[Spridgets] Air Pressure & Lug Nut Torque

Bob Kitterer bkitterer at me.com
Tue Aug 28 11:40:26 MDT 2018


Here are some old guy comments for consideration.

Per the 1960 BMC Service Manual for the Sprite the tire pressures are 18 psi front; 20 psi rear, Road wheel nuts torque 37-39 lb-ft.

Per the 1967 BMC Service Manual for :
Sprite Mk II/Midget Mk I - no change in tire pressure but torque for road wheel nut is listed at 60-63.5 lb-ft.  (???)
For Sprite Mk III /Midget Mk II the tire pressure changes to 22 psi front and 24 psi rear - no change in road wheel nut torque.
For Sprite Mk IV / Midget Mk III with 5.20-13 tubeless tires the pressures are 18 psi front, 20 psi rear, for 145-13 SP 41 tubed tires the pressures are 22 psi front and 24 psi rear and the same pressures for “sustained speeds excess of 80 mph”

Could there be misprints - Yes.  

HOWEVER, all that said these pressures are for cross bias tires and do not apply to radial tires or belted tires.  As I recall radials require a slightly higher pressure because of the thin side walls, on my 155-13 radials I run 24 psi front and 26 psi rear for street use but that is just my thing.  Some while back Michelin had a web page that showed pressures per tire per axle weight but that has disappeared, probably because of the lawyers.  I have encountered “tire experts” ( they worked in a tire store) who said that you should use the tire pressure list on the tire which is incorrect, that is the maximum pressure for the tire and generally at a given vehicle weight.

One last comment from someone who lives in the desert, when the heat goes up you do not want to lower your tire pressure.    Lowering the pressure causes more sidewall flex which generates more heat which added to the already high temperature results in tire failure. That is the biggest cause of tire failure in this area.

Just my 2 cents, will go back to sleep now.


Bob  Kitterer

1960 Austin Healey Sprite (Mk IV in disguise)
1966 Austin Healey Sprite Mk III (Trevor) - still in boxes
2013 Miata
2017 Mazda CX9

Pay it forward.
Thanks Frank

> On Aug 28, 2018, at 5:39 AM, Rick Fisk via Spridgets <spridgets at autox.team.net> wrote:
> 
> Allen,
> 
> Not wanting to start anything here, but your tire pressure recommendations don't make sense to me.  I've never seen the recommended tire pressure is at 32 degrees F spec in a manual anywhere.  ???  Seems to me the tire pressure should be the same no matter what the temperature is.
> 
> For every 10 degree F rise in air temperature the pressure in your tires will rise about 1 psi and fall 1 psi for every 10 degree drop in temperature.  So to maintain the car manufacturer's recommended tire pressure you should reduce the pressure when the temp goes up and raise it when the temp drops.
> 
> Why would you always add 5 psi to the recommended pressure?  Seems to me the car manufacturer probably knows best when it comes to recommended tire pressures for their cars.  
> 
> Rick
> 
> Sent from my keyboard
> 
> On Aug 27, 2018, at 10:39 AM, Allen Hefner via Spridgets <spridgets at autox.team.net <mailto:spridgets at autox.team.net>> wrote:
> 
>> Don't forget that the recommended tire pressure in the manuals is at 32 degrees. You usually add 1 PSI for every 10 degrees above freezing. Nobody seems to know that anymore. The manuals just say ## PSI cold. I always just add 5 PSI to the recommended pressure. 
>> 
>> Allen Hefner
>> Norristown, PA
>>  
>> Current:
>> 2016 Subaru outback somewhere
>> 2006 Chebbie
>> Former:
>> 1963 Sunbeam Alpine Series III
>> 1967 Triumph TR4A IRS
>> 1964 VW Type I
>> 1967 VW Type II
>> 1967 Rover 2000TC
>> 1977 MG Midget (Sniff!)
>> 
>> 
>> On Tue, Aug 21, 2018 at 1:40 PM John Farley via Spridgets <spridgets at autox.team.net <mailto:spridgets at autox.team.net>> wrote:
>> I am running 175/70 R13s on my 1275+ Bugeye with front disc brakes.  What are folk’s recommendations for tire air pressures & lug nut torque?
>> The manual  seems low for both. 
>> Thanks,  John F.
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