Fork Spacing Changes

[Groover]

Does anyone know why some bikes of that same frame/generation have different fork spacing? For example, why does say the G5 have 195mm for spacing and the Le Mans III 180mm both having similar frames and similar wheels. Is there a handling performance enhancement in having the tighter fork spacing? - Less flex?

[wirespokes]

I don't have all the data, but this is what I've put together concerning that: Guzzi was very much into presenting the narrowest and lowest profile possible to reduce wind drag. The wire wheels needed 15mm wider fork spacing so the rest with cast wheels got the narrower 180mm trees.

[Groover]

That makes complete sense, thanks for the reply!

[Rough Edge racing]

I don't have all the data, but this is what I've put together concerning that: Guzzi was very much into presenting the narrowest and lowest profile possible to reduce wind drag. The wire wheels needed 15mm wider fork spacing so the rest with cast wheels got the narrower 180mm trees.

Interesting but what about the two cylinders sticking out in the breeze?  I do land speed racing with naked frame bikes and by far the rider is the biggest aerodynamic drag..

[wirespokes]

For the longest time Guzzi won race after race on the single cylinder bikes using that same formula - the smaller hole you've gotta punch through the atmosphere the faster you'll go. Since the mid 60s all of the Guzzis have cylinders hanging out in the breeze. But I imagine they found in the wind tunnel that wider forks created more drag. It makes sense and seems logical, but we all know that things don't always work out the way we think they should.

If there's a different reason for the forks being narrower on some models, I'm all ears. I don't get all patriotic about my theories.

Along that same line (sort of) I've wondered about caliper shims. The Guzzis are the only bikes where I've encountered needing them. Was there any reason for not machining them exactly? I never had that issue with airheads.

[1down5up]

I don't have all the data, but this is what I've put together concerning that: Guzzi was very much into presenting the narrowest and lowest profile possible to reduce wind drag. The wire wheels needed 15mm wider fork spacing so the rest with cast wheels got the narrower 180mm trees.

Yes, except for

Lemans 2 had 195mm forks,mag wheels with spacers behind the disks

V7 sports (twin disk versions) and 750s/s3 had 180mm forks, they used the narrower bearing carriers that were also used on rear wire wheels.

[Antietam Classic Cycle]

Perhaps, narrower fork is stiffer for better stability on the "sporting" models. Le Mans II/CX100 seems to be the exception in many ways - DeTomaso's lira pinching could be why it has wider forks.