Fork

[King Boonen]

This must be why we've only recently had a British tour winner! Anyone older grew up riding horrible bikes thanks guys, this finishes a lot of arguments!

 

[Boeing]

Just because it's straight doesn't meant it has no rake

 

[ustabe]

From what I'd heard from others Roberts has alway built decent frames, interesting about the rake though. There were builders out there in the 70s and 80s who'd build anything they were asked to build even if the geometry wouldn't work.

The Robertses were very well made frames. One was extraordinarily light and the other had a very nice fastback seatstay treatment. The Gios just fit better and had more of an all-day go-anywhere kind of ride. I think the geometries of the later ones may have been something made for export--the angles looked a little steeper than those on the bikes Roger DeVlaeminck made famous. Of course, he may have been getting custom frames. The durability of the paint was terrible, though.

 

[King Boonen]

DeVlaemnick's frames were custom made for him, I read an article about it in an old issue of Rouleur, particularly his PR frame sets that were designed for the rough stuff but horrible on the road. Apparently his cyclocross riding influenced them a lot.

 

[Hawkwood]

DeVlaemnick's frames were custom made for him, I read an article about it in an old issue of Rouleur, particularly his PR frame sets that were designed for the rough stuff but horrible on the road. Apparently his cyclocross riding influenced them a lot.

For me some of the most iconic photos of cycle racing are of De Vlaeminck, breaking away in Paris-Roubaix, hands on hoods, and right down low on his bike.

Back to the subject, there's a website out there where you can dial in hand angles, fork rakes etc to see the impact on the trail, you can also do it backwards i.e. trail first. It might be worth looking up what sort of trail you want, and then checking out fork rakes on such a website.

 

[tony west]

Can you clarify that, everything Ive read says, reducing the rake (pulling the wheel back) will make the steering faster/jittery/ edgy, I urge everyone to pull up pictures of Plasma1, in 54 size, you will see the head tube is so slack that even a straight fork fork will still be reclining, I must go look myself in case ive got an odd one.

 

[winkybiker]

Can you clarify that, everything Ive read says, reducing the rake (pulling the wheel back) will make the steering faster/jittery/ edgy, I urge everyone to pull up pictures of Plasma1, in 54 size, you will see the head tube is so slack that even a straight fork fork will still be reclining, I must go look myself in case ive got an odd one.

No. It is the opposite. If you put a straighter fork on, pulling the wheel back, it will slow the steering. It moves the axle and contact patch further behind the point where the steering axis touches the ground, increasing castor, making the wheel want to straighten more.

 

[Hawkwood]

No. It is the opposite. If you put a straighter fork on, pulling the wheel back, it will slow the steering. It moves the axle and contact patch further behind the point where the steering axis touches the ground, increasing castor, making the wheel want to straighten more.

Correct, and there's a calculator here: http://yojimg.net/bike/web_tools/trailcalc.php where you can dial in head angles and rakes to see the impact. I can't find a geometry chart for a Plasma 1, but if it's the same as the 2 then it probably has a fork rake of about 43mm, it's head angle is 72.5 for the frame quoted, and with 23mm tyres its trail is 61mm. Changing this to a zero rake fork will make the trail a massive 107mm, and increase the wheel flop to 31mm making the frame possibly difficult to steer even in a straight line. A Bob Jackson touring/winter frame I raced on in the 1970s and early 80s had a trail of about 52mm for comparison.