More or less tyre grip/traction

Norman_Castle

If the problem is when accelerating or braking different grip may be relevant but not at a constant speed.

Iceweasel

schrodie wrote: »

Just checked and there's plenty of even tread across all the tyres.

However the runout line on the new tyre (front driver's side) is 3" in from the outside of the tyre whereas the runout line on the front passengers side tyre is 1" in from the outside of the tyre.

So I'm not sure if this difference would cause the car to drift to the left.

Can you make a perfectly matched pair (run-out line wise) out of the four of them.

If so - put them on the front.

Any tendency of a tyre to veer right or left should have little or no effect on the steering if its fitted to the rear axle.

colino

Why did you need the tyre change? Was it kerbed or potholed and hence you would need the front suspension checked/aligned anyway?

schrodie

GolfBravo wrote: »

In other words, the lines indicate that the front left tyre has a strong tendency to veer left, while the front right tyre has a slight tendency to veer right. So on balance the front of the car veers to the left.

Which is the situation that now exists post fitting of the new tyre!

I have to admit I was very skeptical when the guy at the tyre place suggested the reason for this drift could be due to the new tyre having more or less grip than the other 3!


Also in these tyre places would it be the norm to compare where the runout line was on the tyre opposite the runout line on the new tyre and if there was any discrepancy make the necessary adjustments in the tracking? Or would they normally just leave it and hope that the runout line discrepancy (if there was any) didn't cause too many problems like the car drifting in a particular direction?

GolfBravo wrote: »

The runout lines only indicate the tyre's tendency to steer laterally regardless of any steering wheel movement.

The tyre manufacturer measures the degree of runout at the end of the production line and marks the severity onto the tyre by the position of runout line.

You could have two identical tyres, made on the same production line and on the same day, yet their pull characteristics could be totally different. It all depends on how the belts inside the tyre are positioned (manufacturing imperfections/variance).

Can I just ask what a 'runout line' means in this context, in particular what the word 'runout' means?

schrodie

colino wrote: »

Why did you need the tyre change? Was it kerbed or potholed and hence you would need the front suspension checked/aligned anyway?

It was a slow puncture. 2 screws in the tyre apparently.

GolfBravo

schrodie wrote: »

Can I just ask what a 'runout line' means in this context, in particular what the word 'runout' means?

Tyre runout is a measure of how straight the tyre would run if allowed to roll on a perfectly smooth and even surface, and on a slight decline. Some tyres would run straight, while most would veer to the left or right by varying degrees.

The runout line (usually red or orange) simply indicates the direction and severity of the runout. In a perfect world all tyres would have the runout line right in the middle. However, this is not always possible, so you need to match ("partner") tyres on each axle with the opposite runout characteristics to avoid/minimise any steering pull.

Unfortunately not many tyre places even know what the red line is, or even what the yellow and red dots on the side wall indicate.

PS
Car manufacturers pay particular attention when fitting wheels and tyres to cars on a production line, and tyre suppliers sometimes even match them into pairs for them.

schrodie

Thanks very much GB. I may be able to teach the guy at the tyre place something new when I take it back to get the tracking done to sort this problem out

GolfBravo

schrodie wrote: »

Thanks very much GB. I may be able to teach the guy at the tyre place something new when I take it back to get the tracking done to sort this problem out

If the tyre shop can't even sort out the tyre runouts I wouldn't trust them to do the tracking right either - they would probably make it worse (since your car is only 5 months old).

As Iceweasel says above, see if you can swap rear tyres around to make a matched front pair. The chances are that since the rear tyres are original (presumably) they are already matched by the car manufacturer.

fred7777

JS477 wrote: »

However doesn't the amount of grip or traction a tyre has depend on the frictional force that the tyre exerts between itself (the tyre) and the road surface.

Yes

JS477 wrote: »

The magnitude of the frictional force depends only on coefficient of kinetic friction (~1.0 for rubber and asphalt & ~0.15 for rubber on ice) and the weight of the car. So if a tyre has more or less grip/traction then it would mean that the coefficient of kinetic friction for that particular tyre is different from the other tyres.

Yes

The thing is that different coefficient of friction mean tyres will loose grip at different points. In effect they set a maximum limit of grip so one tyre might spin or lock when others are turning normally. But when all the tyres are turning normally and the car is driving down the road all the tyres will be within their different limits of grip and don't cause a problem.

Richard53

fred7777 wrote: »

But when all the tyres are turning normally and the car is driving down the road all the tyres will be within their different limits of grip and don't cause a problem.

True. My first thought on reading this thread was that grip would be irrelevant, but that different rolling resistance from a different tyre brand or construction would cause a tendency to pull one way or the other. But I had never heard of this 'runout line' thing before, and that makes perfect sense to me. Every day's a schoolday.