Resend my activation email : Register : Log in 
BCF: Bike Chat Forums


Tyre pressures?

Reply to topic
Bike Chat Forums Index -> Offroad & Supermoto
View previous topic : View next topic  
Author Message

stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
Karma :

PostPosted: 13:38 - 13 Feb 2020    Post subject: Tyre pressures? Reply with quote

People are very cagey about this, maybe trade secrets?

I have trials tyres fitted to my Royal Enfield 350 bullet. Specifically a 3.00x19 Cheng Shin C-186 on the front and a 3.50x19 Heidenau K67 on the rear. These aren't full-on trials tyres, they are harder and road legal, the really sticky sort won't last the distances involved in the event I'm doing (and wouldn't pass scrutineering anyway).

Both wheels have rimlocks.

I'm doing a long distance trial event next weekend which will be a mix of rough roads, green lanes and very steep, very muddy tracks. Maybe a couple of special tests on wet, muddy grass. Roughly 100 miles in total.

I'm prepared to go to the effort of adding/removing air at the start and end of observed sections.

I'm planning on setting them to 14/15psi initially but will letting more air out give me a worthwhile advantage? Especially on the soft, muddy stuff?

I'm not really sure how low is "low pressure". You hear of people riding full-on trials bikes with 4 or 5psi in them but I think this may be asking for a snakebite on my bullet?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
 Back to top
View user's profile Send private message You must be logged in to rate posts

MarJay
But it's British!



Joined: 15 Sep 2003
Karma :

PostPosted: 13:47 - 13 Feb 2020    Post subject: Reply with quote

A trials tyre will be almost flat, yes. 4 or 5 Psi. I've also been told that letting out less than 50% of the pressure is pretty much pointless so I wonder if you need to be more in the 5-10 PSI bracket? *shrugs*. I'm not sure if we have any trials riders on here... but I'm sure someone more knowledgeable will be able to comment.
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
 Back to top
View user's profile Send private message Send e-mail You must be logged in to rate posts

Riejufixing
World Chat Champion



Joined: 24 Jun 2018
Karma :

PostPosted: 14:21 - 13 Feb 2020    Post subject: Re: Tyre pressures? Reply with quote

stinkwheel wrote:
I'm planning on setting them to 14/15psi initially but will letting more air out give me a worthwhile advantage? Especially on the soft, muddy stuff?

I'd be inclined to try out your bike/tyres in some conditions hopefully similar to softer ones you will find, which is where you will be going lower pressure, if you have time.
 Back to top
View user's profile Send private message You must be logged in to rate posts

doggone
World Chat Champion



Joined: 20 May 2004
Karma :

PostPosted: 15:03 - 13 Feb 2020    Post subject: Reply with quote

I'd stick with about 15psi you won't want to be letting air out for rather trivial improvement in grip unless it's desperate.
If running more on the road before/after 20-22 would feel less squidgy.
 Back to top
View user's profile Send private message Visit poster's website You must be logged in to rate posts

Fizzer Thou
World Chat Champion



Joined: 06 Aug 2011
Karma :

PostPosted: 23:05 - 13 Feb 2020    Post subject: Reply with quote

On my KTM EXC I run 13 psi in the front & about 11 or 12 psi in the rear when riding on enduro tyres.As trials tyres appear to run much lower pressures so as to get more grip on the irregular off tarmac surfaces I would have thought that under 10 psi would be more appropriate.

I carry a small CO2 gas canister adapter for when riding long distances in Wales so that I can add some if the going gets really stoney,in which case I would run with 14 front and 13 rear.

I rode a long distance trial with others a few years ago.It was great fun riding mostly BOATs and a few UCRs around Hampshire and Berkshire.The last part of the day was a blast around a motocross track at the venue in Hindhead.I did not come first,but then I came nowhere near last.
____________________
Just talk bikes.What else is there?

Always have a 'Plan B'
 Back to top
View user's profile Send private message You must be logged in to rate posts

Easy-X
Super Spammer



Joined: 08 Mar 2019
Karma :

PostPosted: 03:08 - 14 Feb 2020    Post subject: Reply with quote

I think you'll have to do some test rides. That's a relatively heavy bike versus the "standard" lightweight dirt bikes so I don't know you can apply the same "do this PSI" formula they do... less air in the back than the front is about the only certainty Smile
____________________
Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter
 Back to top
View user's profile Send private message You must be logged in to rate posts

steve the grease
Crazy Courier



Joined: 26 Jan 2018
Karma :

PostPosted: 18:58 - 06 Apr 2020    Post subject: Reply with quote

The advantage of letting tyres down is that increases quite dramatically the footprint of the tyre , this therefore gives a considerable improvement in grip. Without grip in soft going, you ain't going anywhere.* The downsides are increased noise, tyrewear, somewhat unpredictable handling and the risk of pinching the tube.

Personally I run the most expensive Michelin motocross 4mm thick Michelin UHD ( ultra heavy duty)innertube that money can buy , they are twenty odd quid , but make other 'heavy duty' inner tubes look like condoms. The other thing I do ( this is on the rear, yes) is run 2 tyre security bolts. My tyre is not moving on the rim. Nor it seems is it puncturing , no matter what low pressure I run. I did a run over to Lampeter, a windy road about 50 miles each way . I thought Bike feels good I'll check the tyre pressure so I know what to run. Ahem , 6 psi!

*At a festival I once saw a rock stars wife (or similar) in some 4x4 BMW all four low profile tyres spinning in the mud Screaming out of the window " I paid nearly £100k for this pile of shit , why won't it move?" Funny.
____________________
All the above is my personal opinion, you can see my lips move, but I'm talking out of my arse.
I've been riding, and fixing , bikes for 50 years, in that time the more I learn, the less I am absolutely sure of.....
 Back to top
View user's profile Send private message You must be logged in to rate posts

stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
Karma :

PostPosted: 22:15 - 06 Apr 2020    Post subject: Reply with quote

It later turned out 6psi was about right. About as much grip as I was likely to get and no pinch flats, even when riding over boulders.

It also turns out the tyre has slipped on the rim, despite the rim-lock. Not doing up the nut on the valve stem means it didn't rip the tube, just sitting at a funny angle now. I'll have to break it down off the rim and move it back round again.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
 Back to top
View user's profile Send private message You must be logged in to rate posts

Easy-X
Super Spammer



Joined: 08 Mar 2019
Karma :

PostPosted: 10:19 - 07 Apr 2020    Post subject: Reply with quote

Better rim-lock or more rim-locks?
____________________
Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter
 Back to top
View user's profile Send private message You must be logged in to rate posts

stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
Karma :

PostPosted: 10:32 - 07 Apr 2020    Post subject: Reply with quote

Easy-X wrote:
Better rim-lock or more rim-locks?


I think it being such a narrow rim/tyre combination doesn't help.

On balance, one rim lock makes fitting etc difficult enough so I'll just keep an eye on it. Pretty sure I know where it happened and that bit was utterly extreme. That section killed three bikes. I'm amazed I didn't get a pinch flat on it (or maybe I did and the oko slime fixed it).
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
 Back to top
View user's profile Send private message You must be logged in to rate posts

trevor saxe-coburg-gotha
World Chat Champion



Joined: 22 Nov 2012
Karma :

PostPosted: 15:51 - 07 Apr 2020    Post subject: Reply with quote

One thing that puts me off running much less than my standard preferred 24 psi when going off road is I'm a bit worried about damaging the wheels' rims. Most of the time I'd almost certainly be fine as there's not much in the way of rocky, stony ground locally. But there is one disused quarry we use and that definitely has rocks. And we tend to attack it with a bit more gusto than on the boats.
____________________
"Life is a sexually transmitted disease and the mortality rate is one hundred percent."

Mobylette Type 50 ---> Raleigh Grifter ---> Neval Minsk 125
 Back to top
View user's profile Send private message You must be logged in to rate posts

stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
Karma :

PostPosted: 17:50 - 07 Apr 2020    Post subject: Reply with quote

trevor saxe-coburg-gotha wrote:
One thing that puts me off running much less than my standard preferred 24 psi when going off road is I'm a bit worried about damaging the wheels' rims. Most of the time I'd almost certainly be fine as there's not much in the way of rocky, stony ground locally. But there is one disused quarry we use and that definitely has rocks. And we tend to attack it with a bit more gusto than on the boats.


You'll be on proper knobblies too so probably less of an issue because they won't hang onto the mud in the tread the same way.

Competition trials tyres are a constant fight for grip, especially the harder compounds you need for a long distance trial. The super-sticky ones won't cope with the amount of road riding. That said, on the deep slimy mud we had on the trial I did, compound becomes irrelevant, contact patch and clearing mud out of the tread is everything.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
 Back to top
View user's profile Send private message You must be logged in to rate posts

trevor saxe-coburg-gotha
World Chat Champion



Joined: 22 Nov 2012
Karma :

PostPosted: 12:39 - 12 Apr 2020    Post subject: Reply with quote

Yeah even with stuff like AC10s I still try to err towards the edge of a track when the tyres clog, in a bid to get the grass (preferably wet grass) to clean the mud out.

I'd be worse than useless on trails tyres. I'd basically have to get off and push every section.
____________________
"Life is a sexually transmitted disease and the mortality rate is one hundred percent."

Mobylette Type 50 ---> Raleigh Grifter ---> Neval Minsk 125
 Back to top
View user's profile Send private message You must be logged in to rate posts

stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
Karma :

PostPosted: 13:39 - 12 Apr 2020    Post subject: Reply with quote

trevor saxe-coburg-gotha wrote:


I'd be worse than useless on trails tyres. I'd basically have to get off and push every section.


The getting off happens all by itself as it turns out. Laughing

There was one point I was trying to walk the bike up a "ride through" section by walking next to it with it in gear. Still couldn't move it. Or particularly walk in fairness.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
 Back to top
View user's profile Send private message You must be logged in to rate posts
Old Thread Alert!

The last post was made 3 years, 351 days ago. Instead of replying here, would creating a new thread be more useful?
  Display posts from previous:   
This page may contain affiliate links, which means we may earn a small commission if a visitor clicks through and makes a purchase. By clicking on an affiliate link, you accept that third-party cookies will be set.

Post new topic   Reply to topic    Bike Chat Forums Index -> Offroad & Supermoto All times are GMT + 1 Hour
Page 1 of 1

 
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum

Read the Terms of Use! - Powered by phpBB © phpBB Group
 

Debug Mode: ON - Server: birks (www) - Page Generation Time: 0.07 Sec - Server Load: 0.41 - MySQL Queries: 17 - Page Size: 89.21 Kb