Tyre Pressures

[Rob Neal]

A65 rebuild is all but finished now apart from a few details and whatever snags the initial runs throw up.  As I'm now venturing out onto the road I'd like to confirm what tyre pressures I should be running.  The Haynes manual states 21psi for the front and 22 psi for the rear which seems a little on the low side to me compared with other similar sized bikes I have.  The BSA has Avon Roadrider Mk II tyres fitted.  Rear size is 100/90-19 and the front  is 90/90-18.  The original front wheel dia should be 19" but the bike came with nice Boranni rims with an 18" on the front so I've stayed with this on the re-build.  What pressures do other folks use on their A65's?

[Catz]

I'm running those tyres on my A10 but both rims are 19" and the pressures that i go with riding with a pillion are 36psi front and 42psi rear. If i was solo i'd go 36/36.
Forget what it says in the Haynes, it's years out of date and modern tyres are made to higher tolerances.

[Rob Neal]

Thanks for the quick response.  Glad I checked as I thought the Haynes figures looked a bit low!

[DAVE BRADY]

Hi,

Try using the figure in the BSA manual. They start at 18psi and the guidance gives increases depending the weight of the rider.  I have found that they are not far off.

Dave.

[DAVE BRADY]

Hi,

Not all manuals have the 'increase for weight' guidance.  I will see if i can find it.

Dave.

[DAVE BRADY]

Hi,

1969 maintenance book gives front 21psi and rear 22psi.  This is said to be for a 150lb rider with the front increased by 1psi per 28lb over this and the rear increased by 2psi.  For a 14stn rider this works out to about 23 and 26.
This still does not seem much but camping gear and a pillion will need more.
I suppose the key to knowing if you are running a good tyre pressure is how long your tyres last and how they wear.
Has anyone got any mileage figures?

Dave.

[iansoady]

I believe that modern tyres are much more flexible and need corresponding higher pressures. I have found that 28 front and 32 rear works very well on my Norton ES2 ridden solo - I'd probably add a couple of pounds either end for your A65.

Why not ask Avon's advice?

[Rob Neal]

Thanks everyone for the input. 28/32 front/rear seems to be what I would expect based on my other bikes so I'll go with that and see how the handling is when I can get a decent run completed.  I can then tweak from there.  Cheers.  Rob

[royblackburn1@btinternet.]

Hi Rob glad to hear you are nearly ready, I see you have 19"rear tyre if your speedo is run off the rear wheel do you know what ratio the speedo gear box is ive been trying to find out. thanks Roy (my A65L is a 1966 import)

[V500]

I believe that modern tyres are much more flexible and need corresponding higher pressures. I have found that 28 front and 32 rear works very well on my Norton ES2 ridden solo - I'd probably add a couple of pounds either end for your A65.

Just to be (slightly) different I use 26(F) and 28(R). The old quoted tyre pressures are far too low for modern flexible tyres, though the 42PSI (quoted above) must be rock-hard!

[DAVE BRADY]

Hi,

I found this on an Avon site.  Obviously the tyre will squash down as the load increases but the idea of increasing tyre pressure is to maintain the correct contact patch.  I would say the illustration is not tyre specific but more an indication of the affects of under and over inflation.

I use 30F and 42R when two up and towing a single wheel trailer loaded with camping gear.  I think that 42psi is the max for the Roadrider.

One up with the trailer loaded I use 25F and 35R and solo with no trailer 23F and 30R

I think tyre life is good indicator of correct inflation pressures and I expect to get about 10,000 miles of mixed use to a rear tyre.
Another indication of correct inflation can be seen on the tyre.  If you have been riding on a straight road and the contact area is across the whole of the tread then the tyre is probably under inflated/overloaded and if there is only a narrow contact area in the middle then it is probably over inflated.

Dave.

[Aquarius]

Years ago, when trying to determine suitable tyre pressures for a kit car with non standard wheels and tyres, I found a puddle in an otherwise dry, flat area and ran the vehicle through it to leave a track on the dry area which allowed assessment of the contact patch (as shown above) to adjust the pressure accordingly. No waiting for tyre wear! 

[Rob Neal]

In response to Roy's comment about the change from 19" to 18" front wheel.  My A65 has the speedo drive running off the front wheel rather than the rear.  I also have a Honda (sorry!) on which I reduced the front wheel from 19" to 18".  The speedo here now runs 5mph high as a result, i.e. if it reads 35 speed is actually 30.  Calibrated this from the speed readout on a TomTom Rider410 satnav.  I assume that the BSA will also now read around 5mph faster.