What width tyre for turbo car?

[emily_mx5]

Hi guys, because i like to plan things i cant afford, I am doing some research into tyre widths re turbo power.
I have an NA8 with an NB8A engine, and hope to have a turbo system soonish aiming for 150 - 170 kw.

Stock NA had 5.5" wide wheels with 185 tyres, lol.

Not so much looking for "handling" info, as obviously wheel offset, coils, sways, alignment are going to affect that hugely.

I just want grip, dont want to be sliding around like all my Silvia friends.

Just wondering what your experiences are with wider tyres? (specifically on the street, not interested in semi-slick-race-track info)

[16bit]

i have personally found 205 50's to be ample.

i first ran 205 50 re001's (the good japanese first batch - not shitty australian ones) on stock nb8a wheels and they were great. heaps of traction and grip.

i then went to 205 50 toyo r1r's and when they were new had more than enough grip for road. these where on 8 inch wide rims though.

i am now using 195 50 re002's and again these have ample traction and grip.

so i would say that 205 50's will be fine as long as the tyre is good quality like ku31's, re002's, michelin pp2's (do they even make these anymore) etc.

[emily_mx5]

Thanks really great answer.

Sooo 225/45 is a bit silly?


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[manga_blue]

Not really. Either is good.

[Lokiel]

I found my Dunlop Durezza Star Spec 205/50/15s fine on my SE at 150rwkw - in the wet they were awesome too. I do love my 225/45/15 Toyo R1Rs though on the track (unless it's wet, then I want my Star Specs).

I have 15x8 6ULs but would suggest the lighter 15x7.5 6ULs rims instead if you don't want to run 225s in future (not sure about 15x7s, if they work for 205s then that's even better).

205s should give you plenty of grip for your power levels.

[elitee]

I'm currently running 225/45 Toyo R888 on my 15x9 6uls, putting out about 160rwkw when cold i get no traction in 2/3/4 but once warm there perfect, once these tires are finished i would defiantly be picking up a set of hankook rs3 in 225/45

[Magpie]

http://www.physicsforums.com/showthread.php?t=131381

This is what I've picked up as a kart racer and on the web - and I believe it.

1) The size of the contact patch is irrelevant - the main factor in determining the grip is the tyre temperature. The colder the day - the higher the trye temp needs to be to get grip.

2) Tyres works best in a very narrow temperature band - usually tryes get too hot on a dry track.

2) The contact patch size is the same for fat and thin tyres for the same psi. (simple physics)

3) Fat tyres are better on a dry track because they contact patch is wide rather than long, so the tyre carcass destorts less when the trye rolls. That keeps the tyre temperatures down.

4) There is no grip without slip - and the coefficient of friction model is a good one for a given temperature.

5) All this goes out the window if a trye aquaplanes - that's why street tyres have nobbly bits - for driving in the wet.

6) For most cars, braking distance is determined by the heat dissapation ability of the brakes. That's why a MacLaren Mercedes can stop s quickly even though its a heavy car.

Also have a look here http://www.autospeed.com/cms/article.html?&title=Tyres-Grip-and-All-That&A=108915 (supports the above statement).

I'm currently running 225/45 Toyo R888

R888's have a very stiff sidewall hence less sidewall stress and better contact shape stability (depending on your alignment etc). So the type of tyre you use is just important as the width.

[M1474]

^this

Area x pressure x traction coefficient = grip

Double the area and you halve the pressure.

[NitroDann]

Tyres use adhesion as well as friction, so it's not 100% true.

Dann

[Magpie]

Another good article (with evidence) on Tire contact patch size is determined mostly by weight and tire pressure http://www.performancesimulations.com/fact-or-fiction-tires-1.htm

Dann have a look here http://technicalf1explained.blogspot.com.au/2012/10/f1-tirespart-1.html

[NitroDann]

I totally agree that it's MOSTLY correct, but a wider contact patch is still faster, due to adhesion. This is why a wide rim is always quicker than a narrow one. More contact patch.

Dann

[Hellmun]

Magpie wide tyres scale much better with weight, I don't have the graph handy (I first saw it in Paul Haneys race tyre book but I think it's in Senna's and a few others books I've got) but there are deformation limits to the tyre contact patch which come into play so there are grip negative returns with the taller contact patch associated with skinnier tyres (a tall thin contact patch gains less area than a wide one in the rotating direction). That said this is getting into race talk... for street use I have 205/50/15's . There aren't a lot of options in street tyres though to tyre up further as all the wide tyres tend to be 630mm diameter+... I'd just use a smart right foot and stick to the 205's with good quality tyres. Your way past factory power and you'll just have to respect what your car is now capable of . Even 225 semi slicks struggle to put down %10 throttle coming out of corners due to the boost ramp up... plus you get the added bonus of the tall skinny tyre being much more manageable in wet conditions where you'll need all the grip you can get. I've only dríven my car once in very light rain so far and it was spinning 5th on boost with near new KU31's. I'm only a little bit over 200kw atw.

[zossy1]

Meh, this makes my head hurt.

I'm running similar to your power numbers. 205/50/15 KU36s. I love them. I would work more on suspension balance and sway bar settings before i'd go any bigger.

Besides, that's part of the fun of boost - you have to break traction once in a while.

[Sean]

I don't think you need to worry any more than you do for an angrily dríven NA powered car.
No matter how much torque you make, you will be able to drive it easily without major traction issues on any decent 185.

Even on a spirited drive, it's not going to be exponentially quicker on a slightly wider tyre.

I used to run 15/195s on my 200+kw 1.6 turbo NA - never had traction issues unless I wanted to...

The quality of tyre is going to mean more than the width for the minor differences in size you can reasonably get under an MX5.

I've seen them lift the fronts with 'little' 14/185s on the rear...