Campaign - Step 2

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tighterse
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Campaign - Step 2

Postby tighterse » Thu Jan 10, 2013 9:08 pm

Tyre pressures on the Ceed are currently 31 all round - checked today.

Assuming I want a 5% increase in rolling radius what increase in pressure do I need (tyres cold). At present the diameter is just under 25" so I need to go up to about 26.25". Tyre size is 205 55 16.
Kia Ceed 1.6 crdi isg Retired undefeated on 25,720 miles and 62.91 mpg overall

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Karl
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Re: Campaign - Step 2

Postby Karl » Fri Jan 11, 2013 9:06 am

Depending on weather conditions I would take them up to the max side wall pressure. This is normally with about 45 or 51 psi.

Not sure how much that would effect the radius as I understand it that they tyres won't expand that much due to the cording and wiring holding them in. Please someone correct me if I'm wrong.
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frv
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Re: Campaign - Step 2

Postby frv » Fri Jan 11, 2013 11:38 am

You are right Karl. Any effect on tyre diameter will be minimal. You need different tyres to get a different diameter.
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MikeMarsUK
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Re: Campaign - Step 2

Postby MikeMarsUK » Fri Jan 11, 2013 3:17 pm

If it *did* affect the radius, it'd be very dangerous to drive since they'd be ballooning out in the centre and you'd only have a tiny contact patch. I've seen chinese budget tyres balloon out, but premium tyres keep their shape.

To get an extra 5% you basically have to go up by two sizes (for example, 175/50 -> 185/55 or 175/60). I went up by a single size, and that gave me +2.7%. If you do go up by 5% or more, you need to be careful that the front tyres do not rub on the inside of the wheelarch at full lock (this can potentially damage brake lines / sensor cables / etc or blow-out the tyre due to wear on the inside edge).


http://www.miata.net/garage/tirecalc.html
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tighterse
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Re: Campaign - Step 2

Postby tighterse » Fri Jan 11, 2013 4:22 pm

I put a yardstick beside the car when I was inflating and, as said, there was no effect on the overall diameter. They are now up to around 37.5 psi and I will run them at that for a while to see what the results are - both MPG and roadholding.

These things take a while with me since my winter mileage is very low. In fact the car hasn't left the drive since Thursday (correction - Tuesday, I think) and is unlikely to move before Monday at the earliest. I've just been told that I will have my standard run next Tuesday so that will give me an early indication although there is a strong possibility of snow next week.
Kia Ceed 1.6 crdi isg Retired undefeated on 25,720 miles and 62.91 mpg overall

Now driving my second Sportage.

Warning. May contain a nut.

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