Steer Ratio

[Paterson]

We are currently deciding on the steering ratio for our new car.

Can someone give use some idea of what other teams are using with regard to this. Secondly, what are the maximum wheel angles which teams have been running for the tracks provided.

Cheers

Craig Paterson
UARC FSAE team 2005

[Denny Trimble]

Teams typically run steering ratios of 5 to 10, and see maximum steering angles at the wheels of 20 to 30 degrees.

[fsae racer]

Denny, you do mean 20-30 total, 10-15 in each direction, right?

[Denny Trimble]

No, 20-30 in each direction. You can calculate it from the rules minimum corner radii and course width, and your vehicle size. I know when we set up a course to those specs we hit steering lock in that range.

[Frank]

we go for 30 deg at the wheels (60 deg total)

or (with ackerman) 25deg loaded wheel, 35deg unloaded wheel

and 270 deg total at the steering wheel


at an absolute minimum i'd use 25 deg ( or 20 / 30 with ackerman)

[fsae racer]

I take it all you guys have your spherical bearings orriented such that the bolt through them is vertical? The max missalignment on our sphericals is only 23, ie max steer angle if perfectly oriented with a horizontal bolt.

[Carlos Torres]

We´ve got:
33? in the inner Wheel
24? in the outer "in 1 direction"
with
100% Ackerman
180 ? at the sterring wheel (total)

so the steer ratio is aprox 3

[Denny Trimble]

Carlos, check your math:
Average wheel angle (outside/inside) = 28.5 deg
Steering wheel angle = 180 deg
"Steering Ratio" = 180 / 28.5 = 6.3

[Carlos Torres]

I think I explained:
In 1 direction 90? at the steering wheel gives 33? in the inner wheel
SR=90/33=2.72 (aprox)
Custom made Rack&Pinion 2.6 total travel and 3" Steering Arm

[Denny Trimble]

Whoops, I missed the "total" comment. 3 is a very fast ratio for FSAE!

[Paterson]

Thanks guys,

very useful info!

Carlos, your drivers find that this quicker ratio is accurate enough for small steering inputs?

[Carlos Torres]

Yes I think that accurate enought for FSAE drivers, a 3 to 4.5 ratio in the best in our cars.
180 to 270? total (lock to lock) at the steering wheel is really good.

- In karting the steer ratio is 1
- In Formula 1 cars the average steering wheel rotation is 180? or less

"Our cars are in the middle of those categories"

[mangel83]

Denny we're building our first car so we don't have any experience driving FSAE cars, but the way we see it with a fast ratio such as 3, there's no need to take the hands off the steering wheel when turning form lock to lock for example(assuming 30deg maximun wheel angle, 180deg total rotation at the steering wheel, 90deg to each side).

Instead, using a ratio of say... 6, would give us 360deg total rotation of the steering wheel, 180deg to each side, and although it's not impossible to go from lock to lock without taking your hands off, it won't be as comfortable for sure.

Maybe it has something to do with the speed we're driving, the track layout or other things we, as a first year team, are not aware of. Any help in this subject would be great. Thanks

Manuel Sanchez
FSAE-LUZ