Cycles In Motion 650b Randonneur

Gumwall made tyres look thinner, they are the same 38mm one.

Still have VBC, will use it in a different project.

@edscoble in being wrong shocker.

I can't find the study right now - could have sworn it was Silca but it's hard to track down. Basically the difference in deflection between the Canyon VCSL split seatpost and the inline Thomson (the most and least compliant) equated to 27psi, when the difference in compression is expressed as a pressure.

The seatpost you use, depending on variables like how much is exposed etc, seems to be the most important variable other than tyre pressure/size on ride feel. Much more so than frame material.

Some initial reading for the insanely bored amongst us:

https://silca.cc/blogs/journal/118397252-tire-size-pressure-aero-comfort-rolling-resistance-and-more-part-1-how-we-got-to-now

http://www.velonews.com/2012/12/training-center/technology/from-the-pages-of-velo-getting-the-most-from-your-post_267560

https://www.cyclingabout.com/seatposts-overlooked-yet-critical-for-cycling-comfort/

http://www.tour-magazin.de/komponenten/sattelstuetzen/sattelstuetzen-testprozedere-in-tour-62011/a10145.html

the last one is a bit outdated now but still then most comprehensive look at seatpost deflection around.

why not just get the 27 psi out and keep using thomson? As there is no better inline seatpost thats light and cheap enough?

.

If your tyres are at 40 psi, you can't just let 27 out

If your tyres are at 180 psi and you let 27 out, I'm not sure you'd feel any difference

So without more info, I'm calling bullshit on 27psi difference for a seatpost. It can't be compared to pressure because the pressure to comfort graph is not a straight line

Unless it equates to 27psi from a specific pressure like 100psi down to 73 etc

i'd be left with 3psi lol

Some of the data is presented here, at the bottom of the page. I can't find the article on Slowtwich that it's referencing; if anyone is familiar with that forum and could find it for me I would be forever in their debt.

https://silca.cc/blogs/journal/part-3b-faq-and-putting-it-together-so-far

EDIT: more info here: http://www.slowtwitch.com/Tech/Thoughts_on_science_perception_4571.html

I might email Josh and see if he's got a copy of his findings somewhere

You're going up against Josh Poertner who probably knows more about tyre pressures than anyone. I know where my money is.

No I'm just saying that an arbitrary figure like 24 PSI is bullshit.
Because as I mentioned a minute ago, 24psi from 30 is a lot more of a difference than 24psi down from 120 or 150.
It is only 24 psi difference from one exact starting pressure, which is not disclosed so essentially, the only thing we know is that the vcls is "some" amount comfier.

I do agree the split VCLS post will add more comfort (probably in more of a percentage as Phil says, rather than an arbitrary X-psi) but Eds point about tyre width still stands. On 4 inch supple slicks with latex tubes the seatpost could be made of scaffolding or be the worlds bounciest carbon, fuck if you'll notice the difference

Id love to blind test people and see if the real world difference is noticeable

just found this thread! so good!!

I don't think it's arbitrary, although obviously you're right in that it's difficult to know what 24psi feels like when you're not sure of the starting point.

If you've got a bicycle with set values for tyres width, pressure etc, then replacing the seatpost will feel like you have reduced the psi by (for example) 24psi. We just don't know what the starting values are. I would presume some kind of industry standard like 25c tyre, 100psi or something. Regardless, it's an interesting study. I'm trying to get hold of Josh from Silca's email to bother him about the data.

Message him on Linkedin haha
https://www.linkedin.com/in/josh-poertner-06665b17/

I want to get stickers made that say 'minus 27 psi'

I specifically said it will make a difference in certain bicycle like a road race one running 25mm rubber;

Do bear in mind that the bike is a lightweight steel bike with clearance for 42mm tyres, seatpost make almost fuck all difference unless the bike is incredibly stiff with high pressure tyres.

Let me be clear, those split VCLS seatpost will make a difference in comfort, but on that Cycles in Motion 650b Randonneur, it make fuck all because it cannot be set high enough to take advantage of it, on top of the fact it's on lightweight 38mm tyres.

As for the pressure difference, I prefer losing a bit of pressure as this provide more grip on poorer road rather than having all the components to make up the difference and run a higher pressure on the tyres.

6 speed cassette with custom spacing, should work better than the bastardised 6 speed block I currently have (from a 7 speed cassette), also got a 14t lock on cog which helped.

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Changed levers to a gutted SRAM Force one, the cantilever brakes take a lots less effort to modulates, so a brake levers without a return spring should enhance this.

Bonus point is reach adjustment and a lots lighter than Cane Creek.

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Remind me again, why 6 speed?

Much narrower, less cross chaining/wear, provide a much better chainline and bring in crank more (q-factor is less than Shimano).
Slightly bigger jump between each cog, meaning you stick with what you're on instead of going back and forth on a 11 speed block despite the advantage of having a more precise gearing for the scenario.

Plus I liked 6 speed on the older bike, I welcome it more on audaxes, as I think less about the gear, and just focus on riding, if anything go wrong, any old derailleur will work, can set screw limiter to 21t sprocket or 18t to get me home (with 46t and 30t), if the hanger is bent, no problem, just re-set the limiter and on your way.

Lastly, I do have that Elephant NFE that will have a new fork to compensate the seat tube angle (make it steeper), and that'll always gonna be shrouded with modern stuff like hydraulic brake, 10 speed, massive tyres etc.

But does the rear brake work with that cable routing?

Oh it does, I have some design idea for the cable hanger that I’ll pass to Dan soon.

Not much solution as the biggest obstruct is the rear dynamo light, which I very much want to keep.

This is why I like 6 speed.

I fit the newer 6 speed cassette, and a 9 speed chain as the 8 speed was a little too wide that need a more precise shifting.

So far, no trimming is needed on the Big or small range, basically an old school version of the SRAM yaw system.

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so worse than sora?