I usually add a little more sealant when running inserts. This may seem counterintuitive since inserts are typically as being non-absorbing, but in my experience, the added surface area still manages to eat up some sealant that would otherwise be available to seal punctures.
Ah, the engineer is still in you James. Dusted off integral calculus for that derivation. 0.3mm for the average film thickness, yes? Those approximations seem pretty good to me based on what I dump in.
I only remembered enough about calculus to know that I needed it to do this properly. I even vaguely remembered what it needed to look like. But I unfortunately didn’t remember enough to actually get it across the finish. Thankfully, I knew the approximation would be close enough :)
Thanks for this James. Always great to have a good starting point. You may have written about it before, but do you have a good formula for tire pressures? I'm aware of the ones you mentioned in the article, but I'd appreciate your spin on the idea.
Yay! Math! Excel! Now you’re in my territory. As a math minor (and a Physics PhD) I’ve always loved math. So, in the future editions math is always welcome. Keep up the great work. I’ve always wondered about the sealant needed and even did the same area calculation. The real question is film thickness and amount of leftover needed for punctures. Here in Arizona cactus spines are the biggest off road problem. Fortunately, they seal easily.
Yep, film thickness is primarily what I played with here, but that's really just a theoretical number since sealant doesn't actually distribute itself that way. I settled on 0.3 mm, but mainly because that's what consistently gave me the amount of pooled sealant I felt was needed to deal with punctures.
The sealant distribution in a rotating wheel will be non-uniform. I think, not based on a calculation, that it will be thicker on the centerline and get thinner as you move away from the center. Kind of a crescent moon shape. I wouldn’t expect any on the rim bed while rotating due to the lack of anything to provide the required centripetal force.
I'm not even sure it'd be a crescent moon as there'd be very little to keep all of the liquid sealant from migrating to the outermost diameter of the tire while the wheel is spinning. That's why it's so important to thoroughly slosh the sealant around during installation to ensure all of the surfaces inside get coated initially. This is one of the reasons why Effetto Mariposa sealants are so interesting. They include a foaming agent into the formula so that – at least in theory – there's also sealant contact with any particular area of tire casing to more quickly seal punctures.
Here's a quick online version https://amenable-puffy-coreopsis.glitch.me/
Love it! Now I'll have to convert the volume to grams so I can weigh it instead.
Sealant density shouldn't be all that different from water so you should be able to just swap units and be close enough.
That's what I figured too. Keep it simple.
How do inserts affect the amount of sealant needed? Does less air volume mean less is needed?
I usually add a little more sealant when running inserts. This may seem counterintuitive since inserts are typically as being non-absorbing, but in my experience, the added surface area still manages to eat up some sealant that would otherwise be available to seal punctures.
Ah, the engineer is still in you James. Dusted off integral calculus for that derivation. 0.3mm for the average film thickness, yes? Those approximations seem pretty good to me based on what I dump in.
I only remembered enough about calculus to know that I needed it to do this properly. I even vaguely remembered what it needed to look like. But I unfortunately didn’t remember enough to actually get it across the finish. Thankfully, I knew the approximation would be close enough :)
James, take the next month off now. You've met your subscription cost to value ratio. I love it.
Ha, I wish! No rest for the weary ;)
You’re telling me dumping sealant in until it ‘looks about right’ isn’t the industry accepted method?
:)
The excel nerd in me immediately wants to make the Rim diameter field a dropdown list....thanks for coming up with this!
That was definitely my original goal, but the practical limitations of Substack unfortunately had other plans.
This genius little calculator is going to see a lot of use. Thanks!
Thanks for this James. Always great to have a good starting point. You may have written about it before, but do you have a good formula for tire pressures? I'm aware of the ones you mentioned in the article, but I'd appreciate your spin on the idea.
I typically just use the Silca calculator as a starting point and then tweak from there based on feel.
Effeto Mariposa has got a calculator (it’s an app!) for their Caffélatex sealant. Wheel size & tire width are the variables.
I want to compare your formula with their recommendations. (I’m very curious.)
Yay! Math! Excel! Now you’re in my territory. As a math minor (and a Physics PhD) I’ve always loved math. So, in the future editions math is always welcome. Keep up the great work. I’ve always wondered about the sealant needed and even did the same area calculation. The real question is film thickness and amount of leftover needed for punctures. Here in Arizona cactus spines are the biggest off road problem. Fortunately, they seal easily.
Yep, film thickness is primarily what I played with here, but that's really just a theoretical number since sealant doesn't actually distribute itself that way. I settled on 0.3 mm, but mainly because that's what consistently gave me the amount of pooled sealant I felt was needed to deal with punctures.
The sealant distribution in a rotating wheel will be non-uniform. I think, not based on a calculation, that it will be thicker on the centerline and get thinner as you move away from the center. Kind of a crescent moon shape. I wouldn’t expect any on the rim bed while rotating due to the lack of anything to provide the required centripetal force.
I'm not even sure it'd be a crescent moon as there'd be very little to keep all of the liquid sealant from migrating to the outermost diameter of the tire while the wheel is spinning. That's why it's so important to thoroughly slosh the sealant around during installation to ensure all of the surfaces inside get coated initially. This is one of the reasons why Effetto Mariposa sealants are so interesting. They include a foaming agent into the formula so that – at least in theory – there's also sealant contact with any particular area of tire casing to more quickly seal punctures.