Measureable speed difference between Alu and Carbon frames
Discussion
I have just changed my road bike from a fairly harsh-riding aluminium frame to a carbon fibre frame, and I have been looking at Garmin data logs from laps around a well known cycle route. The thing that really stuck out was the descent speed down the steep hill with a right-hand bend in it.
On the aluminium bike, the top speed would be never more than 40mph. On the carbon bike, I did three laps, and the speed was 48mph, followed by 49mph followed by 47mph.
Its an amazing difference, and I put it down to the aluminium bike vibrating and fidgeting towards the outside kerb, whilst the carbon bike soaked up the bumps far better and held its line.
On the aluminium bike, the top speed would be never more than 40mph. On the carbon bike, I did three laps, and the speed was 48mph, followed by 49mph followed by 47mph.
Its an amazing difference, and I put it down to the aluminium bike vibrating and fidgeting towards the outside kerb, whilst the carbon bike soaked up the bumps far better and held its line.
I don't buy into the whole "carbon absorbs shocks" stuff compared to ally!
If you do the maths based on material stiffness between carbon and alluminium, yes the carbon IS stiffer, but the ally is already so stiff that it doesn't make really any difference in the actual laods that are transmitted. If you had a frame made of say rubber, then yes, there would be enough deflection (under the typical loads imposed) that vibrations would be damped all the way down to very low frequencies. But between Ally and carbon? at frequecies the human hand can differentiate??
Just try this: Flick your nail against an ally frame and it goes "thunk", do the same for a carbon frame and it's natural frequency looks to be about 15-20% higher. But that is 20% higher than what looks to be about 900Hz. You are not going to get significant deflection (at the handlebars etc) at 700 or 900hz!
I suspect the differences people feel are in the rest of the bike, tyres, tyre pressures, suspension friction and damping etc etc. How many people have ridden an ally bike, then swapped every part without change to an identical frame but one made of carbon??? Not many i'd wager ;-)
If you do the maths based on material stiffness between carbon and alluminium, yes the carbon IS stiffer, but the ally is already so stiff that it doesn't make really any difference in the actual laods that are transmitted. If you had a frame made of say rubber, then yes, there would be enough deflection (under the typical loads imposed) that vibrations would be damped all the way down to very low frequencies. But between Ally and carbon? at frequecies the human hand can differentiate??
Just try this: Flick your nail against an ally frame and it goes "thunk", do the same for a carbon frame and it's natural frequency looks to be about 15-20% higher. But that is 20% higher than what looks to be about 900Hz. You are not going to get significant deflection (at the handlebars etc) at 700 or 900hz!
I suspect the differences people feel are in the rest of the bike, tyres, tyre pressures, suspension friction and damping etc etc. How many people have ridden an ally bike, then swapped every part without change to an identical frame but one made of carbon??? Not many i'd wager ;-)
Regardless of the individual properties of the material, the carbon bike feels like it is floating compared to the aluminium bike, which is always buzzing. A lot of this might be down to frame shape of course. The alu bike had almost totally straight seat-stays for example, which probably account for a large part of that road feedback.
as a recet convert from ally to carbon, i think its a lot to do with the frame absorbing the road buzz and vibrations through the material and the tubes whereas ally frames just seem to send it directly to the rider as quickly as possible. a gopod carbon frame acts like a damper especially if the wrap is deisnged to absorb the shock rather than for outright stiffness...
itsnotarace said:
It's not the material, it's the design.
Wheelbase
Fork rake
Fork axle-to-crown length
Fork symmetry
Stem length
Rider position on the bars
Rider tightness of grip on the bars
Rider centre of gravity
All of these can have a measurable effect on high speed stability.
+1. And what tyres you have and the pressure their at.Wheelbase
Fork rake
Fork axle-to-crown length
Fork symmetry
Stem length
Rider position on the bars
Rider tightness of grip on the bars
Rider centre of gravity
All of these can have a measurable effect on high speed stability.
Ive not spent significant time on an alu bike to pin-point exact differences, but i can say I can easily feel the carbon bikes flexiblem points and its stiff points. Cannondale "claim" to build in stiffness or flex depending on where its needed, sometimes varying across just one tube. Its apparently to do with the weave of the carbon(?) Another example is the rear end on a Scalpel, which relies on just flex in the chainstay to make us of the rear shock - no pivot points!
I can say I definitely need to reduce my stack height now that Im abit more used to it. There is a load of flex coming from that area that is most unwelcome on climbs. But I was expecting that and wanted to ease myself into the full race no-stack, flat-stem lunacy.
I can say I definitely need to reduce my stack height now that Im abit more used to it. There is a load of flex coming from that area that is most unwelcome on climbs. But I was expecting that and wanted to ease myself into the full race no-stack, flat-stem lunacy.
Edited by Reardy Mister on Thursday 26th April 13:31
Kermit power said:
Maybe it's just the photo angle, but it looks like there's a massive difference in saddle angle, with the top one sloping forward and the bottom flat or even sloping backwards.
Don't know whether that would affect downhill speed though?
When those photos were taken, I hadn't even ridden the Pinarello, let alone set it up correctly. The saddle angle is equally wrong on the BH, because that bike is now for sale and I just put a new saddle on it for that photo. Don't know whether that would affect downhill speed though?
Mr Gear said:
Kermit power said:
Maybe it's just the photo angle, but it looks like there's a massive difference in saddle angle, with the top one sloping forward and the bottom flat or even sloping backwards.
Don't know whether that would affect downhill speed though?
When those photos were taken, I hadn't even ridden the Pinarello, let alone set it up correctly. The saddle angle is equally wrong on the BH, because that bike is now for sale and I just put a new saddle on it for that photo. Don't know whether that would affect downhill speed though?
Mr Gear said:
Aluminium bike:
Quote from Nic Crumpton, custom framebuilder http://www.crumptoncycles.com/"9 times out of 10 when someone complains to me about speed wobbles they are on a huge bike with a tiny stem jacked up and the front wheel totally unweighted."
Any bells ringing yet?
itsnotarace said:
Quote from Nic Crumpton, custom framebuilder http://www.crumptoncycles.com/
"9 times out of 10 when someone complains to me about speed wobbles they are on a huge bike with a tiny stem jacked up and the front wheel totally unweighted."
Any bells ringing yet?
Tiny stem? Hardly."9 times out of 10 when someone complains to me about speed wobbles they are on a huge bike with a tiny stem jacked up and the front wheel totally unweighted."
Any bells ringing yet?
Jacked-up? Less than half-way.
Huge bike? Nope.
Speed wobbles? Not at all. It was fantastically stable, but gave a harsh ride over all but the smoothest of surfaces.
EDIT: Just out of interest, why are you trying to be such a smart-arse?
Edited by Mr Gear on Thursday 26th April 14:05
orly? yet your wrote
All aluminium bikes ride exactly the same
All carbon bikes ride exactly the same
All steel bikes ride exactly the same
All titanium bikes ride exactly the same
The geometry and the frame design have absolutely no bearing over how a bike rides whatsoever
You are so in tune with your tyre pressures you can sense when they are 1 psi out
If you were blindfolded and rode a bike on a turbo trainer you could tell exactly what frame material it's made out of
Mr Gear said:
I put it down to the aluminium bike vibrating and fidgeting towards the outside kerb, whilst the carbon bike soaked up the bumps far better and held its line.
I give up. You win.All aluminium bikes ride exactly the same
All carbon bikes ride exactly the same
All steel bikes ride exactly the same
All titanium bikes ride exactly the same
The geometry and the frame design have absolutely no bearing over how a bike rides whatsoever
You are so in tune with your tyre pressures you can sense when they are 1 psi out
If you were blindfolded and rode a bike on a turbo trainer you could tell exactly what frame material it's made out of
itsnotarace said:
orly? yet your wrote
Not the same as speed wobbles at all. It's not even instability. It feels like the tyres skipping across the tarmac at a fairly predictable rate.Mr Gear said:
I put it down to the aluminium bike vibrating and fidgeting towards the outside kerb, whilst the carbon bike soaked up the bumps far better and held its line.
itsnotarace said:
I give up. You win.
All aluminium bikes ride exactly the same
All carbon bikes ride exactly the same
All steel bikes ride exactly the same
All titanium bikes ride exactly the same
The geometry and the frame design have absolutely no bearing over how a bike rides whatsoever
I didn't say ANY of that did I? What are you trying to prove? I even added a pair of pictures to show that the frame shape is significantly different. I totally agree with you on this, so why are you suggesting I disagree? Bizarre.All aluminium bikes ride exactly the same
All carbon bikes ride exactly the same
All steel bikes ride exactly the same
All titanium bikes ride exactly the same
The geometry and the frame design have absolutely no bearing over how a bike rides whatsoever
itsnotarace said:
You are so in tune with your tyre pressures you can sense when they are 1 psi out
If you were blindfolded and rode a bike on a turbo trainer you could tell exactly what frame material it's made out of
My turbo trainer is pretty smooth, so to be honest I wouldn't expect any vibes through it no matter what bike I was on.If you were blindfolded and rode a bike on a turbo trainer you could tell exactly what frame material it's made out of
What's your problem exactly?
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