I did a little research and looks like most people with 275/35r18 are running 6* plus caster on their alignments. I have PST upper control arms and have a feeling the max I’ll get is around 5*. Should that be good enough or do I just save up some money for SPC arms from @BergmanAutoCraft and call it a day.
Caster with 275/35’s?
- Thread starter RAVano
- Start date
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It depends on a lot more info than that. What is the car type and use ?
Road racing/race car ? Street car ? Suspension type ? Steering gear type ? R & P ? Power/manual ?
Tire specs ?
Road racing/race car ? Street car ? Suspension type ? Steering gear type ? R & P ? Power/manual ?
Tire specs ?
DionR
Well-Known Member
My guess is you will be fine, just not quite as stable in a straight line.
What I mean is, the car might not feel as stable as it could and might follow the ruts more than you want, but I bet it won't be unworkable. Just need a little more attention while driving it.
As an example, I am currently running a 245 tire and due to some unknown issue had to balance my caster at like 1 degree. I could get 5 or 7 degrees on one side but the other side went negative on the camber if I tried to push the caster out. I gave up and accepted that until I replace the control arms and do some tweaking, at least I could drive it like that. It sometimes feel skittish depending on how rough the road is and I have to pay attention on rutted roads, but it isn't impossible to drive and feels fine most of the time. Far better than it did with a huge imbalance of caster where it felt like it was constantly trying to drive me off the side of the road and kill me.
So even if you only get 5 degrees, I would bet it would be fine and you can decide then if you need to spring for the SPC arms.
Any pictures of the tires on the car?
What I mean is, the car might not feel as stable as it could and might follow the ruts more than you want, but I bet it won't be unworkable. Just need a little more attention while driving it.
As an example, I am currently running a 245 tire and due to some unknown issue had to balance my caster at like 1 degree. I could get 5 or 7 degrees on one side but the other side went negative on the camber if I tried to push the caster out. I gave up and accepted that until I replace the control arms and do some tweaking, at least I could drive it like that. It sometimes feel skittish depending on how rough the road is and I have to pay attention on rutted roads, but it isn't impossible to drive and feels fine most of the time. Far better than it did with a huge imbalance of caster where it felt like it was constantly trying to drive me off the side of the road and kill me.
So even if you only get 5 degrees, I would bet it would be fine and you can decide then if you need to spring for the SPC arms.
Any pictures of the tires on the car?
It’s a cruise car/driver. I have no problem cruising on the highway at 70/75 mph and just want a stable feel. Won’t see any road race or drag race time. 1.03” torsion bars, box stock lower arms, Borgeson power steering box and 275/35r18
You should be fine with around +5° if that’s all you can get. That’s what I ran on my Challenger with 275/40/17’s and power steering.
On my Duster I’ve run as little as +3.5° and as much as +8°, my personal preference is between +6° and +6.5°. Much more than that and the slow speed steering effort starts to dramatically increase, much less than that and the tendency for the wide front tires to track ruts in the road starts to increase. I have manual steering on the Duster so it’s all a bit more apparent then with power steering.
Like Dion said you might find it a little flighty on rougher or rutted roads. The power steering will probably work to your advantage though. I wouldn’t worry about it, I’d just set max caster and just evaluate how it feels. If it’s fine then don’t worry about it, if it seems a bit flighty then you can consider changing it.
And just FYI, you might not need to use SPC arms. When I had +8° it was actually with a set of generic looking non-adjustable tubular UCA’s that had Moog offset bushings installed in them. A lot of those tubular UCA’s use stock dimension bushings, and if they do, you can install offsets in them. A much cheaper option if they fit.
On my Duster I’ve run as little as +3.5° and as much as +8°, my personal preference is between +6° and +6.5°. Much more than that and the slow speed steering effort starts to dramatically increase, much less than that and the tendency for the wide front tires to track ruts in the road starts to increase. I have manual steering on the Duster so it’s all a bit more apparent then with power steering.
Like Dion said you might find it a little flighty on rougher or rutted roads. The power steering will probably work to your advantage though. I wouldn’t worry about it, I’d just set max caster and just evaluate how it feels. If it’s fine then don’t worry about it, if it seems a bit flighty then you can consider changing it.
And just FYI, you might not need to use SPC arms. When I had +8° it was actually with a set of generic looking non-adjustable tubular UCA’s that had Moog offset bushings installed in them. A lot of those tubular UCA’s use stock dimension bushings, and if they do, you can install offsets in them. A much cheaper option if they fit.
purplehazenils
Well-Known Member
What lower control arm pivot and bushing did you have when you got +8° with generic tubular upper control arms?
I think I remember reading that some lower control arm bushings push the control arm back giving you less positive caster.
I talked to Peter and just ordered a set of SPC control arms for him. I figured these will get me into alignment spec without guessing if my current ones would get that much caster. Thanks for the feed back
Firm Feel greaseable LCA pivots and Energy Suspension polyurethane LCA bushings, with 73+ LCA’s that I reinforced. That was the “low buck” setup before I went to QA1 LCA’s, Delrin bushings from BAC and SPC UCA’s (also from Bergman).
The previous UCA’s may have been Magnumforce, but those tight “V” shaped tubular UCA’s all look about the same.
Most of the non-adjustable UCA’s have enough positive caster built in to get to about +5°.
The SPC arms from Peter are awesome, well worth the money IMO just because of how easy they make it to change the alignment.
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