Riddle me this???? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Suicide-D · 01-28-2003, 10:16 PM

I put different tires on my 68 tonight. I put my 31 x 11.50's on it, replacing 235/75/15's... I increased the contact patch on the ground by atleast half...here's the interesting part. The truck has no power steering... all manual... THE TRUCK DRIVES BETTER. Why? it is easier to turn and it just feels better. even backing up wasn't near as hard? I didn't eat Wheaties for lunch and I don't think I beefed up any over the course of the day... Am I mistaken that bigger tires = more resistance, harder turning??? I'm not complaining... just kinda miffed.

wxman1 · 01-28-2003, 11:13 PM

Ok...I'll take a shot at this! (I knew that college physics
course would come in handy one day)

If the truck weighs...say...4000 lbs and the contact patch
on the old tires was 5" wide and 7" long then it was 35 sq inches.
If we assume that the 4000 lbs is equally distributed to each
wheel (well...its not quite equal...but close enough) then the
pressure of the tire on the ground would be 1000/35 or
roughly 28 lbs/sq in. Now if the contact patch for the new
tires is twice as big then that means the pressure is now
1000/70 or roughly 14 lbs/sq in. If the coefficient of friction
is roughly the same, then it seems to me that the bigger
tire would require less effort to turn. I'm assuming that
both the old and new tires were radials.

Ok...I'll quit now. My brain is tired.

Jim M.
Mt Juliet

Crank · 01-28-2003, 11:32 PM

Yea. What he said.
Brandon

Suicide-D · 01-28-2003, 11:34 PM

now I feel like I have an answer. Well I agree it is easier to turn.

Thanks

Longhorn Man · 01-29-2003, 12:47 AM

While I don't have the education to argue with wxman's physics, I'll blame it on tire compound and tread pattern/depth.
I cant see any way that a bigger tire would not be harder to turn. More rubber = more traction...other wise we'd be putting skinney tires on the back for more traction when we get to the drag strip.
Were your old tires bald? Did they have a lower PSI rating? Did they have steel belts hanging out?
I just don't see it being easier...esp since I have taken 31 10.50's off of the front of a 69 GMC long bed and installed 205/75's on it and it was like adding power steering.

Suicide-D · 01-29-2003, 01:09 AM

the old tires(BFG Radial T/A's) had tons of tread they were dry rotted pretty bad...so they might be harder? The 31's are General Grabber ST's and are a couple of years old but not many miles... It has been my experience to the contrary also...this is a first... thats why I am looking for the PS bracket for the v6?

Longhorn Man · 01-29-2003, 01:25 AM

I haven't forgotten about you on that.
By the way, do you need the pump too? Or just the brackets? It may have some kind of sill looking pump that is not the typical GM deal.
Also, i can sand blast it and paint it for a couple extra bucks if you like.

70 Jimmy · 01-29-2003, 01:46 AM

What about this: You have more contact patch to "help" the direction you want the tire to go. It's similar to pushing a heavier object on wheels and trying to stop it. It wants to keep going more than a lighter object. Once you start the turning process, the tire helps out. Of course all this is moot if your parked. I would say it's harder to turn while parked.

Longhorn Man · 01-29-2003, 01:57 AM

Except that the geomitry of a vehicles front end is to go back to center...well, all vehicles except mine...mine wants to pull into a ditch and gt totaleed. She's suicidal.

Crank · 01-29-2003, 07:49 AM

Yea. See to me the bigger tires are more rotating mass. It's just like when you throw in a lighter crank in your engine it frees up hp. But not you are throwing in more rotating mass and getting more power. Did you change the rims to aluminum or anything? Maybe the new tires are lighter????
Brandon

72C10chevy4x4 · 01-29-2003, 08:04 AM

here is my stab at it, I believe it has to do with the tires. the tires you placed on have a stiffer sidewall so there's less flex. the old ones definitely had a 'mushy' sidewall-turn the wheel and the contact patch is still in the same position-then it slowly makes it's way to the point of less resistance. the other explanation is air pressure-you're new tires can probably handle more air pressure then the old ones (especially if they are LT tires-as in load range E).

01-28-2003, 10:16 PM	#1
Suicide-D Registered User Join Date: Jan 2001 Location: Katy, TX...but the love of my life resides in Dublin,OH. Posts: 1,408	Riddle me this???? I put different tires on my 68 tonight. I put my 31 x 11.50's on it, replacing 235/75/15's... I increased the contact patch on the ground by atleast half...here's the interesting part. The truck has no power steering... all manual... THE TRUCK DRIVES BETTER. Why? it is easier to turn and it just feels better. even backing up wasn't near as hard? I didn't eat Wheaties for lunch and I don't think I beefed up any over the course of the day... Am I mistaken that bigger tires = more resistance, harder turning??? I'm not complaining... just kinda miffed.

01-29-2003, 01:46 AM	#8
70 Jimmy aka Crusher, Crushergmc Join Date: Mar 2000 Location: Oregon Posts: 1,834	What about this: You have more contact patch to "help" the direction you want the tire to go. It's similar to pushing a heavier object on wheels and trying to stop it. It wants to keep going more than a lighter object. Once you start the turning process, the tire helps out. Of course all this is moot if your parked. I would say it's harder to turn while parked. __________________ "KEEP IT DOWN!" 70 Jimmy 454 2wd 56 GMC Big Window "It's funny till someone gets hurt, then it's freakin' hilarious"

01-28-2003, 11:13 PM	#2
wxman1 Senior Member Join Date: May 2002 Location: mt juliet, tennessee, usa Posts: 237	Ok...I'll take a shot at this! (I knew that college physics course would come in handy one day) If the truck weighs...say...4000 lbs and the contact patch on the old tires was 5" wide and 7" long then it was 35 sq inches. If we assume that the 4000 lbs is equally distributed to each wheel (well...its not quite equal...but close enough) then the pressure of the tire on the ground would be 1000/35 or roughly 28 lbs/sq in. Now if the contact patch for the new tires is twice as big then that means the pressure is now 1000/70 or roughly 14 lbs/sq in. If the coefficient of friction is roughly the same, then it seems to me that the bigger tire would require less effort to turn. I'm assuming that both the old and new tires were radials. Ok...I'll quit now. My brain is tired. Jim M. Mt Juliet

01-28-2003, 11:32 PM	#3
Crank Registered User Join Date: Aug 2002 Location: Crittenden, KY Posts: 1,965	Yea. What he said. Brandon

01-28-2003, 11:34 PM	#4
Suicide-D Registered User Join Date: Jan 2001 Location: Katy, TX...but the love of my life resides in Dublin,OH. Posts: 1,408	now I feel like I have an answer. Well I agree it is easier to turn. Thanks

01-29-2003, 12:47 AM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	While I don't have the education to argue with wxman's physics, I'll blame it on tire compound and tread pattern/depth. I cant see any way that a bigger tire would not be harder to turn. More rubber = more traction...other wise we'd be putting skinney tires on the back for more traction when we get to the drag strip. Were your old tires bald? Did they have a lower PSI rating? Did they have steel belts hanging out? I just don't see it being easier...esp since I have taken 31 10.50's off of the front of a 69 GMC long bed and installed 205/75's on it and it was like adding power steering.

01-29-2003, 01:09 AM	#6
Suicide-D Registered User Join Date: Jan 2001 Location: Katy, TX...but the love of my life resides in Dublin,OH. Posts: 1,408	the old tires(BFG Radial T/A's) had tons of tread they were dry rotted pretty bad...so they might be harder? The 31's are General Grabber ST's and are a couple of years old but not many miles... It has been my experience to the contrary also...this is a first... thats why I am looking for the PS bracket for the v6?

01-29-2003, 01:25 AM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	I haven't forgotten about you on that. By the way, do you need the pump too? Or just the brackets? It may have some kind of sill looking pump that is not the typical GM deal. Also, i can sand blast it and paint it for a couple extra bucks if you like.

01-29-2003, 01:57 AM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Except that the geomitry of a vehicles front end is to go back to center...well, all vehicles except mine...mine wants to pull into a ditch and gt totaleed. She's suicidal.

01-29-2003, 07:49 AM	#10
Crank Registered User Join Date: Aug 2002 Location: Crittenden, KY Posts: 1,965	Yea. See to me the bigger tires are more rotating mass. It's just like when you throw in a lighter crank in your engine it frees up hp. But not you are throwing in more rotating mass and getting more power. Did you change the rims to aluminum or anything? Maybe the new tires are lighter???? Brandon

01-29-2003, 08:04 AM	#11
72C10chevy4x4 UK Wildcat Fan! Join Date: Oct 2002 Location: Dover, DE Posts: 515	here is my stab at it, I believe it has to do with the tires. the tires you placed on have a stiffer sidewall so there's less flex. the old ones definitely had a 'mushy' sidewall-turn the wheel and the contact patch is still in the same position-then it slowly makes it's way to the point of less resistance. the other explanation is air pressure-you're new tires can probably handle more air pressure then the old ones (especially if they are LT tires-as in load range E).



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