Advice needed from racing drivers - RF wheel lockup when braking into a turn

[LeRoux Strydom]

To all you racing drivers out there, I need some advice/comments on a recent driving experience:

I was driving my SC down a slight incline slowing down to take a right turn. I stayed on the brakes into the turn, doing perhaps 60kmh (about 40mph ?) when the right front wheel locked up briefly and unexpectedly. Road surface was dry smooth tarmac, no oil/leaves/gravel etc. I was able to modulate the braking and went through the turn without drama, but now I am wondering:

- Which wheel should lock up first when braking into a turn, inside, outside or both?

- Can the corner balance affect this situation (no pros to check this where I live, maybe I should try one of the home methods - Superman's wet tyre patch method come to mind)

- I suppose the car should understeer in this situation, which is exactly what it was doing.

- Is something wrong with my brakes? No preferential lockup in normal straightline braking observed, but then I have never tested this (don't want to flatspot my tyres).

More info if required: alignment is within factory specs, i can dig out my last printout from the alignment shop if anyone wants to see actual numbers. Tyres are about 7000km (4500 miles) old, Yokohama A539's, stock sizes on 6&7x16 Fuchs.

Any advise is highly appreciated.

Regards

LeRoux

[89911]

Your inside tire will lock up on turns since it is getting less force due to weight transfer. Reviewing my track driving (It's been a loooong winter!) you need to have all your braking done in a straight line prior to commiting to a turn unless your flirting with trailbraking, (another lengthy subject). I would say this is not unusual at all. Cornerbalance has something to do with this if your at an radically uneven distribution. Take your car to a secluded place and do a few runs with full on braking. Don't worry about flat spotting unless you are going extremely fast with the brakes on lock out the whole way. As soon as you hear any squeal, gradually let off. It helps to have an observer look for sign of smoke on the locking wheel, sometimes it is hard to tell in the car.

[Don Wohlfarth]

Try not to brake when going into a turn unless you are trying to get car to rotate (trail braking).
You may have tossed the car into the turn with abrupt steering input or it may have been normal turn and the RF became umweighted. Since this seems to be a one time occurance don't worry about it.
With right turn, in order of wheel lockup, RF, then both. If you can lock only the LF in a right turn you may have some serious problems.

[jluetjen]

The geography of the road could also contribute if the road was cambered to the right or had a crown in the center. Both of those situations could cause the RF wheel to become unweighed during a right hand turn. If the car didn't loose it's balance, I wouldn't worry about it. It's only a problem if it caused the car to become unsettled or if it was happening so consistantly that it was damaging the tire.

[carnut169]

I would suggest that you read Skip Barber's "Going Faster". The book does a great job of describing the basics.
What everyone above is saying is correct... your tiers are capabile of doing 100% of what they can do.... if you are using 70% of the tires ability to corner, only 30% is left for braking & the tire will lock-up easier. With the tail happy 911 get your braking done prior to the turn and get back on the throttle at the apex of the turn.

[Superman]

This place gives good advice. I would say that braking analysis is probably superior to the hokey 'wet patch' method for determining if both front wheels weigh the same. In a straight line, the tire that breaks loose first will be the lightest one. The adjustment is very very simple. A couple of twists of an 11mm wrench I think. An unless you stand on the brakes unreasonably, you will not hurt your tires. Also, the car will pull to one side if one front tire breaks loose first. It will pull to the side that is weighted heavier. In other words, if a tire breaks loose and the car pull to the left, the right front tire is too light. If you go to a secluded lot with an 11mm wrench, I believe you can return with a fairly corner-balanced car.

[Vintage911Racer]

The Inside wheel will lock up first. The weight transfer going into the corner takes weight of the inside wheel thus causing it to lock up if you are still on the brakes while making your turn. Best bet, get braking done in a straight line.