9 days with Pedro Burns to determine the perfect Slash setup

The art and science of enduro shock testing

Enduro mountain bike racing is a complex sport by design, an all-encompassing test of endurance and skill comprising a series of timed downhill stages and leg-sapping climbs in between.

Enduro bikes are as unique as the sport itself. They’re engineered to serve paradoxical purposes, to somehow control like a downhill bike, and climb like an XC bike. All the while they need to be durable because riders are often responsible for their own repairs when they’re out on the course. There’s a reason why Trek Factory Racing’s enduro team races on a bike called the “Slash”: It has to do everything well, all at once.

Pedro Burns at the Trek Suspension Lab in California.

The technical minutiae involved at the highest levels of any pro cycling discipline is staggering, but enduro mechanics elevate the craft to an artform. Recently, Chilean TFR rider Pedro Burns went to California to visit the Trek Suspension Lab’s Jose Gonzalez and Ely Woody for nine days of shock testing and tuning in preparation for the 2021 season. The process of getting the bike tuned just right to Burns’ riding style was guided by gut instinct as much as science.

Woody was kind of enough to guide us through what that process looks like, starting as soon as the rider suits up for a long day on the bike.

A piece of obsessive engineering.

Striking a balance

Burns’ trip to California was long overdue. Trek released a new Slash last September, which meant that any tuning beforehand had to be done in the midst of travel restrictions due to the Covid-19 pandemic. Burns was unable to do the sort of in-person testing that both he and Woody would have preferred. As Woody puts it, “we basically showed up, jumped on the new Slash, and went racing.”

Shock tuning involves many micro adjustments to determine the optimal levels of rebound, compression and travel for the rear shock and front fork. Bouncing up and down like a pogo stick? Maybe turn up damping to slow down rebound. Bottoming out on the travel a lot? Increase compression and perhaps add spacers. That’s Woody’s process in broad strokes.

Pedro Burns putting the Slash through its paces.

More specifically, Burns and Woody wanted to test out shock tunes that Gonzalez, founder and director of the suspension lab, had created based on the team’s feedback in 2020. He wanted to add more sensitivity to last year’s shock, but not so much that it bottomed out frequently. Burns and Woody were tasked with testing it.

“Everything in suspension is a balancing act, so finding just the right amount of suppleness without sacrificing mid-stroke support or bottom out resistance,” Woody says. “It’s key to get the validation of team riders on these things as they will be the ones putting them to the test against the clock.”

Burns rode on three different shock tunes, all on a RockShox Super Deluxe thru-shaft air shock, on more than 10 different trails. Woody ran the tunes through a variety of settings until they found a setup that seemed to work best for Burns. Across nine days, they ran a lot of trials.

Jose Gonzalez making adjustments in the field.

A or B

Conditions change drastically from one outdoor bike race to the next. In enduro, riders and mechanics must be prepared for all types of terrain — from rock to mud — and even altitudes, which will affect a shock’s air pressure and volume.

Woody and Burns put the Slash through as many different scenarios as possible, each time running through a battery of A/B tests. Similar to an eye test at an optometrist’s office, Woody would make Burns ride two different shock settings back-to-back and ask him which he liked better — A or B — and why. 

Woody is careful not to explain his adjustments too much to riders before they run tests, “in order to keep things pure and unbiased.”

Everything gets taken apart and put back together.

“We’re looking for raw feedback, and if the tester has too much information going in, it can create expectations that may not be accurate,” Woody says. “After a few runs, or at the end of the day, we discuss the differences between Shock A and Shock B and try to match what the rider was feeling to changes that were made. If necessary, the shock will then go back to the lab for changes and a simulated run before coming back out for another field test session.”

Burns is good at giving honest feedback and keeping an open mind to whatever Woody may want to try. According to Woody, there’s no such thing as being too meticulous.

“This process basically just repeats itself until the rider is happy, comfortable, confident,” Woody says. “And the lap times get shorter!”

Sharing data from out on the trail.

Easy does it

Woody can’t stress this enough: The adjustments made between each test run are small. They have to be, or else the information being gleaned would be much too noisy. 

“We only change one variable at a time in order to isolate the result of each individual adjustment,” Woody says. “Changing multiple settings drastically at once can upset the balance of the process and leave you confused as to what is actually happening with your suspension on the trail.”

Burns isn’t sending down a full trail every run, either. Sometimes, he’ll re-do the same short section — like a sharp corner, or a big drop onto a flat — dozens of times to work out any peculiarities of the shock tune. The process may be tedious, but it pays big dividends once the rider goes back to the full trail.

Pedro Burns prepares for *every* condition.

At the end of nine days, Woody and Burns settled on a shock tune they liked for the season. It isn’t final yet — a copy of the tune was sent to Europe so that Burns’ TFR teammates Florian Nicolai and Hattie Harnden could test it out themselves — but Woody believes they came up with a soft tune that won’t blow through the travel. 

“You have a lot more sensitivity at the start of the stroke, but then also with the volume spacers and an elastomer bump stop in there, it gives you a lot of support right at the end of the stroke,” Woody says.

The tinkering process never truly ends, however. Bike setups evolve throughout the season depending on the race, weather and a rider’s ever-changing needs. And of course, one thing matters above all. 

“Our first Enduro Worlds Series race is in June,” Woody says. “That will be the ultimate test of our efforts!”