"Period Correct" Racing Tyres

[AcecaRacer]

OK gang -
   
   New topic.  I have read all of the previous posts - very few - about tyres (english spelling) and tyre pressures.
   
   Here is the situation:
   I am currently running 5.5 x 15L Dunlop Racing Tyres
   I went to 15 inch from 16 to try to reduce the body/sidewall roll and improve handling.
   I vintage race in the Monterey Historic races among others and they are sticklers for authenticity about tyres from "the period".  Assuming that the UK vintage racing authorities are the true arbiter of what is correct running gear for a 1957 ACECA, what are better (and period correct) tyre options for me to race on?
   I have read about the Michelin "X" tyres as well as Avons.
   What are legal for me?  Do 15 inch handle better than 16?  What pressures are you finding work well front and rear?
   
   Sorry for the long message...
   
   Picture here - http://trackthoughts.com/wp-content/uploads/2011/08/042_M020204.jpg
   
   
   Cheers,
   Rob

[REV]

The Picture!
   
   

[AcecaRacer]

How did you insert the picture like that?  I tried several different ways!

[nikbj68]

Hehehe....Like this!
   
   
   (From the Dennis Grey gallery on General Racing Ltd)
   
   Looks like the 15" sidewalls still roll a bit!
   The site these pictures were on will not allow linking, so Sir REValot and I had to copy & host them elsewhere(in this case, Photobucket, you then copy the 'IMG code' into your message.
   I did a little tutorial HERE,5th post down.
   
   Back on topic, in the 60`s, My dad used to drive his Ace to circuits on 16" wheels, then swap to 15`s to race, will ask if this was more to do with boosting acceleration than handling & which tyres he used then.
   Damn, your Aceca looks great pushing on through the corners!!!!

[BEX308]

308 raced in SCCA events on Michelin X's, 5.50x16 in 1957-1960; with the high aspect ratio of these tires higher inflation pressures definitely help. Both of the owners/drivers from that era are still around and have been following my progress on 308, next time I see them I'll ask about any other tire memories. The roll on hard cornering is an artifact of the essentially equal length upper and lower arms and several disqualifications occured in period East Coast racing for the use of illegal anti-roll (sway) bars. The factory didn't address this issue until the Cobras so they were illegal in SCCA Production Racing with the Aces. Lowering the car with smaller wheels would probably not be nearly as effective as modifying the springs as was done by Bill Wonder on 308 (shorter and less arch).
   Pete

[AcecaRacer]

The picture with the red wheels above is using 16 inch rims...hence the sidewall flex.
   I am currently running 15 inch stainless/chrome rims as shown in the picture at top.
   I have played with the tyre pressures quite a bit.  Most recent experiment was to adjust from my usual 24psi for front and rear (cold) to 27psi front and 22 psi rear in order to try to offset my fairly strong oversteer.  It seemed to wrok rather well I must say.  Front tyres started to scrub a bit more so the back end was not as twitchy. Running 24 x 24psi was making my back end quite squirrely.  As you can see if you google "Aceca" and "Fisher" together and then click on images, you will find many pictures of me with a wide end slide.  Looks good in pics, but I can assure you, it's not the fast way round!
   The key thing for me is to be able to justify using Michelin radials to the authorities if it is indeed "period correct" AND better for the car in terms of handling.  I did drive on radials last year due to a shortage in Dunlop supply.  The handling was much tighter, although at the edges, the radials had a nasty habit of snapping loose without warning.  Took some getting used to in comparison to the usually gentle and predictable non-radials.

[BEX308]

Rob,
   Check page 66 of "Ace Bristol Racing", that's 308 after a crash at Lime Rock in April 1958 and the Michelin logo is clearly visible on the front tire. Can't get documentation for "period correct" more definitive than that! I was told the hot set up at the time was to run Englebert's; but they were prohibitively expensive for most guys.
   Pete

[3.8Jaguar]

Tyre selection can make a critical difference to lap times, period race tyres were nearly all cross ply which as I am sure you all know have very different rates of give in the wall in comparison to radial.
   If you are running relatively low pressures on a car with a bit of mass to it and a high and short roll centre all will conspire to give the symptoms you are experiencing.
   Don't forget you are also looking for good contact patch through out the speeds you are achieving, which is again down to the weight of the car and tyre pressures needed to maintain a good contact patch.
   There has been a fair bit of discussion over the Blockley 5 stud tyres in comparison to the dunlops for competition. The Blockley is a good tyre from my experience but they do benefit form a good scrub in to get the best out of them.
   
   My feeling is that 24 psi for an ACECA for racing is a little low for the weight of the car, if you are feeling the need to lower the pressure to that extent it may be your geometry that needs the development rather than a trade off on tyre pressure.
   
   It sounds a bit serious for club racing but you can learn a lot from your tyre temp.

[shep]

Maybe I'm wrong, but the the red wheels in the photo look awful like 15" rims and Dunlop L tyres. With that setup I used to run 24F and 26R psi on my Ace, but a good friend of mine Ian Moss who used to drive works Astons in the 60s told me to go up to 32F and 34R cold. I tried it and immediately found almost a second a lap at Silverstone, and the sidewalls stiffened beautifully. We still use those pressures on David Emmans' Ace now, although he has some Avon CR6ZZ tyres on 15" rims which are even quicker, although the diameter is smaller which shortens the gearing about 5%. Andy.

[B.P.Bird]

Long time ago, but I used 40 psi on The Ace le Mans for racing with Dunlop L section 5.50 and 5.00 x 15 R5 tread pattern. I have had Blockley radials on the Mk. 1 Cobra for  a while now and they seem to be really very good. They are 205 70 VR 15. Being radials they suit the the transverse leaf spring chassis rather well. On the road 24 psi is fine.
   If you do go up to 40 psi on the Dunlop racing rubber then remember to drastically reduce the pressure if it rains. I have a sneaking suspicion that the Blockley radials may be the answer to the Ace/Aceca/Greyhound/Mk. 1 Cobra tyre problem.

[Gus Meyjes]

I put 40 PSI in my Vredesteins. I did not race them, but they feel great on the road. I have not used Vredesteins for racing.
   
   Gus

[AcecaRacer]

Thanks again to all for the feedback.
   
   Firstly, the red rims are indeed 16 inch wheels. Any pictures you see with chrome wheels are 15 inch wheels.
   
   Secondly, I have never tried going to higher pressures (30+ psi) to achieve better grip.  But maybe the stiffer sidewall will give me the firmness I have been lacking.  I will try, however I am very skeptical as my tires have approached 30PSI by the end of a session and they are usually very squirrely by then.
   
   Thanks to a blown stub axle (again) I was a DNF in the Sonoma Historics so I am awaiting replacements with splined stubs to fix the problem once and for all.
   
   Then I can play with different tyre pressures in anger.
   
   Stay tuned...Much thanks

[Aceca289]

Rob,
   
   FYI - I ran across a vintage 1956 account of an AC Ace running the 1956 Sebring 12 hour in the August 2007 issue of ACtion Archives. It just happens to mention that Hap Dressel, who successfully completed the race in an AC powered Ace, was running Michelin X tires filled with Nitrogen (at 45psi rear and 39psi front).
   
   I hope all works out with getting your car prepared for Laguna Seca in August.
   
   John

[AcecaRacer]

Thank you John.  Stub axles supposedly arriving in the UK on Monday...will advise.

[nikbj68]

quote:Originally posted by AcecaRacer: I have never tried going to higher pressures (30+ psi) to achieve better grip... I will try, however I am very skeptical as my tires have approached 30PSI by the end of a session and they are usually very squirrely by then.

I was going to suggest Nitrogen to stabilise pressure/temperature when John posted this:

quote:Originally posted by AcecaRacer:...Hap Dressel...was running Michelin X tires filled with Nitrogen (at 45psi rear and 39psi front)

   Even my local tyre service are offering Nitrogen filling for £5 per wheel, wonder how many muppet-boy-racers are taking up their offer for street use? [:o)]