Approach Angle
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    1000 Post Club kwschumm's Avatar
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    Approach Angle

    Does anyone know what the approach angle is on a stock GT?

    We're building a new house on a hill and the driveway is fairly steep with nearly a 15% grade.

    I need to know the approach angle so we can design a smooth transition from the street to the driveway so as not to scrape the front belly panel.
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    Just Some Dude in Jersey The Scifi Guy's Avatar
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    I'll try to remember to take that measurement for you today.

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    I was thinking about your post yesterday when I was in the woods with my 4WD. My approach angle on a crossing one way was 35 degrees. Coming back was 55 to 60 degrees. Had to employ the winch and a good load up of engine. WOT. Twas hairy for a min. Sorry to hijack thread. Good luck with driveway. Jarrell
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    Has your car been lowered and/or has a front air dam? Taking the driveway at an angle other than 90° will help but what about the time you forget or someone else drives the GT? You're wise to address it now.

    Not an answer but something else to be considered. I learned the hard way. Slightly lowered and added a front air dam, had to chance my angle of approach pulling off the main road into parking lots.

    Harold

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    Just Some Dude in Jersey The Scifi Guy's Avatar
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    15 degrees

    Here ya go:

    GT Approach Angle 15 degrees (3).jpg GT Approach Angle 15 degrees (1).jpg GT Approach Angle 15 degrees (2).jpg

    I checked all around and measured vertical heights at various locations and took into account that I'm lowered 1" front and rear and have an air dam, etc., etc.. I trimmed my air dam WAY back at the front for just the problem you're trying to remedy. It only protrudes down at the front about 1/2"-1" below the belly pan. I lifted the level 1" to where the front tip of the belly pan is in the pics.

    13-16 degrees, depending on whether you are lowered or normal GT height and whether you measure from directly below the axle or from where the tire actually leaves the ground as I have done it.

    Let's just call it 15 degrees.

    But that doesn't mean that you could simply angle your driveway where it meets the road or driveway apron at, say, 12 degrees and you're good. There's more to it than that. Length of the car, wheel base, shock stiffness, approach angle of the road itself, how long the driveway apron is, whether there is a bump where the driveway meets the road, etc.

    Us Northeasterners have to allow for lots of water drainage, so our roads often slope steeply sideways towards the curb to direct water there. I live in a densely packed row house neighborhood and every square footage on our properties is precious, so we often have short, steep, driveway aprons up to the sidewalks. A couple of years ago my town repaved our street and poured new sidewalks and driveway aprons for everyone. At first glance we thought they had made the driveways too steep and we would all bottom our cars out getting out of our driveways. Here's what they gave us:

    Driveway angle about 5 degrees (1).jpg Driveway angle about 5 degrees (2).jpg

    Doesn't look like much slope does it? It's only about 3-5 degrees off of level. But the street slopes towards the curb at the opposite angle of about 3-5 degrees. That makes a 6-10 degree transition. Sounds like there's plenty of clearance, right? Wrong. There's more factors at play. I had a long and extensive discussion with the road engineer about this driveway apron subject and was surprised at the amount of physics employed in the design. They purposely made the edge of the driveway where it meets the road about 1-2" higher than the road. This causes your car to nose dive upon impact with this bump, but then bounce up. The driveway apron is only 4 feet long from front to rear and then it meets a level sidewalk, then the driveways go uphill at about 5 degrees. We used to have our driveway aprons continue into the sidewalk area. 8 feet, instead of 4 feet, all at a very shallow 3 degree slope. If you road your bicycle down the sidewalk you used to encounter dips at each driveway. Not anymore, now the sidewalk is essentially flat the whole length of the block. When we had the 8 foot long very shallow aprons, we still would crunch the noses of our cars against the road or driveway going in an out of them. Now we're twice as steep and half as long and our cars don't scrape the ground anymore.

    It doesn't sound like it makes sense does it? You bottom out less with a short steep driveway apron than you do when the apron is twice as long and 1/2 as steep. I wouldn't have believed it if I hadn't experienced the difference for myself, but it's true.

    So, does any of this help you or does it make your decision 10 times more complicated. I vote the latter.
    Last edited by The Scifi Guy; 06-22-2019 at 09:48 AM.
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    Thanks for all the information! Very helpful.

    For sure it's more complex than just angles. I've attached a picture of the driveway. It's still gravel, after the build it will be paved and maybe we'll have a chance at flaring it out into the communities private road. Have to check with the neighbors to see if they'd care. It's on a cul-de-sac at the end of the road so they shouldn't care but you know neighbors.

    You're right that it's more complex. The body also changes angles when weight shifts or when tires go over transitions unevenly. My Subaru Baja doesn't scrape going up, but it has going down, and it has a lot more vertical clearance than the GT. My plan was 1" lowered all around with 205/50R15 tires but maybe lowering should be skipped and taller tires needed.

    A wooden model with angle and length adjustable nose would be useful to see how it works in various configurations.
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    GT Owner opelgt722002's Avatar
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    Quote Originally Posted by kwschumm View Post
    Thanks for all the information! Very helpful.

    For sure it's more complex than just angles. I've attached a picture of the driveway. It's still gravel, after the build it will be paved and maybe we'll have a chance at flaring it out into the communities private road. Have to check with the neighbors to see if they'd care. It's on a cul-de-sac at the end of the road so they shouldn't care but you know neighbors.

    You're right that it's more complex. The body also changes angles when weight shifts or when tires go over transitions unevenly. My Subaru Baja doesn't scrape going up, but it has going down, and it has a lot more vertical clearance than the GT. My plan was 1" lowered all around with 205/50R15 tires but maybe lowering should be skipped and taller tires needed.

    A wooden model with angle and length adjustable nose would be useful to see how it works in various configurations.
    We used a wooden model to verify the nose would not scrape. Our driveway had to start at a very slight angle and the angle was increased every ten feet till the middle of the length of the driveway. Then the angle was decreased every ten foot until it reached the parking pad. You must pay attention to the parking pad as much as the street entrance.
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    Bob

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    Quote Originally Posted by opelgt722002 View Post
    We used a wooden model to verify the nose would not scrape. Our driveway had to start at a very slight angle and the angle was increased every ten feet till the middle of the length of the driveway. Then the angle was decreased every ten foot until it reached the parking pad. You must pay attention to the parking pad as much as the street entrance.
    Thanks for the feedback. The driveway climbs and should level out to the parking pad but you bring up an excellent point. The excavator could have other ideas! As far as the lead in I'm not sure we have the luxury of a gradual lead-in. It comes off the road and climbs immediately. It was a lot of work just getting a road that is "only" 15%, any steeper and the fire department would nix the permit. Now I'm worried!

    Maybe I'll need hydraulics like low riders use
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    Just Some Dude in Jersey The Scifi Guy's Avatar
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    The best way to attack a steep slope like that would be at a sideways angle. You could broaden the apron of the driveway where it meets the road, so that you could drive onto and off of your driveway entrance from a sideways angle.

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    Quote Originally Posted by kwschumm View Post
    Thanks for the feedback. The driveway climbs and should level out to the parking pad but you bring up an excellent point. The excavator could have other ideas! As far as the lead in I'm not sure we have the luxury of a gradual lead-in. It comes off the road and climbs immediately. It was a lot of work just getting a road that is "only" 15%, any steeper and the fire department would nix the permit. Now I'm worried!

    Maybe I'll need hydraulics like low riders use
    I didn’t mean to cause alarm. I was just giving an example that it doesn’t have to be a constant angle. My Driveway was not long enough to climb the hill with a constant angle and not scrape the belly pan.
    Bob

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    Quote Originally Posted by The Scifi Guy View Post
    The best way to attack a steep slope like that would be at a sideways angle. You could broaden the apron of the driveway where it meets the road, so that you could drive onto and off of your driveway entrance from a sideways angle.
    I wanted to do that in the first place but it would have meant paving over the water meter
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    Quote Originally Posted by opelgt722002 View Post
    I didn’t mean to cause alarm. I was just giving an example that it doesn’t have to be a constant angle. My Driveway was not long enough to climb the hill with a constant angle and not scrape the belly pan.
    No alarm at all, your input was quite helpful, it's much easier to consider all possible pitfalls than to fall in one.

    The simple fact is that we have to climb 90 feet in elevation in a shorter than ideal distance. We couldn't add switchbacks because that would exceed the amount of non-permeable area the county allows, and we didn't have a more direct route available without breaching a 50' critical slope buffer. The civil engineer advised not to seek a variance for that because we'd spend a lot of money on engineering and they always turn them down anyway. If we can attain a gradual entry off the street the rest should be fine. It's a real PIA to build here. After 3 1/2 years of trying our permit is supposed to be ready "any day now".
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    Your biggest problem is the transition from the road to getting on the driveway slope. Put the entrance at 10° for the first 10 ft. Then start to increase it. As long as you never increase by say more than 13° after that, you're fine. I don't see anything as extreme as that for too long however. In the first 30 ft if you did 10° climb then 12° climb and another 12° climb in 10 ft increments, you'd have climbed 12.5 ft in elevation in 30 ft. That's a pretty steep curved ramp on a driveway but it gives a good way to solve the problem. A curved ramp instead of a fixed grade (sloped) drive way would allow you to gradually work up to the approach angle you need that wouldn't be possible at a straight line.

    How long of a driveway do you have planned and what's the increase in elevation?
    Last edited by Autoholic; 06-22-2019 at 11:07 PM.
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    Quote Originally Posted by Autoholic View Post
    Your biggest problem is the transition from the road to getting on the driveway slope. Put the entrance at 10° for the first 10 ft. Then start to increase it. As long as you never increase by say more than 13° after that, you're fine. I don't see anything as extreme as that for too long however. In the first 30 ft if you did 10° climb then 12° climb and another 12° climb in 10 ft increments, you'd have climbed 12.5 ft in elevation in 30 ft. That's a pretty steep curved ramp on a driveway but it gives a good way to solve the problem. A curved ramp instead of a fixed grade (sloped) drive way would allow you to gradually work up to the approach angle you need that wouldn't be possible at a straight line.

    How long of a driveway do you have planned and what's the increase in elevation?
    From road to top is 90 feet elevation and ~700 feet long to the top. The entire driveway is ~900 feet but the last 200 feet are on the level hilltop. Using these numbers the slope is about 13% but it's not that simple. Coming off the main road the natural terrain *immediately* climbs at 15%, then plateaus, then climbs again. So the combined portions that ascend are shorter than 700 feet. It's much easier to design on a clean sheet of paper than in real life. We could do it easily if we could rearrange all the hills but that's not practical, in time and expense, or allowable by the county. There is a limit on how much soil we can disturb. There's a limit on how much area must remain untouched or impermeable. There's a limit of 15% on the maximum slope on any portion and we're there now. We even made a 15% slope gauge to verify that the slope didn't exceed that number anywhere. There's even more to the expense issue, changing the natural terrain and cutting further into hillsides could result in expensive retaining walls. Spending another 10s of $k on the driveway (after the $70k already spent just to get to gravel) is not within budget. So we're trying to hit a workable compromise while keeping within budget and meeting county requirements.

    We have a preliminary gravel driveway that meets all of the above except the uncertainty about the Opel's approach angle, thus the original question. If I need to enter and exit the driveway at an oblique angle then that is a viable option. Not desirable though, I could easily forget once and crunch it.
    Last edited by kwschumm; 06-23-2019 at 01:56 PM. Reason: Typo
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    My father’s neighbor down in Florida has a Lamborghini. Due to the drainage designs (gated community) the initial driveway slope is rather steep, and he has caused thousands of dollars in damage to the car pulling into the driveway. Rather than constantly repairing the car, he installed an air bag suspension in the front of the car. When he approaches his driveway, he raises the front end height.

    Cheaper than replacing Lambo front bumpers every few months, or planning and executing a variance in the code to get the driveway changed.
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    What about creating something like this?

    https://www.griotsgarage.com/product...xoC6fQQAvD_BwE

    Technically, it’s not permanent and could be a workaround to county ordinance. Something like this rubber ramp could give your driveway the needed transition for your GT if you aren’t allowed to add pavement.

    It might be best to have your GT at standard ride height and run regular tires. Gordo’s GT has less clearance than a stock GT. The best thing to do. Is to measure your GT since it’s your GT at risk.
    Last edited by Autoholic; 06-23-2019 at 11:59 AM.
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    Quote Originally Posted by RallyBob View Post
    My father’s neighbor down in Florida has a Lamborghini. Due to the drainage designs (gated community) the initial driveway slope is rather steep, and he has caused thousands of dollars in damage to the car pulling into the driveway. Rather than constantly repairing the car, he installed an air bag suspension in the front of the car. When he approaches his driveway, he raises the front end height.

    Cheaper than replacing Lambo front bumpers every few months, or planning and executing a variance in the code to get the driveway changed.
    Well that's a possibility for sure. Wonder if anyone has done that with a mostly stock GT before. There certainly seems to be a good amount of hardware available.
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    Also consider that you may have two passengers in the car when you pull it into the driveway, which will lower it a bit more than zero or one passenger. I mention this because my GT doesn’t scrape the driveway with just me in it, but with a passenger it will scrape.

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    Quote Originally Posted by Autoholic View Post
    What about creating something like this?

    https://www.griotsgarage.com/product...xoC6fQQAvD_BwE

    Technically, it’s not permanent and could be a workaround to county ordinance. Something like this rubber ramp could give your driveway the needed transition for your GT if you aren’t allowed to add pavement.

    It might be best to have your GT at standard ride height and run regular tires. Gordo’s GT has less clearance than a stock GT. The best thing to do. Is to measure your GT since it’s your GT at risk.
    Good ideas, thanks. We'll do the best we can with the road and see if that works. Once the county is out of the picture it will be easier to tweak things.

    My GT is currently on a home made dolly with no wheels, and it's in a storage unit until we can get the shop built.
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    Well, I realized I needed to not be lazy and help a forum member out with a good answer to the original question, with a mostly stock GT. My GT is parked in my back yard until I buy a house (hopefully soon) with a garage... and the backyard is all desert so it isn't exactly a place you want to go in the summer. I got a long board out of storage and propped it up till the board went from the base of both tires to the belly pan. Then I measured the angle with my iPhone. I have a level app that gives a very accurate reading. The board did have a slight curve to it - long ways not the short side, but the measurements were 22° for the driver side and 24° for the passenger side. I would round down just to be safe and call it 20°. My GT has aftermarket 16" rims and a stock ride height. I'd say this is pretty close to what a stock GT's approach angle is. The ground was flat however dirt. Oh, and my GT has been sitting for a while so chances are the tires need to be aired up a tad before being driven again. This actually could help a bit here, to simulate 2 people in it as the ride height right now is likely a little lower than if it was in operating condition on asphalt. I'd expect more clearance on a paved road with tires I know are properly inflated, maybe a 1/4" more clearance?
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    Last edited by Autoholic; 06-23-2019 at 05:53 PM.
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