I think this is a great resource. The problem with it is going to be user error, in that 90% of the people that use it will not actually measure the width of their tire and will go by the printed number on the sidewall. Or if they measure it they’re going to hold a tape measure somewhere nearby and eyeball it, and their innate biases will lead them to say it’s 23 mm wide when it’s really 24 or 25 mm wide.
All of which means that most folks are going to still keep on doing what they do now, which is to pump their tires up too high. Tradition dies hard.
The user needs to be really hit on the head about actually measuring the width. And then hit again. Then you’ll start making progress but you still need to hit them over the head again. And again.
so, is everyone using a micrometer to measure tire width? I didn’t realize I needed one in my tool kit. I imagine there is going to be a run on Amazon. Anybody have one they like?
so, is everyone using a micrometer to measure tire width? I didn’t realize I needed one in my tool kit. I imagine there is going to be a run on Amazon. Anybody have one they like?
Did you not realise. 😂😂
Also a pump to adjust pressure to 0.1psi
And a thermometer to measure the tread temp and internal tyre temp for further adjustments.
If you’re not checking and adjusting it every 2km you’re so 2010.
so, is everyone using a micrometer to measure tire width? I didn’t realize I needed one in my tool kit. I imagine there is going to be a run on Amazon. Anybody have one they like?
Did you not realise. 😂😂
Also a pump to adjust pressure to 0.1psi
And a thermometer to measure the tread temp and internal tyre temp for further adjustments.
If you’re not checking and adjusting it every 2km you’re so 2010.
🙄🙄🙄
As long as you like to keep unnecessarily wasting watts, I hope you’re in my age group
At the intersection of affordable and decent quality we’re recommending these:
Analog Calipers
Digital Calipers
The ones we use in our lab
Everybody should have a set really, you will find all sorts of uses for them and they come in handy for all sorts of things that you probably aren’t thinking about yet.
At the intersection of affordable and decent quality we’re recommending these:
Analog Calipers
Digital Calipers
The ones we use in our lab
Everybody should have a set really, you will find all sorts of uses for them and they come in handy for all sorts of things that you probably aren’t thinking about yet.
Oh come on. I gave at least a dozen calipers (as a cardiologist) and I don’t need ‘calipers’ to measure a tire. Bend the paper clip so it’s pretty close to the width of the tire and place it against a ruler.
I will also add that calipers are the best/easiest way to verify the rule of 105…
A pair will help ensure that you aren’t making some simple size and pressure errors with tire choice.
Considering that the penalty of getting these things wrong is probably 3-5x more than you would save by dropping hundreds of $$ on ceramic bearings or the like, the $35 calipers seem like a pretty good value!
J
I will also add that calipers are the best/easiest way to verify the rule of 105…
A pair will help ensure that you aren’t making some simple size and pressure errors with tire choice.
Considering that the penalty of getting these things wrong is probably 3-5x more than you would save by dropping hundreds of $$ on ceramic bearings or the like, the $35 calipers seem like a pretty good value!
J
Hi Josh, one thing that I note is that the 48/52 weight distribution is probably true for a pro with a slammed set up… most mortals are not riding that ratio. My simple trial, ie scale under the front wheel zeroed then sit on the bike and see how much of my weight shows up on the front. (the set up was on a trainer and the bike somewhat leveled) said that my normal on the hoods situation was no where near 48/52 but closer to 40/60. I also note that the ratio of air pressure is not a constant depending upon the tire width but that is not a huge thing because most pumps are only good at +/1 psi (that is the minimum reading), but the numbers change with tire width.
So I suggest another addition and that is for riding on the hoods vs drops and most people spend most of their time on the hoods so that changes the front back weight ratio.
ps, BTW I have a couple of pairs of digital calipers and they cost (on sale) less than $20 and I use them a lot. My 25mm Conti 4000IIs are 25.5 and 25.9mm measured at pressure. The fatter tire is on the rear…
Josh, is optimal pressure for two difference width measurements as simple as running the calculator twice and taking the front/rear value or is there something else we should consider there?
As it stands, with my current setup I would be running 86psi rear and 100psi front (27mm/24mm measured).
Does the 105 rule matter much for rear wheels? It’s been a while since I looked at it so I can’t remember if you addressed that, but I thought the rule related to aero properties so might not apply to rear wheels (as much?)…???
…and it appears to be telling us significantly higher than most of Josh and Silca’s blog posts would indicate. I know its just a beta version but I was under the impression from Josh’s hinting at this that there would be many more variables incorporated. Hopefully he’ll chime in here.
The Rule of 105 also matters for rear wheels, but definitely to a lesser effect. As the front half of the rear wheel is either shielded or running in pretty turbulent air, that part of the system isn’t as sensitive to 105. However, if you are running a deep wheel or disc, having the tire narrower than the rim really helps that flow close up much tighter than if the tire is at or wider than the rim. These effects are probably a watt or so for most setups and most yaw angles, so not huge, but also non-zero.
Interesting results for me: according to the calculator, I’ve been running the pressure on my road bike about 10+ PSI too low (I’m running 70 PSI front / rear, and the calculator is giving me low to mid 80s depending upon the surface). I will have to bump the pressure to more closely match the calculator, and see how things go.
Josh - the one thing I don’t see in the calculator is the tire construction. Does this matter at all? Does tubular vs. tubeless vs. butyl tube vs. latex tube affect the recommended pressure? If so, how? Intuitively I would think these would, as they will change the stiffness of the tire.
