Understanding science of speed difference between two bikes

Question

I have two MTBs and one is slower than the other.

Bike1 has Deore derailleurs and a double chainring with 10 sprockets and Shimano hubs. Which has a great speed irrespective of the gear combination.

Bike2 has Acera derailleurs with a triple chainring and 8 sprockets with acera and Quando hubs.

The second bike is much slower than the first one in terms of speed.

My question is, apart from physical strength, which is more important for speed, a hub or drivetrain?

I want to upgrade my bike. Can anyone guide me to get more-or-less the same speed. Both bikes are from same brand and almost identical in terms of dimensions and shape.

Please help me to understand the science.

Answer 1

There is a myriad of factors that can effect how 'fast' a bike is. By 'fast' I mean both maximum speed and acceleration. When riders talk about a bike being 'fast' they usually means it accelerates well. You don't state it explicitly but because you have Deore and Acera drivetrains I guess you have mountain bikes. Acceleration and climbing ability is much more important on an MTB than straight line speed.

Acceleration is force/mass. More force, less mass means more acceleration. The Acera bike although similar to the Deore bike probably has downgraded components, frame and wheels and weighs more. If you think about it an Deore level bike from the same manufacturer should be designed to be faster than a Acera bike - that's why the Deore bike can cost more.

Anything that soaks up energy will reduce the amount of force applied to the pedals that makes it to the contact patch between the rear tire and the ground:

• Drivetrain losses - friction in the chain, wheel bearings, bottom bracket bearings. Chain friction is dependent on wear, how clean and lubed it as and also the angle it has to run at.
• Rolling resistance of the tires and wheels. This caused by the tire deforming and is heavily dependent on tire size, pressure and construction.
• Suspension losses - if pedaling causes the suspension to bob up and down energy is lost. That's why forks and rear shocks have lockouts
• Anything else that flexes - frame, wheels, crank.

Answer 2

When you say both bikes are same brand and almost identical, I think that's the root cause.

Two bikes of the same model and brand and frame size will be very close, but you've already said one's a triple and ones a double chainring.

That alone implies several years difference between the bikes. Even the same model name can vary a lot in the course of one year's development.

I bet there's a weight difference between the frames, and the wheels will be different too. Even the tyres are likely to be different weights and rolling resistances.

The older bike has components with more years on them. Naturally wear will be higher, and losses will be small but culmulative.

There's a chance your bikes have suspension - that can be a significant loss of power, and its likely the older bike will have more wear and an older format of suspension too.

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tl;dr I suspect you're comparing apples and oranges, and all the little losses in one bike add up to more effort required for the same speed.

Without seeing the bikes, your best upgrades are likely to be a clean and lube of the chain/hubs/BB, then a new chain/cassette, and perhaps new slick road tyres not MTB knobbies.