Dunlop M section CR65 tyre Pressures

[Heightswitch]

So..Have started to shake the old girl down and I am enjoying the experience..I am starting to get a little more comfortable with it but the car still has a hell of a lot more ability than the tubby squidgy bit behind the wheel..

I have started out with 27 PSi all round and worked on evening out pressures to max 30Psi Hot..I have been told that others run much higher pressures on historics so now that I am starting to be a little more consistent I am going to start upping pressures slightly to see what the differences in handling are..

Has anyone got any advice regards pressures that these tyres run? I have heard that some run up to 40 psi ??

I am running 550's front and 600's rear all on 8 inch rims



Neil.

[esper]

Find out what the end pressure in yr tyres is. if this is to high after practise, lower pressure . if you don't get there : you must spank the Blackpool ***** (sorry I meant , red light district lady) harder.

[zefarelly]

If they get too hot its like driving on oil . . . I had mine down to 22 psi cold last summer. they go up 4-5psi when hot, if less, spank harder!

anything over 30 is horrible on the Cortina, some people wind them up in the wet to open the tread but I think that's pointless as you getno heat in them if they don't move about a bit . . .

Having said all that I know bugger all about tyre tech so wait for someone knowledgable to comment . . . . . isn't the interent a wonderful font of bull****!

[Mike Bell]

The problem is Dunlop pressures seem to be very car specific. For example, I run my +4 which has 5" rims with much higher pressures than another car with wider rims and different weight but same width tyres. With the Griff weight distribution (it must be nose heavy?) I wouldn't know where to start, maybe you need to beg some info from Nigel Reuben or someone of his experience, or one of the guys at HP Tyres may have some ideas.

[Robyn Slater]

Originally Posted by zefarelly

some people wind them up in the wet to open the tread but I think that's pointless as you getno heat in them if they don't move about a bit . . .

I'm tending to agree here. I ran lower pressure at Thruxton on a damp track and found myself getting quicker as the race progressed. The last couple of laps as it started to rain, i got even quicker!!

[gt917]

Mike is right, and tyre pressures are very much car specific, and I would advise some experimentation on a test or track day.

I reckon you are running too much pressure, allowing for the fact that the pressure will increase 4-5 psi at least quite quickly.

So many other factors will come into play, from tyre wall flex, corner weighting, castor/camber angles, etc, etc, so I reckon you need to "play" for a day.

[Tel 911S]

One way that we have found for setting up , pressures , suspension , tracking etc , is by taking tyre surface temperatures when testing .
http://www.amazon.com/HDE-Temperatur.../dp/B002YE3FS4

Using something like this [ other types are available ] , across the tread surface will tell if it is too high a pressure [ not much heat at the edges ] too soft [ too much heat at the edges & not in the middle ], & even things like wrong camber or tracking .
Testing does take a lot of time to try to find what works best , but as they say " every little helps "

[morninggents]

I used to run at 30 lbs hot on my Cortina but have gone up a couple of lbs recently. The tyres do gain around 4 lbs in a 15/20 minute session (except for right rear - 3 lbs) so I set them cold at 28 lbs (29 for RR) then adjust as soon as possible after practice to set at 32 all round.

Trial and error is the best, but t(y)resome way to go!

[Heightswitch]

I had heard of people running 40 psi hot pressures and for a moment thought I may be running under inflated..Running 30 hot doesn't sound too far away.. I will next time try a couple above and a couple below..Trouble is Me more than tyres..not really consistent enough and more track time needed

http://www.youtube.com/watch?v=YgG5k...m-upload_owner

It gets interesting after about 12 mins in. Please don't be too critical of my lines it was my very first time at croft. Driver is starting to feel more in tune with the car but still a long way to go.

N.

[terence]

We always ran 32F 34R, took a while to get it just right for the Griff because of the torque/engine weight/rear suspension set up etc. Same pressures wet, it stops the tread from closing up and makes the histo quite a nice tyre for rain use.Ended up using the same pressures for the B as well, obviously worked with a 3:08 in the dry.What are zz s worth per lap? Generally 3to 4 seconds but much more fun on Histos.

[simon drabble]

Originally Posted by terence bower

Ended up using the same pressures for the B as well, obviously worked with a 3:08 in the dry.What are zz s worth per lap? Generally 3to 4 seconds but much more fun on Histos.

When was that Terry? Last time I recall you doing 6 Hour at Spa in your MGB in 2009 you did a 3-20.... However for context the Smith and Cottingham MGB's do indeed do 3-05/8 but not sure if that is on Avons or Dunlops.

[gt917]

Originally Posted by Heightswitch

I had heard of people running 40 psi hot pressures and for a moment thought I may be running under inflated..Running 30 hot doesn't sound too far away.. I will next time try a couple above and a couple below..Trouble is Me more than tyres..not really consistent enough and more track time needed

Please don't be too critical of my lines it was my very first time at croft. Driver is starting to feel more in tune with the car but still a long way to go.

N.

No one here will be critical. Think we would all like your car.

Great onboard footage showing just what a lovely circuit Croft is.

Just experiment with tyre pressures and don,t be scared to lower them even more. It will come right, and may well be surprising in the end pressure results. As a matter of interest just how old are the tyres?

Please keep us posted.

[Mike Bell]

Originally Posted by simon drabble

the Smith and Cottingham MGB's do indeed do 3-05/8 but not sure if that is on Avons or Dunlops.

Avons.

[Heightswitch]

Originally Posted by gt917

No one here will be critical. Think we would all like your car.

Great onboard footage showing just what a lovely circuit Croft is.

Just experiment with tyre pressures and don,t be scared to lower them even more. It will come right, and may well be surprising in the end pressure results. As a matter of interest just how old are the tyres?

Please keep us posted.

Yes they are 11 years old and a little cracked up (like the driver) ..
New set will be on order soon and the old ones will be spares…I wish I had the budget available to me that some other Griff Fia racers have access to??

N.

[Heightswitch]

Originally Posted by terence bower

We always ran 32F 34R, took a while to get it just right for the Griff because of the torque/engine weight/rear suspension set up etc. Same pressures wet, it stops the tread from closing up and makes the histo quite a nice tyre for rain use.Ended up using the same pressures for the B as well, obviously worked with a 3:08 in the dry.What are zz s worth per lap? Generally 3to 4 seconds but much more fun on Histos.

I assume they are hot pressures Terence?
N.

[terence]

That was cold, much lower than 34 rear lets the tyres deform under acceleration.
As Mr Drabble obviously has come out of hibernation , who said anythibg about 6hr? Barry,s race 04, I think it was.

[Heightswitch]

Originally Posted by terence bower

That was cold, much lower than 34 rear lets the tyres deform under acceleration.
As Mr Drabble obviously has come out of hibernation , who said anythibg about 6hr? Barry,s race 04, I think it was.

Interesting.
Next time at croft I will have a play to see if I can feel the difference.
N.

[terence]

Below thirty psi you should have been feeling the back end moving like a porpoising effect?

[Heightswitch]

Originally Posted by terence bower

Below thirty psi you should have been feeling the back end moving like a porpoising effect?

Slightly, Especially at anglesey onto back straight over the bump..Still very controllable and stable though..
One thing I have found is that it doesn't like trail braking..Its a case of all braking in a straight line and turn in off the brakes even if you think you're going a little too quick..

Its quite well balanced but a handful to push at the limit…trouble is that my limit seems to be about 5 seconds slower than the rest of the field at the mo

N.

[terence]

Get it all done in a straight line-trailing will give no advantage in the Griff because of the wheelbase.Just give it time before trying to push it, they dont mind biting back.

[pattlega]

Running Lotus Cortina in HTC class with HSCC and trying to get to the bottom of tyre pressures. Have been running at 28psi Cold coming up to 32psi Hot BUT think this might be way too low. Pictures of car show tyre wall deflection that might suggest pressure too low. Found this article that talks of range of pressures between 32 and 43/44 psi. Spoke to another competitor who suggested they need be to be near 40psi hot. HTP Tyres appear vague in their guidance, as do Dunlop themselves.

Picture of me struggling to get anywhere near apex at Hairpin at Cadwell Park - Look at tyre.

Document attached too.

Rgds

Graham

[Nick JM]

if it helps I run the MGB on 26 cold - they get up to 30 ish when hot.

Terrence are you really up to 30 plus cold on yours?

[Robyn Slater]

Slightly off topic but still concerning Dunlop CR65's.

There used to be a chart on Dunlop's website showing rev's/mile info for various tyre sizes. When i looked recently i couldn't find it. Does anyone have a link or hard copy i can beg?

[terence]

When I had it, yes.32 wet.They will move about a little but being a B etc.

[Mike Bell]

Originally Posted by Robyn Slater

Slightly off topic but still concerning Dunlop CR65's.

There used to be a chart on Dunlop's website showing rev's/mile info for various tyre sizes. When i looked recently i couldn't find it. Does anyone have a link or hard copy i can beg?

Looks like HP have 'improved' their website! The info is still in individual tyre info, though. If you google 'dunlop historic race tyres revs per mile' you can find a chart in Canada, Czech Republic, and probably other countries as well! Tweeks have size charts for L and M on their site also.