hooliganz Posted January 7, 2012 Report Share Posted January 7, 2012 What length rear springs do you recommend for an asphalt sport mod? Link to comment Share on other sites More sharing options...
Truck99 Posted January 7, 2012 Report Share Posted January 7, 2012 What length rear springs do you recommend for an asphalt sport mod? The rear suspensions are basically the same as a truck. In the trucks, you can use either an 11" or 13". I like the 11s better - easier to work with. Link to comment Share on other sites More sharing options...
poorboy Posted January 8, 2012 Report Share Posted January 8, 2012 It depends on the rear spring adjuster installation. My car uses 13 or 16. I have 16 in it right now. Link to comment Share on other sites More sharing options...
jwmbishop Posted January 8, 2012 Report Share Posted January 8, 2012 The tallest spring that will fit and still give a good jacking range. A 13 with 2 inch of jack is far more stable than an 11 with 4. The shorter the spring the more jack bolt exposed to bend in a binding bump. Rate plays a huge role there as well - the softer the spring the the taller you want it at installed height! Link to comment Share on other sites More sharing options...
Truck99 Posted January 8, 2012 Report Share Posted January 8, 2012 The tallest spring that will fit and still give a good jacking range. A 13 with 2 inch of jack is far more stable than an 11 with 4. The shorter the spring the more jack bolt exposed to bend in a binding bump. Rate plays a huge role there as well - the softer the spring the the taller you want it at installed height! I'm not sure I buy this, but I'm interested in hearing more. Am I understanding you correctly in that a taller spring is more stable than a shorter one because it allows less of the jack bolt to be exposed below the threaded collar, and that the jack bolt is likely to flex or distort when the vehicle encounters bumps? Wouldn't the taller spring be more likely to bow and distort moreso than a jack bolt? Or did I misunderstand your point completely? Nick, sounds like a good one for you to chime in on. What about the topic of spring frequency that you touch on in your class. Link to comment Share on other sites More sharing options...
NickHolt Posted January 9, 2012 Report Share Posted January 9, 2012 I'm not at all sure I understand the issue or the question, but here are a few thoughts about linear coil springs. A linear (not progressive or regressive) coil spring that rates out at 1000 pounds per inch is a 1000 pound spring no matter how tall, how short, how many coils or what the wire diameter is. If it rates out at 1000 pounds, it rates out at 1000 pounds. There are three basic factors that determine the rate of linear coil springs if the modulus of elasticity is constant. Modulus of elasticity is just a measure of how much "spring" (ability to return to it's original shape) has. 1) number of coils, and 2) wire diameter, and 3) height of the spring. Basically, a coil spring can be thought of as a coiled up sway bar. The longer the effective length of a sway bar, the softer the rate. The shorter the effective length of the sway bar, the stiffer the rate. Likewise, the thicker the wire diameter, the stiffer the rate. So, a 10 inch tall spring with four coils is much, much stiffer than a 10 inch tall spring that has eight coils if the wire diameter is the same in both springs. That's because if you uncoiled both springs, the four coil spring would have less effective length than the eight coil spring. Likewise, if two 10 inch springs have an equal number of coils, the spring with the thicker wire diameter would be stiffer. A linear coil spring will retain its rate unless it 1) deflects enough to contact some other object such as a frame component or spring bucket/bolt, or 2) binds on one of its own coils, or 3) fails to return to its original shape (fatigues). From my perspective, I doesn't really matter what height spring is used as long as it's the rate the car needs to go fast, as long as it doesn't bind or hit any other component and as long as it's the height needed to obtain the desired ride height. Nick Link to comment Share on other sites More sharing options...
jwmbishop Posted January 11, 2012 Report Share Posted January 11, 2012 let me clarify. take a 8 inch paper towel roll (the center card board) and stand it up and place a plate on it. Now take a toilet paper roll (4 inch) stand it up and use a four inch 1/4-20 bolt to extend it and then place a plate. Without regard to the wobbliness of none of the pieces being bonded - the paper towel set is less likely to tip with a jiggle of the table. The spring is made to flex and return - the bolt is not. It can flex but it will either break or stay! The more bolt is extended the more likely it is to bend. simple leverage. I am not talking bump in normal application - I a mean when suddenly you are bouncing off another car, the curb, a wall etc.... a bump hard enough to use all of the coils and bind em - or temporary side load them. As nick said - a 100 lb inch 10 inch height spring is the same rate as a 100 lb inch 6 inch spring. The 6 inch spring will bind with a 600 lb load while the 10 won't. Thats why I have always used the tallest spring that I can get that has the correct rate... to have a more surviveable setup. Link to comment Share on other sites More sharing options...
NickHolt Posted January 11, 2012 Report Share Posted January 11, 2012 As nick said - a 100 lb inch 10 inch height spring is the same rate as a 100 lb inch 6 inch spring. The 6 inch spring will bind with a 600 lb load while the 10 won't. Thats why I have always used the tallest spring that I can get that has the correct rate... to have a more surviveable setup. Well, in the first place, springs made for stock cars that are rated that soft are always much taller than 10 or 6 inches. But, for the sake of argument, let's take your example of a 10 inch, 100 pound-per-inch spring and a 6 inch, 100 pound-per-inch spring and see what's going on. First, though, we have to assume that both of these springs have the same wire diameter or else we're comparing apples and oranges. And, again, keep in mind that stock car racing springs that are rated that soft are never that short. In order for both of these springs (remember, they have the same wire diameter) to have the same rate, they would have to be the same length if you uncoiled them and laid them out flat like a sway bar. So the taller spring would have coils further apart (in other words, have fewer coils) than the shorter spring and thus be less likely to coil bind under extreme conditions. However, most stock car racing spring manufacturers know this and take steps to insure that all their linear springs that are designed for typical stock car applications can handle 4-5 inches of compression without coil bind. There are some exceptions, of course, but many of those exceptions are used with bump stops that prevent the coil from actually binding (as in some BB/ss setups). Maybe I just haven't run into the jack bolt issue you bring up yet, but I really don't understand why a bolt jack would be more likely to bend or break with a taller spring rather than a shorter spring. Nick Link to comment Share on other sites More sharing options...
jwmbishop Posted January 12, 2012 Report Share Posted January 12, 2012 Simple - the more bolt exposed - the more likely to bend from simple leverage. You ain't gonna bend 1' of 1/2 inch steel. You CAN bend 4" of 1/2 steel. Chased too many setup problems finding runout on the jack bolt to be problem. Not only changing wedge - but also moving spring over. Hard to calculate for THAT. Also a bounce off the wall half way down the straight can try to shove the whole thing over. If that shove is successful (side load to 4" of jack bolt) - you just changed geometry mid straight! I just would rather have 1" of jack bolt rather than 4 to make up difference in 3 inch of spring installed height. I recall one year when I was working for hurst tire - Rick Carrelli threw a fit because "our tires were crap" and he kept cooking his left rear. He went to a different supplier with same result so took the car to Mark Norris (where we also worked on the car I was wrenching for) - when we unhung everything and used an impact to pull the jack bolts out - the perch ends wobbled at least 3/8 of an inch (by late season EVERY one in the winston west had bounced off walls curbs and each other quite a few times). So a half round of wedge not only lifted or lowered 1/32" - it also moved the top of the spring over ~3/8 (which gave very unpredictable results - the geometry change probably made the car do the opposite of what was expected)! Just imagine trying to keep up with it if turning BOTH bolts and seeing the perches spread or narrow over half inch! Rick never apologized for blaming our tires either! Of course Hornaday was running em and smoked the competition that year so we didn't really need it. So I just locked it in the brain to always use the longest spring and shortest jack bolt - of course coilovers eliminate that entirely. Link to comment Share on other sites More sharing options...
NickHolt Posted January 12, 2012 Report Share Posted January 12, 2012 Thanks for that explanation, jwmbishop. I've had coil over adjusters "self adjust" if they weren't taped or tie wrapped, but I really have never seen the scenario you describe. But, I know there's a first time for everything in stock car racing and I'll pay more attention to bolt lengths in the future. I have seen front pig-tail springs jump around in the lower control arm pocket and produce a bunch more (if on the right side) or less (if on the left side) static cross weight when the end of the spring ended up further up the a-arm pocket than originally planned - especially if the car got airborne for a second or two entering the track from an elevated pit road (Thunderhill Raceway for instance) or over the "ski jump" positioned nicely near the back pit gate at San Antonio Speedway or after taking an unplanned flight due to contact with a wall or some other car (always the other guy's fault, of course). We solved that problem by carefully welding a 1/2" bolt on the very tip of the pigtail on its bottom side, drill 1/2" hole through the lower a-arm where the end of the spring should rightfully sit and tighten a nut and washer to the bolt that protruded through the small hole. Worked like a charm. Nick Link to comment Share on other sites More sharing options...
jwmbishop Posted January 12, 2012 Report Share Posted January 12, 2012 Yes - I can see how the front is a worse problem - shorter arc (front control arms are lots shorter than rear so have faster arc) = quicker effective wheel rate change. 1/4" movement of either perch can change that wheel rate a ton. I like your solution. Link to comment Share on other sites More sharing options...
JohnnyT66 Posted January 12, 2012 Report Share Posted January 12, 2012 I thought the Question was about SPORT MOD SPRINGS?????,Although we are slow, Sure seems this went to LEFT FIELD!!...Why talk about a FULL BLOWN Cup Type cars when the Question was about SPORT MODS???..Top speed on a Sport Mod Bouncing off the wall is at SLOW SPEED compared to High speed of even a SLOW Cup type car....And even at our slow speeds, With the tall springs i have Never Seen this ...Now when i wrenched on the CUP CAR for, O, never mind.......Frank T....... Link to comment Share on other sites More sharing options...
jwmbishop Posted January 16, 2012 Report Share Posted January 16, 2012 Sorry -my bad I am an old fart and speak of the winston west as in mid 70's to late 80's. Although even today the Winston West are not "full blown cup cars" back then they were not much different than supers - extra door bars on right and full perimeter frame.. in fact most guys running the west just bolted lead to their exiting home track super and ran them as open comp cars... Yes Davey Allison brung a lot into his runs in the West back then by running what we even THEN called a cup car (more like a lightened Grand National - post Winston Cup) - but he got beat by weight. The Southwest Tour was absorbed by the WW and consisted of the evolution of super stocks to Late Models. On 1\2 and 3\8 asphalt. The tracks I based my experience on were Saugus (old), Cajon, Irwindale (old), Bakersfield etc.... and the cars are real close to the sport mods spring mounts. very relevant to the screw type spring mounts in todays Sports Mods.... yes Sports mods ARE lighter and yea we were slower - 18's on a half compared to sport mods 16's ..... - but increase speed and decrease weights - g"s felt at impact and across the suspension parts are real close to the same.... bouncing a 3800 lb car off the wall at 90 bends just as much as a 2800 lb car at 110! Link to comment Share on other sites More sharing options...
sam71 Posted January 18, 2012 Report Share Posted January 18, 2012 I thought the Question was about SPORT MOD SPRINGS?????,Although we are slow, Sure seems this went to LEFT FIELD!!...Why talk about a FULL BLOWN Cup Type cars when the Question was about SPORT MODS???..Top speed on a Sport Mod Bouncing off the wall is at SLOW SPEED compared to High speed of even a SLOW Cup type car....And even at our slow speeds, With the tall springs i have Never Seen this ...Now when i wrenched on the CUP CAR for, O, never mind.......Frank T....... the only real reason to have either spring is what the chassis builder decides to put the car I stare at a car I set the car footprint in my head and I build to give the look that looks the fastest or them are the only springs I have LOL But I like the longer springs because you have a shorter jack length and that they don't bonce out out as easy under rear end collision I seen a driver lose a track champion on the last nite of points at cc because of that happening Link to comment Share on other sites More sharing options...
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