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Mr. November 2008
2015 BMW 335d xDrive GT Auto
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969 Posts
Discussion Starter · #1 ·
Not directly Forester-related, but I found it an interesting experiment...

My new Juke Nismo came with Michelin PS3's on it, and I found the ride quite jiggly. (Well, not compared to the FSTi, but you know what I mean). The demo car I'd driven a few days before had ContiSport 5's, and I thought the ride on that one was preferable.

I've now driven both cars (which are identical apart from the tyres) over the same roads. Since it isn't often that there is a chance to do this I also made some measurements using the vibrometer part of the Smart Tools app on my phone.

The data below is from one stretch of fairly rough road driven at the same speed in the two cars:



The one on the right is the demonstrator on ContiSportContact 5 tyres, the one on the left is mine on the PS3's.

Above about magnitude 4 both sides are pretty much the same. However, the amount of low-magnitude vibration is quite a bit lower in the case of the Conti's - the area under the curve for mag 1 to 3 is a lot less. That's the 'roughness' sort of magnitude rather than 'bumps'.

Subjectively the demo car felt much smoother, but it jolted and bumped over the really bumpy bits in exactly the same way as mine. It was the low-level background jiggling that was absent on the demo car.

Now it could be that the demo car suspension has settled in, or it could be that there is some other difference between the cars. However, other things being equal I preferred the ride of the Conti's. The dealership is swapping the tyres over for me.

Both tyres are excellent performers, but I found it interesting that there is that much of a subjective (and measurable) element to the way the tyre damps the roughness of the road.

Using the app in that way may be of use with adjustable suspension too - those of you with coilovers could certainly try graphing the different settings.
 

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2014 XE CVT
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1,362 Posts
How many miles had the demo car done? Dampers will soften with usage, especially if the car is loaded and hard driven over rougher roads, as the internal friction reduces.
 

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Mr. November 2008
2015 BMW 335d xDrive GT Auto
Joined
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969 Posts
Discussion Starter · #3 ·
How many miles had the demo car done? Dampers will soften with usage, especially if the car is loaded and hard driven over rougher roads, as the internal friction reduces.
I'm sure there is an element of that - it has done about 4k miles I think, whereas mine is on 159 :)

Be interesting to see what the Conti's are like on mine...
 

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Registered
2008 GRB 20th anniversary 6 MT
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6,575 Posts
Interesting.
4k miles I think is minimal but it would be interesting to see a graph of the Contis in your car.
What do the units in the axes signify?
 

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Mr. November 2008
2015 BMW 335d xDrive GT Auto
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969 Posts
Discussion Starter · #5 ·
Interesting.
4k miles I think is minimal but it would be interesting to see a graph of the Contis in your car.
What do the units in the axes signify?
Now I've got Conti's on my own car I can confirm that there is a subjective difference - they are definitely more supple than the PS3's. It feels like a more luxurious car, if that makes sense. No perceived difference in grip, road noise may be a tiny bit higher on the motorway.

The axes are intensity as the x-axis (across) where the units are nominally MMI (Modified Mercalli Intensity). That's a measurement of movement intensity that is actually derived from earthquake measurements: Mercalli intensity scale - Wikipedia, the free encyclopedia
Its use here is entirely inappropriate, but it does however give a measurement of shaking amplitude and frequency so it sort of fits.

The y-axis is the percentage of each MMI value out of the whole set, so you can see where certain amplitudes tend to occur more frequently. In spite of its rather non-rigorous usage it does seem to give a result that bears out the 'feel' of the ride.

I'll try comparing the Ford Ka and my wife's Mito tomorrow... and I might attempt the trip down to the dealer to see if I can capture the same data as before.
 

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2015 Fiat van Man stick
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4,808 Posts
I fully back up the "feel" of different tyres. Each set I try has a different feel due to tyre construction. Some are "jiggly" like you say and some flex more and absorb little surface imperfections better. Tyre pressure can make a huge difference though so worth trying different pressure before removing tyres I reckon.

My current zline Nokians feel very crisp in a straight line but there is a slightly vagueness on turn in but this is going now they are nearly worn out. The previous Dunlops felt like a knife edge but had loads of grip.

Winters are going on in the next week or so I'll have another tyre update.
 

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Premium Member
MY05 Legacy Tuned by STI; MY05 Impreza Spec C WR Ltd
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1,014 Posts
Tyre manufacturers massively protect their rubber compounds and their build up of strengthening layers in the tyres, so it's no surprise the ride quality is different between different brands.

They also make them to have different properties by selection of materials and the way they are layered together.
 
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