The thoughts that were thunk and the goings on of my life.

Saturday, November 19, 2011

Wide-Profile Rims for 25mm & 28mm Tires

Currently there is an innovative rim in the road-cycling world made by HED called the HED C2, or as a wheelset it's known as the HED Ardennes. The cool thing about these rims is that they are much wider (23mm) than most rims sold (19mm). This has the following advantages:

  • Makes the rim stiffer and stronger
  • Flattens the profile of the tire giving you a better surface contact patch
  • Increases the tire volume, meaning you can run lower pressures
  • Smooths the airflow between the tire and rim giving a more aerodynamic profile
Or in a single picture it does this:

So in general this is everything you could really want a rim to be and with no real disadvantages. 

Except for one: I'm pretty heavy. Not fat mind you. Just heavy for a cyclist. Once you add up me, my bike and the backpack with a laptop, clothes and lunch, I can easily hit 265 lbs on my wheels. Which by the best and most scientific guide I've found means I would need to run 23mm tires at 170psi on the rear. If I rode a 23mm rim I could run 10% lower pressure, but that's still up at 153psi on the rear. And the challenge is that most tires are only rated up to 120psi, so I have a problem.

Because I'm heavier, I have to go for a wider tire. 
  1. The best option is really a 25mm tire.
    These tend to not have too much of a weight penalty over a 23mm tire, but can still take higher pressures (~120psi). The downside of a 25mm is that I'm still on the cusp of needing too much pressure (140psi, or 125psi on the 23mm rim) 
  2. The other option is a 28mm tire.
    These tend to have a fairly large weight penalty though. Few manufacturers make their best tires in this width. And once you get to this width the max pressure typically drops to <100psi. For a guy of my weight I need 115psi on this tire, and I've been fortunate to have found 2 or 3 tires that can handle that and it's what I ride now.

So why don't I just get a 25mm rim for a 25mm tire and similar for a 28mm tire and rim?

  1. Brake calipers on bikes barely fit 23mm rims, so any larger isn't an option.
  2. Just because the scaling on one tire works well doesn't mean it will work on another.
Problem 1:
To get around problem 1 you simply have to use disc brakes instead. This opens a whole realm of wider-profile XC 29er rims. If you don't want to go disc, then you're stuck with 23mm HED C2 rims being the largest you can hope for at this point in time.

Problem 2:
That's what I hope to explore.

Problem Statement:
I want to run 25mm or 28mm tires on a rim that gives the same profile and advantages of using the 23mm tire on a HED C2 rims.

  • Surface area of a tire will remain constant once pressurized
  • Profile of the tire will remain as round as possible regardless of how wide or small a rim is
  • Bead-hooks vary in size and profile by rim. So what really creates the profile of the tire is the inside width of the rim, not the outside width.
  • Aerodynamics aren't really that big of a deal for my style of riding or size, so I'm going to try to optimize for increased volume and cross section profile, not on matching flushly with the rim
    • However, say I end up with a 24mm rim on a 25mm tire, that's still closer than a 19mm rim for smooth airflow, so I'll likely get some advantage.
  • A standard road-rim has a 14mm inside width
    • After emailing HED they informed me that the inside width of the HED C2 rim is 17.6mm
I explored 2 possible solutions:

  1. That the scaling of the rim is scaled linearly from the ratio of 17.6 to 23 and then apply to the 25 & 28mm tires.
  2. That the main goal is to keep the tire profile and surface area constant and see what rim would apply.
Solution 1:
Scale the rim linearly from the ratio of 17.6 to 23 and then apply to the 25 & 28mm tires.

For this it's rather simple:
  • 17.6mm / 23mm = X mm / 25mm => (17.6/23) * 25mm = 19.1mm
  • 17.6mm / 23mm = X mm / 28mm => (17.6/23) * 28mm = 21.4mm
Pros: This solution seems to very closely match existing inside widths for XC rims. 
Cons: This solution seems almost too simple a solution, and after mocking up the profile it does not have the same profile as the HED C2 rim with a 23mm tire.

Additional details. After using SketchUp, I was able to find the following info:

23mm Tire on 17.6mm Rim:
(In parenthesis indicates dimensions for same size tire on a 14mm rim)
  • Surface: 57mm (same)
  • Maximum Diameter: 24.3mm (23mm)
  • Cross-Sectional Area: 408.4mm² (388.0 mm²)
  • Pressure vs. 14mm Rim: 95%
25mm Tire on 19.1mm Rim:
(In parenthesis indicates dimensions for same size tire on a 14mm rim)
  • Surface: 68.3mm (same)
  • Maximum Diameter: 28.4mm (25mm)
  • Cross-Sectional Area: 572.2mm² (464.5 mm²)
  • Pressure vs. 14mm Rim: 81%
28mm Tire on 21.4mm Rim:
(In parenthesis indicates dimensions for same size tire on a 14mm rim)
  • Surface: 73.3mm (same)
  • Maximum Diameter: 30.8mm (28mm)
  • Cross-Sectional Area: 668.1mm² (592.2 mm²)
  • Pressure vs. 14mm Rim: 89%
Solution 2: 
To help myself better visualize everything I mocked up a 23mm tire on a 14mm rim and a 23mm tire on a 17.6mm rim.

Finding of Note: I found is that if you put a 23mm tire on a 17.6mm rim that from the center of the tire to the edge of the rim was a 45 degree angle. This symmetry seemed more than just coincidental.

I used that symmetry to come up with the following equation to simplify things. 45 degrees to each rim meant there was 90 degrees of of 360 degrees taken by the rim and 3/4 of the circle taken by the tire.
  • Max Diameter of Tire * Pi * 3/4 = Cross-Sectional Surface of Tire
Unknown in this equation is Max Diameter of Tire, so solve for this:
  • 25mm: 68.3mm / (3.14 * 3/4) = 29.0mm
  • 28mm: 73.3mm / (3.14 * 3/4) = 31.1mm
Make circles with those dimensions, then  make a line from -45 degrees on the circle to +45 degrees on the circle and you  find the following optimum rim dimensions:

25mm Tire on 20.5mm Rim:
(In parenthesis indicates dimensions for same size tire on a 14mm rim)
  • Surface: 68.3mm (same)
  • Maximum Diameter: 29.0mm (25mm)
  • Cross-Sectional Area: 594.9mm² (464.5 mm²)
  • Pressure vs. 14mm Rim: 78%
28mm Tire on 22.0mm Rim:
(In parenthesis indicates dimensions for same size tire on a 14mm rim)
  • Surface: 73.3mm (same)
  • Maximum Diameter: 31.1mm (28mm)
  • Cross-Sectional Area: 684.6mm² (592.2 mm²)
  • Pressure vs. 14mm Rim: 86%
It appears that Solution 1 would produced more conservative values than Solution 2; however, I believe (at least mathematically) that Solution 2 is the more optimum of the two possibilities.
  • 25mm tires should be on 19.1mm to 20.5mm rims
  • 28mm tires should be on 21.4mm to 22.0mm rims
One other point of note is that 25mm tires seem to gain proportionally more cross-sectional area than either 23mm or 28mm. I would have thought that things just got linearly more and more in favor of the large-diameter tires. If I had time I'd try to create a mathematical model and see where the actual minimum is. However, seeing that I can reduce tire pressure on a 25mm tire by 19-22% is a really big deal for me. That means I can instead of run a lighter stronger and generally better 25mm tire with the same lower pressure that I can run on 28mm tires in a  normal setup. This actually exceeds my expectations and makes me quite excited.

What Now?
Finding the inside widths of rims is actually surprisingly hard. Some manufacturers like Mavic say it in the name (TN719 is 19mm inside), but others don't tell you unless you ask directly or do a lot of searching. Trying to find something as specific as 20.5 will likely be very difficult, so I'll just do my best to find something in the desired range. I'll likely end up with either something that says it's 21mm, but is really a little less, or something that's 19mm, and be glad I'm at least way better off than if I was on a 14mm rim.

Real-World vs. Theoretical-World
I want to see if I can get a bike shop to loan me or let me try mounting a tire on a rim of that width. This should allow me to see if things really work. But finding a shop that A) Would let me do that and B) Wouldn't just say, "You can't do that, the specs say it doesn't work."; is going to be really hard to do. Fortunately I know a few bike shop guys that I think are willing to put rules aside for some experimentation so hopefully I'll be able to report back with some results soon.

Thursday, August 04, 2011

Bosco's First Birthday

A year ago today Bosco was born.

Although we didn't get to see him until the day we picked him up.

Once we got there he said his goodbyes:

And then had a great trip home with us:

And while he was cute and flopsy:

He was also a vicious beast filled with razor-sharp puppy teeth:

Fortunately after being up for a few hours he would sleep:

Wake to explore his world some more:

Run around:

And would wear everybody out:

He managed to grow, and grow, and grow, but finally leveled out:

As he grew we tried to train him:

And taught him to fetch:

And sit:

And to be lazy on Sunday mornings:

Now that he's bigger he's made friends:

And has become the high-flyer of our family:

And we're the ones who get to see this face every day:

He's leveled out at 85 lbs and is 28 tall at the haunches and the withers.

Now that he's gotten older he's starting to run with us, but his max so far is about 2 mi of continuous running. His cardio's getting better, and I'm sure once it cools down he'll be a champ.

He is a bit freaked out by water, but I think that mostly is due to the drought and that it's only rained like 4 days his whole life.
Despite his unease with water we did find a fresh watering hole and teach him to swim. He's actually pretty good at it and one day when there's more water we'll likely take him for more swimming.

He's super sweet, gives us kisses all the time (but not sloppy wet ones thank goodness), he loves to cuddle with us, he has never destroyed anything that isn't his, very even tempered in new situations, nice towards others if they're nice, but he won't take unnecessary crap from aggressive dogs, let's kids jump on him without concern, super calm in the house, but loves to have fun outside. Really he's the best of all worlds and we couldn't ask for better.

So happy birthday little dude!

Wednesday, April 13, 2011

It's Easy Being Green

Being green takes many forms and flavors. You can reduce pollution in local creeks and lakes by using compost instead of fertilizers. You can save water by choosing a lawn that doesn't require (much) watering. You can forego having pets or children because they require food and fart CO2 and CH4. You can spend 1000s on a solar panel that might maybe if you're lucky one day pay for itself.

One of the main areas though where you can think big on being green is how to reduce the energy you use each day. 

Taking a look at the big picture looks something like this:
Just like when budgeting when trying to save, you should start with the big pieces. And when talking about Energy Use in the United States the big pieces are Electric Power and Transportation.

Electric Power:
When looking at your home you can do things like change the lightbulbs, or get more efficient appliances, or upgrading from a plasma TV, and while they help some the actual benefit is not nearly what the companies that market those products would lead you to believe (those 3 are responsible for only about 25% of home energy usage). 

Q: So where does the majority of power go in your home?
A: Heating and Cooling (cooling's the big one in Texas)

Step 1: Adjust the temperature. 
In the summer one thing that can have a large affect by getting screens, opening windows and using fans. You might well save 30% on your bills.

This winter one thing we used was small space heaters in the rooms we were in (living and bedroom) instead of heating the whole house. The heaters paid for themselves within a month, and by the end of the winter we were not only more comfortable than any year prior, but we had also saved about 30% on our heating bill.

Q2: But even that is just an incremental adjustment. So how can I make a big change?
A2: Get a smaller house. Even the greenest of homes if it's very large will suck way more power than a smaller and less efficient home. 

Step 2: Live in a smaller house
We actively made the choice to live in a smallish 1000 sqft home, and while we have a 20 year old AC, and single-pane windows, and no insulation, I'm continually baffled at hearing about how much some other coworkers who live in ginormous houses spend on electricity. Despite that they have the latest split-unit ACs, double- or tripple-paned windows, and great insulation. The simple fact is if you're trying to heat and cool a 3000 sqft house it is going to take a lot of energy. But if you have a tiny house it will only take a tiny bit of energy to heat and cool.

There are other 'green' benefits too. Such as 60 sqft of tile for your bathroom is way less expensive and greener than having to buy 600 sqft. You're not filling room upon room with new furnishings, and since most small homes are older you're not destroying land to put your house on it.

The US is built for cars, I get that. There's not really an easy way to avoid them, but there are a few things you can do.

Step 1: Live, work, and play in the same area. 
If you have an hour commute you're using a lot of fuel. For comparison person A drives a Prius and lives 40 miles away; person B drives a jacked-up monster-truck wannabe and lives nearby-ish at only 3 miles away. So who's being greener? In this case the monster truck actually produces both less smog and less smug.

Step 2: Use alternative transport when possible
While not possible for everybody I try to bike in a few times a week to improve my health and stretch my gas money. Additionally though, think about not using your car when you're at home. Can you walk to that store instead? Can you bike down to that bar you like instead of drive? (Plus you'll be less likely to worry about cops on the way home) On the weekend can you make a day-long excursion downtown on your bike instead of driving? (Think of how much time you'll save trying to find the elusive free street parking!)

Every time you choose to leave a 3000+ lbs piece of steel at home you're saving that much fuel, and often you're getting to spend more quality time with the people you're traveling with, getting some exercise, and soaking in the city and sights around you.

When it comes to energy usage if you're going to go green you should aim for the big targets. And often it's the choices we make of where and how we live that really have the greatest impact.