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29" DH bikes

toodles

toodles

ridiculously corgi proportioned
Aug 24, 2004
5,508
4,760
Australia
I wonder if disc brake rotors will jump up a few sizes now. I'm was surprised when we were still running 8"/200mm rotors from the 26" days on the 27.5" wheelsize, but surely now they're going 29" the wheel to rotor ratio must be getting all wacky?

I'm not doing the math cos I'm lazy and my coffee hasn't kicked in but wouldn't a 8" rotor on a 29" wheel be like running a 7" rotor on a 26"?
 
toodles

toodles

ridiculously corgi proportioned
Aug 24, 2004
5,508
4,760
Australia
Also - does anyone remember the teams that ran 29ers at the Pietermariztspellingmistake World Champs a few years back? If I remember correctly none of them did real well and that course would have suited them. Maybe tyre and rim tech has come far enough to allow a more durable 29er wheel though.
 
DaveW

DaveW

Space Monkey
Jul 2, 2001
11,206
2,730
The bunker at parliament
If it works for you fucking ride it!
If it doesn't then ride something else.
Just for the love of all things cycling stop being a whiney Luddite baby, bikes have been and will continue to be constantly evolving.
Deal with it. :rolleyes:
 
Lelandjt

Lelandjt

Turbo Monkey
Apr 4, 2008
2,514
827
Breckenridge, CO/Lahaina,HI
29" wheels are the first advancement in MTB that makes bikes faster but doesn't make them more fun or feel better for me. If we can ban skin suits because they make you faster but no one wants to use them lets do the same thing for wheels bigger than 27.5". 29s should be allowed in XC racing only.
 
HAB

HAB

Chelsea from Seattle
Apr 28, 2007
11,580
2,006
Seattle
toodles said:
I wonder if disc brake rotors will jump up a few sizes now. I'm was surprised when we were still running 8"/200mm rotors from the 26" days on the 27.5" wheelsize, but surely now they're going 29" the wheel to rotor ratio must be getting all wacky?

I'm not doing the math cos I'm lazy and my coffee hasn't kicked in but wouldn't a 8" rotor on a 29" wheel be like running a 7" rotor on a 26"?
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Also too lazy to do math, but yes, bigger wheels do brake worse with all else being equal.
 
OGRipper

OGRipper

back alley ripper
Feb 3, 2004
10,653
1,128
NORCAL is the hizzle
fwp said:
A victory aboard a 29er would have an asterisk next too it, atleast until the rest of the teams were on 29
.It would be a bummer if 29 er V 10 gives an unfair advantage to the Syndicate. I would rather see all the guys run the same wheelsize and let the best man win.
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Maybe the UCI should supply everyone with the same bike. Same frame, parts, everything. Anything different might give someone an unfair advantage!

Do all the wins on 27.5 have an asterisk too, because they had an unfair advantage over 26"? No, not to me.

It's not an unfair advantage if everyone can do it, and some choose not to. Technological improvements have always been an important part of DH - arguably more than other disciplines. If the rules allow it, it's fair game.
 
dump

dump

Turbo Monkey
Oct 12, 2001
8,221
4,470
OGRipper said:
Maybe the UCI should supply everyone with the same bike. Same frame, parts, everything. Anything different might give someone an unfair advantage!

Do all the wins on 27.5 have an asterisk too, because they had an unfair advantage over 26"? No, not to me.

It's not an unfair advantage if everyone can do it, and some choose not to. Technological improvements have always been an important part of DH - arguably more than other disciplines. If the rules allow it, it's fair game.
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Meanwhile there is a dress code that requires skirts to fall below the knee and no less than 1inch of loose fabric.

This is (getting) dumb.
 
dcamp29

dcamp29

Monkey
Feb 14, 2004
589
63
Colorado
HAB said:
Also too lazy to do math, but yes, bigger wheels do brake worse with all else being equal.
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I *think* wheel radius is only a problem when trying to initiate a skid. Under constant braking I think the brake system is just converting kinetic energy into heat, so unless the 29er was significantly heavier the brake power is roughly equal (as long as the wheel is rolling). But yeah you'd probably want big ass rotors on a 29" dh bike.
 
kidwoo

kidwoo

Artisanal Tweet Curator
Aug 25, 2003
42,146
13,340
Squirtin ketchup n' mustard on charred flesh
ianjenn said:
And in KIDWOO's moto example he forgot that Monster spends more in a season than all the bike companies combined do to run all their teams just in advertising at Moto races.
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I didn't forget, it's just irrelevant. I just used that as an example of not the raddest way to do things being standardized.

29ers are potentially faster in the WC world because they've worn these same 8 tracks into runways.



And fuck monster
 
HAB

HAB

Chelsea from Seattle
Apr 28, 2007
11,580
2,006
Seattle
dcamp29 said:
I *think* wheel radius is only a problem when trying to initiate a skid. Under constant braking I think the brake system is just converting kinetic energy into heat, so unless the 29er was significantly heavier the brake power is roughly equal (as long as the wheel is rolling). But yeah you'd probably want big ass rotors on a 29" dh bike.
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So, yeah, brakes are changing kinetic energy to heat. Power is the rate at which they do that.

Power = (Force x Velocity). The force will be same irrespective of wheel size, as that's just a function of piston size, fluid pressure, and coefficient of friction between the pads and the rotor.

At a given rider speed, a bigger wheel turns slower than a smaller one. Therefore the speed at which the rotor's moving past the caliper decreases, decreasing the total brake power on tap.
 
kidwoo

kidwoo

Artisanal Tweet Curator
Aug 25, 2003
42,146
13,340
Squirtin ketchup n' mustard on charred flesh
HAB said:
So, yeah, brakes are changing kinetic energy to heat. Power is the rate at which they do that.

Power = (Force x Velocity). The force will be same irrespective of wheel size, as that's just a function of piston size, fluid pressure, and coefficient of friction between the pads and the rotor.

At a given rider speed, a bigger wheel turns slower than a smaller one. Therefore the speed at which the rotor's moving past the caliper decreases, decreasing the total brake power on tap.
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fake math

29ers roll SO MUCH GOD DAMN FASTER that rotational velocity isn't less since the rider is going SO MUCH GOD DAMN FASTER .
 
T

trib

not worthy of a Rux.
Jun 22, 2009
1,480
422
Could someone with more time/less lazy than me make an image with Gregs new V29 over his old Orange 222 from the Global days. I bet that thing looks like a kids bike in comparison - it was short even then.
 
Westy

Westy

the teste
Nov 22, 2002
54,438
20,238
Sleazattle
DaveW said:
If it works for you fucking ride it!
If it doesn't then ride something else.
Just for the love of all things cycling stop being a whiney Luddite baby, bikes have been and will continue to be constantly evolving.
Deal with it. :rolleyes:
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Because it would seem trail design follows bike design, the industry doesn't sell trails.
 
buckoW

buckoW

Turbo Monkey
Mar 1, 2007
3,786
4,729
Champery, Switzerland
I have one and it's real fast. My butt touches my rear tire sometimes and it's terrifying depending on the situation. Even though it's faster and has more grip I usually always ride the 27.5 bike. It's more fun for what I do. If I had flatter tracks then maybe I would ride it more often. It's not much of an advantage in Champery where your skills and ball size have a greater effect than wheelsize. I had to reduce the travel to 187mm in the rear to keep my seat where I want it.
I think drifting flat corners is easier on the 29DH bike. It takes a little more commitment when throwing the bike into corners but after you get used to the different timing it's not really an issue.
 
Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
4,915
1,200
dcamp29 said:
I *think* wheel radius is only a problem when trying to initiate a skid. Under constant braking I think the brake system is just converting kinetic energy into heat, so unless the 29er was significantly heavier the brake power is roughly equal (as long as the wheel is rolling).
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The wheel outer radius minus rotor radius is your moment arm, so if you increase the wheel radius without a directly proportional increase in rotor radius, your brakes will suck directly proportional to the delta of lever length.

A 27.5" MTB wheel with equal size rubber has 4% less braking force than a 26" wheel. I calculated this when I switched, funnily enough I've seen NO ONE mention this loss (including the industry, and this forum) except for @toodles way back when 650b first hit the scene. 4% is significant and noticeable (I tested back to back on same bike with geometry corrected).

A 29" MTB wheel will see a further ~6% reduction in braking force, for a total ~10% cut in braking performance. This is not a negligible loss of braking force, there will be pro riders complaining about this already I can guarantee.

Also, the loss is basically linear (i.e. it's a clean loss) - you can pretty well ignore any connection to contact patch. If anything it'll be worse than the linear difference due to cumulative effects over a run like increased heat generation for given deceleration force at the contact patch, without a proportional increase in dissipation area.

I actually wrote a post about this earlier and deleted it, because to be honest I'm not really that fussed by these new standards (seems to be a very polarising issue for many including you - my post about straightlines was tongue in cheek), but since it got brought up here you go.

The other non-negligible downside to bigger wheels is a big increase in weight if you actually maintain the strength of parts - particularly DH tire casing thickness. 120g/end at a guess over 650b, more in tubes/goop/rims/spokes etc but smaller amounts.

I think big wheels are cool, particularly for reducing bump transfer forces to the rider (significant improvement), which also has fringe benefits like ability to trade some % of the bump transfer benefits for stiffer suspension and a more stable / ultimately faster ride - handy for pros. But there's no free lunch, even fixing the brake situation for example adds a bunch of weight.

Watch the 225 rotors make a comeback real soon.
 
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Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
4,915
1,200
buckoW said:
Are you on 220mm rotors?
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Nah, most companies stopped selling them. I wouldn't even consider running 29 for DH without though. The only decently light ones were those Formula ones you had I think, Hopes are a bit porky and Hayes worse.

If anyone cares, 225mm rotors would give pretty close to 10% more braking force, so a pretty even match for the loss from 29".
 
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buckoW

buckoW

Turbo Monkey
Mar 1, 2007
3,786
4,729
Champery, Switzerland
I found a NOS one at work the other day. It's the light one with the red alu center.
I don't have any problems with the power of my brakes on the 29DH bike (more power is always better) but I do have issues slowing down. I thought maybe it might be due to the increased roll over and not "grabbing" the holes to slow down. I have to brake earlier but that might also be due to increased rolling speed or less travel... hard to say.
The biggest issue I see is seat placement, chain stay length and travel on smaller sized bikes.

Also, I can't find any good mud tires in 29 for DH.
 
Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
4,915
1,200
buckoW said:
but I do have issues slowing down. I thought maybe it might be due to the increased roll over and not "grabbing" the holes to slow down. I have to brake earlier but that might also be due to increased rolling speed or less travel... hard to say.
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Yeah it's probably got nothing to do with the clean cut 6.9% loss in braking force. :D
If it was to do with not grabbing holes you'd be front wheel skidding, but I doubt that's happening on the tracks you ride - steep tracks drive the normal force (and so traction force) at the front tire through the roof, and it goes even higher under braking. The other factors would be tiny in comparison to the leverage change.

IMO the only current brakes that would be even mildly competent with a 29" wheel would be the M820 and maybe the Diretissima. I know we like Hope V4s and Formula ROs etc for the reliability but I think they're at the limit with 650b - if I was a bigger/heavier rider I'd still want 220 on those even for 650b. Keep in mind you have hands the size of houses so the force at the input side is greater than for the average joe on the same setup - might be why it's OK for you still. Now I'm wondering if it's just the hands...

Edit - hey, measure the OD of your 29 wheel for me with a 2.35 Magic sometime, do they come in 29? Would be good to work out the exact difference.
 
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norbar

norbar

KESSLER PROBLEM. Just cause
Jun 7, 2007
11,369
1,605
Warsaw :/
Udi said:
Yeah it's probably got nothing to do with the clean cut 6.9% loss in braking force. :D
If it was to do with not grabbing holes you'd be front wheel skidding, but I doubt that's happening on the tracks you ride - steep tracks drive the normal force (and so traction force) at the front tire through the roof, and it goes even higher under braking. The other factors would be tiny in comparison to the leverage change.

IMO the only current brakes that would be even mildly competent with a 29" wheel would be the M820 and maybe the Diretissima. I know we like Hope V4s and Formula ROs etc for the reliability but I think they're at the limit with 650b - if I was a bigger/heavier rider I'd still want 220 on those even for 650b. Keep in mind you have hands the size of houses so the force at the input side is greater than for the average joe on the same setup - might be why it's OK for you still. Now I'm wondering if it's just the hands...

Edit - hey, measure the OD of your 29 wheel for me with a 2.35 Magic sometime, do they come in 29? Would be good to work out the exact difference.
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V4's are not that strong? BTW I feel so progressive for running 220 formula rotor in the front. Not that it's planned. I just needed to buy a rotor quick and the resort shop had only that. Now I'm too lazy to change.
 
sikocycles

sikocycles

Turbo Monkey
Feb 14, 2002
1,530
772
CT
Been on a 29er DH bike for the last 6 years. Glad to see some progress.The tires were the thing but since Maxxis has tires now its better. Bet the V10 is much better then my Lenz IMG_1943.jpg PBJ.jpg
 
Electric_City

Electric_City

Torture wrench
Apr 14, 2007
1,995
716
I hate 29'ers. Why? Cause my 26" bike was fine, but EVERYBODY had to tell me how much my bike sucked compared to theirs. The Industry™ pushed and pushed and pushed, but I never caved in. I always have fun on my bikes. Both are now 27.5...

The Industry™ can come out with a 29" bike if they choose. The WC racers can race on them if they choose (even though they don't get to). Just don't try to force ME onto one. Make both wheel sizes if you want. But don't push me like you do the WC racers. We're riders. Some of us race... Most of us ride cause it's fun as hell. I'm not interested in super light, bigger wheels, single speed, fragile bikes. I want a reliable bike in the size I want. That's it. Fuck you Trek, Special-ed, Giant and the rest of The Industry™.
 
Sandwich

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,076
5,989
borcester rhymes
I'm confused as to what the issue is here. If you want to be at the top of the game, it makes sense to wear a skinsuit, peakless helmet, 29" wheels, rooster tail, batman costume, or whatever. At the top of the pack, the riders should be doing what they need to do to win. Do you really think I give a fuck what's happening in F1? Even if I were to race cars, would I care what a T-foil is if I raced miatas? I'm glad that F1 exists, and I like to watch racing. That doesn't mean I need a KERS on my Rav4, or a halo for dropping my kid off at school.

I still have a 26" DH bike. After 29ers take over DH, I'll still have a 26" DH bike. They work well and parts are cheap. I don't care if the UCI bans disc brakes on the tour de france. I still run them on my road bike because they are better than calipers. 29ers taking over the top rung isn't going to change what the average joe rides on the weekend. How many of you are purely racers anyways? How many ride for enjoyment?
 
blindboxx2334

blindboxx2334

Turbo Monkey
Mar 19, 2013
1,340
101
Wets Coast
I have been waiting for this thread ever since I got made fun of for asking for 2.4 niner tires in the dh tire thread.

I hope this keeps ya'll up late at night. it was only a matter of time. ;)
 
SylentK

SylentK

Turbo Monkey
Feb 25, 2004
2,328
874
coloRADo
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