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I'm selecting suspension and tires for my Buick Roadmaster and I have some questions about clearances:
1) Is there a minimum clearance I should design for between the inner lip of the fender and the tire?
2) Is the minimum distance different for the front and back tires?
3) Does the tire travel straight up in the fender when the springs compress?
4) About how far will the front and tires travel up into the fender?
Thanks for your help
If you're going street rod type coil over on the front, which most MII's are, you'll have about 3" total travel or 1 1/2" each way. I like to have the 1 !/2"+1/2" clearance from fender to tire when the steering is at full lock in either direction. The front tire moves up and down on an arc, but this arc is measured in degrees of camber, usually no more then 7 degrees camber gain. This is all best measured when the suspension is installed at mock up, then time to decide on the tire and wheel size and width. The rear doesn't need as much clearance, 1" is more then enough.
Hi Dave,
Thanks for the feedback. Please check my math. One of my favorite options for my 1937 Buick Roadmaster is a 2003-2004 Crown Vic/Grand Marquis front suspension. See attached picture of one my friend just installed one on his ford truck. Initially I thought the suspen was too wide based on dimensions another hot rod builder shared. Turns our his Buick was the same year as mine, but was a 2dr bus. coupe where-as mine is a large 4-dr sedan. So I finally got my garage built and my car moved in. I measured the front fenders by clamping 2x4s to the outside using a level to make them vertical. Measuring this distance and then subtracting the width of the lip on each fender I have 74.37 inside clearance directly in-line with the front axle.
The 03 Crown Vic front track is 63.4" and stock tires are 225/60-16 or a width of 8.8". Adding this to the track gives an outside dim of 72.26" or 1.06" clearance per side. If I use 205 (8.07") wide tires the clearance per side increases to 1.45".
1) This does not take into account the lock to lock clearance, or the camber gain you mentioned.
2) Does clearance reduce, or increase when wheels are turned?
3) You mentioned that clearance is checked at mock-up. Do you remove the springs/shocks to check clearance at extremes?
4) You mentioned 7 deg camber gain. Does this translate to the top or the wheel moving outward at a 7 deg angle. Radius of a 205-65 R16 tire is 13.25" so by trig does this means the top moves out 1.62"? If so, then do I need at least 1.5+1.62=3.13" clearance on each side in the middle postion of travel?
5) I want to be sure an option will work before I buy a suspension. I could probably find a Crown Vic to measure clearances in center, and locked positions so I can see how turning effects clearance. I could also go to a narrower tire if needed.
Thanks for your help
I thought you were going with an MII system on the Buick???
Your math appears to be correct--but my experience has shown that the only sure way to get everything right is to strip the existing front frame on the Buick to the bare rails, mock up the replacement front suspension, then with shocks, springs, and stabilizers removed, run everything through it's entire range of motion to verify clearances, caster, camber, toe-in, bump steer, Ackerman angle, roll center, etc....
Back in the late 70's, early 80's many people chose to weld on a Camaro subframe to their project cuz it was quick, easy, and cheap. Got to say that I saw more done wrong then I ever did see done right. With the Crown Vic assembly being the current rage, from what I've seen of them most appear to follow the same tendency. The only real + I see to using the Crown Vic is that it's cheap, but as with anything you get what you pay for!
I'm probably not the right guy to ask about using a Crown Vic, Camaro, or whatever grafted onto a car. I use either a MII system with tubular arms and all new parts or I design my own..... Sorry, but I've been at this stuff so many years that quick, easy, and cheap are no longer a consideration on the stuff I build......
Thanks again for your help.
Sorry for not discussing the latest suspension I was considering in my question on clearances. Just thought a generic question would yield more results. Mustang II front suspension may still be my choice, but I measured the car and found that the crown vic suspension might fit. Still deciding which way to go.
1) Does my calculation on the camber gain make sense and would I indeed have to allow over three inches of clearance to accomodate the camber gain and the 1.5" clearance you recommend? This seems excessive because most modern cars have the tires much closer to the inner fender at the top.
2) Is it possible other modern suspensions do not have as much camber gain as the Mustang II?
Thanks
No idea, you'd have to put a camber gauge on the hub, run the suspension through it's travel, and see what it is.
PS--your calculations are wrong, the upper and lower arms are unequal length and also must allow for the placement of the spindle itself in relationship to the height of the upright. Calculations would have to include all of this, plus issues like ball joint placement in relation to the A-Arm and length of the stud in the ball joint. I just through out 7 degrees as a max number. Clearance has to also allow for sidewall flex and edge rolling on the tire!!! 7 degrees would allow plenty of room for camber gain, tire flex, edge rolling, caster gain, and any bump steer issues.
I'll study up on all this.
Thanks so much for your help.