Bike weights, make much difference ?

vegnomeat

Hi,

Around 6 weeks ago I returned to cycling (after 30 years spent running) and purchased a Carrera subway from Halfords.

6 weeks later I find that I have a few questions, if someone would be so kind as to answer.

Does the weight of a bike make much difference to it's speed ? ie, will you go quicker for the same effort on a lighter bike, and by how much ?

Is there an optimum riding position, I have experimented with lots of positions (oohh er missus) and can't seem to find the optimum position.

Do thinner tyres help, I only ride on the road and the tyres on the Carrera are pretty wide with a large contact patch.

Regards

veggie

idaviesmoore

vegnomeat wrote:

Hi,
Does the weight of a bike make much difference to it's speed ? ie, will you go quicker for the same effort on a lighter bike, and by how much ?

Losing weight is better, overall, than having a light bike. But I'm not saying you shouldn't have a feather light. But for starters your Carrera is just dandy.

However, don't discount the psychological advantage having a very light bike will give you

alfablue

I just got a Planet-X SL Pro Carbon Dura Ace, approx 8kg. Compared to my Dawes Audax (Reynolds 531 steel) it is quicker. This could be partly down to the psychological effect. Ride position could affect it too (more aero) but I have this set up more or less the same. The bike itself is also more aero, and has deeper section wheels with bladed spokes. The biggest difference was with climbing, even though the gearing is higher (compact 50/34, 12/27 cassette on the PX versus triple 52/44/30, 11-27 cassette on the Dawes) the PX flies up hills. Although the bike is probably 2kg lighter than the Dawes I suspect the main difference is wheel weight, the PX has "Model B" wheels with lightweight tubes and tyres, and very smooth running hubs, and I think they may be up to 700g lighter (maybe more) than my Open Pro 36 hole wheels on the Audax, it is said that revolving weight is far more important than total bike weight. My cruising speed on the flat is also higher by about 2mph, which I would have thought was less to do with weight, however.

Narrower, slick, lighter tyres may make a worthwhile difference for you.

Alex_Simmons/RST

vegnomeat wrote:

Does the weight of a bike make much difference to it's speed ? ie, will you go quicker for the same effort on a lighter bike, and by how much ?

The only times where additional mass will have significant impact on speed is for climbing hills and for accelerating. The latter is only of concern if you are planning to race and need to sprint. Even then, the dynamics of the frame and the rider's sprint abilities are far more important that the bike's mass.

When climbing hills, as the gradient gets steeper, then the speed difference will be roughly in proportion to the change in total mass. So if you + light bike = 85kg and you + heavy bike = 87kg, then up a steep climb you'll be roughly 2% slower on the heavy bike at the same power output.

vegnomeat

Thanks for the replies,

I am currently riding around 100 miles a week (commuting) and manage about 25 on a Saturday.

My previous running career (hampered by shortened achilles) was a mix of marathons and half marathons (over 150). However, now I am cycling I have gotten the bug to be quicker. I find that I can average around 17 miles an hour for 15 miles and am looking at ways to lower my times.

Hence the question about weight and optimum riding position.

Regards

veggie

alfablue

great answer Alex!

synchronicity

Light bikes tend to help when you're climbing, especially as the gradient becomes steeper. They're also quicker to accelerate.

But it is a very subtle thing; if you don't have the fitness, you won't appreciate it. I got my road bike down to 6.2kg when I myself weighed about 67kg. Now I'm more like 73 kg, so a slightly heavier bike is okay (probably better for me). With some heavier wheels, the bike probably weighs around 6.8kg...

Light bikes don't descend well in my opinion. Add to that the fear of something lightweight breaking at high speed... I'll actually be buying a second road bike soon which will be in the 8.5kg ballpark and looking forward to it.

So long as it weighs under about 9 or 10kg it's alright!

tiny_pens

Tyre width is another of cyclings white elephants. The actual width of a tyre doesn't affect the speed in any noticable way for the purposes of commuting. Even when racing I would question the real gains to be had.

What does make a difference is rolling resistance. This is probably most easily assessed by looking at tyre pressure ranges. This is an oversimplification of course but one that seems to work in general.

Consider:
Typical racing bike tyre pressure is in the region of 120psi
Typical mountain bike tyre pressure is in the region of 35psi.

Leads you to believe that higher tyre pressures will result in a faster tyre with all other things being equal which is pretty much what you expect to see in the real world.

So what does this all mean. Well I believe that the carrera subway tyres are rated from 40psi to 60psi. I would reckon that the difference for your average between the max and min tyre pressures would be 1-2mph so you would be wanting to make sure the pressure was at the maximum on a fairly regular basis.
The highest pressure slicks I have personally seen for a 26" wheel were about 100psi (rare 1" mtb slicks). I would estimate you might get another 1-2mph (aero efficiency would diminish the returns) if you could track them down.

Then of course you would want to change the wheels. Lighter wheels would accelerate faster and with better hubs would roll better giving you another 1-2mph advantage. Plus if you got disc compatible hubs you could reuse the wheels if you ever upgraded the bike


Tiny Pens

tiny_pens

Tyre width is another of cyclings white elephants. The actual width of a tyre doesn't affect the speed in any noticable way for the purposes of commuting. Even when racing I would question the real gains to be had.

What does make a difference is rolling resistance. This is probably most easily assessed by looking at tyre pressure ranges. This is an oversimplification of course but one that seems to work in general.

Consider:
Typical racing bike tyre pressure is in the region of 120psi
Typical mountain bike tyre pressure is in the region of 35psi.

Leads you to believe that higher tyre pressures will result in a faster tyre with all other things being equal which is pretty much what you expect to see in the real world.

So what does this all mean. Well I believe that the carrera subway tyres are rated from 40psi to 60psi. I would reckon that the difference for your average between the max and min tyre pressures would be 1-2mph so you would be wanting to make sure the pressure was at the maximum on a fairly regular basis.
The highest pressure slicks I have personally seen for a 26" wheel were about 100psi (rare 1" mtb slicks). I would estimate you might get another 1-2mph (aero efficiency would diminish the returns) if you could track them down.

Then of course you would want to change the wheels. Lighter wheels would accelerate faster and with better hubs would roll better giving you another 1-2mph advantage. Plus if you got disc compatible hubs you could reuse the wheels if you ever upgraded the bike


Tiny Pens

alfablue

If you want those elusive 26x1 slicks then there are the Specialized All Conditions Pro's. I have done thousands of miles commuting with these, fast,light, grippy, zero punctures, rated at 115-125psi. Review.

vegnomeat

Might be a bone question, but do these tyres use inner tubes ?

veggie

roger_merriman

most road tires need inner tubes unless tubs or tubless which i think you can get some.

so the answer is yes you need inner tubes

alfablue

vegnomeat wrote:

Might be a bone question, but do these tyres use inner tubes ?

veggie

yes they do, 26x1" inner tubes are not that common, but I got some specialized ones with no problem.

alfablue

Nutrak ones in 26x1.0-1.25 here.

vegnomeat

Thanks gents,

This is a really excellent resource, made possible by all of you

Thanks again

antfly

If narrow tyres don`t make you quicker why is no-one racing on wide ones?I`ve just switched from 25mm to 23mm and go about 1mph faster which is a far bigger jump than I would get if I changed anything else on the bike.

cakewalk

antfly wrote:

If narrow tyres don`t make you quicker why is no-one racing on wide ones?I`ve just switched from 25mm to 23mm and go about 1mph faster which is a far bigger jump than I would get if I changed anything else on the bike.

Excellent news. I was just about to go the other way!

alfablue

antfly wrote:

If narrow tyres don`t make you quicker why is no-one racing on wide ones?I`ve just switched from 25mm to 23mm and go about 1mph faster which is a far bigger jump than I would get if I changed anything else on the bike.

If I understand correctly, I think Tiny Todger is suggesting that narrow tyres = higher pressure = lower rolling resistance, so it is the pressure that permits this, but it is a bit of a moot point.

antfly

Rolling resistance varies with different tyres aswell,of course.I`m running my new ones at the same pressure as my wider ones,so it can`t be the pressure.
I`m now using conti GP 4000s which I thoroughly reccommend.I will say that the wider tyres were noticeably more comfortable so it`s a trade off between comfort and speed.

tiny_pens

antfly wrote:

If narrow tyres don`t make you quicker why is no-one racing on wide ones?I`ve just switched from 25mm to 23mm and go about 1mph faster which is a far bigger jump than I would get if I changed anything else on the bike.

I would imagine that its because its easier to make a stiffer sidewall to the tyres. The stiffer sidewall would contribute to a lower rolling resistance.

HTH

oldwelshman

tiny_pens wrote:

Tyre width is another of cyclings white elephants. The actual width of a tyre doesn't affect the speed in any noticable way for the purposes of commuting. Even when racing I would question the real gains to be had.

What does make a difference is rolling resistance. This is probably most easily assessed by looking at tyre pressure ranges. This is an oversimplification of course but one that seems to work in general.

Consider:
Typical racing bike tyre pressure is in the region of 120psi
Typical mountain bike tyre pressure is in the region of 35psi.

Leads you to believe that higher tyre pressures will result in a faster tyre with all other things being equal which is pretty much what you expect to see in the real world.

So what does this all mean. Well I believe that the carrera subway tyres are rated from 40psi to 60psi. I would reckon that the difference for your average between the max and min tyre pressures would be 1-2mph so you would be wanting to make sure the pressure was at the maximum on a fairly regular basis.
The highest pressure slicks I have personally seen for a 26" wheel were about 100psi (rare 1" mtb slicks). I would estimate you might get another 1-2mph (aero efficiency would diminish the returns) if you could track them down.

Then of course you would want to change the wheels. Lighter wheels would accelerate faster and with better hubs would roll better giving you another 1-2mph advantage. Plus if you got disc compatible hubs you could reuse the wheels if you ever upgraded the bike


Tiny Pens

Of course weight of bike and tyre width have no effect, thats why Chris HOy rode a MTB with 1.75" tyres for the spint !!

felgen

ooh... some top tyres there - thanks for the pointers.... found some more as well....wihch are rated to 125 psi (no weight quoted though)
http://www.chainreactioncycles.com/Models.aspx?ModelID=18797

or these... look a bargain...though they dont say what pressure they can take
http://www.chainreactioncycles.com/Models.aspx?ModelID=14593

Alex_Simmons/RST

Narrow high pressure road tyres are faster for road conditions. However, within road tyres, there are still wide variations in rolling resistance. There are some technical forums that collate data on which tyres are the fastest.

Once you venture off good surfaces however, other considerations comes into play making such tyres inappropriate.

Wheel weight has very very little to do with rolling speed. If that were the case then disk wheels would be slow. What matters for rolling speed is aerodynamics. Always ahead of wheel mass.

Road Red

Alex_Simmons/RST wrote:

vegnomeat wrote:

Does the weight of a bike make much difference to it's speed ? ie, will you go quicker for the same effort on a lighter bike, and by how much ?

The only times where additional mass will have significant impact on speed is for climbing hills and for accelerating. The latter is only of concern if you are planning to race and need to sprint. Even then, the dynamics of the frame and the rider's sprint abilities are far more important that the bike's mass.

When climbing hills, as the gradient gets steeper, then the speed difference will be roughly in proportion to the change in total mass. So if you + light bike = 85kg and you + heavy bike = 87kg, then up a steep climb you'll be roughly 2% slower on the heavy bike at the same power output.

Can that be extrpolated to meaning that each kg leads to a 1% increase/decrease in speed?

alfablue

felgen wrote:

ooh... some top tyres there - thanks for the pointers.... found some more as well....wihch are rated to 125 psi (no weight quoted though)
http://www.chainreactioncycles.com/Models.aspx?ModelID=18797

or these... look a bargain...though they dont say what pressure they can take
http://www.chainreactioncycles.com/Models.aspx?ModelID=14593

Don't know about the WTB's but the conti's wear quick and are puncture prone c/w the specialized.

antfly

Road Red wrote:

Alex_Simmons/RST wrote:

vegnomeat wrote:

Does the weight of a bike make much difference to it's speed ? ie, will you go quicker for the same effort on a lighter bike, and by how much ?

The only times where additional mass will have significant impact on speed is for climbing hills and for accelerating. The latter is only of concern if you are planning to race and need to sprint. Even then, the dynamics of the frame and the rider's sprint abilities are far more important that the bike's mass.

When climbing hills, as the gradient gets steeper, then the speed difference will be roughly in proportion to the change in total mass. So if you + light bike = 85kg and you + heavy bike = 87kg, then up a steep climb you'll be roughly 2% slower on the heavy bike at the same power output.

Can that be extrpolated to meaning that each kg leads to a 1% increase/decrease in speed?

No.He should have said if you plus the bike = 100kg then his percentage would have been more accurate.Obviously the heavier you are the harder it is to go uphill so twice the weight probably means twice the effort,not half the speed.There must be an equation in physics that deals with this.Anyone?

zenzinnia

The Subway maybe a good commuting and general use bike but it isn't built for speed or going longer distances at speed on the road. You should realy be looking at something with drop handlebars and racing geometry so that you can get a more aerodynamic position. A good race bike will pay dividends and - given that you used to do long distance running - it should be able to make longer rides far quicker. It's not just about weight or even aerodynamics but handling, brake performance comfort over longer time (additional hand positions) and more I'm sure.

However if you just want speed then try looking into time trialling and the related bikes with special bars, wheels and aerodynamics.

simon_e

'Optimum' riding position? That depends if you want comfort (upright, nearly all of your weight on the saddle) or speed (head down, back nearly horizontal, more weight on the bars) or somewhere in between. When I first returned to a road (racing) bike I found the position too stretched out for my liking, and it has taken a while for it to be really comfortable.

Aerodynamics apart, tyres and wheels seem to make the most difference to how quickly you go for given amount of effort. Lighter, narrower, smooth tyres pumped up hard will roll much better than the OE fat treaded ones normally fitted (and no, you don't need tread on road tyres, even in the wet).

One trick I amused myself with when commuting on my MTB was to adopt a low position with my wrists resting near the middle of the bars like time trialists (but only on straight, empty sections of road or cyclepath, I hasten to add!). Bending down and tucking in like this gave me 1.5~2km/h gain for no extra effort.

Clipless pedals and shoes help, they reduce the amount of your effort is wasted. The double-sided SPD pedals are probably better for general riding and the shoes are usually easier to walk in than the true road type. And cheaper

Alex_Simmons/RST

antfly wrote:

Road Red wrote:

Alex_Simmons/RST wrote:

vegnomeat wrote:

Does the weight of a bike make much difference to it's speed ? ie, will you go quicker for the same effort on a lighter bike, and by how much ?

The only times where additional mass will have significant impact on speed is for climbing hills and for accelerating. The latter is only of concern if you are planning to race and need to sprint. Even then, the dynamics of the frame and the rider's sprint abilities are far more important that the bike's mass.

When climbing hills, as the gradient gets steeper, then the speed difference will be roughly in proportion to the change in total mass. So if you + light bike = 85kg and you + heavy bike = 87kg, then up a steep climb you'll be roughly 2% slower on the heavy bike at the same power output.

Can that be extrpolated to meaning that each kg leads to a 1% increase/decrease in speed?

No.He should have said if you plus the bike = 100kg then his percentage would have been more accurate.Obviously the heavier you are the harder it is to go uphill so twice the weight probably means twice the effort,not half the speed.

That's not what I should have said at all. What I should have said is exactly what I said, i.e. :"the speed difference will be roughly in proportion to the change in total mass".

I wasn't attempting to provide a precise indicator of the impact of 1kg as there are many variables to consider, not least of which is the actual gradient and current total mass. While somewhat reduced when climbing, the impacts of rolling resistance, drivetrain friction and air drag are still factors.

Even if you mean 1kg on a 100kg total mass, then it still won't precisely = a 1% decrease in speed at same power. But it's close enough on steep gradients.

antfly wrote:

There must be an equation in physics that deals with this.Anyone?

There is.

If you really want to know the answer, then all you have to do is solve the equations of motion for a cyclist or use a good on-line calculator. See this link for details:

http://www.bikeradar.com/forums/viewtop ... 7#14994767

antfly

Thanks for the links but it`s a bit complicated.
"Even if you mean 1kg on a 100kg total mass, then it still won't precisely = a 1% decrease in speed at same power. But it's close enough on steep gradients. "

That`s pretty much agreeing with what I said - 1kg less than 100kg would be closer to 1% than 1kg out of 87kg, even roughly.

Alex_Simmons/RST

antfly wrote:

Thanks for the links but it`s a bit complicated.
"Even if you mean 1kg on a 100kg total mass, then it still won't precisely = a 1% decrease in speed at same power. But it's close enough on steep gradients. "

That`s pretty much agreeing with what I said - 1kg less than 100kg would be closer to 1% than 1kg out of 87kg, even roughly.

Well it won't actually. I provided the link so you could check it....... Complicated? It's just plugging a few numbers into the analyticcycling.com calculator - and you did express interest in seeing the physics equations for it.

A rider with a total bike + rider mass of 100kg up say a 7% gradient, will go 0.9% slower at same power if you add 1kg of mass.

An 87kg bike + rider mass will go 1.0% slower at same power if you add 1kg of mass.