Tire pressure for Queenie

Time to buy new tires for my 365 GT 2+2. I like the way the slightly lower profile 215/70VR15 tires look better than the look of the stock 205VR15 tires, so I've been using those for years. But I've never got around to find out what the proper pressure should be for the 70 profile tires and just kept going with what the user manual said for full the profile 205s. (27/33 psi front/rear)

This time I thought I'd do it right, so here's my question: What tire pressure would be correct for 215/70VR15 Pirelli Cinturato tires on a heavy car like this? Correct pressure for same profile Michelins?

 

As with any car or tire, I usually start with factory recommendation and depending on (personal) comfort, vehicle handling/performance, thread wear, type of driving (city/suburbia, highway), speeds, etc try different (higher and/or lower) settings until I find the one I prefer.
In some cases, it might take a few trials (perhaps 100-500 miles each ?) to find the ideal preference for you and your car.

 

Is a Ferrari that heavy?
And if so most cars like these have tires with larg reserves to the GAWR's.

Copied this from my post in other forumtopic, so I dont have to write it all over again.

Needed tire-pressure is to give tire a deflection, so heatproduction a cycle, that wont overheat any part of tire-material, when driving the speed constantly, for wich the pressure is determined.

Other things, like riding quality, comfort and gripp, and energy use, are also important, but for tiremakers this is main goal.

Maxload of tire is calculated for this goal, and for the reference-speed and - pressure.

That deflection is made by the relation pressure/load on tire.
So to laws of nature you can calculate your specific pressures if you know load on tire, and maximum speed used, wich you wont go over for even a minute.

To mother nature you must be hounest about your maximum speed, and determining the axleloads, or better axle-end loads 99% acurate, is the greatest chalence, and your responcibility.

I determined once that if 90% of loadcapacity used for the pressure for 160kmph /99mph, that then comfort and gripp is still acceptable.

You can use this reserve to cover inacuracies in pressure measure measurement, pressure loss in time, misyudged weight on tires, etc.

I can make a cold pressure /axleload-capacity list for your tires, with that build in reserve.
But if you want for higher speed, write it, and I make it for that speed.

Then you "ONLY" have to determine the axleloads 99% acurate and search them back in the list for the needed cold pressure.

To make that list, I need from tires.
1. Maximum load or loadindex
2. SL or XL to determine the referencepressure.
3. Speedcode, less important, Q and above have referencespeed of 160kmph/99mph.

 

Here is my super-low-budget version to determine tire pressure:
Wet the tires, roll down the dry driveway and check the "print".

Fear not, there is a super-high-budget version also:
Get on a track, go around a few laps with a comfortable pace (not racing) and use a tire pyrometer to evaluate outside, middle and inside of each tire. The one with a needle.If you want to race, same as above, but under racing pace (obviously).

Or call Roger Kraus Racing and ask them

On a side note, my 911RS required 1.8 Bar cold to get to 2.5 Bar hot (track). It had 205/50/17 and 255/40/17. Your truth is between 1.8 and 2.5 Bar.



Left Rear tire (example)

Inside, Center, Outside.


Center too hot - example: I 170° - C 180° - O 170°
Too high air pressure. This can be too high cold or "starting" pressure or excessive heat caused by sliding due to car setup or driving style.

Center too low - example: I 180° - C 160° - O 170°
Too low air pressure. This can be too low cold or "starting" pressure, car setup or driving

 

Start out with 35 psi COLD all around, drive the car and see how you like it. Make adjustments from there as you feel a need. 35psi all around works for most Ferraris from that era, except for Daytona's which seem to like 40 psi.

 

Thanks for all the responses!

@ TTR - Therein lies the problem. The suggestions from the manufacturers are "look at the sticker on the door post" which won't work for obvious reasons... When hard pressed they reluctantly give you a very wide range, almost from empty to about to pop. Unfortunately, my driving style borders on "like I stole the car", if one can call that "style" - that would mean go toward the high end for starting point, right?

@jadatis - Ha ha! Yes, I should have said "heavy for a vintage Ferrari"! I'll see if I can collect that info for the main contenders (Pirelli Cinturato & Michelin XWX look like best options, if a bit pricey) and then I will come to you crying for help with the calculations.

@dominik - Your super-high-budget option is very tempting since I live very close to the track.

 

@DRW46 - Wow, that's actually a pretty big deviation from what the manual says: 27/33 normal driving "up to 200 kph", 34/40 "motor way". I'll give 35/35 a shot and see how it feels. Is the higher pressure for the Daytona due to the stock 70 profile tires? If so, this might be a hint for the "correct" pressure.

 

Manicotto: The higher pressures for the Daytona are to help "lighten" the steering effort. Generally, the higher the pressure, the more quickly the car will react to steering inputs, but the ride will become stiffer. You will find a good compromise.

 

Because of your recomended 27F/33R, i suspect motor in back, I dont know anything about yoyr car, so dont laugh now.
Mayby if 2 seater, persons also closer to rear axle. Gives higher axleload rear then front.

And I already googled your 215/70R15.
Found loadindex 95 in Standard load, and 98 in XL/reinforced / extraload..

But comfirm this or corect it

 

I don't see a "problem", per se, since I believe your 365 GT 2+2 has factory recommended (not mandated) tire pressure settings specified in your owner manual for the car.
Besides, like I & Dyke (DRW46) noted, you must start somewhere, whether it's the factory or tire manufacturer recommendation for the given car or tire or some close-by number (35 psi ?) and keep adjusting to your liking & driving style.
I change tire pressures in my vintage cars fairly frequently, depending type of driving, loads/passengers in them, road conditions, etc.
Not rocket science, just part of old school ownership practices that have worked for me since I started driving vintage cars nearly 45 years ago.

 

@TTR - Thanks for your reply! I think I'll skip the recommended settings in the manual and start with 35F/35R, since a) they're for the full profile tires, and not the 70 profile I like and b) everybody on the forum seem to prefer higher pressures.

@jadatis - The dry weight is about 1580 kg, which is a bit high for a vintage Ferrari. (Thus the "Queen Mother" epithet.) The engine and gearbox are both in front and it's a 2+2. Still the manual says 27/34 up 200 kph with the stock tires. Wonderful highway car and not bad at all in the mountains.

 

@DWR46 - Thanks for your reply! Since steering effort is not a big issue with the power steering, I think I'll start it out at 35 psi all way around and see where I'll end up.

 

also it is important if you use "normal air" or nitrogen

 

@turbo-joe This one gets fresh, fragrant country air!

 

Hi

You can contemplate going back to standard, because Pirelli have made them again. they are a bit taller so they will fill your wheel arches correctly, and lift the car a bit further above the speed bumps.

https://www.borrani.com/ferrari-wheels/365-gt-2-2.html

However the 215/70VR15 Michelin XWX are a great option as is the Pirelli 215/70R15 Cinturato.

I think a 215/70 has a very similar volume of air inside them to carry the weight of a Ferrari. If you are comcerned add a couple of psi. More pressure is safer than less.

 

Thanks for the information and the link! Not a bad price either.

 

Buying setd like this are the best value

https://www.borrani.com/205-r-15-pirelli-cinturato-cn72.html

 

always buy michelin tubes. the cheaper ones always need air added.

 

agreed

https://www.longstonetyres.co.uk/classic-tyre-inner-tubes.html

Always put inner tubes in wire wheels.

 

Thanks guys! Yes, I learned that the hard way with another car...

 

I prefer to use a gas mix of 78.08 percent nitrogen, 20.95 percent oxygen, and 0.93 percent argon, with just a trace of water and lubricating oil. aka "shop air"

 

@turbo-joe: Thanks for the tip! I suppose you add some antifreeze in the cold months?

 

sure, and in the summertime some ice to cool the tires

 

some tyre stations here in germany use up to 95% nitrogen. so the same as airplanes use in their tires and also racecars.

 

As hot as it's been this summer, maybe 100% liquid nitrogen would be a good option?