What are you guys running for tire pressures? I've got the stock 415mm wheels and the Ferrari factory sticker on the windshield lists the tire pressure at 3.0KG/cm2 (which converts to 42.6psi !) front/back. The Amerispec sticker in the glove box lists it at: 38psi front/back at maximum load. The stock Michelin TRX tires are stamped 36psi MAX on the sidewalls... ????????
Frank, Doesn't that seem kinda high to you? The TRX tires have a maximum pressure rating of 36 psi (cold) stamped right on them. I've never owned any vehicle that had a tire pressure setting of anywhere near 43 psi front/rear... My other cars are around 28-32psi.
Hi Gary, After being in the tire business for a few years I can corraborate your concern for correct pressure. I would go with the tire manufacture's recommendation while at the same time taking note of the maximum weight ratings of the tire. Running a large 225/50-15 on my 240Z (as opposed to the stock 6.50-15) requires that I run a lower pressure in the tire because of the light weight of the car 2450 lbs. vs the load capability of the tire which is well above what is required for the 240. I run somewhere around 26 lbs. psi. If I ran the same tire on my 308 I would be running around 32 psi because the 308 weighs close to 3400 lbs. To help determine the pressure on a given application I rely on a visual record of side wall 'bulge' and tread depth measurements. If there is more wear in the center of the tread it is safe to assume you are running over inflated. In the case of outer edge tread wear it is not as cut and dried due to steering geometry and camber settings both front and rear, notorious for premature shoulder wear on performance cars. To try to get the tread to wear evenly straight across would involve running the tire slightly over inflated to compromise for the camber settings. This will create a pretty rough ride but maintains fairly crisp steering response. In summery; Look at the gross weight of your car and try to calculate where the actual weight of your car will be during most drives. Look at the gross weight limitations that are stamped on your tire (for reference) Look at the max tire pressures recommended stamped on the tire. Don't go above any of the maximum limits listed on the tire. Try running 5 to 8 lbs below the max listed on the tire and look at the side wall bulge. It will be pretty obvious if you are under inflated by the 'pronounced' bulge. If you are REALLY underinflated you will experience front end 'push' in the corners. (Very dangerous) Or worse yet, the Ford Explorer phenomena (roll over) Note; side walls ARE supposed to bulge somewhat under normal conditions. Tread depth gauges are available at most parts stores, cheap! Hope this helps, DJ
Another note when dealing with metric to imperial measurements. I have found in numerous places in my workshop manual where the converted values/quatities were not accurate for what the engine and car actually used or required. DJ
Thanks DJ, You confirmed my thoughts on the matter. I'm going to run around 30-32psi max. The tires are rated at a maximum load limit of 1,710 pounds each, at the 36psi maximum pressure listed on the tires. That load limit is about twice (6,840 pounds) as much as the car actually weighs. ------------------ Frank- I think that you should consider -lowering- your tire pressures. 43 psi cold, could be VERY dangerous, especially in the summer time and driving at speed.
I agree. On the same note, After setting your pressures during the summer one should recheck pressure when the cooler weather hits. You'll find underinflated tires due to contraction of the air in the tire. DJ
Gary , my TRXs do not have 36psi max on them ? So either our TRX tires are different, the psi rating has changed or one of our sets of tires are wrong. I will contact Michelin and see what they say. But, everything I have ever read on tire pressure indicates that you go with what's on the car, not whats on the tire.
Frank, What do your tires have stamped on them for a max pressure rating? Do you know how old your tires are? Maybe mine are newer and the pressure rating/construction has changed? I have a receipt that shows they were bought new in 1997 and installed. They have less than 5K miles on them.
I called Michelin's technical info line and the lady on the phone said to use 36psi. However, she said that the TRX 240VR55-415 tires were not the OEM tires for a 1982 BB512i. So, I'm not sure she knew what she was talking about. I also sent an e-mail to Michelin and I will report back what I get back.
After looking at my tires again they do say 36psi max. I have contacted both Ferrari Spa and FNA to see what they say. FYI Gary, my 2000 M5 does call for 44psi in the tires as I recall but I don't have the manual with me.
I just received an e-mail response from Michelin and it too indicates 36psi should be used. I still have not heard from Ferrari yet.
I just received an e-mail response from Ferrari Customer Service from the Ferrari Owner's site. They stand by their manual and TRX window sticker that 43psi is the correct pressure to use in 240VR55-415 tires.
Better change to Goodyear! My Eagle F1 GSD3s will take 44PSI. They ride kinda bumpy, when pumped that hard!
Speedy, Michelin is the only company that makes tires that fit TRX wheels, which on the BB512i are 415mm which computes to 16.34 inches .
I have now also received a reply to my query from Michelin in the U.K.. They agree with Ferrari to use 3.0 Bar in the TRX tires which they calculate as 44psi rather than 43psi !
I believe the TR OMs might give some explanation to the confusion -- For speeds < 160 MPH, the recommended tire pressures are in the 2.4~2.6 bar range (depending on wheel and tire type) For speeds > 160 MPH, the recommended tire pressures are in the 2.8~3.2 bar range (depending on wheel and tire type) So if the BB512(i) OMs only have a (high) single tire pressure value, I'd bet they just assume you're going > 160 MPH
Well, to add more to the confusion, my Boxer has a sticker in the glove box that Amerispec put there when they Federalized the car for the US market. It states that the tire pressures should be set at 38psi front/rear.
I just got off the phone with Dick Fritz, the owner of Amerispec. He's probably worked on/Federalized more Boxers than anyone in the USA. He recommends 38psi front/rear and to only run 43 if you are going to be driving at VERY high speeds. He said that 43psi would be a very rough ride. Gary
I just found out from Harold at FOA that FNA called him to get the answer to respond to my e-mail and that Harold had just looked in the Boxer manual and told FNA that it said 43psi which FNA then e-mailed to me. I have now e-mailed FNA again requesting that they find out the correct info from Ferrari Spa. Since the Boxer was never officially imported to the USA, I suppose FNA has very little if any technical info on the car. Hopefully they will find out the correct info and let me know ? I ws told by a former employee of NTW that he thought that since 32psi to 36psi was the common max pressure for most tires when the TRX was made that Michelin may have failed to change that info in the molds for the low volume TRX tires regarding max pressure and made the TRXs with 36psi max instead of the 43psi that Ferrari had had them design in the TRXs for the Boxer? He said he had seen such other errors in tires over the years he worked for NTW and had even seen tire size info incorrectly stamped on tires. I will let you know if FNA gets an answer from Ferrari Spa or not.
I just received another e-mail from FNA and they have advised that what's in the manual and what's stamped on the TRX tires is all the info they have. I have again requested that they check with Ferrari Spa engineering to find out the correct answer. I will post again if and when I hear from them again.
