Small Bikes - Handling

DaveH <[email protected]> wrote:
> I am about to buy a road bike for my wife. She will need a bike in a
> frame size about 52cm. However I note that manufacturers now seem to
> be using one fork rake for all their bike sizes, with head angles
> varying from 71 to 74 degrees, eg Giant (XS - 71 deg and 45mm rake),
> Fuji (52cm, 72 deg and 43mm rake) Colnago (52cm 71deg and 43mm). This
> leads to high trail figures of 65mm to 69mm. The ideal trail is
> (apparently) around 56mm.

> Such trail must really negatively affect the handling of these bikes,
> making it slow and with a self centering action.

Doesn't the Giant use 650c wheels on the XS size? That would reduce trail
a bit compared to a 700c wheel.

Obviously toe overlap is an issue with small frames. But I don't see why
they wouldn't use more offset (aka "rake") to bring the trail number into
line when using slack head angles. More offset would also improve toe
clearance.

Art Harris

DaveH wrote:

> I am about to buy a road bike for my wife. She will need a bike in a
> frame size about 52cm. However I note that manufacturers now seem to
> be using one fork rake for all their bike sizes, with head angles
> varying from 71 to 74 degrees, eg Giant (XS - 71 deg and 45mm rake),
> Fuji (52cm, 72 deg and 43mm rake) Colnago (52cm 71deg and 43mm). This
> leads to high trail figures of 65mm to 69mm. The ideal trail is
> (apparently) around 56mm.
>
> Such trail must really negatively affect the handling of these bikes,
> making it slow and with a self centering action.
>
> There must be riders out there who are using these bikes. How do you
> find the handling? What are you thoughts?

Mine - Colnago so-called 54 cm frame (actually 52,5 cm from centre of
bottom bracket to top of top tube, so this particular frame might be good
fit for your wife but I'm going to ride this one until I break it ;-).
Geometry is 74 deg seat tube, 71,5 deg head tube. Fork blades are
straight but are angled from the steerer to cause effective rake.

I find the handling very stable, almost lazy in feel. By this, I mean the
*opposite* of nervous or twitchy. Very nice bike for long distance
competitions or credit card touring. Relaxing.

I have had quite twitchy frames in earlier years (e.g. a custom 73,5 deg
seat and 73,5 head, with short-rake forks, or an Alan 75 deg seat and 74
head, similar short forks). Both were much fun in the crits I rode but
slightly irritating on longer rides (always spent some energy making sure
I rode in a straight line, for some reason).

Unfortunately I cannot help you on the evaluation of trail - I have not
yet read up on it to understand the correlation with handling
characteristics.

/Robert

"DaveH" <[email protected]> wrote in message
news:[email protected]...
> I am about to buy a road bike for my wife. She will need a bike in a
> frame size about 52cm. However I note that manufacturers now seem to
> be using one fork rake for all their bike sizes, with head angles
> varying from 71 to 74 degrees, eg Giant (XS - 71 deg and 45mm rake),
> Fuji (52cm, 72 deg and 43mm rake) Colnago (52cm 71deg and 43mm). This
> leads to high trail figures of 65mm to 69mm. The ideal trail is
> (apparently) around 56mm.
>
> Such trail must really negatively affect the handling of these bikes,
> making it slow and with a self centering action.

If I calculate it correctly, the Bianchi Brava 52cm, with fork rake of 50mm
and head angle of 72 degrees, has a trail of 61. Still a bit high, but
better than on the bikes you note.

The way to reduce this is to go to 650mm wheels, but these are only used on
very small frames.

The problem is that the manufacturers don't want to make a bunch of
different forks.