Thursday
Oct162014

Thursday Test - 24 v 28 spokes

A lovely rainy day to show some wheel testing.  First up, a comparison between a 24 hole Pacenti rear, and a 28 hole Pacenti rear. We've also included a 28h Stan's Alpha 400 as a foil.  

In order to test deflections, we hold each wheel in the frame fixture as shown, and apply a calibrated downforce by hanging a weight (or mass, if you prefer) from the blue rope with the red stop ball in the foreground. Deflections are measured at the places where each red arrow points.  

Different wheels are known to respond differently.  For example, a very stiff rim without enough spokes would deflect significantly downward at the front arrow (the 0* point on our table below), and significantly upward at the rearmost arrow (the 180* point). It would typically not deflect much at the 90* point (arrow to the left).  A soft rim would deflect downward quite a lot at 0*, upward quite a bit at 90*, and downward a bit at 180*. This is why rims hitting brakepads is often not a sign that your rims are not stiff enough, but rather that they are underspoked.  

The magic of system design is to build the wheel to minimize deflection all around. In a race wheel, you want to be just at the point of diminishing returns in order to minimize weight, where in a training wheel you might want a bit more margin for error in the system. The softer (edit) the rim, the more spokes you need, simple as that. A softer rim will "sag" more between spokes. I think of the distance between spokes as the "unsupported span." On the 24h Pacenti rim, the unsupported span is 75mm, on the 28h Pacenti it is 64mm, and on the 28h Stan's rim, it is 65mm. The unsupported span per given spoke count decreases with increased rim depth - a 24h Rail 52 has an unsupported span of 68mm, which is closer to the span of the 28h Pacenti than it is to the 24h Pacenti. The stiffer the rim and the shorter the unsupported span, the fewer spokes you typically need - up to a point.  That point is where the rim "overpowers" the spokes, and you get the "tilted" deflection where the rim goes down hard at 0* and up hard at 180*.

It's not super easy to see in this photo comparison, but the distance between spokes is just about 11mm more on the bottom photo. In case anyone wonders, we are big fans of the Pacenti SL23. It's a nice, stiff rim that's well construction and relatively light. I often ride them, and am currently using them to test a new hub we're evaluating.   

As you can see from the data in the table below, the 24h build comes closest to overpowering the spokes. It deflects downward the most in the front, and upward the most in the back. The actual amounts are worthless in comparison to tests not done on this rig, but from what we've learned these characteristics get you close to where we don't want to be.  You start to put a lot of stress on the rim at the nipples as the rim "works" against the spokes, and this is often borne out by the failure of "underspoked" wheels coming through cracking at the spoke holes. It's not necessarily the static load that gets them, it's the dynamic load transmitted through the deflection.  

A last point to make is how rim depth affects this whole calculus. A deeper rim makes for a better spoke bracing angle. As you move the hub and the rim closer together, the angle that the drive side spokes makes from hub to rim becomes more acute.  This is always a good thing.  

The stated deflection increments are thousandths of an inch.  .177" is very roughly equivalent to 3/16." A 25 pound kettlebell is used to create the deflection load.  

There are a few other things going on here, like how critical each spoke becomes as you have fewer and fewer (a not great builder plus few spokes often equals disaster) but we are running out of time here as it is.  

 

Rim

Pacenti SL23 Pacenti SL23 Stan's 400
Hub WI T11 WI T11 WI T11
Spoke Type CX Ray CX Ray CX Ray
Lacing Pattern 2x/2x 2x/2x 2x/2x
Spoke Count 28 24 28
0* Deflection -0.176 -0.185 -0.177
90* Deflection 0.007 0.006 0.006
180* Deflection 0.051 0.062 0.048
Wheel Weight 803 783 824
Distance Between Spokes 64mm 75mm 65mm

Monday
Oct132014

Stiffness testing in practice

So we do all this fancy testing and figure out which wheels are stiff and which wheels aren't and all of that fancy stuff, but what good does any of it do? How does it help us make better wheels for you? Numbers ALWAYS tell a story, and sometimes they tell several all at once. The stories we try to look for in these numbers are ones about points of diminishing returns, points of transferability, and stories about use optimization.  

First, let's take a quick look at why a stiff front wheel is a good thing, and some of the other factors going on there. To me the primary benefit of a stiff front wheel is in steering. A soft front wheel can lead to noticeable understeer. You don't want this. A soft front wheel will also potentially clang back and forth on the brake pads as you climb out of the saddle, or especially when you sprint. When you sprint, you typically weight the front of the bike much more than just in general riding. Without crashing because of it, take note of what your tire does the next time your sprint - yup, that bounciness is because you are weighting and stressing the wheel much more than you just just riding along.  Other factors are strength, which can be described as the wheel's ability to handle unusual stresses (airborne instances, crappy roads), and durability. The more spokes you have, the less work each one has to do - many hands make light work. Last, you have to think about the hub flange. Radial lacing is great for 20 and 24 hole fronts, but start putting 28 holes in that same circle and all of a sudden there's not much meat to handle the higher radial spoke load. Crossing works much better with higher spoke counts.  

We've advocated 24/28 laced alloy wheels for a long time. Where other people said a 20/24 build was appropriate for 190 pound riders, we were saying you should be thinking about going to 28/32 for the same weight. Among the things we've learned is that we were both right and wrong. With rear wheels, we were right. There's a lot going on with rear wheels, especially with the move to 11 speed hubs, and this piece is mostly about fronts, but a 28 spoke alloy rear does a lot of stuff a lot better than a 24 hole alloy rear. Up front, not so much. Because front wheels are inherently such better wheels than rears, front wheels with stiff rims really start to get quite good at 20 spokes.  A Pacenti SL23 (quite stiff for an alloy rim) laced to a White Industries T11 front hub with 20 spokes isn't appreciably less stiff than the same setup with 4 more spokes.  Some people understandably like a bit of redundancy in their setups, so there's still plenty of room in the world for the 24 spoke alternate, but you're not getting what you might call primary benefit from it. Note that one of the next things we're taking a look at is the implications of 1x lacing on 24h fronts, just in deference to the flange issue discuess above.  

Conversely, yesterday I talked about a 28h Stan's Alpha 340 being a nice stiff wheel. The rim is soft enough that it needs a lot of spokes, but when you add enough spokes such that the distance between them gets small enough that adjacent spokes are working together to keep the rim in line, that rim comes into its own. With any of the front hubs we use, that's going to be a nice wheel. It's not the most aerodynamic wheel under the sun, but it's quite light (a 20h Rail front with equal hub is the only lighter front wheel we do) and also quite stiff.  The 2x lacing relieves stress on the hub flange, and the spoke count means that if you somehow manage to break a spoke, you're still riding home.  Add the benefit of tubeless and this is an ideal high mileage winter wheel.  

When spec'd properly, an amazing wheel Disc front builds will never be as good as rim-brake front builds for the simple reasons that disc hubs have narrower flanges, and the wheels are dished, so it works out fine that disc hubs start at 24h. Even then, a 20h build on a rim-brake hub is going to be stiffer than a 24h disc build using the same rim and spokes. Disc rims also highlight suitability for application. As an example, a Rail 52 on a CLD hub, with 24 spokes, is a bit stiffer than a 28h HED C2 disc specific tubular with a CLD hub. But it's also about 80g heavier. On a road disc build, where aerodynamics still matter a bunch, the 52 makes a lot of sense.  On a cx disc build, where you might still really want to use tubulars, and weight seems to be at a higher premium (**the debate on the actual value of which may never end), and where aero is quite distantly far from everything, all of a sudden the higher spoke count C2 looks really good.

It's always going to be a challenge to correlate bench test results with real world application, but that's no excuse not to learn everything you can about how wheels react to stresses designed to mimic what they will see in use. 

Wednesday
Oct082014

Anatomy of a test

Earlier on, when we initially announced the Rail, some chucklehead on a forum somewhere threw the BS flag at us, saying essentially "let me get this straight - the company that makes no bones about selling other people's products that they haven't developed, and does no testing, is going to develop and launch their 'own' product. No f-ing way." It was easy to shoot the guy down, simply because we had always been completely up front about how we did what we did. When we did open mold stuff, we were unique in that we didn't BS about "we had design input here" or "this is a product we developed in house" like other people were doing. Mostly that's called lying, and we're not fans.  

Anyway, that one encounter/accusation, though misplaced since we actually had done a bunch of testing, had a big impact on us. We've always wanted to know as much as possible about how everything we work with works, and to share that knowledge wherever possible. A lot of our testing is iterative, as it should be - the real world is always going to tell you things that the bench doesn't, and what you see in the real world makes your bench tests better. Sometimes the best test is a hybrid - after paying a lot of attention to tubeless cross tire setups for the last couple of months, I've got a test track set up that is designed to produce the dreaded burp if the dreaded burp is there to be produced. 

This was a pain in the butt but worth itThis rig is one of our most important test fixtures. With it, we can measure the stiffness of any wheel we build. We use it to isolate variables like spoke count, spoke lacing, spoke choice, hub choice, and rim stiffness within a build. Benchmark a known entity, then test a controlled variant of it. Our accuracy is to within a couple thousandths of an inch. By changing the configuration, we're able to measure rim stiffness in isolation, and we've measured several samples of every rim we've build with, along with several that we don't. Testing components both as parts and then within assemblies gives good insight. For example, some rims might not be very stiff on their own, but can shine as a component of a properly spec'd assembly. We wouldn't sell you a 20h Stan's 340 front build, but put that rim in a 28 build and it becomes the backbone of a great wheel - light, stiff, strong, durable, and ready for tubeless. If you want an awesome wheel to do your heavy mileage on all winter without worry, it's a great choice.  

What gets measured gets managedEveryone's got a scale, so everyone pays attention to what things weigh. Weight is also an important part of inbound QC - we don't like to see a lot of variance at all. Alloy rims will move around a bit more than carbons, simply because as the tooling wears, the parts get heavier.  You have to account for that in stiffness testing, too - weight and stiffness impact each other, so you have to normalize for component weight when checking stiffness. "Claimed weight" is a large stack of BS - things weigh what they weigh. We fully expect that everyone who's concerned about weight will weigh what we deliver to them. Anyone who makes a purchase decision based on what something's supposed to weigh, and then doesn't weigh it? Yeah...

This is our newest test calamity, lovingly named Frank the Tank. With Frank, we can test brake heat, rolling resistance, brake track durability, bearing effectiveness, lube effectiveness, and probably a bunch of other stuff we haven't even figured out that we can test yet. This one was a pain in the butt to sort out, but will give us a huge depth of insight into a world of different stuff.  

As we develop products, we'll always try and quantify any aspect of their performance that we can. We're right now on the hunt for some great hubs that offer a good compromise between the top end hub selection that we've got now and the OEM stuff that's around. We've got some candidates identified, so we're testing the crap out of them in every dimension to see if any are going to make the team.

Mike has jokingly asked a few times whether it's possible to build a wind tunnel from the McMaster catalog. He should not joke about such things. For the time being, that remains something we're happy to outsource, but don't think I don't have a few pages bookmarked for when the time comes.

 

Monday
Oct062014

Dirty Tubeless

Last blog was all about road tubeless, where this one will be more and less "controversial" than that one: tubeless for cross (more controversy) and mountain (no controversy).

Let's get the easy one out of the way - mountain bikes. To set up a mountain bike wheel tubeless, you need a mountain bike wheel, a mountain bike tire of the same size as your wheel, rim tape, a valve stem, and sealant. Tape the rim, put the valve stem in, mostly mount the tire, pour the sealant in, finish installing tire, inflate, ride. If the tire is super loose on the rim, add another layer or two of tape. You can use duct tape. Seriously, this one is easy, almost everyone does it, and it almost never causes problems.  Why anyone would want to use tubes on a cross country or all-mountain mountain bike at this point is beyond me.    

Cross tubeless is another bag of goldfish entirely. First let's start at the beginning and ask why you'd want to go tubeless for cross. In any dirt riding, lower tire pressure equals better traction. Period. That's why tubulars are still so popular in cross - you can go wicked low pressure with minimal risk of pinch flatting, even though it's not impossible (you guessed it - I've done it!). The other huge benefit to low pressure is suspension - it smooths out the ride. Which, in turn, increases traction both from keeping the tire on the ground and from allowing you to weight the bike properly.  

The book on cross tubeless is still being written all the time. The leading proponents are the Stan's team, who use Stan's rims (primarily the Grail, currently) and Kenda tires. They use one wrap of Stan's tape and that's it - no strip, no Gorilla tape, nothing. Just one wrap of tape. I overheard Mical (in photo) say she'd used a Kwicker and 22psi in the front at the Night Weasels race, a super muddy, greasy, and always off camber race in which she'd gotten a close second. Jake Wells is pretty good, and he uses the same pressures he would otherwise use on tubulars with his Stan's/Kenda setup.I'm 99% sure she's in Grail rims and Happy Medium tires here

I've got a few different tubeless cross setups I'm feeling out. My favorite has been a pair of Stan's Iron Cross rims with a Stan's Raven tire front and Kenda Small Block Eight rear.  I've raced these at 24 front/27 rear and felt like I was able to ride the bike better than on any other setup. Then I crashed the front into a hidden stump and ruined the rim, along with my shoulder. That setup was perfect for the drought conditions the season started in, but with any moisture those treads are useless.  Totally unrelated to tire setups, I've been running into a lot of stuff this year, at great cost to my personal parts and pieces (knee and ribs at the moment). Currently, in addition to the Iron Cross/Small Block Eight, the Stan's Arch EX/Clement PDX combo is working like a freaking champ. All of these setups are disc rims, but can be closely replicated with rim brake setups.  

The dreaded outcome of cross tubeless setups is of course the dreaded burp. The burp is a momentary break of the rim/tire seal, which allows some amount of air to escape.  It's never good, but it can range between inconvenient and tragic in magnitude. Much like a rolled tubular, best case you are riding gingerly to the pits, worst case you are running to the pits.  Most people who've used a tubeless setup have "found minimum pressure" with a burp. I have. Never in a race, touch wood. I choose to wreck my races in other ways!

So the natural question then is "why tubeless?" When set up well, tubeless cross allows the same low pressures and pinch flat protection as tubulars, with huge flexibility and cost advantages over tubulars. Even at its worst, installing a tubeless tire is way less involved than gluing a tubular, and requires no drying time. If it's Friday and you have a set of dry conditions tires on when it starts pouring at dinner, you have every opportunity to switch tires before tomorrow's race. Tubeless tires also cost about half as much as tubulars. 

I'd rate the chances of disc brake ubiquity as perfect - that day will come. I make no such forecast for tubeless in cross. The very top players, with no real resource constraints and the ability to travel with dozens of sets of wheels, will suffer any inconvenience to enjoy whatever marginal benefit continues to exist. For the rest of us, tubeless is starting to look attractive. With some bugs left to iron out, it's no slam dunk, but there are some pretty resourceful and talented people fighting those bugs all the time.  

Monday
Sep292014

Mike goes tubeless

This weekend, Mike set up his first set of tubeless tires. They are Hutchinson Fusion 3s on wheels built with WI T11 hubs, Stan's Alpha 400 rims, and CX Ray spokes with 20/28 lacing. They are a lot like the wheels in the picture below except Mike has reb hubs (color!) and his front wheel has fewer spokes. My first tubeless setup came several years ago on my mountain bike, and now have tubeless setups on road, cx, and mountain.  

Mike's reluctance to going tubeless was typical of most people who haven't yet tried it. The typical resistance points are:

1. It's difficult to set up

2. I'll need a compressor to inflate my tires

3. It doesn't offer any real benefit 

4. My rims aren't tubeless ready

5. Tire selection is limited

As with many things in life, there is both truth and BS in each of these, so let's take them in order, but first a PSA - for road, YOU MUST USE TUBELESS TIRES. Tubeless road tires have a stronger bead than non-tubeless tires. At the higher pressures you use on the road, there is a serious risk of blowout if you use a non-tubeless tire. Do not try it, do not listen to anyone who says it might be okay. For road tubeless, use road tubeless tires, period, end of story.  

ROAD SET UP: Depending on the wheels and tires you are setting up, going tubeless can either be as simple as installing tubed tires, or somewhat complicated. In Mike's case, he's using Stan's Alpha 400 rims, which have a great tubeless interface. Tubeless tires mount, inflate, and seat easily and securely on them. To prep these and similar rims, all you need to do is use two wraps of Stan's tape (or similar) per rim, and install a tubeless valve in each rim. November supplies all Stan's builds with two wraps of tubeless tape and valves pre-installed, so you don't have to worry about that step. When you install the tape, pull hard and stretch it so it conforms to the rim bed and becomes airtight.  

While the tires you use for road tubeless MUST be tubeless specific, your rims needn't be. I'm using Stan's rims for illustrative purposes here, just because setting them up is child's play. I told someone a few weeks ago that at this point I could install a dirty t-shirt on a Ritz cracker and get it to inflate and seal, but I've been screwing around with tubeless for a while.

When you're ready to install your tire, wet the inside of the rim with some soapy water. Be generous with the soap, and don't worry about the water, it will evaporate soon enough.  

As you see in the pic, this rim has a channel in the middle. When you install the tire, push the tire beads into the channel. This makes mounting the tire much easier. This channel is a big part of the reason why you want to stretch the tape.  Mount the tire almost all the way, and then before you do the last bit of the second bead, shake up your sealant and install it.  Just pour it in.  November supplies Stan's builds with a cute little 2oz bottle of sealant which is plenty for a pair of road tires.

 After your sealant is in, rotate the wheel so you don't pour the sealant back out when you're putting the last bit of the bead on, and voila. At this point, you should have no problem inflating the tire with a floor pump. You will hear the bead pop into place, which is normal but can be jarring. If there are any air leaks, you will see bubbles forming there (thanks, soapy water!) so simply shake the wheel to get some sealant there and they will seal up quickly enough.

INFLATION

I've installed road tubeless tires on Rails, Stan's 340s and 400s, Kinlin XC279s, and Pacenti SL23s, and have yet to need a compressor to inflate any of them. If you find that you can't inflate your tires, take a Presta to Schrader converter plug ($2 from a jar on the checkout counter of every bike shop in the world, and you should keep one in your flat kit anyway) and 4 quarters, and head down to the gas station and use their compressor. In the unlikely event you flat on the road, don't worry about reinflation - you'll use a tube then anyway.

BENEFITS

I'm something of a chronic flatter, so much so that I've even done the ultra-rare tubeless pinch flat. With tubeless, apart from that one instance, I don't get flats. I also love the way they ride and find a better feel with lower psi. We'll be testing rolling resistance of a lot of setups this week to learn more about that aspect, but reports we've read suggest that there are gains on that front.  I've removed a worn out mountain bike tire and found two dozen little sealant asteroids on the inside of the tire - each of them representing a flat that I got but didn't get. It's awesome.  

Before using tubeless, I'd never in my life worn a road tire out without getting at least one flat. Since using road tubeless, I've now done it three times.  

TUBELESS RIMS

While tubeless specific rims generally make tubeless installation easier, they are not necessary. Some rims specifically prohibit tubeless setup, and it's best to listen to the rim supplier in those cases. Some rims are also known to have a poor response to sealant. Of the rims I've set up for road tubeless use, Stan's and Pacentis are designed with a tubeless rim bed, but Kinlins and Rails were easy to go tubeless, and none of them have any adverse response to sealant in my experience. 

TIRE SELECTION

It's true that a lot of tires aren't yet available in a tubeless ready model. In mtb, this doesn't matter even at all - any tire can be used tubeless. For cx, some work better than others (more on this in a subsequent post), but you can find a great tire for any condition that's going to do great as a tubeless tire. For road, your options are a bit limited. There are plenty of great road tubeless tires, but it's a classic chicken and egg deal - the tire makers are loathe to invest in tubeless products when the market isn't clamoring for them, and the market is loathe to adopt road tubeless en masse without all of the favorite tire options available in tubeless ready versions.

We'll check in with Mike periodically to see how he's enjoying his tubeless experience, but personally I'm a convert. I've got my cx tubeless setup so dialed that I have no desire to go back to tubulars. I'm using the same pressures tubeless that I did with tubulars. For road, it's my preferred option as well. For mountain, I think I'd rather go for a road ride than ride mountain bikes with tubed wheels.  

CONCLUSION

Don't be afraid of tubeless. Like any new technology, it takes a bit of getting used to how you do things, but once you do, a whole realm of convenience and performance opens up to you. As we head toward the long slog of cold winter miles where getting a flat REALLY REALLY stinks, check out a tubeless setup and we bet you'll be glad you did. If Mike found it to be as easy as he did, chances are you'll find getting started to be a total breeze.