Tyre wear, Petrol vs Diesel

[Bill_56]

I am my 2nd S60 SE, the first was a 2.4D, the current is a 2.0T petrol. Two identical cars, apart from the engines.

One very obvious difference is becoming apparent, which is the wear-rate of the front tyres.

The diesel always ate through the front treads in about 12k miles. The petrol car had knackered tyres when I bought it, so I immediately replaced them with the same Michelins that I always used on the diesel. But curiously, the front tyres have now done 7k miles, and still have nearly 7mm tread remaining, they're looking good for about double the mileage that the diesel obtained.

Has anybody else noticed this disparity between tyre wear on petrol/diesel cars? Or any explanation for it? It's of significant proportion to make quite a hole in the economics of the diesel/petrol comparison.

Tyre wear on the diesel was always perfectly even and symmetrical (and on the petrol too), so I'm not inclined to think there was any underlying fault that could explain the difference. The petrol car has much sharper acceleration too, so I'd expect tyres to wear faster, not slower.

[yoda960]

Fairly simple really - diesels have a lot of torque compared to petrol motors :thumbs_up:

[Bill_56]

Fairly simple really - diesels have a lot of torque compared to petrol motors :thumbs_up:

Thanks, but I'm not sure it's that simple.

It's true that diesels produce more torque at the crankshaft, but the gearbox ratios are completely different from a petrol car, and hence the torque at the driveshafts is usually pretty much the same.

If the torque at the driveshafts were greater then the car would accelerate faster but, in the case of the 2.4D (vs petrol 2.0) that didn't happen.

One fairly far-fetched idea that's occurred to me is that the diesel's higher compression and slower RPM may lead to a 'jerkier' torque, with more prominent torque pulses superimposed on the steady torque. These pulses should be smoothed out by the flywheel, but is it possible that a small element of that 'jerkier' force might make it all the way to the tyres, thereby causing more rapid wear?

[Bernard333]

I agree front tyre wear on a P2 V70 seems to me to be more rapid on a D5 than a T5 even though they have the same maximum torque of about 330Nm . The D5 max torque comes in I think at something less than 2000rpm and rapidly drops off but the T5 gradually increases until about 5000 rpm . For most driving I find the D5 easier and much less gear changing than a T5 even though the petrol car has 87bhp more maximum power and is much quicker when floored . Matching the acceleration per rpm on a T5 and D5 I think the D5 would seem a more powerful car up to about 3000rpm but after that the situation reverses . I think this is the reason for the increased tyre wear as I think most people would be in the maximum torque band for a diesel most of the time for normal driving whereas with a petrol it would only happen occasionally and especially when accelerating through corners or bends the tyres on the diesel take more punishment .

[scr8pdo]

One word..weight.

[baggy798]

Diesel engine is heavier so more weight over the front? Higher compression so the tyres are under more 'stress' on the overrun?

Just throwing this out there.

[scr8pdo]

Its true, if you run a rubber over a hard surface or even sandpaper lightly it wont erode as much as if you applied heavier pressure to it, the same priciple as heavier weight over the front tyres in a car, there will always be some friction even if the wheels dont spin/lose traction, you have steering, cornering etc, more weight = more wear

[Bill_56]

Its true, if you run a rubber over a hard surface or even sandpaper lightly it wont erode as much as if you applied heavier pressure to it, the same priciple as heavier weight over the front tyres in a car, there will always be some friction even if the wheels dont spin/lose traction, you have steering, cornering etc, more weight = more wear

But is the D5 that much heavier than the T5?

Traditionally, diesel engines were great heavy lumps of cast iron I know. But I'm pretty sure the Volvo D5 has aluminium alloy block & head, much like the petrol engines.

[t5_monkey]

I think the weight is probably the main cause of additional wear here.

[RobbieH]

But is the D5 that much heavier than the T5?

Traditionally, diesel engines were great heavy lumps of cast iron I know. But I'm pretty sure the Volvo D5 has aluminium alloy block & head, much like the petrol engines.

D5 heavier than T5 - Nope.

And yes, the D5 is an all aluminium engine. Quite light in the general scheme of things, not the "lump" they used to be :thumbs_up:


Taken from official Volvo specs for 2005 model: http://www.volvoclub.org.uk/current/VolvoV70MY05PricesTechSpecs.pdf

Min. kerb weight (kg)
(actual kerb weight dependent on spec.)

2.0T 1565
2.4 (140 bhp) 1528
2.4 (170 bhp) 1525
2.5T 1569
2.5T AWD 1657
D5 1611
D5 AWD 1710
T5 1600

My D5 is probably used for 60% motorway / 40% twisty stuff. I got 20k out of the last set of GY F1's on the front (to about 2mm tread left, now on my track wheels). Currently running Neuton NT5000 (225/45/17) and after about 8k the fronts still have 6-7mm of tread left. Treadware rating of 320 iirc - HARD rubber!

[Palmer]

My old boss had a 3L V6 diesel vectra chipped to 250bhp i think.

Any corner if you stomp on the throttle it would just drive in a straight line... that could be why if u have a heavy foot lmao :P

[scr8pdo]

D5 heavier than T5 - Nope.

And yes, the D5 is an all aluminium engine. Quite light in the general scheme of things, not the "lump" they used to be :thumbs_up:


Taken from official Volvo specs for 2005 model: http://www.volvoclub.org.uk/current/VolvoV70MY05PricesTechSpecs.pdf

Min. kerb weight (kg)
(actual kerb weight dependent on spec.)

2.0T 1565
2.4 (140 bhp) 1528
2.4 (170 bhp) 1525
2.5T 1569
2.5T AWD 1657
D5 1611
D5 AWD 1710
T5 1600

My D5 is probably used for 60% motorway / 40% twisty stuff. I got 20k out of the last set of GY F1's on the front (to about 2mm tread left, now on my track wheels). Currently running Neuton NT5000 (225/45/17) and after about 8k the fronts still have 6-7mm of tread left. Treadware rating of 320 iirc - HARD rubber!


But the 2.0T is lighter than the D5, thats what the OP was comparing

[scr8pdo]

As for T5 vs D5 I can only concur what was said that at lower revs the diesel has more torque, this is where normal driving would take place but I bet if you use a T5 to its full potential the tyres would wear much quicker on the T5

[Bill_56]

But the 2.0T is lighter than the D5, thats what the OP was comparing

Fair point and correct. But is it enough to explain 2 x tyre life?

I remain completely unconvinced that the higher engine torque is the reason either, arguing as explained earlier, that the higher torque of the diesel engine is diluted by the higher ratio gearbox. Thus torque at the driveshafts would be much the same, and hence much the same frictional forces of tyre against road surface.

The best way to view torque at the driveshafts, is purely a function of engine's bhp and the wheels rotational speed, as defined gearbox ratios. The engine's torque, since it is modified by the gearbox before reaching the wheels, really bears no relation to the torque at the driveshafts (and thus force on the tyres), whereas the bhp at the flywheel will (allowing for minor inefficiencies) be similar to the bhp at the road wheels.

I'm beginning to favour my earlier theory, that the motive forces of the diesel may be less clean owing to the flywheel being less successful in smoothing out the delivery. As an extreme example, if the tyre is being given a series of kicks, rather than a nice smooth push, it could accelerate wear. But try as I might, I've failed to find any evidence to support the theory.

[scr8pdo]

I know that weight does make a big difference, over the years working in various garages and fast fit places you see it, heavier cars wear tyres far more quicker, you used to see it more when older cars didnt have power steering, PAS kills tyres, but big heavy cars with FWD and PAS eat tyres for fun, there is a lot of strain put onto tyres in this situation, its not just rolling around in a straight line as compared to the back, as for the difference with a T5 and a D5 I cant say, I know my 850 T5 ate tyres compared to other cars

[owyn]

I think the torque thing is important.

If I come to a slip road in my T5 with a modern diesel (lets say something like a 2.0 TDI type thing) they would leave me in a 3rd gear drag race until we got up to 50ish mph. If I kept it floored I would then fly past them but how often do you do that? In order to go faster than them, ie give the wheels more torque I would need to be in 2nd.

What I'm getting at is a petrol car can give the wheels more torque, therefore power and therefore tyre shreddingness but in the real world its pretty rare you ever do that. Where as a diesel car is more likely to be in a position to give you maximum torque without driving like you stole it!

[Bill_56]

I think the torque thing is important.
What I'm getting at is a petrol car can give the wheels more torque, therefore power and therefore tyre shreddingness but in the real world its pretty rare you ever do that. Where as a diesel car is more likely to be in a position to give you maximum torque without driving like you stole it!

You might well have a point, though I'd insist that we look at it in terms of engine power rather than engine torque, since the power is what dictates the the ultimate force of the rubber against the road surface, and hence the tyre wear rates.

We'd need to compare both cars, when driven in a 'comfortable' gear at the same speeds, then calculate the corresponding rpm of the engines and see what power output each engine is producing at their respective rpm's, should the driver floor the throttle. The engine that produces the most power is the one that should in theory generate the most torque at the driveshafts, and hence inflict most tyre wear.

The power of the engine is the product of torque and rotational speed, so it is possible that the power output of the diesel, by virtue of increased low rpm torque, may exceed the power output of the petrol from its increased rpm, when each is under the same notional constraint of a 'comfortable' gear. I will need to find some time (and some reference data) to satisfy myself whether or not that is the case.

In any event, it's been satisfying to find that there seems to be some broad agreement, that diesels eat tyres faster than petrols. Thanks for all responses.

- Bill

[jackd]

I'm beginning to favour my earlier theory, that the motive forces of the diesel may be less clean owing to the flywheel being less successful in smoothing out the delivery. As an extreme example, if the tyre is being given a series of kicks, rather than a nice smooth push, it could accelerate wear. But try as I might, I've failed to find any evidence to support the theory.


I would tend to agree with you on this one. Have you ever noticed the visible jerkiness in the power delivery of a rough old diesel when starting from a standstill if observed from outside? It is especially apparent in manuals when the clutch is not fully engaged. You can actually see the wheel juddering as starts to transmit the force to the road. On a modern smoother diesel it may not be as clear - but just because you can't see it doesn't mean it isn't happening!

On the whole I would suspect it is a combination of the extra weight, less consistent and smooth power delivery (as you hypothesised) and the likelihood of the driver being in a position where maximum accelerating force can be applied to the wheels (be it torque or power). I know when I had my last car, a 2.2 diesel Mondeo, I always used more of the engines power purely because it was so readily available in everyday driving circumstances.

Jack.