Trek Cytronex - First Impressions.

[coops]

Yes, and climbing a 15% hill with 20-25% sections is all the more creditable given the extra 2 stone you said you're carrying!

I just don't want others, who think they might be equally 'unfit', to be disappointed if they didn't get similar performance and I think they'd be miscalculating if they think they would: its very complicated to assess how the same bike will perform with different rider inputs and so exact figures are rather 'pie in the sky' but I wouldn't expect an average strength rider to manage those gradients, speeds or ranges on a bike with those specs.

I'd estimate (based on all the figures) about 10% to be an approximate gradient limit for gentle pedalling on the cytronex and up to around 12% for moderately strong input, and thats for a rider of 13 stone or 83kg.

And its already been alluded in the other thread that you might get 20 miles range (at 15mph) with moderate pedalling & in ideal conditions, but with gradients or winds that would take rather stronger pedalling .

Stuart.

 

[Cyclezee]

Chris
Have you thought about fitting a prop stand and a battery lock?
I know Mark was looking into fitting a battery lock which I think is fairly essential.

As for the fitness thing, although a decade or so younger than you, I hit the scales this morning at 103Kg Four years ago, I got myself down from 111Kg to 82Kg, the ideal weight for my body mass index. Personally, I think my ideal weight is 90Kg due to my fairly large frame and that is what I am aiming to acheive by sensible eating, which is all I did to get down to 82Kg, and to be honest was not that difficult, just requiring self disipline

I have a sedentry occupation and am a mild asthmatic so I want to cycle to improve my cardio vascular system and this seems to be working, no wheezing and less reliance on medication.

I'm hoping the Cytronex, being more like a normal bike will force me to ride it more like a normal bike, with just enough assistance when I really need it.
The Agattu is great and I love it, but almost too easy with all the assistance I need, but, in my opinion too heavy to pedal unassisted.
With bikes like the Torq and Wisper, I found it all too easy just to open the throttle and wizz around which although great fun, is not really cycling and does very little to improve fitness.
However, it was bikes like that which got me back on 2 wheels after a gap of 20 years.

Sorry if this is a bit of a ramble and a bit off thread

J hn

 

[Chris_Bike]

I think you have got it absolutely spot on John. I have loved cycling and bikes all my life and I certainly don't want to ride a bike like a moped. So I expect to pedal on a hill. But yesterday's ride involved pedaling on the hills (and they are proper hills) not much harder than I did on the flat without the motor. Many people underestimate the importance of the weight of the bike (and especially rolling weight) to climbing ability, and that is certainly one area where the Trek scores. (Though I can see lots of areas where I could reduce weight further!). As to range, if you let the motor pull you along all the time you will certainly get less than 20 miles per charge. But, as I wrote in the other thread, what's the point of that?

My wife wants a prop stand so I am on the lookout for one. I think Mark intends to start manufacturing batteries with loops to take a D lock as you lock the bike up. I always just take the battery with me when I lock the bike.

I'm at at town centre race in Brentford this morning with my son - sadly no opportunity to ride the Trek, though I hope to get back to it this evening.

Chris

 

[coops]

I certainly don't want to ride a bike like a moped. So I expect to pedal on a hill. But yesterday's ride involved pedaling on the hills (and they are proper hills) not much harder than I did on the flat without the motor.

They are all pedal-assist bikes so pedalling is always expected and especially so on hills. Your relatively small variation in power level between flats & hills is usual for power-assist riding on suitable terrain, and if your power level on the flat is high then clearly even a small increase for hills would give strong hill-climbing ability.

Many people underestimate the importance of the weight of the bike (and especially rolling weight) to climbing ability, and that is certainly one area where the Trek scores. (Though I can see lots of areas where I could reduce weight further!). As to range, if you let the motor pull you along all the time you will certainly get less than 20 miles per charge. But, as I wrote in the other thread, what's the point of that?

A bike weight difference of a few kg makes little difference to climbing ability, even on a non-motorised bike and as has been said some will get significantly less than the 20 miles 'average' range even with moderate pedalling with the motor and not being just pulled along by the motor.

Stuart.

 

[oldosc]

As for the fitness thing, although a decade or so younger than you, I hit the scales this morning at 103Kg Four years ago, I got myself down from 111Kg to 82Kg, the ideal weight for my body mass index.
I have taken exception with my doctor over this (a bit)
I claim your bmi increases with age due to the way it is calculated..At 18 I was 6..5" at 70 I am 5.10" (nearly),this is due to compression of the inter leave disks in my spine (all 32 of them,this is usual with ageing nothing to do with increased roast potato, and beer (honest)

 

[Chris_Bike]

A bike weight difference of a few kg makes little difference to climbing ability.

Try telling that to Lance Armstrong!

 

[coops]

A few kg extra would still only equate to a few percent less climb speed, even for Lance Armstrong.

Other people are more likely to overlook the usually larger negative impact of excess bodyweight on climbing ability, about a 12% penalty for both of us, for example, which I imagine the likes of Lance Armstrong should tackle as a first priority.

P.S. On the subject of weight watching, I find body fat percentage measurement a much better guide to optimum weight than BMI, oldosc.

Stuart.

 

[Chris_Bike]

I fear we may be boring others...... But, whilst most climbers over the years have been slight (Charly Gaul, Robert Miller). Others like Armstrong were of average weight (for a competitive cyclist) and some like Indurain, and Merckx before him, were actually quite heavy. They were all fit and all sought advantage by using the lightest bikes available in the mountains, weight in the wheels (and especially the drive wheel and the rims) making the greatest difference. As a fatty, I can get up a hill best on my lightest bike. My 1980s Pinarello beating the Cytronex easily (unless I turn on the motor!).

Chris

 

[coops]

Interesting (to me!) Chris I suppose once we're fit & optimum weightwise a lighter bike will be one of the best gains available, whereas until then its our best hope to get up hills!

I was quite surprised to learn that weight reduction off the wheel counts for double that weight from the frame, but how to apply that to hub motor wheels is beyond me - one for the engineers! (and probably for another thread as you say... )

Stuart.

 

[Chris_Bike]

Interesting (to me!) I was quite surprised to learn that weight reduction off the wheel counts for double that weight from the frame, but how to apply that to hub motor wheels is beyond me - one for the engineers! (and probably for another thread as you say... )

Stuart.

Triuble is, you've got me going on an issue that interests me.........

From first principles, and a base of knowledge from non-electric bikes, I would expect the following. All other things being equal (motor drag etc), a front hub motor should be better that a rear one (it's still the rear wheel we turn with our legs) but direct drive through the chain might be expected to be better than both (motor weight isolated from rolling weight).

That said there are plenty of other things to confound the above....... Hub gears offer more frictional resistance that derrailleur gears (if the latter are properly maintained), they also weigh considerably more.

When it comes to weight in the wheel, I wouldn't assert it is necessarily twice as important than weight in the frame (though it might well be). There's been a lot of work put into assessing the efficiency of modern racing wheels (see a French Site called Roues Artinasal: http://www.rouesartisanales.com/article-2141818.html: ). The most importand determinants of performance are thought to be aerodnamics (crucial at speed) and inertia (mostly related to weight and determining the effort to get , and keep, the wheel moving). The search for aerodynamics has led to fewer, specially shaped spokes and deeper rims. Reducing inertia has led to lighter wheels and the use of carbon fibre, especially in the rims. The rims matter much more that the hubs, because the further the weight is from the point of rotation, the greater the force required to move it.

So....... If I was trying to improve the climbing ability of the Trek (or any other bike) I would try to save weight, but especially rotating weight. A good pair of modern racing wheels can weigh as little as 1Kg. The Trek's weigh twice this, even without the motor. I would try lighter rims and lighter, livlier tyres thereby losing puncture resistance!) Elsewhere, a good pair of cyclo cross carbon forks, perhaps carbon bars and a lighter chainset. I guess all that could get 1.5Kg + off the weight, but it could cost £500, even building the wheels yourself!

Train journey nearly over, so I guess I had better leave it here.

Chris

 

[john]

So....... If I was trying to improve the climbing ability of the Trek (or any other bike) I would try to save weight, but especially rotating weight.

Weight at the wheel rim counts twice as much as weight on the frame, but only for acceleration, not hill climbing.

This is because the wheel rim travels at twice the speed of the frame and so must be given twice the acceleration to achieve this. That isn't an issue when traveling uphill where all weight counts the same (including the weight of the rider!)

 

[Chris_Bike]

Weight at the wheel rim counts twice as much as weight on the frame, but only for acceleration, not hill climbing.

This is because the wheel rim travels at twice the speed of the frame and so must be given twice the acceleration to achieve this. That isn't an issue when traveling uphill where all weight counts the same (including the weight of the rider!)

Hang about John, why do you assert that the rim travels twice as fast as the bike? The speed of the outer circumference of the tyre (which is in contact with the road) is, by definition, the same as the road speed on the bike. Indeed, this is how bike computers calculate your speed (and the reason why you have to enter your tyre size into the computer). As to the effect of climbing and wheel weight, I can only suggest you compare a few wheels in the same bike frame. I have, and I can assure you that my son's Bontrager XXX's (weight about 1200 gms) take a damn site less effort to get up a hill than his winter training wheels at twice the weight.

Chris

 

[the_killjoy]

I had always assumed one of the main affects of the bike weight was in terms of the sprung/unsprung weight.

 

[john]

Hang about John, why do you assert that the rim travels twice as fast as the bike? The speed of the outer circumference of the tyre (which is in contact with the road) is, by definition, the same as the road speed on the bike. Indeed, this is how bike computers calculate your speed (and the reason why you have to enter your tyre size into the computer).
Chris

The computer measures the speed of the tyre relative to the frame, but that doesn't help us much anyway as it is just counting rotations.

Yes, the tyre is rotating at the speed of the road, but the whole wheel is also moving forward at the speed of the road too.

Let my try to explain like this...

Imagine you are on your bike traveling at 5 mph on ice with the brakes on, locking the wheels (entirely hypothetical). Clearly everything including the wheels is traveling at 5 mph. Now let go of the brakes and spin the wheels to roll with the road (lets say pedal for the back wheel and motor for the front). They are now rotating at 5 mph at the rim. It took 2 lots of 0-5 mph acceleration to get there.

 

[john]

Elsewhere, a good pair of cyclo cross carbon forks
Chris

You would need to be careful putting the motor into these forks, at least adding a substatial torque arm which might cancel out the weight saving.

 

[Chris_Bike]

The computer measures the speed of the tyre relative to the frame, but that doesn't help us much anyway as it is just counting rotations.

Yes, the tyre is rotating at the speed of the road, but the whole wheel is also moving forward at the speed of the road too.

Let my try to explain like this...

Imagine you are on your bike traveling at 5 mph on ice with the brakes on, locking the wheels (entirely hypothetical). Clearly everything including the wheels is traveling at 5 mph. Now let go of the brakes and spin the wheels to roll with the road (lets say pedal for the back wheel and motor for the front). They are now rotating at 5 mph at the rim. It took 2 lots of 0-5 mph acceleration to get there.

I understand where you are coming from John, but your figure of "twice" is artbitrary, you cannot assume that the force required to accelerate the wheels (in mid-air or on ice) is the same as that required to accellerate the bike (it depends on the mass of the bike + rider). Anyway, I think we both agree that wheel mass has a significant effect on acceleration. My real point of disagreement was with your assertion that wheel mass was not related to ease of climbing. As I said, just get on some light wheels and try it - it is not hard to detect the difference.

Ps. I quite agree on the carbon forks issue. I would be concerned about the bonding of the (alloy) dropouts into the resin - although cyclo cross forks are designed to take some punishment.

Chris

 

[john]

but your figure of "twice" is artbitrary, you cannot assume that the force required to accelerate the wheels (in mid-air or on ice) is the same as that required to accellerate the bike (it depends on the mass of the bike + rider).
Chris

The force required to accelerate the wheels (in mid-air or on ice) is the same as that required to accelerate the wheels (in a straight line without spinning) not the bike. Twice is the exact figure (assuming that all the weight is at the rim, a little less in reality), it is not arbitrary.

I don't deny anyone's personal experience which or course is very valuable, I just like to get the theory right too.

Anyway, since climbing a hill doesn't (usually) involve accelerating, the weight effect must be the same wherever you put it.

 

[frank9755]

Agreed in princple John, however a further complication is if you climb a steep hill using pedal power you will accelerate on the downstrokes and slow down in between times, so you are actually doing quite a bit of accelerating!

Big picture though, a bit of weight can make a few seconds difference, which matters a lot to someone in a race, but on my commute to work, a few minutes either way is not significant!

 

[john]

Agreed in princple John, however a further complication is if you climb a steep hill using pedal power you will accelerate on the downstrokes and slow down in between times, so you are actually doing quite a bit of accelerating!

Yes but with a heavier wheel, the deceleration will be less, meaning less acceleration needed, the effect cancelling out exactly (at least in energy terms - the feel may be different).

Big picture though, a bit of weight can make a few seconds difference, which matters a lot to someone in a race, but on my commute to work, a few minutes either way is not significant!

Certainly agree with that, thankfully, a few seconds late for work doesn't lose me my job

 

[Chris_Bike]

I admit to no longer being a physicist, but it seems to me that when you climb you are also accelerating to defeat gravity (9.8m/s/s downwards).

Chris