Jeremy: You may have seen a video that we did a couple of months back about how tire width
affects braking performance. If you haven't seen that video, you definitely need to go back and
check it out. It was a good one. Below that video in the comments section, many of you were asking
how does tire pressure affect braking performance. In that video, I was able to set my own preferred
tire pressure, no questions asked, no problems. But today, strap on your seatbelts,
or I guess in cycling it's buckle up your shoes tighter because we're about to find out.
Let's talk about some of what we're going to be using in the rules for today. First of all,
I'm going to be starting out on these 32c Pirelli Cinturato tubeless road tires versus
these Pirelli P Zero 25c tubed tires. This is going to be a duel for the ages. 32 versus 25,
it's like the old versus the new, the thick versus the thin. This is going to be serious.
We're also going to come flying down this hill at 30 miles per hour, which is
48 kilometers per hour. We're going to set a predetermined spot where we hit the brakes every
time then we're going to measure it out, just like we did in the other video, and find out how
quickly we could stop and what the different tire pressures that we run and how that affects our
braking performance. I'm thinking something like maybe just over 100 psi and then all the way down
to probably around 50. Whatever the manufacturer says is okay, we'll probably go with that.
I think I'm just going to lay the line down here. I'll come down here flying down and then just send
this right down here. Let's see how we do. Okay. [music]
The thing about doing these videos, I love doing these videos, but
I'm seriously going to end up doing like 100 reps of this climb right here today.
Oh my God. We got to go from that. That was only 50 pounds of pressure.
[music] The thing with people and tire
pressure it seems like is that everybody always thought back in the day, they'd have their 23c
tires at 120 psi and they'd be like, when they had a flat tire, things would just go everywhere.
I'd even show up to Cyclocross races and people would have their Cyclocross tires at 70 psi and
they'd ask, "Do you know anybody that does back work? My back is absolutely killing me."
I think that we know by now that with tubeless tires and bigger, wider tires
that running 100-plus pounds of pressure on your tires doesn't necessarily always make the
most sense. We're definitely going to find out how it affects braking performance right now.
Heart's going, adrenaline's going. First test of the day. These are the 32
Cinturatos at just at 100 psi. We're going to get this up to speed and then we'll measure it out.
All right, here we go. [music]
All right. Best out of three. Let's see what happens. One more time.
We'll put a little piece of tape right here. 32 at 100 psi. I did three tests.
That's the 32 at 100 psi. The other thing that I think I noticed about the 100 psi
is that it breaks free quicker. On the first two runs that I did, I lost basically the back
end. It started to skid on me way sooner when I got on the brakes hard so that was
one big takeaway that I think I noticed immediately with the high pressure
in these. Let's drop these down to 75 and see what happens. We're at 80.
All right, 75. [music]
All right, well, that’s my 32 over 100 and this right now is a little shorter.
That's my marker. Just to see, I'll do another test just to confirm the result.
Even shorter. This was my second attempt and let's see.
I think that middle one if I split the difference, that's what I did last time. I just
averaged everything out. All right, let's bring these down
to 50. Let's see how these do. All right. Here we go.
That's nuts. All right, everyone, so we've got some serious results here. Hang on a minute.
I want to give everything away, but this is some very interesting findings. What do you guys think,
should we do one more? Should we just go down to like 40 just to see what happens?
That's crazy. I don't know if you guys can see a pattern that's happening here, but
there is one. How low do you want to go?
All right, so we've got to switch these out now over to the 25c tires at 100 psi, has not happened
in my life in a long time. The bike is just like a little dart, it just darts all over the place. I
can't imagine that we used to race criteriums and stuff like that on these. It's definitely very
different to have 25c tires on this, but we’re going to find out how these brake under pressure.
[music]
All right. Wow. That's hilarious. That is dead spot on in the middle of the two spots.
What do you think is going to happen?
Let's mark this one down. First shot. The exact same spot.
Ladies and gentlemen, that's the test.
[music] The moment that you've all been waiting for,
the results. Here we go. The longest amount of time that it took to stop was with 100 psi with
25c tires. I know. You guys are thinking, "What the heck?" but, it actually took us 1,111 inches
or 28.21 meters to stop. Our next tire was the 32c tire at 100 psi. That was 1,055 inches or 26.797
meters. Back up to there, it was 75 psi at 25c, which was 997 inches or 25.324 meters. Here,
we have 50 psi in 25c. That was 980 inches or 24.892 meters. Then here we had the 32c tire
at 75 psi, which was 24.485 meters. Then way back up here, we had this bad boy. 32c at 50 psi,
863 inches or 21.92 meters. Then, yes, the winner, 32c 40 psi, which was 788 inches or 20.015 meters.
Pretty unbelievable how that all worked out to look at these numbers. The difference between
the 32c tire at 40 psi and the 25c tire at 100 psi was significant. The difference between going
through an intersection and being able to stop or not if a red light or an accident were to happen.
I was really blown away by how much of a difference there was. I would say everything
that we did seemed pretty legit. I start at the exact same spot. I spun the bike out all the way,
got it to 30 miles an hour, and hit it from that line all the way down here, and got on the brakes
super heavy. It feels like a very scientific way to do this. I'm really happy with the
results. I think it came out good and I think that we have some real tangible results here.
All right, so that is a day at the races with our shoes buckled tight. We've got some results out of
this. This was, of course, a very scientific way to do this, but I had a lot of fun doing it. Let
us know what you think. Between the other video about tire width and braking performance and now
with tire pressure and braking performance, I would love to know what you all think of
what we came away with here today. Was it what you expected? Is it not what you expected? Will you be
buying some wider tires and running them at lower pressure to potentially stop faster?
Let us know down in the comments. Thank you all so much for watching. We'll see you next time.
All right, here we go. One last test. I can't just leave without not doing this test. Okay,
let's see what we can do. How far can we go? Oh, gosh. I'm going still. I'm going.
I'm past 360 inches. That's all I wanted to do.
[laughs] I don't need to measure it, I'm good. [00:10:16] [END OF AUDIO]