Check my math? Max driveway angles - LotusTalk - The Lotus Cars Community
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post #1 of 37 (permalink) Old 05-30-2008, 03:51 PM Thread Starter
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Check my math? Max driveway angles

Hey guys,

I put in an offer on a house yesterday. The garage is slightly below street level and the driveway is has a pretty sharp, greater than 180 degree angle off the street, ramps down, and then angles less than 180 degrees to flatten into the actual garage. So, something like this:
street____
********\
*********------ garage

Just eyeballing the driveway we knew getting the Lotus in was going to be dubious, so I drove it over and tested it out. No way. I'm going to try to find out if the driveway can be altered in order for the Elise to get in and out sufficiently but needed numbers.

Given a standard (no sport pack) Elise with clearance of 6" (did not account for the car sitting down with a passenger or two... significant?) and a wheelbase of 90.6", I came up with a maximum angle for the top slope of 181.5583 in order for the car not to bottom out in the center.

At the bottom of the driveway, again with 6" clearance and a 32" nose length, I came up with a minimum angle of 168.8514 degrees for the nose not to scrape.

I thought this might be of interest to others, and hopefully someone here can check my math, as it's been a while since geometry in Junior High. That top angle seems too small.

TIA!

Last edited by dana; 05-30-2008 at 03:58 PM.
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post #2 of 37 (permalink) Old 05-30-2008, 04:25 PM
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Quote:
Originally Posted by dana View Post
The garage is slightly below street level and the driveway is has a pretty sharp, greater than 180 degree angle off the street, ramps down, and then angles less than 180 degrees to flatten into the actual garage. So, something like this:
street____
********\
*********------ garage
I have no effin' clue what the heck you're trying to say. Greater than 180 degrees? Do you mean that there's a vertical drop off between the street level and the driveway?


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post #3 of 37 (permalink) Old 05-30-2008, 04:48 PM Thread Starter
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Hmm, I guess I'm not explaining clearly enough.

The driveway slopes down in order for vehicles to get from the street level to the garage level. Flat is 180 degrees, so the angle of the driveway between the street surface and the ramp surface is greater than that. The question is, how large can that angle be before the Elise bottoms out?

The ramp then ends where the flat of the garage begins. The ramp was less than horizontal, so the angle between the ramp's surface and the garage surface is less than 180 degrees. The question is, what is the minimum angle it can be for the Elise not to scrape her little nose?

See this picture here? http://i29.tinypic.com/10cvo0y.jpg
The driveway of the house in question kinda does the opposite -- it goes down instead of up. Hopefully that helps.
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post #4 of 37 (permalink) Old 05-30-2008, 05:25 PM
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This is going to depend on your car. If you have lowered your car at all it is going to change the angle.

An easy way to measure the needed angle:

Get a yard stick (or maybe a two yard stick) and put it up against the front tire. Lift the yard stick up until it touches the front clam. Use another ruler to measure how high the end of the stick is off the ground. You now know the max angle that will almost work (or will with some simple algebra). I'd probably reduce the height by about half and go with that. This assumes you are going UP the driveway to the street. If you are going DOWN the driveway from the street then you will have to take into account the weight of the car pressing down on the front suspension as you go down the 'hill'.

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post #5 of 37 (permalink) Old 05-30-2008, 05:27 PM
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And yes, you can have your driveway modified to make it work.

And yes, with driver and passenger in the car you are going to change the angles.

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post #6 of 37 (permalink) Old 05-30-2008, 05:37 PM
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Quote:
Originally Posted by dana View Post
Hmm, I guess I'm not explaining clearly enough.

The driveway slopes down in order for vehicles to get from the street level to the garage level. Flat is 180 degrees, so the angle of the driveway between the street surface and the ramp surface is greater than that. The question is, how large can that angle be before the Elise bottoms out?

The ramp then ends where the flat of the garage begins. The ramp was less than horizontal, so the angle between the ramp's surface and the garage surface is less than 180 degrees. The question is, what is the minimum angle it can be for the Elise not to scrape her little nose?

See this picture here? http://i29.tinypic.com/10cvo0y.jpg
The driveway of the house in question kinda does the opposite -- it goes down instead of up. Hopefully that helps.
Well I hope yours isnt as steep as that. All the adjustments in the world wouldnt get an elise up that hill.
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post #7 of 37 (permalink) Old 05-30-2008, 06:52 PM
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[QUOTE=dana;1018389]Hmm, I guess I'm not explaining clearly enough.

The driveway slopes down in order for vehicles to get from the street level to the garage level. Flat is 180 degrees, so the angle of the driveway between the street surface and the ramp surface is greater than that. The question is, how large can that angle be before the Elise bottoms out?

The ramp then ends where the flat of the garage begins. The ramp was less than horizontal, so the angle between the ramp's surface and the garage surface is less than 180 degrees. The question is, what is the minimum angle it can be for the Elise not to scrape her little nose?

See this picture here? http://i29.tinypic.com/10cvo0y.jpg
The driveway of the house in question kinda does the opposite -- it goes down instead of up. Hopefully that helps.[/QUOTE

If your driveway looks anything like the picture, then you need a Hummer, not an Elise.

p.s. The ground clearance on an Elise is 5", not 6".

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post #8 of 37 (permalink) Old 05-30-2008, 09:15 PM
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2 sharp angles:

1) street to ramp angle, where you'd be concerned about the breakover angle:


and
2) the ramp to garage angle, where you need to be concerned about the angle of approach & angle of departure:



I thought these terms may be useful, although I'm of no help in actually solving this issue. But I do hope your driveway isn't anywhere as steep as that picture!!!

Cheers,
-Darryl

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post #9 of 37 (permalink) Old 05-30-2008, 09:29 PM
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I really hope that garage has good drainage...that's horrible design (Darn SF hills)

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post #10 of 37 (permalink) Old 05-31-2008, 05:13 AM
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Your math is assuming your car approaches parallel to the driveway...is it wide enough to approach at an angle instead?

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post #11 of 37 (permalink) Old 05-31-2008, 09:07 AM Thread Starter
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Originally Posted by MattG View Post
Your math is assuming your car approaches parallel to the driveway...is it wide enough to approach at an angle instead?
No, unfortunately it's a single car width driveway, with obstructions on either side.

djo: thanks for finding the terminology, that's very helpful.

All: the pic I included is not actually the driveway in question. I was just using it as an example to illustrate the nature of the problem we're facing. I'm about to take my (lowered) Bimmer over there to see if it will make it down the driveway also.

Any ideas on how much it might cost to break up and re-lay about 25 ft^2 of concrete?
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post #12 of 37 (permalink) Old 05-31-2008, 09:51 AM
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Another thing you MUST consider is the speed you are going over at. If going >1.5mph (estimation), the suspension will compress causing the car to bottom out. Many things the Elise CAN clear if driven very slowly, but I guess we're just too impatient or under-estimate the steepness. Guilty as charged.

So to be safe, you should probably alter the driveway to be even lower than you calculated.

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post #13 of 37 (permalink) Old 05-31-2008, 10:37 AM
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Quote:
Originally Posted by Mr. Know View Post
I really hope that garage has good drainage...that's horrible design (Darn SF hills)
+1 I'd hate to have a flooded garage/car/house because the grade around the property slopes TWARDS the house.

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post #14 of 37 (permalink) Old 05-31-2008, 01:16 PM
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To make your discussion clear, do not set "flat" to 180 degrees. Set "flat" to 0 degrees, then reference the angles away from zero, as in "20 degrees down, then 20 degrees back to flat again.

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post #15 of 37 (permalink) Old 05-31-2008, 02:23 PM Thread Starter
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+1 I'd hate to have a flooded garage/car/house because the grade around the property slopes TWARDS the house.
Yep, there's a drain at the seam where the driveway meets the garage; it's pretty standard around here.

Well, we tried more cars this afternoon, and the bimmer can't make it over the top lip, and neither can either of the real estate agents' cars (mini cooper, another bimmer). So it looks like this is something that we're going to have to negotiate to have fixed. Not what I wanted to deal with, but hey, it's not rocket science.
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post #16 of 37 (permalink) Old 06-03-2008, 11:59 AM
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A quick graphical analysis (AutoCAD), using your dimensions, indicates 195.36 deg. and 168.99 deg. respectively.

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post #17 of 37 (permalink) Old 06-03-2008, 12:04 PM
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African or European? Laden or unladen?

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post #18 of 37 (permalink) Old 06-03-2008, 12:59 PM
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Car lift???

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post #19 of 37 (permalink) Old 06-04-2008, 09:04 AM Thread Starter
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Originally Posted by webowser View Post
A quick graphical analysis (AutoCAD), using your dimensions, indicates 195.36 deg. and 168.99 deg. respectively.

Bill Bowser
Awesome! Thank you. What I calculated as the top angle just didn't feel right. I had a contractor come out and quote me $8-900 for a not pretty but workable job, or $2500 + 3 months' permit time and fees for a pretty job. This, I can take.
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post #20 of 37 (permalink) Old 06-04-2008, 09:12 AM
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Are you going to account for suspension compression?

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