Just fitted a lightweight wheelset - Pro2Evo/Crest 1530g. Previously running DT Swiss 370/317rims 1984g.
Was out last night for its maiden voyage and it seemed to fly up the climbs with ease. Is this weight saving advantage completely in my head like when you had new trainers as a kid, you could definitely run faster?!! Or is there a science behind it? I hear talk of un-sprung weight but cant get my head round that either.
Any help appreciated. 
it's not all in your head.
weight at edges of wheels is harder to lug about than weight anywhere else on the bike because you are having to spin it round all the time as well as carrying it.
does that make sense?
yup I reckon wheels/tires make more difference than just about anything else on a bike.
whilst that's true, its only more work when you're accellerating or decellerating - once a wheel is in motion it isn't extra work to keep it going.
the bike will feel much more lively, and therefore 'feel' quicker. less unsprung weight means the suspension will work better and the wheels will stay on the ground for more % of the time. However that's about it, you won't actually be any quicker than if you just had a 500gram poo before your ride
Yeah I guess so..
I've always found advantages and disadvantages.
Lighter wheels make a bike feel more 'alive' - it accelerates quicker, seems more nimble and is easier to hop around.
On the other hand, heavier wheels get knocked off line less easily and thus make a bike feel more solid in places. And I don't constantly knock and ding them to pieces every few months.
All personal impressions obviously!
the more imediate thing you'll notice is accelerating/decellerating the wheels: mass at the outer circumerence has the greatest effect, a heavy hub is less of an issue but obviously it's still mass you have to put work in to move....
Overall mass of the wheel also has an effect on the performance of suspension (Unsprung mass) as the weight of the wheel/swingarm/etc is acting on the shock too, but quite whether you'll notice this effect so much I don't know...
It's all relative too - my Pro 2/Crests are my heavy wheels and I dislike how the bike rides with them, put my light (1246g) wheels on and it feels far better!
Light wheels feel better, but they don't actualymake an apapreciable difference to speed on a smoth trail, however I guess a light bike (and in paricular the unsprung mass of the wheeels) will be faster over a rough trail as it absorbs less momentum? So the lighest wheels you can get away with without destroying them will be the fastest.
Unsprung mass: the weight of everything that isn't suspened byt he suspension. So wheels+tyres+cassette+mech+50% of the swingarm. This weight requires energy to make it move/vibrate every time it takes an impact (whereas the rest of the bike and you don't). Thus over rough ground you want to minimise it.
On a road bike light wheels feel better, but theres more advantage (apparenlty) in heavier aero wheels when the UCI weight limit comes into play.
I've always found advantages and disadvantages.Lighter wheels make a bike feel more 'alive' - it accelerates quicker, seems more nimble and is easier to hop around.
On the other hand, heavier wheels get knocked off line less easily and thus make a bike feel more solid in places. And I don't constantly knock and ding them to pieces every few months.
All personal impressions obviously!
My experience too, which is why I've "lightened" my ASR-5 do everything + enduro's bike with a 1720g wheelset*, and lightened my HT race wheels to 1480g wheels. I'll always take the ASR-5 to trail centres peaks etc so I need the wheels to be able to cope, yet the HT is used for 50k race formats in the SE, & training loops.
I have ProII's on 819's, wondering if its worth selling the wheelset and getting a new lighter set or just changing the rims to crests. What do we reckon?
IMO you would have to ditch 500g off the wheels to make it a good difference. The weight you would save over the Stans rims both running without tubes over a 819 would not be worth the hassle and expense for such a small difference.
You might as well sell and splash out on some lighter wheels with lighter hubs, spokes and rims and save as much weight as you can if spending the £££
I think the difference is noticable personally (though I've not upgraded my old 819 wheelset, on the grounds of cost vs benefits). People say that a big part of the difference only comes when accelerating, and that's true- but mountain biking isn't a constant speed sport, we're always accelerating and decelerating, so that advantage is there an awful lot of the time
Buuut, it's hard to say how much is real. A mate of mine reckoned he could feel the difference in weight between my Traversees and his 2100g Superstars- not noticing that I had dualplies fitted and he didn't, his wheelpack was almost exactly the same weight.
if you want to remove weight, its much better to reduce it from the rim/tyres than the hub, as it reduces the rotational 'weight' more (thats probably not scientifically correct, but you should be able to get what I mean)
Put the bike on a work stand or turn it upside down. You will now find that using just a couple of fingers you can accelerate the wheel up to speed quite easily. Compared to accelerating you and the rest of the bike up to speed (which takes your leg muscles not just a couple of fingers) the power needed to rotate the wheels is practically insignificant so the difference you felt is likely to be due to the placaebo effect.
Better and cheaper to lose some blubber off yourself if you want to go faster.
Put the bike on a work stand or turn it upside down. You will now find that using just a couple of fingers you can accelerate the wheel up to speed quite easily. Compared to accelerating you and the rest of the bike up to speed (which takes your leg muscles not just a couple of fingers) the power needed to rotate the wheels is practically insignificant so the difference you felt is likely to be due to the placaebo effect.now is this Science FACT?
now is this Science FACT?
Why yes it is
From http://en.wikipedia.org/wiki/Bicycle_performance#Kinetic_energy_of_a_rotating_wheel
"Another place where light wheels are claimed to have great advantage is in climbing. Though one may hear expressions such as "these wheels were worth 1–2 mph", etc. The formula for power suggests that 1 lb saved is worth 0.06 mph (0.1 km/h) on a 7% grade, and even a 4 lb saving is worth only 0.25 mph (0.4 km/h) for a light rider. So, where is the big savings in wheel weight reduction coming from? One argument is that there is no such improvement; that it is "placebo effect""
Looks like your new wheels will save you about 30 seconds climbing Alpe-d'Huez
I upgraded my race wheels this season and dropped 400grams or so, what got me was not the lightness but the performance gain due to the increased stiffness. Better tracking and more feedback meant I had greater control and more confidence when corning.
I've done the same and agree its the stiffness that is the main difference with a good wheel set. Plus stiff wheels somehow sound better when you get them past 30 kph.
Looks like your new wheels will save you about 30 seconds climbing Alpe-d'Huezcheers for the science FACT!!
I've done the same and agree its the stiffness that is the main difference with a good wheel set. Plus stiff wheels somehow sound better when you get them past 30 kph.My pro 2's sound like a wasp/moped over 30 mph.
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