Bike Weight

T4 Mark

Hi,
Can anyone give me advice about the weight of bikes, and how a few pounds extra will effect the performance.

The reason is, that i currently own a Giant Rincon, and want to upgrade to a full-sus. I know that the weight of a full-sus will be more, but if i weigh 148lb, should i be worried about shaving a few pound of the bike, against a lot of pounds from my pocket. Because surley it would be just as tough for someone with the same fitness level as my self, weighing 153lb on a 28lb bike to cycle the same track as me on a 33lb bike.[/quote][/b]

milkywhite

Your body mass is much easier to move around than the mass of the bike. Losing 2lb from the weight of the bike will definitely be noticeable, but I'm not sure the same could be said if you lost 2lb in body weight.

Lighter bikes are easier to ride and handle better...generally (I'm sure someone will disagree here!!!)

Same reason as why carrying a rucksack is better than having whatever you're carrying strapped to the bike in some way.

cjw

You may be surprised by my answer (if you notice my bike), but it is very debatable.

Some recent research on rotating wheel weight (can't remember where I saw it - sorry) showed that for roadies the difference in wheel weight (supposedly the most effective weight reduction) was largely all in the mind as the reduction was negligable compared to the rider + bike weight in total and fractional increases in acceleration would not be detectable. There was an improvement in wheel quality wit more expensive / better quality (which are almost always lighter) wheels being stiffer etc... but that was it.

This becomes more so if you look at other weight reductions. I've recently reduced the weight of my bike by over .5Kg but have done so as part of replacing parts that were wearing out or annoyed me. I didn't specifically set out to reduce weight per-se, but the parts I chose had that effect. Can I note the difference in the ride ease to get up hills..... Nope :shock: But this was reducing a 10.1Kg bike to 9.6Kg (so very light to begin with). Add in rider weight an that is only 0.5% reduction.

I can save the same weight with a little less water in the camelbak - but you can do that as well.

Bottom line. I reckon if you go from a 13, 14kg bike to a 10 - 11 Kg bike you will notice a difference, but trimming grams off will be unnoticable apart from on the mind - and that can be important.

supersonic

No point carrying about uneccesary weight - ie if you are going to ride XC, why bother getting a 130mm forked heavy duty hardtail?

As milkywhite says, the weight is more noticable on the bike than yourself, the way it handles and accelerates. I think most riders have a bike weight they feel comfortable with, and a bit either side can be felt. Bit like a bowling ball - I can use a 12lbs with ease: a 14 pound feels clumsy, 16 pound nigh on impossible, while 8 and 10 feel like I can throw them down lol.

A few grams is not going to be noticable - but they add up. Save 50g on each bike part, and on average you'll lose 2lbs. I wouldn't however change a part solely to save a few grams on a new bike, except tyres (or if you sell the old parts from new). Upgrading when parts wear, or you want a different set up is the best bet. Why buy a 200g stem, when you can get a 130g one? For medium weight XC and trail riders, you won't notice a difference in 'performace' of the unit.

My Idrive is around 30lbs, the Zaskar around 22lbs. The difference is night and day. I can ride a LOT longer on the Zaskar, and it accelerates much quicker.

salsarider79

You may find yourself faster on a full sus anyway, because you can take more direct lines, etc.
Weight is a different thing to different people. My last full sus weighted in at 29lbs, but was a comfortable all day trail bike. Wasn't the fastest because of the weight, but was sooo comfortable. I also had a 19.9lbs bike which was so light it was unridable. Went uphill fine, but it skipped all over the place on anything rougher than pavement. Normally I would go for the lightest bike possible, but I prefered the full sus...
Go for comfort.

supersonic

Yes, too light brings with it problems of flex and unreliability unless you pay a lot of money. Luckily we are seeing light and stiff now, not like the days of the 90s with flexy everything!

I think you can get some very reasonably priced light equipment nowadays that performs well.

T4 Mark

Thanks all for the advice. It all makes perfect sence.

I think that what i might do is keep the Rincon, for now and change the wheels and tyres to a lighter set, that i will use on road and easy off-road tracks.

I have had a look around at new Full-Sus bikes sub £800:00 (Kids cost to Much), and have thought about the Mongoose Teocali Comp as the 2008 Model is quite cheap at the minute, and the frame and set up has had a good few reviews.
Then as parts ware/break and need replacing fit the best and lightest that i can afford.
Hopefully then in a few years time i will have fairly competent and mid weight bike that will be at home on singletrack and mountain bridle ways.

Is ther any thing wrong in my thinking? :roll:

supersonic

Yes, I think that makes sense. The Teocali is not a featherweight frame though: if riding xc might want to look at the shorter travel Canaan. The Teocali is built to be a bit tougher to start with.

supersonic

Like this:

http://www.tredz.co.uk/.Mongoose-Canaan ... _14082.htm

cjw

Found the weight link

http://en.wikipedia.org/wiki/Bicycle_performance#cite_note-Compton-9

Wikipedia so it must be true

Key calculation regarding weight comes at the end where they calculate a 1Kg weight saving gives only 1 second advantage over 25miles (this sounds too small to me - might work through the maths to check it out if I get bored) ...

Shaving 1 kg off the weight of the bike/rider would save 0.01 m/s at 9m/s on the flats (1 second in a 25 mph (40 km/h), 25 mile (40 km) TT). Losing 1 kg on a 7% grade would be worth 0.04m/s (90 kg bike + rider) to 0.07m/s (65 kg bike + rider). If one climbed for 1 hour, saving 1 lb. would gain between 225 and 350 feet (107 m) - less effect for the heavier bike + rider combination (e.g. 0.04 mph (0.06 km/h) * 1 hr * 5,280 ft (1,609 m)/mile = 225 ft).

Here's another one with the same results.

http://www.biketechreview.com/archive/wheel_theory.htm

cjw

And this script;

http://wiki.vanguardsw.com/bin/browse.dsb?det/Engineering/Mechanical/Bike%20Race%20Simulation

models bicycle performance - you can change the various weights to see the (calculated) effects.

I've just run the 2008 model and the theoretical difference between a 20lb bike and 30lb bike over 20 miles is 4426 seconds to 4504 secs.

johnsav

worth thinking about weight saved on wheels, which obviously is rotating mass and a different kettle O fish

supersonic

More to it than time saved - energy lifting bike over obstacles, lifting front end up, accelerating.

cjw

johnsav wrote:

worth thinking about weight saved on wheels, which obviously is rotating mass and a different kettle O fish

But that is exactly what these guys argue... that even the rotating mass argument is irrelevant and mathematically doesn't hold water - actually even more so than total weight.

supersonic

Rotating mass only makes a difference for acceleration. At constant speed, on smooth surfaces the energy requirement keep the bike moving (providing tyre profile and pressures are the same, the rest of the bike is the same, and same overall weight) is the same for heavy or light wheels.

cjw

supersonic wrote:

More to it than time saved - energy lifting bike over obstacles, lifting front end up, accelerating.

The model I found tries to model acceleration / climbing etc etc and just one of the outputs is time.

Hmmmm... I'm still keeping my featherweight scale though - never did trust models

dave_hill

cjw wrote:

You may be surprised by my answer (if you notice my bike), but it is very debatable.

I'd agree that it's debatable. Rotating mass (i.e. wheels) is without a shadow of a doubt the best place to shed weight from a bike.

With roadies the difference in weight between two wheelsets might only be a few grams so yes it is going to be difficult to notice any difference.

But with a budget MTB, fitting a lighter wheelset with careful choice of rims, spokes, tyres, tubes and hubs could save a kilo or more and that will make a HUGE difference.

It might be hard to imagine but until you've experienced the difference that a good lightweight wheelset can make it's difficult to appreciate.

johnsav

supersonic wrote:

Rotating mass only makes a difference for acceleration. At constant speed, on smooth surfaces the energy requirement keep the bike moving (providing tyre profile and pressures are the same, the rest of the bike is the same, and same overall weight) is the same for heavy or light wheels.

surely also effects the feel of cornering, agility etc...

supersonic

Never really though about cornering and wheel weight! Heavier wheels may corner faster... hmmm.

johnsav

flywheel effect...

DEBATE!

supersonic

Lol, it is that flywheel effect that in a straight line means you need the same energy input to carry on at a set speed, once you have got to the speed, regardless of wheel weight. (on two equally weight bikes). Lighter wheel easier to turn but less flywheel if you get the picture.

But in a corner? Will have to put on back burner, brain is fried today how it is!

johnsav

likewise, and ive just been made a nice curry. Over and out!

milkywhite

I seem to remember some experiment at school where you spin a disc on an axle then tip it to one side as if to replicate the leaning of a bike in a corner. Then you put on a heavier disc and repeat. The heavier disc is harder to tilt.

I'd expect it's the same with wheel weight.

realnumber 1

milkywhite wrote:

I seem to remember some experiment at school where you spin a disc on an axle then tip it to one side as if to replicate the leaning of a bike in a corner. Then you put on a heavier disc and repeat. The heavier disc is harder to tilt.

I'd expect it's the same with wheel weight.

Isn't that the gyroscopic effect of the wheel?
The weight makes a big difference in that case..

robertpb

A couple of weeks ago on a Saturday run, when half way up my lane, I kept thinking to myself why do I feel like a ton of lard riding.

I'm only a lightweight and I thought that I must have over done the vegetable stew the night before. Keeping my eye on this over the following week I came to the conclusion that it was more to do with the extra 1.5 kilos of water in the hydro that I carry on the longer ride on Saturday.

Checking the speed I'm still travelling as fast, so our brain tells us there's a difference in weight but exaggerates it a bit.

Newton would say it doesn't matter if it's a pound of lard or a pound of metal it takes the same amount of energy to move it.

With MTB's the calculation for the increase in weight to the extra time taken to travel a distance are a bit different to a road bike. The calculations are done on a smooth road, no rocks, roots etc as an MTB rides over these energy is being absorbed this increases with more weight so more oomph has to be put in.

cjw

What calculations are you talking about. Try out the model and see what it does....

You can adjust for MTB in the following;

narrow tubular tires range from - 0.004 to 0.0055
26 x 1.125 inch tires - 0.0047
27 x 1.25 inch tires - 0.0051
26 x 1.375 - 0.0066
for mountain bike tires - 0.0120

Multiplier:
Velodrome track - 1.0
Pavement - 1.1 - 1.3
Dry, hard dirt or cinder - 1.2 - 2
Wet, firm cinder/sand - 2.0 - 3.0
Deep mud - 5+
Deep, dry sand - 6+

I've just mtried it with MTB tyres and deep mud.

Time for a 20lb bike is now 7710 secs and for a 30lb 8016. So that's 5 mins over 2 hours. Now that is a bigger difference.

dave_hill

realnumber 1 wrote:

milkywhite wrote:

I seem to remember some experiment at school where you spin a disc on an axle then tip it to one side as if to replicate the leaning of a bike in a corner. Then you put on a heavier disc and repeat. The heavier disc is harder to tilt.

I'd expect it's the same with wheel weight.

Isn't that the gyroscopic effect of the wheel?
The weight makes a big difference in that case..

Correct. A heavier wheel will roll for longer once up to speed, but because of the extra weight is harder to accelerate and more resistant to changes in direction.

On a downhill bike this isn't so much of an issue because a lot of your acceleration and direction changes are gravity assisted. But for trail/XC use it can be a big help to have lighter wheels.

cjw

Dave,

But others argue that the effect is negligable...

In summary, wheels account for almost 10% of the total power required to race your bike and the dominant factor in wheel performance is aerodynamics. Wheel mass is a second order effect (nearly 10 times less significant) and wheel inertia is a third order effect (nearly 100 times less significant).

Again this for roadies so there are differences. It would be interesting to run a double blind test with DT SWISS XC1250 wheels and a few MTB racers. Have all wheels look identical, but half of the sets weighted with lead inside. Have the racers run the same courses with each set and see the times.

Bet the manufacturers wouldn't like it though - if there was no difference Swiss wouldn't be able to charge £2000 a pop

T4 Mark

I suppose it goes along the same lines as whats classified as unsprung weight on a motorcycle.
This is the amount of force generated by the wheel set. the heavier the wheels the harder it is to lean in and out of corners, again down to the gyroscopic forces exerted by a rotating object. Thats why most race bikes will run on a set of ultra light magnesium wheels

Gyroscopic forces, friction and gravity all set aside. It still appears to be down to the overall weight of the rider and the rig, although a would have to agree that the best weight saving would be on the wheels, as this is the component that needs the initial force to move the bike in the direction of travel.

Just as a note, i weighed the Rincon, it's 32kG, so the Mongoose is about 1kG Heavier. But i am willing to sacrfice a bit of time to have a smoother ride on single track and Mountain passes. Maybe i will make up the time on the decents, as i will be able to carry a bit more speed down the bumpy stuff, instead of the feeling of trying to ride a shopping trolley around Penmachno.

cjw

After all that, I've just realised from my old physics how easy this is to work out (the weight bit, not wheel inertia).

power = work/time
work = force * distance
force = mass * acceleration

Lets work it out for 1Kg over 2 hours.

Force = 1 x 9.98 = 9.98 (assuming acceleration due to gravity)

Time is 7200 seconds

Distance (ie the amount of height increase) say 1000m over 2 hours that would be a pretty hilly route.

Total work to lift 1Kg over 2 hours up 1000 = 9.98*1000 = 9980J

Power = 9980 / 7200 = 1.4 Watts.

We cycle at around 300 - 500 Watts so a 1Kg weight over 1,000m height over 2 hours would take about 0.5% extra 'effort'.

Never really thought about it going back to basics like that before....

johnsav

this getting far to technical!