Impact of changing front chain ring?

[gps315]

May be a daft question but ....

I have a road bike with a 50 up front and a CX with a 46 up front

My average speed on road bike is 17 to 18 mph over 30 miles the same route on the CX is 15 to 16 mph

Would the front chain ring contribute to the difference? Crank arms are same length.

The road bike is a Triban 7 and the CX is a Cannondale CADAX 105

What do you think? Would swapping out the 46 for a 50 make much difference?

 

[T.M.H.N.E.T]

The CX is inevitably going to be slower before gearing is considered

 

[gps315]

Why is that, forgot to mention its running 28 gatorskins not the knobblies it came with..

 

[outlash]

I'm surprised it's that much of a difference TBH. I'd normally drop off only about .5 -1 mph on average on rides on the same route if I was using my cross bike instead of my road bike and that's with the 35 semi slicks the bike came with. Gearing isn't an issue unless you're doing 30+ where you'd be spinning out on the cross. Since I put mudguards on mine, it's made it a little slower again.

I'd put it down to you're sitting a fair bit higher up on the cross leading to more drag and it's a little heavier(although not a lot in it between your two bikes).


Tony.

 

[User6179]

My Caadx 105 is no slower than my good bike , changing chain ring will make zero difference .

 

[DaveS]

Originally I suspected tires but you said you changed those. That pretty much just leaves aerodynamics. I am assuming you are not actually spinning out thru being under geared?
I agree with the other respondents, should make zero difference to change the chainring.

 

[boydj]

Check the setup on both bikes - saddle height and saddle to handlebars (drop and distance) - as it could be that your position on one bike is more efficient.