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"Advantages" of bigger wheels and angular momentum

Wa-Aw

Monkey
Jul 30, 2010
354
0
Philippines
Talk about kicking the dead horse but with ultra-aggressive marketing of 27.5 wheels these days and some publicity/input from WC pros I had to ask about this...

The biggest advantage I seem to hear of is that they are just more stable at speed. I'm going stay away from the whole "better traction because of larger contact patch" or "smoother on the bumps because the wheel is bigger" arguments because people who claim to feels those are the same kind of people who claim that Ti springs are plusher.


Personally, I think it's all about the angular momentum. But my beef with this is that the same symptoms can be achieved by simply running heavier wheels. These are the same things I feel when going from a lighter to a heavier wheelset. More sluggish in the corners and accelerating but it doesn't deflect as badly at high speed.

The "larger diameter of the wheel making it smoother over bumps" argument is a valid one but it's not independent of suspension quality and compensating with one for the other is possible in this regard. Another remark relevant to this that I heard was in Andorra the 27.5 riders were running 26's because they fell into the braking bumps easier making braking easier. But if this isn't bull then it seems the opposite is valid as well (27.5's will get you moving over braking bumps easier).

Thoughts?
 

supercow

Monkey
Feb 18, 2009
969
128
My thoughts are that I'll just buy whatever everyone else is buying, because it will mean that I'll have spares when I need them.
 

bizutch

Delicate CUSTOM flower
Dec 11, 2001
15,928
24
Over your shoulder whispering
All I know is that when I tried to ride a dialed in 27.5 trail bike at my local trails, I could tell the wheel liked to "maintain" speed up a climb hitting all the little chatter and ripples in the trail, but that I was having to exert more effort to get them rolling and keep them rolling than my 26" wheels.

In the turns, which were BIG, SWEEPING turns...I had the distinct scary feeling like I was gonna overshoot them. It came as a surprise to me because the wheels weren't that much bigger than my own.

In quick turns and "wiggly" situations, they were very much harder to manuever. Not gonna switch to them if they'll allow me to stay on 26" bikes. I've always bought a bike almost too small for my size.

LOVE a quick turning bike.
 

frorider

Monkey
Jul 21, 2004
971
20
cali
I'm going stay away from the whole ..."smoother on the bumps because the wheel is bigger" arguments
Science. you should try it. Seriously, there has never ever been any question that all else being equal (similar tire casing volume, etc) a bigger wheel will roll over **** better. If you doubt this, try riding your skateboard on a rocky trail. Or ride a 24 inch hardtail on that trail without using any body english to compensate. The question has been whether the tradeoffs are worth it.

Personally I don't notice much advantage to 275 or 29 wheels on fast rocky descents if I'm on a bike with a reasonable amt of travel. Where I strongly notice the rollover advantage is on flat or uphill sections that are chunky and require pedalling. I also notice the front wheel advantage in sandy corners. There's nothing imaginary about that. There are sections of local trail like this I've ridden hundreds of times in the last decade, sections I ride 4+ days a week on various bikes with various wheel sizes, and on those types of sections the wheel size difference is definitely noticeable. My 275 wheels are slightly lighter than any of my 26er wheels which compensates for the extra 40 g or so of the tire.
 
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Jm_

sled dog's bollocks
Jan 14, 2002
18,850
9,556
AK
The "larger diameter of the wheel making it smoother over bumps" argument is a valid one but it's not independent of suspension quality and compensating with one for the other is possible in this regard.
I've never found this to be the case. I've found that you will roll over stuff easier/faster than a lesser-travel bike IF you can hold on, but going over a pile of rocks on a 6" 29er feels like, well, 6" of travel, it doesn't feel like 8" and it doesn't make up for the fact that the longer-travel bike has more. If you had more travel, you could go even faster with more control. As it stands, you can can go faster, but you don't necessarily have that control IMO, because you don't have the travel.

I feel that a 29er hardtail makes a 4" travel 26 FS bike redundant if you are interested in speed, keeping up with others, going faster than others, because the 29er will end up lighter and have significant advantages for roll-over and climbing, but it won't be a more comfortable ride, it won't be like having 4" of suspension.
 

bizutch

Delicate CUSTOM flower
Dec 11, 2001
15,928
24
Over your shoulder whispering
Did I mention I ride trails with DH casing tires at all times because I tend to ride agressive and "smash" style? Can't imagine how much a 27.5 with casing thick enough to keep my gorilla arse from crashing would weigh.
 

Cant Climb

Turbo Monkey
May 9, 2004
2,683
10
My trail bike is a 26" 100mm travel.
Has good geo and a dropper post.
I can reach near DH speeds on local general MTB trails.
But the 26 wheels hit stuff harsh on these flatter trails.
You can't pedal everywhere and these trails aren't pure gravity trails.

I'm looking forward to trying 27.5.
I think for trail riding it's going to enhance the ride.
The 27.5 will carry more speed uphill and downhill with less fatigue to the rider.
 

frorider

Monkey
Jul 21, 2004
971
20
cali
Did I mention I ride trails with DH casing tires at all times because I tend to ride agressive and "smash" style? Can't imagine how much a 27.5 with casing thick enough to keep my gorilla arse from crashing would weigh.
I tend to run 800-900 g 1.5 ply tires on my 26er trail/AM bikes, and in that tire category the 27.5 version of the same tire is around 40 to 50 g heavier. I have some proto DH 2 ply michelin 275 tires that I can't provide a direct weight comparison for to an identical 26 version, but the difference is in the 70-100 g range from what I can tell. It's not like DH 29er tires, which (to the extent they even existed) were a big jump in weight.

http://www.maxxis.com/Bicycle/Mountain/High-Roller-II.aspx gives some comparisons for Exo maxxis HR II. I've heard there are 2 ply wire bead 275 DHFs out there but I don't seen them on the maxxis site and don't know the weight.
 
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HAB

Chelsea from Seattle
Apr 28, 2007
11,580
2,005
Seattle
Teh mathz say that an identically constructed 650b tire should weigh 4.5% more.
 

saruti

Turbo Monkey
Oct 29, 2006
1,167
73
Israel
tried a friend Norco 27.5 bike on a trail I know well...
my 26" bike on the same trail felt better. maybe\probably the suspension type(?)
and the 27.5 felt sluggish coming out of turns ....
I think the best will be checking 2 same bikes with different wheel size...
but, for now, I'll stay with my 26er
 

marshalolson

Turbo Monkey
May 25, 2006
1,770
519
Hooray for technology that weighs more and takes longer to get up to speed with more effort to do so...and slower turner. :tinfoil:
they also roll over stuff more efficiently, and therefore you need less tire to protect from flats.


data point only but: i had to run 26" 2.5 DHF's on my old trail bike, even 1000g super gravity tires would last only a couple rides before the inevitable cut. i am on 750g 29'er tires without an issue currently (about 30 rides), and according to the iphonage, am riding the same trails at the same speeds/times.

so yeah, saving 400g per tire is pretty awesome.
 
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kidwoo

Artisanal Tweet Curator
Hooray for technology that weighs more and takes longer to get up to speed with more effort to do so...and slower turner. :tinfoil:

I've been running a dh casing tire on the rear of my trail bike too. What I'm actually hoping happens when I have no choice anymore but to buy wagon wheels is that the mellower angle of attack on sharp things actually lets you run more normal/lighter tires without getting holes punched in them. It might at least get the tradeoff to a null set in terms of rotating mass.
 

Uncle Cliffy

Turbo Monkey
Jan 28, 2008
4,490
42
Southern Oregon
I've heard there are 2 ply wire bead 275 DHFs out there but I don't seen them on the maxxis site and don't know the weight.
The EXO version is listed on their site now. The claimed weight is 825 grams for a "2.3" folding version. I was told they'll be available this month at some point, and I'm betting the weight will be closer to 900 after production.

No listings for a DH version yet.
 

Wa-Aw

Monkey
Jul 30, 2010
354
0
Philippines
they also roll over stuff more efficiently, and therefore you need less tire to protect from flats.


data point only but: i had to run 26" 2.5 DHF's on my old trail bike, even 1000g super gravity tires would last only a couple rides before the inevitable cut. i am on 750g 29'er tires without an issue currently (about 30 rides), and according to the iphonage, am riding the same trails at the same speeds/times.

so yeah, saving 400g per tire is pretty awesome.
I didn't think of this benefit since it would make sense that all (or at least most) of the energy would have to be absorbed and transmitted by the tire before the suspension acts.

But I'm going to have to be a biggot and stand in disbelief over your approval of single ply tires. Has the technology improved in the last few years? I agree with you in the impact being less on straight on hits but do you think the same marginal increase in the contact patch means the gives more support in corners? My only memories of single plies are insta-flatting tires at 50psi on the first corner of the DH track. and rolling beads on hard berms and sideways cornerning-landings.


I just find it strange that lots of companies are jumping onto the boat like it's some kind of revolution. My tin foil hat says it's definitely a conspiracy to open a totally new market and sell more frames.
 

FlipFantasia

Turbo Monkey
Oct 4, 2001
1,659
492
Sea to Sky BC
I just spent over 3 months on a Rocky Altitude, it wasn't slower to get up to speed, or any less maneuverable than a 26"...but hey, that's actual long term experience on one, I know you guys don't like that here.
 

frorider

Monkey
Jul 21, 2004
971
20
cali
Good stuff on wheel sizes from Keith Scott, starting with the basics:

http://bansheebikes.blogspot.com/2013/10/wheel-size-facts-part-1-dimensions.html
pretty basic stuff there that I would hope most people would know, but I like the fact that he's drama-free about the topic. he did leave out the fact that many e-riders throw around the term 'angular velocity' without realizing that a larger diameter wheel has a slower angular velocity. Therefore when 'spinning it up to speed' the delta in angular velocity is less than w/ a 26er. Not saying Keith is wrong, just that he appeared to repeat the simplistic analysis found in other places.

I haven't pinch flatted an exo sidewall rear tire on my Bronson but I sorta doubt the angle of incidence is the explanation for that. I am in no hurry to convert to a 27.5 DH bike but I suppose in 5 yrs most of us will be on one. At least 27.5 is coinciding with the recent trend toward affordable carbon fiber rims. http://www.derbyrims.com/ etc
 

marshalolson

Turbo Monkey
May 25, 2006
1,770
519
But I'm going to have to be a biggot and stand in disbelief over your approval of single ply tires. Has the technology improved in the last few years? I agree with you in the impact being less on straight on hits but do you think the same marginal increase in the contact patch means the gives more support in corners? My only memories of single plies are insta-flatting tires at 50psi on the first corner of the DH track. and rolling beads on hard berms and sideways cornerning-landings.
ha, no i am talking about trail bikes. i can't even run tubeless on my DH bike.
 

bizutch

Delicate CUSTOM flower
Dec 11, 2001
15,928
24
Over your shoulder whispering
Here's a thought and if it refers to this angular velocity crap...my apologies.

If I hold a 26" wheel and someone spins it at high speed and I try to lean it to 45 degrees quickly, it will be easier than doing the same with a 27.8675309 wheel...right?
 

MDJ

Monkey
Dec 15, 2005
669
0
San Jose, CA
so what size chainrings are you 26" guys running on your triples? and can one of you tell me how to adjust my v-brakes?
 

dhbrigade

Chimp
Feb 21, 2006
89
2
so what size chainrings are you 26" guys running on your triples? and can one of you tell me how to adjust my v-brakes?
Sorry that some of us still use their brain. Not everyone gets hooked on empty marketing slogans as quick as you...
 

bizutch

Delicate CUSTOM flower
Dec 11, 2001
15,928
24
Over your shoulder whispering
Depends on the mass of each

For the same rim, spokes, tire casing/tread just different sizes, yes.


There's a reason all the 29er stuff was so damn pinner for a while.
So, bigger wheel. More weight. More effort to turn (specifically lean or change direction whilst spinning)? Is it centrifugal force I'm thinking of?
 
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Pslide

Turbo Monkey
So, bigger wheel. More weight. More effort to turn (specifically lean or change direction whilst spinning)? Is it centrifugal force I'm thinking of?
You are probably thinking about gyroscopic forces, but I think their effect is not to noticeable. The reason 29ers are slower to change direction is actually related to camber thrust - basically that bigger wheels carve a larger turn radius for a given lean angle. So you've got to lean a 29er more more to get it to turn.



:D
 
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SkullCrack

Monkey
Sep 3, 2004
705
127
PNW
The reason 29ers are slower to change direction is actually related to camber thrust - basically that bigger wheels carve a larger turn radius for a given lean angle. So you've got to lean a 29er more more to get it to turn.
So does running two different size wheels (ex. 27.5 front & 26 rear) feel funky when cornering?
 

bizutch

Delicate CUSTOM flower
Dec 11, 2001
15,928
24
Over your shoulder whispering
You are probably thinking about gyroscopic forces, but I think their effect is not to noticeable. The reason 29ers are slower to change direction is actually related to camber thrust - basically that bigger wheels carve a larger turn radius for a given lean angle. So you've got to lean a 29er more more to get it to turn.





:D
Gyroscopic force. That's it.

And excellent explanation.
 

Pslide

Turbo Monkey
So does running two different size wheels (ex. 27.5 front & 26 rear) feel funky when cornering?
I've never ridden one, but judging by the absolute non-success of 69ers, I'd say there was definitely some funk going on. Physics says if you're leaning a 69er over into a corner, the front wheel wants to carve a different radius than the back wheel, which doesn't sound good.

Then again, engineers are always trying tricky stuff in race cars with the back wheels doing different things than the front, so maybe you could work it out to your advantage!