Is there an optimal tire height in relation to lowering the car? (A-Body)

[Barrrf]

I wouldnt run anything taller than 26" on the front and 27" on the back of 2" dropped A body Chevelles. I cannot speak for other A body models.

[71OLDS]

I wouldnt run anything taller than 26" on the front and 27" on the back of 2" dropped A body Chevelles. I cannot speak for other A body models.

The lowest point of my header collector is 4" off the ground right now. If I did 26/27 on my 442 I would guess that would drop a full inch to only being 3" clearance. I drive about 5000 miles a year in my car and occasionally have to go over speed bumps and dips in the highway or in and out of driveways or entrances. Plus I have my front spoiler that would be closer to the ground too.



I agree for performance lower would be better but would be scared to go any lower for all the street driving I do.

[Barrrf]

Both of my tires are 26" tall on a 2" drop on my Chevelle. The frame is roughly 6" off the ground. The headers and exhaust are a little lower but tucked up as high as I can get them. So far so good but I avoid terrible roads. Some parking lots I have to avoid because of the approach and departure angles.

I was only commenting on the amount of clearance in the wheel wells for tall rubber on a dropped car.

[WallaceMFG]

Here is our Chevelle with 275/35R18 on all 4 corners. Wheels are 18" x 9.5", +20mm offset, 6.00" BS. We have a 3/8" spacer on the rear, no spacer on the front, but a 1/4" would be good up there.

We had the car too low when we first got it driving, these pictures are after we had driven it and decided to lift it up from full low. I would not go lower than this for street driving, we have to be careful around speed bumps or the frame can drag.

Yes, I know it is on wheel dollies but it's the only good side picture I have. Keep in mind that 69 (and I think 70-72) Chevelles the fender lips are not even, the rear is lower than the front.

[USAZR1]

I've got Fatman/ridetech 2" drop spindles on the front and UMI 2" drop spindles on the rear. At the moment, wheels are 18x8 w/4.5" backspace (0 offset) and 20x10 w/5.75" backspace (+6 offset). Tires are 255/35/18's (25.1" tall) and 305/30/20's (27.2" tall) Headers are mid-length so ground clearance isn't any concern. Car has at least 4" ground clearance and front crossmember is the lowest point, underneath. By the time Fall rolls around, I plan to purchase a set of Forgestar wheels in either a 19/19 or 19/20 combo, with a 285 front and 315 or 325 rear.

[krom]

Here is our Chevelle with 275/35R18 on all 4 corners. Wheels are 18" x 9.5", +20mm offset, 6.00" BS. We have a 3/8" spacer on the rear, no spacer on the front, but a 1/4" would be good up there.

We had the car too low when we first got it driving, these pictures are after we had driven it and decided to lift it up from full low. I would not go lower than this for street driving, we have to be careful around speed bumps or the frame can drag.

Yes, I know it is on wheel dollies but it's the only good side picture I have. Keep in mind that 69 (and I think 70-72) Chevelles the fender lips are not even, the rear is lower than the front.

What was the measurment between the bottom of the crossmember and the ground when it was too low? How about now?

[Yanchik]

For reference on this thread I'm running 27" (26.97" to be exact) tall tires on the front 255/45/18 and almost 29" (28.78") on the rear with 305/45/18s. For me running a taller tire has 2 benefits: 1. You can lower the car less but it "appears" to be lowered more because the tire will tuck into the wheel well more 2. You will have more ground clearance for headers for speed bumps and dips in the road or driveways. That said I would guess a slightly shorter tire might out perform the taller one in hard cornering performance simply because the entire car will be closer to the ground. Here's a few pics of mine:




Details on rims and tires:
Front Tires/rims- NewGen500 18x8 rims (5.25” BS- {old rims w/stock spindles and rotors were 4.5}) w/Nitto*** 555 255/45/18s
10”sw – 26.97”d
Rear Tires/rims- NewGen500 18x10 rims (6.0” BS – {old rims w/stock rotors were 5.5}) w/Nitto*** 555r 305/45/18s
drag radials 12.02”sw – 28.78”d
***Nitto words sanded off and BFG Raised white letters glued on for show***

One note on the rear - may be adding rear coilovers and if so will get that rear down that last 3/4 of an inch or so to match the front. Running standard springs now in the rear and they are just a little too high for what I like.

Very true, a tall tire can make the car seem lowered and give a nice and tucked look. That’s a sick stance by the way!

[Yanchik]

I wouldnt run anything taller than 26" on the front and 27" on the back of 2" dropped A body Chevelles. I cannot speak for other A body models.

Now I’m questioning wether or not I need coilovers. Sounds like a 2” drop spindle will lower my car just fine on the front

[andrewb70]

I like 26" front and 27" rear, give or take. I currently run 275/35-18 in the front and 295/35-18 in the rear, and I feel they are a tad short.

Andrew

[WallaceMFG]

What was the measurment between the bottom of the crossmember and the ground when it was too low? How about now?

There was about 4" under the cross member, 5" under the frame behind the front wheels. We lifted the car 0.5-1". We found that when there were four people in the car the rear suspension was nearly sitting on the pinion snubber and the front would drag the frame on speed bumps. AZ is notorious for putting huge speed bumps everywhere since we don't have to deal with plowing snow. Some stiffer springs were installed along with raising the car the amount above. It is in a good position now, still looks nice and low, but no worries except for the steepest driveways.

[71OLDS]

Sorry this is sooooo long!

I spent about 2 hours on the phone yesterday with Mark Savitske at SC&C author of "How to make Your Muscle Car Handle".

http://scandc.com

The knowledge and experience he has working with 68-72 GM A Body's is pretty crazy. I got my AFX spindles and a few other suspension parts from him. Some parts of our conversation related to this topic and I was really surprised by some of the things he told me so I thought I would share in case anyone else finds it useful/helpful. It definitely contradicts what I thought and sadly goes against the look that I love on my car (being nice and low on the stance). Most of the time I talk to Mark about 20% of what he says goes over my head so it's safer to get the real info directly from him but I'll try to generalize at a high level.

First he talked about The roll center on 68-72 GM A Bodies and how it is very high and as you lower the rear of a GM A-body, the rear roll center goes up. Then he brought up the part that concerned me the most. He said lowering the rear more than 1” could cause issues and suggested the perfect lowering amount for 68-72 GM A body is 2” front and 1” rear assuming you're using the stock frame. This will prevent the rear roll center from going up = worse handling. Meaning if you lower a stock frame GM A body more than 2” front and 1” rear the car will actually handle WORSE. I always thought the lower you could get the car to the ground the better it would handle. Apparently this could be true if you got an aftermarket frame with a different roll center but is not the case for those of us running stock frames.

I specifically asked about tire height and if a shorter or taller tire would change the roll center and he said no. He did say one thing that was consistent with my current setup (and probably the only thing that's consistent) related to the tire size. He said going with a taller tire setup like mine would help the tires tuck more (than a shorter tire) giving it at least the appearance that is was lower. I know on my car if I had shorter tires and only went with 2" drop in the front and 1" drop in the rear there would be a gap between the top of the tire and the wheel well - that would be my worst nightmare! Currently I'm at about a 2.5" drop in the front (.8 AFX Spindle and about 1.75 coilovers) and I'm running way too stiff 2" drop springs (CPP 240 rating) in the rear. Sadly as I mentioned in one of the posts above I was hoping to go to 2.5" all the way around so the wheel well sat right at the top of my rim. That's the look I love. Mark asks me - "do you care about look or performance/handling?" He said where my car is now is hurting me and if I go lower it will be worse. He said my roll center has been raised because I'm too low and my car is going to handle worse because of it. I said so you're telling me if I raise the front a 1/2" and the rear 1" my car should handle and corner better and he said absolutely. I'm going to give it a try. I probably won't have my car back on the road until Sept/Oct but will update my results/changes on my normal post in the project updates section (link in sig below) as always.

Really going to miss the lowered look but if it handles better I'll take performance over look any day. I'm also going with coil springs only (not coil overs) and double adjustable shocks. Long story for why on the coil springs but it's mostly because of my driving style and habits: 5000 street miles/year and pounding the car really hard on a regular basis (hard corners and WOT blasts even on the street) plus autocross events & 1/8th mile and 1/4 mile runs. Mark suggested something like 550/135 14" springs and then adjust with the dbl adjustable shocks for street/corners/track etc. He was very specific about choosing a shock that allows higher rebound settings. Apparently some dbl adjustable brands max out at 450 = OK for drag race but not good for street or autocross/cornering. He said since I have all the geometry issues resolved with my AFX spindles, and the other suspension parts (tubular uppers/lowers, Lee 800 box, front/rear sway bars, chassis brace etc) that if I work with the natural roll center of the car I can get amazing handling with the modest spring rates and high end shocks. If I lower the car too much and raise the roll center then I would have to "band aid" the issues I have created with stiff springs and/or really wide wheels tires etc. We'll see how the changes work out.

-Joe

[Barrrf]

Mark knows everything about A bodies.

But I have to ask, when it says it handles worse, how much worse? Marginally worse? Extraordinarily worse? I dont track my car like ever and I like the way 2" low looks with the tire tucked a bit. And Im definitely not disappointed with the way the car handles on the street.

[USAZR1]

I don't track my car ever and I like the way 2" low looks with the tire tucked a bit. And I'm definitely not disappointed with the way the car handles on the street.

Same here. I'm not concerned with the last bit of handling performance and doubt I will miss it.

[71OLDS]

Valid question and I have no idea "how much worse". I remember asking the same thing when I heard all the issues with my B-body spindles and took the plunge to switch to the AFX spindles. It's probably different for all our cars depending on our setups and how we drive. So far I've listened to all of Mark's other advice and suggestions so I'm going to give it a try. I guess I'll have even more ground clearance for speed bumps and hwy dips now!!

[Yanchik]

Sorry this is sooooo long!

I spent about 2 hours on the phone yesterday with Mark Savitske at SC&C author of "How to make Your Muscle Car Handle".

http://scandc.com

The knowledge and experience he has working with 68-72 GM A Body's is pretty crazy. I got my AFX spindles and a few other suspension parts from him. Some parts of our conversation related to this topic and I was really surprised by some of the things he told me so I thought I would share in case anyone else finds it useful/helpful. It definitely contradicts what I thought and sadly goes against the look that I love on my car (being nice and low on the stance). Most of the time I talk to Mark about 20% of what he says goes over my head so it's safer to get the real info directly from him but I'll try to generalize at a high level.

First he talked about The roll center on 68-72 GM A Bodies and how it is very high and as you lower the rear of a GM A-body, the rear roll center goes up. Then he brought up the part that concerned me the most. He said lowering the rear more than 1” could cause issues and suggested the perfect lowering amount for 68-72 GM A body is 2” front and 1” rear assuming you're using the stock frame. This will prevent the rear roll center from going up = worse handling. Meaning if you lower a stock frame GM A body more than 2” front and 1” rear the car will actually handle WORSE. I always thought the lower you could get the car to the ground the better it would handle. Apparently this could be true if you got an aftermarket frame with a different roll center but is not the case for those of us running stock frames.

I specifically asked about tire height and if a shorter or taller tire would change the roll center and he said no. He did say one thing that was consistent with my current setup (and probably the only thing that's consistent) related to the tire size. He said going with a taller tire setup like mine would help the tires tuck more (than a shorter tire) giving it at least the appearance that is was lower. I know on my car if I had shorter tires and only went with 2" drop in the front and 1" drop in the rear there would be a gap between the top of the tire and the wheel well - that would be my worst nightmare! Currently I'm at about a 2.5" drop in the front (.8 AFX Spindle and about 1.75 coilovers) and I'm running way too stiff 2" drop springs (CPP 240 rating) in the rear. Sadly as I mentioned in one of the posts above I was hoping to go to 2.5" all the way around so the wheel well sat right at the top of my rim. That's the look I love. Mark asks me - "do you care about look or performance/handling?" He said where my car is now is hurting me and if I go lower it will be worse. He said my roll center has been raised because I'm too low and my car is going to handle worse because of it. I said so you're telling me if I raise the front a 1/2" and the rear 1" my car should handle and corner better and he said absolutely. I'm going to give it a try. I probably won't have my car back on the road until Sept/Oct but will update my results/changes on my normal post in the project updates section (link in sig below) as always.

Really going to miss the lowered look but if it handles better I'll take performance over look any day. I'm also going with coil springs only (not coil overs) and double adjustable shocks. Long story for why on the coil springs but it's mostly because of my driving style and habits: 5000 street miles/year and pounding the car really hard on a regular basis (hard corners and WOT blasts even on the street) plus autocross events & 1/8th mile and 1/4 mile runs. Mark suggested something like 550/135 14" springs and then adjust with the dbl adjustable shocks for street/corners/track etc. He was very specific about choosing a shock that allows higher rebound settings. Apparently some dbl adjustable brands max out at 450 = OK for drag race but not good for street or autocross/cornering. He said since I have all the geometry issues resolved with my AFX spindles, and the other suspension parts (tubular uppers/lowers, Lee 800 box, front/rear sway bars, chassis brace etc) that if I work with the natural roll center of the car I can get amazing handling with the modest spring rates and high end shocks. If I lower the car too much and raise the roll center then I would have to "band aid" the issues I have created with stiff springs and/or really wide wheels tires etc. We'll see how the changes work out.

-Joe

Coil + Spring will take more of a beating than coilovers? I’m only asking because I plan on driving my car fairly hard, and if coilovers are weaker, then I’ll go spring+coil.

Plus it’s cheaper

And thank you for the information on lowering the car. Definitely gave me a better insight as to what I use to think was “best”

[71OLDS]

Coil + Spring will take more of a beating than coilovers? I’m only asking because I plan on driving my car fairly hard, and if coilovers are weaker, then I’ll go spring+coil.

Plus it’s cheaper

You should definitely call Mark and talk to him about this and make sure it applies to your car like it did mine. Coilovers are obviously the big craze right now and they can certainly be made and set up to take abuse but it's lots more work and usually cutting and welding and reinforcing is required. That said most of the coilovers end up being a really short skinny spring to begin with and if you lower the car more (which is the reason most get the coil overs in the first place for the ride height adjustments) you end up making a 10" (or even shorter spring) shorter and shorter. It seems like the vendors are finding ways to make them a little longer like the chicane weld in option for the top or the new control arms that drop down lower. These only give you an extra inch or two in length and that's not a lot to support our 2 ton beasts. Contrast that with a long thick coil spring that has been holding up 4,000+ lbs cars for hundreds of thousands of miles for decades and decades and i think it's hard to argue that the standard coil spring can take a beating. So if you can find a ride height that youre happy with and still be able to adjust the dbl adjustable shock to your liking with compression and rebound (that is supporting no weight by they way), why not just stick with the old reliable? For me for when I'm drag racing some would argue the longer spring also has more stored energy and might help with launches. Others say that's BS and a 10" spring would be exactly the same as a 14" spring if they were rated the same....I'm certainly no expert just trying to find what works best for my car and all the crazy stuff I want to do in it. It is amazing that I'm going back to basically the same 1" drop springs I had back in the 90s that I got from Hotchkis. Of course back then I don't think there were any coil overs yet - at least not for our cars and of course no AFX spindles either. But soon there after came the B-body spindle option and I jumped all over that one!!