We suffer from "snake-bites". We use a 700x34 as a back wheel, it stands 3.5 Bar/50 PSI. It seems to be not enough for light gravel. My wife is absolutely not heavy, she is tiny and very slim. I am not heavy as well and we don't carry much luggage with us. Should we use 700x38 or even broader? Should we go for more pressure?

Thanks for your advice

Run that tire to it's max pressure, 3.5 BAR is way too low for a tandem. We run 32mm on ours, and I keep the pressure right around 65-70 PSI in the rear with my wife as the stoker.

And way too narrow a tire for gravel. I would install the largest tire I could fit, somewhere in the mid 40mm’s and run more air.

Thanks. That's what I thought.
Hm. Our tires get to end of life, I will think of replacing them with thicker ones.

if that won’t fit in a 700c size replacing the hub with a 650b will allow you to run a much wider tire.

You need much more air in the tires since it is bottoming out and causing the snake bite tube failures, which can also cause damage to the tire and rim. There is good gravel and there is bad gravel, hence 'your' riding conditions and expectations dictate the ideal tire width, of which personal preference also makes a claim. But let's start with the snake bike problem which is happening frequently from the sounds of it and that points to running too low of a pressure.

Appropriate tire pressure, for the team weight, is of course determined by.... the 'team weight' and the 'bike weight', combined. Whether your tire and rim combination is up to handling the actual needed pressure to support the team (and the loaded ready to ride bike) is another thing. Tires on a quint (5 person bike) with adult sized riders, supporting the vast majority of a 1/2 ton of weight on 1.5" (38mm) tires, needs a minimum of 120 psi, to be steerable and rideable, with regard to the front wheel. Ideally more would be better, both front and rear, but the 120 psi pretty much maxes or exceeds, at least on paper, the capability of available components, i.e., rims and tires. That is of course an extreme yet real life example. A typical somewhat light to middle weight team of say 180 captain and 110 stoker would balance out well with near equal weight front and rear on the wheels with 110-120psi in 28mm tires working out as a near ideal pressure. A 32mm on the rear, with the same team, works well at 95-105psi. Just my 200,000+ miles and 38 years experience being shared. YMMV

Try this -->> To determine your needed tire pressure, put a scale under the front wheel and read the weight with both of you mounted up. A helper and a wall come in hand here! Repeat for the rear. Then apply that new found info to this chart and see what tire pressure would likely work out best for your total weight / tire width combination.

https://www.precisiontandems.com/pho...tirechartx.jpg

There are many online pressure calculators available these days. I am confident all of them will say that more air pressure is needed.

Thanks, tandemdr ,, that's a good explanation.

We run 32mm tires at 95 lbs., have for many years. I worked up to that pressure by experiment. Below that, we'd get the occasional pinch flat. We're a 290 lb. team. That's about the pressure indicated by the chart in the #6 comment.

We are heavier. I am 77 kg (I am tall), my wife 50 (including all dresses, shoes, ..), the tandem 15 and luggage 15 kg, that's a bit more than 150 kg. This is approx 350 lb (funny units you use)

Actually, it's not. Sorry, it isn't, and I doubt very much you are going to go through all of that just to figure out what pressure to use in your tires! Here's a better way: locate the min/max pressures suggested on the tire sidewall. Subtract 10psi from the MAX psi. Badabing badaboom. BTW there should be a really good reason to have different sized tires f/r on a bike.

That's been my original approach. It didn't work. I now have 10 % more than maximum, and it seems to work. We finished our tour and I'll buy other tires that officially can stand the pressure I desire.

If 50psi was 10psi less than max for 34mm tires they are seriously subpar. The max on my 50mm tires is 70psi! Better built tires are definitely available.

These are Challenge Gravel Grinders, no cheap China tires. Their maximum is 3.7 Bar / 52 PSI. They are super fast on paved roads and fine on medium gravel. But I'll change to Secialized Pathfinder TLR Gravel Racing 700x40. They can stand 4 Bar (60 TPI)

Up to about 15 years ago, we used Continental Top Touring 700x35/37 on our tandem for credit card touring. On one trip along the Canal du Midi tow path, we got so many pinched flats (tires at slightly above max rated pressure) that I ran out of patches and spare tubes. Protruding rocks are just really hard on on tires of that size.

My solution was to replace the 700C tandem with 26" wheel'ed tandem when I had the tandem rebuilt (basically new frame and wheels). Now we use 26"x2" slick tires and have not had any snake bite punctures since. YMMV.

26" won't run well, so we will not use 26" for sure. and our bike is made for 28", and it's absolutely great. We're now using a Specialized Pathfinder TLR Gravel Racing 700x40 instead of the Gravel Grinder 700x34, pressure is 3.4 bar, so not too much, but sufficient, the problem seems to be solved.

The strange thing about it is: We tried what tandemdr suggested. Front weight 75 kg, back weight 65 kg, not including luggage. That's a total of just 140 kg. We carry luggage on the back rack, so we have to add a 15 kg for a longer trip. This would be almost the same weight for both wheels. Why do we get these snake bites on the back side only? No matter, we did some hundred kms without any problems, so it seems to be OK now.

Your rear admiral cannot see individual rocks that's coming so have no ways to unload the rear wheel by standing and it's impractical to do so if there are lots of rocks. You, the captain, can't possible call out 'rock' every second. When you hit rocks, snakebites will happen. 65Kg+ seated (note '+' because weight shifts are dynamic) is enough weight to cause snakebites if you don't have enough air volume. On a tandem, you basically have twice the stress there is on a single bike. When we went from 700x35/37 Continental Top Touring, which are very good tires, to 26"x2" Schwalbe Kojak, snakebites never happened again. Kojak is not a better tire than Top Touring just bigger and fatter.

That's what I thought. But it also happened on overgrown ways. And I can't see stones there as well. No matter, it seems like we solved the problem by using fatter tires. The original ones had been in alignment with UCI regulations, but that's of no interest for private rides, we still can use the UCI compliant ones for races.

I have been happy riding various Schwalbe tires for a lot of years without a single flat. Of course with proper pressure as many posters have offered.