The first question depends on the second. For all the talk about latex losing pressure, then I would have zero qualms and no need to pump. Let's face it for most people by the time you setup in transition, faff, swim 3.8km and then do 180km you're not far off 7 hours.

But. If you overinflate the latex tubes they will lose pressure quicker. And so at minimum test at home before, but really I'd get the right tubes - I've not tried my 23mm in my 28mm tubes - I use the 'right' size latex. So I'm not sure if it's going to mean you need to re-inflate, but more that if I was doing an 8 hour ride I'd not want to risk any kit - you've trained for a 250k ride, so don't blow that for the sake of $30 of tubes and 5mins to order online.

I generally don't bother. You might lose something in the 5-10PSI neighborhood over that time frame, not a big issue.

I generally like to match nominal tube size to tire size, but being one size down isn't a big problem.
The main risk factor with latex tubes is the install, so it's not like you should be swapping these in right before the event anyway. If you're concerned about how they'll work, stick them in your tires right now and ride on them until your event.

Or just buy the 25/28 ones online. They're currently in stock on Vittoria's website and from other sellers.

Quote:

If you overinflate the latex tubes they will lose pressure quicker.

Do you mean if I inflate the smaller sized tube to a bigger tire (i.e.: overinflate by size) or overinflate by pressure? I was planning to go by the silca calculator ballpark, which was IIRC ~5.8 bars

Quote:

And so at minimum test at home before

I can't ride for 7-8 hours before the event. Should I just put weights on the saddle/bar with the bike on the trainer? or just pump it up and check pressure every few hours?

Quote:

don't blow that for the sake of $30 of tubes and 5mins to order online.

If the usual (online) vendors had it in stock, I wouldn't hesitate to buy it, but just the venders I could find had too long delivery times (based on their website promises and/or past experience with them). I'll search some more, but my choices look to be between butyl and too small latex tubes (should have planned more ahead, but knowing I had 4 new latex tubes in the drawer, the sizing question haven't occur to me until I took them out this morning)

Overinflate by size, not pressure. It will result in the latext stretching more, so be thinner and therefore more permeable and also less robust. In this case I'd go quality butyl, even though I'd be giving up the 'feel' and rolling resistance. However, I do notice the latex way more on my 23mm bike than my 28mm bike, so the larger volume and lower pressures on the bigger tyres narrow the gap IMHO.

Rule of thumb is latex loses 10% per day. Whether you're riding or whether it is loaded will make negligible difference.

I'm the same weight as you and have done 3 day trips with 8-10 hours of daily riding without reinflating latex tubes. Since my small travel pump doesn't have a gauge, I just add an extra 10% on the first morning. So by the 3rd day I'm still around 90% of the recommended pressure (per Silca calculator). Never had an issue nor really felt the difference of that +/- 10%.

Latex is very flexible so I don't see it being an issue in a 28c tire if it is rated for 25c. Since it stretches only 10% more, maybe it's fair to assume porosity increases about that much.

No need to put weights on the bike, that won't alter the pressure appreciably. I'd expect the difference in movement is more of a factor, but I still wouldn't bother doing more than a static test.


If you're on 28mm tyres, then I presume your pressure won't be huge? I'd decide on your nominal pressure, lets say 70psi just as an example, and then at a guess, or based on a static test assume you'll lose 3-5psi during the ride. Inflate to around 71-72psi before the ride and forget about it.... You can expect to be in the 68-72psi range throughout the ride (ignoring the impact of heating etc as everyone always does!) and if it does drop lower than that it's unlikely to have much effect unless it's really dramatic and you end up with a pinch puncture. But latex tubes don't lose 50% of their pressure during a ride, it's in the single figures so no big deal. If you are worried and not using sealant, then perhaps that will help. I don't use sealant with latex but it should reduce pressure loss. I'm sure others can confirm this and perhaps quantify it.

I use undersized tubes in 'cross all the time (28s in 33mm tires). I've never had a problem.

As the Tour of Flanders was just won on Latex Tubes in around 6:20hrs I think you will be fine.

Similar to jstone, I've been running Vittoria 25/28 latex tubes in 32 cross tires without issue for a few years now. Run what you got and don't worry about it. Same goes for butyl tubes.

I have many years using Vittoria latex tubes in 18/23 and 25/28 in tires from 22-28mm. Good quality tube will lose 0.5-1.5psi per hour. I would agree with the earlier comment that the 25/28 tubes seem to leak a bit slower than the 18/23 tubes presumably as they are less stretched. Definitely top them up and check back 8-12 hours later to see how much yours actually leak down.

I've also done multiple 200k, 300k, and 400k brevets running 8-18 hours using latex tubes. Just add 2-5psi more than optimum at the start to allow for the slight drop down. So if you target 80psi using 28s then start the ride at 83 or so and you should finish with 75-80. For really long rides (PBP or RAGBRAI where I don't want to air up for multiple days) then I would switch to lightweight butyl but for an 8 hour ride you'll be fine.

Only note to add is if you could get a pair of the 25/28 tubes in hand for $30 or so by the time of your event that would probably be ideal but with supply chains as they are that could be hard. Then just keep them on the road bike long term. If you can't get the 25/28s just use the 18/23 tubes and add an extra PSI or two to account for the larger drop. The smaller ones will stretch to fill the 28 and work fine but likely lose air a bit faster and theoretically puncture more easily due to the extra stretch.

The only time I've ever had to pump up my latex tubes while on a ride is when I've had a puncture or leak. 6-7 hour rides are fairly common and it's never been an issue.

---

---

Tubes in CX is still a thing?

---

I have deceptive speed.........I'm slower than I look!

Can be. I run about the same PSI in tubes and tubulars. In other words, considerably lower than tubeless. And dang is it nice to swap out treads for the weekend!

Pro cyclists have used tubular tires with latex tubes for years for 5-7hr. races without issue. Ditto for pro triathletes (before most switched to clinchers), and from the time you pump the tires race morning until you roll into T2 is ~7hrs even for a pro.

For races, I assume that I'll lose ~1% pressure per hour, so I slightly overinflate my tires so that they will be at target pressure mid-ride.

Example: I want 100psi in the tires. It will be 4hrs from pumping until T2 (2hrs prerace/swim, 2hrs on the bike). I would pump the tires to 103psi so that 1/2way through the bike (3hrs from pumping) they would be at 100psi. The ride would start at 101psi, and finish at 99psi*.

*given that most pumps have a few% error, I'm way overthinking it, I know.

---

ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

Wow short answer is no. As long as they don't have a leak they will only lose a couple psi during that ride. Your pump's pressure gauge isn't even accurate enough to make this difference matter. Also FYI latex tubes have been used for rides like this in pro races for decades, and by many amateurs too. Personally I ride latex tubes 100% of the time and I do rides like that twice per week and never think about it. Tire pressure is not something that has to be *that* precise. (And this coming from someone who coaches world tour TT'ers and does regular testing of tires and tubes.)

You do 8 hour rides 2x / week?!? My wife would kill me :)

Thanks all for the info, feel much more comfortable now riding it for the duration. And I've found a store with the right sized tubes this morning, so I should be all set! (but will experiment with smaller sized tubes after event)

You've had better luck than I have then. I can't come close to the low psi of tubeless with latex or butyl tubes without constant flats. How low pressure are you going? And what is your weight?

Tx,
Scott

---

I have deceptive speed.........I'm slower than I look!

Put about an ouce to 1.5 oz of sealent in the tubes. The liquid latex cuts the leakdown quite a bit and while it doesn't work as well as a real tubeless setup, I have saved a couple races when the sealent saved the day.

I haven't in the past for 6-10hr rides. Been fine.

Never tried re: tube size difference in that direction though. Works the other way for sure.

---

Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
-------------------------------------------------------------------------------------------------------------------------------------------------
📱 Check out our app → Saturday: Pro Fuel & Hydration, a performance nutrition coach in your pocket.
Join us on YouTube → Saturday Morning | Ride & Run Faster and our growing Saturday User Hub