Setting caster without turn plates

Technical and Repair Discussions
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PostPosted: Tue May 10, 2016 9:18 pm
I need some creative ideas. Anyone have experience with an alternate to turn plates when setting caster? I have the camber/caster gauge and just need a way to get the +/- 15 deg. turn. I tried the salt between two linoleum tile trick which let the wheels rotate fairly well. Measuring the angle was tough.
Thanks.
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PostPosted: Wed May 11, 2016 9:10 am
I just use the steering lock to lock (+/- 20) for setting camber. It is easy and repeatable.

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PostPosted: Wed May 11, 2016 9:28 am
If you want a precise measurement, put the toe strings on your car, mark a 15 degree angle on a small piece of plywood, hold the plywood against the wheel and turn the steering wheel until the angle on the plywood aligns with the 15 degree line on the plywood. (Obviously, you need four pair of hands :) ). Frankly, as Bob does, lock to lock is the way I usually do it.

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PostPosted: Wed May 11, 2016 11:30 am
I bought something similar to the link below and it works remarkably well when I check my caster after measuring it with turn plates. If you could create a bracket to attach it to, thereby eliminating any variability of placing it against the UBJ bracket, I think you could almost certainly toss the turn plates out.

http://www.amazon.com/GemRed-Digital-Pr ... le+measure
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PostPosted: Wed May 11, 2016 11:55 am
I was wondering if I was the only one doing this. What I do is measure caster when I'm doing the bump steer. Everything is disconnected and the wheels are removed. Raise the center of the hub to the proper height and use a digital gauge against the upper ball joint bracket and read the castor directly.

I've double checked it a few times using the traditional method and the readings are within 0.2 every time. Quoting Carrol Smith again, the amount of caster is less important than having it the same side to side.

Hint to save running out and buying a gauge, there are apps that can be downloaded to your phone that work as well. AND it's easier to get your thin phone against the bracket than one of larger store bought gauge.
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PostPosted: Wed May 11, 2016 3:41 pm
Lee Spuhler wrote:I was wondering if I was the only one doing this. What I do is measure caster when I'm doing the bump steer. Everything is disconnected and the wheels are removed. Raise the center of the hub to the proper height and use a digital gauge against the upper ball joint bracket and read the castor directly.

I've double checked it a few times using the traditional method and the readings are within 0.2 every time. Quoting Carrol Smith again, the amount of caster is less important than having it the same side to side.

Hint to save running out and buying a gauge, there are apps that can be downloaded to your phone that work as well. AND it's easier to get your thin phone against the bracket than one of larger store bought gauge.


I think repeatability if most important. Good or bad what I did is the following.

- made three stands that adjust from about 2.75 to 4 inches out of bolt, washer, nut, and steel square tube
- set car on two stands in front and one in rear at desired height without shocks attached.
- adjusted bump steer, caster, camber, and toe
- added shocks and adjusted so that car just lightly touching stand
- scaled car and adjusted rear shocks to get left/right balance
- adjust shock rebound
- connect swaybar
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PostPosted: Thu May 12, 2016 10:05 am
If you're using the Smart Camber gauge, the angle of the frame of the gauge is the correct angle for caster checking. I generally just do lock-to-lock, but eyeball using the gauge between the tire and the frame (at one point I built a cardboard template that fit between the tire and frame.) Side to side is important as a significant difference will cause the steering wheel to off center when going straight (I chased that once after crash repair and kept rechecking the steering wheel until I found I was 1/2 degree of caster off side-to-side.)

For those unfamiliar with the process, Take the two camber measures at full lock (20 degrees) then subtract the two numbers and multiply by 1.5. The numbers should be both negative, but it's technically possible for one of the measures to be in positive camber so take into account (e.g. add the positive and negative numbers rather than subtract.)

Oh, and don't do what I saw someone try once and put in negative caster (can you say shopping cart!)
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PostPosted: Thu May 12, 2016 1:11 pm
here is my hi tech approach using the smart level from the camber gauge:

Image

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PostPosted: Sun Feb 12, 2017 8:13 pm
For the first time I checked the static caster (wheels straight and level on ball joint bracket bolts). The positive castor was only 2.7 or so. I have never adjusted castor or bump steer myself and I have two questions. First, would it be best to do the 15 degree turn on turn plates for a more accurate reading. Second, my number is way off the Hoosier recommendation. What would 3 more degrees of castor do? I tried to look up but not much info. Thanks Lee
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PostPosted: Mon Feb 13, 2017 2:13 pm
Make the steering a lot stiffer! If you have scales, take a look at what happens when you turn the wheel lock-to-lock. There will be significantly more weight transfer corner-to-corner (e.g. as you turn the steering wheel right, the left front and right rear will gain weight and the opposite corners will lose weight). Also note the increase in camber on the left front. The car will tend to turn in better due to more favorable camber and initial outside front loading, but may also exhibit mid-corner understeer. This will more dramatic on slow speed corners than high speed, though the increased caster can also be helpful at higher speeds due to stronger self-centering so the car won't feel like it's "hunting" back and forth on the straight (especially if you run toe-out at the front).

I get a bit freaked out when driving someone else's car with low caster as it feels noticeably more "darty" in a straight line (and feels like it has power steering, both in terms of effort and lack of feel). It is easier to feel the limit of the tires with more caster, as the heavier steering effort will change more dramatically when you've reached or exceeded the limits of the tire, giving you more feedback at the limits of the tires.

Downside, high caster angles can be more tiring to drive with the extra effort required, especially with high-downforce tracks and long, high speed corners.
Bob Breton - SRF 51 - San Francisco Region
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