MGA Forum

I have recently aquired a 1959 MGA 1500.
Steel wheels, with 165/80/15 tyres.

What would a correct wheel nut torque be?
What is correct tyrepressure for normal street cruising?

Bjorn-Anders
Norway

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'59 MGA 1500 roadster
'77 MGB GT Jubilee #163
'77 MGB Roadster

All MGA owners will want to frequent this forum and bookmark the MGA Guru's Tech Pages: https://www.mgaguru.com/mgtech/index.htm

See: https://www.mgaguru.com/mgtech/tires/tire1.htm & https://www.mgaguru.com/mgtech/tires/ti102.htm

For normal road driving I like to use ~ 2 - 3 psi higher in the rear vs the front. For track/autocross the pressures can be more equal. Slightly higher rear pressures maintain a slight understeer effect - generally safer than an oversteering car.

I don't know if lug nut torque was ever specified. MGAs have 7/16" x 20 UNF threads. Torque charts for this size nut lists 41 - 58 lbs/ft. I'd try something in between - say 50 lbs/ft (67 NM)

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Eric Russell ~ Mebane, NC
1961 MGA #61, 1981 Alfa Romeo GTV6, 1984 Alfa Romeo Spider, 1991 Honda ST1100

I torque my wheels to 60 ft lbs.

Assuming radial tires, I would run 30 to 32 psi cold - 34-36 psi hot.

If you find car pulling on hard braking, check to make sure your front tire pressures are equal. Doesn't take much.

Interesting. If the car was pulling to the right, say, would you expect to find the r/h to be higher or lower than the l/h?

I would expect the reduced diameter tire to be dragging pulling you to that side

Workshop manual gives road wheel nuts as 60- 62.5 lb. ft.
Tyre pressures are listed for crossplies, for radials 25 psi is a good starting point, depends on usage and comfort. I wouldn't go less than 19 or mode than 32. Unlike modern low profile tyres the tyres do a lot of suspension damping. They are also better at resisting pothole damage another plus for MGAs

Regarding the car pulling to one side if tire pressures are unequal, I think it has more to do with grip. The tire with the lower pressure will have a slightly larger tire patch, resulting in that tire having greater tire to pavement grip under braking.

Of course, that’s just my theory! Untested by any method other than driving too fast coming into a corner!

So far just theory on this suggestion.

Problem with that idea of low pressure = more grip is sidewall deflection causing reduced contact patch and loss of adhesion in cornering. Straight line braking yes the tyre with lower pressure will grab on a dry surface but less in the wet.
The other factor is tyre temperature. Anyone who has done any track work will monitor their temperature and pressure to maintain an even contact patch often varying by 10 psi. An underinflated tyre will generate more heat and increase tyre wear, overinflation can cause poor handling and loss of grip. For normal use there is a lot of tolerance but fast driving requires tyres to be spot on. For the track a digital pyrometer is very useful.

Thanks all

I ended with 26 at front, 28 at rear - and 70Nm torque to the wheel nuts.
Feels good.

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'59 MGA 1500 roadster
'77 MGB GT Jubilee #163
'77 MGB Roadster

A tire with less air has more rolling resistance.
Easy to prove. Push the car. Let air out of tires and push again.
Harder to steer if pressure low. Easier to steer when parking with high pressure.
The increase in rolling resistance is caused by increased internal friction from lower pressure. The internal tire plies flex more and generates heat through friction. This phenomenon is why the Ford Exploder tires exploded. Ford chose to lower the pressure on a heavier vehicle to change the handling characteristics. The truck and the SUV shared the same tire but Ford recommended higher pressures in the lighter vehicle. Failure was not an issue on the truck. Typical failure was long trip on a hot day low on air. Tire overheated and failed. Firestone built a tire to Fords specification. Ford misapplied the tire and blamed Firestone.
The energy is converted to heat through friction. The energy used to push the tire forward is turned into heat. That energy is then not available towards forward motion.