Tyre stagger (or not???), same tyres (or not)

[kentsmudger]

There are 1000's of MK3 drivers out there, not connected with the forum, driving cars with all sorts of tyre compounds, makes, profiles, etc.....
VERY few (if any) have ever been near a ditch.....! Imagine how many pairs front or rear tyres have been changed, leaving the other axle tyres of a different make, by KwikFit or similar..?
The replacements MAY well maintain the correct stagger but the compound WILL be different from the other axle if they're a different make......

Which is probably how my car came to have such a nasty set-up. Many of these "MK3 drivers out there" will just think their car is supposed to drive like that, and hopefully learn to deal with it and never have an accident. Some might have a prang and perpetuate myths like "They were well known for being a bit twitchy those MR2's "

I really don't understand how anyone can be critical of the club for recommending to people that they stick with the manufacturer prescribed specification.

Especially when newbies are coming here for help and advice

[Jaik]

After all, we are simply disagreeing about essentially an extra couple of square centimeters of rear tyre contact with the road...?

This is what people on here mean when we say only people who really know what they're doing should mess around. The area of the contact patch doesn't change whe altering the tyre width or profile, assuming all other variables stay the same, but the shape of it does. I thought it was worthwhile pointing out that this kind of mistake is a common one made by those who don't understand the physics of tyres as well as they think.

I'm not claiming I know more than you or anyone else, it's not an area I'm too clued up on, I'm just illustrating how easy it is to get unexpected results unless you really know what you're talking about.

[GSB]

Is this debate really continuing? Really?

Sigh...


It is a fact that some issues need to be revisited from time to time in order to ascertain weather the circumstances that dictated the original outcome of the debate surrounding them are still current. Humanity has managed to prove itself wrong on countless occasions. Take for example the Criminal Justice system. Here in the UK the death penalty was repealed, as the evolving public opinion moved from the bloodlust encountered at the Tyburn Gallows, to a general feeling of distaste and an unwillingness to accept such barbarity. Closer to our chosen field of debate are the various rules regading vehicle manufacture and use. Seatbelts becoming compulsory were seen as a hideous infraction of personal liberty, the same with speed limits, the banning of pop up headlights, the introducion of the roadside breath test... It goes on and on and on, just like the debate we're having here.

Unlike all the other debates however, the outcome of this one will not change just because someone now feels its wrong. Until the laws of physics are repealed, the fact will remain that it is thoroughly inadvisable to upset the delicate balance of a machine by changing the specifications of fundamental components without recourse to proper consideration for ALL potential effects, such things should never be changed on a whim. That applies to ANY machine, and in my own personal case, especially any machine that i am entrusting the health and wellbeing of myself and my loved ones to. Whether that means my car, my central heating boiler, or something as mundane as a set of kitchen knives makes no difference.

In the case of tyres on the MR2, the collated experience of a large number of people indicates that while the car will run on mixed tyres or tyres sized outside of the manufacturers specifications, it will alter the utlimate balance of the chassis. When set up as the OEM provided the car, the chassis has defined and predictable behaviours when at the limit of the tyres adhesion. These behaviours have been the subject of thousands of miles of testing in controlled conditions. If you change these paramters, you should expect those behaviours to change too. We already know that on a lightwieght car such as the MR2, a small change can have a very big difference. For instance, a fraction of a degree change in toe or camber, one or two punds per sq. inch of air pressure in the tyres, or the removal or addition of a small amount of wieght from the car (The spare tyre springs immediately to mind). The differences are marked, and very often unwelcome. Running the car with set of tyres that have significantly changed the characteristics of grip and slip on only one end of the car, will make a big difference. Anyone with an IQ above single digits shouldbe able to see that if a very minor change like dropping one or two psi has a big difference, then altering the tyres contact patch in 10 or 20mm lumps is going to have a huge effect.

Granted, you may never see the true nature of the effect you have created, and may even percieve some positive effects, such as a more lively turn-in to corners brought about by the increased slip at the rear end. But, at the limit, or in an emergency, the effect will be very marked indeed. What the effect will be is hard to predict, and as already stated, will be down to the effects of more variables thane we can discuss here. One thing is absolutley certain though, It wont be the nice predicatable effect that Toyota's engineers envisaged.

Many people have witnessed this to their cost. That the effect exists is beyond question. No amount of debate will change it. The fact that people do it and get away with it is not an indicator of safety, the fact the Kwik fit will happily sell you a full set of 195's will not make it safe.

This is why we as club, and me as an individual will strongly reccomend that you dont do it.  No amount of petulant fist shaking and "You cant possibly understand all the variables" will make any difference.  Your assertion that the tyres contact patch grows with tyre width proves that you dont know your material quite so well as you think you do, so you should carefully consider what else you dont know, and perhaps consider that the combined experience of several people, who have between them a total of several hundreds of thousands of miles, several hundred sets of tyres, and thousands of hours driving these cars on every road, on every continent and in every climate that the world can offer, might just know what they are talking about...

Dyn-Evo, please do not reply to this message expecting a reply from me. You wont get one. I've discussed this topic in this forum more times than I care to remember and am unwilling to discuss it further today. I personally believe that your continued arguments amount to nothing more than trolling in order to provoke argument, but I am willing to give you the benefit of the doubt. Hence this rather long winded post.

Drive safe.

[Anonymous]

Had a look at a 2 for sale last week (Shipley, W Yorks), nice shade of blue, w reg, low miles,  just out of curiosity.  It had 205's on the front and 185's on the back.  I did point this out but the salesman didn't seem that interested   s:( s:(

[roger]

Had a look at a 2 for sale last week (Shipley, W Yorks), nice shade of blue, w reg, low miles,  just out of curiosity.  It had 205's on the front and 185's on the back.  I did point this out but the salesman didn't seem that interested   s:( s:(

... and if he sells it in that condition and the new owner doesn't come on here,   s:crazyeyes: :crazyeyes: s:crazyeyes:  

What will the end result* be blamed on? Bet it won't be the garage.


* that might be a badly handling car, might be loss of control, might be a crash or perhaps a very disallusioned owner who will never touch another sports car, or a Toyota ever again.

[ChrisGB]

Just to chip in again, the area of the tyre contact patch will vary with width, as well as the shape.

If you put a wider tyre on the same rim, you get an increase in section. This will nominally increase the ratio of width to length of the contact patch. This in turn changes the feel of the steering and the balance between lateral and longitudinal traction.

Now if the rim width stays the same, the contact patch will not go up in width as much as if the rim size goes up with it (the tyre pinches on a small rim).

When you look in the handbooks of most cars where tyres of different sizes are fitted, you will notice that the tyre pressures are different for various fitments. So a car on wider tyres will generally run lower pressures than the same car on narrower ones. This is to keep the contact patch shape similar (as this has a big effect on dynamics and feel). Where the pressure is reduced on a wider tyre, the contact patch will get bigger than the patch on the narrower tyre at higher pressure.

As for alarmist, running mixed tyres on any car is a compromise, on a mid engined car it is generally the same compromise, but the results are harder to recover from.

When I was looking around at MR2s I drove a few and the ones on mixed front and rear tyres felt plain wrong (my comment to one dealer keen to impress me with the car: "it handles like a turd"). And that was before I read about it on here.

So if a noob likes to shop for wheels (and some of the horrendous tyres) that Halfrauds market, so be it, but if the noob is interested in having his car nicely balanced and behaving consistently across a range of surfaces and conditions, then said noob would be well advised to stick with the club advice to begin with and experiment once he / she has learned the car.

All those people out there in their '2s with mixed tyres may well keep out of harms way if they never push it or have an emergency.

Toyota did a huge amount of development to get the MR2 right. You only need to drive one to know this. It is in a different league to many of its competitors when it comes to driver involvement, and that is not accidental. Attention to detail was such that when they went with a heavier 6 speed box, they even upped the f/r stagger to keep it neutral with a safe helping of understeer for when you get in too hot.

If it ain't broke, don't fix it.

Chris

[kentsmudger]

Attention to detail was such that when they went with a heavier 6 speed box, they even upped the f/r stagger to keep it neutral with a safe helping of understeer for when you get in too hot.

I had no idea that that was the reason, interesting.

[Dyn-Evo]

Coca Cola IS better than Pepsi......!

Hell...even I'm starting to get  bored of this, now......  s:roll: :roll: s:roll:  

Re: contact area....

Well...all things remaining the same, if you double the width of a given tyre, THEORETICALLY the contact area SHOULD remain the same..but in reality the area WILL increase slightly, especially if your compound or, as mentioned, tyre pressures, are softer / lower.....

Two of my variables, incidentally......!  s:wink: :wink: s:wink:  

Have a read:  m http://spyderchat.com/forums/showthread ... re+stagger m

Bored now.......over and out....!  s:lol: :lol: s:lol:

[markiii]

I'll still take my experience Vs your theory any day

[Dyn-Evo]

I'll still take my experience Vs your theory any day

'Course you will....!

I never doubted it for a second.....  s:wink: :wink: s:wink:

[ChrisGB]

I think the simplest way to look at this is to cosider that generally a tyre of a certain compound, construction and tread pattern will behave broadly similarly over a wide range of surfaces and conditions. So on a correctly sized matched set. The car should maintain its balance in most conditions and respond consistently to driver inputs. This makes a matched set of four in the correct size a good choice.

Alternatively you could go for mixed where the car may be balanced in all conditions and across all surfaces. But given the variables, how likely is that? You may be lucky, but you may end up with a car that understeers in the dry and oversteers in the wet, or maybe oversteers in damp but understeers in the wet, or overteers on one surface and understeers on another. With luck, you may find a mixed set solution that works, but why trust to luck to save a few bob?

Same with size and section. Lower and wider changes contact patch shape and size, camber sensitivity and a host of other factors. Again, may work, may not.

The problem is that the time you generally find that the combination you have does not work is when you overstep the limit of adhesion. A little under or oversteer shimmy may be easy enough to catch, but if it happens where the space is limited or the verge or oncoming traffic is close, it will not be so much fun. Throw in tyres with a potential to exaggerate the loss of adhesion and you have a harder time catching it.

To claim in any way that mixing tyres and. / or reducing stagger on any car is a good idea is plain wrong. To suggest it is ok on a mid engined car is worse.

Take your pick. It's a free country.

[GSB]

Bored now.......over and out....!  s:lol: :lol: s:lol:

[MOD] Indeed you are. Thread locked.

If anyone has something constructive to add to this debate, then by all means PM me or one of the other Mods / Admins and it will be unlocked. If you simply want to continue provoking argument for arguments sake, please don't.[/MOD]