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I have to disagree with you on this.
I have 275 18's in the front of my scratch built Cobra replica. I used C5 Corvette spindles and control arms with a custom manual rack. Also used C5 rear suspension and diff, (converted to take a drive shaft), C5 wheels and tires, brakes, LS6 with a T56 trans. It is VERY easy to steer. (everyone that tries it thinks that it has power steering), is 100% stable, even at high speeds on the track, and on the road at legal speeds and has zero tram lining. I use it as my daily driver as much as possible. It is the front end geometry, correct parts, correct alignment, along with the correct wheel offset that effects these qualities, not the tire size. |
is it possible to fit bigger tires if one wanted to? I.e. 265's or 285's? Any fitment issues?
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Gary
A couple of thoughts......" What it would take to install power steering....... What is your bump steer..... What ia your Ackerman...... As you go to a larger tire and try to go fast with racing tires slicks......you will find that the steering gets very difficult .... If you can move your rack back so there is a 10* degree difference from the steering arm on the upright......and ball joint of the rack..... the car wiil track around a corner with ease... And on the rear ....can you rotate the upright a small amount to get the rear bump steer going in the right direction. Morris |
Morris:
"If you can move your rack back so there is a 10* degree difference from the steering arm on the upright......and ball joint of the rack..... the car Will track around a corner with ease..." Are you saying the tie rod (as viewed from above) will form a 10* angle from the centerline of the rack? With the rack behind the pivot point of the of the upright steering arm.....or in front of the upright steering arm? (i.e. the tire rods are angled "forward" or "back"?) Thanks, John P.S. of course a diagram is worth a thousand words....;) |
John
Yes that is what I'm saying. And if you do draw it out......the inside tire will will be turning a smaller radis then the outside tire. The rack needs to be behind the steering arm of the upright.....on a front steer car.. That's how you get Ackerman on a front steer car...... Morris |
BTW.....Ackerman is good in a race car......an street car....
Especially on GT type of cars. |
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Yes .......or larger wheels allow longer steering arms.......
That's why when designing a suspension you always start with the wheel size first....... Or in the planning stage the verticle tubes are moved back the amount to get the 10*degrees from the rack to the steering arm..... Moving the rack up an down will affect the bump steer ...... So a GT car set up with 5*- 7* degrees of castor (now you need power steering) and -3* degrees neg camber and 1/8th" tow in and 10* degrees of Ackerman will go straight as a arrow at 185 mph and go around a corner provided it has been bump steered to .015" inch in 4 inches of travel....... Hope I didn't get to far off track........my brain is much faster then my fingers. |
I agree with you Morris. Also agree that when racing with slicks that power steering would probably be necessary. (I've never had slicks on my car) I think that the scrub radius would have a large effect on steering effort. On my street Cobra I run 6.9 degrees of castor, have a zero scrub radius and a manual rack. It is sooooooo easy to steer that I wouldn't want power steering. Even when parked I can turn it lock to lock with a finger. By the way my rack is adjustable for Ackerman and bump steer.
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[quote=Morris;1198008]Yes .......or larger wheels allow longer steering arms.......
I think the front wheels are 18" already,so not much more room. I wonder if the CC&AR design means some standard suspension design items change significantly? |
You could also change the control arms to move the spindle forward as well.......
But the real question is what is the application of the suspension.....street,track,or pleasure .... |
any updates?
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we have zero bump steer as we dont like bump steer as it makes the car less pridictable, and the ackerman is not perfect becaus we can not get the ball joint out far enough because of the brake disc but it is good enough to allow for slip angle Gary. |
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If you could mount the rack in the position indicated by the 'yellow' rack outline with the tie rod ends above the steering arms you would get the necessary ackerman effect plus gain a bit of clearance from brake rotors to tie rod ends.
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Exactly.......and zero bump steer on both front and rear.....or .005" per inch of travel up and down.......
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Morris,
I have found that 10 degrees is excessive on this length wheelbase car unless you are using it for autocross type tracks or street use. I have many times utilized reverse Ackermann on ground effect type vehicles due to the very large slip angles generated. Below is a photo of the JBL with Willow Springs steering setup that is optimized for 450 foot radius corners. It is a bit of a compromise but the high speed sections are a very large portion of that track. For Blackhawk I would use a greater angle similar to what you suggest. For instance, this is done on the JBL by changing the steering arm and the rack spacers that you can see in the photos. Also one can argue that a little bit of front toe in under braking on a rough track is a very good thing indeed. (Turn 5 at Road America comes to mind here. At least the last time I was there.:3DSMILE:) http://www.jblmotor.com/images/ch11.jpg Gary..... Nice looking piece you have designed there. I will be interested to see how you like it when you start testing. Beautiful sheet metal work as well. Congrats... Interesting brake calipers. I guess one can never have enough pistons but I do wonder the reason for 5? Are they trying for high beam stiffness or are the pistons of various sizes to give even pad clamping? |
Hey Richard
It's great to hear from you.......we like the adjustability of the JBL.....and all cars should be able to be adjusted ......but only if the people know where they are going with the adjustments...... We did test at Road America and we actually have about 9*degrees angle on our rack to steering arm and the car stuck good in the Carousal turn as well as turn 5 at the bottom of the hill..... Then we took KMP259 to St Louis a Oval and small infield track and ran GT-1 times.....very happy with that performance...... If you can make a chassis go around a corner easier.... Then make the adjustment....like everything, chassis are a compromise....depending on the need at the time. |
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