the pedals than when sitting more over the cranks pushing down as on modern bikes.

The top time trialists sit forward in the saddle rather than back precisely to get more power. I know when I raced you adopted that position when the hammer went down (As did everyone else) to get more power through the cranks. I can't for the life of me see how a laid back seat tube angle can give any increase to a riders power output.

 

[Ian H]

Strictly speaking, the angle of the seat-tube will have no effect on power. The position of your saddle in relation to the bottom-bracket is the thing. I always position the saddle the same regardless of geometry. It can involve sourcing seat-posts with more or less lay-back.

 

[SkipdiverJohn]

Your query had me reaching for my usual bibles on these matters.... I think the usual logic is that a steeper seat-tube allows better power transfer, but is less comfortable, hence more likely to be seen on a sprint bike than on a tourer. Interesting observation you have there about different perceived rate of exertion for same gear inch. Probably needs more research .

It may well be the case that the steeper geometry, combined with standing up on the pedals at times, facilitates higher peak power outputs, but the thing is this can only ever occur for brief periods for acceleration and competitive climbing, not sustained, constant speed cycling. You might ride like this at the start of a race, or to get away briskly from a set of traffic lights, but you are not going to ride for 5 or 10 miles out of the saddle or just on the nose of the saddle.

The top time trialists sit forward in the saddle rather than back precisely to get more power. I know when I raced you adopted that position when the hammer went down (As did everyone else) to get more power through the cranks. I can't for the life of me see how a laid back seat tube angle can give any increase to a riders power output.

As above, there is a vast difference between the way a TT competitor approaches a ride, and the way a non-competitive cyclist rides. In a TT, the ultimate aim is to go as fast as humanly possible, with little consideration for comfort or the ability to maintain this style of riding over a long duration. I doubt you'd ride a 25 mile event as aggressively as you would a 10 mile one.
What I am talking about is not the ability to produce a high peak power, but the ability to produce a steady cruising power output with the minimum cadence or minimum fatigue cost. My perception of riding bikes of a similar weight and aerodynamic profile, but differing geometry, is that for a given road speed, a slack geometry frame seems to allow a slightly higher gearing at a slightly lower cadence, probably due to differing muscle recruitment patterns. Compared to a slack frame, a steeper frame seems to be harder on the thighs, even with the same saddle height. The effect feels similar to riding with the saddle set too low up a gradient.

Strictly speaking, the angle of the seat-tube will have no effect on power. The position of your saddle in relation to the bottom-bracket is the thing.

Agree completely, when I talk about seat angle, I am assuming the saddle is located on the same position on it's rails in each case. The effective seat angle may be more or less than the geometry chart, depending on where the saddle is set on the rails. On my gravel & woods MTB, which has a long TT and long stem, I can reduce pedalling effort by moving the saddle back to slacken the effective seat angle, but if I overdo it, the reach becomes uncomfortable because of the stem length. I have another identical geometry MTB frame, but running road tyres, on which I am going to fit the shorter stem from a scrap Pioneer to allow a better overall fit.

 

[rogerzilla]

Pushing your saddle back does the same thing as slackening rhe seat angle. There is a setback that feels right for any given rider and going beyond that won't help.

Generally, power increases with saddle height until you start to run the risk of over-extending your knees. My saddles are 95% of (trouser) inside leg length.

 

[SkipdiverJohn]

Pushing your saddle back does the same thing as slackening rhe seat angle. There is a setback that feels right for any given rider and going beyond that won't help.

Generally, power increases with saddle height until you start to run the risk of over-extending your knees.

I agree, there is definitely a sweet spot in both saddle set-back and saddle height. The trouble is though, to optimise position on a steep frame might mean ending up with an uncomfortable reach or having to run a silly short stem. If the TT is roughly the right length to begin with, every bit you shove the saddle back has to come off the stem length to compensate. It's easier to avoid overly steep angled frames and go for more comfortable ones, IMHO.

 

[gilespargiter]

^ As you say. Thing is first get your saddle in the right place and then adjust the reach. Sod the modern fashions about what supposedly "looks" right. Most modern road positions are way to far stretched and also the handlebars are to low for comfortable sustained effort. Hence all this nonsense one reads about drops being to difficult and don't get used that one keeps reading - the tops are where the drops need to be. . . so you can't reach the drops! No wonder so many people have back and neck trouble on long rides, although a lot of people seem to think two hours on a bike is a long time. You don't want to be pulling your belly into the top tube you need to be curling your hips towards the handle bars - like love making - way hey no back pain.
So long as your stem is in front of the steerer it really makes very little difference to the steering how long it is, although saying that it does make slightly more difference to steep angled frames. Of course with these scaffold clamps they use nowadays instead of lovely sculptured stems they are neither easy nor cheap to adjust. The steep angles also make the frames more twitchy so that you have to steer them all the time instead of them steering themselves. The shorter wheelbase (like narrower tyres) also gives more feedback from the road which gives a perception of speed, which does not translate to actual speed.
Then again if you like buying labels and looks - then their is nothing more to be said. I rather suspect that like me you like riding practical comfortable bikes.

 

[SkipdiverJohn]

So long as your stem is in front of the steerer it really makes very little difference to the steering how long it is, although saying that it does make slightly more difference to steep angled frames. Of course with these scaffold clamps they use nowadays instead of lovely sculptured stems they are neither easy nor cheap to adjust. The steep angles also make the frames more twitchy so that you have to steer them all the time instead of them steering themselves. The shorter wheelbase (like narrower tyres) also gives more feedback from the road which gives a perception of speed, which does not translate to actual speed.
Then again if you like buying labels and looks - then their is nothing more to be said. I rather suspect that like me you like riding practical comfortable bikes.

All my bikes have always had quill stems and always will. Threadless steerers needing a stack of spacers to adjust them must be one of the most crap pieces of bicycle design ever invented. They're ugly too, the spacers make the stem much larger than a quill. Even a cheapo black steel MTB stem looks better than any of that threadless rubbish and I can adjust them in two minutes with an allen key. No contest, quill every time.
Comfort, practicality, and durability are my main bike choice criteria. I'm not interested in flimsy gimmicky rubbish, or following stupid fashions for the sake of appearance. I do appreciate a nice looking machine, and the fact someone cared about what they were designing and building. With a very few modern exceptions, the only stuff I will generally consider owning and riding is older steel. Doesn't need to be exotic, but does need to be well designed and at least look like a proper bike, not some piece of weird abstract sculpture.
What interests me is getting the most out of my bikes in terms of making them as comfortable, efficient, and practical as possible with a tweak here & there - hence my interest in such matters as geometry characteristics and saddle/bar positioning.

 

[gilespargiter]

Much as myself then. I completely agree about the steerers. I'am not in a position to at the moment but a couple of times I have thought to my self that before I purchased a bike if they did not finish fitting the headset properly by cutting a thread and then fitting a nicely made quill stem with precisely the rise and reach that I require - in the price - then it would totally break the deal for me. I would prefer to find a good frame in a skip (usually not difficult) fettle and fit it to my precise wishes, and have it enamelled and sign written by hand.

 

[SkipdiverJohn]

There is definitely something to the geometry/effort thing with regards to gearing. Earlier today (well technically yesterday) I took my ratty old 3-speed Puch Touring gas pipe roadster out on my usual weekend ride instead of my MTB or Hybrid. I spent more time in the 88 inch High gear than I would have done on any of my other bikes. OK, a straight comparison to an MTB on knobblys probably isn't ideal as the tyres will be draggier, but the roadster and hybrid tyres will not roll much different to each other yet I still wouldn't gear up as high on the hybrid. Despite pushing a slightly higher gear on average on the 3 speed, my average speed wasn't any worse than normal, and I didn't feel as tired at the end of it. The total amount of work done can't have been much different given the distance, rider weight, and bike weights, yet the 3-speed riding position seemed to take less out of me. Very strange, those old-time frame designers were bang on the money when it comes to ergonomics, as we would now term it.

 

[DCBassman]

Maybe simply that your personal geometry matches that type of frame geometry, others really dig the twitchy stuff. Like you, I like it easy-going, and the hybrid rebuild will likely end up as No 1 for that reason.

 

[SkipdiverJohn]

Maybe simply that your personal geometry matches that type of frame geometry, others really dig the twitchy stuff

There must be an element of that, as you say. I'm just about to do a 20 mile round trip to go and see someone this afternoon, and I've decided to take the old ratty 3-speed instead of my usual hybrid. It will be interesting to compare journey times - and how knackered I feel at the end of it. There's a couple of quite nasty gradients at the far end of the outbound trip - should be fun with wide-ratio SA hub gears...... I've done the same route 20+ years ago on a 3-speed, but I somehow doubt I'm going to be so quick now.

 

[SkipdiverJohn]

As I expected, I was a few minutes slower on the outbound trip, as I had to grind up some gradients in a less-than-ideal 53 inch Low gear. My knees didn't enjoy that bit very much. What surprised me though, is the return journey was actually a few minutes quicker than I'd normally achieve on the hybrid. The overall journey time for the round trip was pretty much the same, and the overall exertion level was possibly slightly less, and I didn't get so hot or drink so much water. Riding a hub gear bike again in traffic is an absolute pleasure compared with using derailleurs. Instant perfect gearchanges every time, and if you get caught out by a red light, you don't find yourself grinding away from a standstill in too high a gear. Just click & go.
All I need is to do now is increase the rear sprocket count by just one tooth and the gearing would be pretty much perfect.