*Sonic*

OK

apart from the rolling radius being marginally different, are there any other differences between 215/40/17 (which I currently have on Prodrive PD7's) and 215/45/17's (which I think they put on P1's as standard on 17's)

Im sure I read in here that 215/40/17 is about as close to the original 16" tyre size, this information is definatly wrong

I had a puncture in one of mine, and put a std 16" (on OE tread) next to my 17 and there was a big difference in size

Also I found a tyre checker, and this said that 215/45/17 is only 1% difference in rolling radius to the original

Im looking at getting a new set of tyres, and want to know wether I should stick with the 215/40/17's or switch to 215/45/17

Is there any difference in handling, as my car does seem to handle slightly better on the OE wheels (this could be because the tyres are slightly better tho )

Cheers

Steve

MDBinaWagon

The tyre checker I was using gives 215/45 17 as 14mm diameter bigger than the 205/50 16, and 215/40 17 as 7mm smaller.

I've just bought some MY01 17" wheels from Gooner, and I'm replacing the 215/45 with 215/40 as soon as the tyre fitters call me to say they've arrived.

I've also just had an Origin B2 arrive, so I may pop it onto the dash (going to attempt to hard wire it over the weekend), and see what my speedo reads at a GPS indicated 30 with each tyre size fitted. I'll try and remember to stick the results here.

Martin.

Geddon

Try this- quite useful tyre calculator:
http://www.miata.net/garage/tirecalc.html

MDBinaWagon

Right, the results of the not-so scientific testing are...
Speedo Origin B2 - 215/45 (worn) 215/40 (New)
30 27 27
40 36 36
50 48 45
60 56 55
70 67 65

The 215/45s were Bridgestone Potenzas, and the 215/40s are Avon ZZ3.
I have to admit, I'm surprised how close they are lower down, ans could be tempted to go for 215/45s next time. I know the fitters will lynch me if I go back for more 215/40s given how hard (very tight) they were to fit

Martin.

Jerry B

Don't forget tyre wear decreases the rolling radius. A new tyre compared to an old will have a difference as much as 10 mm (not cm! ) in diameter.
The difference between a 40 and a 45 may not be that far off, so you have a fair margin of tolerence that the car is working to even with the same size tyres on, which makes the +/- 3% rule (I think) understandable.
Also a 45 may compress slightly more or less under load than a 40, meaning the appearance may not be a true indication of the rolling difference.....I'm just thinking out loud here.

I ran 40s as they were closer and would generally give a lower speed at a given speedo reading than the 45's, thereby giving me a better chance against a speed trap should I be a bit heavy footed. Or so my logic went...

Just my thoughts....

Geddon

is that not 10mm?

*Sonic*

one would hope so

thanks for the info guys, guess ill stick with 40's then, now I need to find a decent set of rubber

robbo_64

Have got 215/40 Yoko's on my MY98 with Eibachs, they don't rub etc.
Have got a Road Angel as well and the speedo is 7mph high at 60mph according to the Road Angels speed readout !!
Tyres are ready to be changed, though
Robbo

Jerry B

oh yeah, 10cm would be quite a difference!

vindaloo

*Sonic*

P1 didn't come on 215/45 17s but 205/45 17s.

People changed from 205/45 'cos it's an odd size. More tyres available in 215/40s, cheaper too in some cases.

I'd recommend using a tyre rolling radius checker, preferably one that gives you percentages.

You can go from 215/40s to 215/45s depending on the offset of the rim and the specific tyre chosen. I think classic v bug/blobeye offset is 53mm v 48mm. If it rubs, it's normally on the outside of the rear wheelarch lips which can be rolled back with the right tools.


Jeremy.

*Sonic*

Cheers Vindaloo

I did check on a RR checker, and it said 45's where only 1% different, and 40's were about 7 or 8 % different

I have PD7's and the offset is 53mm or 52mm, std 16" wheels are 48 offset

Hoppy

Sonic, you have OEM 16in wheels with 48mm off-set? Summat's wrong there. OEM is ET53.

But no matter. Your PD7s will be 52mm and the tyres you want are either 205/45x17 or 215/40x17. 99% of peeps on here go for the latter as good tyres are readily available in that size (Goodyear, Toyo).

Richard.

*Sonic*

Oops Hoppy

I may have got the offsets back to front

im going to stick with 40's tho

bartmanuk

i thought the offset for the classic can range from 48 to 53 IIRC.

BM