Why is my new bike slower than my old one? Aero?
Discussion
I have two road bikes, and I have now come to the conclusion that my new (and more expensive) carbon bike is slower than my old Alu one when descending. On my old bike I could easily hit 65kph+ and do over 70kph if my nerves were up to it, but on the new one 65 is a real effort, even on a long and flowing Cat 2 or 3 descent.
The new bike is an Eastway RD 1.0, the old one is a Genesis Volant 00, there's about 2kg difference in weight, and the Eastway is now running a set of carbon wheels on Novatec hubs (I had been blaming the old heavy standard wheels for my lack of speed before). Both are on Michelin Pro4 Service Course tyres (25c on the Genesis, 23c on the Eastway)and run at the same pressures. The discs are set up properly on the Eastway so there is no rubbing, and both bikes have a compact chainset and the Eastway has a 11-28 cassette vs a 12-15 on the Genesis so again no reason there for the speed difference.
I'm now wondering if it's rider positioning and aero that is making the difference? The Genesis has a longer stem and slightly racier geometry (it's the 2013 model, not the more relaxed 2014) and also has deeper drop bars. I'm now thinking I need a 130mm stem and some new bars as the Eastway has a ridiculously shallow drop and the stem feels a bit too short. The Genesis riding position feels a bit more comfortable for me, which I think also has something to do with it.
For the record, I'm 186cm tall and weigh 61kg, and am fairly athletic/flexible if it makes a difference. Links to the two bikes below:
http://www.cyclingweekly.co.uk/reviews/touringauda...
http://www.bikeradar.com/road/gear/category/bikes/...
Any suggestions, before I go down the stem and bars route?
The new bike is an Eastway RD 1.0, the old one is a Genesis Volant 00, there's about 2kg difference in weight, and the Eastway is now running a set of carbon wheels on Novatec hubs (I had been blaming the old heavy standard wheels for my lack of speed before). Both are on Michelin Pro4 Service Course tyres (25c on the Genesis, 23c on the Eastway)and run at the same pressures. The discs are set up properly on the Eastway so there is no rubbing, and both bikes have a compact chainset and the Eastway has a 11-28 cassette vs a 12-15 on the Genesis so again no reason there for the speed difference.
I'm now wondering if it's rider positioning and aero that is making the difference? The Genesis has a longer stem and slightly racier geometry (it's the 2013 model, not the more relaxed 2014) and also has deeper drop bars. I'm now thinking I need a 130mm stem and some new bars as the Eastway has a ridiculously shallow drop and the stem feels a bit too short. The Genesis riding position feels a bit more comfortable for me, which I think also has something to do with it.
For the record, I'm 186cm tall and weigh 61kg, and am fairly athletic/flexible if it makes a difference. Links to the two bikes below:
http://www.cyclingweekly.co.uk/reviews/touringauda...
http://www.bikeradar.com/road/gear/category/bikes/...
Any suggestions, before I go down the stem and bars route?
In the same way it's easier for you to now ride UP a hill, it's also more difficult for you to get speed going down.
Riders used to be given water bottles full of lead at the top of mountain passes
It's amazing how much difference a very aero position makes going down a hill; try and work on that perhaps? (not with new stems, just with modifying your tuck position for example)
Riders used to be given water bottles full of lead at the top of mountain passes
It's amazing how much difference a very aero position makes going down a hill; try and work on that perhaps? (not with new stems, just with modifying your tuck position for example)
el stovey said:
Is this really a physics question about whether a heavier object will descend faster? 
I think it is a physics question actually. The weight difference in the bikes is minimal when my weight is added in (about 1.5%) but the aero difference could be fairly big.Without pedalling at all I hit 45kph freewheeling down this hill at the weekend on the old bike, I'll try it on the new one when I get time and see how that goes.
http://www.strava.com/segments/5069469
What I'm struggling with, is that the new bike has better hubs, aero rims and spokes, and a more aero frame (disc brakes excluded) so I guess it must be my position on the bike that's causing the issues.
jamiebae said:
el stovey said:
Is this really a physics question about whether a heavier object will descend faster?
I think it is a physics question actually. The weight difference in the bikes is minimal when my weight is added in (about 1.5%) but the aero difference could be fairly big.Without pedalling at all I hit 45kph freewheeling down this hill at the weekend on the old bike, I'll try it on the new one when I get time and see how that goes.
http://www.strava.com/segments/5069469
What I'm struggling with, is that the new bike has better hubs, aero rims and spokes, and a more aero frame (disc brakes excluded) so I guess it must be my position on the bike that's causing the issues.
If you've reduced friction with better hubs, components etc and the road surface is the same, if the weight is almost the same then it must be your body position. Assuming the wind was the similar.
All the other aero improvements are fairly small compared to your body position.
There could also be a little bit of new components wearing in, a tiny amount of friction somewhere could account for a 5kmph top speed difference yet not be felt under normal riding.
As you've already mentioned though, the different riding position will make much much more difference than almost anything else at that point.
Edited to add
When I shifted to shallow drop bars I found a very small difference in my flat out top end, but being able to use the drops more seemed to make it easier to maintain a higher average. Lost out a little on full tuck aero but gained a little the rest of the time.
As you've already mentioned though, the different riding position will make much much more difference than almost anything else at that point.
Edited to add
When I shifted to shallow drop bars I found a very small difference in my flat out top end, but being able to use the drops more seemed to make it easier to maintain a higher average. Lost out a little on full tuck aero but gained a little the rest of the time.
Edited by TheLemming on Tuesday 5th August 12:22
pablo said:
I'd say is probably psychological, you're probably being a little bit more cautious on the new bike given its only 5 kmh difference, in your head you know that it was expensive and carbon breaks if you tumble....
It's absolutely not caution causing the problem, if I break the bike it's just an excuse to buy another new one! The more I think about the physics of it the only real possible cause is drag, and as I think I've isolated mechanical drag it must be air resistance. If I can get lower and more stretched out on the bike then that should help, I'll also go for some slightly narrower bars to reduce frontal area a bit.even on the same bike changing the tuck position can make a huge difference on a descent. On road I know to be pretty smooth I have taken to resting my forearms on the bar tops and adopting a position more akin to what you would get using tribars. Switching from this to the standard position on drops feels like putting an air brake on, moving up to the hoods can easily knock a several mph off.
Don't ruin your normal comfortable riding position for the sake of the descent though. I recently went to a shorter stem as I was feeling a little more stretched out than I would like, my areo is probably worse but I am much more comfortable which for me is more important when on a long ride.
Don't ruin your normal comfortable riding position for the sake of the descent though. I recently went to a shorter stem as I was feeling a little more stretched out than I would like, my areo is probably worse but I am much more comfortable which for me is more important when on a long ride.
The old bike feels a bit more comfortable to me as well, so I think that even with a large frame size the geo of the carbon bike doesn't suit me as well. I'm thinking that with a more stretched out position I'll be more aero as well as more comfy so it should be a win/win.
I tend to always be on the drops when descending, as it makes it easier to grab a handful of brake without unsettling the bike when moving from the top of the bars.
I think I will hit Wiggle this evening (after measuring my shoulder width), order a few bits and see what a difference it makes with a change of bars and stem.
I tend to always be on the drops when descending, as it makes it easier to grab a handful of brake without unsettling the bike when moving from the top of the bars.
I think I will hit Wiggle this evening (after measuring my shoulder width), order a few bits and see what a difference it makes with a change of bars and stem.
How does it feel climbing? I assume on average you will be faster over a ride, so wouldn't worry about the descending speed too much.
I think its just to do with the momentum of the heavier wheels that keep your speed up on the descents, i found the same going from a standard to lightweight flywheel on an old car.
I think its just to do with the momentum of the heavier wheels that keep your speed up on the descents, i found the same going from a standard to lightweight flywheel on an old car.
okgo said:
Why exactly do you care how fast you are going down a hill?
Because I enjoy it. Also, I'm probably missing out on some efficiency on the flat as well and I want to know why, but it's most noticeable going downhill as my Garmin makes it pretty clear that I'm losing a good 5-10kph on a lot of descents.jamiebae said:
okgo said:
Why exactly do you care how fast you are going down a hill?
Because I enjoy it. Also, I'm probably missing out on some efficiency on the flat as well and I want to know why, but it's most noticeable going downhill as my Garmin makes it pretty clear that I'm losing a good 5-10kph on a lot of descents.
A quick measure up of the two bikes shows the old one has a 130mm stem, the new one a 100mm so that'll be making a bit of a difference. Both have 440mm bars but I'm going to order some 420mm ones with a deeper drop which are more similar in profile to the Genesis ones and see how I get on with them.
A new Garmin is tempting, as I'd like maps but maybe that's one purchase too far, for this month at least...
A new Garmin is tempting, as I'd like maps but maybe that's one purchase too far, for this month at least...
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