Author Topic: Tyre pressures  (Read 587 times)

Blodwyn Pig

  • what a nice chap
Tyre pressures
« on: January 03, 2020, 09:13:27 pm »
On a  fully suspended 20/26 machine, such as a street machine, what would be a good pressure  F + R.   Is there any speed advantage to having them at max pressure, as presumably the suspension will take the edge off, or is softer ( wider footprint ) better / faster.

Re: Tyre pressures
« Reply #1 on: January 03, 2020, 09:47:00 pm »
Pro peloton upwrongers have taken to riding wider tyres at lower pressures over the last couple of years, and the general consensus now seems to be that lower pressures allow tyres to absorb and roll over bumps, stones and road furniture. The thinking is that hard narrow rubber bounces off obstructions which slows overall progress.

Rider and bike weight will also play a big factor in setting pressures.

If you fancy a (bit of a long) read check out Sheldon Brown and his merry men's take on it here: https://www.sheldonbrown.com/tyres-husband.html

At an all up weight of roughly 112kgs I ride 25mm tyres at 80psi on the upwrong road bike, 21 psi in 2.4 inch wide tyres on the mountain bike and a pressure yet to be determined on the PDQ as I'm still building it!
Rebuilding a PDQ frame to restart my recumbent collection!

Kim

  • Timelord
Re: Tyre pressures
« Reply #2 on: January 03, 2020, 10:31:03 pm »
The Vorsprung Durch HPVelotechnik will take the short sharp shocks off (potholes, comedy off-roading and so on), but the higher frequency stuff is still down to the tyres.  On a Streetmachine style bike, that's more about optimising grip and rolling resistance than avoiding road buzz injury to your hands or feet as you would on a DF or unsuspended recumbent.

FWIW I pump the 40mm Marathons on my Streetmachine to 70-80PSI for fully loaded touring on road, leave it un-topped-up for months on end for unloaded riding (particularly in winter), and deliberately reduce it a bit if I know I'm going to be dealing with proper amounts of rough stuff (which includes Dutch paving).  It doesn't seem particularly critical with Marathons, unlike the rear suspension, which has a definite sweet spot for load and conditions.

(I tend to go with the same pressure front and rear, it's not like an upright where the rear carries most of the weight.)

ETA: Possibly useful factoid if you don't have Streetmachine experience:  This is the bike where you can have a puncture and simply not notice.  On the rear it's almost indistinguishable from a strong headwind, and the front can get surprisingly low before the steering is substantially affected, especially off-road.
Careful, Kim. Your sarcasm's showing...

Re: Tyre pressures
« Reply #3 on: January 03, 2020, 11:52:08 pm »
As I understand it that bouncing from over inflated tires is lost energy, that is transferred to the rider creating fatigue.

I use supple wall 44mm (which need slightly higher pressures) I did a pretty big ride today with them at 50psi (I was concerned about losing pressure as they were recently set up) It felt too high and I'll drop them to 40 next ride. As someone else mentioned I would drop them down again to about 35 for off road.  Bike and rider about 100 kg.

On another narrower wheel set I have 30/32mm and run the at 60 psi.
often lost.

Kim

  • Timelord
Re: Tyre pressures
« Reply #4 on: January 04, 2020, 12:05:17 am »
Meanwhile, at the other end of the spectrum, on the unsuspended Baron low-racer I have 28mm road tyres.  Usually Duranos for day-to-day riding.  It's *extremely* sensitive to tyre pressure, particularly on the front wheel.  Below 80PSI the steering feels scarily vague and sluggish, like it's about to drop you on the deck, but above 90 and your feet get shaken violently on crappy chipseal type surfaces, to the point of sore heels and the occasional chain derailment.  The rear's more forgiving of low pressure, but too hard and it will rattle your BRANEZ until they leak out of your ears.

It's a pleasure to pump the tyres up hard and ride it on a properly surfaced[1] race track.



[1] I'm not including the bit under the trees at dePreston, which nearly had me sliding sideways at speeds in excess of R17.
Careful, Kim. Your sarcasm's showing...

Re: Tyre pressures
« Reply #5 on: January 04, 2020, 12:22:44 am »
On a  fully suspended 20/26 machine, such as a street machine, what would be a good pressure  F + R.   Is there any speed advantage to having them at max pressure, as presumably the suspension will take the edge off, or is softer ( wider footprint ) better / faster.
I think it's entirely dependent on the the tyre...  I have wide 50mm+ slick skin wall tubed tyres that will only roll well on the road @40-50psi which tends to negate the attenuation of suspension losses and grip of a wide tyre.  Conversely, I am currently riding Schwalbe tubeless G-One 35mm tyres at the same pressure that roll significantly faster, smoother and safer.
Most of the stuff I say is true because I saw it in a dream and I don't have the presence of mind to make up lies when I'm asleep.   Bryan Andreas

Re: Tyre pressures
« Reply #6 on: January 04, 2020, 03:19:54 am »
I pump the tyres on my ICE sprint FS up to the point that I just start to feel some road buzz.
That just over 60 psi with 42-406 Marathon Supremes on the front and a 50-406 Big Apple on the back.
If I've put a bit much in and the road buzz is to annoying then I'll let some air out.
I tend to go a month or so before I'll re-inflate them in which time they may have dropped to the low 50's psi without any noticeable side effects.

So it's more a question of what works for you and you'll need to find the sweet spot pressure wise for the tyres you're using.

Luck ..........  :D

ElyDave

  • Royal and Ancient Polar Bear Society member 263583
Re: Tyre pressures
« Reply #7 on: January 04, 2020, 07:55:01 am »
I'm riding 28mm conti gp 4 seasons on both road bike and cruzbike ATM with 700c wheels, generally working at 7 bar/ 100-105 psi, with 70kg of rider and another 12-15 of bike.

Had a visitation on the giant just before Christmas and was unable to reinflate it to that by the roadside. Although I didn't notice any hit on performance as it was effin' windy, I was constantly looking down for fear that it was too soft on the back lanes and I was going to bash the rim on the edge of a chasm Cambridgeshire pothole.

Might try reducing pressures on both to about 80 psi and see what happens, might even improve front wheel grip uphill and on the slippery stuff for the fwd cruzbike, which can be an issue.
“Procrastination is the thief of time, collar him.” –Charles Dickens

Re: Tyre pressures
« Reply #8 on: January 04, 2020, 03:16:35 pm »
I'd expect the suspension to mean more advantage to higher pressures - you can keep the rolling resistance advantage of high pressure on smooth roads without getting bounced around when the surface does get rough. Certainly I feel faster with higher tire pressure and tend to go right up to the limit (120). That's on heavy stiff tyres though - I'd guess that on supple tyres you wouldn't gain as much.

ElyDave

  • Royal and Ancient Polar Bear Society member 263583
Re: Tyre pressures
« Reply #9 on: January 04, 2020, 05:39:45 pm »
the CB is unsuspended, so I think it might be worth a try
“Procrastination is the thief of time, collar him.” –Charles Dickens

Re: Tyre pressures
« Reply #10 on: January 04, 2020, 07:08:47 pm »
I'd expect the suspension to mean more advantage to higher pressures -
I first thought that when I got my full suspension trike but now after a few years I don't find that.
I've found that the full suspension on my ICE trike is more tuned for slow movements while the tyres can be tuned for fast movements by varying the pressure.
So the full suspension tends to work best for big road defects like potholes or manhole covers, while the tyres works best for road buzz caused by rough tarmac.
So they work together to counteract the opposite ends of the road defect spectrum to give you the best ride possible.

YMMV .............. :D

Kim

  • Timelord
Re: Tyre pressures
« Reply #11 on: January 04, 2020, 11:41:38 pm »
I think it holds when you have smooth roads with occasional large defects, but they tend not to go together.  If there are potholes, there's probably worn-out tarmac, chipseal and stuff.
Careful, Kim. Your sarcasm's showing...

Re: Tyre pressures
« Reply #12 on: January 05, 2020, 12:37:20 pm »
At the moment I run a 40mm Marathon Greenguard at the front, and a 32mm Marathon Supreme at the back. Front is 406 and rear 700. This is on an unsuspended Lightning P38. The rear I run at 70 psi, close to the 67 psi the 15% drop calculator comes up with. I run the Marathon Greenguard at 50 psi. The calculator says 40 PSI but Schwalbe min pressure is 50 psi. I’ve crashed through some pot holes without issue. Come Spring I’ll put a more supple lighter tyre up front in 37 or 38 mm, and run around 40-45 psi.

I’ve read somewhere to inflate your tyres to where you think they should be. Then increase or decrease by 5 psi till you start to feel road buzz. Then back off 5 psi. But on the recumbent you barely notice road buzz as your touch on the bars is so light and My having a mesh seat acts like suspension.

If you don’t make time for exercise now, sooner or later you’ll need to make time for ill health.

Kim

  • Timelord
Re: Tyre pressures
« Reply #13 on: January 05, 2020, 02:31:10 pm »
I’ve read somewhere to inflate your tyres to where you think they should be. Then increase or decrease by 5 psi till you start to feel road buzz. Then back off 5 psi. But on the recumbent you barely notice road buzz as your touch on the bars is so light and My having a mesh seat acts like suspension.

Depends on the machine.  Between the suspension and the comfort-oriented riding position I find that the main symptom of road buzz on the Streetmachine is mechanical noises.  Rattly rear mudguard, chain flapping about, chainring guard and kickstand rattling, that sort of thing.  On the Baron it's violent shaking of the front end.  On the ICE Sprint without front suspension[1], the vibration's predominantly on the roll axis, and while you do get a bit of coupling through the bars, it's more that the image in your mirrors turns to mush, and there's a noticeable drop[2] in rolling efficiency.  Presumably anything with a fairing on efficiently converts road buzz into LOUD.


[1] We found that Big Apples help quite a bit.
[2] Like a less severe version of the way chipseal often feels like riding through treacle on a Brompton.  I put it down to small wheels with insufficiently compliant tyres, whether that's through high pressure or lack of suppleness.  (On the Brom I'm generally more concerned with warding off fairy visits than efficiency.)
Careful, Kim. Your sarcasm's showing...