Speedo adjustment for 255/35s

[SturdyHSV]

Not as in swimming trunks... What would I have to change in EFI Live to account for the increased circumference if I put 255/35s on there?

I only ask as they're £174.60 on camskill currently:

http://camskill.co.uk/m55b0s337p102415/Michelin_Ty...

Whereas the 245/35 are £184.15

http://camskill.co.uk/m55b0s336p102409/Michelin_Ty...

Would rather more sidewall than less, hence going 255/35 rather than 255/30...

[ARAF]

Standard rollong radius is 2055mm. The 255/35 will give you a RR of 2077mm and the 255/30 will be 1997mm

So, on the 255/35 your speedo will read 1% slower (70mph will be an indicated 69.3), and the 255/30 will read 2% faster (70mph will be an indicated 71.4).

I'm sure others have fitted them without problems, so go for it.

BTW, your sidewall will now be 4mm taller, whereas with the 30 profiles it will be 9mm shorter.

[SturdyHSV]

ARAF said:

Standard rollong radius is 2055mm. The 255/35 will give you a RR of 2077mm and the 255/30 will be 1997mm

So, on the 255/35 your speedo will read 1% slower (70mph will be an indicated 69.3), and the 255/30 will read 2% faster (70mph will be an indicated 71.4).

I'm sure others have fitted them without problems, so go for it.

BTW, your sidewall will now be 4mm taller, whereas with the 30 profiles it will be 9mm shorter.

That's a fair point, it's a pretty minimal difference isn't it? Didn't bother to work it out

[arh1a]

Has anyone got any pics of 255 mounted on Monaro VXR wheels? Just wondering if it will look like the tyres are slightly too big although it would help protect the rim better. £10 cheaper and wider does seem like a win win situation to me though

[ARAF]

SturdyHSV said:

....Didn't bother to work it out

Are you trying to tell me that I worked it out because you couldn't be arsed?

[stigmundfreud]

sturdy the adjustment is a simple table change and you can, from memory, calculate it inside the tool itself but ask Richard

or ask tuner B who put a tune on my car with the speedo wildly misrepresented in the tune meaning when I thought I was doing 60 I was doing closer to 70.

[wozzza]

arh1a said:

Has anyone got any pics of 255 mounted on Monaro VXR wheels? Just wondering if it will look like the tyres are slightly too big although it would help protect the rim better. £10 cheaper and wider does seem like a win win situation to me though

They don't really look any different. Bit muddy here but you can at least see the 255 rear compared to the 245 front. Real world, speedo seems completely unaffected it's pretty much spot on. According to the radar signs that show speed and my navigation.

Edited by wozzza on Tuesday 1st July 00:38

Edited by wozzza on Tuesday 1st July 00:39

[ringram]

ARAF said:

SturdyHSV said:

....Didn't bother to work it out

Are you trying to tell me that I worked it out because you couldn't be arsed?

Dont be surprised mate. Most people cant be bothered to use google properly either. The worlds answers existing in there if people can be bothered.

No offence Mr S

[Black VXR]

do need wheel spacers on the front with a fraction wider tyres?

My car needs them to clear the standard tyres and wheels (otherwise it just polishes the paint off the legs (its that close)

[SturdyHSV]

ringram said:

ARAF said:

SturdyHSV said:

....Didn't bother to work it out

Are you trying to tell me that I worked it out because you couldn't be arsed?

Dont be surprised mate. Most people cant be bothered to use google properly either. The worlds answers existing in there if people can be bothered.

No offence Mr S

None taken Mr I, the thread was actually aimed at your good self really, in regards to changing EFI Live tables, I've previously given it a good googling (although I can't remember why...) and eventually found what appeared to be an 'authoritative' answer with a few confirmations of success, but that was related to changing the diff etc.

As is typical of the modern world, it seemed simpler to just ask on here where at least a few people have probably done it and have a log of specifically what had to be changed as opposed to re-googling and then adjusting the relevant pulses per mph field or what have you.

On the other hand, if everyone just googled everything this forum would die

ARAF, it wasn't necessarily I couldn't be bothered, more it just hadn't dawned on me to compare the % difference to then realise there's actually hardly any change at all... So thank you

[wozzza]

Black VXR said:

do need wheel spacers on the front with a fraction wider tyres?

My car needs them to clear the standard tyres and wheels (otherwise it just polishes the paint off the legs (its that close)

How much wider you talking? As the 245/35/19 MPSS on the front actually measure 258mm, according to whoever measured them on here. They fit my stock 19's perfectly fine with no rubbing or spacers etc.

While the rear 255's are around 270mm.

[arh1a]

wozzza said:

They don't really look any different. Bit muddy here but you can at least see the 255 rear compared to the 245 front. Real world, speedo seems completely unaffected it's pretty much spot on. According to the radar signs that show speed and my navigation.

Edited by wozzza on Tuesday 1st July 00:38

Edited by wozzza on Tuesday 1st July 00:39

Thanks for the photo, I agree there is hardly any noticeable difference. Will be changing the fronts and rears over to MPSS 255/35 when they need changing

[Black VXR]

Mine rub (just brush the dirt off) with standard tyres, standard wheels and AP Brakes

I was also advised against going for a larger, wider tyre on the rear only, as it could confuse the wheel speed sensors

arh1a said:

Thanks for the photo, I agree there is hardly any noticeable difference. Will be changing the fronts and rears over to MPSS 255/35 when they need changing

[KMud]

Just fitted my 235/40/18 (i.e., standard CV8 size) PS3s, and you can see the extra width of the Michelins over the Bridgestones.

[wozzza]

arh1a said:

Thanks for the photo, I agree there is hardly any noticeable difference. Will be changing the fronts and rears over to MPSS 255/35 when they need changing

Everyone on here when I asked the same question told me to leave the 245 on the front. With people saying it could negatively impact handling changing the front to a wider tyre.

Black VXR said:

Mine rub (just brush the dirt off) with standard tyres, standard wheels and AP Brakes

I was also advised against going for a larger, wider tyre on the rear only, as it could confuse the wheel speed sensors

Wider on the rear is a good thing, better with a wider tyre these cars already have a tiny rear tyre for the power they are putting down. Plenty people on here running wider tyres. The mini tub guys are running 285's and wider without any issue. You generally keep the rolling radius roughly the same so it make very little impact. In this case the difference between a 245/35 and 255/35 in terms of rolling radius is a little over 1%. So about the same as a part worn tyre.

[ARAF]

SturdyHSV said:

ARAF, it wasn't necessarily I couldn't be bothered, more it just hadn't dawned on me to compare the % difference to then realise there's actually hardly any change at all... So thank you

That was meant as a joke. I'm always happy to put myself out for those (like yourself) who make a contribution to the well being of these cars here, and on other forums.

[arh1a]

wozzza said:

arh1a said:

Thanks for the photo, I agree there is hardly any noticeable difference. Will be changing the fronts and rears over to MPSS 255/35 when they need changing

Everyone on here when I asked the same question told me to leave the 245 on the front. With people saying it could negatively impact handling changing the front to a wider tyre.

Ok thanks for confirming but just thought as they had the same size tyres all round as standard which isn't the best or normal setup for a RWD car it would be ok to have 255 all round.

[wozzza]

I think the front clearance is also smaller, so something to keep in mind.

I have not tried an MPSS 255/35 up front to know if it has any rubbing issues or not though to be honest. Got to keep in mind they are wider than they say they are though if you go for a Super sport.

[jameshsv]

arh1a said:

Thanks for the photo, I agree there is hardly any noticeable difference. Will be changing the fronts and rears over to MPSS 255/35 when they need changing

I don't think its advisable to put 255s on the front.

[arh1a]

wozzza said:

I think the front clearance is also smaller, so something to keep in mind.

I have not tried an MPSS 255/35 up front to know if it has any rubbing issues or not though to be honest. Got to keep in mind they are wider than they say they are though if you go for a Super sport.

jameshsv said:

I don't think its advisable to put 255s on the front.

I will stick to the MPSS 255's on the back then in that case and my OCD can cope with the ever so slight difference in look to get some extra grip on the rear. Wozzza do you happen to have any other photos of the slight difference between the MPSS 245's and 255's mounted to the wheels?

As I have AP brakes and having a puncher on the front tyre would mean swapping the front and back wheels as the space saver will only fit over the rear brakes it would be good to know if MPSS 255's do have enough clearance on the front even it its just to get the car home.