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Rake for Spec Miata?

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#1
Flyntgr

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I have read Jim Daniels' set up guide till I can almost quote it verbatim, but one question lingers: on my '99 SM, should I have a small amount of rake for my flat-as-a fitter CW race track? I have spoken to several guys who say rake helps the car turn-in, and God knows our track at NOLA needs a car to have great turn-in, or "hand it up".

I have been running 4 7/16th all around, but am considering 1/8" rake in front (4 5/1 6" each side) with 4 7/16" rear on both sides. Our turns are fast, and turn-in is very important at our track. As I said, the track is FLAT all the way around.

Can you tell me what works for you on such a track: either 1.8 miles or 2.9 miles?
By the way, cross weight is 50.6%. We have more right turns than left, and the most important turns are rights. It is CW ONLY. Thank you. Flyntgr

#2
FTodaro

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In general, running rake in your car, all things equal will loosen up the rear and thus make the car turn better, until its too lose and then make the rear end slide out to much. My point there is go to the track with what ever the ride height, and make adjustments till it feels right.

When I do a set up for a track, in my mind that set up is a starting point for the weekend, if I am lucky, I will hit it right on. I am just not that lucky.

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#3
Danny Steyn

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Flyntgr, its all a matter of personal preference. I prefer to de-rake my '99 for most tracks, seems to suit me better.

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#4
Jim Drago

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I have been running 4 7/16th all around, but am considering 1/8" rake in front (4 5/1 6" each side) with 4 7/16" rear on both sides. Our turns are fast, and turn-in is very important at our track. As I said, the track is FLAT all the way around.


We call that the Texas Chopper look :)

Never been anywhere that I felt that was advantageous, more often than not people incorrectly try to add rake in the car to cover up for another handling issue they don't realize they have. You need not move too much higher or lower in rear, more than 1/4 difference, you probably starting to get off into an area you would probably would be better off not going IMO.

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#5
DrDomm

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Flyntgr, its all a matter of personal preference. I prefer to de-rake my '99 for most tracks, seems to suit me better.


Danny, does that mean "no rake" or "negative rake"?
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#6
Flyntgr

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Okay, I'll put it back to 50% CW and 4 7/16" all around. How's that for a setup?

#7
FTodaro

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Not trying to be a smart ass but I have no idea, you either have to have the attitude that you will go to the track with that set up and try it and adjust from that point or go find one of the fast guys in the paddock who will help you and find out there base line.

Do you make adjustments at the track?

There are two camps out there, those who adjust on the car and those that don't.

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#8
Danny Steyn

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Danny, does that mean "no rake" or "negative rake"?


Negative rake - higher in the front than in the rear - I give up a bit on corner entry in order to get to WOT sooner
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#9
Flyntgr

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I do make adjustments at the track if the car isn't handling well, but we have several important turns which require entry at speed. Our Ss are similar to Road Atlanta (though our track is flat, so no down-hill runs like RA), so running all-out is important there. I need to have good entry in order to do that. Honestly, my best runs are without rake, but I haven't given rake a chance with proper alignment, including correct camber and caster settings. I had bent rear control arms that I had to diagnose and repair while getting my best time without adequate camber in rear. With those repairs made, I'll in the future use my own string, camber gauge at track (they arrive tomorrow), but it's hard to find a really level spot in our parking areas. I'll try to use the floor in the main maintenance building for that purpose.

But headed to the track I want to have the absolute best guessed setup entering the track so I can concentrate on driving more than wrench turning.

#10
Jim Drago

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I sent you an email.. Too much to say on forums. All those 1.6 guys might learn something :spin:

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#11
davew

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My opinion. Adjust your rake at the rear. You can go up or down one full turn on the rear without effecting toe. Any change in the front will effect toe.

Take your best shot in the shop. Run a session, raise the car, see if you like it. Then lower the car, see what you think.

The car driven 100% with a wildman mentality will want something totally different than a 90% driver with a smooth style.

Dave
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#12
ChrisA

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When setting rake at the shop, are you doing it with the fuel tank full, 1/2 or near empty? Then, when at track at track changes are made for handling adjustments, what level is the tank? Do you want to make them when you are carrying more weight at the beginning of the race or when near empty, as you should be near the end of the race? Or does it not change enough with fuel load to even matter?

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#13
Muda

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Funny how the guys who go in faster and deeper need less rake.
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#14
SaulSpeedwell

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My $0.04:

All the rules of thumb and Carroll Smith comments on rake, "ride height", and roll center are either irrelevant, misleading, or plain wrong for an SM. Unlike every "real" racecar in the world, an SM is simultaneously oversprung, underdamped, and most important - starved for "shock travel".

Forget rake (and the meaningless pinch weld measurements that don't take into account chassis twist vs. the subframes or whether you are running 0/32" Toyos, much taller 4/32" Hoosiers or 8/32" rains) and start paying attention to your individual shock travels.

If you hit the bumpstop sooner or harder, at that moment that wheel end is much "stiffer" until you get back off the bumpstop. During those moments, the car will act like any other car would if you stiffened that corner (or that end).

I can't stress enough how much this effect DOMINATES the SM's chassis behavior - more than alignment, more than shocks, more than swaybars, more than anything but tires and % cross, I'd say.

Try +2 turns in the back, and then try -2 turns in the back. If you want extra credit, have some slotted urethane discs in various thicknesses made that your pit guy can slide onto the shock shaft to change shock travel quickly without altering anything else. It isn't illegal to use them for practice and test days and you'll learn more in one test session than anything the Internet commentariat could ever tell you. (I didn't invent this great idea, I just copied it ... ).

I've found myself telling a lot of people this over the phone: "It is better to run way too high or way too low than it is to hit the bumpstop at the worst time in every corner". With many SMs being camber starved, this ends up translating into "It is better to run too low ....".

Good luck and have fun :)
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#15
Tom Sager

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My $0.04:

All the rules of thumb and Carroll Smith comments on rake, "ride height", and roll center are either irrelevant, misleading, or plain wrong for an SM. Unlike every "real" racecar in the world, an SM is simultaneously oversprung, underdamped, and most important - starved for "shock travel".

Forget rake (and the meaningless pinch weld measurements that don't take into account chassis twist vs. the subframes or whether you are running 0/32" Toyos, much taller 4/32" Hoosiers or 8/32" rains) and start paying attention to your individual shock travels.

If you hit the bumpstop sooner or harder, at that moment that wheel end is much "stiffer" until you get back off the bumpstop. During those moments, the car will act like any other car would if you stiffened that corner (or that end).

I can't stress enough how much this effect DOMINATES the SM's chassis behavior - more than alignment, more than shocks, more than swaybars, more than anything but tires and % cross, I'd say.

Try +2 turns in the back, and then try -2 turns in the back. If you want extra credit, have some slotted urethane discs in various thicknesses made that your pit guy can slide onto the shock shaft to change shock travel quickly without altering anything else. It isn't illegal to use them for practice and test days and you'll learn more in one test session than anything the Internet commentariat could ever tell you. (I didn't invent this great idea, I just copied it ... ).

I've found myself telling a lot of people this over the phone: "It is better to run way too high or way too low than it is to hit the bumpstop at the worst time in every corner". With many SMs being camber starved, this ends up translating into "It is better to run too low ....".

Good luck and have fun :)


That's exceptional advice. I have tried the -2 turns (in the rear) and spun the car on the outlap. I also took a Fatcat bumpstop to a guy who measured the spring rate as it was compressed. You get a nominal (but still meaningful) rate during the first 1/8" - 1/4" or so of compression, As you compress it further than that the spring rate goes through the roof. The term "bump STOP" is very appropriate for this part.
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#16
FTodaro

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I do use the pinch weld measurements for ride height now, but that was after I got a point of reference of where that put me on the clearance between the shock and the bump stop.

If you set up your car to low and you get into the bump stops, you better have fast hands.

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#17
DrDomm

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I tried measuring shock travel last year with zip-ties around the shafts. All 4 zip-ties were jammed up inside the bumpstops. I figured it was a useless experiment, and that it was just the product of bouncing off the curbs. Was I wrong? Was the car too low? Where should the zip-ties be? Why do we have bumpstops if you shouldn't use them?
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#18
FTodaro

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The handling characteristics of the car will change and be unpredictable if you regularly get into them. Did you ever get into a corner and your car get wicked loose?

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#19
DrDomm

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The handling characteristics of the car will change and be unpredictable if you regularly get into them. Did you ever get into a corner and your car get wicked loose?


Yeah, I can think of an occasion that surprised me. Maybe that was what happened.

I'm probably not being clear with my question though...why are bumpstops so important (in any racecar) if you should rarely be at full shock compression? I just assumed SMs relied on them frequently because of the limited shock travel.
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#20
Keith Novak

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I tried the same zip tie trick and found the same zip tie buried in the bump stop thing so I did a bit of inquiring about it. Things have changed since the Fatcat kit has become the norm. The bump stops aren't nearly as harsh now and often you will be on them. That's fine but you don't want to hit them suddenly.

Hitting the bump stops is like switching from the rate of your springs to a much stiffer spring. If you gradually compress your shocks to the point where you're on them and the track is smooth, you may not notice you're on the bump stops. If you're on a bumpy track with sudden elevation changes and your car is set too low, you will definitely realize why you don't want to go to low.

I learned what Saul recommended by accident. I'd heard it before but I hadn't done it. I left my car setup where I liked it for a smooth flat track and drove on a bumpy rough track. Within 2 laps my eyes were dinner plate size, it felt like my butt was being hit with a bat, and my hand speed was tested to the limit. I jacked it up about 2 turns (1 didn't seem nearly enough as bad as things were) and lo and behold I had suspension again. Point being a little bit of driving on the bump stops isn't necessarily bad. Slamming into them everywhere is not something you want in my humble opinion.
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