You have touched on a very "little understood" fact in respect to wider than stock tyres. The tyre "footprint" (the area of rubber contact with the road surface) remains almost exactly the same, regardless of how narrow, or wide, you choose to go. This is due to weight distribution. A narrow tyre may have an almost square-shaped footprint area, whilst a much wider tyre will produce an elongated rectangular footprint(with almost identical surface area). In dry conditions this makes relatively little difference, BUT, in wet conditions the wider tyre provides a better opportunity to trap water between the roadway and the tyre(the tyre actually climbs up on top of the water rather than cutting through it), thus promoting aquaplaning.
politically incorrect be carefull there. i got a warning for refering to a member as an "old man" i think in this case you should have said "querulous age advanced individual"
dRiFtiN yeah i dont think i have ever once drifted my zed in the true sense of the word. ive had alot of power oversteer situations which i thought the zed was very controllable, which is why it is still in one peice i guess. but i would like ot have a go at a genuine drift
RE: 9" rims on the back.... Very happy with the combination.... to the extent I converted my second standard ZX (2+2) to the same wheel /tyre size. I'm running Dunlop 'Formula RSV's' in a 245/45ZR17 on the back rims of both cars, they measure ( physically with a tape ) to be 20mm wider than the same size tyre in other brands, they 'just' scrape when a decent step in the road is struck.... and I mean just, we're talking poofterthous here ! Originally both cars had 7"s on the front and 8"s on the back, both had differing styles of after market mags too. I've sold one set from the std Z and I havent decided as to what I'll do with the 2nd set of Rays / Volk racing rims I have. The combination of 8"s on the front and the 9"s on the back works really well for me, in the dry atleast! ..... In the wet the std ZX (2+2) seems very happy and is certainly very drivable providing a very confident grip level, I havent managed to drift the back end out as yet ( intentionally or un-intentionally ). The suspension setup is dead stock standard bar for the fitting of adjustable rear camber arms to "square up" the rear end for better tyre wear...... my missus drives this car so it has to be a "female aware" car In the modded ZX ( around the 400kw mark & a 2+0 ) the dry road grip is awsome to the point I've noticed I use the brakes far less than before on the same section of road and at the same "pushing it" speeds, ...... yes as a driver I've had to alter my 'style' to accomindate the change in this cars handling, the car now feels like its on rails and it can be pushed very much harder into corners. This car by the way is running a very stiff suspension setup & yes you 'feel' every little bump in the road !! The down side to the tyres is the wet roads, like I said in my other post "it aquaplanes"..... BADLY ! Its definately more noticable in the modded 2+0, its almost physco in the wet and spinning up the rears or drifting the tail out even at speeds of 140 is childs play, the problem is if someone that's not a driver ever gets behind the wheel of this car then the end will be tragic. The 2+2 however doesnt aquaplane anywhere near as much and even on water covered roads where you can actually see the water moving over the road the car is very stable and predictable with the big rubber fitted up. I'm lucky...... I have two ZX's to choose from, one for the wet and one for the dry ! :zlove:
thats interesting...i always wondered why people said wider tyres are worse in the wet but never knew why.....well there go my plans on getting 285s on the back...ill stick with 256s instead cheers chili
i spoke to an engineer once who said wider tyres arent always good for grip even in the dry, reason being that the zed has a certain weight and the tyres used 215's have blocks of tread on them, each block would have a certain amount of distrubuted weight onto it, when using a wider tyre (285 for instance) you now have more blocks of rubber making contact with the ground, and each one would be distributing weight, so instead of 500kg on each block of rubber, you may only get 250kg on each block, lessening the grip. how true is this? i dont know.. this was based on radials btw.
Hmmmm..... Well the force due to friction is the coeffeiciant of friction multiplied by the normal force. Therefore the size of the tyre should be irrelevant. Doubt this works in the real world though... As for Chili's comment on contact area here are the numbers: Stock size tyre 225 Longitudinal distance of contact: approx 75mm Width: 225mm Area: 16875mm^2 Big Tyre 265 Longitudinal distance of contact: approx 75mm Width: 265mm Area: 19875mm^2 So that's a differance of 3000mm^2 or a square with sides the length of 54mm. To my small engineer brain this seems significant. This extra tyre could help dissipate excess heat, provide more tread before replacement in necessary etc, etc. As for Mafi's coment on less force being distributed on each block. There is the same amount of normal force regardless of the width of the tyre so the force will be evenly distributed over the width of the tyre. Cooeffeciant of frction stays the same, normal foce stays the same therefore the grip should be the same.
That's all that needs to be said, tires dont have shit to do with it really. It's the same for just about every rwd that shares the characteristics the Z does, there's things u can do to minimalize the affect but it will always do that. It's the nature of the beast as they say. Now days cars come with traction control bullshit and all this other junk to help people who cant drive. A half decent driver should be able to recover a car when the back end steps out on them, infact it's quite fun when you get pro at it!
theory the theory seems right but that would mean that a space saver could have the same grip as a 275? or am i reading it wrong?
no one mentioned a space saver??? they are like 185mm if that so you would have to work it out again using that measurement.
Where did you get the longitudinal distance of contact figures from? I do not agree that the wider tyre has the same LD of C as the narrower tyre. You do not have the same weight per sq.in. bearing down on the footprint of two different width tyres, therefore the wider tyre distributes the vehicle downforce over a larger area at a reduced weight per sq.in. The only way downforce can remain the same for both tyres, is if both have the identical footprint area. Ask any Eskimo when he puts on his snowshoes, whether he still sinks down into the snow. He doesn't, because his same weight is spread over a larger footprint thereby reducing the downforce.
The size of the footprint is determined by the tyre pressure, with minimal help from the side walls. Width of tyre does not affect the size of the footprint, just the shape. Footprint = weight / tyre pressure. Higher pressure, smaller footprint. A narrow tyre is better in the wet. It gets a long narrow footprint which means there is less water (the width of the tyre) to push out of the way. A wide tyre gets a wider footprint, so has to move more water. That's also why my 19"s with 40+ psi give less traction than the 16's with 32 psi. Smaller footprint, higher contact pressure, but overall less traction. We are all floating on air.
Our day at the skid pan answered that question. All the cars with LSD would slide the tail easily. (WET + LSD + Floor it = Sideways) The Commodore with a spinner diff (ie NOT LSD) took a lot of effort to get sideways, because for the most part, one wheel was just spinning like crazy while the other wheel held the tail in place. Any RWD car with LSD will tend to do the same.
Even a car with an open diff i.e an earlier Z will still step out if given enough curry. Commodores are huge and the power/size/weight distribution has alot to do with the reason why it's hard to get sideways in a big ass boat of a car like that.
A car with no LSD will only step out under momentum - not under power. Doesnt matter what kind of car it is.
That's true in theory I agree but stepping out is stepping out. I have Z's both with an open diff and an LSD and I can easily get sideways when cooking up one wheel at 12psi. Hell, I can even whip the ass out sideways big time in the wet with my NA with an open diff.
What's LD of C? Your "downforce" does not make sense. The normal force CAN NOT change it is a resultant of mass and acceleration only, ie mass of car and acceleration due to gravity. As for the snow shoe thing, that is pressure, a distribution of force, not the normal force which is one of 2 variables when determining fricitonal force (the other certainly isn't area). My original longitudinal contact area was a guestimate looking at the my Z's tyres. I think that you need to crack out the old dusty physics book Refer above, in the perfect world the grip is dependant on normal force and cooefeciant of friction. The contact area HAS to increase with the increase of width, of course there will be a reduction in longitudinal contact with wider tyres (if at identical pressures) but would be negligible considering the pressures vs the mass that each tyre sees.
