| Different tire size on front [message #263178] |
Thu, 02 October 2014 15:56  |
An87ttype
Messages: 157
Registered: September 2012
Karma: 0
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Senior Member |
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The PO had 245s on the coach when I got it. I would just like to change the fronts to 225s. I like the way the bigger tires look but I really would like the gearing back. What issues, if any, would be the problem with mixing the sizes?
1975 Eleganza II
Hudson Valley NY
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| Re: Different tire size on front [message #263184 is a reply to message #263178] |
Thu, 02 October 2014 17:20  |
winter
Messages: 247
Registered: September 2007
Location: MPLS MN
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You will lose some caster by raising the rear up with the larger tires unless you readjust the rear ride height.
Or add more caster to the front adjustment.
Or you could also raise your front height to compensate for the difference in tire radius.
I was thinking of doing something similar as i have plenty of 245 take off tires from my truck and plenty of 225 take off tires from my trailblazer. Using those tires keeps new tires on the snow driven vehicles and keeps the rv tires from getting too old.
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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| Re: [GMCnet] Different tire size on front [message #263191 is a reply to message #263184] |
Thu, 02 October 2014 18:20 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
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The rig will compensate for the tire difference if the height control system is in working order.
Todd Sullivan
Sully
77 royale
Seattle
> On Oct 2, 2014, at 3:20 PM, jerrod winter wrote:
>
> You will lose some caster by raising the rear up with the larger tires unless you readjust the rear ride height.
>
> Or add more caster to the front adjustment.
>
> Or you could also raise your front height to compensate for the difference in tire radius.
>
> I was thinking of doing something similar as i have plenty of 245 take off tires from my truck and plenty of 225 take off tires from my trailblazer.
> Using those tires keeps new tires on the snow driven vehicles and keeps the rv tires from getting too old.
> --
> Jerrod Winter
> 1977 Palm Beach
> Green Jelly Bean
> Twin Cities, Minnesota
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: [GMCnet] Different tire size on front [message #263224 is a reply to message #263201] |
Thu, 02 October 2014 21:43 |
sgltrac
Messages: 2797
Registered: April 2011
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So then if the ground under the front or the rear changes why don't you have to change the tires to get the coach to level?
Todd Sullivan
Sully
77 royale
Seattle
> On Oct 2, 2014, at 5:33 PM, A. wrote:
>
> sgltrac wrote on Thu, 02 October 2014 18:20
>> The rig will compensate for the tire difference if the height control system is in working order.
>> Todd Sullivan
>>
>> Sully
>> 77 royale
>> Seattle
> If the rear was correct, it will stay correct. If the front was correct with the oversized tires, it will need to be raised with the smaller tires.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> Perpetually annoyed that "political correctness" and Secular Humanism control every aspect of American life
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: [GMCnet] Different tire size on front [message #263229 is a reply to message #263228] |
Thu, 02 October 2014 22:33 |
sgltrac
Messages: 2797
Registered: April 2011
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If the frame follows would not the weight shift as well corresponding with rear lift which would be registered by the height control linkage and switch in the rear?
Todd Sullivan
Sully
77 royale
Seattle
> On Oct 2, 2014, at 8:23 PM, A. wrote:
>
> sgltrac wrote on Thu, 02 October 2014 21:43
>> So then if the ground under the front or the rear changes why don't you have to change the tires to get the coach to level?
>>
>> Todd Sullivan
>>
>> Sully
>> 77 royale
>> Seattle
> If you don't understand what I am saying, imagine 4' diameter wheels all the way around, then put 2' diameter wheels on the front. The front axle gets
> closer to the ground, the frame at the front gets closer to the ground. Ride height is measured at the frame. The frame will slope forward A LOT.
>
> A 245/70R16 tire is about a tenth of an inch smaller in diameter than a 225/75R16 tire. So that probably wouldn't require any adjustment. But a
> 245/75R16 tire is about 5/8" LARGER in diameter than a 225/75R16 tire. Replacing a 245/75R16 tire with a 225/75R16 tire would put the axle 5/16"
> closer to the ground, and the frame will follow. There's a good chance the pork chop will have to be twisted.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> Perpetually annoyed that "political correctness" and Secular Humanism control every aspect of American life
> _______________________________________________
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: [GMCnet] Different tire size on front [message #263230 is a reply to message #263228] |
Thu, 02 October 2014 22:35 |
sgltrac
Messages: 2797
Registered: April 2011
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So the relative heights from an rear would remain the same but overall heights would be off?
Todd Sullivan
Sully
77 royale
Seattle
> On Oct 2, 2014, at 8:23 PM, A. wrote:
>
> sgltrac wrote on Thu, 02 October 2014 21:43
>> So then if the ground under the front or the rear changes why don't you have to change the tires to get the coach to level?
>>
>> Todd Sullivan
>>
>> Sully
>> 77 royale
>> Seattle
> If you don't understand what I am saying, imagine 4' diameter wheels all the way around, then put 2' diameter wheels on the front. The front axle gets
> closer to the ground, the frame at the front gets closer to the ground. Ride height is measured at the frame. The frame will slope forward A LOT.
>
> A 245/70R16 tire is about a tenth of an inch smaller in diameter than a 225/75R16 tire. So that probably wouldn't require any adjustment. But a
> 245/75R16 tire is about 5/8" LARGER in diameter than a 225/75R16 tire. Replacing a 245/75R16 tire with a 225/75R16 tire would put the axle 5/16"
> closer to the ground, and the frame will follow. There's a good chance the pork chop will have to be twisted.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> Perpetually annoyed that "political correctness" and Secular Humanism control every aspect of American life
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: [GMCnet] Different tire size on front [message #263244 is a reply to message #263239] |
Fri, 03 October 2014 01:42 |
sgltrac
Messages: 2797
Registered: April 2011
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Apparently one or both of us is a retard I guess. I have two different tire sizes on The pig. Four tires are the same size as each other and two tires are the same as each other but not the same as the other four. One set ( pair) has a smaller od which is visibly apparent. I can run the smaller diameter tires on the front with a detectable difference in low end snap and a higher engine rpm at the same hi way speed as when two of the larger mounted wheels ( same size wheels but different diameter tires) are in the front. The coach otherwise handles the same and auto levels the same. I can also trade that pair to the front set of the rear bogies and gain lower rpm for a given speed with a corresponding lack of snap with no noticeable change in coach attitude/ handling. So what am I missing?
Todd Sullivan
Sully
77 royale
Seattle
> On Oct 2, 2014, at 9:10 PM, A. wrote:
>
> sgltrac wrote on Thu, 02 October 2014 22:35
>> So the relative heights from an rear would remain the same but overall heights would be off?
>> Todd Sullivan
>>
>> Sully
>> 77 royale
>> Seattle
> This whole discussion is based on the proposal to leave oversized tires on the rear and replace the oversized tires on the front with OEM size tires.
> Did you miss that part?
>
> If the ride height was correct front and rear with oversized tires all around, the FRONT WILL DROP WITH SMALLER DIAMETER TIRES on the front and the
> rear will not change. When the front axle gets closer to the ground, the front frame gets closer to the ground.
>
> Fronts do not self adjust.
>
> Did you miss that or are you just messing with me or are you having that much trouble understanding this?
>
>
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> Perpetually annoyed that "political correctness" and Secular Humanism control every aspect of American life
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: [GMCnet] Different tire size on front [message #263254 is a reply to message #263244] |
Fri, 03 October 2014 08:44 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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G'day,
I'm confused too! There are three areas to address:
1) Road Gear Ratio
2) Ride Height
3) Alignment
1) Road Gear Ratio - I think everyone would agree that going from 225 tires to 245 tires would result in a higher gear ratio which
in turn would result in slower acceleration and lower RPM at highway speed.
2) Ride Height - since the 245 tires have a larger diameter changing the front tires from 225 would change the ride height requiring
the ride height to be reset by changing the setting on the torsion bars. When it comes to the rear tires I believe it would be
necessary to reset it as well, none of the systems would do it automatically. When you set the rear ride height the ride height
valves (pneumatic or electronic) control the pressure to the bags which sets the height. The valves do not check the distance from
frame to the ground. Therefore if you put larger diameter tires the frame will move up you will have to adjust them.
3) Alignment - I'm not 100% sure of this but a larger diameter tire on the front end may require an alignment after the ride height
is reset; maybe yes, maybe no, if I did the swap I'd check the alignment.
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
USA '75 Avion - Double Trouble TZE365V100426
AUS '75 Avion - The Blue Streak TZE365V100428
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Todd Sullivan
Sent: Friday, October 03, 2014 1:43 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Different tire size on front
Apparently one or both of us is a retard I guess. I have two different tire sizes on The pig. Four tires are the same size as each
other and two tires are the same as each other but not the same as the other four. One set ( pair) has a smaller od which is
visibly apparent. I can run the smaller diameter tires on the front with a detectable difference in low end snap and a higher
engine rpm at the same hi way speed as when two of the larger mounted wheels ( same size wheels but different diameter tires) are in
the front. The coach otherwise handles the same and auto levels the same. I can also trade that pair to the front set of the rear
bogies and gain lower rpm for a given speed with a corresponding lack of snap with no noticeable change in coach attitude/ handling.
So what am I missing?
Todd Sullivan
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Different tire size on front [message #263263 is a reply to message #263244] |
Fri, 03 October 2014 10:20 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Senior Member |
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sgltrac wrote on Fri, 03 October 2014 01:42Apparently one or both of us is a retard I guess. I have two different tire sizes on The pig. Four tires are the same size as each other and two tires are the same as each other but not the same as the other four. One set ( pair) has a smaller od which is visibly apparent. I can run the smaller diameter tires on the front with a detectable difference in low end snap and a higher engine rpm at the same hi way speed as when two of the larger mounted wheels ( same size wheels but different diameter tires) are in the front. The coach otherwise handles the same and auto levels the same. I can also trade that pair to the front set of the rear bogies and gain lower rpm for a given speed with a corresponding lack of snap with no noticeable change in coach attitude/ handling. So what am I missing?
Todd Sullivan
Sully
77 royale
Seattle I see what you are saying. The rear adjusts the angle of the frame and the swing arms to remain the same. So if you start with correct ride height (which puts the front 1-13/16" higher than the rear) with OEM sized tires, then change the wheel size on the front or the back, the rear will adjust to maintain that orientation, and the front will still be 1-13/16" higher than the rear. In other words, if you raise or lower the front, the rear will follow.
But the ride height will be higher all around with the larger wheels, or lower all around with smaller diameter wheels, because the rears will adjust to keep the rear 1-13/16" lower than the front. So handling is substantially not affected.
But if you want correct ride height (and not just maintain the DIFFERENCE in height front to back), the front will need to be adjusted if you go from same size tires all around to different size tires on the front than the back.
A 5/8" diameter difference would be 5/16" in distance from axle to ground. If you shuffle the different sized tires front to back like you do, that cuts that difference in half again. Given the hysteresis in the front end, you might not even be able to measure the difference in your case.
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