I just had a Ford narrowed 9" rear end with coil overs and Speedway vintage looking ladder bars put in my T roadster which weighs about 1900 pounds. The hot rod shop that did it has a lot of experience and they did a beautiful job. However it still rides like when it had the model A rear end with buggy spring.Hit a few bumps and it will shake your teeth loose. The shop installed the lightest weight springs made. I've got 7'00 x 16 tube type rear tires on old ford wire wheels and am going to try reducing tire pressure from 30 psi to ?? What is the lowest I could go on tire pressure? This car has a fibergl*** body and the *** end weighs next to nothing. Should I put a sack of concrete in the trunk also? Sure would like to smooth this ride out before I shake the car to pieces. Thanks
How many plies are your 7.00x16s. Most that I have seen are 6 ply minimum and as high as 10 or 12 ply. Sometimes the price of cool is almost unbearable. When the raven had the 10 ply 7.00x16s on his '27 it rode like a lumber wagon and eventually we got his pressure down to 18 PSI. Now he runs 15" tires that look different but no one can tell when he is running down the road @ 70+. He is not one of the "Cool" guys now unless you can count cool as being 200 miles to race for the weekend and 200 miles back with a minimum of body pain. Oh I meant to mention, most coil overs have an adjustable preload. I seldom see them set on light and that may help. Check and see if your have an adjusting collar and if so where it is set.
You need to find out what the spring rate your springs are. Then you can check with other dealers or manufacturers to get a softer spring, might even have to have one custom made to get what you need. The tires you can just try lowering the air 2 lb. at a time but watch how soft the side walls get (wiggle sideways). 22 or 24 would be as low as I would want to go.
I see where and why your going in the direction you are. Here's some food for thought. Your 1900 lbs Roadster is like that of a pick-up truck with nothing in the bed even though you have soft springs. If your quest about tire pressure (or even softer springs as other's mentioned) leads you no where. Then possibly consider adding weight to the rear of your ride. Where to put it and how to hide it ? Well that would have to be figured out. Just for ****'s and giggles try putting what ever you have that is heavy (HEAVY !) in the trunk and see what happen's. If it work's to your benefit ? Then follow thru with it. Now mind you, 2500 lbs is not the goal. Just enough weight to make it all good is all that's needed.
We suggest lowering the tire pressure all the time. I have even mentioned it. It works but it is a stop gap measure. One thing that we should think about is the Ford Explorer and the rollovers. The roll overs were caused by tire failure and the tire failure was caused by the tires overheating from being under inflated. Ford under inflated the tires to compensate for the rough ride. it was cheaper and quicker than the redesign that the suspension needed to make it right.
The Explorers were over-weighted at that lower air pressure, hence the overheating. The OP should not have this problem with such a light car.
Cl***ic symptoms of the term "incorrect unsprung weight ratio"; meaning a very heavy rear axle in a very light back end of the car. If you try to go too soft with spring rate and shock rate, the car will be better until you hit a sharper bump that lets the axle rebound like a basketball bounce. It is a trial and error situation to get the spring soft enough, but still have a shock that can handle the upward fast movement of the axle without getting it too stiff again. I ***ume it now has coilovers? I prefer leaf springs that can be tweaked, and then physically "feel" the shock selections by hand, to check the compression rate and extension rates. there is a huge wide range of tubular shocks out there. A good example of how an incorrect shock can ruin ride quality is back in the VW bug days, Sears used to run cheap deals on new shocks. They got the mounting distance correct, but the shock made the front end seem like a dump truck....because the bug weighed almost nothing up front. And by the way; VW air pressure factory specs on bias tires were 17 front and 24 rear! . .
get some weight in the back of the car. we have a newer GM cab over delivery truck for our stores and it rides like **** empty. when we load it with a bunch of weight in the back delivering equipment, it rides like a caddy!
Actually they put p***enger car tires on explorers, that was the cause of the rolls. We had one. I put LT tires on it and it was fine and rode better. The OP might try calking his tires to check contact patch. If they are only running in the middle drop the pressure until the tread is almost all touching. Used to be common practice in the off road world where E rated tires on jeeps were used for sidewall strength.
Actually the tires in question were bridgstones and they were LTs. The roll over crashes were caused by tire failure ( with the exception of the dummies that thought you could take a street corner @ 40) at least that was what the final lawsuits said.
F&J has it right. Sprung to unsprung weight ratio is about 80% of the issue. Should have put a Jag IRS in it instead of a 9" Ford, given the weight of the car. Read my signature line below. But the suggested methods of dealing with what you have are on track. Tire construction, tire pressure, spring rates and shock characteristics all have an influence on the results. Ray
T Bucket rear coil over shocks........ 165lb. to 180lb. springs. I dropped the coin for QA1's and it changed everything for the better.
When you say the shop installed the lightest springs they had, do they actually know the rate [or did the grab what looked the lightest] You need approx. 70- 85lb/in springs in the rear [guess] To do this properly you need to weigh the rear of the car. Then jack up the rear with the springs disconnected and weigh the whole un-sprung rear end ,then subtract this amount to calculate how much weight is supported. lets ***ume your car is 50/50 weight distribution and the driver is 200lbs 1900lbs + 200lbs = 2100lbs [ 50/50= 1050lbs at the rear footprint] Now deduct 250lbs for the rear un-sprung weight [I'm guessing] = 800lbs That equals 400lb per side For a comfortable ride the spring frequency needs to be quite low [5:1 to 6:1] At 5:1 you need 80lb/in spring stiffness. Now you also need to set the spring load. The spring will need to be set 5" higher than the normal ride height You'll need a spring compressor to install them In normal cir***stances a car is normally lifted up 5"+ before the wheel leaves the ground [using a jack]
The tire are 6 ply rating, tread 4 plies nylon, sidewall 4 plies nylon. 7'00 x 16 LT Tornel brand, made in Mexico. I reduced tire pressure from 30 psi to about 22 psi and noticed quite a difference. I think the hot rod builder told me the springs are 80 or 85 pounds. He ordered them, didn't just grab something off the shelf. Next I'll try a 60 pound sack of concrete in the trunk. How low could I go on tire pressure? I don't drive this car hard in the turns, just do straight line acceleration, stop light to stop light.
I have the same issue with my '29 roadster. When first built I discovered the main rear leaf was too wide causing the spring not to function properly......had a shorter leaf made.....helped some but still pretty stiff. I have added 3 bags of water softener salt in the rumble seat floor (nice option for me cause I use that salt in my water system in the house), helped some. Lowered my 700 x 16 bias ply pressure from 30lbs to 28lbs., helped some and for now will live with it and put some miles on it.
That will be a judgment call by you for your car and tires, trial and error. Like has been said already, the shocks or shock settings will change things also. The shocks, springs and tires all need to work together. If you get the tire pressure too low a hard hit in a pothole could bend that old rim.
My 2cents, Two things right off.tire psi should be lowered tell you see just a little flex in the side wall down near the road=that will be right for the tire load of your car, other thing may piss off some here,but running old design bysply vs radils is very stupid to me,the newer design are far better ride n much safer{looks just are not enough def.. There a number of miss takes done on hotrod builds that are repeted over an over becuz they see it an copy,one is how springs n shocks are mounted=often too close to center of car for shocks an often too strong springs or wrong shackel angle that have not been adjusted to that cars over all loading. Young guys are soft kind of,in that all the cars in your time on earth have better ride LOL,but there is still right an wrong things to do. Hope something in that rambull helps.
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