Tyre Pressure Leaderboard

Postby mfw on Tue 7/Apr/15 6:17am

COLLECTED DATA:

Code: Select all
                     PSI    PSI  TUBE/
NAME       TONNAGE  FRONT   REAR  T/L  INNER RIM/TYRE WIDTH, Other info
swtchbckr     90       4      4   ?    75mm   4.25 Charge Cooker Maxi 2 (Wowee, that's extreme)
mfw           76      18     18   TL   32mm   2.4  (must ride like a softie)
swtchbckr     90      20     20   Tube 29/30  2.4  5 Spot, doesn't care about weight anymore
Velocip'trian 70      20     23   Tube 25mm   2.4  Pinch flats ~every six months
mbl77         65      21     23   ?    23mm   2.3
Matahina       ?      22     23   ?    ?      2.35
mfw           76      23     23   TL   19mm   2.4  Glad to ditch these skinny rims
wachtourak    73      23     26   TL   23mm   2.35
mbl77         65      24     27   ?    17/19  2.2
Percy Pig     99      25     30   ?    24.5mm 2.3  Trail and DH, dents rims
shmoodiver   120      26     30   TL   23mm   2.35 (fast downhill)
Wobbler      110      32     32   TL   25.5mm 2.5
el_booto     200      30     35   TL   23mm   2.4/2.25 Smooth style with gnar streaming tendancies
cyclenutnz   103      30     35   Tube  ?     2.3 or 2.4
AgrAde        75      32     35   TL   23mm   2.3  Don't like burps
dwgknz        75      35     35   TL   19mm   2.25
AgrAde        85      ?      40   TL   23mm   2.3
el_booto     200      40     40   Tube 24.5mm 2.5 Smooth style with gnar streaming tendancies
Farm         100      45     45   Tube ?      2.35 Burps and bashes regularly
BikeKiller   130      50     50   Tube ?      2.35

---------------------------------------------------
ORIGINAL POST:

I measured my MTB weight balance on scales, in downhill position the balance was 40/60 front/rear.
So theoretically to get tyres to behave the same I should use the same pressure balance front to rear?

That feels like an extreme balance, currently running 18psi front and rear, that would mean raising the rear to 27psi which feels horrible, and dropping the front any more brings fear of rock strikes.

Seems to be suprisingly undocumented on the internet, heaps of info but all talks of tyre pressure collectively. Stans does have a formula http://www.notubes.com/help/tirepressure.aspx but this is non linear which raises question marks, and doesn't amount to much of a difference either.
Anyone done any experiments around this?
Last edited by mfw on Fri 10/Apr/15 3:34pm, edited 3 times in total.
mfw
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Re: Tyre Pressure Front / Rear Balance

Postby Astoria Paranoia on Tue 7/Apr/15 7:04am

mfw wrote:I measured my MTB weight balance on scales, in downhill position the balance was 40/60 front/rear.


Did you take into account weight shift when braking?
You'll find you need more in the front.

Personally, I adjust my tire pressures individually.
Never heard of linked values.
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Re: Tyre Pressure Front / Rear Balance

Postby Percy Pig on Tue 7/Apr/15 8:12am

Trail boike, 25 pies front, 30 rear.
DH sled pretty much the same.

And I still manage to dent teh rimz... :paranoid:

Any more rear pressure and it starts getting sketchy, which can be amusing at times, scary at others! :blink:
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Re: Tyre Pressure Front / Rear Balance

Postby shmoodiver on Tue 7/Apr/15 8:31am

Percy Pig wrote:Trail boike, 25 pies front, 30 rear.
DH sled pretty much the same.

And I still manage to dent teh rimz... :paranoid:

Any more rear pressure and it starts getting sketchy, which can be amusing at times, scary at others! :blink:



I don't dent rims but run similar pressures.
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Re: Tyre Pressure Front / Rear Balance

Postby mfw on Tue 7/Apr/15 9:13am

Astoria Paranoia wrote:
mfw wrote:I measured my MTB weight balance on scales, in downhill position the balance was 40/60 front/rear.


Did you take into account weight shift when braking?
You'll find you need more in the front.

Personally, I adjust my tire pressures individually.
Never heard of linked values.

Hmm, didn't think about weight shift, dropped out of physics LOL, if you do it the http://www.mtbskillsclinics.co.nz/ way (all weight on pedals and heels dropped) do you still get weight transfer?

Btw: I'm on wide wheels+tyres, I used to run 23-24psi on my old wheels, again with same pressures front and back.
mfw
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Re: Tyre Pressure Front / Rear Balance

Postby Wobbler on Tue 7/Apr/15 9:16am

You always get weight shift when braking

its science
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Re: Tyre Pressure Front / Rear Balance

Postby shmoodiver on Tue 7/Apr/15 9:26am

Even when braking uphill?!?
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Re: Tyre Pressure Front / Rear Balance

Postby Kev on Tue 7/Apr/15 9:26am

or in the air?
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Re: Tyre Pressure Front / Rear Balance

Postby Percy Pig on Tue 7/Apr/15 9:47am

shmoodiver wrote:
Percy Pig wrote:Trail boike, 25 pies front, 30 rear.
DH sled pretty much the same.

And I still manage to dent teh rimz... :paranoid:

Any more rear pressure and it starts getting sketchy, which can be amusing at times, scary at others! :blink:



I don't dent rims but run similar pressures.

Ride harder, or moar mong, or ignore moar stuff in front of you! :D

Ahem, I blame Marzocchi for making the Shiver so damn good at steaming teh gnurr. :thumbsup:
Percy Pig
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Re: Tyre Pressure Front / Rear Balance

Postby ryda on Tue 7/Apr/15 10:02am

mfw wrote:I measured my MTB weight balance on scales, in downhill position the balance was 40/60 front/rear.
So theoretically to get tyres to behave the same I should use the same pressure balance front to rear?
I'm intrigued as to what brough this train of thought on

If you going to go down the end end weights thing to work out tyre pressure? I would have thought in cornering (and maybe under brakes) where your tyres doing it job is most critical would have been more important?

and I'd guess in corners where tyres and pressure's make difference there would be more weight on the front than the rear
ryda
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Re: Tyre Pressure Front / Rear Balance

Postby mfw on Tue 7/Apr/15 10:39am

ryda wrote:
mfw wrote:I measured my MTB weight balance on scales, in downhill position the balance was 40/60 front/rear.
So theoretically to get tyres to behave the same I should use the same pressure balance front to rear?
I'm intrigued as to what brough this train of thought on


I thought I read in some article giving tips for fast gravel road descents, use matched tyres with same tyre deformation i.e. balanced pressures, it seemed to make sense at the time but I didn't realise until recently when I got on the scales how much rear bias there was.
mfw
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Re: Tyre Pressure Front / Rear Balance

Postby Velocipedestrian on Tue 7/Apr/15 10:53am

Was your scale on flat ground? Do you often use your downhill position on flat ground?
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Re: Tyre Pressure Front / Rear Balance

Postby Wobbler on Tue 7/Apr/15 11:23am

Velocipedestrian wrote:Was your scale on flat ground? Do you often use your downhill position on flat ground?


I concur, even if you "downhill" position on flat ground + scales it will be different to actually pointing down a hill.
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Re: Tyre Pressure Front / Rear Balance

Postby mfw on Tue 7/Apr/15 12:31pm

Scales were flat.

Yes I use downhill riding position on flat :p
OK, actually what I mean is the 'attack' position, the main point being that most of the weight is on the cranks, not bars or seat.

Without doing some trigonometry, I think I can see where you're going - when downhill with this riding position the weight might be centred on the cranks but the plumb line will still move towards the front wheel, therefore loading it up more. And that's before your apply the front brake which exaggerates this further.

So what we really need is active tyre pressures, like they do on trucks, or fancy cars :rolleyes:
Last edited by mfw on Tue 7/Apr/15 8:15pm, edited 1 time in total.
mfw
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Re: Tyre Pressure Front / Rear Balance

Postby NickCW on Tue 7/Apr/15 1:02pm

mfw wrote:So what we really need is active tyre pressures, like they do on trucks, or fancy cars


This exists, be sure to post back findings after purchase

http://adaptrac.com/

Image

I would probably want this if I was German
NickCW
Member for: 9 years 5 months

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