Acceleration Problem BMC GF02
 

Hi Guys,

I have just purchased a new 2016 BMC GF02 105. On my first daily commute (8miles either way) it all feels a little wrong. From a standing start I was being out accelerated by rusty folding bikes. Up hills I was dying. At speed and down hill, the bike was fine, but any attempt to accelerate took considerable effort. Now I have read that the GF02 has weighty wheels however when I came home to ride my old bike, a 63cm Trek 7.0, I instantly realised that I could out accelerate the GF02 on my old £200 Trek 7.0.

For comparison my 61cm GF02 is almost half the weight of the Trek. There is also no way that the wheels on my BMC weigh more than those on my Trek. On closer inspection turning the bottom bracket I can hear a clicking.

Has anyone had this issue? Am I correct in assuming the problem is with the bottom bracket? The tube angle on both bikes are almost identical as is the seat height and crank length, so I cannot believe it has anything to do with my positioning. I can also not report the smooth shifting of the 105's everyone has spoken about. I am clearly going to take this back, but before I accuse anyone of being sold a faulty bike, I would like to have my facts correct.

Does the above point to a faulty bike? What should I do?

Thanks,
Ryan

Brakes rubbing ?? Rear wheel off center rubbing the frame ? Underinflated tires ?
Reverse placebo ? The shiny new bike doesn't feel as "fast" as you expected.

Not enough info on the "clicking" but not likely to make you slower. Could be a mis-adjusted front derailleur.

Thanks for responding Homebrew. Wheels spin perfectly on the BMC, no rubbing or wonkeyness, by contrasts the breaks rub on the Trek :-(... At first I though it was a placebo as I beat most of the times I did on my Trek bike in the commute. However when I came home, I tested both bikes from standing and the Trek is quicker off the line.

Could you explain what you mean by "mis-adjusted front derailleur"? Sorry if it's an amateur question.

You would hear this, although as the bike is new, and guessing you got it from Evans, the pre-delivery inspection should have made sure this was correctly adjusted, as with all the other possibility, less tire pressure.

Would be looking at a few things -

Time the commute, compare on Strava or similar to see which bike is quicker.

It's a new bike, have you got it adjusted to fit you correctly yet, this may take a few rides.

Stick the bike in a stand to see that everything is free/smooth moving, to eliminate any issues.

For the Trek, what gearing does it have? from the photo, it looks like it has a MTB/Touring triple, with a 22/26 lowest vs the 34 on the BMC, that will make a massive difference for the initial acceleration.

Have you considered that the rusty folder rider may just be way faster than you, never judge a rider by their bike.

Might be the front derailleur rubbing slightly against the chain when pedaling that's causing the clicking. Could be a mis-adjustment, or you need to "trim" adjust the front sometimes while riding. As you shift the rear, then chain can sometimes rub the front.

BUT, you need to diagnose and explain the "clicking" better, because there are lots of possibilities.
Could be as simple as the surplus front derailleur cable hitting the crankarm in certain gears.

There are soooo many variable when comparing 1 bike to another, that it's not usually the bike itself that accounts for different "speeds".
Posture, wind shifts, tire pressures, traffic, fit, along with all the human variables from 1 day to the next... mood, sleep, food, time of day, stress ......

You say the wheels are not rubbing on the brake, but are the hubs spinning freely? It is quite common for hub cones to be overtightenend from the factory, perhaps hub bearings are binding a little? How many revolutions do you get for comparative-force spin on Trek vs BMC wheels?

When you compared the acceleration of Trek vs BMC, were you in comparable gears? Trying to accelerate from standing using too large/hard of a gear would be quite slow. Like if you tried to start a drag race in a car with the stick in 4th gear, doesn't matter how fast the car is, it's not gonna be quick off the line.

Different bikes feel different. You said it yourself that you ARE faster on the new bike. Why worry about it? Do you spend a lot of time accelerating?

I also wonder what gear ratio you're using to accelerate in on the Trek versus the BMC. Obviously accelerating in a lower gear will make it easier.

Try riding both bikes back-to-back. Instead of acceleration which is hard to keep track of, try riding at a constant speed for a km or so. Use the same speed for each bike. Increase the speed each time and see how that feels. You will feel drag trying to maintain a high constant speed.

I hate to repeat this, but check the obvious things again like tire pressure, brakes rubbing, and crankset not turning freely. Remove the chain from the crankset so it can spin freely. Make sure it's not hard to turn. Remove the wheels and check the wheel bearings AT THE HUBS to make sure they feel ok.

My first thought as well.

The BMC comes with Shimano WH-RS010 wheels which do have loose ball bearings. Further, I have read more than one account of Shimano hubs being adjusted too tight when new, so I would definitely check this out.

Remember, the axles should have a drop of play in them when not mounted in the frame; that play gets taken up when the QRs are tightened down...

Please don't take offence OP, but are you sure you're using your gears correctly?

Acceleration is a function of force, mass, resistance (drag) and inertia. The OP stated that the heavier bike accelerated harder off the line, but had a longer time to cover a fixed distance (cruising speed).

Cruising speed is basically independent of mass - on the flat anyway - but hugely effected by resistance - we can safely say that the new bike has less resistance (aerodynamic, bearing, drivetrain, etc)

We will also say that the OP is putting the same effort into both bikes.

Given the above, the only thing left for initial acceleration is inertia. ->> which leads to gearing as mentioned by [MENTION=193959]FastJake[/MENTION] and [MENTION=35181]Reynolds[/MENTION] above.

[MENTION=104655]jimc101[/MENTION] thanks for the suggestions. Timed on strava was almost identical. I had minor adjustments made to saddle height and had a smaller stem fitted. Also pumped up tyres... All had a positive effect, but none alleviated the problem. I only use the 52 cog on my Trek so it's not low gearing comparisons.

[MENTION=2667]Homebrew[/MENTION] I tested the standing starts on both bikes on as similar a gearing as I could get. The BMC requires more force through my legs to get moving irrespective of gearing.

[MENTION=252435]RubeRad[/MENTION] the BMC wheels spin much more freely than the trek. It's not even comparable. The brakes rub on the Trek so it's lucky if it does 3 full rotations.

[MENTION=345109]corrado33[/MENTION] I cycle in London dude. It is dangerous to not be able to pull away at traffic lights easily. I'm having to use a gear so low to move off that after two turns I'm changing up.

[MENTION=193959]FastJake[/MENTION] I have tested the bikes back to back (see above). The cranks on my trek appear to move more freely than the BMC. When spinning backwards the BMC cranks stops sooner. The BMC also creates a clicking sound between the pedals (bottom bracket)

[MENTION=256459]rmf[/MENTION]lna the wheels are spinning freely. Honestly there is nothing slowing the wheels down.

[MENTION=35181]Reynolds[/MENTION] that's literally offensive and not helpful at all

[MENTION=81612]NFM[/MENTION]iso Good analysis and the BMC clearly has less rolling resistance. I can feel this when going down hills. The point missed is the Trek is converting more power from my legs to forward motion than the BMC. As soon as I need to pedal (to accelerate or maintain speed on an incline) the Trek outperforms my BMC. Let me say it another way. I can climb a hill easier in any gear on my heavier Trek with rubbing breaks than I can with the lightweight BMC. However if I go to the top of a hill and let both bikes just roll down and see how far they go when the road flattens the BMC will roll further with ease.

**The best way to describe it is as if someone has put gum between the cogs of a car gearbox. It wouldn't matter what gear you selected, the engine would need more power to get the car moving.**

On the BMC, it just takes more effort to turn the wheels from the pedals than it does on the Trek no matter the gear.

Sorry ryanisjones, no offence meant.I don't know your experience level and assumed it wasn't high, because you thought a BB clicking could be the cause of slow acceleration - that and your suspect about a "faulty bike". Seems I was wrong.

Do both wheels spin freely? If yes, this "problem" of yours is in your head.

The only remaining possibilities are:
1. The BMC has drag somewhere in the drivetrain, e.g. bottom bracket.
2. The BMC has really excessive frame flex.
3. Your position is substantially different on the two bikes.
4. You're imagining it.

1 is easy to check. Remove chain from chainring, drape it on the bottom bracket shell, and turn the crank. It should turn easily - it won't spin for a minute like wheels will, but should freely spin several turns.
2 is really unlikely. You'd notice such a mushy frame.
3 is easy to check too. Position differences, if large enough, can have a significant effect on effort - you are used to using certain muscles. So place the bikes side by side and see if the bottom bracket, saddle, bars, hubs all line up.
4 is harder to check. You believe the BMC is a slug, so you will tend to look for confirmation - it is natural. I would ride the same longish climb in the same gear (exactly the same) at the same heartrate and see what Strava says.

IMO - no single mechanical factor alone can account for a very noticeable difference in acceleration, except maybe tire pressure. It would be a stretch to imaging multiple factors to exist simultaneously without being observed.

I have to wonder if there's a difference in gearing. If for some reason, you're riding a higher gear on the newer bike, that could have a very measuring effect on acceleration. For example if the older bike had a 53/12 high gear, and the new one a 53/11 and you are riding comparable gear positions, then the higher resulting gear will be higher and harder to accelerate from a standing start.

Your Trek should have a 48T max, not 52T, you may want to check that.

BTW, on BF it's better to use a hash tag # with names (i.e. #ryanisjones ) as it associates to that user, rather that @ as this doesn't associate with anything useful.

Seems that way. Everything else appears to be ruled out.

Fit and posture on the 2 bikes can be different, which gives a different feel.
OP says he's using equivalent gears, so without knowing the specific chainring-cog combinations and wheel size, have to assume they are the same. But a small difference in gears can be a big difference in feel.

Hybrid (Trek) vs road (BMC) from the info/photos, the Trek (guessing 48t max with a 11-32/34 cassette) has a lower gearing than the BMC 50/34-11/32.

Your right about feel, when I swap from road to hybird a long time on one, it can take a moment to get used to the feel of the other again.

These two statements do not support each other. "Having" to use a low gear yet "only" staying in the large chainring.

I think it's in your head/positional differences. Ride the BMC for a month and compare strava times then.

Are you sure about that? I used [MENTION=104655]jimc101[/MENTION] and thought it was a "mentioned".




If the OP is comparing big rings thinking they are the same teeth number, that might be the problem.

And me, just sayin... :p

If OP is really conducting tests with the same gear ratio (dude, go count teeth and let us know), then I think suspicion reverts back to this mysteriously-clicking bottom-bracket. New BB should not click. Maybe it's faulty and adding a lot of friction to the system.

I've been following this thread with amusement. It's very likely we'll never really "know" what is the reason. The more I read the more I look at the rider and not the bike. At first I thought of rider positioning, then gearing (although I would think the rider would already have considered this, but...), I never really though that tire pressure or brake rub would be involved (again believing that the rider would have considered this but then his post #13 suggests at first he didn't...). So I find myself going back to the rider and his perception being involved. The only mechanical not yet discussed is crank arm length. Go for it guys:) Andy.

Hmm, your Trek doesn't have a 52T chainring. 48T should be the largest. And even though you "only use" that chainring your picture shows the bike in a small/small combination! Something is not right here.

My theories, in order of likelihood:

1) Different gearing is confounding it.
2) It's in your head.
3) The fit of the BMC is way off causing your legs not to work well on it.
4) Something is wrong with the bottom bracket.

Thanks everybody for your feedback.

I was hoping my foray into road bikes would be a lot less messy. Special thanks to #jimc101 as I had assumed the same teeth in the Chainset when in fact the BMC does have 4 more teeth. So #Reynolds maybe I was a bit ignorant of gearing. If #jimc101 is right then the 4 teeth extra on the chainset is equivalent to less than an extra half wheel spin for one full pedal rotation in the highest gear (11T cog) and likely less than a quarter more wheel spin in the gear I was kicking both bikes off from. With that said I will test this again tonight and use way more accurate gearing.

If it helps, I am 6"3 and have a 93cm inseam. I like to ride with a low cadence. I rode the Trek again last night and seriously, it just takes less effort to speed up. Its like jumping from a road bike to a full suspension fat wheel mountain bike. Yes you can choose the right gear, but it takes way more power to go as quick, and the drag is not occurring in the wheels, as I have tested them and they spin freely on the BMC with no break rub.

Another thanks to #Jyl for this list.

Answers

1. I am taking the bike to Evans tonight to check the bottom bracket.
2. I have no experience in the effects of stiffness, but I hope this isn't what it is.
3. My position is subtly different. Both bikes have similar tube angles but the road bike has lower bars further forward.
3.a Seat heights are the same
3.b Tyre pressures are good on both
3.c Breaks rub on Trek not on BMC

4. This is the easy answer. Of course we can say it's in my head, and I have not ruled this out. But I have ridden other road bikes (that both fit and did not fit) and never experienced this lethargy to moving off and accelerating. The feeling is so distinct it has led me to believe the bike is broken.

I will report back tomorrow after Evans have checked the bike with what I find.

Thanks All!

Count the teeth. Since you seem to like the acceleration of some particular gear of the trek, count the teeth used, and then count teeth on the BMC and choose a gearing that has as close as possible a front/rear tooth quotient. Maybe you can even find an exact match, like 50/20=2.5 seems to be an available gearing on the BMC (your chainrings are 'compact' 50-34, and it looks like your cassette offers 11-12-13-14-16-18-20-22-25-28-32), maybe the Trek has like 40/16=2.5 or something. If you can't find a suitable exact equal, round up to the slightly larger on the BMC, because the Trek has larger tires, thus a slightly larger wheel diameter and full-revolution rollout distance.

Thanks #RubeRad Will do exactly this

I don't think the picture shows the Trek owned by the OP, there's no way that's a 63cm.

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