dirt road tyre pressures

[Krizz]

A friend and I did a weekend trip into the interior of South Africa. It included riding some 4x4 tracks in the Cederberg mountains and then crossing over into the semi-desert areas of the Hantam Karoo, Bushmanland and back to Cape Town through Namaqualand. Over 1000 kilometres in total of which a good 700 were on dirt roads. On the dirt roads we saw 5 other vehicles in total over 3 days of riding. Very safe from a traffic point of view.

The dirt roads in the Karoo are mostly compacted light coloured shale with loose gravel separating wheel tracks with some small rocks mixed in and punctuated by small sandy dry-river-bed-crossings . And in Bushmanland the roads are hardened compacted red sand, coated with a layer of red sandy powder. We lowered our tyre pressures, but the handling was not entirely confidence inspiring.

Then in Calvinia, whilst having a cold beer on the hotel's "stoep" (veranda), a local dude drove past my parked AT in his Isuzu "bakkie" (pick-up truck). He stopped, reversed and then said we must wait, he'll be back soon. A few minutes later he arrived on his own AT. Had a few beers with him and then asked him about the tyre pressures.

He said that his AT runs best on the dirt roads with 1,2 bar in the front tyre and 0,8 bar in the rear. He *only* rides dirt roads with his AT and he has never had a puncture. The next morning I lowered my tyre pressures even further and it gave me an arm chair ride. It made it possible to run nicely at 120km/h.

Now, I am only concerned about the heat in the tyres. The day temperatures in these areas are around 30 degrees celsius in any case. Assuming day-long speeds between 90 and 120 km/h - is 0,8 advisable? (I did it and am home safely, but what if I do this for a week?). What sort of tyre pressures do you guys run when on dirt? (Of course on tar I stick to 2 bar front and rear).

Oh, I am running a pair of Metzeler Sahara's

Thanks
Chris

[YEN_POWELL]

I don't know what 0.8bar is in psi, but on my AT when I was offroad using Michelin Desert tyres I ran at about 15psi front and back. I don't think this was low enough, as they weren't really spreading. On the other hand the bike was pretty good offroad especially without the luggage. Once the front had worn a bit, this pressure was okay on tarmac as well. I had rimlocks fitted.

Did about 3,000 miles, front was knackered, still plenty of life in the rear which I was saving for the Cambrian Rally until I heard it was £100 to enter. (sound of wallet contracting!)

[Krizz]

It makes sense - more or less the same.

BTW - To convert psi into bar - multiply with .06895 - SO, 15 psi would be marginally over 1 bar. And to convert bar into psi - multiply with 14.503 - SO 0.8 bar = 11.6 psi

[iswoolley]

My only experience in conditions similar to yours is also in Morocco. I was running MT21s on an XT600 and ran 1 bar at the front and 1.2 at the rear. My logic was that the rear was more heavily loaded and thus would spread the tyre more than the front. With tyres like the Michelin Desert you could go lower with the pressures as they've got amazingly stiff sidewalls. But an @ is ~40kg heavier than an XT, so somewhere around 1 bar is going to be about right.

However I would be worried about running these pressures for prolonged periods at high speed. On hard pack you probably don't need to go so low as grip isn't so much of an issue.

Iain

[Maverick]

The dirt roads in the Karoo are mostly compacted light coloured shale with loose gravel separating wheel tracks with some small rocks mixed in and punctuated by small sandy dry-river-bed-crossings . And in Bushmanland the roads are hardened compacted red sand, coated with a layer of red sandy powder. We lowered our tyre pressures, but the handling was not entirely confidence inspiring.

Howzit Chris (for those non South-Africans that roughly translates to Hallo Chris )

We spend 3 weeks visiting family and friends in SA on October and don't know if you have been but a place worth while going to is Swartberg Pass and The Hell (equally as warm but not as bad )

We did some MTB riding down the pass and from the top it was 19km down to Prince Albert.



A few km's from the top you will encounter the Hell's road which goes for 50 km's west to Gamka's kloof. The only road in and the only road out but spectacular!



Now tell me you guys would not love to do this on a bike...



We went down last year with a car and unfortenately did not have enough time this year with a bike.

At least I got to overtake a motorcycle with my MTB downhill, ok it was a girl and I could see she was nervous...



Hopefully next year I will have two wheels down in SA to go and play!! For now need to get through this winter.....brrrrrrrr



Ohh yes before I forget maybe worthwhile riding with one of those cheapie car compressors around as they don't wheigh much and inflate your tyres when hitting the warm tarmac. Don't think the heat would have such a big effect on gravel. Fit a plug on the bike so you can run it off the battery as needed. I know of some guys who have stripped the plastic off around the compressor and fixed it permanently on the frame or under the plastics of the bike.

Goeie dag verder bru!

[Krizz]

Howzit bru,

Great pics of Gamkaskloof (!!!) The irony is that I grew up in Barrydale and am very familiar with the empty part of Karoo between the R62 (Montagu/Barrydale/Ladismith/Calitzdorp/Oudtshoorn) and the N1 (Laingsburg/Touwsrivier). The network of gravel roads in that area is where I started biking - without a licence mind you - first on an old yellow suzuki (I cannot remember the model) and later on a Yamaha DT. Amazing how one did not care about things like tyre pressures back then *LOL*

Have not been into Gamkaskloof or "Die Hel" on a motorcycle yet. Did it twice on horseback though - riding a "mule path" across the mountains from Calitzdorp. It is a bit difficult to find your way - but the first time we had a guy called Karel Cordier to guide us (he lived in Barrydale). The Cordier's were one of the original "Hell-families" - before the road towards the Swartberg pass was made passable for vehicles. The quickest way to get to The Hell was with this mule-path from Calitzdorp. Scary stuff sometimes - on the southern faces the vegetation is sometimes saddle height and then your not always sure that the horse can see where it is supposed to go! Well, your pics made me decide to take the AT out there this December

Been thinking that Seweweekspoort (off the R62) is also a great dirt road with awesome scenery (keep that in mind when you visit in future). The other thing to do would be Baviaanskloof from Willowmore towards PE.

Oh and the guy from Calvinia also carries a 12V compressor on the bike. He showed me how to attach an extension from the battery to make running any 12V appliance from it with ease. Seems like a good idea.

BTW - that guy also made his own chain-oiler - seemed to work like a charm. I am partial to chainwax, but for under R30 this guy made an oiler that does a pretty good job. I suppose it is a case of a "boer maak 'n plan"

Cheers
Christiaan

[jvaughan]

The Pix look awsome. I have no idea what language you are speaking at times though ..... My ignorance I guess..... I'll get my Coat !