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Thread: Ask the experts
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08-01-2021, 10:37 AM #5626
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08-01-2021, 10:41 AM #5627
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08-01-2021, 10:42 AM #5628
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08-01-2021, 12:54 PM #5629
The difference between wheels and other components is that wheels are pre-stressed, which means their stiffness (up to the point where the preload in the spokes drops to zero) is dramatically higher relative to both their weight and the stiffness of the individual components of the wheel.
That said, I remember conversing with Brandt on usenet and it did strike me that he was a little overconfident about using a static model to approximate dynamic events. (And to be fair, he was using the best tools at the time.) The statement that you can't tell the difference unless you can feel a piece of paper on your driveway when you ride over it was one example: the thickness of the paper might be the predicted deflection of the static models, but it doesn't account for the fact that what riders feel is mostly the natural frequency, not the magnitude of deflection. (That's one reason you'll see references to frequencies when describing overall suspension stiffness in cars.) The faster you ride over that piece of paper the better your chances of feeling it--via the vibration it generates, not the nanosecond of deflection at "impact."
The question isn't really whether or not a rider can detect the difference in stiffness between two wheels--you can probably do that just by listening to them on pavement. The question is whether or not it matters. If there are road bikers trying to figure out what the optimal sound is for maximum traction and handling I've never heard of it. And this definitely has more effect there than on a full squish with fat tires. In all likelihood the only meaningful difference in handling or traction between rims on a mountain bike based on stiffness is whether or not the rider gets distracted by one feel or another. Frequency means more to your hands than to the dirt.
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08-01-2021, 01:19 PM #5630
^^^ that all makes sense, although I do think there's a noticeable difference in both ride quality and traction. Like grinch said, world cup teams have been chasing traction via wheel stiffness modifications for decades. But for me, a stiff wheel is noticeably more jarring, particularly on short travel bikes / hardtails. Thankfully most of the newer wheels have that issue sorted out - it's been a bit since I rode a rim that felt excessively stiff.
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08-01-2021, 01:20 PM #5631
I don’t have a dog I the ‘can you feel the stiffness of a carbon rim’ fight. I am a mechanical engineer, but I have not and have no intentions of digging into the theoretical deflections of carbon vs aluminum rims, and since I have never owned carbon wheels I’m not going to discount the opinions of those who say they can feel a difference for whatever reason (I do buy into jono’s theory of frequency having some effect somewhat, but again wouldn’t argue with someone who disagrees).
That said, the videos that Toast posted do have me pretty convinced that the shallow carbon rims are going to be less likely to sustain impact damage vs a deeper section carbon rim. Pretty sure a deep section rim would crack at a lower level of rim deflection than a shallow section, and allowing that rim deflection should help spread the impact forces around the wheel instead of concentrating them in one section of the rim.
Of course that’s just comparing shallow vs deep carbon; an aluminum rim would also allow quite a bit of flex to spread the impact forces around. Not sure what level of rim deformation is acceptable for aluminum vs carbon. (i.e. does the same level of impact cause an aluminum rim to be permanently bent but a shallow carbon rim is not damaged, or does that impact cause the carbon rim to crack whereas the aluminum rim springs back to shape?)
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08-01-2021, 01:55 PM #5632
I don't mean that to sound dismissive of feel at all. I have been on bikes that inspired confidence by feeling like the tires were sticking and I went faster than the guy next to me purely because of that. It matters. But it's biomechanical, not purely mechanical, so what works for one person may not always be ideal for another, etc. It's possible to tune your own senses to pick up on different feedback and if someone likes a stiffer rim that's a valid choice. But most likely even if super stiff rims could be faster (which I'm not arguing is the case), getting experienced riders to adapt to a major change in feel is nearly impossible (as we see repeatedly). Better to stick closer to what they're familiar with.
Also, what helps for racing may not be as durable. Especially if they're running low spoke tension and just swapping stuff out before it has a chance to fail in fatigue. Brandt's models may not have covered everything but they're still useful in predicting strength, and letting spoke tension fall to zero is not going to help durability.
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08-01-2021, 01:56 PM #5633
Do I only post stupid questions in this thread? Yes, yes I do. Sorry!
But! Say I want to put a coil shock on a bike, but it hasn't been out long enough for the internet to form a consensus over what spring rate a person my size should run. Is there a tool to help calculate what spring I should run? Or am I missing something obvious? First time running a coil, would rather not buy a bunch of springs before I find something that works.
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08-01-2021, 02:03 PM #5634
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08-01-2021, 02:04 PM #5635
I won't fault anyone for taking Brandt at his word--that's been the right answer for a long time. But there's no way anyone can stand next to a road triathlon for five minutes and imagine that there's no feel difference. Stiff rims sound different from quite a distance. Carbon aero sections, obviously, but I have an old road bike with deeper section aluminum rims that sing their own tune, too. This whole debate has just been based on the wrong measurement.
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08-01-2021, 02:20 PM #5636
yeah, so I’ not saying there’s no right answer, I just don’t have it myself due having no experience, so I’ll leave it to others to make the argument.
That said - to play devil’s advocate - it’s possible the level of stiffness would be perceptible on a high pressure/low volume road tire, but not on a low pressure/high volume MTB tire, no?
EDIT: Also, could the ‘singing there own tune’ not cause a rider to ‘perceive’ a different level of harshness, even if it’s just due to sound and not actual vibration?
Anyway, if I do end up buying some carbon rims, I’ll be sure to pick a side and be a dick about it!Last edited by J. Barron DeJong; 08-01-2021 at 03:02 PM.
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08-01-2021, 05:51 PM #5637
Yes and yes, but obviously sound is vibration, so it's pretty unlikely you'd hear it and not also feel it, even unconsciously. Your bones can transmit "inaudible" sounds, so there are a lot of cues you might tune in to and even us hacks tend to get pretty focused. Pretty much what I was saying to toast above: it's pretty unlikely that perceptions wouldn't be influenced, whether that's beneficial or not.
I'm kind of intrigued by the outside chance that some tires' connection to the ground might be disturbed slightly by some low amplitude/high frequency vibration. But considering it would have to transmit from the rim through to the tread, even extreme differences seem pretty unlikely to matter.
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08-01-2021, 05:53 PM #5638Registered User
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Anyone though about putting sandblaster media in tire sealant? I have 60 and 120 grit glass. I think it would improve sealing performance.
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08-01-2021, 08:21 PM #5639
FWIW, the I’ve been riding the ever-loving piss out of a Revel RW30 wheel set for the past year, and anecdotally, they are fucking awesome.
Spent a few years on M70s with the impact strip, and the RW30s are noticeably “smoother” feeling.
I borrowed some of those Zipp Moto wheels from the rep for a few weeks when they first launched. They felt pretty cool. Lots of grip, especially on off camber roots and rock chatter. They did feel slow to accelerate out of turns, but that might be balanced by the control and speed carried through bumpy turns.
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08-02-2021, 09:19 AM #5640
All this wheel talk is interesting. me 230# with pack, etc. Have a deal on some DT swiss wheels. xm1700 with 350 hubs, 28h. Am I gonna regret the 28h and not getting something stronger? Ride lots of trail with the occasional downhill days at bike parks with kid. bronson v3. My current wheels are ar27's that while their time is ending I haven't "trashed" in 3 years of riding. I'd like to think I know a little about where to put my tires vs beating them against every rock. Have never bought a wheelset before......
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08-02-2021, 09:36 AM #5641
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08-02-2021, 09:53 AM #5642
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08-02-2021, 04:10 PM #5643
So, how hard is it to turn my 230 x 60 Fox X2 into a 230 x 62.5?
Easy job at home?Forum Cross Pollinator, gratuitously strident
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08-02-2021, 04:36 PM #5644
Im not positive but a friend had it done when he got a shock service. I think the suspension service had a machine shop cut the spacer for accurate tolerance. I guess you could disassemble the shock and get a machinist to do the cut if thats the case.
I just got my 230 x 65 jade coil back from a rebuild so i want to take my dpx2 in for a service and get it changed from a 62.5 to 65 as well. Post up how you make out if youre first. Ill do the same
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08-03-2021, 11:05 AM #5645
Best place to unload a road bike? Other than local classifieds and FB? There was a mention upthread of the Pros Closet, gotta look into it. I've sold tons of MTB stuff, included a full bike, on Pinkbike, what's the roadie equivalent?
And if anyone's interested I'd be happy to give a solid mag deal on this thing."Your wife being mad is temporary, but pow turns do not get unmade" - mallwalker the wise
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08-03-2021, 11:25 AM #5646Not a skibum
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08-03-2021, 11:34 AM #5647Not a skibum
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Ask the experts
Do have a question though - Any opinions on mixing 12 speed quick links between brands. I've done it for years on 11/10/9, but read a few things about it not being as cross compatible as it used to.
Smashed my Shimano chain/chainring into a rock, seems one link took the brunt of it, but I don't have any 12s Shimano quicklinks (nor are any available I could find) so thinking I could use a SRAM 12s link. Did order some knock offs from amazon that'll be here soon, but would be good to use SRAM that I trust more if it'll work. Most google searches turn up 11s info.
Edit - ordered a Gx 12 speed chain, in the interim giving sram QL in Shimano chain a go. Seems to be fine in the stand. We’ll seeLast edited by VTskibum; 08-03-2021 at 02:19 PM.
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08-03-2021, 11:45 AM #5648
Thanks, looked back at the 2015 catalogue and the sizing chart is all kinds of fucked up, looks like the top tube length is 55.5 and the seat tube length is 52. I'll remove the number in the description and stick with the L size only.
Edit: I ran a SRAM link on a 12-sp Shimano chain and didn't notice a difference. Then again I have a fully obliterated cassette after 1200 miles so there might be some issues there that aren't visually obvious..."Your wife being mad is temporary, but pow turns do not get unmade" - mallwalker the wise
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08-03-2021, 12:04 PM #5649
Are Shimano hydraulic brake hoses and banjo bolts the same size on all their brakes? Or at least on Zee and SLX M7000?
I think I'm going to move some Zee brakes onto a bike that currently has the SLX and has internal brake hose routing for the rear - - thinking it might be easiest if I leave the hose in place and detach the caliper and brake lever assembly, then bleed afterwards.
The hose fittings look identical at both ends.
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08-03-2021, 12:52 PM #5650
I think I answered my own Q -- both use BH90, should be totally interchangeable.
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