I am experiencing some strange phenomenon and would like some opinions about what may be causing this. It's really weird and it's driving me a little batty trying to figure it out.

My bike "A" and bike "B" are running the exact same tire brand, model, size and pressure. They both have 170mm crank arms, identical gear ratios, identical chains, identical rear hubs, close enough to identical front hubs. Inner tubes are identical. The saddles (sit bone dents even) on both bikes are identical distances from from cranks spindle center, as well as fore/aft distance from the crank spindle. Reach is equal on both bikes. All bearings and chains are operating like greased butter. No drag at any of the wheels and both BBs spin like a Top on wet glass.

Here's what's tripping me out. Bike "A" weighs 7+ lbs more than bike "B", and has heavier rims than bike "B". But bike "A" feels much easier to accelerate on. It's VERY noticeable. From a stop bike "A" GOES now and I can achieve 90 RPM with much less effort than on bike "B". That makes no sense considering the heavier rims. Also, if I am already at speed and want to sprint to build more speed in preparation for an upcoming hill, the "burst effort" seems way more productive.

The frame and fork flex are actually greater on bike "A".

The wheelbase is much longer on bike "A".

I thought maybe it was an illusion caused by a nourishment/hydration/different weather/wind thing so I did a same day back-to-back test. I'd ride "A" for a couple miles, immediately jump on "B" for a couple miles, repeat, repeat, repeat, repeat. That only made the difference pronounced, and it aint insignificant. Even hills were noticeably different. "A" happily zipped up them making me feel like some sorta strong quad cyclist dude while "B" reminded me that I am a weak mortal. Bike "B" felt more and more like I was pulling an invisible trailer or riding on flypaper.



The reason I'm so curious is simply because on paper it makes no sense at all, and if I can figure it out maybe I can improve bike "B". I'd also like to understand what's causing this so I know what to look for when choosing frames and components (or combinations?) in the future.

Is there something magical about "A", or is there something wrong with "B".

W.T.F. ?

Any clues?





** I await the "You are stoned", "You are crazy", "Check the ratios", "Get a new Air pressure gauge" comments with great anticipation.

I'd guess it's a difference in handlebar reach /height/hand position. Bike A has you positioned in your sweet spot. Or you're high.

Let me suggest you try a coast down test to see the the overall drag is the same. Take both bikes to the top of a hill, and measure the time it takes to coast to some specific point at the bottom. Try to sit in the same relative position on both bikes to equalize the wind drag. If the bikes are actually identical, then the heavier bike will be a bit faster due the added propulsion force provided by its added weight.

The only thing I can think of is that each frame isn't 'stiff' or 'flexy' in the way you think they are.

Interesting. Seems like an accurate way to measure. But I'd have to limit the top speed (timing cutoff point) to the same speed that I am capable of generating myself though, right?

The "light and slow" bike does have much wider fork blades and bigger frame tubes than the "heavy and fast" bike, but would that matter from a a stop to 15mph?

Confirmation bias? Have you had anyone else test them?

This is an excellent idea. Maybe that should be first on the list of things to try.

Without power meter(s) a heart rate monitor, well controlled test environment like a velodrome, identical position/kit and servicing your "easier to accelerate on A" is just a "feeling" that it occurs at all.

Placebo effect: "A" must be a faster color.

-Bandera

Position is the same, to the mm. The slow bike is a much faster color.

I think Bandera nailed it. We could sit here and guess all day. Both bikes are mechanically sound, one is just a dog.

I'm at the point now where I just want to know what makes it a dog for the sake of understanding, even if it's something (likely) that can't be remedied.





I'm waiting for Scrod to bounce in with, "I can't ****ing believe people think about this ****. Go ride your ****ing bike."

If your maximum speed is only 15mph, then I doubt that frame and fork aerodynamics will have a significant effect. Your own body position is by far the major contributor to wind drag. Do either of these bikes have coaster brakes ? Sometimes coaster brakes can drag when pedaling even though they seem fine when spun in a workstand.

You are sure the gear ratios are the same? And that both have adequately loose chains? I've spaced and done rides thinking I was on a different cog and been mystified by either my super strength or lack of it.

Another possibility. Someone snuck in and installed one of those seat rube motors and hooked it up to a resistor. Rewire that puppy and you will be able to dazzle your friends.

Ben

Oh man...

Doped Bikes

I just used 0-15 as an example because I have read in the past that aerodynamics play almost no role until you reach speed higher than that. And since I am experiencing the "ease of acceleration" any where from 0-15 that's what confuses me.

Like if I'm riding along at 12mph and jump on it, I can reach spin out velocity in a shorter distance on one bike vs the other.

They are both Shimano CB-E110 coasters. But, and it's a big but, I've done the exact same drag eliminating modifications to the clutches/return spring, shoes and bearings on both. The clutch mechanisms can be rotated with the fingernail on your pinky. There is no identifiable drag in either, and what does exist would be identical.

Not only did I double check the factory stampings, I counted the teeth to be sure.

This is your chance to do the 1st in history controlled A/B time to distance test regimen of coaster brake bicycles, mainly since no one else in the history of cycling cared(s) to or ever will.

-Bandera

I can't afford nice bikes with snazzy hand brakes.

Yeah, I've decided that I'm riding alone from now on.

But whats your fork clearance like!?

About 50 mm