MGB Tire pressure for 1980 MGB

[jr234]

Hopefully this should be a real easy one...My 1980 MGB has alloy wheels and 205/70/R14 tires. The manual refers to a slightly smaller tire on that rim (185/70/R14). The recommended pressure for the 185 size tire is 21 psi front and 26 psi rear. I inflated to that limit. I received a suggestion that perhaps the car would handle better if I inflated the tires (all four) to the max allowed psi on the tires (35 psi).

Call me paranoid, but it seems inflating to that max is asking for trouble. Any thoughts, or should I leave it at the manual's 21/26 recommended inflation? Appreciate any opinions.

 

[DrEntropy]

Try 28 front, 32 rear as a start.

 

[jr234]

Try 28 front, 32 rear as a start.

I appreciate the feedback. I'll give those tires the extra inflation and see how it drives. Having just gotten the car back into running shape and shifting shape, this will be another revived experience!

Have a happy and safe Thanksgiving holiday!

 

[Bristol401]

You will have better grip at lower pressures. Oversized tires will tend to have less contact patch at the same pressure.

 

[YakkoWarner]

My experiences (and note I am neither tire professional nor a professional driver) are that firmer pressures do seem to handle better. Even in the past 10-15 years tire design has changed a lot - I remember tires having a 30-35PSI max rating written on the sidewall. Almost every tire I've gotten in the past 5 years has had a max rating close to if not slightly over 50PSI. Running those tires at 26-28 is not fun, you can feel the sidewalls compressing down in a turn and it gives a lot of body lean. Using higher pressure gives a more positive feel, steering response becomes crisper and roll and sway decrease.

The other side of the equation is that firmer tires transfer more impact to the suspension in regards to bumps and holes. Higher pressure can reduce the size of the contact patch and mean less overall traction.

Excessively low pressure can also reduce traction because the edges bear more weight than the center of the tread surface.
Running higher pressures can shorten tire life because the center wears more than the edges

End result is that I trust the tire manufacturer with regard to pressure. The people who designed and spec'd the tire pressures on older cars had never seen tires like we have today. Those specs are exactly correct for the tires the car was designed with, but not only are sizes different now but the whole construction of the tires is different. I (possibly incorrectly) trust that whoever designed the tires knows more than I do with regard to how its designed. I usually start with a little under the max rating of the tire and see how it feels both in terms of traction and handling response, and adjust downward if they seem to lose grip too soon. And keep and eye on them as you drive - if you see the center wearing more than the edge you have too much, if the edges are wearing away too soon you have too little. On my truck I usually have the back ones down more than the front unless I'm carrying heavy stuff - otherwise I wear the centers out too soon and truck tires are expensive.

 

[Bristol401]

NEVER set tire pressures to the max stated on the tire. It’s called the max for a reason. Run at the pressure stated in the car’s manual. For better grip in turns.. drop pressure. I ran my Lotus Super 7 at 18 psi, after laps on the track and checking temps across the tread on all 4 tires. Won the ‘98 Sonoma Wine Country Classic with that setup. Trucks and full size sedans will definitely need more pressure than that.

 

[jr234]

You will have better grip at lower pressures. Oversized tires will tend to have less contact patch at the same pressure.

Bristol,
Thank you for the reply. I agree with your observation about the relationship between grip and pressure, as well as the size of the tires. As I mentioned in an earlier post, the MG manual (assuming it was the original with the car) is nearly 45 years old, so the tires I have were not even in the table for tire pressure/size and wheel type.

I went with the suggested increase of PSI, 28 front and 32 rear, and I'll keep an eye and ear out for how the car handles on city streets. I was leery about going max on both front and rear (35 PSI on the sidewall) as it didn't seem to leave much room for error. I've also received feedback that 32 on both front and rear would work, and that may be something to consider if the car handles better with equal PSI.

 

[jr234]

My experiences (and note I am neither tire professional nor a professional driver) are that firmer pressures do seem to handle better. Even in the past 10-15 years tire design has changed a lot - I remember tires having a 30-35PSI max rating written on the sidewall. Almost every tire I've gotten in the past 5 years has had a max rating close to if not slightly over 50PSI. Running those tires at 26-28 is not fun, you can feel the sidewalls compressing down in a turn and it gives a lot of body lean. Using higher pressure gives a more positive feel, steering response becomes crisper and roll and sway decrease.

The other side of the equation is that firmer tires transfer more impact to the suspension in regards to bumps and holes. Higher pressure can reduce the size of the contact patch and mean less overall traction.

Excessively low pressure can also reduce traction because the edges bear more weight than the center of the tread surface.
Running higher pressures can shorten tire life because the center wears more than the edges

End result is that I trust the tire manufacturer with regard to pressure. The people who designed and spec'd the tire pressures on older cars had never seen tires like we have today. Those specs are exactly correct for the tires the car was designed with, but not only are sizes different now but the whole construction of the tires is different. I (possibly incorrectly) trust that whoever designed the tires knows more than I do with regard to how its designed. I usually start with a little under the max rating of the tire and see how it feels both in terms of traction and handling response, and adjust downward if they seem to lose grip too soon. And keep and eye on them as you drive - if you see the center wearing more than the edge you have too much, if the edges are wearing away too soon you have too little. On my truck I usually have the back ones down more than the front unless I'm carrying heavy stuff - otherwise I wear the centers out too soon and truck tires are expensive.

Jedi Warrior,

Appreciate the response to my question on tire PSI. I try to keep all my vehicle tires checked (monthly or thereabouts) to keep them at the manufacturer's recommended setting. Of course, the difference is, my other cars are a MINI Cooper S and a BMW X-3, so the handling is quite different than a 1980 MGB! The MG manual didn't conceive of modern (today's modern) tires, so I was fortunate to have several folks with experience here in the forum and elsewhere give me some ideas of the pros and cons of inflating the tires to meet safe and enjoyable driving.

The MG hadn't been driven in several years, sitting in the garage, with some engine problems (needed to replace the carbs) and then clutch cylinders to permit shifting (without leaking all the brake fluid out of the system). I have taken the MG out on the neighborhood roads (top posted limit is 35 MPH) to see how it runs and ensure the leaks are fixed. Everything appears to be okay (still needs some tweaking, to be honest), but the handling is obviously not what I'm used to in my other cars. I'll attribute that to the unfair advantage my other cars are designed for different driving situations and the MG doesn't have modern steering conveniences. I'll continue to see how the car feels around town and adjust the PSI if it seems to need it.

Thanks again for the info and suggestions.

 

[DrEntropy]

As stated, the 28/32 suggestion is for a start. Observing wear patterns will tell whether the pressures need increasing or decreasing over time, in most driving conditions. If doing something like autocross, the seat-of-the-pants and times will be more revealing.

In the case of Bristol's Seven, it weighs slightly more than nothing, so low pressures are fine. I was usually told the Elan needed to have more than the 18/22 I'd show up with, made me inflate to something that would make the car handle like it was on ice! So "clandestinely" I would lower them back down... lots of F.T.D. times were turned. Optimal pressures are determined by a number of factors. It would seem the O.P. has driving around casually as the plan, hence my 28/32 suggestion as a "base" considering that MG is ±2,500 lb. and the 205/70's are wide enough to show/see wear patterns quickly. Trying different settings based on that wear, for differing driving conditions is the way to go, IMHO.

P.S... the 4-ish lb. front/rear bias on the MGB lends itself to slight oversteer. Much more desirable than scrubbing the nose out from under it!

 

[jr234]

Dr. Entropy,

I don't expect to see any significant wear on the tires in a short term, as I don't anticipate a lot of driving. I certainly don't plan on getting involved in road racing or that sort of thing, just an occasional local drive to the store on a nice day sort of thing. Once I feel comfortable that the work we've put in to getting it road worthy is sufficient, we may take it on an occasional short road trip beyond the neighborhood.

I imagine the Brit Car aficionados might cringe to hear my limited use of the MG, but after the problems I have had with the car, I feel safe is better than sorry, and I can't keep calling AAA for a tow home. Now that the weather here in South Florida is getting a bit less hot and humid, taking it out more is highly likely, and that may give me the confidence to extend the driving range.

 

[mikephillips]

You mean you won't be one of those guys who make the news doing donuts and lots of tire smoke in an intersection, with 20 other guys hanging off the car?? Well, I for one am disappointed......

 

[jr234]

Hi, Mike,

I would gladly perform the feats of deering-do in the MG, however, here in SoFla, there is a long waiting list on most nights at the intersections for a variety of attempts to overcome the laws of physics (two objects occupying the same space simultaneously).

Back when I was "taller" (i.e., a lot younger), I had my share of unintended moments of sheer terror, both involving driving home from college. I was allowed to borrow my dad's 1966 Chrysler, winter time. As I approached a curve leading into a bridge, I hit "black ice" and did several 360's across the bridge. No oncoming traffic and by the grace of God, never touched either side of the bridge. The other incident involved me driving home in the spring from the same college (Wichita State) in my '65 Corvair. It was the same country road, no traffic, and a long downhill stretch. I decided to see what the Corvair could do, especially with the help of gravity in my favor. As the speedometer headed into the 90 mph range, I became confused, as the horizon started to drop below the front of the hood. It took a few milliseconds, but I realized the front end was rising off the ground. Again, that higher authority was co-pilot, and I was able to slooooowly lighten the foot on the gas pedal and the wheels were straight aligned. Never did that again.

I've had other "moments", involving piloting an assault helicopter on missions over Laos, but that's another story.

 

[Basil]

Since this topic is a specific question related to the MGB, I have moved it to the MG forum. I'll leave a "redirect" in the Pub for a couple weeks. If you're reading this now, you are in the MG forum.

 

[jr234]

As stated, the 28/32 suggestion is for a start. Observing wear patterns will tell whether the pressures need increasing or decreasing over time, in most driving conditions. If doing something like autocross, the seat-of-the-pants and times will be more revealing.

In the case of Bristol's Seven, it weighs slightly more than nothing, so low pressures are fine. I was usually told the Elan needed to have more than the 18/22 I'd show up with, made me inflate to something that would make the car handle like it was on ice! So "clandestinely" I would lower them back down... lots of F.T.D. times were turned. Optimal pressures are determined by a number of factors. It would seem the O.P. has driving around casually as the plan, hence my 28/32 suggestion as a "base" considering that MG is ±2,500 lb. and the 205/70's are wide enough to show/see wear patterns quickly. Trying different settings based on that wear, for differing driving conditions is the way to go, IMHO.

P.S... the 4-ish lb. front/rear bias on the MGB lends itself to slight oversteer. Much more desirable than scrubbing the nose out from under it!

DrEntropy,

Update on the tire pressure issue...a couple of weeks ago I took the MG out to fill the gas tank, got about a block from the house and the rear passenger tire blew, totally shredded. It wasn't the tire pressure setting (IMHO), it was the years of the tires on the car, in the garage. The tread on the tires were quite ample, but as we know (and I ignored) environmental forces deteriorated the rubber. Instead of getting fuel, I had to order replacement tires, ordered 5 as I assumed the tire in the trunk was also of similar material deterioration. The tire techs at Costco set the pressure at 32 all around, but I'll keep an eye on the wear patterns if adjustment is indicated.

Haven't put much mileage on these new tires, but everything seems to be working satisfactorily as far as the relative comfort of the ride and handling. Thanks to everyone who voiced experience advice.

 

[DrEntropy]

Haven't put much mileage on these new tires, but everything seems to be working satisfactorily as far as the relative comfort of the ride and handling.

A couple things... The Port St Lucie Fair kicks off this week and on Wednesday the "Texas Trick Riders" will be there. Good trip a bit north in an MGB!!!

...and we may need to gossip about things S.E.A.