Home » Public Forums » GMCnet » Tire size and ride height
| Tire size and ride height [message #253361] |
Thu, 26 June 2014 17:12  |
An87ttype
Messages: 157
Registered: September 2012
Karma: 0
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Senior Member |
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My PO had 245's on 16" Alcoa's when I got the coach. Although they are in great condition, they are now aged out. I am considering going back to 225's for a couple of reasons. One, the speedo is off and it would be nice if it was a little closer to accurate. The other thing is, I think its not running at a high enough rpm with the original FD. I also might want to tow something someday and I think the gearing is especially high with the bigger tires. The thing I do like about the bigger tires are the way the look. They do fill out the wheel well very nicely.
So the question is, the coach will be lower with smaller tires and I wonder if it will effect the ride. I have no idea how the PO originally set the ride height - if at all. Is this something I should be thinking about? Or should I just get the new tires and forget it. It seems like it shouldn't make any difference, but I feel like I should at least ask hive for some feedback. The other thing is, the air bags have been moved up on brackets that allow more space for the larger tire. Should I put them back to the original position?
Thanks all for your thoughts...
1975 Eleganza II
Hudson Valley NY
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| Re: Tire size and ride height [message #253366 is a reply to message #253361] |
Thu, 26 June 2014 17:45  |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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An87ttype wrote on Thu, 26 June 2014 15:12My PO had 245's on 16" Alcoa's when I got the coach. Although they are in great condition, they are now aged out. I am considering going back to 225's for a couple of reasons. One, the speedo is off and it would be nice if it was a little closer to accurate. The other thing is, I think its not running at a high enough rpm with the original FD. I also might want to tow something someday and I think the gearing is especially high with the bigger tires. The thing I do like about the bigger tires are the way the look. They do fill out the wheel well very nicely.
So the question is, the coach will be lower with smaller tires and I wonder if it will effect the ride. I have no idea how the PO originally set the ride height - if at all. Is this something I should be thinking about? Or should I just get the new tires and forget it. It seems like it shouldn't make any difference, but I feel like I should at least ask hive for some feedback. The other thing is, the air bags have been moved up on brackets that allow more space for the larger tire. Should I put them back to the original position?
Thanks all for your thoughts...
The difference in diameter between the 225 and 245 size tires is only about 1-1/2". That means your coach will only sit about 3/4" lower with the smaller tires on it. I wouldn't worry about it too much. Regardless, it would be a good idea to check the ride height after installing the new tires and adjusting it if necessary.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Tire size and ride height [message #253380 is a reply to message #253366] |
Thu, 26 June 2014 19:43 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Senior Member |
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The brackets that were attached to change the position of the air bags changes the ride quality. If you remove them when you put new 225's on, you will need to adjust for ride height also.
With stock gearing and stock engine, I do not see any advantage to the larger tire. JMT
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] Tire size and ride height [message #253427 is a reply to message #253380] |
Fri, 27 June 2014 09:39 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Daryn,
The small tire will give you back your factory 3.07 ratio and raise your rpm back to about 2320 give or take @ 65MPH. The 3.07 ratio is really not the ideal ratio for our motorhomes. The 403 really doesn’t wake up until about 2750 rpm when it gets up on the camshaft. People who still run a 3.07 say the coach really runs good and 75+mph and I really noticed it in our first coach. We live in the Midwest and at the time did mostly flat land driving and went to a 3.55 ration from Jim K. Brought the sweet spot down to 64/65 mph for the motor and the rpm was right about 2750 rpm. The coach would get out and move if need for passing or hills and did not have to struggle as it had before with the 3.07. The 455 motor was somewhat better with the 3.07, but not much. Both motor appreciate the low gearing whether it be 3.55 or 3.70 or 4.10. Presently with the stretch we run a 3.21 final and a 3.50 Manny chain drive for an overall ratio of 3.66 and I can cruise the West without issues.
As for checking your ride height it is alway good practice when making changes to insure best performance. On the stretch is came from the PO with 245s all the way around and it changed my final ratio back to a 3.50ish. When back to 225 on the front to gain back the 3.66, but left the 245 on the rear. The 245s had minor clearance issue with the Buskirk 4 bag suspension and I believe caused a bag failure for the PO. At the last Dothan GMCMI convention we had the coach weighed in it's fully loaded configuration. The per tire weight was under the upper load rating of the 225 tire so when we got back we change the 245s our for 225 on the rear and removed any clearance issues for the rear. This past fall I did a complete ride height adjustment before going to Tucson. It doesn’t matter how the PO adjusted, it is how you do it. There is a good procedure on how to adjust the right height correctly recently but I cannot find it. Anyone what to repost?
JR Wright
GMC Great Laker MHC
GMC Eastern States
GMCMHI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan
On Jun 26, 2014, at 8:43 PM, Thomas Phipps wrote:
> The brackets that were attached to change the position of the air bags changes the ride quality. If you remove them when you put new 225's on, you
> will need to adjust for ride height also.
> With stock gearing and stock engine, I do not see any advantage to the larger tire. JMT
> Tom, MS II
> --
> 1975 GMC Avion
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] Tire size and ride height [message #253432 is a reply to message #253427] |
Fri, 27 June 2014 09:53 |
Bruce Hart
Messages: 1500
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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John,
Is this the procedure you are referring to:
http://www.gmcws.org/Tech/height-align.pdf
On Fri, Jun 27, 2014 at 8:39 AM, John Wright wrote:
> Daryn,
> The small tire will give you back your factory 3.07 ratio and raise your
> rpm back to about 2320 give or take @ 65MPH. The 3.07 ratio is really not
> the ideal ratio for our motorhomes. The 403 really doesn't wake up until
> about 2750 rpm when it gets up on the camshaft. People who still run a
> 3.07 say the coach really runs good and 75+mph and I really noticed it in
> our first coach. We live in the Midwest and at the time did mostly flat
> land driving and went to a 3.55 ration from Jim K. Brought the sweet spot
> down to 64/65 mph for the motor and the rpm was right about 2750 rpm. The
> coach would get out and move if need for passing or hills and did not have
> to struggle as it had before with the 3.07. The 455 motor was somewhat
> better with the 3.07, but not much. Both motor appreciate the low gearing
> whether it be 3.55 or 3.70 or 4.10. Presently with the stretch we run a
> 3.21 final and a 3.50 Manny chain drive for an overall ratio of 3.66 and I
> can cruise the West without issues.
>
> As for checking your ride height it is alway good practice when making
> changes to insure best performance. On the stretch is came from the PO
> with 245s all the way around and it changed my final ratio back to a
> 3.50ish. When back to 225 on the front to gain back the 3.66, but left the
> 245 on the rear. The 245s had minor clearance issue with the Buskirk 4 bag
> suspension and I believe caused a bag failure for the PO. At the last
> Dothan GMCMI convention we had the coach weighed in it's fully loaded
> configuration. The per tire weight was under the upper load rating of the
> 225 tire so when we got back we change the 245s our for 225 on the rear and
> removed any clearance issues for the rear. This past fall I did a complete
> ride height adjustment before going to Tucson. It doesn't matter how the
> PO adjusted, it is how you do it. There is a good procedure on how to
> adjust the right height correctly recently but I cannot find it. Anyone
> what to repost?
>
> JR Wright
> GMC Great Laker MHC
> GMC Eastern States
> GMCMHI
> 78 GMC Buskirk 30' Stretch
> 1975 GMC Avion (Under Reconstruction)
> Michigan
>
> On Jun 26, 2014, at 8:43 PM, Thomas Phipps wrote:
>
>> The brackets that were attached to change the position of the air bags
> changes the ride quality. If you remove them when you put new 225's on, you
>> will need to adjust for ride height also.
>> With stock gearing and stock engine, I do not see any advantage to the
> larger tire. JMT
>> Tom, MS II
>> --
>> 1975 GMC Avion
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
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Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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| Re: [GMCnet] Tire size and ride height [message #253448 is a reply to message #253432] |
Fri, 27 June 2014 14:11 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Thanks Bruce, I had looked in GMCES but not in GMCWS.
JR Wright
GMC Great Laker MHC
GMC Eastern States
GMCMHI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan
On Jun 27, 2014, at 10:53 AM, Bruce Hart wrote:
> John,
> Is this the procedure you are referring to:
>
> http://www.gmcws.org/Tech/height-align.pdf
>
>
> On Fri, Jun 27, 2014 at 8:39 AM, John Wright wrote:
>
>> Daryn,
>> The small tire will give you back your factory 3.07 ratio and raise your
>> rpm back to about 2320 give or take @ 65MPH. The 3.07 ratio is really not
>> the ideal ratio for our motorhomes. The 403 really doesn't wake up until
>> about 2750 rpm when it gets up on the camshaft. People who still run a
>> 3.07 say the coach really runs good and 75+mph and I really noticed it in
>> our first coach. We live in the Midwest and at the time did mostly flat
>> land driving and went to a 3.55 ration from Jim K. Brought the sweet spot
>> down to 64/65 mph for the motor and the rpm was right about 2750 rpm. The
>> coach would get out and move if need for passing or hills and did not have
>> to struggle as it had before with the 3.07. The 455 motor was somewhat
>> better with the 3.07, but not much. Both motor appreciate the low gearing
>> whether it be 3.55 or 3.70 or 4.10. Presently with the stretch we run a
>> 3.21 final and a 3.50 Manny chain drive for an overall ratio of 3.66 and I
>> can cruise the West without issues.
>>
>> As for checking your ride height it is alway good practice when making
>> changes to insure best performance. On the stretch is came from the PO
>> with 245s all the way around and it changed my final ratio back to a
>> 3.50ish. When back to 225 on the front to gain back the 3.66, but left the
>> 245 on the rear. The 245s had minor clearance issue with the Buskirk 4 bag
>> suspension and I believe caused a bag failure for the PO. At the last
>> Dothan GMCMI convention we had the coach weighed in it's fully loaded
>> configuration. The per tire weight was under the upper load rating of the
>> 225 tire so when we got back we change the 245s our for 225 on the rear and
>> removed any clearance issues for the rear. This past fall I did a complete
>> ride height adjustment before going to Tucson. It doesn't matter how the
>> PO adjusted, it is how you do it. There is a good procedure on how to
>> adjust the right height correctly recently but I cannot find it. Anyone
>> what to repost?
>>
>> JR Wright
>> GMC Great Laker MHC
>> GMC Eastern States
>> GMCMHI
>> 78 GMC Buskirk 30' Stretch
>> 1975 GMC Avion (Under Reconstruction)
>> Michigan
>>
>> On Jun 26, 2014, at 8:43 PM, Thomas Phipps wrote:
>>
>>> The brackets that were attached to change the position of the air bags
>> changes the ride quality. If you remove them when you put new 225's on, you
>>> will need to adjust for ride height also.
>>> With stock gearing and stock engine, I do not see any advantage to the
>> larger tire. JMT
>>> Tom, MS II
>>> --
>>> 1975 GMC Avion
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
>
>
>
> --
> Bruce Hart
> 1976 Palm Beach
> Milliken, Co
> GMC=Got More Class
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] Tire size and ride height [message #301192 is a reply to message #301190] |
Fri, 27 May 2016 12:40 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Senior Member |
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225/R16 tire diameter is extremely close to the same as the design 8.75 16.5 bias ply tire. 225 might be better on the rear 4, with 245 on the front. Solve clearance in the rear suspension problem.
Disclaimer, I run 225 on all six wheels.
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: Tire size and ride height [message #301212 is a reply to message #253361] |
Fri, 27 May 2016 21:41 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Ride height is just a ref to measure to get the suspension geometry correct, established with the OE tire size Going larger tires, you would add the Radius increase to the factory spec height. Going to all the same larger tires won't change the relation of the centers of the spindles to the coach.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Tire size and ride height [message #301215 is a reply to message #253427] |
Fri, 27 May 2016 21:51 |
Tom Whitton
Messages: 235
Registered: February 2004
Location: Paducah, KY
Karma: 0
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Senior Member |
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Dave and Mac,
Thanks for setting me straight. Learned something today that I should have known.
Old but still learning,,
Tom Whitton
26 foot updated GMC
Paducah, KY
Date: Fri, 27 May 2016 11:45:14 -0600
From: "Dave Mumert"
To:
Subject: Re: [GMCnet] Tire size and ride height
Message-ID:
Content-Type: text/plain; charset="us-ascii"
Hi
The Static Loaded Radius of the 875-16.5 is 13.8 inches, the 225-75R16 is 13.6 inches. So to be precise you should set it .2 inches
lower.
Dave Mumert
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