FRAME STIFFNESS

[531colin]

I'm 11 stone, and I can compare the same tyres/pressures (32mm Marathon Supreme, 60 front, 70 rear, according to my pump) on 2 bikes....
This titanium disc bike with carbon fork/ 1 1/8" alloy steerer oversize bars
My old Columbus tubed Orbit gold Medal 1" steerer, 631 forks, 26mm bars (very forgiving forks by modern standards)....oversize aheadstem

On road, I can't fault the disc bike.
On the local bridlepath (hardpack, with embedded stones sticking up maybe an inch) the disc bike is OK, but I'm faster on the "old technology"
I guess if I went down to 25mm tyres and upped the pressure then I would find a difference on tarmac between the 2 bikes.

[james-o]

Colin, imo you're bob-on re the head tube, TT and DT shaping in your first post. We did the same things with 'XX44' head sets and head tubes when I 'designed' (I like your use of inverted commas there, I agree, most of us specify frames, design is a stretch and over-used in the industry imo) the Genesis ti and steel bikes to use the 44mm ID head tube. Reynolds' first HT in that format was done for Genesis back then. I think you may use the same Ti supplier as Genesis did and they made a flat-oval TT for us for the same reasons, I see they make quite a few variations on it now. The flat oval tube idea had been done before, 1930s or perhaps before even that, but the 44mm ID non-taper HT pulled a few benefits together there. Vertically ovalised Ti DTs have drawbacks at the lower edge of the HT end.

And chainstays with minimal crimping, can't agree more. Sometimes needed but good to avoid.

Planing is a funny one. Like many things in BQ the point is well-argued and hard to dispute yet for me it comes down to feel. Either you like flex there and / or low trail or you don't. Bikes are about feedback and feedback loops as much as demonstrable engineering sense and proven mechanics imo.

[531colin]

To my mind its more "pick and mix" from what the industry produces than "designing". I could wish the industry was a bit more adventurous in making things like forks with an offset different to 45mm, or chainsets and front mechs/shifters outside the Shimano straightjacket available at commodity prices, but its not going to happen any time soon.
We have just found a supplier of offset dropouts like Surly use on the Disc Trucker so you don't have to dent the fork blade to clear the disc rotor, and now I find Ridgeback put a mudguard mount at the very bottom of the fork blade, so the stays have an easier route past the caliper....every day is a schoolday!
We tend to gusset the downtube/headtube join in preference to going up a size for the downtube.

[samsbike]

I'm 11 stone, and I can compare the same tyres/pressures (32mm Marathon Supreme, 60 front, 70 rear, according to my pump) on 2 bikes....
This titanium disc bike with carbon fork/ 1 1/8" alloy steerer oversize bars
My old Columbus tubed Orbit gold Medal 1" steerer, 631 forks, 26mm bars (very forgiving forks by modern standards)....oversize aheadstem

On road, I can't fault the disc bike.
On the local bridlepath (hardpack, with embedded stones sticking up maybe an inch) the disc bike is OK, but I'm faster on the "old technology"
I guess if I went down to 25mm tyres and upped the pressure then I would find a difference on tarmac between the 2 bikes.

Thanks, that's good to know. So at least on the road, the disc forks are fairly close to a more traditional steel feel.

[old_windbag]

Where flame flexing at the BB is concerned and frame stiffness. Is it not the case that because the pedal is offset on the crank that the downward force at the top of the stroke in effect resolves to downward force but also a turning moment about the BB via crank. We are tied to this due to the spacing of our pistons on our hips. If the frame has give in it this will deflect slightly, though having seen a Ti Enigma Etape it deflected a lot visually. Does this also, whether stiff or not, transfer through the whole rigid frame to the contact points and steering. In other words the two tyres( steering + saddle too ) which then may give laterally being deformable. But at the headtube/steering there may need to be a tiny input to counter the change to to steering direction. Not sure if this plays to no handed steering where some input at the saddle is needed to keep the bike straight. On a bike with no rider it will steer straight by the gyro effect of the front wheel, but with a rider pushing pedals there would be also no need for steering input, but there is. The forces on the crank and moments vary around its path and also if ones factors in push and pull from both legs it may exacerbate the effect. Clearly pedalling lightly the effect would be tiny perhaps imperceptible, but under great crank force perhaps it is noticeable.

It's one of those things that when you think in 3D about all the motion and forces on the bike as ridden it gets complex, the flexing in the earlier posting on the simulation is what I expect. Perhaps if we had super wide hips and 45 degree crank arms outward from BB it may be more noticeable.

[reohn2]

.......Planing is a funny one. Like many things in BQ the point is well-argued and hard to dispute yet for me it comes down to feel. Either you like flex there and / or low trail or you don't. Bikes are about feedback and feedback loops as much as demonstrable engineering sense and proven mechanics imo.

I completely agree.
I don't know anything at all about bicycle frame design,but I do know when I'm riding something that's comfy,rides well and accelerates well.
I've two Salsa Vaya's an earlier 2011(bronze coloured)one,and a 2015(Baby Blue)one,both bikes are identically built by me with the same kit,but the later(Baby Blue)one feels evveerr soo slightly stiffer,at first I thought it was the colour ,until I measured the tube diameters.
The top tube of the BabyBlue one is slightly larger (I forget by how much,but it ain't much but needs the seatube end ovalised).It's just as comfy as the old one and weighs the same,but the feel under acceleration is more power goes to the rear wheel,I find this odd but it's a fact.

[Brucey]

Where flame flexing at the BB is concerned and frame stiffness. .... Does this also, whether stiff or not, transfer through the whole rigid frame to the contact points...

yes, there has to be a reaction to 'the other end of the piston'

....and steering.....

-only if you are hauling on the bars, or throwing your weight around on the bike (a fair bit).

In other words the two tyres( steering + saddle too ) which then may give laterally being deformable.

That is a good point; if the chainstays are laterally loaded (which I think happens when you are working the bars or throwing your weight around, but not so much when pedalling normally) then the tyre(s) is/are laterally loaded too.

If you ride out of the saddle on wide, soft tyres, you can see them squirming around all over the place. But when pedalling normally (no handlebar input) there is very little lateral deformation in the tyres to be seen (on my bike....), which (if this is what other people see too) would imply that the lateral loads in the chainstays are similarly low.

cheers

[531colin]

........
The top tube of the BabyBlue one is slightly larger (I forget by how much,but it ain't much but needs the seatube end ovalised).It's just as comfy as the old one and weighs the same,but the feel under acceleration is more power goes to the rear wheel,I find this odd but it's a fact.

Assuming 27.2mm seatpost and 28.6 seat tube, thats a big top tube in steel (31.8mm) (latest steel Vayas also have oversize head tube)
only the really big Spa tourers get a top tube that big in steel

[reohn2]

Colin
I'll measure both in the morning and post the results.
Is it so bad to have an oversize toptub?
The discussion so far has been about stiffness around the BB(planing(?))how does the toptube diameter affect that?

[531colin]

If the frame is comfortable and suitable for your use, it isn't bad at all.
A frame with bigger tubes than you need might be stiffer than you need and less comfortable than it could be with smaller tubes, but defining what you need is far from straightforward. On the plus side, a frame with big tubes is probably less likely to shimmy, and can transmit your pedaling effort very directly into forward motion.(Brucey tells us above that a stiff main triangle can be efficient at turning pedal pushing into motion particularly when that pedal pushing involves a degree of working the bars, as in accelerating......which I think is what you said about your blue Vaya.)
All frames were once inch top tube (25mm) and inch and eighth (28.6mm) seat and down tubes, and the tiny frame in my picture has those tube sizes. The big one has 31.8 top tube and 34.9 down tube, its a huge frame and designed for loaded touring. (I kept the seat tube at 28.6 for all sizes, wrongly or rightly)
Small changes in tube diameter make surprising differences in stiffness.

[fatboy]

Interesting thread. As a rider of Spa tourer (built from a frame rather than a complete bike) I can say that in normal riding with a saddle bag it's the most comfy bike I've ever ridden. But I was slightly disappointed with the side to side (can't remember whether it's lateral or not but in my defence I did ride 150 miles today so am knackered!) wobble around the BB when loaded with four panniers and a tent. I made it better by getting the centre of gravity of the rear panniers in line with the axel and the tent forward of the rear axle so much as to be a non problem. What I'd like is tips of how to load a tourer so it works right when fully loaded. Any tips/golden rules appreciated.

[JohnW]

Has anyone ever rigged up strain gauges to a frame and looked at the loads while riding? It would seem to be a fairly easy and obvious experiment to do, but haven't ever seen anything along these lines.

Yes, somebody did. (Don't know why the front part doesn't load)

Keezx - that is amazingly informative (at least, it was to me). Thanks for that.

[531colin]

Interesting thread. As a rider of Spa tourer (built from a frame rather than a complete bike) I can say that in normal riding with a saddle bag it's the most comfy bike I've ever ridden. But I was slightly disappointed with the side to side (can't remember whether it's lateral or not but in my defence I did ride 150 miles today so am knackered!) wobble around the BB when loaded with four panniers and a tent. I made it better by getting the centre of gravity of the rear panniers in line with the axel and the tent forward of the rear axle so much as to be a non problem. What I'd like is tips of how to load a tourer so it works right when fully loaded. Any tips/golden rules appreciated.

"how to load a tourer" has been up before, I'm a bit surprised i didn't find it in "too good to lose". Somebody with better search skills (or memory!) than me might be along and point it out.....or you might want to start a different thread?
But I think you have got the basics. Make sure your racks can't wobble.
Heavy stuff in the bottom of the rear panniers, at the front. If a heavy tent tent has to go on top of the rack, put it right at the front.
Front panniers take (much) less than half the weight, anything (relatively) heavy in the front panniers goes at the bottom, close to the steering axis.
Your post perfectly expresses the difficulty in designing a "tourer"......one bike can't be "ideal" for unladen riding and also loaded up with 4 panniers. I'm light for my height, (skinny) so I often end up riding bikes that are overbuilt. Somebody heavy for their height (muscular) might hit the opposite problem.
I would like to design a "light tourer", that would be a bike with low gears, good brakes and taking a sensible range of tyre sizes, but built light for day rides and B&B touring....but I think a "light tourer" would have an image problem, and the more different bikes you list, the more money you have sitting on shelves.
EDIT....can I ask if yours is a steel or titanium bike? The steel bikes are generally a bit stiffer.

[reohn2]

If the frame is comfortable and suitable for your use, it isn't bad at all.

That's all that matters.
EDIT:-The Kona Dew Drop I had was very planklike,extremely stiff,it was OK up to about 60ish miles then it began to hurt a little,my knees and backside felt it most,it was that experience that made me consider the planing theory put forward by JH as having some merit.

A frame with bigger tubes than you need might be stiffer than you need and less comfortable than it could be with smaller tubes, but defining what you need is far from straightforward. On the plus side, a frame with big tubes is probably less likely to shimmy, and can transmit your pedaling effort very directly into forward motion.(Brucey tells us above that a stiff main triangle can be efficient at turning pedal pushing into motion particularly when that pedal pushing involves a degree of working the bars, as in accelerating......which I think is what you said about your blue Vaya.)

Though the Big tube Blue Vaya isn't discernibly more or less uncomfortable on longer rides than the earlier Bronze one*.

All frames were once inch top tube (25mm) and inch and eighth (28.6mm) seat and down tubes, and the tiny frame in my picture has those tube sizes. The big one has 31.8 top tube and 34.9 down tube, its a huge frame and designed for loaded touring. (I kept the seat tube at 28.6 for all sizes, wrongly or rightly)
Small changes in tube diameter make surprising differences in stiffness.

The blue Vaye's toptube is 32mm,the Bronze one is 28.65mm,the 0.0bitsmm will be paint I think.

*Due to the heart attack at the beginning of last December It's so long since I've ridden any distance I'm going off memory

[fatboy]

Interesting thread. As a rider of Spa tourer (built from a frame rather than a complete bike) I can say that in normal riding with a saddle bag it's the most comfy bike I've ever ridden. But I was slightly disappointed with the side to side (can't remember whether it's lateral or not but in my defence I did ride 150 miles today so am knackered!) wobble around the BB when loaded with four panniers and a tent. I made it better by getting the centre of gravity of the rear panniers in line with the axel and the tent forward of the rear axle so much as to be a non problem. What I'd like is tips of how to load a tourer so it works right when fully loaded. Any tips/golden rules appreciated.

"how to load a tourer" has been up before, I'm a bit surprised i didn't find it in "too good to lose". Somebody with better search skills (or memory!) than me might be along and point it out.....or you might want to start a different thread?
But I think you have got the basics. Make sure your racks can't wobble.
Heavy stuff in the bottom of the rear panniers, at the front. If a heavy tent tent has to go on top of the rack, put it right at the front.
Front panniers take (much) less than half the weight, anything (relatively) heavy in the front panniers goes at the bottom, close to the steering axis.
Your post perfectly expresses the difficulty in designing a "tourer"......one bike can't be "ideal" for unladen riding and also loaded up with 4 panniers. I'm light for my height, (skinny) so I often end up riding bikes that are overbuilt. Somebody heavy for their height (muscular) might hit the opposite problem.
I would like to design a "light tourer", that would be a bike with low gears, good brakes and taking a sensible range of tyre sizes, but built light for day rides and B&B touring....but I think a "light tourer" would have an image problem, and the more different bikes you list, the more money you have sitting on shelves.
EDIT....can I ask if yours is a steel or titanium bike? The steel bikes are generally a bit stiffer.

Cracking advice. Sounds like I got there on the end.. Mine is a steel framed bike by the way