2 road bikes with same Geometry but feel different in size

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2 road bikes with same Geometry but feel different in size

Postby GreyhoundCycle » Fri Nov 09, 2012 12:16 pm

Question for owners with multiple road bikes!

For the ease of reference, my current bike which I have been riding for 1.5 years is “Bike A”. The recently built a bike with ISP frame, let’s call it “Bike B”.

I was trying to make bike B the same geometry as bike A – which has a set up I like and used to.
Bike B’s frame was a 2nd hand, and I ensured it had the same seat tube length from centre of BB to rail as bike A before purchase.

The horizontal top tube length, crank arm length were also the same between the 2 bikes. After fitting the saddle, stem and handlebar, both bikes have the same BB to top of the saddle height, same length from tip of saddle to steer, and the same length of stem were used. Both even have the same groupset and paddle model.

Now, I test rode Bike B around the block and it felt smaller, leg extension at the bottom of the crank was not as far as bike A. And Bike B felt a bit lower to the ground despite all measurements suggest it shouldn’t.
The difference I could find between bike A and B was the seat tube angle of Bike A is 73 compare to Bike B’s 72.6 and mm of difference in BB drop.

Does anyone know why or has similar experience? Because bike B is an ISP frame, there is not much I can do to raise the height of the seat tube.
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by BNA » Fri Nov 09, 2012 2:59 pm


Re: 2 road bikes with same Geometry but feel different in si

Postby ozdavo » Fri Nov 09, 2012 2:59 pm

The seat toppers usually have some degree on movement(10-20mm), either with spacers or just moving it up/down like a seatpost.
Also are you using same pedals/cleats/shoes?
Always looking for new rides & ride partners in SE QLD area
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Re: 2 road bikes with same Geometry but feel different in si

Postby rustychisel » Fri Nov 09, 2012 4:21 pm

apart from material used in frame manufacture (you don't say, so I can guess bike B is carbon) and wheels, which make a helluva difference, how sure are you the geometry is the same?

A difference of 2cm in chainstay length can be quite appreciable, a half degree difference in head tube angle even more dramatic.... is the bottom bracket drop the same on both bikes? hmmmmmm

and is your saddle setback the same on both, dictated by reach to bars or positional to bottom bracket junction. That half degree angle you note is likely to translate to 15mm fore and aft movement on a 900mm leg length measurement, you know.
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Re: 2 road bikes with same Geometry but feel different in si

Postby baabaa » Fri Nov 09, 2012 7:23 pm

Try this if you have all your frame and contact point specs....
http://gearinches.com/blog/misc/bike-ge ... comparator
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