Confused: Should I get wider tyres before any engine mods?

mazmad · Postby **mazmad** » Fri Sep 14, 2012 2:42 pm

Thanks for all the advice and input fellas.

Went with 205's and the 8 inch wheels (from 205's on I think 6 1/2s). Hard to tell whether the biggest impact was from going to semi-slicks or the wider wheels but the combination certainly took a chunk out of my WP time.

Suspense · Postby **Suspense** » Fri Sep 14, 2012 4:34 pm

How'd your time go and which semis did you go with?

Edit: and which wheels! 6UL?

Black_Penguin · Postby **Black_Penguin** » Fri Sep 14, 2012 6:12 pm

Toyo R888's on 6UL's and the laptime was a low 1:16 from memory.

mazmad · Postby **mazmad** » Fri Sep 14, 2012 6:56 pm

Yeah a few 1.16s and then a 1.160 even in the last session.

Suspense · Postby **Suspense** » Fri Sep 14, 2012 7:17 pm

Nice work Craig. Sounds like both of you smashed it this week. I'm going to have to bolt on a turbo if I'm going to have any chance of keeping up with you guys again at the next club day!

mazmad · Postby **mazmad** » Fri Sep 14, 2012 7:27 pm

Thanks Spencer. You were pretty slick, I think you will do ok without it

949Racing · Postby **949Racing** » Thu Oct 04, 2012 4:31 pm

Suspense wrote:What does significant mean though? So a 205 on an 8" rim is 'faster' than a 205 on a 7.5", which is 'faster' than a 205 on a 7", which is 'faster' than a 205 on a 6.5", but I'm curious what sort of difference we're actually talking about with the same driver and car. So holding everything equal, including tyre, but changing the rim width.

Everything else being equal, 2:00 course, about 1s going from 6.5" to 8" with a race compound tire. 225/45, similarly gain about 1.2s going from 8 to 9". Precise gain depends on course, driver, setup and what not but the gains are significant and repeatable. Look no further than your favorite high end sports car to see wheels as wide as the tread as OEM equipment. It's not ground breaking tech or anything, just something new to the insular Miata community. Here in the US, the community has already accepted 8's and moved onto 9's. It helps that we have a better, and less expensive selection of 225/45's to choose from.

Suspense · Postby **Suspense** » Thu Oct 04, 2012 5:01 pm

Thanks Emilio.

You're right on the cheaper tyres in the US, even with shipping from Tire Rack to Australia doubling the total cost it's still cheaper than buying locally. For those running a single set of wheels for street and track we're technically limited by an increase of 1" over OEM to remain street legal (which would mean 7.5" on an NB8B).

sailaholic · Postby **sailaholic** » Thu Oct 04, 2012 5:39 pm

Suspense wrote:Thanks Emilio.

You're right on the cheaper tyres in the US, even with shipping from Tire Rack to Australia doubling the total cost it's still cheaper than buying locally. For those running a single set of wheels for street and track we're technically limited by an increase of 1" over OEM to remain street legal (which would mean 7.5" on an NB8B).

Not true once NCOP comes in, maybe not true now depending on your state.

NCOP wrote:4.2.8 Maximum Passenger Car Tyre and Rim Width
Tyres fitted to passenger cars or passenger car derivatives must not be more than 30% wider
than vehicle manufacturer’s widest optional tyre.
The rim width must not exceed the recommendations for the tyre fitted.
For example, if the original widest optional tyre is 185mm, the maximum tyre width is 1.3 times
185mm = 240.5mm, i.e. a 235mm wide tyre. The maximum rim width for a 235mm tyre is
9 inches if the aspect ratio is 60 or below.

Page 22 of 85 on National Code Of Practise Section LS

Suspense · Postby **Suspense** » Thu Oct 04, 2012 6:23 pm

Interesting, although I'm curious about how this document is intended to fit in with all of the different standards and guidelines - i.e. what legal standing.

At face value it just seems highly unlikely that such a broad standard would replace the relatively strict rules we have in place. Take an NB8B for example, with stock rims of 6.5" wrapped in 205/45/16 rubber. The 30% increase in rubber would allow for rims 9-10" wide.

I'm really sceptical that we'd go from a system (in NSW) that allows an increase of 26mm, from 6.5" to 7", to 9-10". Happy to be (conclusively) proven wrong though.

The current system allows for greater widths if they're signed off by an engineer. Perhaps that's what the NCOP rules will mean, that the max wheel width with a 30% increase in tyre width is the max that could be signed off by an engineer.