Road Cycling - Physics and where to spend my $

Howdy,

I was talking with friends recently about what to get when I buy my next bike. They were split into two camps 1) Buy the best frame you can get, and 2) Spec a bike with the lightest set of wheels I can afford.

I understand the rationale for the folks who say get the best frame, but, I'm planning on spending between $2250 - $2750 on the bike and assume in this range most frames will be comparable (with the exception of ride characteristics specific frame material I choose).

I also understand conceptually why I would want light rims as it requires more effort (watts) to spin a heavier object when it is further from its axis. However, no one could quantify for me what this difference would be...

Can someone help me with the physics of this? If I'm looking at two bikes that are both 18 lbs, what would the relative advantage be to go with a 300 gram lighter set of rims? I'm assuming that if I go with best frame or best wheelset both bikes would weigh the same as the lighter wheelset would come at the expense of a heavier group set.

[a] Frame / Fork
[b] Wheelset
[c] Components

Always, in that order.
A top grade frame will last 10 years. A Litespeed Vortex, Merlin Extralight, Trek 5900, etc. will last a long, long time. I doubt if you'll find wheels that'll last that long. You can buy a very very good wheelset (e.g., the Velomax Ascents) for $400 (last year's sale price at Supergo). Frames will cost you thousands.

Best.

[a] Frame / Fork
[b] Wheelset
[c] Components


I'm familiar with the heuristic you provided above, however I was hoping for something more quantifiable (hence the physics) as frame quality seems to be pretty subjective to me when you are operating within a specific price range. Maybe these bikes are comparable and maybe they're not but I found an 04 Giant TCR Composite for $2400 and a Pinarello Prince for $3000 (both with Ultegra groups on the Wrench Science website) and also saw the same Giant on sale on another website (with Ultegra) for $1999.

What makes the Pinarello aluminum frame $600 - $1000 better than the Giant carbon frame? Both are light... Both are race proven...

Aside from being able to say you've got an Italian bike (and don't get me wrong because I would love to own a Pinarello), it seems like the price difference has more to do with paying for the name than frame quality.

Aside from being able to say you've got an Italian bike (and don't get me wrong because I would love to own a Pinarello), it seems like the price difference has more to do with paying for the name than frame quality.

I believe you just hit the nail on the head. When you get into the price range you're looking at, you're not going to find bad quality frames. What you will find are frames that -- due to their gemoetry -- are not suited to the type of riding you want to do. Super-quick steering criterium frames, for instance, might not be the best choice for riding centuries.

As for the physics questions... The topic of how much energy it really takes to accelerate a wheel has been debated endlessly on here and the various rec.bicycles.* newsgroups. A quick search for "wheel acceleration" produced 1,950 hits on the rec.bicycles.* groups in Google. You might also want to check out http://www.analyticcycling.com/ which enables you to answer all kinds of bicycle-related physics questions.

While it does take more energy to accelerate a wheel with higher rotational inertia at the same rate as one with less there isn't enough difference between any wheels you would consider to be significant given the relative inertia's of the wheels versus the total vehicle inertia and the low speeds a bicycle is capable of.

I don't have the data here to run through the calcs for you but you can try a simple test. With the bike on a workstand give the wheel a quick spin with your hand. I'm guessing one quick spin should be good for 20 mph or so and be pretty easy to do. To put that same amount of energy into the bike with your legs while riding would be much easier to do. Now reduce the effort proportionally by how much longer it takes to accelerate to 20 mph while you're riding. Think how seldom you accelerate by 20 mph and you start to get a feel for how insignificant the slight difference in rotational inertia between different wheels is.

Get your dream frame and a decent set of wheels. I've heard Ti frames are great.

[a]
Frames will cost you thousands.

Best.
A Cdale caad4 frameset from GVHbikes. com is $495 and is more frame than most riders. Good enough to win the Giro and Tour stages,and good enough for DA or record if one has the bucks.

As for the physics questions... A quick search for "wheel acceleration" produced 1,950 hits on the rec.bicycles.* groups in Google. You might also want to check out http://www.analyticcycling.com/ which enables you to answer all kinds of bicycle-related physics questions.

Thanks! I figured there had to be loads of conversation on this topic but I'm fairly new on the forum and wasn't sure what the best search phrase would be...

I promise I'm gunna be the only one who says this, but I LIKE HEAVY WHEELS. :) ..well, not necessarily heavy, but big and stiff -- at least on the back.

I know all the physics, and I had Mavic Open Pros and CD4s, but one day I was desperate for a rear wheel in a big hurry, and my bike shop guy lent me a 2nd hand 30mm Rigida DP18, and WOW! I've never ridden Cosmic Carbons or anything similarly exotic, but I couldn't believe how STIFF and fast the 30mm deep rim felt (on the back) compared to all the standard profile rims I'd used.

I recently bought a "lightish" DT RR1.1 rim, and hated it; too "spongey".

I should say that I'm a bit of a fat hack, at 190lbs.

The weight difference isn't all that huge; a DT RR1.1 rim weighs about 416g (i weighed it), and something like a Velocity Deep V (30mm dish) weighs 539g, less about 10g for the shorter spokes makes a difference of 113g. Okay, that's rotating mass, etc, etc.

Having said all that, I recommend a Mavic CXP33, or something in similar weight and dimensions, because they are a very good compromise of weight (~440g) and rigidity (~23.5mm deep).

Anyway, my 2 cents.

Get your dream frame and a decent set of wheels. I've heard Ti frames are great.

I was considering a Ti Airborne or Guru because two LBS's close by carry these brands so I could find out if I liked their geometry and the feel of Ti (I've heard it really soaks up the road bumps but that it's also kind of squishy or bouncy). While I was searching for other Ti bikes I checked out Litespeed and saw an assortment of bikes in the 5 - 7K range and decided that carbon might be a better route to go - same road dampening properties but easier for manufacturers' to work with (lower cost to me if I don't pay a premium for a name).

That's what led to my post - I figured if I could get a good frame that's light and reliable (I don't need top shelf as I only race for town signs) and then could stack it with light wheels and good components I have a combination that provides great value... My one question was what percentage to spend on frame versus wheelset.

The highest payoff will be in lowest body weight. Reduced body weight reduces the work load on the heart more than a reduction in bike weight. So spend the $'s on good food to achieve the proper body weight if your not already there. A leaner, narrower body also reduces air drag, which even at 15 mph can be 70% of the total resistance to forward motion and most of the air drag is due to the rider. Then I'd worry about the weight on anything that rotates. You get twice as much benefit from reducing rotating mass as frame mass. This would include wheels, cranks, pedals and shoes. If you race, then possibly you need the best frame you can afford too, otherwise you'll find that the difference between the real expensive frames and the lower priced ones are but a few ounces.

Most of the frames today are pretty good. Performance is dependent on the rider more than anything else. The exception might be if you're good enough to match the performance of those road racers of a decade or more in the past who had those "clunky" bikes available then.

Al

> What makes the Pinarello aluminum frame $600 - $1000 better than the Giant carbon frame?

Absolutely nothing.

> it seems like the price difference has more to do with paying for the name than frame quality.

Buying a Pinarello (DeRosa, etc.) is like buying a Sony, BMW, Steinway ... You KNOW you're paying for the name somewhere along the line. That doesn't mean they don't make a quality product.

> Get your dream frame and a decent set of wheels. I've heard Ti frames are great.

Concur. I ride a Litespeed and am quite pleased with it. Prior bike was a Medici (steel).

> A Cdale caad4 frameset from GVHbikes. com is $495 and is more frame than most riders.

Is this Al? I'm lighter (< 150) and wouldn't touch/consider any Al frame from any manufacturer. My choices when I got the LS were Ti, Carbon, or Ti/Carbon.

> if I could get a good frame that's light and reliable and then could stack it with light wheels and good components I have a combination that provides great value...

If you're seriously looking at Ti, then you're in luck. Sep is when I've seen Litespeeds and Merlins have substantial price drops. I got mine in Sep 02 from here:

http://www.hi-techbikes.com/cgi/display.cgi?5

Last year, a friend bought his wife a Litespeed Tuscany from them for $1200 with the fork. He upgraded the fork to an Easton EC90. Ultegra build and Mavic Open Pro wheels cost him < $2400.

> My one question was what percentage to spend on frame versus wheelset.

The Merlin Agilis is a wonderful frame. I've seen Sienas down to $1200 w/ fork. If you can find something like that ... let's say ~$1200 (give or take). Velomax Ascents for ~$400, then you're looking at approximately 1/3 the cost of the frame to spend on the wheelset.

I think you could easily score a good Ti frame, good wheelset, and Ultegra build well within your price range.

Best.

Hi-

I am a new rider who has been researching road bikes. I found Airborn's website where you can buy the Valkyrie, very well equppied for around $2500. From all that I have read, it is a great bike! The frame should last forever and the whole bike with all components weighs less tha 19 lbs.

Don't forget steel, such as Reynolds 853.

Great ride, strong and light. Will last a long time!

Spend the money on the frame. While the wheels make a huge difference, they are easily replaced later. Get a decent wheelset, not crap, so you can ride well. When you are ready, invest in a top-flite set of wheels. I've recently put a better set of wheels on my old bike and it makes a huge difference, but its the frame I had custom built for me that I still ride 20+ years later. When I think of how out of reach a custom frame would be for me now, I'm thankful I did it when I was single and had the cash.

Without going into the physics of it, weight taken off the wheels matters more than weight taken off a seatpost. Weight taken off your middle matters even more, although if you're a 140lb 20 year old, that isn't a factor (yet, but trust me, it will be someday:).

Thanks to all for your input and help :)

Colorado Cyclist latest flyer has really good prices on selected Litespeeds right now.
www.coloradocyclist.com

As noted air resistance, not weight is the major factor in linear speed. That is the
reason time trialers and tri folk go after heavy wheels that are aerodynamic. If you
ride consistently above 20mph, especially above 24mph then aero gets you a lot more
than weight. Weight in wheels is most siqnificant in acceleration, a scenario some
'leisure' riders get riding with fast groups that speed up and slow down a lot but that
is mostly seen on the racing scene in rides such as criteriums and many road races
where constant changes in pace occur. Weight is always significant on hill climbs
as by definition you have to accelerate constantly to combat gravity.
The www.analyticcycling.com site is a bit opaque but useful to get an idea how much
power Lance and Tyler have to generate to do what they do. Steve