Even just a few years ago, we were still suggesting front pressures as much as 8-10% lower than rear pressures, but as our data set has grown larger, we find that some of the most successful CX racers at the professional levels are running front pressures within between 0-3% lower than the rear. We’ve even found that front pressures are occasionally higher front than rear if the course has particularly steep downhill sections with roots, rocks or other obstacles where
rim and tire damage seems to be more concentrated on front wheels.
Tire size and choice. We strongly recommend the largest tire you can fit in your frame or if
you are racing UCI, the largest tire that will fit within the rules. There are no courses or conditions we have ever seen in cross that favor narrower tires. For years the conventional wisdom was that narrower tires were faster on
harder pack surfaces when conditions were dry. It was believed that the narrower tires would roll faster at slightly
higher pressures and also that the reduced weight was a significant advantage. Modern data collection
combining power measurements with highly accurate GPS have shown this to really never be true. The weight advantage of a
1-2mm narrower tire is very small and the rolling resistance penalty to higher tire pressures on rough surfaces can be quite high. For this reason, we recommend the lightest, most supple tire you can find at the widest width you are allowed to use in
your event. And of course, if you are not running tubeless, then you MUST be running latex tubes whether you are
riding clinchers or tubulars. Latex tubes have lower rolling resistance by as much as 3-4 watts per tube, are more
resistant to pinch and puncture flats, are lighter weight, and provide significantly improved ground feel through the tire. It has been shown over and over again in testing that riders on latex tubes are not only faster at the same power
output, but also have a better feel for what is happening at the contact patch of the tire.
To start optimizing your pressure, we recommend
1. Keep a log book or journal of your experiences.
Since no two riders will sit on the bike in the same way or pick lines
in the same way, your optimal pressure will be specific to you and to each
course. Using the experience of others
is a tremendous time saver in establishing a baseline, but it is important to
note that another rider of similar size and weight will almost certainly have
an optimal that is near, but different than yours..and for this reason, keeping
a journal will help you dial your numbers faster and with better certainty than
any other method. This will also give
you a solid baseline for future events on a given course.
2. Buy a high quality gauge or pump with high quality gauge and ONLY use it.
All gauges are subject to various types of error.
Buying a high quality one will ensure your numbers are more accurate,
and using the same pump or gauge will ensure your precision is high. I always refer back to my Paris-Roubaix story
where we found the 3 pumps on the CSC truck at Roubaix varied by 12psi when
exposed to the same pressure, and the team was breaking rims and flatting
because of it. Standard gauge error is
+/-5% on most bicycle pumps and +/-3% on most digital gauges (SILCA gauges are
all either +/-1% or +/-2% with precision of better than 1%) this means that 2
of the ‘identical pump’ can have as much 2-3psi difference between them at CX
3. Use the ‘conventional wisdom’ of others as a starting point.
If you have a teammate or friend similar in size, use their experience as a starting point.
If not, start a little bit high and comedown. For 33mm wide tire, 150 lb rider,
I’d start at 28psi and work your way down.
At the top UCI pro level we see riders at this weight commonly running
pressures in the low 20’s and lighter weight riders in the UCI women and junior
fields have been known to run in the 17-19psi range with success… but it is
important to remember that as rider weight goes up, the minimum pressure should
go up as well. Also note that more
experienced riders tend to ‘ride lighter’ than less experienced riders. We see that at the top UCI level, riders can
generally run as much as 1psi lower than their weight might suggest. Again, this is an area to exercise caution as
riders will tend to ‘ride heavier’ as they fatigue which brings us to our next
4. For non-professional CX racers, we recommend reducing pressure until you experience
1 light bottom out of the tire through the roughest section of your course.
I recommend re-riding this area numerous times to be sure that you are
comfortable with it, you may also find certain lines to be softer than
others. Then, we recommend adding
0.5-1.0 psi to that pressure knowing that your race speeds will be higher than
your pre-ride and also that you may have less choice of racing line during your
event. If your event is longer than
typical for your category, we recommend adding 1.0-1.5psi over this bottom-out
pressure. So if you are generally riding
40 minute races and you are entered in one that is 50 or 60 minutes, add another
0.5psi. This can be critical in mitigating
rim or tire damage. We commonly see that
riders who do suffer equipment failures of this type most often do so at the
end of their event, and if the event is longer than standard the likelihood of
damage can be even higher.
5. Write it all down.
The more data you compile, the better your knowledge will be as you move forward.
Top teams and riders keep highly detailed notebooks on pressure and tire
type and other critical course details.
Our experience shows that with some minimal effort to log your
performance you can gain critical seconds per lap and reduce or eliminate the
likelihood of a pinch flat or rim damage.