| Tire(Tyre) Options [message #366199] |
Wed, 18 August 2021 04:45  |
jeff.conlan
Messages: 3
Registered: August 2021
Karma: 0
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I was looking at tyre wheel options for a recently purchased 1978 GMC Motorhome. I see that a 17" Ion rim is possible but the recommend tyre was a 225 75 17
but to my calculation a 245 65 17 would be a better match in terms of rolling radius. I can find no articles or info on anyone ever having fitted this combination to a GMC does anyone here know if this would work?
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| Re: Tire(Tyre) Options [message #366201 is a reply to message #366199] |
Wed, 18 August 2021 09:38  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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First step is to check the load rating on your 17” tire selections to see if they measure up or are eliminated by lower rating. Next issue would be if the rears will rub bags with a 245 section width. Not sure as aspect ratio also interacts. Also are wheels hub centric? If not that rules them out for me, though some will say they are safe as lug centered. No thanks.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Tire(Tyre) Options [message #366204 is a reply to message #366203] |
Wed, 18 August 2021 11:21 |
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Richard RV
Messages: 631
Registered: July 2012
Location: Full-timer for 12 years, ...
Karma: -17
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Senior Member |
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Jeff,
Maximum tire load is at AFAIK specified at maximum tire pressure. Tire pressure should be set based on the actual load on that tire. The correct tire pressure determines the size of the road contact patch and whether the tire will wear evenly.
It's important to weigh all 6 wheels then reference the manufacturer's tire load/pressure chart to determine the correct psi. Weighing your coach also will point out lateral load imbalance. If the lateral load imbalance exceeds 250 pounds in the front or 600 pounds in the rear it will affect handling.
Most all imbalance affects handling, but the GMC's rear air suspension masks the higher/lower corner that would be readily apparent on a non-ride-height-controlled vehicle suspension. That is, you can't see a load imbalance in a GMC. At some of the weigh-ins at rallies we've seen some waaay out of balance coaches.
You may find that 17" tire might require >75 psi to carry the load. That would be a pretty harsh ride I'd reckon.
Richard
'77 Birchaven TZE...777;
'76 Palm Beach under construction;
‘76 Edgemont waiting its turn
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| [GMCnet] Re: Tire(Tyre) Options [message #366205 is a reply to message #366204] |
Wed, 18 August 2021 11:50 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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https://www.gmcrvparts.com/product-p/ap417.htm
The recommended tire is there,
On Wed, Aug 18, 2021 at 9:21 AM Richard wrote:
> Jeff,
>
> Maximum tire load is at AFAIK specified at maximum tire pressure. Tire
> pressure should be set based on the actual load on that tire. The correct
> tire pressure determines the size of the road contact patch and whether
> the tire will wear evenly.
>
> It's important to weigh all 6 wheels then reference the manufacturer's
> tire load/pressure chart to determine the correct psi. Weighing your coach
> also will point out lateral load imbalance. If the lateral load imbalance
> exceeds 250 pounds in the front or 600 pounds in the rear it will affect
> handling.
>
> Most all imbalance affects handling, but the GMC's rear air suspension
> masks the higher/lower corner that would be readily apparent on a
> non-ride-height-controlled vehicle suspension. That is, you can't see a
> load imbalance in a GMC. At some of the weigh-ins at rallies we've seen
> some
> waaay out of balance coaches.
>
> You may find that 17" tire might require >75 psi to carry the load. That
> would be a pretty harsh ride I'd reckon.
>
> Richard
> --
> '77 Birchaven TZE...777;
> '76 Palm Beach under construction;
> ‘76 Edgemonte waiting its turn
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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