MTB Specific: What Tyre Pressures

[Straight Line]

Run the highest pressures you can within your comfort zone. Tyre casing distortion increases progressively as pressure is reduced. The net result is a higher wear factor all round on tyre casing and tread. Tyres with reinforced sidewalls and/or bigger air volume are almost mandatory for any rocky surface riding (ie Cape Epic, Cape Pioneer, Attakwas etc).  

[DieselnDust]

Wider rims equal lower pressure. Think it has to do with volume, but I'm not sure about the sciency stuff..

 

I do however run slightly higher pressure on rocky terrain due to fear of pinch-flat and rim strikes. But it took me some getting used to the idea of lower pressure on wider rims when inflating.

Hardest I go now will be 1.5 at the rear, maybe 1.8 if it's dirt road ride over a longer distance. 

 

 

I make some scale sketches. the increase in volume due to a wider rim is very very small its almost nothing. I'm starting to think that the extra support is purely due to the lower bracing angle the side wall of the tyre provides. For illustration of the point. if you have a rod anchored at its base  and yo apply a downward force the rod will resist compression more the closer to vertical it stands. the more you lean the rod over the easier it is to bend the rods free end down to the ground. A tyres side wall behaves similarly.

Also I find that lower pressure doesn't feel very nice when I'm going fast. Its ok if i'm pedaling slowly. I run my tyres harder now - 22psi front and 24psi rear for 72kg rider clothed. I et more benefit from tuning my suspension correctly ito sag and high speed rebound

[Dirt Tracker]

85kgs without kit and just go with 22psi front and back on 35mm internal rims. No issues. 

[DieselnDust]

85kgs without kit and just go with 22psi front and back on 35mm internal rims. No issues. 

 

 

tyre dimensions and style of riding?

[Dirt Tracker]

tyre dimensions and style of riding?

 

Tokai, Jonkers, Conties, Table Mountain, Paarl shuttle loop, Glen and so on.  2.6 Spez Eliminator in Grid on the front / 2.3 Spez Slaughter DH casing on the back at the moment but have pretty much run that pressure across most of the recent rubber I've run. Style? That's a very subjective thing but trails I enjoy are pointed down! 

[Captain Fastbastard Mayhem]

I make some scale sketches. the increase in volume due to a wider rim is very very small its almost nothing. I'm starting to think that the extra support is purely due to the lower bracing angle the side wall of the tyre provides. For illustration of the point. if you have a rod anchored at its base  and yo apply a downward force the rod will resist compression more the closer to vertical it stands. the more you lean the rod over the easier it is to bend the rods free end down to the ground. A tyres side wall behaves similarly.

Also I find that lower pressure doesn't feel very nice when I'm going fast. Its ok if i'm pedaling slowly. I run my tyres harder now - 22psi front and 24psi rear for 72kg rider clothed. I et more benefit from tuning my suspension correctly ito sag and high speed rebound

Tim, serious q now. STARTING to think? Surely not.... That's pretty much the basis for why wider rims are betterer (to a point, in teh testing I've read that the advantage ends at 35mm for modern 60-63mm wide tyres, and the sweet spot is 30-35mm)

 

The theory (scientific, not "normal") has been around for aeons. The lower pressure is an advantage, yes, but not as much as the better support as a result of the larger "base" width (less pinching) and it's only 1 to 2 psi difference that you're able to run. But again, that's purely down to the extra volume which comes from the larger base width. 

 

oh and re the bold bit - yeah, the extra support of the wider helps that to an extent, but if you still have weak sidewalls the squirm is gonna remain at lower pressures. I HATE squirm. 

Edited October 8, 2019 by Captain Fastbastard Mayhem

[Captain Fastbastard Mayhem]

Tokai, Jonkers, Conties, Table Mountain, Paarl shuttle loop, Glen and so on.  2.6 Spez Eliminator in Grid on the front / 2.3 Spez Slaughter DH casing on the back at the moment but have pretty much run that pressure across most of the recent rubber I've run. Style? That's a very subjective thing but trails I enjoy are pointed down! 

Perfect combo, except the back may have been a bit wanting on the weekend...

[Dirt Tracker]

Perfect combo, except the back may have been a bit wanting on the weekend...

 

I was surprised at how good the Slaughter held in during most of the stages in Jonkers. It was a given that I did add a little more in the back for that day out but only to about 28psi. Only in the very dusty parts did it start getting loose but nothing unmanageable. I am constantly impressed by how planted if feels and how much traction you can get out of a semi slick like the Slaughter. 

[Dirt Tracker]

oh and re the bold bit - yeah, the extra support of the wider helps that to an extent, but if you still have weak sidewalls the squirm is gonna remain at lower pressures. I HATE squirm. 

 

Squirm is a deal breaker for me. If a new tyres shows any of that it comes off and it's gone. Like the death gap, I don't need to be thinking 'I hope this stays where I put it' as I head towards any feature.

[Eddy Gordo]

Squirm is a deal breaker for me. If a new tyres shows any of that it comes off and it's gone. Like the death gap, I don't need to be thinking 'I hope this stays where I put it' as I head towards any feature.

 

You will like the convict, you will just lean more and more and more. I have not yet had it squirm at normal pressure for me. Once at tokai a month or so back, but then it was underinflated and I didnt bother adding air as the sidewalls are solid.

[Dirt Tracker]

You will like the convict, you will just lean more and more and more. I have not yet had it squirm at normal pressure for me. Once at tokai a month or so back, but then it was underinflated and I didnt bother adding air as the sidewalls are solid.

 

I was thinking of looking at the Judge / Verdict combo as that has been talked up a bit recently but I'd have to abandon all my convictions about rolling resistance. 

 

https://www.pinkbike.com/news/review-judge-and-verdict-wtbs-most-aggressive-dry-condition-tire-combo.html

Edited October 8, 2019 by Dirt Tracker

[Captain Fastbastard Mayhem]

Squirm is a deal breaker for me. If a new tyres shows any of that it comes off and it's gone. Like the death gap, I don't need to be thinking 'I hope this stays where I put it' as I head towards any feature.

100%. 

[Captain Fastbastard Mayhem]

I was thinking of looking at the Judge / Verdict combo as that has been talked up a bit recently but I'd have to abandon all my convictions about rolling resistance. 

 

https://www.pinkbike.com/news/review-judge-and-verdict-wtbs-most-aggressive-dry-condition-tire-combo.html

Then you may as well slap the assguy back on. 

 

Waiting patiently for the Dissector, I am. Another 6 months or so, with the way things are. 

[DieselnDust]

Tokai, Jonkers, Conties, Table Mountain, Paarl shuttle loop, Glen and so on.  2.6 Spez Eliminator in Grid on the front / 2.3 Spez Slaughter DH casing on the back at the moment but have pretty much run that pressure across most of the recent rubber I've run. Style? That's a very subjective thing but trails I enjoy are pointed down! 

 

 

Yeah with those tyres I think you can get away with it. for Marathon or XCO/M the tyres that perform for those disciplines will be better off with a bit more pressure

[Eddy Gordo]

I was thinking of looking at the Judge / Verdict combo as that has been talked up a bit recently but I'd have to abandon all my convictions about rolling resistance. 

 

https://www.pinkbike.com/news/review-judge-and-verdict-wtbs-most-aggressive-dry-condition-tire-combo.html

https://reviews.mtbr.com/wtb-convict-2-5-first-impressions

[DieselnDust]

Tim, serious q now. STARTING to think? Surely not.... That's pretty much the basis for why wider rims are betterer (to a point, in teh testing I've read that the advantage ends at 35mm for modern 60-63mm wide tyres, and the sweet spot is 30-35mm)

 

The theory (scientific, not "normal") has been around for aeons. The lower pressure is an advantage, yes, but not as much as the better support as a result of the larger "base" width (less pinching) and it's only 1 to 2 psi difference that you're able to run. But again, that's purely down to the extra volume which comes from the larger base width. 

 

oh and re the bold bit - yeah, the extra support of the wider helps that to an extent, but if you still have weak sidewalls the squirm is gonna remain at lower pressures. I HATE squirm. 

 

 

 

"starting to think" = a slight dash of sarcasm.

the theory has been around for years but the volue increase is very negligable. volume is often touted as the benefit but it is really almost purely the mechanical support as you rightly say. 

 

the issue is the common language always describes wider as better due to the volume increase and I see many illustrations in marketing that shows of this gross exaggeration. I'd like to see the dialogue return to science and talk about how much more supportive a wider rim is for the tyre. Same in cars and motorcycles, wider base of support gives a less squirrely tyre.

 

using low profiles on a car as an example, the volume there is drastically reduced but the side walls support the tyre more effectively and the car handles better. Any additional volume is really gained from a bigger tyre. For Enduro, big volumous tyres wide rims = happiniss is.

XCO/XCM wider to a point so that 2.2 to 2.35 tyre is well supported is where a limit exists till they start to make the tyres more round. I also run my tyres harder to achieve that more round profile at the contact patch and thus actually reducing the size of the contact patch and get better feel and grip from the tyres. Played around with tyre pressures a few weekends ago (after dinging my carbon rim) and found that sweet spot is really the point at which the tyre doesn't rebound uncontrollably.

 

In closing, there's little difference in performance between a 23mm rim to a 27mm rim and again from 27 to a 30mm

But ay of those is a huge leap forward from a 19mm internal width rim.

I agree for trial/ AM/Enduro 30-35mm is perfect if tyre is 2.5 and over.

For 2.0 to 2.5 23-27 is great .

 

BUT , tyre pressure is where the real performance can be unlocked. I see far too many under-inflated XC tyres. An 80kg rider running 18psi front 20psi rear is way too soft IMO.

 

Tyrewiz is another useful tool that rider should play around with. Too expensive to justify ownership for me ....