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Hey all,

I'm in need of some new rubber and want to go for 235 70 15's (28" diameter) as the 205 50 15's (22.7" diameter) don't give enough grip and I'm looking at also making 1st gear useful. My question is, has anyone run 235's (15") without rolling the guards?

Measuring up the 205's I have on BMW rims with 25mm offset, I have calculated that I would need 8" rims with a 45 mm offset, anyone done this? If so, what sort of rims (make, weight etc) and what did they come off?

Cheers
Bazz

btw, the speedo error doesn't concern me

Hey Woo,
I'm not sure about the 235s but someone on the big forum or CR will know.

I can confirm that one of our most experience motorsport gurus, Ian Lewis, runs 16x8 all around on 225s semi-slick (higher sidewalls too) on his NA6 with the factory offset

Click here for link to his car

Hope you get what you need, especially with all that horsepower

Would tyres in such a size use harder compound rubber by virtue of being designed for much heavier barges?

Try the tire size calculator from Miata.net to calculate width as well as rolling diameter/profile.

on a 9 inch rim you can run 275/35/15s with a 36 offset. it requires rolling and pulling of guards. she'll be right - i would be more concerned about inner clearance.

You wouldn't want to go with 235 70's as the sidewall height would make the car look ridiculous.
A 235/40 would be OK.

I have run 225/40/17's on the rear of my SP and they fitted with no gaurd rolling required.

I think Woo is looking at drag strip duty and drag tyres, not road tyres... no other reason to go to 70 profile unless he's added 4WD and wants to go offroad

Yeah you're on the money BigDog.... drags it is.
The tyre will be Hoosiers which look hotter the taller they are Benny. My mistake I should of explained.

16bit, I want to avoid rolling or pulling guards although a wide body kit may be on the cards next year (just dont tell the treasurer )

All the calculations have been done Hammer, now all I have to do is fit 28" diameter tyres under there. Most people reduce the diameter and sacrifice top speed, but for drags you need top speed too

Damo, Hoosier make heaps of different compounds. You're correct, on street tyres manufacturers increase the load rating for big cars by putting extra belts in making the tyre less likely to deform when fitted to a light car but the compound usually stays the same though. (Breaks traction due to smaller contact patch)

Thanks for the link MX52NV, nice car , I'm trying to keep to 15's but it shows me that 225's will work and that my offset measurement (45 mm) is on the money, cheers

Thanks for the continuing input guys, hopefully the purpose of the new tyres is a bit clearer now

Bazz

Not quite the same, but I run Hoosier Vintage TD race tyres on my Buchanan - they are a great tyre, but they are a touch exe! I seem to recall Sean or NFS13B were running 28 inch drag tyres without modding the guards, but I don't recall how wide they were. Good luck, and don't forget to tell us when you're running so we can come and cheer you on.

Bigger heavier tyres are going to reduce the lifespan of your box...

Seems so obvious you were talking about drag tyres now.

Adam_NAclubman wrote:Bigger heavier tyres are going to reduce the lifespan of your box...

I'm actually hoping for the opposite Adam.
Less full throttle gear changes must be kinder on the box (and faster down the track)
At the moment I use 1st, 2nd, 3rd and 5th to get down the quarter. What I'm looking for is more legs in 1st so I can use 1,2,3 and 4th and still clock 200+kph

Don't worry Damo, if I had of phrased it properly to start with .....

Bigdog, if you're in Melbourne feel free to drop into Calder Park. I'll get some pics and movies together for you interstaters

Still sounds like 225's are as big as most have gone

Bazz

Yeah but on the launch they're going to put way more load on the drivetrain not only from the massive change in gearing but also the weight