Author Topic: Tyre pressures, a word of caution  (Read 3478 times)

Offline Rusty nuts

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Tyre pressures, a word of caution
« on: 25.08. 2009 09:25 »
I'm sure for most this is probably a case of "teaching Grandma how to suck eggs", but If there's only one member out there who isn't aware of this it could help avoid a very nasty incident.

Yesterday having washed the bike I went for a quick spin round the block to dry everything off, quick spin turns into slightly longer ride as you do!
Two miles from home have sudden catastrophic failure of rear tube.
Plodding along at 30 mph suddenly old plunger is doing very good impression of speedway bike cornering, much to amusement of local hoodies hanging out at the "One Stop" that is until I nearly plough into them.
Having regained my composure I fire her up put her in first & begin the long push/walk/jog alongside home, uphill all the way!
Much huffing & puffing & a very cold shower later I remove the rear wheel & pull out the tube. The valve has ripped clean from the tube.
Tube (Continental) & tyre (Avon SM) have only covered 150 miles since new.

Straight on phone to supplier.
What pressures are you running he asks?
20 psi front 23 rear which is slightly higher than the Haynes pamphlet! says me.
That's your problem he says, modern tyres need to run at much higher pressures.
Modern tyre construction is different he explains with different materials used, much softer sidewalls & they aren't made of rubber, sir!
Now I accept that modern tyres are made of a different compound but surely it is still rubber I think to myself.
Anyway he suggests I fit a security bolt which I think is a bit overkill on a bike that produces 20 something horses but never mind.
I politely suggest that it could be a lifesaver to put a sticker on the tubes or just a note on the invoice explaining this.
Hate to think what would have happened if cornering at higher speed.
Not my resposibility mate, he replies. Do I want to buy a new tube he asks?.
Yes I do, but not from you thanks I reply & hang up.

Call Brian at Lightning spares who confirms the issue of pressures. He recommends at  30-32 psi rear 28 front.
Says he's lost count of the number of soft tyres he's seen at BSA meets only to be told by proud owner they are running at BSA handbook stated pressures.
So it seems I'm not the only one!
Bought my tube from Brian, and err a few bits for the new project!
1949 A7 Plunger
1947 A7 Rigid Star Twin
1969 Triumph T120R
1972 Triumph T120V

Offline terryk

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Re: Tyre pressures, a word of caution
« Reply #1 on: 25.08. 2009 10:11 »
Thanks for the info thats worth knowing thats for sure.
1950-53 A10 rigid/plungers, 1958-61 A10 super rockets, 1947-50 A7 longstrokes, 1949 Star twin,
1951-54 A7 plungers, 1940s M21, WDM20s,
1948-50s B33s rigid/plunger/swingarm, 1948-50s b31s rigid/plunger/swingarm

Offline tombeau

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Re: Tyre pressures, a word of caution
« Reply #2 on: 25.08. 2009 10:14 »
I expect with the higher tyre pressure on a rigid or plungers back wheel you start bouncing a lot more on  rough surfaces. The tyre acting as less of a cushion.
Cheers,
Iain

Offline a10gf

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Re: Tyre pressures, a word of caution
« Reply #3 on: 25.08. 2009 10:32 »
Thanks for bringing this up, Rusty. 'The valve has ripped clean from the tube', yes, too low tire pressure > less tire pressure\friction on the rim > slipping > tube valve goes.

(btw, sold my xt350 today to a member of the younger generation, it's got a tire to rim locking system on the rear, to allow driving with next to no pressure (or even with a flat for a short distance).

tombeau wrote:
Quote
plungers back wheel you start bouncing a lot more
...but preferable to bouncing into the bushes if the tire fails :O)


A10 GF '53 My A10 website
"Success only gets you a ticket to a much more difficult task"

Offline Rusty nuts

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Re: Tyre pressures, a word of caution
« Reply #4 on: 25.08. 2009 11:03 »
I expect with the higher tyre pressure on a rigid or plungers back wheel you start bouncing a lot more on  rough surfaces.
As long as it's the bikes rear end bouncing on the hard suface & not mine I'll put up with it *smile*
1949 A7 Plunger
1947 A7 Rigid Star Twin
1969 Triumph T120R
1972 Triumph T120V

Online Triton Thrasher

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Re: Tyre pressures, a word of caution
« Reply #5 on: 25.08. 2009 11:19 »
Rusty
The guy gave a correct and helpful answer to your query.  He didn't get an awful lot of thanks.  It's hardly his fault BSA don't issue service updates.

Offline Rusty nuts

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Re: Tyre pressures, a word of caution
« Reply #6 on: 25.08. 2009 11:30 »
Triton Thrasher,

You are right it wasn't the answer, which was correct, but I found his tone of voice & general attitude  not to be what I would expect of one of my own employees, so I chose to purchase replacement elsewhere.

Rusty
1949 A7 Plunger
1947 A7 Rigid Star Twin
1969 Triumph T120R
1972 Triumph T120V

Online BSA_54A10

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Re: Tyre pressures, a word of caution
« Reply #7 on: 25.08. 2009 11:43 »
The works bikes ( Yammie SR 500 & XJ 650 /'s 750's ) were always run close to 40 psi.
The A65L runs 30 to 35 psi
OTOH the rigid M20 runs 16 & 18 comparred to BSA's recommended 12-14 & 14-18 or it bounces all over the road.
Lower pressures with modern tyres really need to have security bolts fitted and the security bolts need to be the right size for the rim.

Bike Beesa
Trevor
Bike Beesa
Trevor

Online Triton Thrasher

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Re: Tyre pressures, a word of caution
« Reply #8 on: 25.08. 2009 11:56 »
I found his tone of voice & general attitude  not to be what I would expect of one of my own employees, so I chose to purchase replacement elsewhere.

Rusty

That sounds fair enough.

Offline beezalex

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Re: Tyre pressures, a word of caution
« Reply #9 on: 25.08. 2009 13:55 »
Thanks, that was helpful, though I have never run less than 28 psi since lower pressures moosh up the cornering.  With a sprung saddle, though, they seem comfy enough.
Alex

Too many BSA's


Offline dpaddock

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Re: Tyre pressures, a word of caution
« Reply #10 on: 29.08. 2009 19:20 »
Thanks for sharing this, Rusty.

David
David
'57 Spitfire