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Old 05-16-2018, 09:31 AM   #1
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Tyre Inflation vs Handling

This is just a theory:

When the pressure in a tyre is reduced the contact patch is enlarged. The total dynamics of the rolling tyre start where the “rubber hits the road”. As such one half of the increase in the contact patch length is added to the mechanical trail there by increasing the straight line stability in the same manner as increasing the caster angle.

(Mechanical Trail is the moment arm between the steering pivot point (fore) and the center of the contact patch (aft))
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Old 05-16-2018, 10:24 AM   #2
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Bad theory. Contact patch is only one small part of the equation. Pounds per square inch come into play, sidewall pressure is a major factor in stability and under inflated tires add a lot of heat to the tire which will increase your pressure anyway, a severely deflated tire will just heat up and fail. This is the quick version but the take home is that your tire was designed to run at a certain PSI and that is where the tire should be set. Only in extreme conditions (racing) can you go outside the recommended pressures because of the extreme heat and pressures you are putting the tires through.
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Old 05-16-2018, 12:14 PM   #3
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Quote:
Originally Posted by Harvard View Post
This is just a theory:

When the pressure in a tyre is reduced the contact patch is enlarged. The total dynamics of the rolling tyre start where the “rubber hits the road”. As such one half of the increase in the contact patch length is added to the mechanical trail there by increasing the straight line stability in the same manner as increasing the caster angle.

(Mechanical Trail is the moment arm between the steering pivot point (fore) and the center of the contact patch (aft))
With bigger footprint would you not increase the foward distance equal to the rear distance leaving the pivot point the same as original? Also to low of pressure is bad. Pressure should be where tire mfr recommends for actual weight on tire.
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Old 05-16-2018, 01:30 PM   #4
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Never really thought about it!

But from experience, low tire pressure = sway or poor handling. fully inflated equals excellent handling.
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Old 05-16-2018, 01:31 PM   #5
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Run fronts at 75 psi and rears at 80 psi and all is good.

If you have your rig weights measured you might could drop your fronts to 70 or 72 psi without any problem.

If max pressures for your tires is 80 psi your not going to hurt anything running 70 psi if your not overloaded. The fronts of class C’s with gas engines like the Greyhawk run light on the front so 70-75 psi should not be a problem. That said have your MH weighed!

I wouldn’t go any lower than this because of what others have posted. Always run your rears at max psi!

Reducing your speed will have the greatest impact on handling. 60-65 seems to be the sweet spot for me. As speed increases handling decreases.

Slow down and enjoy yourself. Your drives will be less stressful and arrival time not that much more.
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Old 05-16-2018, 01:47 PM   #6
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Originally Posted by cabinetmaker View Post
Run fronts at 75 psi and rears at 80 psi and all is good.

If you have your rig weights measured you might could drop your fronts to 70 or 72 psi without any problem.

If max pressures for your tires is 80 psi your not going to hurt anything running 70 psi if your not overloaded. The fronts of class C’s with gas engines like the Greyhawk run light on the front so 70-75 psi should not be a problem. That said have your MH weighed!

I wouldn’t go any lower than this because of what others have posted. Always run your rears at max psi!

Reducing your speed will have the greatest impact on handling. 60-65 seems to be the sweet spot for me. As speed increases handling decreases.

Slow down and enjoy yourself. Your drives will be less stressful and arrival time not that much more.
Have it weighed but run at the max?

Weighed yes. Max maybe. Use the sticker from the coach manufacturer as a starting point.

P.S. We don't claim to be automotive engineers, but we did stay at a Holiday Inn last night.
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Old 05-16-2018, 02:09 PM   #7
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Have it weighed but run at the max?

Weighed yes. Max maybe. Use the sticker from the coach manufacturer as a starting point.

P.S. We don't claim to be automotive engineers, but we did stay at a Holiday Inn last night.
Sticker on Greyhawks says 80 psi rear which is max. Your Seneca has bigger tires and may not be needed at max on the rears like regular class C’s.

Have it weighed to determine front pressure not rear. Run rears always at 80psi which is max on a Greyhawk.

Weighed will help make sure your not overloaded on the rear and will help with determination of front tire pressure.

Greyhawks and Seneca’s are two completely different animals.
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Old 05-16-2018, 03:24 PM   #8
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Sticker on Greyhawks says 80 psi rear which is max. Your Seneca has bigger tires and may not be needed at max on the rears like regular class C’s.

Have it weighed to determine front pressure not rear. Run rears always at 80psi which is max on a Greyhawk.

Weighed will help make sure your not overloaded on the rear and will help with determination of front tire pressure.

Greyhawks and Seneca’s are two completely different animals.
They are vastly different but share the same name.

P.S. You may want to white out the VIN from your stickers as these are public forums.
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Old 05-16-2018, 03:32 PM   #9
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They are vastly different but share the same name.

P.S. You may want to white out the VIN from your stickers as these are public forums.
I checked before I posted and VIN is not shown on the Ford one as I only posted the end where tire info was and the Jayco one VIN number I thought was blurred beyond recognition so I felt ok posting them. Looks like the Jayco one is somewhat visible.

Yea, you can’t be too careful in this crazy world today!
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Old 05-16-2018, 06:50 PM   #10
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Norty1 helped me out and deleted those attachments showing my VIN. Here they are again this time no VIN’s showing.

Notice factory says 75 psi front and 80 psi rear.
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