Why aren't there 29er downhill bikes?

[squirrl_poker]

Sure the wheels aren't as inherently strong but a little extra weight would do the trick and wouldn't hurt performance. It seems like a natural choice to me. Are there rules against racing them? Even so I would think they'd make good recreational downhill bikes.

[riderx]

Just a few guesses, but the larger wheels may limit the amount of travel you can get out of the frame. Also, 29ers are still relatively new and things take a while to work their way into the various MTB subcultures. Combine that with lack of dh tires and forks.

[DancingBear]

I agree with you, but the parts aren't out there. There are no DH 29er tires, no DH frames, and no DH forks. Really, the only way things like that get developed these days is if there's an OEM order to finance the cost of development and tool-up. A good example is Rockshox' new 29er fork, they only produced it because Gary Fisher made a big OEM order for them. Rockshox had expressed no interest in entering the 29er market before that.

[Cloxxki]

700c rims with 2.5" tires, that'd be 30", and that's what's it's called already, though no 30"-specific parts yet exists.
I've been working on a 30" project for some time, trying to get it off the ground, but bike brands are too affraid to make costs they cannot turn into profits short-term. Most vital, again as with 29", is the tire. Tires are expensive to build mold for, and unless some rich DH pro takes up the bill, it won't happen the first few years, though 30" very likely has traits for DG as well, and could be turned into profit with prize money, specially keeping it for yourself for some time.
Rims can just be made out of extrusion that already exist. A frame can be custom-made, and the fork actually already exists. Any long-travel upside-down fork can be tuned to limit travel somewhat, and that's all you need. With larger rims, you can suffice with less travel anyway. perhaps a Pro would want a lower handlebar, well it's not that difficult to make a DH flat bar.
The rear suspension, in order to get the required ~180mm out of it to be able to compete, would need a smart design optimizing chainstay length versus travel. But if competitive 230mm machines can be built now, so can 30"/200mm ones.

So it doesn't seem like it's going to happen any time soon (if people in the industry would ever put serious money in a product out of curiousity, we'd all been XC'ing on 29"ers since the 70's), but we're closing in for sure.
WTB has announced a true 2.35" Epic Wolf tire. The 2.1" Nanoraptor is already over 50mm wide, so that promises quite something.
White Brothers have always pioneered with 29" forks, and are considering putting out an 130mm XC fork, that most likely will be strong enough to withstand freeride testing. And, WB has already announced that they'll change any of their upside-down forks for 29"/30", come the occasion. So we practically have the fork already. Frames can be custom-ordered for about $2000-3000, perhaps a builder would give you a deal if you were making a 30" machine to happen.
Rim companies are like their product should be, very rigid. They keep whining about how expensive tooling it, while they al too often offer a single extrusion in various rim sizes, to SAVE money. Some big shot rider or manufacturer will have to do a bit of a campaign to ever convince any of them.
But even hen, tires are way expensive. The person that orders the 30" tire mold, will be the frst owner of a 30" bike, for not too much money even.

To beef up the wheels, wide-flange hubs will be helpfull. 165mm rear hubs are getting more and more the standard, that helps. On the front, perhaps a wider hub standard will have to happen to optimize 30" wheel strength to weight.

Till then, I'm awaiting the WTB 2.35" Epic Wolf, and already have some 36h rims, 28mm wide and 700g strong. Rhynolites and Vuelta V's. With that, a 130mm WB fork and a custom frame, one might be able to build a freeride bike, useful for races such as the Alpe d'Huez DH in France.
Can you imagine thát? I think if you can make the rims wheels to hold up, some DH pro's would even be able to go fast with it, on selected WC courses. And, with the UCI's wicked rules, "our" 30" is legal as 29"! It's LEGAL, but no-one's trying it. Too certain it won't work. But think of it this way, every WC rider is riding the largest rims the market offers. The 24" exceptions are fading away, not fast enough to be worth is.

[squirrl_poker]

Sounds like a good challenge for anybody that's got the dough. I'd be mighty tempted by some 29er WTB weirwolf tires. Currently I use the Bontrager Jones ACX 2.2 and they seem well rounded, but I'm always interested in any tire that will let me carve the turns a little sharper, preferably with a lower resistance center tread.

[The Rose]

check out the Kenda Klaw or The WTB Nanoraptor ( I think it's the nano ). I have ridden the 26 inch version of the Klaw and I like them very much. And like you had mentioned they have a good rollin' center tread.

[FLAPJACK]

Ever ride a XC bike with 26"x1.95" back to back with a DH Bike with 26x 2.5 DH tires?

What I noticed first is the weight of the wheels/tires. The DH bike takes alot more ummph to change direction. Now think what happens with a 30"x2.5 DH tire and big 700c rim combo. The centrifical force would make the bike very stable but damn hard to turn.
Just one of the reasons I see that will keep the 30" tire of the DH courses.

[Cloxxki]

You could also say that 29" hardly takes more ummph to move than 26" (some don't even notice), so going from 26"x2.5" to 30"x2.5 won't make such a difference either. Also, as bigger wheels as for a bit steeper angles, the front of the bike gets shorther and perhaps 2.6-2.7" won't even be necessary as often, 2.5" could suffice for a lot of riding and same some extra weight.
I'm no DH'er, but I know there's more to DH bikes than heavy wheels. With 30", just the wheels would gain 10% of weight, the rest of the bike stays the same, total weiht increase would be around 4% max.

Kenda's indeed offer a lot of grip/traction, but are not the fastest rollers out there. If theings get wet, they'll take good care of you.


Ever ride a XC bike with 26"x1.95" back to back with a DH Bike with 26x 2.5 DH tires?

What I noticed first is the weight of the wheels/tires. The DH bike takes alot more ummph to change direction. Now think what happens with a 30"x2.5 DH tire and big 700c rim combo. The centrifical force would make the bike very stable but damn hard to turn.
Just one of the reasons I see that will keep the 30" tire of the DH courses.

[Johnny]

As I understand it, 29" wheels carry momentum better than 26" wheels. Sounds great; but they are also harder to slow down than 26ers, so one would have to brake harder, earlier on a DH course. Also, a 29" doesn't wind up as quickly as a 26", so it's harder to accelerate out of a corner. That, and the whole "not so good at turning" thing...
Sure, the greater angle of attack of a larger tire would be nice in technical sections (this, I think, is why 24's are becoming less popular,) but I think too much speed would be sacrificed with a 29er.

[Cloxxki]

The brake weight disadvantage is real, though minute, considering you're slowing down a 200+lbs total weight, and adding just ounces. The longer contact patch will more likely place the brake point later, you're simply finding more traction, and a more table one to boot. That's what happens with 29" over 26" at least.
The slower steering is real as well, but when you correct fork trial by adding a single degree of headtube angle (slightly shortening the front of the bike), you have that sorted. All that remains is the few ounces of rubber and metal to be muscled around, which I don't think will be an issue, considering the whole front end is more relaxed.
Accelerating (10-25% of the time?) indeed would be slower, all else being equal, due to the extra ounces but then again, rolling resistance will be reduced by 10% for all of the time the wheels touch the ground (95% of the time?).
The momentum story you hear I found to be real, but could be partly due to the improved roll-over ability and lowered rolling resistance. Those also mean that you'll lose less speed over a giving course.

Main traits of 30" over 26" for DH, I'd say :
-Crossing ultra-rough surfaces with less energy output in shorter time
-Taking a smoother line, higher cornering speed and higher exit speed.
-Choosing and keeping aline more easily
-Simply higher top speeds
-Less upper body fatique due to smoother rolling
-Maybe a reason to go one size tire narrower without suffering grip or control, possibly even saving weight
-A bit less travel might suffice, giving back some control to the rider himself, using shorter forks.

cons :
-changing direction in mid-air
-getting off the starting line
-sitting behing the seat on real steeps

[Johnny]

Sure, a 29" wheel only adds ounces to a bike; but those are OUNCES of rotating weight placed further from the axle, in such a way that GRAMS make a palpable difference. Don't get me wrong; I've ridden a full suspension 29er, and I think it's great fun. It's just not my weapon of choice for fast, tight, technical trails, because it just doesn't feel as nimble as a 26er. I'm not sure where you get the idea of higher cornering speed from a slower handling bike with a longer wheelbase.
If you build a 30" DH bike, please let me know, I'd love to try it. I just don't think I'd have expectations quite as high as yours...

[Cloxxki]

Indeed, wheel ounches count almost as pounds. still, when you do the math, it's really nothing compared to a continuous loss of 10% of rolling resistance, which is the highest factor in offroad cycling. If I remember correctly, 29" over 26" means a loss of 2% of acceleration, which depending on the course and riding style, is only active for a brief part of the ride. You notice it most on a parking lot dead start.
I must admit I never had the chance to ride a 29" FS. But I've never heard of a purpose-built 29" XC racing bike with the appropriate angles, geometries tend to be more aimed at all-day riding and high-speed descends rather than tight stuff. It can be done, though, to an extent. It takes a smart frame layout to keep the rear end short enough.

[geckoman]

I agree on the Kenda Klaw. I had the priviledge of winning some from the rag. They were great tires but I ruined them out doing stupid stuff and riding on the road too much. They will be my next set of tires when the moto raptors my new bike came with run out.