RSMartin

It was explained to me, by discount tire, that a 225.50.16 for a '85 928 automatic had to be a "93" load weight . However a manual of the same can be a "91" these "are DOT safety standards". They wouldn't be able to sell me the tire due to liability issues.
This is still resonating in my head. Butler tire said they never heard that.
​​​Anyway I bought different tires elsewhere.
​​​​​​Anyone else hear of this ?
PS, I buy my company tires at discount tire because my employees can get service for their vehicles easily

jpitman2

Maybe the listed weight of the auto tips it over into the higher rating requirement?
jp 83 Euro S AT 57k

Speedtoys

I only checked one source, but the max GVWR's for 5spd and auto the same year (85) are the same.

RSMartin

So my question was if I go on a diet I can buy your tire

hb253

Per the ISO metric standard, a 91 index tire can support 1356 lbs at 36 PSI inflation pressure, a 93 index tire can support 1456 lbs at 36 psi.

4 x 1356 = 5424 (91 index)
4 x 1456 = 5824 (93 index)

I've posted it in other threads. This link from Toyo [[url]https://www.toyotires.com/tires-101/tire-load-and-inflation-tables] has a great summary of P-metric, ISO-metric inflation pressure and load index.

According to the Technical Specifications book for the 85-89 model years, the 1985 928S has a maximum permissible weight of 4123 lbs, maximum permissible "axial" loads of 1984 lbs front, 2205 lbs rear - no idea why the axial numbers don't add up to 4123, I'm not sure if "maximum permissible" is the same as GVWR.

My interpretation is that both 91 and 93 load index tires would be adequate even at lower inflation pressures.

Hugo

RSMartin

* I should consult owners manual. That's why smarter people than me bothered to write it.
WOW truth is I need to loose 100lbs so My car can have proper tires. Too many skinny Germans ?

FredR

Your model is supposed to have 92Y load rated tyres as a minimum and as I am aware was equipped with 225x50x16 all round. My late 90S4 had 245x45 on the rears rated as a 94Y load factor.

In a society as litigious as the USA it would not surprise me at all if there was legislation regarding supply and fitment of such but I do not know that for a fact. I know Germany is very tough and the UK less so.

Your dealer probably offered you a 93Y because he did not have a 92Y in stock but then given OEM rubber required the Porsche N rating as well one might presume that the same logic applies to that. I have not run with Porsche N rated rubber for years and never had a problem but that does not make it right, but then my rubber is also wider and by definition such tyres can carry more load anyway.

Bottom line: your dealer was probably legally correct operating in your best interests - it would be interesting to know if some of our US based friends can add more detail based on known fact. It may even be one of those things that vary state to state???

KenRudd

I ran in to this issue as well. Brought the rims in off the car. Shop was then happy to mount the tires I wanted. ( In this case NT01's )

Petza914

Ran into this exact same issue with Discount Tire trying to order the Nitto Invos I run on my 928 Spyder. My car has a canvas roof so it's quite a bit lighter than a standard 928 (also has a lower Cg)

To resolve my issue, I called back the next day, told them I was ordering tires for my 914 Race Car and 2 days later had the tires I wanted for the 928 sitting on my front porch because when they looked up the weight of the 914 and the load index on the tires, the rating was plenty high. As I recall, it was only the fronts or the rears that raised the issue.

dr bob

I follow KenRudd's method, and pretty much never bring a car to the store for tire work. It's safer for the car if I do the wheel R&R and they do the tire install on the wheels. I've gotten the "can't put that [over-] size tire on your car" while they have no trouble fitting them to my wheels when they arrive in the back of the Pilot DD. They don't put them on the car, they don't assume any responsibility.