Tandem Cycling - Replacing Wound Up fork for Alpha Q on Robusta Co-Mo

Hello,

We are new to this forum and have question to the members regarding two tandem forks.

Just wanted to hear from Co Mo Robusta owners if anyone changed their original Waundup fork for lighter Alpha Q tandem fork.

After speaking with Co-Motion owner, he mentioned that Robusta model we ( 3 years old ) own won't work with any Carbon Tandem forks becouse the axle -crown fork race distance is shorter and will efect the front end handling.

Wound Up is 387mm lenght from axle -fork crown. Rake is 45

Alpha Q is only 374mm & rake is 41

Curentlly my tandem floor to the top of the handlebars set up is way taller than my road racing bike ( close to 1.5" ) so I could use much lower position of my bars.

I know that less rake and shorter fork blades could make for very agile/ quick & responsive handling, but how much can I feel?

I raced bikes now for 36 years and rode ton of difrent bikes with difrent angles geometries, but here we dealing with double of our weight etc & tandem is only 26lbs with lot of high end parts on it.

As far as our combine skills and bike handling , there is no problem since we both raced for many years with multi national and state titles track road and tandem events.

I would love to get second opinion on the fork set up and see what everynoes who rides same parts toughts are.

BTW, This year was our 6th NWTR in Oregon and was awesome time! great organization, awesome smooth roads and great people to ride with.

We rode on 4th July in our National title jerseys from 06' team time trial championships on Blue/White fade Co - Motion Robusta tandem.

Best Regards,
Les & Cheryl Korcala
North Bend, Washington
USA

Fork will work fine, but will change the handling and geometry of the bike a little. It's personal preference whether you like it and whether the lower bb is an issue will depend on whether you ride like a crit rider and use long cranks or short ones.

The 41mm rake plus steeper head tube angle resulting from the lower crown will speed things up a bit, and may be a bit much given that you are starting with an already reasonably quick-steering bike. I expect the bike will be twitchy like a track bike at low speeds, then quite stable when doing 20+ mph.

I had exactly the same problem with a Trek T2000 so swapped a steel fork with enough space to get my finger in between a 28mm tyre and the bottom of the steerer and lots of rake to an Alpha Q 44mm rake for exactly the same reason. I also added a -17 degree stem to help get the bars down.

Outcome is that the steering is quicker and more single-bike like and the bottom bracket is slightly lower at the front. I only notice the lower front end, better brakes, better handling and better bump absorbtion. Lower weight isn't really noticeable, but it all adds up.

So that you are not negatively surprised, you should accurately calculate the real benefit of a lower fork. basically the bb also gets lower when you lower the fork as you rotate the frame so the real bar height reduction is the cosine of the angular rotation of the frame * the reach of the top tube, i.e. a bit less than half the lowering from the fork.

For a more objective view on handling you can also calculate the trail and compare with other bikes. There are various calculators available on the web for this.

Another thing I considered was to use a frame facing tool to cut down the head tube. This is an easy way to reduce head tube height. On most Al frames this is fine as the head tube is not normally lathed down in the centre so should be fine. It will however void your warranty if you take off a noticeable amount. On steel frames this is generally a bad idea as headtubes have reinforcing rings.

Overall I would recommend a Deda track stem as a cheaper starting alternative to the fork.

I'd talk to the folks at Co-Motion, and see what they think.

The current Robusta is spec'd with the Alpha QX2. So one obvious question is any differences in the geometry, of your Robusta and the current RObusta.

Also if you look on Co-Motion's web site, the geometry of the Roadster, which is shown with a woundup fork apears to have the same geometry as the Robusta.

Thanks guys for all your help.

Les