Staggered Wheel Sizes

[AngryRB]

Does anyone run staggered wheel sizes? as in eg. 18*9.5 on the rear and 17*9 on the front?

I'm assuming it wouldn't be too legal, but would it be that noticeable, as I think it kind of makes sense as porches and other super cars tend to have aggressive rear wheels on the

back and wider tyres.

opinions?

[sweefu]

You can do it, it's fine. If you want to, you could choose tyre sizes with very similar rolling diameters and the difference wouldn't be much.

I have an S14 and run 16/17 or 17/18 stagger.

[GTSBoy]

Nah, it's daft.

Porsches and other mid/rear engined cars do it because they need a LOT of tyre at the rear (due to large weight fraction and lots of power), and often have significant brake size at the rear too. They wouldn't do it if not for those reasons.

On a skyline or other more normal car, you want bigger brakes at the front, so you're unlikely to need a bigger diameter wheel at the rear. Width is another issue. If people want to run wider tyres at the rear in the mistaken belief that it improves something that isn't as good when the front tyres are as big as the rears, then that's their business.

Edited January 8, 2014 by GTSBoy

[Kinkstaah]

As someone who has pretty terrible rear grip, can you expand on the last part of that post?

Surely a 235 won't hold on as well as a 335 on the back with the same tyre? Or is this related to total handling as opposed to just rear grip under power?

My brain can never quite grasp this concept after googling it.

[GTSBoy]

If you ask a Year 11 Physics teacher they will tell you that it doesn't matter how wide your tyres are, they still have the same sized contact patch (at a given tyre pressure) and so only put the exact same amount of rubber on the road. Therefore (according to the Physics teacher) wider tyres cannot give you more grip.

Of course it's not quite as simple as that, but there are elements of truth in there. I'll come back to that in a sec.

My particular comment was more aimed at the fact that in normal cars like Skylines, you can generally fit exactly as large tyres on the front as you can on the back, or at worst the rear ones can be a little wider. On that basis, unlike a supercar, if large tyres were a desirable thing for you, then you would put the largest tyres you could on the rear, and also on the front, because the front ones do the steering and the braking, which are kind of important functions.

Back to the different grip levels from different width tyres. The main thing to consider with wide tyres is that the shape of the contact patch changes as you go wider. On a fixed rim diameter and with a fixed overall tyre diameter a wider tyre end has a wider and shorter contact patch. This will enhance lateral grip (just think about dragging the contact patch sideways against the ground vs dragging it forwards and imagine how rubber reacts when it grips/releases from a surface like bitumen and you can understand why this might be so) and of course it will therefore cost you in longitudinal grip. ie, wider tyres in theory have less ability to put down power. But again, it gets more complicated.

When you go wider and the contact patch changes shape the effect on what happens to the tyre carcasse as it rolls over the ground is interesting. A wider and shorter contact patch means the tyre undergoes less deflection. Think about the contact patch. It is flat. Flat on the ground. A longer, narrower contact patch undergoes more deflection. One of the key design parameters for a tyre is how much heat it can tolerate. A lot of deflection leads to a lot of internal frictional heating and higher running temperatures, meaning you have to use harder rubber compounds. The wider tyre can use softer rubber, which is where the extra grip comes from.

It gets even more complicated than that, because tyres are not designed to quite so narrow specifications - they are meant to be used on a range of cars at a range of weights in a range of ambient temperatures and speeds and so on, but broadly speaking, a 175/75 must use harder rubber than a 235/45, even though they might be called on to run at the same speed on the same car. A 235 is a very pedestrian tyre by comparison to a 335, so you'd then expect a 335 to have softer compound again. Even so, I would expect launch/longitudinal traction to not be substantially better on a 335 vs a 235 of the same tyre (if they existed). I would expect maybe some small difference, and that might be worthwhile, but it couldn't be night and day. Trouble is....you only need "enough" traction, and the difference might be between not enough and enough, so in some cases it might feel like night and day!

Another point to think about is that tyres are not smooth surfaces. At the micro level the rubber actually gets pushed into the irregularities in the road surface (and vice versa). The softer the compound the more this happens, so softer compounds can really rapidly increase grip levels even more than their smooth surface friction coefficient tests might indicate.

[hardsteppa]

jeezuz...welll, i'm confused...very in-depth post, can you dumb it down for me, in layman's terms? Re "Even so, I would expect launch/longitudinal traction to not be substantially better on a 335 vs a 235 of the same tyre (if they existed). I would expect maybe some small difference, and that might be worthwhile, but it couldn't be night and day." in theory then given a dry day on a bitumen surface of reasonable quality, a 195 cheesecutter would have roughly equivalent grip to say a 265?

[GTSBoy]

I'll try. It's difficult because there is a hell of a lot more going on than it is easy to talk about, so generalisations tend to be wrong, and specifics tend to ignore the general truths.

A 335 is a seriously wide tyre, generally only available in really high performance tyre models and hence rubber compounds. I haven't looked, but there are probably very few tyres available for the same rim diameters in 235 and 335, which is why I said "(if they existed)". But if there was a single type of tyre that was available in both those sizes, it would be quite likely that the 335 would be made in a softer compound rubber than the 235. This would give the 335 the ability to offer more grip. It would DEFINITELY grip better laterally. It would have monster corner grip compared to the 235, because the shape of the contact patch AND the compound would be working to its advantage. However, whilst the compound would offer more grip when looking at longitudinal forces (accel/braking), the shape of the contact patch is less favourable for grip in that direction than the 235's. So it is an each way bet as to whether the longitudinal grip would be better or not. It really depends on whether the change in compound is more significant than the change on contact patch shape.

So your 195 vs 265 case is more or less the same situation. A typical 195 (that is not a low profile tyre, because if we're comparing them, then we need them to be on the same diameter rim and have the same rolling diameter) is not a performance tyre and a typical 265 would most likely be at least a performance tyre, if not some sort of EHP or UHP tyre. So the 265 would almost certainly have softer compound and the whole discussion from the above paragraph holds true.

IF the 195 and the 265 had the same compound then I'd wager on the 195 offerring better longitudinal grip than the 265. The 265 would be better in the corners.

I learnt these things from reading a suspension book. Can't remember if it was Milliken or or another one. There was an extensive section on how tyres work and how they generate the forces that make them work.

[simpletool]

^^^ YES, except wider tyres are typically a softer compound. I've had various sizes on the rear and wider does offer more exit grip. however the feel also changes which you may or may not like.

If I was to buy rims now they would be:

18 x 9" +25 front , 235/40/18 tyres.

18 x 10" +35 rear , 265/35/18 tyres.

Plus, wider rubber does look quite nice. HOWEVER, the rear would need more care in the very wet conditions.

[Kinkstaah]

Thanks GTSboy for that gem of a post.

Layman's way for me to understand it is (this came to me while stuck in a mall)

The same weight is pressing the tyre into the road, be it 195, 265, or 335 in width. This is why the contact patch is the 'same' (but different shape)

Unless your 335 rims weigh a metric ton vs the 195's there won't be any more force pushing them into the road. This is from my understanding why low tyre pressure and higher sidewalls work. Weight transfer pushes the back of the car down, and if there's more 'give' in the rear you get more force pushing the tyre against the road.

Should be a sticky post from GTSBoy for sure lol