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Re: Avon tyre sizes

Posted: Sun Mar 27, 2016 10:47 am
by Roger King
Paul Blore wrote:Ahh, I see. I misunderstood the meaning of "these". I thought you meant Cobras, but I see now that you're referring to your list. :D
It would be interesting to see what your weight distribution actually is given that it should be identical to a new original 289. I'd hazard a guess at 47/53 with driver and half a tank of fuel.

Paul
That's pretty much what I reckon.
The Mustang's 60/40, which can be interesting at times (as I think you have observed...).

Re: Avon tyre sizes

Posted: Mon Mar 28, 2016 7:31 am
by French BRA 289
In The cobra club de France,everybody (80% )with Avon C6

Since I run my tyres at 32 psi all round. It seems fine to me.my friends in 427 and their very big tyres are all arround 22 psi

Re: Avon tyre sizes

Posted: Wed Mar 30, 2016 12:49 am
by Colin Newbold
Being somewhat anal around tyres (the only thing between you and the scene of the accident - and only a tiny contact patch in relation to the vehicle's size), most of the 'old stagers' will know I've long been a fan of these Avon tyres. I've experimented over the years with various tyre pressures/shock absorber settings and would be loathe to offer guidance as my results clearly show its not an exact science.

My (limited) racing experience (much of it also on these same Avons) would lead me to humbly remind you that the more air in a tyre, the wider the grooves in the tread. In other words, the tread opens up, which is why the considered wisdom amongst racers is to increase tyre pressures in the wet (but only by 2-3 lbs/ft).

All in all, my own time with all 9 Cobra reps I have owned suggests starting at say 22 all round, then gradually try increasing the pressures 1 lb at a time (per axle) to see what feels right for you - in other words until you arrive at the optimal ride/handling combo. Currently that's 24F/26R unless I have the wife's luggage on board which means 25F/27.5R :lol:

Colin

Re: Avon tyre sizes

Posted: Sat Apr 09, 2016 10:27 pm
by peterc
Clive
Firstly my mileage is embarrassingly low 15k in 15 years!
I would agree that with a 46%- 54% bias to the rear that you would expect the rears to be a higher pressure but then mine are larger being an FIA. It seemed to work quite well but the Avons appear good on equal pressure.
Next step is to recheck all the system settings.
Peter C

Re: Avon tyre sizes

Posted: Sat Apr 09, 2016 11:39 pm
by Dave Woodward
Out of interest I've got my spare wheel with Avon 205/70's in the wheel well now. Had to let all of the air out though to reduce the diameter of the tyre before it would fit. My P4000's used to fit fully inflated with c. 1cm diameter to spare.

Anybody else running with an Avon spare on the boot?

Smarty pants 427 and FIA owners need not apply :D

Re: Avon tyre sizes

Posted: Sun Apr 10, 2016 12:04 am
by Roger King
Dave Woodward wrote:Out of interest I've got my spare wheel with Avon 205/70's in the wheel well now. Had to let all of the air out though to reduce the diameter of the tyre before it would fit. My P4000's used to fit fully inflated with c. 1cm diameter to spare.

Anybody else running with an Avon spare on the boot?

Smarty pants 427 and FIA owners need not apply :D
Dave, I presume you have these Avons all round. Do you know what the tyre diameter is? If they won't fit in the spare wheel well inflated, they must be significantly bigger than the SP Sports which I have fitted, or the P4000s as you have noted. This will lengthen your overall gearing quite noticeably, which with a 3.07 diff will drop your revs at 70mph by around 250rpm, or produce an equivalent speed increase of around 5mph. This means your engine will be turning over at around 2500 at 70mph in top.
Be interested to know how far the centre of the spinner is off the ground with tyres at working pressure, if you get the chance to whip the tape out.

Re: Avon tyre sizes

Posted: Sun Apr 10, 2016 8:14 am
by Dave Woodward
Will sort some measurements later today Roger.

The slight increase in leg length will be welcome on those long cruises tbh. Previously 70 = c. 3000 rpm.

Just looking at compact tyre inflators now!!

Re: Avon tyre sizes

Posted: Sun Apr 10, 2016 9:27 am
by Roger King
Dave Woodward wrote:Will sort some measurements later today Roger.

The slight increase in leg length will be welcome on those long cruises tbh. Previously 70 = c. 3000 rpm.

Just looking at compact tyre inflators now!!
Don't get too ambitious - for reasons given elsewhere, I wouldn't really want to drop much below 3000rpm at 70, if at all. Do you know at what rpm your timing is all in? You really want full advance and the carb(s) comfortably on main circuits (assuming they're fixed-jet carbs) while you're cruising.

Re: Avon tyre sizes

Posted: Sun Apr 10, 2016 2:32 pm
by Dave Woodward
Not sure Roger. How would I check.

Feels 'full on' well before that :D

Re: Avon tyre sizes

Posted: Sun Apr 10, 2016 4:24 pm
by peterc
Dave
A smarty pants FIA owner replying here!
I have a 205 x 70 in the boot which I guess can only be used as an emergency space saver equivalent but it is (was) at 30 psi
Like your experience it's Pirelli from memory and certainly has enough space for a carpet cover over/ around it.

I think Colin's approach sounds right on pressures though. We all have our own driving style and expectations. Having said that its nice to know we should be expecting around 24-26 psi
It's also nice to know that I 'm not the only one to travel with someone who needs twice as much luggage!
Peter C