Author Topic: Tyre Pressures  (Read 13475 times)

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Offline Manley

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Tyre Pressures
« on: 14 May 2006 at 21:57 »
Just wondered what tyre pressures people have been running with?  I dont know and have no info on what mine should be.
« Last Edit: 15 May 2006 at 02:57 by Doug »
2004 Modified Triumph Thruxton
1986 ME
1972 MG B
1967 MG Midget (Sold)
1936 Aero 500
Not Enough Time to Play

Offline graeme

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Re: Tyre Pressures
« Reply #1 on: 18 May 2006 at 06:10 »
Try running 20psi in the front and 22psi in the back. No point in blowing them up too hard - the tyres are pretty much the main suspension on girder/rigid machines!
Cheers, Graeme

Offline Doug

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Re: Tyre Pressures
« Reply #2 on: 18 May 2006 at 23:22 »
Also, it depends on if your Douglas is fitted with wired on tires (or tyres) or beaded edge tires used prior to about 1930. Wired on you can run lower pressures to soften the ride. My understanding of beaded edge is the air pressure is what keeps the tire on the rim, and if it gets too low you could demount the tire and roll it off the rim. I have no personal experience with maintaining zen on beaded edge, but I have seen pressures quoted in old books of upwards of 70psi, though I believe 50-60 was typical. Comments out there?

The only direct experience I have had with beaded edge was keeping them on the rim due to too much pressure. In my case, the rim was old and worn, and the clench (we call them clincher rims in the USA) did not retain the bead very well on the tire. One I found demounted on the other side of the basement from where I had placed it. The other let go right under my nose while I was leaning over to inflate it. That left me stone deaf for a ten minutes and a further two hours of tintinitous. It was like a shotgun blast, and of course it shreded my new inner tubes. No harm done to the tires, but I did cough up for new replacement rims and sold the old ones on to someone trying to save a buck and in need of a lesson about where not to economise!

-Doug

Offline Ian

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Re: Tyre Pressures
« Reply #3 on: 19 May 2006 at 00:20 »
For beaded edge absolute minimum 40 psi and prefereably 45-60 !!

Offline Clive

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Re: Tyre Pressures
« Reply #4 on: 20 May 2006 at 05:44 »
[]Hi All,
I have been riding my 1926 EW for 10yrs now and covered many thousands of kilo meters .The tyres have always been inflated to 22lbs front and rear as per the 1926 Douglas Brief Running Instructions for EW Model  fitted with beaded edge tyres actually it says 15 for the Front and 20/22 for the Rear but i have found with my weight 22 suits me perfectly . I cant imagin the ride with tyre pressures as suggested by some owners and i can hear the bang from here if they where blown up literally to pressures of in excess of 50 lbs per sq ins these tyres have little reinforcing and are hand made in some cases so be careful out there with these high pressures 20lbs was high pressure in 1926 . 
I know the reason for correct inflaction and have only known B/E tyres roll off the rim if the tyre is vertually flat or the machine is being ridden by a speed freak.

Offline Doug

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Re: Tyre Pressures
« Reply #5 on: 20 May 2006 at 06:08 »
Well sure enough, the early EW owner's book does say 20-22psi! What I believe to be the later edition mentions some additional tire choices, but neglects to mention inflation pressures at all. 

-Doug

Offline Chris

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Re: Tyre Pressures
« Reply #6 on: 20 May 2006 at 11:18 »
On one occasion on the Pioneer Run on a 1913 2.3/4hp. about 8 miles out of Brighton I had the front tyre go soft on me. I thought I had a slow puncture, tried to pump up the tyre but the air came out as fast as it went in. However, the pressure still did not go below about 8/10psi. I risked proceeding and arrived successfully in Brighton. It was a bit hairy especially on roundabouts where needless to say I rode very carefully with the front end floating about a bit. Removal of the tyre later revealed that an undersize tube had been fitted which had simply split around the outer seam. Riding with such a low pressure is not recommended. I normally keep my beaded edge tyres between 35 and 40psi and have never had a problem. Chris.

Offline graeme

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Re: Tyre Pressures
« Reply #7 on: 23 May 2006 at 06:51 »
I too had always been led to believe that you should pump BE tyres up to 45 or 50 psi. However, on a veteran run last weekend I spoke to several riders who said that they shouldn't be pumped to more than 30 psi. I'm willing to try a lower pressure, as it is certainly a very harsh ride at 50 psi! BTW, two riders had valves pull out of their tubes on the run - one with a well-base tyre pumped to 18 psi, the other with a BE pumped to 45psi. No pattern there!

Offline Ian

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Re: Tyre Pressures
« Reply #8 on: 23 May 2006 at 07:29 »
I agree Graeme, would be nice not to have such high pressures. I was also wondering if the required pressure differed by size. The 26 x 2.5 tyres are much narrower than the 26 x 3 - maybe the more balloon style tyres require less pressure ? I had a look through all my amnuals for the early Douglas and the 1912 Triumph and they do not mention pressures at all !!

Offline Daren W Australia

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Re: Tyre Pressures
« Reply #9 on: 23 May 2006 at 08:00 »
Hi would the high pressure myth for bikes have come about by large veteran cars like Rolls Royce & Vauxhall in the over 2 ton class rolling there beaded edge tyres of if under inflated ? Regards Daren
too many dougli not enough time!

Offline trevorp

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Re: Tyre Pressures
« Reply #10 on: 23 May 2006 at 13:43 »
an easy way to check is to feel the middle of the sidewall after running at lower pressures
what normally kills a tyre is when u run then too low a pressure and the sidewalls overheat and melt this is the major cause of blowouts
the higher the pressure the lower the temperature of the tyre because it doesnt flex as much
i think the newer materials these days may be fine but its a simple check

Offline Ian

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Re: Tyre Pressures
« Reply #11 on: 23 May 2006 at 22:36 »
The problem with the BE tyres has been that people say the bead will not hold in the rim unless higher pressures are used. My guess is maybe daren is right that this has come from the car world where side pressures on tyres are high. For a solo motorcycle  the sideways pressures are lower so the tendency to roll off the rim should be significantly reduced.

Offline Chris

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Re: Tyre Pressures
« Reply #12 on: 24 May 2006 at 06:04 »
This sideways pressure applying to cars must also apply to my CW sidecar outfit. (not many of these on the road). Perhaps I should increase my tyre pressures on that model. However, as I said before I have had no problems with 35 to 40 psi. but then the performance of a 1925 2.3/4hp pulling a chair is not exactly scintillating and likely to rip tyres off rims.
Chris.

Offline trevorp

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Re: Tyre Pressures
« Reply #13 on: 24 May 2006 at 14:21 »
Another thing to watch is some lubricants they use to fit tyre to rim,some fitters are a bit over zealous[mainly because they dont want to wreck your rims] and would be the major cause of the valve ripping out or the tube tearing away from valve

Offline Derek

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Re: Tyre Pressures
« Reply #14 on: 04 Jun 2006 at 12:02 »
Dear All
In relation to tyre pressures in my 1926EW, personally I am now running about 40 psi. This is after previously running 25psi on a rally at Dubbo NSW and cutting the valves off two tubes (rear wheel) when the 26x3 beaded edge rear tyre rotated on the rim at this pressure. It can go down awfull quick when this happens.
On advice from others at this pre 39 rally, I increased the pressure to 40 psi and didnt have a problem after that.
However another friend on a 23 CW runs the same size tyres at a lower pressure - however the brand of tyre and origin is different (mine are new and made in Vietnam and his are older from Japan) and his rims are in rougher condition (mine had just been illmenite blasted and repainted). On this basis it may be that the BE profile of some makes of BE tyres is slightly different to that of the rim and other makes of tyres or it may be even the mounding lubricant on newer tyres or the paint and condition of the rim. You have to take into account that most of the 26x3 BE tyres available (for us in Australia anyway) are from asia and are used for hand driven push carts and motorized 3 wheelers - the quality and the profile may not be what it was in 1926 or so. 
On the basis of my direct experience, I will be running 40 psi to ensure that the beaded edge of the tyre is really bedded into the rim, it is really disconcerting losing the rear tire when in a corner, which happened when I was trial running the bike at work, in front of a heap of my employees (earning me the nickname 'Buster' after the crash test dummy on Mythbusters). The second time, at the rally (which Ian also attended) was at least in a straight line and not nearly as dramatic (quite stately actually - however, as Ian will attest to, it may have been the copius amount of oil from the incorrectly connected oiling system - which started another forum topic - that assisted the 'slip' of the tyre on this occasion).
Overall I would run 40 psi however, if you decide to run less, perhaps if they are new tyres, ensure any coating from the manufacture process has been removed from the beaded edge.
Another tip given to me at the Dubbo rally, was to leave the locking nut on the valve stem loose by 5mm or so - then if the tyre is starting to rotate, you have a chance on inspection after a short run (and after each run thereafter) to pick up if the valve stem has been pushed over (indicating the tyre is rotating ever so slightly less than your rim - which is not a good thing). This allows you to deflate the tyre a bit, kick it back around so the valve is square again and FULLY reinflate to a higher pressure - all before it goes far enough to actually cut the valve off.
Hope the above assists and prevents you from potentially scratching a (probably) newly restored bike. The other option is to position yourself (quickly) between the bike and the road, as I successfully did at work when I cut the valve off the first time (and thought it was a faulty tube).
Since running at 40 psi I didnt have a problem, I just sheared a magneto shaft instead.   
Best Regards
Derek

     

Offline alwyn

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Re: Tyre Pressures
« Reply #15 on: 04 Jun 2006 at 13:48 »
Hi all,
All this talk about tyre pressures and beaded edge tyres carries me back to when I began my motorcycling career as a youth on a 1928 10/12 Harley (with coffin attached often) and beaded edge tyres of course. After tearing a tube or two by ripping out the valve stems from the rear wheel, I can recall fitting a tyre clamp within the tyre diametrically opposite the valve - never had the wheel rotate inside the tyre from then on. So if you want the comfort ride afforded by softly inflated rear tyres, my suggestion is that you fit a tyre clamp to keep that tyre in a fixed position relative to the rim, almost essential anyway given the enormous power transmitted to the tarmac via the rear tyre, especially by the 2-3/4 hp Dougies.  :wink:  Come to think about it, I experienced tyre rotation on my T35 in later years too but instead of clamping it I used to smear a liberal coating of rubber solution around the bead at the time of fitting and that stopped the rotation too.

Alwyn
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