Tandem Weight Distribution for Tire Pressures

[John Hawrylak]

what is a good front/rear weight distribution for a tandem to calculate the "optimum" (15 tire deflection) pressures  (2007 BQ article with F Berto's graph)???  I would think at least 40%/60%, but is it more, like 30%/70%????.

Trying to help a couple get the optimum pressure for a Al tandem with 28mm tires and 300# total weight.  Currently using 105 psig F/R, with the optimum being 90 & 138 psig (F/R) with a 40%/60% split.  They get quite a few rear flats, probably no surprise from the results.  Also, trying to show them the advantages of a 32mm rear (pressure decreases by 22 psig, to 116 psig)

John Hawrylak

Woodstown NJ

[Bubba]

I would think a tandem is closer to 50/50 than a single bike, because the Captain's weight is biased forward, more on the front tire than the rear.  The Stoker's weight is certainly much more on the rear tire than the front, but if the captain is heavier than the stoker, I'd start at 50/50.  Otherwise, two bathroom scales will help you determine it empirically.  

Bill Lindsay

El Cerrito, CA

[Nick Bull]

Where do you find a 700x32 that takes 116psi?  Most that I know of (Panaracer Pasela, Grand Bois Cypres) take 95 max.

On the tandem, I assume the weight distribution is roughly 50/50 and pump both 700x32 Pasela's to 95psi.

FWIW, I've ridden 11112 miles like that and can only think of three flats, one of which was because we ran over a piece of clear glass mixed in with shards of ice on a winter day, and one because I accidentally ran the tires down to the threads and the innertube extruded and flatted.  I'm not running the Tourguard version, just the steel-bead, non-Tourguard case.

[John Hawrylak]

Nick

The 116 psig was calculated using the 15% tire drop method in the 2007 BQ article on F Berto's work.  Thanks for pointing out it is > Mfg Max Pressure.  F Berto had an article in which he stated the Mfg Pressure rating is determined by testing the tire to TWICE the rating and verified the tire remained on the rim.  The rim used has a "normal" hook.  So a 95 psig rating on the Pasela indicates Panaracer tested the tire to 190 psig and it remained on the rim.  Inflating > 95 psig reduces the margin for the tire blowing off the rim. This is one reason to go to a wider tire.

John Hawrylak

Woodstown NJ

On Tuesday, November 4, 2014 2:31:39 PM UTC-5, Nick Bull wrote:

Where do you find a 700x32 that takes 116psi?  Most that I know of (Panaracer Pasela, Grand Bois Cypres) take 95 max.

On the tandem, I assume the weight distribution is roughly 50/50 and pump both 700x32 Pasela's to 95psi.So a 32mm Pasela would be tested to 190 psig

[Allan in Portland]

Another data point in favor of a 50/50 split is that my tandem has fairly even wear between the front & back tires. I don't see that on my single bikes, which obviously have more weight on the rear and the rear wears faster.

-Allan

On Monday, November 3, 2014 3:24:06 PM UTC-8, John Hawrylak wrote:

[Nick Bull]

Hi, John,

I know the conventional wisdom is that mfg's list max psi ratings as half of the tested blow-off pressure, but even if this was true many years ago, it may not be true any longer.  I'd be hesitant to go so far above max psi, since there doesn't seem to be much benefit to doing so, based on BQ's more recent tests of rolling resistance variation with tire pressure, which showed rolling resistance increasing with higher psi, above a certain point.  With my Pasela 700x32's at 95psi front and back, I've never had problems either with pinch flats or with feeling like the tires are flexing too much in turns or when standing up.  So going with high pressure seems like it doesn't really "solve a problem."  And to the extent that you are taking on some amount of risk, your stoker might be happier for you not to do so.  Hard, extended braking on a downhill can certainly heat a rim enough to increase the effective psi on a tire, so if the tire is already potentially somewhat overstressed taking downhill corners at 40mph with 300+ pounds of weight on it, then overpressuring it might actually get you closer to the blowoff point than is comfortable.

FWIW, I asked Jan Heine about using the Grand Bois Cypres (700x30) on a tandem and he discouraged that idea.  Which is a little too bad, because on one ride where I hadn't noticed that I had run the Pasela down to the threads, the tire finally wore through and we got a flat and fortunately we were carrying a Cypres as a spare.  It felt notably plushier than the Pasela, even on the back of the tandem.

Nick