Lance Dopestrong wrote:And what about tube length? And oversize tube may be stiff, but a long one has more flex than a short one.
that is allowed for in the head tube length, and the difference between compact and standard frame geometries.
I can't see that this proposed system is going to make any kind of meaningful system for judging a frames rigidity.
instead of dismissing it (perhaps without even having read it carefully), you could try using it to compare bikes you have ridden and see for yourself how it works.
Brucey wrote:Mathematically speaking, in the loosest terms, whatever bending moment exists in the steerer (which, near the crown is the highest bending moment in a normal fork) is reacted by the sum of the moments in the head tube and down tube, (which are highest near the head tube). In many (most) steel frames the average diameter of the down and top tubes is about the same as the steerer, and the steerer is about double the wall thickness. Thus the bending stresses in the steerer, head tube and down tube are about the same as one another, and they all flex, too.
cheers
I can't 'see' the flex. I can see it in the fork,tips moving upward and forward. I can see that as the fork tips move up and forward some of that force can be tranferred so the steerer will try to bow rearward between the two headset bearings(it's fixed points). I still can't see how the top and down tubes bend or if they do appreciably enough to affect comfort.If they were extremely small diameter or extremely long tubes or both then yes. But not on modern bicycle tubing. I understand the forces involved,but can't see they affect ride comfort appreciably. The fork design yes I agree.
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"All we are not stares back at what we are"
W H Auden
Brucey wrote:Mathematically speaking, in the loosest terms, whatever bending moment exists in the steerer (which, near the crown is the highest bending moment in a normal fork) is reacted by the sum of the moments in the head tube and down tube, (which are highest near the head tube). In many (most) steel frames the average diameter of the down and top tubes is about the same as the steerer, and the steerer is about double the wall thickness. Thus the bending stresses in the steerer, head tube and down tube are about the same as one another, and they all flex, too.
cheers
I can't 'see' the flex. I can see it in the fork,tips moving upward and forward. I can see that as the fork tips move up and forward some of that force can be tranferred so the steerer will try to bow rearward between the two headset bearings(it's fixed points). I still can't see how the top and down tubes bend or if they do appreciably enough to affect comfort.If they were extremely small diameter or extremely long tubes or both then yes. But not on modern bicycle tubing.
read what I wrote before; however much you think the steerer is flexing, the top tube and down tube will be flexing a comparable amount, and this contributes to the movement of the fork tips in the same way. That you 'can't see it' doesn't mean it isn't there and that it isn't important.
I understand the forces involved,but can't see they affect ride comfort appreciably. The fork design yes I agree.
The fork and the frame are both important. In modern steel framesets the extent of this varies from the fork being about half as much again important as the frame, to both being about as important as one another.
The 'not on modern bicycle tubing' comment makes me chuckle because that is basically the point; if you buy a steel frameset built in oversized tubes, with disc mounts, etc it will (in the context of unladen riding) likely be very stiff and plank-like vs some other frames. Basically you are taking everything that has been learned over the previous hundred years or so about lightweight bike frame design and chucking it in the bin. The reason modern frames are made this way is so that frames (frames that will accept the loads imposed on them by the, uh, 'upper percentiles of the modern bodyweight spectrum' -as well as any luggage that might be piled on regardless of then manufacturer's recommendations) can be welded cheaply, not because 'they are better to ride'. Once you have such a frame, the only way you have to redress the comfort balance is to fit fatter tyres.
If you take (say) a ride on a conventional ~6lb 531 DB frameset with (say) 25mm tyres, and then put those wheels and tyres into a typical modern steel frameset with oversized tubes and a 1-1/8" steerer, I guarantee that you will notice a big difference in ride quality. That is the difference in frame and fork flex! But to take that observation and conclude that 'the only way to be comfortable on the road is to use fat tyres' is just wrong, or at least only true from a starting point of some framesets.
It also ignores the possibility of using a compliant frameset and fatter tyres; this can be super-comfy (and is more or less what JH is driving at; too bad that most of his would-be acolytes end up with the fat tyres attached to lookalike frames that are actually plank-like.... ).
BTW in many respects I am not a big fan of carbon forks; I think that they are susceptible to hidden damage and that they have some nasty failure modes. But they are also the saving grace of many modern framesets; carbon forks are mostly a fair bit more flexy than a modern steel fork, and without one, many modern framesets are actually pretty horrible to ride.
Lance Dopestrong wrote:And what about tube length? And oversize tube may be stiff, but a long one has more flex than a short one.
that is allowed for in the head tube length, and the difference between compact and standard frame geometries.
I can't see that this proposed system is going to make any kind of meaningful system for judging a frames rigidity.
instead of dismissing it (perhaps without even having read it carefully), you could try using it to compare bikes you have ridden and see for yourself how it works.
cheers
Well, it actually is not allowed for, for the simple reason that no two manufacturers scale their frame sizes up and down in the same way, to the same ratios. Even the same brand can scale them differently dependent upon the types of bike. Then there are female frames of different proportions to men's frames, all scaled differently.
There are hundreds of variables which differ across thousands of manufacturers, and you're proposing that a dozen or so will be sufficient make a meaningful yardstick for comparing different offerings? You may as well count the loose change in my penny jar to calculate my salary for all the good it'll do.
MIAS L5.1 instructor - advanded road and off road skills, FAST aid and casualty care, defensive tactics, SAR skills, nav, group riding, maintenance, ride and group leader qual'd. Cytec 2 - exponent of hammer applied brute force.
it is easy enough to knock something and make wisecrack remarks but again I'd ask you to actually read what I've written and to try and understand the implications.
If you did that you would perhaps notice that the weight of the frame and fork are also included; this allows for the effect of some usual variations in tube gauges.
I'm not claiming that this scheme is perfect in every way, I'm sure it can be improved upon. Instead of being dismissive, try it and see, feed back some constructive criticism instead, why not...?
In terms of being a useful tool, anything is surely better than nothing, inasmuch as at present, most people only have guesswork and hearsay (of very variable quality) to go on.
I see a lot of people very confused by the whole topic of what frame might suit them and how it should ride; for example there is another thread on this forum right now where a rider is trying to understand why his modern bike (even with fat tyres) is no more comfortable than his older one -even though it has skinny tyres fitted.
Frame flex. The following blog post (and the linked article) give details of a double blind test in which the Bicycle Quarterly folks compared bikes that were identical except for variation in the top and down tubes. If these tubes do not flex then there should be no difference but the high priests of planing found differences between them.... https://janheine.wordpress.com/2014/11/ ... s-planing/
Hi, Just to clarify my forks were ok, the frame was creased on both tubes behind the HT and I rode it 3 months till the DT snapped, rode it home holding the ends together with hand then got another frame
NA Thinks Just End 2 End Return + Bivvy - Some day Soon I hope You'll Still Find Me At The Top Of A Hill Please forgive the poor Grammar I blame it on my mobile and phat thinkers.
Intrigued by this – enough to do some calculations on 3 of my bikes, two with Reynolds tubesets and one with Dedacciai (Deda Italian steel).
Bob Jackson, 731 oversized tubes, Dolan Dedacciai, seriously oversized tubes and the bike I use to tour with, and 753, normal sized tubes, lightweight and not designed to carry loads. All are traditional frame designs, ie horizontal top tubes, raked forks and caliper brakes.
I use the BJ for lightweight touring and long distance riding or if I need a triple for ridiculously steep hills (like last week getting out of Egton Bridge with it’s 33% signpost on a hill – but it’s not really that steep). Comfortable all day in the saddle (I use Brooks and randonneur bars), fast, springy and responsive, certainly stiff enough for me and secure on long and fast descents, no shimmy, even trying to keep up with my son hurtling down Terrington Bank at 45 mph. Fix rack on with P clips when carrying luggage.
The Dolan has been used for long distance touring including Alpine hills (for example, happy coming down the bends of Alpe d’Huez on this, long wheel base, so extremely stable). Again, all day comfort (this has a Spa leather saddle) and absorbs road vibration. Robust enough to survive air travel NOT in a box or bike bag (complicated story) and what I use when I need a bombproof bike or everyday town bike with mudguards. Has mounts for rack and mudguards. Fillet brazed, not lugged like the other two. In terms of flex in the frame this is the stiffest of the three - the tubes are big – but still feels fast, responsive and comfortable. It's off to Spain next week to get me up some mountains.
The 753 is my favourite bike. Fast, light, sprightly, responsive, even on the harsh roads of North Yorkshire, I still get a buzz watching the fork rake flex on the rough surfaces. Another of my sons borrowed this the other w/e and was impressed enough to text me commenting how fast it is. Although it wasn’t designed for comfort I find this fine for all day riding (Brooks saddle) and don’t experience the harshness some feel with this tubeset.
The BJ and Dolan have same wheelsets, from Spa, using Ultegra hubs and Chrina rims, the 753 has slightly lighter wheelset. I move up from 23 mm tyres to 25 or 28 for long trips so have scored all at 25 mm. I find the extra volume does add some comfort as well as the added bonus that as pressure reduces on a long journey (when no access to track pump), there is less obvious reduction. I’m 76 kg at the moment, but pull weight down for planned long rides during the summer.
So, what scores did I get?
Bob Jackson, +2, Dolan Dedacciai, +9 and 753, -2.
Not certain I understand yet what the scores mean, assume the lower indicates a firmer ride and a higher score more comfort. The Dolan is the heaviest frame at just over 5 lbs and with a 2 lb fork whereas the other two are both under 4 lbs with 1.5 lb forks. All have 7” headtubes.
All three bikes are comfortable for me, they are set up the same and I’m fussy about getting the position right, a big part of comfort and happy all day riding. Reflecting on what the scores say and how and when I use the bikes this feels about right, ie comfortable, long distance touring, with camping gear, I’d use the Dolan; fast lightweight would be the BJ, especially when there’s big hills; and just to be fast and fun it would be the 753.
Hope you get good responses to inform the thinking further, as you say, it’s difficult making sense of the conflicting opinions about stiffness / comfort / frame materials / tyre size and all the other factors that influence our choices. I’ll read the posts with interest.
Dawes Galaxy 1979; Mercian 531 1982; Peugeot 753 1987; Peugeot 531 Pro 1988; Peugeot 653 1990; Bob Jackson 731 OS 1992; Gazelle 731 OS Exception 1996; Dolan Dedacciai 2004; Trek 8000 MTB 2011; Focus Izalco Pro 2012
Chat Noir wrote:Intrigued by this – enough to do some calculations on 3 of my bikes, two with Reynolds tubesets and one with Dedacciai (Deda Italian steel).
Bob Jackson, 731 oversized tubes, Dolan Dedacciai, seriously oversized tubes and the bike I use to tour with, and 753, normal sized tubes, lightweight and not designed to carry loads. All are traditional frame designs, ie horizontal top tubes, raked forks and caliper brakes......
The 753 is my favourite bike. Fast, light, sprightly, responsive, even on the harsh roads of North Yorkshire, I still get a buzz watching the fork rake flex on the rough surfaces. Another of my sons borrowed this the other w/e and was impressed enough to text me commenting how fast it is. Although it wasn’t designed for comfort I find this fine for all day riding (Brooks saddle) and don’t experience the harshness some feel with this tubeset.
So, what scores did I get?
Bob Jackson, +2, Dolan Dedacciai, +9 and 753, -2.
Not certain I understand yet what the scores mean, assume the lower indicates a firmer ride and a higher score more comfort....
thanks for having a go; the scoring is meant to work such that that low scores = less stiffness, more comfort. All three of your bikes fall in the same target area more or less, but the Dolan is meant to carry a load, so ought to have scored highest, and at the other end I'm not surprised the 753 scores 'best' (lowest), and that it is your favourite bike.
Ok, I see a car going down the road. The wheels are going round. I can't see the engine, so it must be the wheels that are powering the car along, because i can see them move. You see the fork tips move. You can't see the frame flex, so all the fork tip movement must come from the fork blades flexing. I can see the fork tips move. My view of the world is that the forks must be totally rigid, otherwise they would collapse under my weight when I hit a pothole, so all of the movement i see at the fork tip must come from the frame flexing. Now prove me wrong.
say the fork tips move 20mm in response to a bump. If half of that movement is due to the top and down tubes flexing, the head tube angle will change by one degree, and the tubes will have a bend worth one degree. I can't see that, I'll have to have a stern word with my optician.
Steerer flex servo-ing a cantilever brake is fixed using an uphanger....if you can't find it, just Google some combination of Tricross, and brake shudder.
531colin wrote:Ok, I see a car going down the road. The wheels are going round. I can't see the engine, so it must be the wheels that are powering the car along, because i can see them move. You see the fork tips move. You can't see the frame flex, so all the fork tip movement must come from the fork blades flexing. I can see the fork tips move. My view of the world is that the forks must be totally rigid, otherwise they would collapse under my weight when I hit a pothole, so all of the movement i see at the fork tip must come from the frame flexing. Now prove me wrong.
say the fork tips move 20mm in response to a bump. If half of that movement is due to the top and down tubes flexing, the head tube angle will change by one degree, and the tubes will have a bend worth one degree. I can't see that, I'll have to have a stern word with my optician.
In the absence of proof we'll have to agree to differ.
Steerer flex servo-ing a cantilever brake is fixed using an uphanger....if you can't find it, just Google some combination of Tricross, and brake shudder.
OK,but does that mean between the frame and the canti bosses there's a bending moment or that the frame itself in bending toward the canti bosses? The two could be different for different reasons.
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"All we are not stares back at what we are"
W H Auden
Brucey wrote: +3 for oversize tubes +2 for a frame designed to carry a load +4 for disc brake mounts +2 for a 'compact' frame design +3 per 1/8" of steerer dia over 1" (at the fork crown) +1 for every 1" less of head tube under 7" -1 for every 1" more of head tube over 7" +2 for every one lb over 7lbs for the frameset -2 for every one lb less than 7lbs for the frameset +2 for every 1/2lb of fork weight over 1.5lbs (steel fork) +4 per 1" less than 27" in nominal wheel size +2 for no mudguard clearance +5 for tyres with very good puncture resistance -3 if you are using the lowest Crr tyres available (in a given width) -1 per mm of tyre over 23mm section +2 per 1lb over 5lbs for the wheelset (including tyres) +2 per 5lbs over 22lbs for the whole bike (without luggage)
Ok, here my calculations.
Bike 1 - Woodrup 531 competition (early 90s edition)
1.5 I reckon. Light frame and fork - would 7lb be fair (I never weighed it)? , 6" head tube, built to be reliable not light (dynamo hub etc) so giving it +1.5 for weight (not sure about this - the ways in which it are heavy don't really impact on comfort too much), 25mm front tyre, 23mm back A nice bike to ride but not spectacular by any means. Quite comfortable but not especially lively (compared to a 653 racing bike I used to have and a carbon racing bike I currently have).
The frame replaced an oversize aluminium frame and carbon fork and was a big improvement, but I would say most noticeably in terms of liveliness and less in comfort.
Dawes Hybrid, 531ST (early 90s edition), beefy unicrown cromoly fork but with Compass Extralight 32mm tyres 2 I think - scoring well primarily because of the tyres. In terms of comfort my assessment would be that the tyres more than make up for the stiffer frame and fork on the Woodrup. On a bumpy road the Dawes is much nicer. However, it is by no means lively and feels quite different to the Woodrup in that respect.
I only weigh 60kg so I suspect both bikes are a bit overbuilt for me.
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