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Two K5 questions

I work in a 12 story building. Seems when I look over the side at the all the cars in the parking lot, the ass ends all look narrower than the fronts. Trucks more than cars, cause you can watch the bed sides get closer together near the tailgate.

I always thought it was to help them track straighter on the freeway. Regardless, I can stuff my rear tire inside the wheel well :D Not sure I could if it was 1.5" wider per side :)
 
Not sure of the official names of why it does what it does when the rear is narrower.

However it does, when I put the van rear end in my Burb the turning radius increased, noticeably.
 
I was told to use wheel spacers if I wanted them to match in width but that sounds like one more thing to go wrong to me. I do like the idea of both wheel wells being filled the same amount but really dont want two different offsets or anything so I guess I will not worry about it. Thanks for all the post. PG
 
Has anyone ever measured the wheelwell openings front and rear, with the body off?

I'm running one of the 14SF's that is "as wide" as the front, but looking at it, the rear tires stick out further than the front. As GM advertised the 1981 body design as being more aerodynamic, I'm curious to know if they tapered the body front to rear. It is obviously better to keep the tires tucked in for aerodynamics, but I also notice a lot more junk is thrown off the tires onto the body with the wider rear, and it's only ~1.5" per side.

Turning radius may be better because the tires had more wheelwell clearance than if they were tucked in closer...they can be turned further before needing stops.
 
The front being wider isn't really what helps turning radius. It's more of a stability thing. The only thing a wider front helps is to keep the tires off the framerail when turned at full lock.

What helps turning radius is the narrower rear. The farther you can move the tires inboard, the closer you move the pivot point to the centerline of the truck. Theoretically, if you moved the tires all the way in and could turn the front wheels infinitely, the truck would basically rotate on the centerline of the rear diff. Obviously, that's not practical. Just trying to explain the point.
 
rebelgregory said:
The front being wider isn't really what helps turning radius. It's more of a stability thing. The only thing a wider front helps is to keep the tires off the framerail when turned at full lock.

What helps turning radius is the narrower rear. The farther you can move the tires inboard, the closer you move the pivot point to the centerline of the truck. Theoretically, if you moved the tires all the way in and could turn the front wheels infinitely, the truck would basically rotate on the centerline of the rear diff. Obviously, that's not practical. Just trying to explain the point.
Click to expand...

This still doesn't make sense. If I could turn the front wheels infinitely, I could rotate around the centerline of the rear diff no matter how wide the wheels were spaced (I'm playing with my Erector set racecar at the moment to demonstrate it to myself).

I'm not seeing the connection yet. :dunno:
 
rebelgregory said:
The front being wider isn't really what helps turning radius. It's more of a stability thing. The only thing a wider front helps is to keep the tires off the framerail when turned at full lock.
Click to expand...

If you inboarded the front wheels 1.5" (to match the rear), aren't we in agreement that turning radius would be increased?

Excluding all other variables, if you can't turn the wheels as far, your turning radius increases. Am I missing something?
 
It's not the easiest thing to explain, but I'll try.

Inboarding the front wheels will only hurt turning radius if the angle the front wheels can achieve is affected because they now interfere with the frame. Turning radius is technically hurt by a wider front axle since it is "officially" measured from the center of the outer front wheel while turning. But this is negligible for what we're talking about. Bottom line - A vehicle with a wide front with the wheels turned at 45deg will turn at the same arc as a vehicle with a slightly narrower front axle with the wheels at 45deg.

However...

Keep the front wheels at 45deg and now start narrowing the rear axle. The inside rear wheel is considered the 'pivot wheel'. The closer the pivot wheel is to centerline of the vehicle, the closer the centerline of the vehicle is to center of the turning circle. Voila, reduced turning radius. This is true in any circumstance until you reach the point where the pivot wheel goes stationary or starts to go backwards. At that point the vehicle is truly turning on itself and axle width is irrelevant. (Perhaps the infinite wheel turning thing was a bad example in my previous post)

On K5s, the short wheelbase is the biggest advantage to turning radius. However the shorter the wheelbase, the sharper the difference you get by playing with axle widths. That's one reason why a matching-width axle on the rear will have a noticeable difference in turning radius.

I'm an engineer, and I don't mean that in a "trust me, I'm an engineer" kind of way. I just overthink mundane stuff like this until it makes sense to me. I used to see everybody post that it helps turning radius, but nobody would explain why. I finally drew it all out in CAD one night until I understood it. I may not be explaining it well, and who knows, I could be wrong. But I think it's worth understanding if for no other reason than knowing what effect modifications will have...so continue to bring on the questions.
 
I'm glad somebody brought this up. I noticed that the rears on m Blazer looked narrower and thought I had wheels with wrong backspacing.

It is much more noticeable with the pizza cutter wheels than it is with the beefy BFG AT's
 
Yeah I don't expect that it's a massive amount of difference, and it is more interesting to think about the reasoning than it is necessary to know. :)

You'd have to figure compression into the clearance at full lock, and the maximum tire diameter used. Even then I'm sure they designed a margin of error into that clearance.
 
As far as the narrow front end goes it was always my understanding that it is that way for tracking. Not so much on highway but more along the lines of dirt road in wet weather. The front of our trucks are a bit heavier than the rears and can cut a deeper grove in a wet dirt road. With the rear being narrowed it allows the rear drive tires to find purchase on ground that has not been rutted, or at least less rutted? And to not drive the weight of the rig deeper.

It may have an offset with the turning radius to make it tighter rather than making the rear wider to have the same track. The engineers had two options and narrowing make have helped in the steering capabilities rather than "needing 40 acres to turn this thing around".
 
rebelgregory said:
It's not the easiest thing to explain, but I'll try.

Inboarding the front wheels will only hurt turning radius if the angle the front wheels can achieve is affected because they now interfere with the frame. Turning radius is technically hurt by a wider front axle since it is "officially" measured from the center of the outer front wheel while turning. But this is negligible for what we're talking about. Bottom line - A vehicle with a wide front with the wheels turned at 45deg will turn at the same arc as a vehicle with a slightly narrower front axle with the wheels at 45deg.

However...

Keep the front wheels at 45deg and now start narrowing the rear axle. The inside rear wheel is considered the 'pivot wheel'. The closer the pivot wheel is to centerline of the vehicle, the closer the centerline of the vehicle is to center of the turning circle. Voila, reduced turning radius. This is true in any circumstance until you reach the point where the pivot wheel goes stationary or starts to go backwards. At that point the vehicle is truly turning on itself and axle width is irrelevant. (Perhaps the infinite wheel turning thing was a bad example in my previous post)

On K5s, the short wheelbase is the biggest advantage to turning radius. However the shorter the wheelbase, the sharper the difference you get by playing with axle widths. That's one reason why a matching-width axle on the rear will have a noticeable difference in turning radius.

I'm an engineer, and I don't mean that in a "trust me, I'm an engineer" kind of way. I just overthink mundane stuff like this until it makes sense to me. I used to see everybody post that it helps turning radius, but nobody would explain why. I finally drew it all out in CAD one night until I understood it. I may not be explaining it well, and who knows, I could be wrong. But I think it's worth understanding if for no other reason than knowing what effect modifications will have...so continue to bring on the questions.
Click to expand...

Thanks! That was exactly what I was looking for. Thanks for making the distinction between having forward motion on the rear wheel and letting it run backwards (as I was doing yesterday with my model). Our trucks can't turn sharply enough to enter this mode of transit, so they are always operating with forward motion on all wheels (and subject to the width effects described above). I am starting to see downsides to running the inboard wheel backwards, now that I think about it, so it is making sense now that they would try to avoid that condition.


rebelgregory said:
I'm an engineer, and I don't mean that in a "trust me, I'm an engineer" kind of way. I just overthink mundane stuff like this until it makes sense to me. I used to see everybody post that it helps turning radius, but nobody would explain why. I finally drew it all out in CAD one night until I understood it. I may not be explaining it well, and who knows, I could be wrong. But I think it's worth understanding if for no other reason than knowing what effect modifications will have...so continue to bring on the questions.
Click to expand...

I'm also an engineer. I also overthink mundane stuff like this until it makes sense. And that's what prompted the question. :thumb:

(You did a great job explaining that concisely, BTW)
 
For those who have switched to wider rear axles, how much difference have you noticed? I swapped my suburban from stock 10-bolt to G3500 14bff van axle (2" wider on each side, IIRC), but I haven't directly noticed the difference yet. But it does seem to swing wider than my K10, despite having a shorter wheelbase. :dunno:
 
I can't tell a difference really. It seems like I scrub sometimes, but I've got a gov-lock so no telling if it might bind up every once in awhile.
 
campfire said:
I'm also an engineer. I also overthink mundane stuff like this until it makes sense.
Click to expand...

It can be an affliction sometimes for us left-brainers. Something piques our interest, the brain goes all "COMPUTING...COMPUTING...COMPUTING", and it tends to become a mission until it clicks. Such is life.
 
rebelgregory said:
campfire said:
I'm also an engineer. I also overthink mundane stuff like this until it makes sense.
Click to expand...
It can be an affliction sometimes for us left-brainers. Something piques our interest, the brain goes all "COMPUTING...COMPUTING...COMPUTING", and it tends to become a mission until it clicks. Such is life.
Click to expand...

I hear ya. It's not all bad, but it can be annoying... :doah:
 
campfire said:
For those who have switched to wider rear axles, how much difference have you noticed? I swapped my suburban from stock 10-bolt to G3500 14bff van axle (2" wider on each side, IIRC), but I haven't directly noticed the difference yet. But it does seem to swing wider than my K10, despite having a shorter wheelbase. :dunno:
Click to expand...
I don't notice any difference. The way I look at it is the vehicle pivots around a line drawn through the rear axle. It doesn't matter if it has 1 rear wheel or 2 wheels 10 feet apart. I think the turning radius depends on the wheel base and the angle the front wheels will turn. I wish I had measured the turning radius before I swapped axles to know for sure.
steering-turning.jpg
 
Maybe someone with rear wheel spacers could measure the turning radius and then remove the spacers and measure it again to settle this debate. :whistle:
 
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