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PostPosted: March 28, 2011, 11:09 am 
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I've sourced a Miata rear subframe/arms/uprights/etc, and I've narrowed it (the subframe itself) by 9.5", giving me 49" rotor to rotor. My challenge is now that I've tacked my car's rear frame rails and subframe mounts into place; at ride height, I'll get 2.25" MAX bump travel before I get frame-on-suspension interference. It took some frame notching and upper control arm notching to get to this point (the car will sit pretty low)...

So the question is- is 2.25" bump (and conversely about 2.25 droop- 4.5" total travel) "enough" travel for a very small 1300# car? I ask because I have no idea what the stock Miata suspension was designed to give, and although it would be a ton of work, I'm at a place where if I need more travel, I'd better rip it all out and fix it now..- is 4" to 5" total travel common for street cars??

Two additional thoughts.. my axles will now be very short, limiting my permissable travel, and in the big picture I'm just trying to get this little car enough travel so that it's not constantly bottoming out (it will be a BEC daily driver).

Thanks- ccrunner

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PostPosted: March 28, 2011, 11:23 am 
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If I remember correctly the stock miata only had about 3" to begin with. Someone else will chime in that is more familiar.

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PostPosted: March 28, 2011, 3:01 pm 
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Seems plenty to me.


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PostPosted: March 28, 2011, 3:12 pm 
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4.5" is twice what I consider the minimum total travel for me to have functioning kidneys. ..
That and maybe 3.5-4" of static ground clearance and you should be good to go.
You're more likely to compress the suspension than extend it in normal street use and even a lifted inside tire is controllable to a degree, just lean really far over like its a catamaran :lol:

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PostPosted: March 28, 2011, 3:17 pm 
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I would think 4.5" total (more specifically 2.25" bump) would be enough too, but I've been spending a lot of time in the off-road world where you want more more more travel.. Then as I started mocking this thing up, I got to wondering how much total travel was originally engineered into a typical streetcar (in my case Miata) to begin with?! As it sits, I've got about 5.5" of ground clearance.. I don't want to go too much lower..

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PostPosted: March 28, 2011, 3:59 pm 
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I'm planning for 2" of bump and 1" of droop, at a 4.5 inch ride height. So sounds like you should have enough. Obviously you don't want your full bump to have a chance of contacting the frame, so give yourself a little room for error.


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PostPosted: March 28, 2011, 5:04 pm 
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You didn't tell us how you planned on using the car.

My autocross-only Lotus had one inch of bump and one inch of droop that was limited by shock length and ground clearance. I could have change the spring rates and ride height and run as much as 3 inches of bump and 2.5 inches of droop, but the 1+1 was appropriate for it's planned use.


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PostPosted: March 28, 2011, 6:04 pm 
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modernbeat wrote:
You didn't tell us how you planned on using the car.

ccrunner wrote:
(it will be a BEC daily driver).


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PostPosted: March 28, 2011, 6:28 pm 
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gtivr4 wrote:
I'm planning for 2" of bump and 1" of droop...

I agree, but it's a bad idea for the shocks to serve as the suspension limiter and have them crash into their stops. 2" of compression is fine, but you need at least another 0.5" for a bump rubber, 1" is better. 5"-stroke shocks are a good starting point.

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PostPosted: March 29, 2011, 12:12 am 
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ccrunner wrote:

So the question is- is 2.25" bump (and conversely about 2.25 droop- 4.5" total travel) "enough" travel for a very small 1300# car? I ask because I have no idea what the stock Miata suspension was designed to give, and although it would be a ton of work, I'm at a place where if I need more travel, I'd better rip it all out and fix it now..- is 4" to 5" total travel common for street cars??


Thats about perfect for daily street cars or you could go to about 2" bump that includes a 1" bump stop which gives you 1.5" of bump total (allowing for rule of the thumb 50% compression of the bump stop) for sportier driving (lowered car of course). This would leave you with 2.5" of droop which would be excellent - don't underestimate the importance of droop for street use as so many people do. Too much can be not so good for the race track but thats the race track, streets have bumps, potholes, varying cambers and undulations to be dealt with. You don't want less than 4" total for street use if you want to retain pleasantness and comfort. Sit the car on it's shocks without springs but bump stops in place and you should have about 1" clearance.

Don't forget that the rubber in you mounting eyes (if have rubber) also give 50% compression and that is part of your travel.


gtivr4 wrote:
I'm planning for 2" of bump and 1" of droop, at a 4.5 inch ride height. So sounds like you should have enough. Obviously you don't want your full bump to have a chance of contacting the frame, so give yourself a little room for error.


If I was running such short travel I would at least be dragging the floor on the road to get some advantage, you have the worst of both worlds there. I use 1/2" as "room for error" on road cars and zero on track cars then add my bump rubbers and have very seldom bottomed out. Unless your going to do a lot of racing increase you droop travel or you'll get bored with the lack of ride comfort and topping out fairly quickly. You can add leather straps or return assist springs to limit droop on track days anyway if required.


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PostPosted: March 29, 2011, 12:28 am 
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My opinion (and it's just my opinion) is to have almost as much bump travel as you have ground clearance. If your chassis is 4" off the ground - have just less than 4" of bump travel.

Having driven (and raced) cars and trucks with not enough bump travel, I aim for as much as I can give it. You can always shim that extra travel away if you want, but it's really hard to add more if you need it. You have nothing to gain by limiting your bump travel to such a wee amount.

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PostPosted: March 29, 2011, 9:43 am 
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Do the math - or at least jack up the car - to see how much droop there actually is. How much the shock lets the suspension extend (droop) has nothing to do with the actual operation of the spring. If the spring rattles loose at 1" of droop it makes no sense to design in any more than that. Having 2" of droop might sound good, but with the shock falling loose at 1" bad things will happen when hitting bumps. The car will like a rock - with no spring to slow it - until it finally reaches the spring and starts to compress it. And there's a good chance that when it does, the spring won't magically line up with the spring perch, causing suspension weirdness due to the sudden spring offset.

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PostPosted: March 29, 2011, 10:36 am 
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KB58 wrote:
Do the math - or at least jack up the car - to see how much droop there actually is. How much the shock lets the suspension extend (droop) has nothing to do with the actual operation of the spring. If the spring rattles loose at 1" of droop it makes no sense to design in any more than that. Having 2" of droop might sound good, but with the shock falling loose at 1" bad things will happen when hitting bumps. The car will like a rock - with no spring to slow it - until it finally reaches the spring and starts to compress it. And there's a good chance that when it does, the spring won't magically line up with the spring perch, causing suspension weirdness due to the sudden spring offset.


Indeed great safety advice and thats why all good race, rally and fast road cars have assistance in the form of either double springs or internal return springs. This allows you to determine where the car settles at while maintaining droop without the main spring flopping out. You see people tie wiring (or a zillion zip ties) their springs to the upper and lower perches sometimes too, seems to work for them - when you go to droop the spring stays with the perches and extends.

Droop is a serious requirement for good handling in normal everyday road encounters, not just comfort but that is a bonus. Droop for racing cars almost totally went away there for a while but modern raised track corner perimeter curbing has seen it come back some.

Don't have to judge on my mumbles, simply run your own test, go get some form of strapping, best is an old seat belt strap, limit your droop to zero and go for a drive and see what you think. Those doing Xcross and track days may actually like it, you car will turn in quicker and get more bite on the outside on cold tyres - stay of the curbs though.


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PostPosted: March 29, 2011, 12:31 pm 
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I never said to limit droop to zero...

Once the spring isn't positively loaded, the traction generated by the unsprung mass of the tire, wheel, and upright is basically zero. If the spring is wired to the perch to limit droop, once the suspension droops more than the springs natural length, the spring is now lessening the tire load even further. Said another way, in droop the spring is trying to lift the tire off the road. So I guess I'm digging in my heals, that once droop passes the point of full spring extension, any more is a waste and actually lessens traction.

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PostPosted: March 29, 2011, 1:56 pm 
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KB58 wrote:
I never said to limit droop to zero...


Didn't mean to imply you did, I quoted your post for the safety tip. I suggest people should try it for themselves though as it's easy to do.


KB58 wrote:
Said another way, in droop the spring is trying to lift the tire off the road. So I guess I'm digging in my heals, that once droop passes the point of full spring extension, any more is a waste and actually lessens traction.


Wow, thats one strange post and entirely and utterly untrue if you live on a Planet with gravity, inertia plays a bit part as well.

May I suggest you have a coffee and consider it for a bit.


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