to wear out quickly. It’s no different for tires in motorcycle, F1 and
Rubber compounding is an art. There are four basic properties of
Polymer: Rubber itself. Can be natural, synthetic or a mixture of
Carbon black: Powder mixed in. Affects durability, hardness
and traction. Also makes the rubber black.
Oils: Several different types mixed in. Affects traction, wear rate
Fillers: Mixed in to prevent cracking and to protect against ozone
and those types of things.
I’m not a chemist, but I have been designing basic formulas for
rubber compounds for many years and have a good understanding
of how changes to the main properties affect the end result. I
determine the basic formula by analyzing a variety of compounds
through field testing and laboratory research.
Rubber compounding is all about finding the right combination of
durometer (hard or soft), rubber strength, durability, traction, weight
and TLR (tubeless-ready) sealing.
MBA: How do tire designers decide between a round and square
FS: For me, it’s all about understanding the tire’s intended
application. For example, rounder, inflated profiles are typically
found on XC tires to achieve a fast-rolling, lightweight feel at the
Flatter, inflated profiles are typically found on trail and enduro
tires designed to perform on a wide range of terrain and provide a
good balance of characteristics for climbing, braking and cornering.
Downhill tires have the flattest inflated profile. The focus is on
hard braking and a quick transition from straight-up to extreme lean
angles when cornering. You want the shoulder knobs to bite hard.
MBA: Do you ever sipe or clip tires for your racers? Do you do
anything else special for the fastest guys?
FS: We’re still clipping knobs on the World Cup circuit. Not so
much in XC, but definitely for enduro and DH. We’ll clip hard-terrain
tires to make semi-slicks, only using these on the rear. We’ll clip
mud spikes for certain wet and muddy applications, mostly when
it’s wet in the wooded areas where there are tree roots or rocks.
The clipped spike tread provides more traction in those conditions.
We’re also playing with a variety of air pressures, depending on
rim width and tire choice. We’re searching for a balance of traction,
handling and minimal burping. Weekends can get very busy!
MBA: Is tubeless the best solution for everyone? Why would
anyone use tubes anymore?
FS: For XC and enduro applications, tubeless is pretty finely
tuned; however, tubeless for DH applications still has some
downfalls. But, it’s getting better. The biggest issue is the high
speed, high loads and low tire pressure the riders want to run.
Rims just can’t take the punishment over and over again before
something has to give. Once the rim loses its seal, the tire is flat.
We’ve been working on new technology for DH TLR applications,
and we’re currently testing on the DH World Cup circuit. It’s working
very well. Hopefully, we’ll have something to show the world before
the start of the 2017 DH World Cup season. Stay tuned!
MBA: How much does wheel size affect tire footprint?
FS: I can’t provide percentages or dimension details because
they’re confidential, but obviously with a 26-inch to 27.5-inch to
29-inch tire, the tread footprint lengthens, which means more tread
on the ground and more traction. The wide rim movement is adding
another level of traction. It’s all good.
MBA: Would you prefer a fat bike or a 26-inch bike for better
FS: I’ve never compared the two bikes back to back, but in my
opinion, the fat bike with fat tires is going to have a higher level
of traction on almost any type of dirt compared to the 26-inch
tire; however, when the terrain gets tight, bumpy or there are high
cornering loads, the 26-inch bike should outperform the fat bike.
The fat tires tend to bounce around a lot at speed, and the sidewall
rolls over easily when cornering hard, mostly because the fat tires
require super-low tire pressure to perform properly. ❏
Always tinkering: Frank spends as much time in the field as he
does in the office to work with athletes and design the right treads.
Simply put, the work is never done.
Dialed, simply dialed: Rocky terrain is no problem for the right
tire with enough rubber to protect the rims and give it enough
traction. There are plenty of options that may seem appealing
for this type of riding that will likely leave you stranded.