Abe_Froman

So...I've been looking around for a new wheelset for cyclocross racing. Doing research on both wheels, and cycling physics in general. The aura of wheelset weight importance has always struck me as a bit nonsensical.

I stumbled upon this calculator: https://www.cyclingpowerlab.com/Acce...ndInertia.aspx

Entering in my weight, and a prescribed acceleration of 15-20kph over 2 seconds, which I would say is a pretty accurate representation of accelerating out of multiple corners a lap in CX. If I got a new wheelset that was a full 1000 GRAMS lighter than my current one, it would save me a grand total of: 5 WATTS over the same 2 second acceleration, dropping from 335.2 to 329.7, with less than half of that (2.3 watts) coming from rotational inertia (IE...the effect of lessened rotating mass vs static).

This sure doesn't seem to warrant going to any great lengths to get a new wheelset. Any thoughts?

colnago62

wphamilton

Sounds about right. The linear component is the same as with weight on any other part of the bike, and the (additional) rotational component something less than half of that.

Also keep in mind that uphill keeping a steady speed, the cost due to rotational inertia is very much reduced from that (would be zero if you kept exactly the same speed, but we can't).

It's a case of "every tiny bit helps" but it does seem to me that cyclists tend to overstate the helpful impact of lighter wheels.

jamesdak 

Well, I can't give any statistical data but I quite enjoy lighter wheels. They just make the bike feel livelier and quicker. So from that aspect they are truly worth it to me. Maybe mentally they will help you in a race as you may not question if you're getting fatigued or not due to the lighter wheels making you feel "fresher"?

Abe_Froman

I've considered this as well. And I think you're right. The difference in feel is I imagine the biggest thing people are talking about in regards to wheels, not any measurable or noticeable difference in performance.

Also...assuming that the feel is what you're really after, the best bang for your buck then would be to just get an ultra light front wheel, and leave the rear stock.

Dean V

The difference is in the lower gyroscopic effect which alters how the bike feels quite a bit.
Actual acceleration difference, as you have calculated, is very small.

woodcraft

If you're racing the Marin Four Corners, a 1lb lighter wheelset wouldn't be that noticeable

compared to the 6 lbs or more saved by switching to a better bike.

A tubular wheelset with some nice low pressure tires will also gain much more speed than lighter clinchers.

A used set can be got for cheap.

Abe_Froman

Nah, I've got a Focus Mares now, which is much more than 6lbs lighter than the Marin. I imagine it's closer to 6kg difference

I'm not sure I'm willing to go the tubular route. Mainly because it sort of eliminates the possibility of using different tires for different purposes/times of year. If the bike was ONLY used for CX, and it were rim brake, I probably would find a dirt cheap set of tubulars.

Disc brake though, and I use it for pretty much everything except commuting. So I'm likely going tubeless.

woodcraft

Yeah, I was thinking of rim brake- cheap & easy wheel swap.

Abe_Froman

It's almost a shame really. One of the races I was at had a set of ~1400gram carbon tubulars, new tires glued on, for like $250. If I had a rim brake bike would have bought them on the spot and raced them that day...

Psimet2001 

I also take issue with anyone touting aero data saying that anything aero saves them xxx second over a 40k TT. It's all relative. In my experience the faster racer always wins and it seldom has anything to do with the gear.

Lighter wheels that are still stiff feel amazing to ride. It also has a ton to do with where the weight is as well. Light rims even with a lot of spokes feel amazing to ride compared to wheel systems that are the same weight but have fewer spokes (meaning more material in the rim to withstand the loading).

As for cyclocross - that's 1000% my wheelhouse. If you're not looking at tubular then you're not serious about using them to perform. It's really the main discipline left where you can say that (track is another but...). In those scenarios its how stiff the wheel is and how well is support the tire in its conformance to the terrain. Doubt it or want to argue it - fastest riders in the world run ~1 bar in pressure. That's roughly 13 psi.

We have a new rim coming out that is specifically for that arena and still ends up lighter than the premium (priced) setups but it's for racing (not a commercial).

Psimet2001 

I have piles of new carbon tubular rims for road that I can't give away. Everyone stopped with them hard stop like 2 years ago.

Tubular for cross will always be there and be superior. Cyclocross by definition is racing. It doesn't exist in a format outside of racing. Example - we don't say "I'm going to go criterium riding today". cyclocross riding is racing on a cross course. In that respect cyclocross will always be tubular. It just outperforms even the best tubeless even today.

Riding a cross bike without racing it is formally called "gravel", "groad", "adventure"

Totally get what you mean though with "if it were only for cross I would get tubulars" though.

Abe_Froman

Agree completely for the most part. I'm a cat 4 rider (just up from spending the Chicrosscup in cat 5)...hoping to move up to cat 3 this year. If I start being competitive in the cat 3 races...maybe then I'd start looking at tubulars. Right now though...I'm fairly confident it aint the wheels/tires holding me back

rubiksoval

1000 grams? In CX where you're picking up your bike multiple times? That'd be an even bigger benefit than acceleration for me, though admittedly my upper body strength is lacking quite a bit.

63rickert

Original example is 15kph to 20kph in 2 seconds. That is a nothing acceleration. Of course there is no gain had with a lighter wheel in that case. Try figuring out a kilo rider doing a standing start, 0Kph to 60kph in 3 seconds.
Get some light wheels and try them. If you are the rare rider who notices nothing then you don't need light wheels.

Abe_Froman

Lol, have you raced cross? Try doing it 50 times a lap.

And besides...I'm not making any comment as to whether lighntess of wheels is noticeable. I'm questioning performance benefits.

79pmooney

The place where lighter rims/tires can make a real difference is mass start road racing. If lighter wheels means just once, you make the split instead of coming 2 feet short, that could mean being in the winning move, minutes ahead and many places at the finish.

As a small engined racer, I was a big fan of light rims and tires. Races Fiamme Ergal rims (290g) and Criterium Seta sewups (250g), sometimes the matte thread version @ 220g. Spokes that were the equivalent if DT Revolutions weight-wise.

Ben

Dean V

0-60kph in 3 seconds?? No way is that happening.

HTupolev

0 to 60kph in 3 seconds would require the rider to do about 50W/kg to overcome inertia alone, and while badly overgeared. If you look at video of world-class kilo efforts, the riders are usually still grinding a fairly low cadence at the 3-second mark, and acceleration continues to some degree through most of the first lap.

63rickert

It's called hyperbole.

63rickert

I've raced cross. And worked the races. And promoted CX races. Going back to 1968.

From 9mph to 12mph is a nothing acceleration that could happen without even noticing. If traveling that slow because the course is buried in mud, no, lighter wheels make no difference. If going that slow is happening 50 times per lap and the course is not buried in mud then I question the course design.

Instead of asking the question and then arguing with those of us who have already done the experiment wouldn't it make more sense to borrow a pair of light wheels and find out for yourself?

Abe_Froman

And how exactly do you propose I gauge accurately changes in accelleration due to wheel weight?

We should first start by asking whether you are making the claim that my calculations in the OP are off. It seems you're implying they are, but have not explicitly said so.

Also...if you want to quibble about corner speeds...pick whatever number you want. 12-15mph if like.

Jean_TX

I too enjoy lighter wheels. I have two routes that I ride. Both routes have lots of stops/near-stops and one route has some significant hills. I ride with the intent of maintaining a certain overall average speed. Replacing my bike’s stock wheels with wheels that are 650 grams lighter has increased my average speed by about 1mph and seems to take less effort overall. Those benefits may not be meaningful to some riders, but they are meaningful to me.

I think whether or not the decrease in acceleration effort and/or time is worthwhile depends on the rider’s goal, the course being ridden (hills, points where one has to stop or slow down for turns), and the rider’s energy reserves.

If the rider is racing and/or is focused on cruising as fast as possible, the difference in the time needed to get up to racing speed may, or may not, be important.

If the rider is intent on maintaining or bettering a specific average speed and the route has many stop lights, stop signs, turns, or hills, then
(1) the ability to accelerate more quickly may provide a boost in average speed, and/or
(2) the decreased effort required to accelerate up to the desired average speed may make the difference in whether or not the rider bonks before the entire route is done.

Abe_Froman

1mph difference is a LOT, at any speed.

However, I have a pretty hard time believing, under any circumstances, the speed difference is due to the 650 grams. Are the wheels the same depth, shape, etc? same tires on each wheelset? 1mph is a believable difference just by swapping tires, depending on the tires. I would also say it is at the upper bounds of reasonableness if you're going from shallow box section wheels to deeper aero wheels.

650 grams = 1 mph? I'm not sure I'd believe that even if you were scaling the side of a building on your bike.

Dan333SP

This. There are too many variables that go into the average speed of a ride on an open road to attribute 1 mph to lighter wheels.