Hi Ian!
Well done Dan
you are nothing if not thorough, not to mention "careful".
Thanks! Also relieved to be this far along in the process and with a positive outcome.
I think handling improved because the bike was designed around 1.5 and 1.75 tyres and stretches to the now more fashionable 2.0 at the expense of handling finesse.
Exactly the same thought I've been having, Ian. I have a ultimate solution in mind for that, but I'm not quite "there" yet in testing to confirm it.
It is also worth remembering that we're talking pretty large differences in both tire width and profile here compared to road bikes. I can really notice a difference in handling on my road bikes when I switch from one 28mm tire to the identical model in 32mm, and that's just 4mm difference. When I changed from the 2.0 Duremes (at 47mm) to the 1.5 Matrix Road Warriors (at 37mm) are a whole
centimeter different in width and sidewall height (profile). It's a big jump. I really see the difference when I look at the empty space between the tires and the fenders with the 1.5s in place. The difference looks even greater than it is.
I originally built my Sherpa with 2.0" Marathon Supremes and found that on a narrow rim (19mm Etrto) they were too flexible in the sidewall unless pumped up to 65psi plus...
Yes, Ian, I agree; the 2.0 Duremes I regularly use are a great source of lateral movement, and the culprit is the sidewall. I do believe this is also the reason for their relatively low rolling resistance, but it comes at a cost in lost lateral stability under heavy load. I found the same as you -- stiffening the sidewalls via elevated pressure soon led to diminishing returns. Now, of course, I want to tease out just what result is due to which factor. I wish I had a 1.5 Dureme at my disposal for a direct comparison, and set of 1.75s as well. In my case, I had the 1.5 slicks ready-to-hand on the tandem and they were enough different from the 2.0 Duremes I figured if there was a difference, it would be large enough to tell me if I was on the right track.
When you see all the "lighter than Shimano" (cheaper to make) skewer reviews in webshops they all have a long bolt in torsion that many people snap! I'm suprised you weren't using a Shimano skewer in the first place as they are torsion free and therefore tight/reliable and no windage to slacken them off in use. Usually you seem to have covered EVERY angle in advance by yourself.
Well, I had "help" in this case in the form of the SON product information guide. It makes such a point of the very low tightening torque needed to secure the hub, and with good reason. The thrust spacer between the bearings is not as one would expect in, say, a Phil Wood hub and it is easy -- oh, so easy! -- to overtighten the skewer and pre-load the bearings in a way that would lead to a quick demise of the hub. Because of that, I went with the Schmidt-supplied bolt-on skewer so I could install it with a torque wrench and stay on the right side of things. In my case, it doesn't seem to be working well insofar as staying tensioned properly. I do *not* want to risk a front-wheel loss (enough whole-face reconstructive surgeries and five broken noses behind me already), so it is back to a standard q/r. I wholly agree with your comments on the dangers of boutique q/rs and avoid them like the plague. The closest I have come is the old Sachs Quartz series of external-cam q/rs that reside on my two Centurions and the in-progress Folder build, but those are all used with vertical dropouts and I have tested them over a very long period and to measure the clamping force. Otherwise -- despite all the prettiness, as you've observed -- it is awfully hard to beat the traditional old-school internal-cam q/r for reliability and maximum clamping force. I broke my own rule in trying the SON bolt-on skewer, but I'm back on-track now.
Fingers crossed, let's hope you remain wobble free
Thanks so much, Ian; I'm hoping too! I'll take it easy and ramp up gradually on my downhilling efforts. I've had my unloaded single bikes up past 58mph/93kph on Green Hill, and it might hurt Sherpa if we went down at that speed, so caution is well-advised.
...not only solved your problem but pointed the way...
Thank you, Jim; I think there's Bigger Lessons hiding in here for all of us. I know I've learned volumes just by keeping the permutations logged and straight and noting the results. It really helped to have a modular load, so I could add or subtract at will. Though the problem is technically solved for me at present, I'd still like to use those larger 2.0 Duremes for this next tour, and I want to really tease out the root cause. It still niggles the corner of my mind that I might have missed a possibly loose bolt-on SON skewer to start with...otherwise why the sudden appearance of shimmy with a lesser load when there had been no sign of it with more. I do believe there are many causes of shimmy, and there is no one universal solution. Still, it would be really nice to develop a laundry list of ranked, discrete causes so others could try them in order instead of taking shots in the dark.
I've been considering tires more in the 40mm zone and your experience sure adds fuel to that fire!
If you can possibly borrow or try a set of narrower ones, I think it would be worth it, considering how completely they transformed the bike
with the same heavy Rigida Andra rims. It was really unbelievable. Of course, the smaller-diameter tires required a computer recalibration, but they also required a physical and mental one. I was flying along one gear higher, wondering if this is what blood-doping feels like, when I realized the tires had also effectively lowered the gearing. I could see the need to go up or down one chainring tooth-size on a Rohloff bike that went from one extreme in tire width/profile to the other.
All the best,
Dan.
