Working out the Best tyre pressures

[nobby]

I punctured yesterday.

Out on the Black Country canal circuit with Cycleman just 18km from where we started the front Marathon not plus went flat. Cue much crowing from the old chap on the Trice with his £1.99 still inflated tyres.

Neither of us could find anything poking through the tyre carcase. The tube turned out to be punctured on the inner circumference about 60º from the valve suggesting a spoke head poking through but they are double wall rims. We both passed a fine eye and a sensitive finger around the rim and could find nothing amiss. Two Park's 'Super' patches failed to hold so I turned to my traditional glue kit to find that both tubes of glue, one unopened had dried out. Ho hum.
Cycleman offered his traditional kit - that he never travels further than the bathroom without - only to discover he had left it in Slough He didn't offer to ride home for it!
Following a double careful check of the rim interior again I put the spare tube in; 4km later it was flat.
I bailed out, Cycleman carried on and, apparently, a young chap from Dudley engaged in conversation with Cycleman and is now in hospital with a bent ear.

At home I discovered that the second tube was punctured in the same place as the first. Peeled off the rim tape and the backing is flecked with aluminium swarf.

[rogerzilla]

I think Tom Boonen would have been on tubs for Paris-Roubaix (probably expensive Dugast ones with a different sponsor's logo stuck on them) so no snakebites.  That's an extreme example and he would have willingly sacrificed speed on the tarmac for being able to see straight on the pavė.

As an aside, I wonder how easy it is to wangle a wheel change just before the first pavė starts?  IIRC there's a lot of decent road before the cobbles start.

When you get into human losses on rough roads, it all becomes unmeasurable and woo-woo, dependent on too many factors like position, body weight vs bike weight, gear choice and personal tolerance.  And if I lost 200W, I'd be going backwards 

[cycleman]

The young chap in  dudley is infact in fine health and seems very interested in joining the forum. It is a very rare occasion for the "be prepared "nobby to be unprepared  .  Not a opertunaty to be missed 😁

[sojournermike]

....  And if I lost 200W, I'd be going backwards 

Riding fixed again?

[andrew_s]

When you get into human losses on rough roads, it all becomes unmeasurable and woo-woo, dependent on too many factors like position, body weight vs bike weight, gear choice and personal tolerance.  And if I lost 200W, I'd be going backwards 

It was in USAnia, derived from comparing power meter readings riding along the rumble strip at the side of the road. and on the road immediately off the rumble strip.
IIRC, the difference was 270 W at 17 mph, with 17 mph being selected because that was as fast as the test rider could cope with for the necessary number of repeat runs.

For those that haven't seen them, US rumble strips are a series of gouges taken out of the road surface after it has been constructed, something like 12" wide, 4" long, 0.5" deep, and 6" apart

[quixoticgeek]

For those that haven't seen them, US rumble strips are a series of gouges taken out of the road surface after it has been constructed, something like 12" wide, 4" long, 0.5" deep, and 6" apart

Why?

J

[Kim]

That's well into comedy on-roading territory.  For a more meaningful real-world test, you need to find a suitable BRITISH county boundary, where it's decent tarmac on one side, and decaying chipseal on the other.  Sort of thing that feels like you've been plunged into treacle when you ride across it on a Brompton.

[LittleWheelsandBig]

The rumble strips wake up sleepy drivers drifting into the hardshoulder.

When I rode the 259km Paris-Roubaix Cyclo back in 2004(?), I had a heartrate monitor but not a powermeter. Entering pave sectors gave me an instant 10 beats higher for the same speed.

[sojournermike]

Tonight on 'good Yorkshire tarmacadam'^TM I would swear I was producing something over 400 watts, but the average speed and the power meter both suggest that I lost more than 200 watts in body losses during the course of the ride. Pesky 23mm Corsa Speeds...

More seriously, it is a thing that I suspect we've all experienced.

[Lightning Phil]

I use http://www.dorkypantsr.us/bike-tire-pressure-calculator.html which has it set for 15% drop and Michelin values as well.

I have 37mm on front , and 32mm on rear of recumbent.  I have the pressures at 40 psi and 60 psi for my combined weight.  They work just great, no vibration of note.  At those pressures it holds fairly well so I don’t check them all the time (other than the squeeze test). Maybe once every 2-3 weeks.

I haven’t tried different pressures to see if it makes a difference to my average speeds.

As to puncture protection. The front is a Panaracer Pasela with no puncture belt. Two punctures in 6 months, though one was downhill and did lead to some elbow and leg scrapes. In winter I’ll bung Marathon back on.

[cygnet]

I think Tom Boonen would have been on tubs for Paris-Roubaix (probably expensive Dugast ones with a different sponsor's logo stuck on them) so no snakebites.  That's an extreme example and he would have willingly sacrificed speed on the tarmac for being able to see straight on the pavė.

Until one year the similarly heavy Cancellara did the same but with aero rims to reduce the watts lost on the tarmac. Next year all the favourites were on them

As an aside, I wonder how easy it is to wangle a wheel change just before the first pavė starts?  IIRC there's a lot of decent road before the cobbles start.

A similar era Lars Boom swapped to a cross bike before the cobbles, back when you could get a bike change from a bloke at the side of the road, instead of off the team car miles behind.

[Cudzoziemiec]

For those that haven't seen them, US rumble strips are a series of gouges taken out of the road surface after it has been constructed, something like 12" wide, 4" long, 0.5" deep, and 6" apart

Why?

J

Because Usanians don't use metric, of course!

[ElyDave]

I use http://www.dorkypantsr.us/bike-tire-pressure-calculator.html which has it set for 15% drop and Michelin values as well.

I have 37mm on front , and 32mm on rear of recumbent.  I have the pressures at 40 psi and 60 psi for my combined weight.  They work just great, no vibration of note.  At those pressures it holds fairly well so I don’t check them all the time (other than the squeeze test). Maybe once every 2-3 weeks.

I haven’t tried different pressures to see if it makes a difference to my average speeds.

As to puncture protection. The front is a Panaracer Pasela with no puncture belt. Two punctures in 6 months, though one was downhill and did lead to some elbow and leg scrapes. In winter I’ll bung Marathon back on.

Well for 150lb of rider + 30lb of recumbent with 28mm tyres that says either 137psi F&R or 52psi front and 80 psi rear - that's a massive variation.

I think I'll stick to my 7-8 bar F&R

[Brucey]

I use http://www.dorkypantsr.us/bike-tire-pressure-calculator.html which has it set for 15% drop and Michelin values as well.

Well for 150lb of rider + 30lb of recumbent with 28mm tyres that says either 137psi F&R or 52psi front and 80 psi rear - that's a massive variation.

It is badly worded perhaps but it says no such thing.

 The top panel in the calculator allows you to enter the weight measured at each wheel of the loaded bike (eg using bathroom scales). Hence it says 'weight measured at wheel'.

The second panel assumes that the weight distribution is 40% front 60% rear or 45% front 55% rear; you get to choose between the two settings but if neither is correct (and it probably isn't, not for a recumbent) then you shouldn't be using the second panel at all.

So an example;  if your recumbent is front heavy (many are) then your actual weight distribution might be 100lbs front, 80lbs rear.  For 28mm tyres, using the top panel  this gives recommended  pressures of 74psi front, 59psi rear.

cheers

[ElyDave]

Very badly worded in that case, because "Weight Measured at Wheel" as you say is not the same as "Bike plus rider"

Even so, on a road bike, assuming the same distribution as them, with 180lb of road bike, rider and "stuff" the recommendation is 3.5 bar for a 28mm tyre from the bottom panel.

Your example is barely 5 bar.

[Brucey]

I don't necessarily agree with the recommendation in all cases, but at least we can understand what it is trying to tell us.  I probably wouldn't ever go any lower than that recommendation even on a DF bike, and that would certainly be the case for a recumbent.

IME running low-ish tyre pressures on a recumbent is just begging for bent rims etc, since even if you see a pothole coming, you cannot 'unweight' the bike in the same way; you are pretty much sat on the thing like a sack of potatoes and there isn't much you can do as you plunge into every pothole apart from grin and bear it.  Higher tyre pressures reduce the chances of pinch punctures and pothole damage to the rims etc. with narrower tyres, even if they do nothing for comfort.

cheers