tyre suspension effect (from Are touring bikes old fashioned)

[pwa]

When using small cross-section tyres I prefer forks with a bit of give, and the best I've had in that regard were straight blade forks made with thin walled high end steel. I don't think it was the straight blade them made them flex, I think it was the modest cross section and the thin walls, combining with the fact that the blades are angled in such a way that they can flex upward at the dropouts. Being straight doesn't make a length of metal inflexible. Cold working steel, as you do when you bend it into a curve, may take out some of the flex. Even a steel girder flexes when enough force is applied and it isn't held vertically. My straight blades managed to give a surprisingly plush ride in spite of the tyres being 23mm and pumped up good and hard, as you have to with small cross-section tyres to prevent your rims being damaged on poor road surfaces. I reckon the thin walls on the blades combined with them not being too chunky, to give a bit of flex. I've ridden 531c curvy blades and they were okay, but if, anything, slightly harsher. 531st curvy blades were definitely harsher and I would have welcomed being able to use wider tyres when I had those.

But on a bike where there is clearance for much more rubber, you don't need to rely on the forks to do the flexing. The best tyres with supple casings and adequate volume, not inflated to high pressure, can do an even better job at taking out the sting. I suspect that the steel forks on my Spa tourer aren't particularly forgiving, but I don't know for sure because the Marathon Supreme tyres (35mm) I have on that bike are quite supple and do all the cushioning I want. Regular Marathons on the same bike gave a harsh ride, so I took them off and they hang, almost unused, on a hook on the garage wall. These days, I think we can rely on the tyres to supply the plushness and leave the frame and forks to resist unwanted distortion that might adversely affect steering. And as someone who has had serious shimmy issues with a bespoke steel frame and fork in the past, I love a solid riding frameset. So long as the tyres are up to the job.

Now that we have tyres that can fulfill that role, and frames taking wider tyres are more common, we can have the best of both worlds and have plushness supplied by larger volume supple tyres, whilst at the same time benefitting from stiffer framesets that resist twisting better than more flexy framesets. Separate those two functions and reap the benefits.

[iandusud]

Whilst I have no doubt that the choice of tyres and their pressure has the biggest bearing on comfort I feel I must relate my experience. For about 25 years the only road bike I had was a Moulton, but I was mainly mountain biking during that time. I decided to build up a fixed wheel bike to do some road training and bought a nice s/h Columbus framed road bike which I converted. Forward a couple of years when I moved back to London where the fixie served me well for commuting. However I decided to buy a road bike with gears and bought a Giant Defy fitted with and alloy frame and carbon front fork. The difference in comfort at the front end was astounding. I had been running the fixie with 28mm tyres and the Giant came fitted with 23mm tyres and still it was far more comfortable. So there you have it, my 2d worth.

[bgnukem]

I think its perfectly possible to have both, some fork flex to take the front end shocks and a laterally stiff main frame to prevent shimmy/flex under power.

I suspect a lot of disc front forks are over-engineered to prevent legal action resulting from people breaking them when they fit an oversized front disc, or go offroading, etc, etc. Its no doubt convenient ,and cheap, but making everything as stiff as possible is just a lack of engineering sophistication. See also oversized bars, stems, seatposts, frames, etc, etc.....

I'm likely returning to rim brakes on my next frame build, and may even convert my commuting bike back to a front rim brake, because I'm fed up of the forks crashing into every little road ripple and having to ride on soft tyres to try to achieve a tolerable ride quality.

[slowster]

Thorn offer their Mercury tourer with a choice of forks. The disc brake fork is Reynolds 525 and has low rider bosses, whereas the V brake fork is 853 and Thorn state it must not be used with a front rack. Thorn make a big point of the greater comfort of the V brake fork in their promotional literature. Most Mercury owners and users of these forks will probably be using fairly wide tyres, i.e. 35mm-40mm. SJS also sell the forks on their own, and the 853 fork is more than twice the price of the disc fork.

I doubt Thorn/SJS would have gone down the route of offering separate disc and V brake forks, and moreover with such a higher price for the V brake fork, without having satisfied themselves beforehand with prototypes that the difference in comfort was significant.

https://www.sjscycles.co.uk/forks/46-70 ... lue-imron/

https://www.sjscycles.co.uk/forks/46-70 ... lue-imron/

[PH]

Thorn offer their Mercury tourer with a choice of forks. The disc brake fork is Reynolds 525 and has low rider bosses, whereas the V brake fork is 853 and Thorn state it must not be used with a front rack.

Thorn offer two V- brake forks for the Mercury, the 853 and ST, I have them both, I have two Mercurys (That wasn't a plan, one was crashed and repaired, the other the insurance replacement) Same 32mm tyres and I can notice the difference, 40mm tyres and I can't. I also have a Surly with a girder like fork which is normally comfortable with it's 50mm tyres, I ran the Mercury's 32mm wheel in it to test a dynamo/light issue, it isn't something I'd do again, jarring to the point of unpleasant.
I have no doubt that tyres make the biggest difference to any bike, I don't think that clashes with the idea of comfortable forks, neither am I sure that the movement is directly comparable. My Hewitt Cheviot with a 1" Aheadset is as comfortable as any fork I've had, I've attributed that to the size, but have no way of knowing, though sizes have increased for stiffness so it doesn't seem an unreasonable assumption.

[bgnukem]

I think Brucey has previously commented on here that a smaller diameter steerer tube (for 1" headset) is likely to flex more longitudinally, between the headset bearings, as a result of bending forces transmitted through the fork legs when the fork meets bumps, thus not all the flex is in the fork legs.

My old Dawes also has a 1" headset and smaller steerer tube diameter and is very comfy, despite unicrown Reynolds 531ST fork legs. It maybe helps that the frame size is 64cm so there is a long length of steerer tube between the top and bottom headsea bearings.

[djb]

But on a bike where there is clearance for much more rubber, you don't need to rely on the forks to do the flexing. The best tyres with supple casings and adequate volume, not inflated to high pressure, can do an even better job at taking out the sting. I suspect that the steel forks on my Spa tourer aren't particularly forgiving, but I don't know for sure because the Marathon Supreme tyres (35mm) I have on that bike are quite supple and do all the cushioning I want. Regular Marathons on the same bike gave a harsh ride, so I took them off and they hang, almost unused, on a hook on the garage wall. These days, I think we can rely on the tyres to supply the plushness and leave the frame and forks to resist unwanted distortion that might adversely affect steering. And as someone who has had serious shimmy issues with a bespoke steel frame and fork in the past, I love a solid riding frameset. So long as the tyres are up to the job.

Now that we have tyres that can fulfill that role, and frames taking wider tyres are more common, we can have the best of both worlds and have plushness supplied by larger volume supple tyres, whilst at the same time benefitting from stiffer framesets that resist twisting better than more flexy framesets. Separate those two functions and reap the benefits.

your comments here mirror what I was trying to express in my posts, as my experience is very similar to yours.
My 1990 Japanese tourer was/is a nice bike, but I have had shimmy touring with it that required a combination of weight distribution and limiting total weight carried to manage.
Cue forward to my Surly Troll that I've used touring carrying more weight than ever because of specific touring locations, and the combo of stiffer fork/headset as well as better racks than back in the day, meant this bike is just more competent with a load, but the larger tires (Supremes also) give a great ride.

anyway, just wanted to say that your last paragraph very much sums up my views on this topic.
I've ridden my Troll with tires from 1.5in (37-40mm depending on specific tire) to 2.5in , so I really like that this frame can be used or set up for many types of riding.
Heck, even my wifes newer Troll can take up to 3in. tires, which really opens up possibilities of types of riding one can do, which I find pretty neat for flexibility of one bike.

[slowster]

Handlebars and stem will potentially make a significant difference. Although 1" threaded steerers may flex more than their 1 1/8" threadless counterparts, I suspect the quill stems will make a bigger contribution, especially if the stem is long and/or a lot of the shaft is exposed above the headset. Similarly all other things being equal, wider bars will flex more, and a 25.4mm/26mm clamp diameter bar will be less stiff than an equivalent 31.8mm modern standard. Furthermore some bars are heat treated to increase their stiffness, e.g. I think the wider versions of Nitto's bars are usually heat treated. I have two old 3T handlebars - both are 46cm wide and the same pattern, but one was the bottom of range and the other was the more expensive, lighter, butted and heat treated top of the range model. The cheaper bar is much more flexible.

[kylecycler]

I think Brucey has previously commented on here that a smaller diameter steerer tube (for 1" headset) is likely to flex more longitudinally, between the headset bearings, as a result of bending forces transmitted through the fork legs when the fork meets bumps, thus not all the flex is in the fork legs.

My old Dawes also has a 1" headset and smaller steerer tube diameter and is very comfy, despite unicrown Reynolds 531ST fork legs. It maybe helps that the frame size is 64cm so there is a long length of steerer tube between the top and bottom headset bearings.

Brucey often suggested that, right enough, although of course most bikes nowadays have a 1 1/8" steerer. A 1 1/8" tube isn't just 1/8 stiffer than a 1" tube, it's quite a lot more than that - same goes for length as for diameter (CJ will know the exact figures!).

I even remember al_yrpal suggesting that the 'trekking' bars - the loopy kind - he fitted to his old Carrera Subway tourer cushioned the shocks to his hands, which I quite believe but would never have thought of. Makes perfect sense, though, when you consider the bars' overall length.