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Discussion Starter · #1 ·
I am starting a new thread on setting rake. This thread had its start in a discussion on some spin-outs I had at Buttonwillow and car handling.

Here is a link sent to me by IT L GO on setting rake.
http://www.z06vette.com/forums/showthread.php?t=77438&highlight=rake

That is the first explanantion I have seen on how to measure and set for rake.

I am still left with the question of "what are the implications of rake?" What happens if it is not set right? There is a 1/2" to 3/4" range. How does the car behave at the lower end of this range vs. the higher?

Does anyone know these answers?

:-? :-? :-?
 

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http://www.caterham.co.uk/aftersales/upgrades/suspension.htm
Adjustable platform also allow for changing the rake of the car, which can be used to tune the handling. Typically, around 15mm of rake is used on the Seven - that is, the rear of the chassis is 15mm higher at the rear wheels compared to the front. Lowering the front will reduce understeer, or promote oversteer. This is because having the front of the car lower than the rear will incline the roll-axis down to the front, which will cause a diagonal load transfer from the rear to the front outside tyre during cornering. Having the rear of the car sitting lower than the front (or less than the 'usual' rake) will have the reverse effect. :cheers:
 

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Discussion Starter · #5 ·
Hey, maybe a little more rake and I would not have spun trail braking into Riverside at right about 100mph... :mah:

I have just under 1/2" (7/16") as measured at the frame rail behind the front wheel and just ahead of the rear wheel. But that measurement can be meaningless. I am sure those are not necessarily engineered to be perfectly even to the ground. There must be some other more legitimate place and way to measure rake absolutely correctly on the Z06.
:-? :-? :-?
 

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Rake is very important, otherwise you will have grass in your fingernails and on your hands possibly causing you to miss a shift.

:bang: :bang: :-?

According to C4C5specialist. rake is 153mm front and 158mm rear measured from outside the frame rail shipping holes to the ground.

Sabot
 

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Discussion Starter · #7 ·
My car has been lowered on stock bolts, but without cutting the bushings, so it is lower than 150mm measured this way. Following these measuring guidelines I have only about 2.5 millimeters of difference between the two measurements, with the front being the lower of the two. My calipers did not fit under the car, so I had to improvise and my measurements could be a few millimeters off.

It still leaves me wondering. Is this close enough? Or is there a tangible difference dialing the rear up a few more millimeters???
:cry: :cry: :cry:
 

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Well Oli I moved this from the original thread:

Coming in 4th fastest time 3 seconds off the leader and you a newbie sounds to me like you can drive. I wish I could do that. Granted the Z hp and torque help but it is not always a slam dunk to drive a high HP car well. Unfortunately the only way to check your rake is to try changing it. Maybe DJ/subdriver or others can post here how sensitive a Z is to chassis rake. My non-Z I can feel 1/2" changes. So if you really are new maybe you can try dropping the rear 1" and go back to the track and see what happens. Personally I adjust from one end or the other only so as to not confuse myself. In my case with a rear heavy car 40/60% weight bias I notice that if I lower the back more than stock I get better 100mph+ braking stability and my rear sticks better and I get less terminal oversteer ala 911 porsche. I would think that this would be especially benefiical with a hi torque Z. However, while I own a Z I have no track experience with one. DJ others who race you guys have comments?

Also, areodynamics has almost zero to do with it at our speeds. IMO rake should be used to tune over steer understeer as you can with tire pressures to a point or rollbars and tune high speed braking stability along with chassis alignment settings. Forexample you can run the nose higher and then more toeout and equalized the negative/positive effects of each under high speed >100mph threashold braking. That up to a pint may give better turn-in and more rear grip to prevent spins. Raise the nose too much and you get too much push and defeat the ability to throttle steer. But assuming you are not going to change parts the rake is a good place to play. I do not think that there is enough rake adjustment in the Z to upset the Aero. Also, if you could adjust the rake ideal for sub aero issues then dump a wing in the back you about have a whole new way to adjust. However, that makes for new problems for the newbie. I no F1 driver and using real aero is a different world. Using real aero on a total chasis like the 360 Ferrari challenge cars and you get what happenend in the early races losts of spins and crashes until the drivers figured out how not to upset the aero.
 

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Discussion Starter · #9 ·
Thanks for the compliments FTB:

John Wurth of Speedventures drives a fully T1 prepped Z06 and ran easily much faster than me. Ed/AmericanMusl who sometimes frequents this forum was also running faster than me by about 1.5 seconds, so he is also a better driver. But I vow to put in the track time and discipline to close those gaps and then move beyond!

I am not sure what Ed has to say about that though!?!?!

He won't give it up easily.
 

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From your last post I say forget the rake issues. If you are new as you say and close to those guys you got some talent I wish I had. Interestingly I swear a good seat properly mounted that holds you in with a 5 point harness and pedals properly set for heeltoe are good right there for some time. You see if you slide around in your seat you have to hold on to the steering wheel. If you are well held in the seat you can gently hold the wheel and that improves your feel for grip.
 

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Discussion Starter · #11 ·
Agreed FTB:

My last track day at BW on the 15th was my first day with a race seat. I could feel much better what the car was doing and I was not bracing myself with my knees and such.
:usa: :usa: :usa:
 

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speedpup said:
Pocono, Lime Rock and VIR cars will see 140-165 and aero has a bunch to do with the rake.
Well yes but when tuning the car you tune without/minimal aero first then adjust tune as you tune in aero. A real wing even at zero angle should provide downforce. Aero has significant effect in our streetcars less about rake and the relationship to your hand out the window at 80mph and more about air flow under the car. as we know much can be done here if you have the $ for a windtunnel. I have never been to VIR etc. but at tracks like Laguna seca and Willow Springs or Butonwillow on the west where laptimes in streetcars are perhaps 1:25-2:10ish for a fairly quick car even high numbers like 145mph are seen for just seconds while the effect of aero is significant at 145 for us it is less so at 100 and less still at 80 and at Buttonwillow depending on configuration there are places on the track that are second gear for easily as long as you can go 130. So considering one of our fastest tracks is WSIR the SCCA T-1 track record over a 2.5 mile course was run at a 92mph average. How much of that is aero? I have no idea....Maybe that is a bad way to compare but average means some time must have been slower than this and some time must be faster than this. Even at the average 92mph how much aero do you get with a C5 shapped brick?
 

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aero helps under braking also. I'm doing 125 at the slowest on Nascar Turn 1 at Pocono and coming to the Tunnel Turn at 165. I made my Grand Sport level and it is down right scary at 160 and I don't scare to easy. The wind tunnel info for the body I have is feed back from GM wind tunnel. Slower courses I will increase wing angle. Going 125 is going to create significant force. I think at 80+ wing would be noticeable. Rake in a C5 is creating suction from below.
 

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speedpup said:
aero helps under braking also. I'm doing 125 at the slowest on Nascar Turn 1 at Pocono and coming to the Tunnel Turn at 165. I made my Grand Sport level and it is down right scary at 160 and I don't scare to easy. The wind tunnel info for the body I have is feed back from GM wind tunnel. Slower courses I will increase wing angle. Going 125 is going to create significant force. I think at 80+ wing would be noticeable. Rake in a C5 is creating suction from below.

Wow! 165mph? Well you better have your aero right. And I agree 100%. I find the aero most important for braking stability but I have never seen 165 I have nothing that fast. I assume you are doing road courses and most are in the 2-4 mile variety with 10 or so turns. That means you got some serious horsepower. Are you running a basically stock T-1 Z06 with a ALMS wing? Or have you modified the engine to do better than 375 at the wheels? If you are doing ovals like California speedway then I can see your sppeds but that is too fast for me. Bad things can happen at near NASCAR speeds with not a real racecar. 165 in our stock Vette chassis seems dicey to me. You do not have a chassis designed to take the huge hits like NASCAR and you probably do not run HANS, 6 points, full containment seats and left right nets, fuel cell, fire system and roof spoilers full welded cage with NASCAR bars or tear down the suspension after every race do you?
 

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yes on the HANS and I try to keep a close eye on the car. 4 point which will wrap around my head at those speeds :rofl: Hope to run it this weekend weather permiting at Pocono. 450+ RWHP and modified suspension. ACP WC body kit. Car runs solid and smooth. Mechanical failure at that speed and I'll be an interesting topic on the forum. :bang: I run slicks but did that speed on Hoosiers 275/315 x 17 also. I know a old C4 WC car that was behind me last year. He said he knocked 4 seconds off his best time ever following me last year on Pocono long course. It was a memory for a lifetime. We had a great run. Hope to post some vid's this year. Did a few more aero mods for this season. :idea:
 

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Speedpup,

Have you done any underbody stuff like a rear difuser? If you got some pics of your car that would be cool. Yes at those speeds a aluminium ultrashield full containment seat/headnets and a full cage could serve you well... there is spent $3k more of your money. How did you get eh 450rwhp? Cam/air intake? Headwork?
 

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3,000 won't get a cage and a seat. I have a Kirkey Deluxe Road Race seat and head containment piece for the seat. No one will tell me if I need a full cage to use it :bang: I want to cage it so I can run some wheel to wheel events next year. Motor is Vette Doctors H&C which is about two years old. I would like to make an LS2 stroker for next year for another 100 HP or so. I'll see what shakes out this year with the tuners and 402 LS2's. I took about 110 lb out for this year which should help a tad. Worth about 18 hp or 3-4 tenth at Lime Rock. I'll be running it this weekend weather permitting and next Friday. I'll post some pictures after this weekend.
 

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I know I was being nice on the $3000. Be careful safety is a tough issue. If you ahve the Kirk with the HC then make sure you add the shoulder support too. If you hit lateral and your head stops you still rip the carotids as the shoulders keep moving. Also for cheap look at the BSR website and get a right head/shoulder net. They are the only ones who make a big enough net to trap both. This net is used when the hit is oblique and you come out of your seat toward your RF wheel. The window net helps for the left but some us a dedicated left head/shoulder net too. Yes you should have a full welded cage with door bars preferably NASCAR bars. Do not add the petty bar that goes from right temple to right front passenger foot area. People hit their heads on these and they don't add much to stiffen the car. Yes post some pics I'd like to see your ride and general set-up.
 
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