Grand Bois Cypress 700x30, recommended pressure for 260 lb rider?

[Jim Bronson]

Just curious to see what other people are running on this tire as far
as pressure goes and what they might recommend for a 260 lb rider. I
rode the tires 13 miles last night after putting them on and I rode at
95 psi and it was very cushy. It also rolled very nicely, better than
the old 700x28 Gatorskins they replaced (that I kept inflated to 120
psi!) and they corner well. Unfortunately the wind direction changed
to the north, the temperature plummeted from 75 to 50 and it started
raining, so I had to scurry back home after only 13 miles. Otherwise
I might have kept going all night on these wonderful tires.

I imagine other people are running less pressure. The VBQ article
mentioned 55-75 psi. They seemed a bit squishy even at 95 though,
although it was not reflected in the handling characteristics. Maybe
I could go a bit lower to 85.

Thoughts?

--
I ride my bike, to ride my bike.

[GJones]

I am not sure if I am doing what is "correct" but I have found them to
be a big improvement for my hands on long rides due to the lack of
road vibration.

I am running them at about 80 or 85 lbs on a tandem that is carrying
more than I can admit to. I would like to run with a higher pressure,
but I think that is the maximum that the tire is rated for. I have
already blown off a front tire (different brand) on a steep descent on
the tandem due to heat from the brakes. I have no desire to do that
again.

[John McClellan]

I use them on a tandem with ~350 lbs of riders and stuff at 90 lbs and
that seems to work well for us. I've pinch flatted other brands of
32mm tires at 90 lbs on my favorite rough rural roads, so I'm not
inclined to go lower than 90 on the tandem. I would think 80 should
be great at 260 lbs.

> > I ride my bike, to ride my bike.- Hide quoted text -
>
> - Show quoted text -

[Jim Bronson]

Well I don't have room for tires any wider than that, in fact the 30mm
Cypress are pretty close to the brakes, within a couple mm. I have
one of the few Rivendells out there that use short-reach brakes. It
was custom built for someone else of similar stature so I didn't get
to choose.

My bike probably weighs 25 lbs unloaded.

So to solve this problem, I guess I'll just have to lose at least 15 lbs :-)
I've been thinking I should do that anyways, I'm sure it would help me
on the hills.

On Dec 13, 2007 11:55 AM, Jan Heine <hei...@earthlink.net> wrote:
>
> The maximum pressure ratings of the various Grand Bois tires are as follows:
>
> 700C x 28 mm: 105 psi
> 700C x 30 mm: 95 psi
> 650B x 32 mm: 75 psi
> 650B x 42 mm: 75 psi
>
> For the new 700C x 26 mm, I'll have the pressure ratings when the
> shipment arrives.
>
> In Bicycle Quarterly Volume 5, No. 4, p. 29, Frank Berto showed how
> to get the recommended 15% tire drop for various tire sizes and
> weights by adjusting the pressure. According to Berto's data, you get
> the following maximum weights for these tires:
>
> - 700C x 28 mm: 270 lbs. (at 105 psi)
> - 700C x 30 mm: 270 lbs. (at 95 psi)
> - 650B x 32 mm: 250 lbs. (at 75 psi)
> - 650B x 42 mm: 300+ lbs. (off the chart at 65 psi)
>
> So basically, you are fine at 260 lbs. on 700C x 30 mm tires, riding
> your front tire at 80-85 psi and your rear tire at 90-95 psi. You can
> fine-tune this by measuring the weight distribution of your bike, and
> looking at the table in BQ. Note that you need to count your bike and
> luggage in the weight, too, not just your body.
>
> If you weigh more than the maximum weights shown above, that is not a
> problem, it's just you get sub-optimal performance, because your tire
> drop exceeds 15%. In that case, I would recommend that you use wider
> tires.
>
> Some makers say that the recommended maximum pressures have some
> leeway in them. These ratings assume a slightly poorer than average
> fit of tire to rim, plus a margin of safety. If your tire is tight on
> the rim, you may be safe to inflate a little more. If your tire is
> really loose on the rim, you should be careful. (Rims and tires both
> have tolerances, with the worst-case scenario being a slightly
> oversize tire on a slightly undersize rim.)
>
> I don't obsess over tire pressures too much, partially because I know
> most pressure gauges are not very accurate. Comparing two floor pumps
> showed that at the same pressure, one indicated 75 psi, the other 65
> psi. I usually run my tires with a tire drop of about 12%, so if my
> pressure gauge is off, I still am in the recommended range.
>
> Tire drop: This is how much the tire deforms under load. Basically,
> it compares how high the tire stands empty with its height under
> load. For optimum speed, you want enough tire deformation that the
> bike does not vibrate much on road irregularities (the vibrations sap
> energy), but not so much deformation that the casing has to work too
> much (working the casing saps energy), or even so much deformation
> that you get a pinch-flat. Our real-road rolling resistance tests
> showed that around 12-15% tire drop is the optimum compromise between
> comfort and speed. Higher pressures don't gain any significant speed.
> Lower pressures are more comfortable, but you begin to slow
> considerably. If you want to run lower pressures, get wider tires so
> that your tire drop is back in the 12-15% range.
>
> Coincidentally, most tire manufacturers recommend running their tires
> at a tire drop of 15%.
>
> Disclaimer: Vintage Bicycle Press sells Grand Bois tires.
>
> Jan Heine
> Editor
> Bicycle Quarterly
> 140 Lakeside Ave #C
> Seattle WA 98122
> www.bikequarterly.com