Make it handle

[Grimee]

Hey Everyone this is my 1st post here Ive read this thread a few time and i am impressed with Robs Knowlege and willingness to share . that being said I have a couple of questions for Rob or any one else that wants to chime in with advice. I am currently finishing a build on my 1998 2 door 2wd tahoe that we are setting up to autocross it has chopping block upper and lower control arms set up for coilovers 1 1/4 speedway eng front solid sway bar and Baer tracker tie rods to help correct bump steer and Baer 15 inch rotors and 6S calipers the rear has Early Classic Trailing arms narrowed rear end (6 inchs) panard bar,Baer 14inch rotors with 6s calipers and a cantilever set up for the coil overs the rocker arms are 2 to 1 ratio so I will end up with about 8 inches of total travel and a 1 inch hollow speedway eng. rear sway bar. Front weight 2280 rear weight 1860 any suggestions on spring rates ? I am currently working with ride tech and waiting for there new stuff But I have a set of Romics sitting here should i run what I have or go with the new Ride Tech stuff They seem to know whats up . I will be at the Truckin Throwdown and the good guys in Pleasonton if they will let me run ,not quite sure what class they would put me in .Any help would will be appreciated .I also plan on running any other autocross events we can get to here in Ca. Next question Tires? what is everyone else running I have a set of 20's on the tahoe who makes a decent tire that is legal at these events? also if there is a thread that is better suited to the 88 to 99 body style if so can i get a link ,all of you guys are building and running earlier truck so if these ?s are to far off topic let me know

[robnolimit]

GrimeeFirst off, congrats on the invite to the Trucking Throwdown, it's a long and fun day. Sounds like a good set up. I have no knowledge of those contlor arms but I'll try to help. - even though you will be my competition at the Throwdown. For spring rates, I like to have about 4" of static spring compression at ride hieght, so on the rear, you have appx 930 lbs per side, at a 2 to 1 ratio, so 1860 on the coilover & spring. Divide 1860lbs by 4 inches gives you 465 lbs/in. 450 may be a starting point on the rear. With 2280 on the front, thats 1140 on each side. I'd about 1.5 to 1 on the lower arm, (just a guess, use your true #) So 1140 x 1.5 = 1710, divide by four inches to get 427 lbs/in spring. Before you go out and use a 450 spring up front, I'll help you out. Your Blazer is top heavy, and nose heavy so add to the spring rate in front to help control it. To your true number I would add 20% - 427 x 1.2 = 512 lbs/in. But again, this is a guess on the lower arm ratio. I run between a 500 and a 550 in front, 1880 ft wt, and a 300 or 325 in the rear, 1470 rr wt, 1.6 rocker. When it comes to tires, Goodguys rule is a 180 treadwear. Kumho's are the stickiest. Most other events are 200 tw, so Nito NT05, or the Falken 615. B F Goodrich supports many of these events, and without them we wouldn't get to go play so much. The BFG KDW tire is a 300 tw, and will last most of the season. I run the BFG's to help support them, and as of yet haven't needed to change to beat the competition, even on the stickier rubber. It's all about the set-up. The Tahoe's shorter wheelbase should be an advantage on the short coarse. Best of luck getting it together in time, and let me know if you need some more help. See you at El-Toro

[Conundrum]

Originally Posted by robnolimit

Hmm, now I have to check into this. IF, both of the springs are the same length from the axle center pin to the front eye, then I would choose the longer one. It will have a bit softer rate. BUT, if they are different, and the longer spring is longer from the pin to the front eye, then I would choose the shorter one. It would have less axle wrap, and better grip through the corners. Trick question, and I don't know what the spring measurements are. Any help?

I meant to look while I was working on the truck tonight, but I think that the distance from the front spring eye to the pin is the same for both lengths of springs. I will be sure to look tomorrow evening and get back with you on it. Unless someone else knows for sure?

[hotroddr]

One of the big arguments against using air suspension in a high performance vehicle is that the spring rate is really not adjustable since you have a certain pressure in the bag that is needed to get the ride height to its sweet spot. Adding any air will raise the ride height, and removing air will lower it. Since this is the case, many people feel that they may as well just use a conventional spring.

Has anyone set up their air ride with both air bags and spring height adjusters (wedge adjusters) so that you can tune spring rate and then compensate with the wedge adjustment for the changed ride height? This seems like an ideal setup for an all purpose vehicle since you could change spring rate without changing springs or ride height. I couldnt find anyone doing this in all of my searching online. Im not sure if there is a good reason that no one is doing this, or if no one has thought of it or felt the need for it.

[Mechanic77]

I'm sure Rob will chime in, but I actually considered the same thing on my truck. Rob suggested that it would be a lot simpler to leave a little extra clearance in your spring pocket to allow for aluminum spacers to be added to adjust your air pressure vs. ride height. I decided to follow Rob's advice and save myself all the fabrication headache of the screw jacks. Just my 2 cents

[Grimee]

Originally Posted by robnolimit

GrimeeFirst off, congrats on the invite to the Trucking Throwdown, it's a long and fun day. Sounds like a good set up. I have no knowledge of those contlor arms but I'll try to help. - even though you will be my competition at the Throwdown. For spring rates, I like to have about 4" of static spring compression at ride hieght, so on the rear, you have appx 930 lbs per side, at a 2 to 1 ratio, so 1860 on the coilover & spring. Divide 1860lbs by 4 inches gives you 465 lbs/in. 450 may be a starting point on the rear. With 2280 on the front, thats 1140 on each side. I'd about 1.5 to 1 on the lower arm, (just a guess, use your true #) So 1140 x 1.5 = 1710, divide by four inches to get 427 lbs/in spring. Before you go out and use a 450 spring up front, I'll help you out. Your Blazer is top heavy, and nose heavy so add to the spring rate in front to help control it. To your true number I would add 20% - 427 x 1.2 = 512 lbs/in. But again, this is a guess on the lower arm ratio. I run between a 500 and a 550 in front, 1880 ft wt, and a 300 or 325 in the rear, 1470 rr wt, 1.6 rocker. When it comes to tires, Goodguys rule is a 180 treadwear. Kumho's are the stickiest. Most other events are 200 tw, so Nito NT05, or the Falken 615. B F Goodrich supports many of these events, and without them we wouldn't get to go play so much. The BFG KDW tire is a 300 tw, and will last most of the season. I run the BFG's to help support them, and as of yet haven't needed to change to beat the competition, even on the stickier rubber. It's all about the set-up. The Tahoe's shorter wheelbase should be an advantage on the short coarse. Best of luck getting it together in time, and let me know if you need some more help. See you at El-Toro

Hey Rob
Thanks for the response I know I wont be any compition for you and the Bullit ,All I am after is not embarresing myself this will be the maiden voyage for the tahoe .I will double check the ratio of the control arms then do the math .have you or any one else had experiense with the toyo R888 ?they happen to make the same size tire that i am running. I ran a dirt track late model for years and we ran around 55% rear weight and had the motor set back 4 inches to help get there my question is I am getting ready to drop in a LS motor What are your thoughts on moving the motor back and down as much as possible? how much rear wieght should i be shooting for ? what are your thouhgts I have Romics sittting here or or should i spend the money and try new ride tech triple adjustables? They were super cool to me at Sema I had issues with the coil overs i had on it at the time and they offered to help me out after i got invited to an event after the show
I want to thank you again for the help
Grimee

[robnolimit]

Grimee Dude, you need to get back in the garage, you've got a lot of work to do in three weeks. R888 is the R-1 replacement, great tire, but with a 100 tw, Goodguys and SCCA won't let it run, Super Chevy will, Optima won't. Up to you, there are no tire rules at the Truckin Throwdown, so I expect to see some there. Yes, move the motor down and back. Keep the trans pan just above the bottom of the frame rail - 1/4", for safety. Move it back as far as you can, within reason. If you could get to 50/50 wieght that would be great 51% rear is the target for the most part.
Here's the science. It's all about lbs/sq.in. on the tire contact patch. If you could calculate the tire's contact patch, in sq. in. for the front and rear tires, you might get something like 24.6 sq.in. front, and 31.2 sq.in. rear. To get the percentage, divide the front arear by the total area, or, 24.6 / 55.8 = .44, or 44% of the contact patch is on the front. Before you think that you should put 44% of the wieght up front to be perfect, remember that wieght transfers back under acceleration, and thats when you're turning, so you need to add 4% to 8% to your front contact % to get the perfect wieght. Now, As you move wieght, or change air pressure in the tires, the size of the contact patch changes slightly. So, just try to get close, you'll tune from there.
Shocks is another topic, and you're puttin me in the middle here. We use and sell Romic's in our IFS kits and 4-Bar kits. Romic has worket with us for years, and have been changing shock valving, adjustment rates, and base compresion rates until we we're happy. Kugal, So-Cal and others have all had great things to say about Romic's performance and ride quality, especially since we have been working with them. I have also used and sold RideTech (Air Ride Tech) for as long as they've been around. The're new shock program with Fox is top notch. I have used the single adjustables, and they are very good shocks. Here's the thing, with no experience in the Blazer yet, you have almost no feedback on what valving you need. I'd bolt the Romic's in and drive it, especially since you have them. Then tune them in the best you can. If you end up on one end of the tuning range, that will tell you if you need a softer or firmer range to tune in. Then, go spend some $$, but spend it smart.

[Conundrum]

Ok so i'm almost positive that the 52" springs are 4" shorter in the rear than the 56" springs. So (I may get scolded for this one but...) could you flip the shorter springs end for end and move the front hanger rearward 4" if the pin on the longer springs are dead center of the springs? That would help with the axle wrap yes?


Nevermind, I looked again and it appears that the shorter springs have the pin centered.

[aggie91]

Originally Posted by robnolimit

Grimee ... Here's the science. It's all about lbs/sq.in. on the tire contact patch. If you could calculate the tire's contact patch, in sq. in. for the front and rear tires, you might get something like 24.6 sq.in. front, and 31.2 sq.in. rear. To get the percentage, divide the front arear by the total area, or, 24.6 / 55.8 = .44, or 44% of the contact patch is on the front. Before you think that you should put 44% of the wieght up front to be perfect, remember that wieght transfers back under acceleration, and thats when you're turning, so you need to add 4% to 8% to your front contact % to get the perfect wieght. ...

Rob

this may be a dumb question or idea, but what if you put a tire with more contact patch in the front to compensate for the truck having a high weight bias to the front?

I am new to the handling issue going around turns, but you learn from asking questions...

Thanks for haveing this thread, it has been educational.

[robnolimit]

Yes that helps. We run a 285/35/18 on the front of the 'bullit. But you wouldn't want to give up any rear area just to make the balance match. More rubber is better. One of the Pro-toung.com guys showed up in Del-Mar with 315's on all four corners of a 70 Nova, and yes, he was fast.

[Grimee]

Thanks Again Rob! Was not trying to put you on the spot I guess i should have asked about single vs triple adjustable shocks some times it seems like more choices with adjustments makes it easier to screw it up. Not trying to get the new motor in before the Throw down going to run the old one for now and see if more hp will help and if it does how much more and still maintain drivability dont want to end up something that you cant touch the gas pedal on with out blowin rear tires off the thing . Thanks for the heads up on the R888 dont want to end up at an event and not get to play cause you got the wrong tires . I need to get it out see how it does before i spend money and ride quality is important as i will be driving it almost daily .Hope fully ill be able to do a little tuning during the daily commute its about 55 miles and 3/4s of its in the mountains

[Rstone1]

This is my first post here. Question for Rob – I’m building an 84 Blazer. It used to be a 4 wheel drive and I’m converting it to 2 wheel drive. I am going to use a set of truck arms out off an older truck with a set of coilovers on rocker arms with a long panhard rod and a splined sway bar for the rear. Question is on the front – I have a stock cross member. Should I modify the stock suspension to work with better geometry or should I start from scratch? I want a good handling truck. It will be my daily driver and I will be running some autocrosses with it when it’s done.

I did a 76 blazer back in the 90’s. I kind of did everything you have said to do on these trucks purely by accident. I didn’t have a lot of money to I lowered it so using parts I had and parts I got from the wrecking yard. In the front I raised the cross member 2” on the frame, modified my pitman arm and moved my idler arm to move the steering up, swapped the outer tie rods so they were on the bottom of the spindle, modified my drag link to clear the harmonic balancer, moved the lower ball joint forward and back toward the center of the truck (to get rid of the stack of shims on the upper A arm) also to get more caster. I also moved the upper A arm mounting point up an 1’ to slow the camber gain and also take the bind out of the upper ball joint. It had ¾ ton suburban coils with 1 coil cut out for springs. I also ran a 1 ton sway bar mounted upside down and directly to the frame as the truck was too low to run the factory sway bar stands and it was mounted upside down because that’s the only way it would connect to the control arms. In the rear I had got a set of 4 wheel drive leaf springs (because they are pretty flat and have no real arch to them) flipped the rear end on top. This made the truck way lower that I expected. (This is what caused all the modification to front). Frame was notched almost all the way through to get 3” of travel, towers were built to reinforce the frame, bed was notched all the way across, and shocks mounts were moved to the towers, 1 ton sway bar was added the cross member in front of the rear end had to have the center removed and replaced with a driveshaft loop because the drive shaft was hitting it and was also rubbing on the bottom of the cab floor between the seats so that was also moved up. All cross members were moved up above the bottom of the frame. I didn’t have the money for good shocks so I just put dual shocks on all four corners. The only real money was spent on the shafts and u joint to get the steering shaft over the upper A arm. After all this I had about 4 1/2” from the frame to the ground. Had little to no body lean and it stuck like glue. The only limiting factor was my tires. I had factory pick up 15x8 rally on the front with 265 50 15 euro TA’s and in the rear had 15x12 rally with 305 50 15 euro TA’s. Really miss that Blazer.

Thank You in advance for any advice you can give.

[Conundrum]

Originally Posted by Rstone1

In the rear I had got a set of 4 wheel drive leaf springs (because they are pretty flat and have no real arch to them) flipped the rear end on top.

Off the front of a 4wd?

[Rstone1]

No off the rear. They have less of an arch than the 2 wheel drive springs. At least the ones I've seen.

[Conundrum]

I may have to check that out, I haven't noticed but I really hadn't looked at them that closely.

[Rstone1]

I had a 76 1/2 ton short bead at the same time that had the rear flipped and with the 4 wheel drive springs on the blazer I was about 3 to 4 inches lower than the truck.

[Scot_Douglas]

Getting closer...

[Grimee]

Originally Posted by Scot_Douglas

Getting closer...

NICE RACK & pinion! Whats it out of ?

[robnolimit]

Rstone1 I'd guess the answer has some to do with budget concerns, and what you have. A complete IFS will run you about $2800 bucks. For that you will get a power R&P, big brakes, tube arms and coil-overs and sway bars. If you have some drop spindles, or some aftermarket arms you may be ahead of the game to use the stock layout. We raised the crossmember in the J.T. 1 1/2", 3" drop spindle, and 1 1/2" spring to get 6" static drop. If the steering is remounted to the lower side of the steering arm there is no need to notch the frame. Sounds like a good build, how about some more info? wheel/tire size? motor? trans?....

[Scot_Douglas]

Originally Posted by Grimee

NICE RACK & pinion! Whats it out of ?

1987 T-bird. Same dimensions as a MII rack, but far cheaper at Rock Auto.

[Rstone1]

Well Budget is still a problem for me unfortunately. I was thinking of building my own A arms and mounts. I don’t have any aftermarket parts at all for the truck. I have always just modified the stock stuff to make it work for what I needed. As for detailing, the motor with just be a small block with a 700r4. I still have to be able to smog it since I’m in CA. and don’t have a budget for a LS motor. I will probably be sticking with 15” wheels with some Nitto 325 50 15 in the rear and 275 50 15 in the front. Either I spend the money on the suspension or I buy 18” wheels. I think the suspension is a better investment at this point. I know the 15” wheels are going to be an issue suspension layout wise but hay they make it work in Nascar. So where I’m at now is figuring out what spindle to use and how to lay out my pick up points to work the best. I need to invest in some suspension layout software because laying it out the old way by hand takes too long to make changes. What software do you use? Any suggestions on spindles?

Thanks again for your help. And thank you for all your work on this thread.

[robnolimit]

I use a program called front suspension design pro, from autoware. When it comes to spindles for a custom design, there are a few I like. Both Fatman and Hiedt's have a tall, dropped, 'A' body spindle. These use a bolt on steering arm, so you can set the acreman and turn radius, based on steering arm length. The late '80s to early 90s Impala is good, match that with a '98 to '05 chev 1/2 ton rack & pinion. The droped, modular style '55 - '57 chevy spindle is very adaptable with many brake choices, also, the C-4 & C-5 Vette.

[Rstone1]

Thanks for the info on the software. I just remembered i do have a complete suspension cradle out of an 84 Corvette. those spindles would be a good palce to start.

[robnolimit]

Chassis Pictures
You have asked about chassis bracing, so here are some picts of a chassis we are prepping to go to Ireland. Attatching the swaybar link to the upper arm gives you a longer link, and that allows for more suspension travel without binding. Most of the bracing was done 'below' the chassis. setting the bottom edge of the tubing even with the bottom of the running board mounts, or, the lowest part of the body. This makes the frame think it's taller.

[robnolimit]

Frame Bracing. The tubing used is 1 1/2" x .120 wall steel. The front boxing plated were extended back to the cab mounts and tubing tie-in points.