This is an on-going debate at my local Cars & Coffee meet. A fairly rigorous Google search turns up nothing. Regarding wear indicator ridges, on my Yokos those little triangle symbols are spaced 10" evenly around the tire, the wear indicators are spaced 3" apart. In other words, they don't line up, on my tires at least.


I too found the chalk mark method doesn't offer any useful information other then a relative left side/right side comparison. That's why I was so excited about the so-called scuff indicators. I'd sure like to see a reference somewhere.

Sorry Michael, those marks are not “scuff indicators”. The mark the position on the tread where the wear indicator ridges are...

The instructors may choose to label them so but its a personal opinion. As mentioned, some use a chalk test to see how far the the tyre is rolling over but I’ve not been able to find any useful advice as to how far up the sidewall the tyre should be allowed to roll.

Minis use the tyre deflection as part of the suspension travel and a lot (IMHO) depends on the roughness of the road/track. Tracks are usually smooth so I use a few extra psi to reduce tyre squirm during the transition part of turns. On lumpy territory I find those extra pounds can throw the car around removing any benefit the stiffer sidewall may offer.

I don’t think there’s a sensible answer to the question of optimal tyre pressure. The responses to such a question is “Where?” And “For why?”.

That’s why (most?) timed events allow you a few practice runs .. to try a few options (shock settings (if you have some) and tyre pressures to find out what’s working on the day.

FWIW I run the road tyres (165 A008s) on my Traveller at 30/26 cold.

Cheers, Ian

I enrolled in a 3-day high performance driving class a few years ago. We drove our own cars and the class was about 60% track time and 40% classroom time. The instructors pointed out the "scuff indictors" that some of our tires had. The instructors said that "basically, tire pressure should be lowered until the scuff indictors come into play." The students without scuff indictors chalked their tires and required a little more trial and error before an optimum pressure was found.

Of course, optimum tire pressure has everything to do with the kind of driving you're planning on doing. The track we were driving on was highly technical, with lots of low speed (<35 mph) sharp turns. The pic is a shot of my Yoko A032s after being driven around town for a bit. I'd say my current pressure is about right for going to the grocery store and picking up my grandkids from school. On the other hand, if I were going for a spirited drive though Malibu Canyon, I suspect I'd have to add 2 to 3 psi in order to keep the scuff indictors happy.

Best way to figure it out is with a chalk test. Mine is a pickup with SPI and automatic transmission, so much heavier on the front wheels than the back. I got the best chalk transfer (for best grip) with 31 psi front and 15 psi in the rear. With 20 psi or more on the rear I could push it sideways across my garage floor for lack of traction. I originally started with 28 up front, but increasing gave me a better imprint of the center tread.

Quite the revival. Almost 10 years to the day it was created. 
But I'm interested none the less. Haven't gotten my Vtec-convert finished yet, but this type of chat and knowledge would be good to know, as I am running A032-10's.

Reviving this thread just to confirm my thought process...is the general consensus to run the rears 1-2 pounds lower than the fronts because most of the weight is upfront and if they were equal all around, rear traction would suffer?

I run 12" Falkens and usually go with 30/28.

30 front 28 rear for me.

28psi all the way around.

When used on LWB Minis being driven hard.

It certainly slams the door on 145 series Michelins.

Kelley

Now that's what I call "slamming the door" on that!

dan

Now you and I know the rest of the story....

I have just picked up this blog and thought I had better reply as I did write THE Mini Book.

The tyre pressure recommendations on page 75 were not just the manufacturer's but from the experience David Marshall and I had from running eight or nine Mini varients on the road and track over 20 years plus.

The recommendation for running front tyre pressures two pounds lower than rear when using Michelin X or XAS was from Michelin but was confirmed by my own experience on the road. I ran a Mini Traveller for over 100,000 miles on the road with ever increasing engine size and power output. In the final version before sale it had a 1310cc Cooper S block, mild competition camshaft, single one and three-quarter inch SU carburetter. Our own make of competition exhaust with absorbtion silencer. Close ratio, straight cut gearbox, Cooper S brakes front and rear and XAS tyres on 4.5 inch Cooper S wheels.I always used the lower pressures at the front.

As it tended (in my youth) to get driven rather hard, the tyre pressures were usually about two pounds higher than spec for a comfort ride but the handling was superb. 

You should note that most of the high speed experience I had was with the Traveller version, which having a slightly longer wheelbase, was more stable on the road.

So good was the handling of the Traveller that our racing team stopped using the standard Mini bodyshell and built a Traveller version which we race in the BRDC Special Saloon Championship over many years, winning our class in at least five years of competition before changing the body to a Reliant Kitten Traveller shape for aerodynamic drag reasons.

I did actually try those pressures way back then, and I wasn't impressed. Understeer anyone? It had it in spades.

This is what the Marshall/Fraser printed text says on page 75:

"The tyre pressures recommended by the the manufacturers are as follows:

Dunlop C 41 or equivalent braced tyre. Front 24 psi. Rear 22 psi.

Dunlop SP 41 or eqivalent nylon braced tyre. Front 28 psi. Rear 26 psi.

Michelin X wire braced tyre. Front 22 psi. Rear 24 psi.

Note that, in the case of the Michelin wire-braced tyres, the pressure differential, front to rear is reversed.  Also remember that, with these tyres, the front track is adjusted so that the wheels run parallel instead of toeing out."

Clearly, they believed what they wrote as the specific notation addresses the anomally.

 

I reckon that Marshall & Fraser book quote is a typo.

Oz Cooper S BMC handbook stated 28psi front, 26 rear, for 145-10 radials. I ran 145 Michelin XAs back then and it was fine at that, I have never seen a factory recommendation for 165/70-10s, they didn't exist back then.
I run my A008s 30F 28R so I don't need to check pressures as often.

I don't believe it...  more likely a typo.  Was the comment "(YES, the tyre pressure differential was reversed, lower at front than rear).." part of the original text??

I've run Cooper Ss in period with both X and XAS tyres.  We used the same pressures as for SP3s/41s etc....definitely with more pressure up front.  From memory, Xs cost UKP5 ea.  You only bought a new X if you ran over a curb or somesuch; they NEVER wore out.  XASs on the other hand were the AO32s of their day.

If you were really chasing tail happy, we used to motorkhana (AutoX on dirt) using good 165s up front and bald 145 crossplies at 50psi.....

Cheers, Ian

It's what Marshall and Fraser wrote...44 years ago.

I've driven with steel belted radials at 26 front/28 rear, zero toe at rear/standard toe out at front...not tail happy.

Biggest tail happy issues I've seen arise with installing front disc versus twin leading shoe brakes and failure to drop size of rear wheel cylinder bore to 5/8".

Would be good to have today's "tire/suspension experts" chime in!

Steel-braced radial ply tyres, e.g. Michelin X and XAS, Dunlop SP44

Front 22 psi, Rear 24 psi and ZERO TOE at front (YES, the tyre pressure differential was reversed, lower at front than rear)"
Rick,
Whoever wrote that must really like tail happy cars.  Just for grins, add toe out at the rear......

Historical note:  SOURCE BMC MINIS (revised), Marshall, David and Fraser, Ian, Foulis, London/Edinburgh (1965) 1968

Early cross ply tyres, e.g. Dunlop C41 (were standard on Minis), Goodyear G8, Firestone F7, Pirelli Sempione

      Front 24 psi, Rear 22 psi

Braced tread tyres (all textile-braced radials), e.g. Dunlop SP41 or SP Sport, Goodyear G800, Pirelli Cinturato

      Front 28 psi, Rear 26 psi

"Tyre life and car handling may be slightly improved, at the cost of a slightly rougher ride, by running the tyres 2-3 psi above the normal recommended pressure." page 74

Steel-braced radial ply tyres, e.g. Michelin X and XAS, Dunlop SP44

      Front 22 psi, Rear 24 psi and ZERO TOE at front (YES, the tyre pressure differential was reversed, lower at front than rear)