Different profile tyres front and back...how bad?

[ian_cab28]

Girlfriend took Chrysler PT Cruiser to have new rear tyres fitted. Turns out the tyres on the front are the wrong profile (205/50/16) and not the 205/55/16 they should be. Tyre man suggested this might have been done for aesthetic reasons to make rear ride slightly higher. WTF !

However now we have the correct size on the front, and the lower profile ones on the back (I suggested this anyway for wear reasons but tyre man also thought it better to put them to the back too)

So in short 55 profile front. 50 profile rear, good tread. How bad is this, doesn't look too noticeable. She's no ayrton senna but will this shift the oversteer/understeer balance and or stability under braking.

Less than ideal obviously but worth chucking away a decent set of 50 profiles to even it up.

Thoughts???

[LeoSayer]

I would recommend reading your insurance policy documents closely before driving any further.

[Presuming Ed]

Wouldn't worry about it. Just means the cars slightly less comfy now.

[slinky]

6.4cm difference in circumference, 2.05cm difference in diameter..

I don't think it'll make an appreciable difference to handling on a PT Cruiser, but I'm no authority on that...

[EDLT]

[PH Tyre snob] You will definitely be killed to death as soon as you look at the car. Go and buy the most expensive tyres you can find right now[/PH Tyre Snob]

Otherwise, it'll be fine.

[300bhp/ton]

LeoSayer said:

I would recommend reading your insurance policy documents closely before driving any further.

Why have they already told the insurers what size tyres where on the car when they bought it, or have the insurers been out to inspect the car first?

[ian_cab28]

Re: slinky's comments. Thanks for the maths was going to do the same myself as I understand the widths are identical at 205mm the profile ratio change has come off the sidewall height and overall diameter of the tyre/alloy. I guess if it was 4wd or had sophisticated dynamic stability control (only has abs) then it might be a issue and upset things a bit more.

I guess at 9/10ths and above it would be noticeable with less slip angle at rears vs fronts or something but it rarely goes above 5/10ths :-)

Thanks for advice, think we'll keep them. re: insurance, well it was sold like that and we didn't realise, not anticipating a speed related accident... any write off /assessor inspection more likely to stem from low speed spatial awareness issues !

[J4CKO]

Would love to see a PT Cruiser at 10/10ths

Doubt it will make any appreciable difference, I suspect even on a track with different sets of tyres available to try you would be hard pushed to notice even driven back to back, the good tread/decent brand part of the argument is the most important.

[marcosgt]

Any corner is 10/10th in a PT Cruiser.

Even straights are a challenge!

M

[reggie82]

300bhp/ton said:

LeoSayer said:

I would recommend reading your insurance policy documents closely before driving any further.

Why have they already told the insurers what size tyres where on the car when they bought it, or have the insurers been out to inspect the car first?

Are you sure that's good advice?

I would presume it is the drivers responsibility to ensure the tyres are the correct size? I'm guessing the only thing that would mean it's not a problem is that the insurance company would have a hard time proving that the tyres contributed to the accident (if that even matters) - you can bet they'll argue it though!

[slinky]

ian_cab28 said:

Re: slinky's comments. Thanks for the maths was going to do the same myself as I understand the widths are identical at 205mm the profile ratio change has come off the sidewall height and overall diameter of the tyre/alloy. I guess if it was 4wd or had sophisticated dynamic stability control (only has abs) then it might be a issue and upset things a bit more.

I guess at 9/10ths and above it would be noticeable with less slip angle at rears vs fronts or something but it rarely goes above 5/10ths :-)

Thanks for advice, think we'll keep them. re: insurance, well it was sold like that and we didn't realise, not anticipating a speed related accident... any write off /assessor inspection more likely to stem from low speed spatial awareness issues !

No worries, I built a calculator a while back whilst doing some excel tinkering, it's evolved into something a tad larger now, with gearbox ratio calculations and all sorts.. Feel free to drop me a line via my profile if you want a copy..

[slinky]

Figured I'd stick that calculator online, tis here : http://dl.dropbox.com/u/8021077/Tyre_Calculator.xl...

[ian_cab28]

Talking of 9/10ths in a pt cruiser....had a massive oversteer moment when entering my works business park at lunchtime. Was rushing back in a making progress kind of way.... although I have never really driven the car much before, entered the business park onto a block paved road, bit greasy today, massive tail out slide/45 degree drift until it came back !!! . no feel of understeer or front loading up at all.

A little worried by this either different grip from back to front, or sidewall height difference having an impact or me driving more like a k**b than I thought I was. Shall find a quite place and test again. Not happy if limits are so low that mild enthusiasm results in such a squeaky bum episode.

[Caulkhead]

It's the insurance implications that would concern me.

http://www.honestjohn.co.uk/askhj/answer/20078/dif...