Tyre situation, Need help.

[marcusus]

kuhmpo ecsta ku31. You drove mine on the run (granted they were on the 16s) but they were only $110 a corner.

Good in the wet, although they are a good street tyre, they are prone to graining on a spirited run. I haven't tracked them, but if they hold up like the cdrives gthen they should only get squirmyafter 4 laps.

You should know when you're close to their limits because they squeal like a stuck pig before they let go.

Don't know about that. Went for a spin down McCarr's tonight with Kuhmo's all round. Taking a corner with a bit more power than I should have, the rear stepped out a bit without much warning at all. Didn't really hear any tyre squeals. It just gave out.

Now that I'm getting a bit more experience under my belt, I'm finding the Kuhmo's aren't really giving me grip when I'd like it. They were definitely fine for regular everyday driving, but I'm finding that in my eyes they're slowly deteriorating when it comes to spirited driving.

Track wise, it's much the same. They'll grip OK and all that, but they don't seem to grip when I want them to. There's also this odd sort of vibration that comes on at about 130km/h+, although I haven't really narrowed that down to the tyres though.

[Patty]

Thanks for the replies.

So does a wider tyre actually give you more grip? I read in a few places that going wider makes the contact patch smaller or not much bigger. This is since the weight is spread more so it doesn't mush the tyre into the ground as much, so the contact patch gets wider but thinner too.

I don't get it, why would you go wider tyres then? Corvettes have like 375mm tyres, surely a wider tyre will give more grip. What about in the wet??

Contact patch stays theoretically the same with wider tyres if you run the same pressure. Pressure = Force/Area. Since the mass of the car and tyre pressure are the same, then the areas (contact patch) is the same. However, wider tyres have more thermal mass and surface area to radiate heat, so you can run softer compounds to generate more grip.

Force(Grip)=coefficientOfFriction(COF)*NormalForce(=mass*gravity). Your COF remains constant since it's a property between the material of your tyre and of the road, and NOT related to contact patch. This means that your grip here is not related to tyre width but to the mass of your car, material of your tyre and the type of road Thats why RWD cars should be harder than FWD to wheelspin.

If wider tyres increases contact patch (which [Will] says doesn't) it would probably only work against you because it equates to lower force per area or less equivalent mass on you wheels.

[Adam_NAclubman]

Ok When I say I want to be able to floor it without spinning tyres with 200whp, I dont meen clutch dumping from 7k, who does that? Did you see that skyline whos I think flywheel or something broke off and nearly sliced his legs off, another part put a hole up through the bonnet and high in the air.
What I want is to be able to take off like a sane person, then be able to floor it in a straight line through first and second without the wheels spinning. Its not too much to ask is it?
Every time I go to mania and mention superchargers they just say turbos are way better beause they're faster. I say what about lag and they say you get wheel spin from 2000rpm. Well I don't want that. Is this wheel spin in 1st generally accepted in the turbo mx5 community?

Dude, its easier to spin semis than road tyres when you suddenly apply power (like, say... a turbo coming on boost) because they have stiff sidewalls. My RE55's and RE540's were way easier to do burnouts on in my Skyline than my normal tyres.

Yes, its generally accepted that reasonably powerful (for their weight/size) cars will wheelspin if you floor it in first. They all do it, especially if they have stiffish suspension (you did say you want coilovers in another thread didnt you?), its half the fun of having power. If you have a decent predictable diff and half a brain its not much of a problem when it occurs

[Adam_NAclubman]

oops

[Fatty]

honestly for day to day driving on street tyres in all conditions, wheel spin is not an issue, unless you are a total nube with no idea about throttle control. i don't think you fit that description.

i get a chirp now and then, but that's more due to my new 8 puck clutch than the turbo.

[Patty]

Try this site Sasso:

http://www.newton.dep.anl.gov/newton/askasci/1993/physics/PHY2.HTM

[Benny]

Just my 2c worth.

Have you thought about buying a set of used tyres?
Many tyre dealers carry stock of various sizes and types, and sometimes you can pick up virtually new tyres for a song.
Often, they even come with rims, so you may get lucky and pick up a set of 15\" or 16\" tyres and wheels for less than buying 2 new tyres.

Personally, I'd prefer to drive on a good set of 2nd hand tyres than new crap.

[Hellmun]

Adam, How does a stiffer sidewall make a wheel spin more easily? Maybe those semi's aren't as good in the cold as the R888's which are known to be fantastic all round tyre, just a little slower on the track when its hot, but they last longer.

If a tyre deforms under pressure it will form a larger flat surface. If the sidewall is too stiff it resists the deformation and you get a small contact patch. Watch a drag-car take off from a side profile and it'll probaly make more sense.

Remember stiff sidewalls are only for cornering grip, it's a negative for acceleration and deceleration. Compromise as everything is in cars. Nothing does everything the best.

[Alex]

Force(Grip)=coefficientOfFriction(COF)*NormalForce(=mass*gravity). Your COF remains constant since it's a property between the material of your tyre and of the road, and NOT related to contact patch. This means that your grip here is not related to tyre width but to the mass of your car, material of your tyre and the type of road Thats why RWD cars should be harder than FWD to wheelspin.

If wider tyres increases contact patch (which [Will] says doesn't) it would probably only work against you because it equates to lower force per area or less equivalent mass on you wheels.

not quite, tyres can't be looked at this way because of how soft they are, unless they are on a totally flat surface
tyre's will deform to a certain extent , so there is also shear force involved not just friction

wider tyres have a larger contact patch hence the area that is in shear is increased resulting in more overall force

[jules]

oops

titter...

Jules

[marcusus]

I think your flatspotginity is gone.

Might have a looksee at the car if I get a chance to jack it up. Not sure whether that's exactly the case, but it wouldn't surprise me considering I first noticed it when I was at Eastern Creek ages back.

[rjastra2]

Ahhh, remember the old days when 5.7L Ford GTHOs were shod with 185/70x14 tyres

[Patty]

not quite, tyres can't be looked at this way because of how soft they are, unless they are on a totally flat surface
tyre's will deform to a certain extent , so there is also shear force involved not just friction

wider tyres have a larger contact patch hence the area that is in shear is increased resulting in more overall force

Yeah thanks SM. I retract my previous statement re:tyre width. Did some more reading Basically what I was saying before is that contact patch itself does not directly translate to friction if it was a pure friction application. The article in that link says that it's not pure friction because the tyres can become sticky so it's gripping the road by adhesion (you called it shear force) and basically giving a COF>1. Therefore more contact patch = more grip. Aah, enlightenment.

[marcusus]

Marcus it sounds exactly like my car, and its the flatspot. Wouldn't be surprised if you started feeling it after the track, specially the amount of times you were facing the wrong direction at wakefield last time

I'm trying to think of a way to get the car up to that speed with you in it to compare, but legally so...

[[Will]]

On width and contact patch size (and shape), this article sums it up quite well:

http://www.autospeed.com/A_108915/cms/article.html

However, the bit about aquaplaning and higher pressure doesn't mention that the reduced contact patch if you go really high in pressure (e.g. 50psi) would means that although you didn't aquaplane off the road, you'd just skate off because the F=uN rule isn't perfectly linear, if N gets big enough, then F doesn't go up proportionally. Read any race car/suspension book and they will draw this graph for you.

Regardless, still a good article, but just keep in mind that at the extremes, the rules don't apply as plain and simple.