Wider lower profile tyres = lower pressure?

Zuma · 20 Mar 2008 at 14:57

If i go from 205 50r15 to 235 35r19 how should i adjust the tyre pressures? do they need to be lowered? i tried searching for a calculator but there don't seem to be any rules for this.

[TW]Fox · 20 Mar 2008 at 15:00

I have nothing to add beyond the fact I'm struggling to think of a car which comes with 15 inch wheels and won't look absolutely ridiculous on 19's.

You are aware its going to cost you 500 quid every time for a set of half decent tyres in this size, yes?

kaiowas · 20 Mar 2008 at 15:01

Are those sizes right, by my reckoning your rolling radius is going to change by a huge amount on those tyres.

GravyMonster · 20 Mar 2008 at 15:06

Thats a 10% increase in rolling radius! :eek:

*Edit*
to keep it *just* within the 3% tolerances you need 235/25 19s... good luck finding them, and if you do I hope you know a good chiropractor.

ethos · 20 Mar 2008 at 15:07

[TW]Fox;11335785 said:
I have nothing to add beyond the fact I'm struggling to think of a car which comes with 15 inch wheels and won't look absolutely ridiculous on 19's.

Haha, I was thinking this also.

InvaderGIR · 20 Mar 2008 at 15:07

kaiowas said:
Are those sizes right, by my reckoning your rolling radius is going to change by a huge amount on those tyres.

Just a bit...

White rings are the old size, black and grey is the new one.

InvG

Zuma · 20 Mar 2008 at 15:53

ok so i didn't explain myself properly in the first post cos i was in a bit of a hurry.

it's not my car, so it's not my problem how expensive the tyres are or how accurate the speedo will be.
but i have fitted the wheels and don't know what to set the tyres to.

for the guessmiesters i will add more clues and wait for you to work out what car it is.

front tyres are 195 60 r15 and the rears are 205 50 r15

think i'm gonna just put them at 28 all round and let the customer work it out for himself.

ethos · 20 Mar 2008 at 15:58

What car is it?

MarkDavis · 20 Mar 2008 at 16:00

Yeah, what car is it?

Confused · 20 Mar 2008 at 16:02

Set the tyres to the same pressure as if it was on the original wheels/tyres.

InvaderGIR · 20 Mar 2008 at 16:04

Confused said:
Set the tyres to the same pressure as if it was on the original wheels/tyres.

That's what I've always done when changing sizes, but thought I'd leave it for someone else to say.

Also I've never done any quite so dramatic changes.

InvG

Jonners · 20 Mar 2008 at 16:10

I used the same pressures when changing from 185/55/15 to 205/40/17

Hawk Tuah · 20 Mar 2008 at 16:16

Hold on. You are a professional tyre fitter, and you're asking a Internet forum of geeks what pressure to inflate them to? :confused:

GravyMonster · 20 Mar 2008 at 16:18

As for the car, I reckon MkIV Golf.

Hawk Tuah · 20 Mar 2008 at 16:19

I reckon its going to be something phat yo..

photoshop · 20 Mar 2008 at 16:24

the tyre pressures (to use) should be written on the inside of the fuel cap, failing that ring the dealer - its only a phone call

GravyMonster · 20 Mar 2008 at 16:30

the problem is though, these aren't OEM wheels, so the details no the flap or in the owners manual are irrelevant and the dealers aren't going to give you an (accurate) answer.

[TW]Fox · 20 Mar 2008 at 16:36

Zuma said:
think i'm gonna just put them at 28 all round and let the customer work it out for himself.

You are a professional and you think that the wrong rolling radius is 'not your problem' and feel its good to ask on OcUK about tyre pressures?

Who do you work for so that we may ensure we never, ever use their services?

Jeez...

I do hope you are not charging your customer for this bodge work?

chrislusty · 20 Mar 2008 at 16:37

I recon it could be an mgf, just put the psi around 30.

Jonners · 20 Mar 2008 at 16:38

Do you work for Halfords?