Are My Tyre Calculations Correct?

[Piranha]

Hi All

 

I am looking to replace 2 tyre's and wondered if anyone can confirm my calculations / logic is correct. Firstly my car is a 2003 v35 built on same chassis as 350z just a bit longer.

 

In 2003 the standard stock wheel / Tyre setup was 225/45/18 FR & 245/45/18 R

 

My car came with aftermarket alloys setup of 225/40/19 FR & 245/40/19 R and this matches the OEM Tyre set up from 2005.

 

If I am correct the speed calibration is based on the rear wheels so the change from 18 to 19 setup above makes no real difference to the speedo reading.

 

My current rears are Pirelli P ZERO almost new, the fronts are cheepo budget tyres again almost new.

 

My plan is to shift the P Zeros to the front and add either goodyearF1 A/S or MPPS to the rear. Therefore only needing to buy 2 tyres.

 

The setup would then be 245/40/19 FR & 265/40/19 R, from my calculations this would ever so slightly reduce the speedo reading to: 29.6 MPH when doing 30 & 59.3 mph when doing 60, again quite a small change.

 

Are there benefits to increasing the width of fr & R tyres in this way, or should I stick with the current widths, i do not want to mess up traction control.

 

Thanks In advance

Edited January 29, 2015 by Piranha

[Ekona]

If you're going mix tyres, be aware of the possible consequences: Have a read of the Sticky in this forum so you know what you're risking.

 

Tiny changes in the speedo aren't the problem, it's whether the TCS has a hissy fit with the difference. Some cars are more sensitive than others!

[Piranha]

If you're going mix tyres, be aware of the possible consequences: Have a read of the Sticky in this forum so you know what you're risking.

 

Tiny changes in the speedo aren't the problem, it's whether the TCS has a hissy fit with the difference. Some cars are more sensitive than others!

 

Ok thanks i will have a look.

[Piranha]

If you're going mix tyres, be aware of the possible consequences: Have a read of the Sticky in this forum so you know what you're risking.

 

Tiny changes in the speedo aren't the problem, it's whether the TCS has a hissy fit with the difference. Some cars are more sensitive than others!

 

Ok first of all great post , I feel a bit stupid now for not finding it.

 

What u say makes sense, I always thought mixed tyres were ok as long as they were same tread pattern on front and rear even though different brands.

 

This means that my current set up is mixed and not good.

 

So I'm thinking now I should move rears to front and put new 265/40/19 p zero on rear making sure I match tread all round. ?

[Ekona]

Tbh I hate Pirellis with a passion, so I'd flog the decent pair you have then get something better matching all round. MPSS, Eagle F1, hell even FK453: Any of those would work, assuming they're available in the sizes you're after.

[Piranha]

Tbh I hate Pirellis with a passion, so I'd flog the decent pair you have then get something better matching all round. MPSS, Eagle F1, hell even FK453: Any of those would work, assuming they're available in the sizes you're after.

 

Thanks for advice, I did notice they were not great on fuel economy but seemed to have good wet rating, I use car as a daily runner so not planning to track.

 

I may up the rear width to 275 because it seems to level out speedo to an accurate reading and the P Zeros come up as available in this bigger width.

 

with the current mixed set up on the car, I have already experienced your example of loss of traction when going other uneven repaired road and some times the slip light flashes when I'm turning right on uneven road. So thinking I should sort sooner than later.