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 Post subject: High clearance locost
PostPosted: October 1, 2018, 1:17 pm 
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Location: Spencer WV
Hello everyone,

Been lurking for years. Great site with lots of good info.

I've been thinking about a Locost for years. Used to live in NE Ohio in the city - back then I didn't have the garage space.

Now I have plenty of garage space, but am in very rural West Virginia. I drive a lot these days with around a 45 minute commute.

Probably 75% of my driving is on 55mph rural routes. Paved, curved, heckuva lot of fun. Problem is, the other 25% is on one-lane dirt/gravel, including our road that also has some pretty steep hills, mud, ruts and, in the winter, ice. We have a '13 Escape with AWD and wide tires, and a good part of the winter and spring, we can't get it down our road both due to the wide tires and the lack of ground clearance. Other two vehicles are an 00 Sierra 4wd and my DD which is an 01 Cherokee (also 4wd). I didn't have the Cherokee last winter - the truck was able to get up and down the road, although sometimes tire chains were required. I have some more aggressive tires for the Cherokee and am hoping they will get me by (but I will have tire chains in back just in case)

Despite both of the 4wd vehicles having essentially the same type of drivetrain, the Cherokee is far more competent. I attribute this to the lack of weight compared to the truck - the truck really gets stuck easily. That's what had me looking into a lightweight platform. The jeep has straight live axles. I have put urethane bushings on the Cherokee, and for what it is, it handles pretty well on the twisty roads, but I'd like to build something a little more competent on the pavement that I can still get to and from home. It also rides pretty hard. Looking for lightweight plus independent suspension also brought me back to the Locost idea.

My first thought was to build a typical Locost, and then add some sort of suspension lift (hydraulic/air) to get the clearance i'd need. But you can imagine what that does to the camber with a typical setup, especially going from, say 4" ride height to 8" ride height. Not to mention the CV joint angles, which over time, are going to end up in that raised position quite a bit of time.

Then I started thinking about how much I could accomplish simply with wheels and tires. The Cherokee has 235/75r15s on it, which are pretty tall, narrow and are available in pavement-friendly, all-terrain, and mud-terrain versions. It's also a very common size in the area since we have a lot of Cherokees running around and this is the largest size that will fit without a lift. Having two cars with the same size tires/wheels also has some benefit, especially if I was able to match the bolt pattern.

Been playing with vsusp with some of the suspension configs I found on the web, especially the car9, and found just putting those wheels/tires on the various models gets me a pretty respectable ride height - about 7" to get the camber close to the original setting at 3.6 ride height. That keeps the CVs within their normal range, keeps all the suspension out of the weeds for the most part.

The Cherokee has about 9" to the bottom of the differential and suspension brackets - about 12" to the bottom of the axle tube. I haven't measured the truck yet. Neither has ever bottomed out on our road. I'm thinking 7-8" might be good enough with a belly pan/skid plate as insurance. Maybe some sort of mild lift system that would add an inch or two would be worth adding for the worst times.

Suspension design is not my forte, but I'm a pretty decent googler. There's not a lot of info out there on setting up suspension for a high-clearance, vehicle with tall/narrow tires other than for fully offroad. For example, should I manipulate the control arm mounting points and lengths to get the roll center back down closer to the ground? How much camber change should I be shooting for during compression? Or is just raising the existing suspension with taller tires pretty sufficient for a road-going vehicle? Should I build it with the clearance I need, or try to design a suspension that keeps reasonable camber throughout a long travel and lift it when I need and then lower when I don't? It seems there are plenty of SUVs out there with pretty high clearance and they're not rolling off the side of the road (for the most part) due to terrible geometry. Seems something more sporty with the same clearance should be attainable? Not that they handled all that well, but the early cars had some pretty good ground clearance for the same reasons I need it.

This isn't something I want to race. The goal is for something that's fun to drive and does better on-road than our other 4wd vehicles, which, just with lower CG alone, seems like it should be doable. That's kind of a low bar and I'd like to do better if possible. It doesn't make sense to invest the time in a car build if I can't at least drive it most of the year, nor if it isn't safe. If I have the clearance, drivetrain and tires, I don't think traction will be a problem off the pavement. It's getting that setup to work on pavement reasonably well that is perplexing me.

I know this way off the beaten path but I was hoping maybe someone had some thoughts on if this is doable and where I might head next in terms of research and design. Maybe someone's thought along the same lines before? Any thoughts/ideas/suggestions appreciated.


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PostPosted: October 1, 2018, 2:59 pm 
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Joined: June 15, 2010, 8:29 am
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Maybe take a look at this for some inspiration.
https://www.arielmotor.co.uk/nomad/
Others on this site have built At-om clones and so you should be able to glean what you need frame-wise from those builds.

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PostPosted: October 1, 2018, 3:42 pm 
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Location: Spencer WV
JPS Europa wrote:
Maybe take a look at this for some inspiration.
https://www.arielmotor.co.uk/nomad/
Others on this site have built At-om clones and so you should be able to glean what you need frame-wise from those builds.


I thought I'd tried every possible search term and never came across that. Pretty neat. I will look into that Nomad further...


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PostPosted: October 1, 2018, 4:03 pm 
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try this out https://www.locostusa.com/forums/viewto ... 18&t=18025
Or google "off road lotus 7"

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PostPosted: October 2, 2018, 4:29 am 
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trialsmangasgas wrote:
Or google "off road lotus 7"

You might also Google 'Troll T6':

Image

Several of the very early Lotuses were dual-purpose trials cars, of course, and while UK trials cars have become very specialised indeed, they're still not a million miles away from the Lotus 7 in design.

The Troll was probably the best (least specialised) dual-purpose road/trials car of recent years, and was very well regarded for its road behaviour.


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PostPosted: October 2, 2018, 8:00 am 
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Joined: June 21, 2010, 9:02 pm
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Location: Spencer WV
Thanks for the great suggestions. Have a lot more research to do now...


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PostPosted: October 2, 2018, 8:21 am 
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The T6 has quite a few similarities with the Locost/7 chassis.

Image

You could pretty easily mistake it for a Locost.

Image


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PostPosted: October 3, 2018, 11:38 am 
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Found this old (ca 1990s) Top Gear video on youtube. It's mostly about trial racing but the first few minutes are about the Troll

https://www.youtube.com/watch?v=yPPXXn9UZ98

around 1:44 or so, it says the Troll has a 10" ground clearance, which sounds about right for what I'm looking for, and "handles brilliantly on tarmac" according to the talking head.

I've yet to find any specifics on the suspension config. I may have to result to a ruler and some photos and see if I can get close enough to put it through vsusp or some other software and see what results.

Of course, the 1990s were a couple decades ago, but at least it's a starting point to figure out what worked then and go from there.


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PostPosted: October 3, 2018, 4:06 pm 
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I've played around with the idea of a Troll like Seven. It probably would be easier to get inspected (at least around here) than a Nomad, as it would be quite period correct. The biggest issue would be sourcing the wheels and tires. To get any ground clearance, you would need a 18" or 19" wheel that also has to be narrow enough to match the car. They are available, but very pricey. http://www.rallyamerica.com/Street_Rod_Wire_Bare.html
Tires can be found here: https://www.cokertire.com/excelsior-comp-h.html But again, nothing Locost
The suspension geometry would not have to be much different, it would be more dictated by your choice of rear end and front frame width. Sway bars (roll bars) would be helpful to control body roll, with a softer spring rate and higher ground clearance, but that's easy to do.
I think it be a great project. :cheers:

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PostPosted: October 4, 2018, 10:30 am 
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I would think there would be plenty of off-road tires that you could get in relatively reasonable sizes and still use a "typical" locost donor style wheel. Something like this maybe? Could still use a 14 or 15" wheel.

I really like the idea of this!

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PostPosted: October 4, 2018, 1:10 pm 
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I think your original thoughts are on the right path, and would probably try not overthink it too much beyond that.

Plenty of 7's (including Caterham's) have oil pans hanging lower than the frame and run up to 6" or so for frame clearance because of it. Probably the most common tire sizes have around a 23" diameter. So if you don't let the oil pan hang below the bottom of the frame and trade up to common 215/75-15 or 235/75-15 all-terrain tires, then that should immediately put you in the 8-9 inch clearance range without even changing anything else in the suspension.

The roll centers moving up with the sprung mass should be fine, and will mostly just help keep body roll in check. The only real geometry concerns I'd see are scrub radius decreasing and trail increasing in the front. Running a lower offset wheels should correct the scrub radius, and the mechanical trail increase shouldn't cause any significant issues. Obviously there are a few other (potential) tire to body/frame considerations to watch out for, but that just means a bit of planning ahead.

Alternatively...Jeep Cherokee donor? :mrgreen:

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PostPosted: October 4, 2018, 2:52 pm 
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Driven5 wrote:
I think your original thoughts are on the right path, and would probably try not overthink it too much beyond that.

Plenty of 7's (including Caterham's) have oil pans hanging lower than the frame and run up to 6" or so for frame clearance because of it. Probably the most common tire sizes have around a 23" diameter. So if you don't let the oil pan hang below the bottom of the frame and trade up to common 215/75-15 or 235/75-15 all-terrain tires, then that should immediately put you in the 8-9 inch clearance range without even changing anything else in the suspension.

The roll centers moving up with the sprung mass should be fine, and will mostly just help keep body roll in check. The only real geometry concerns I'd see are scrub radius decreasing and trail increasing in the front. Running a lower offset wheels should correct the scrub radius, and the mechanical trail increase shouldn't cause any significant issues. Obviously there are a few other (potential) tire to body/frame considerations to watch out for, but that just means a bit of planning ahead.

Alternatively...Jeep Cherokee donor? :mrgreen:


I haven't decided on uprights yet, although leaning towards front S-10 blazer all the way around or Solstice. I like that the Solstice are aluminum, but I also like that the the blazers come off a vehicle designed for 4wd. Blazers also came with 15" wheels IIRC. I think the stock Solstice brakes require a 16" wheel minimum (although there are obviously workarounds). Thinking I should maybe have longer control arms to preserve turning radius with larger diameter tires. I'll have to draw it out first.

I do plan on using the Cherokee xfer case. I have the NP242 in mine which has a differential to give what is essentially AWD and then has full time 4wd, full time 4wd lo and 2wd. I rarely, if ever, run mine on the differential, but it doesn't have enough power to spin the rear wheels unless I'm in a situation were 4wd makes sense. That could be different in a lighter vehicle with more power.

Still undecided on the drivetrain, but I'm leaning towards the Cadillac 4.9 because of the light weight and simple design, mated up to an AR5 out of a Colorado pickup.

But, at least in my mind, the drivetrain is the easy part. The rest of the package needs to be sorted in my head first.


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PostPosted: October 5, 2018, 4:16 pm 
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The original Mk1 Lotus 7 had a full 6" of ground clearance. It also had a nearly-flat bottom like a VW Beetle.

The Beetles got a good reputation as off-roaders, not so much for ground clearance, but that the flat bottom didn't get hung up on rocks or other obstructions. The 1970 model was rated at 6.3".


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PostPosted: October 5, 2018, 4:33 pm 
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For tires you could run a 235/80/17, that's a pickup size that has decent availability and is about 31" tall. It's the tallest skinny tire I found a few years ago when I was looking for my pickup. Tires that tall are fairly heavy though.
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PostPosted: October 7, 2018, 9:38 am 
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turbo_bird wrote:
For tires you could run a 235/80/17, that's a pickup size that has decent availability and is about 31" tall. It's the tallest skinny tire I found a few years ago when I was looking for my pickup. Tires that tall are fairly heavy though.
Kristian


I've wondered about going with a larger wheel. I think I can fit more than adequate brakes under a 15" wheel so anything above that would have to be driven by other reasons. To a certain extent, a tall sidewall makes sense in my application, both for the additional height and also to protect the rim going through ruts and rocks. I'm undecided on aluminum vs steel wheels too. Aluminum cracks while steel dents but aluminum is lighter. But the taller the sidewall, the less of a factor that becomes and this isn't a rally car - when I go over rough terrain, I slow down, if only because it just beats my suspension to heck and then I'm underneath changing suspension bits sooner than I need.

Does the weight become better or worse having a larger wheel vs a taller sidewall for a given overall diameter and is that calculus different on aluminum vs steel?


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