A special gem recently left the Dönni family's bike garage and found a new home. The advertisement on one of the popular bike sales platforms drew Ride's attention to it. However, the pictures of the pretty 20-inch projectile were only half the story. Patrick Dönni, responsible for this child's dream of pedaling, can also write, which is why we let him have the floor here:

Mini racing file: Yasec custom bike 20 inch

"My then 6-year-old son weighed around 20 kg. If he had to ride a children's bike available on the market, it would be the same as if I had to ride a hardtail that was heavier than the 1905 ordnance bike. I couldn't do that to my son."

The inventor was unable to find a sufficiently light frame for 20-inch wheels. However, he came across a Hungarian frame builder who welds aluminum frames to size. The tubes were actually intended for a triathlon bike. "To get the maximum out of the lightweight construction, only the thin-walled middle sections of the conical tubes were used." The 850 gram frame was fitted with a carbon fork. "And as is the case with lightweight construction; once you start, you almost can't stop. So the bike was fitted with fine and lightweight components, such as Formula R1 disc brakes, feather-light cranks, tuned Sram Red rear derailleur, Tiso 10-speed aluminum cassette spaced to 7 gears, titanium bolts, etc. The weight of the complete bike was under 5 kg." Patrick found neither trigger nor twist shifters suitable for children. "Archer Components fitted. I replaced the springs on the shift paddle with softer ones. This means that the gears can be operated very ergonomically with minimal effort and shift almost as quickly as my AXS."

The bike not only pleased the builder. "Even if this uncompromising project has a somewhat decadent aftertaste, this bike enabled us to take our son on technically demanding and extended, sometimes very steep MTB tours at an early age without compromising on fun. The reactions of observers ranged from shaking their heads to grinning. Strange children who rode the bike once didn't want to let it out of their hands. That almost caused a fight with other parents once."

The son grew out of the bike. So that his little sister would enjoy it just as much, it was given a new paint job. Unlike her brother, she didn't like riding races. She still enjoyed it though.

Patrick's screwdriver story: lightweight construction until the bike breaks

As for his own mountain bike story, Patrick writes: "In my late teens, I was able to experience the heyday of the mountain bike, when one invention followed another. I was particularly fascinated by the smaller bike workshops in the USA with their hand-made bikes and CNC-milled, brightly anodized add-on parts. I mainly followed the scene in the bike magazines."

15 years later, he was able to afford the dream bikes of his youth. "I bought frames and add-on parts from all over the world and built up a manageable collection over the years. The fleet included gems from Yeti, Ritchey, Mountaingoat, Manitou and some exotic bikes such as Extreme, Curtlo and Landshark. Later, I also started trading in sought-after bikes and parts to finance new projects and expand the collection."

A Ritchey P-20 also impressed him with its riding characteristics. It just needed to be a little lighter. When he got below 8.5 kilograms, the seat post broke and the rear wheel broke because the tires were too light. "That's how I learned where the limits of sensible weight tuning lie. The passion has remained to this day and instead of buying a bike off the shelf, I always build all the bikes for our family of five individually and with great attention to detail. Even our current bikes hardly weigh a gram too much, with function and safety being the main focus today."

He learned the trade during his apprenticeship as a mechanic, but not only that: "As a teenager, I rebuilt everything on wheels with my older brother. Old bikes were suddenly powered by petrol engines, our mopeds were reminiscent of choppers from the 70s and we fitted a self-built sidecar to a disused 125cc motorcycle." He gained further experience with older Saab models. "I've been working in the IT industry for over 20 years now and maintain my hobby as a craftsman, whether in the garden, on my cars or in the bike workshop as a balance to pure mental work."

Another custom frame: Sarto 24 inch

The 20-inch bike soon became too small for his racing-enthusiastic son. Dönni decided against it, after all, this bike would also be ridden by his younger sister. "I found an off-the-peg bike kind of boring and a frame from China wasn't my thing either. So for a suitable successor, we had to build another custom bike."

This time, the Italian frame builder Sarto was awarded the contract. "For the geometry data, I chose a steeper seat angle for high contact pressure and an even shorter chainstay for the necessary maneuverability on the twisty XC race courses, based on average values from some well-known manufacturers. I would actually have preferred a slightly curved shape. However, Antonio Sarto said that the tube-to-tube process with prefabricated, straight tubes would be necessary to achieve my sporty weight target of 800 grams."

To finance this project, Patrick Dönni sold a bike from his sizeable retro MTB collection. He also reduced the costs by drawing on previous lightweight construction projects: a Formula R1 Racing brake and a 10-speed titanium cassette were fitted to the bike. The fork: Ritchey WCS Cyclocross, the wheels of course also individually assembled with Stan's No Tubes Crest and Sapin XC-Ray spokes. "The total weight of 1190 grams including rim tape was satisfactory for the price-performance ratio."

This time it had to be a mechanical drivetrain: "After all, my son had enough strength in his fingers and the DI2 was not yet available on the second-hand market at a reasonable price." There were extra thin BMX handlebar grips for the small hands of children, and the brake levers of the R1 were set as close to the handlebars as possible. "Measured with the hanging scales, the finished bike weighs a sensational 5.79 kg without pedals. I suspect that this bike is also the lightest 24-inch children's bike in the world.

Scott Scale SL 26 inch with tuned RockShox SID

Kids grow fast, Patrick knew what was coming next. "With the 26" wheel size, I was finally able to fall back on standard frames." His choice fell on a Scott Scale 899. In size S, the frame weighs just 890 grams.

He had been looking for the perfect suspension fork for some time. "The second generation of the Rockshox SID turned out to be particularly suitable. Not only is it inherently lightweight, it also offers extensive adjustment options and plenty of tuning potential." The experienced retro bike mechanic procured several SID forks from 2002-2007 in the version with carbon bridge as well as the necessary special tools. He took over several kilos of spring tuning material from an acquaintance. "I started experimenting with that."

After a super-light version, which only had a damper in one fork leg, he returned to an original equipped model, but mixed damper oil in two different viscosities. In other words, he tinkered with the mixing ratio until he had achieved the desired damper behavior. "The fork doesn't work very efficiently on every blade of grass, but on every real bump."

Once again, only super-lightweight parts were light enough, so AX-Lightness wheels and handlebars, a Mighty aluminum cassette, a carbon seat post and saddle combination. "To match the frameset, which already looked old-school in 2020, I had an unused Tune Fast Foot crank in a limited children's size (145 millimetre arm length) and the matching titanium bottom bracket, although I needed a shorter axle again to get a clean chain line."

This time, the son shifts with an XTR/XT combo and brakes with the Formula R1. Without pedals, the racing file weighs 6.7 kilograms. "With the Ritchey WCS rigid fork, I even just cracked the 6 kg limit."

In the meantime, he has also outgrown this bike. The next step is 27.5. Patrick is currently working on the set-up for the 2024 season with 29er wheels. But that's for another time.