scrub radius poll

[bird2]

Hey guys im taking a poll of what your scrub radii are. of the people running an outboard hub, how are you keeping scrub to a minimum?

[Dash]

Less than an inch, and I use suspension geometry for the most part.

[sbrenaman]

~2" on 2010, ~1" on 2011.

Need a lot of positive wheel offset and if you're still having issues, you can use Kingpin Angle to get it to 0" easily. However, I was able to get ~1" with only ~1deg of KPA.

[Fyhr]

We've also run 25mm for a long time, with 0 deg KPA.

A recent video of the tyre under load makes me question the accuracy and effect of our static scrub though: http://www.youtube.com/watch?v=ZnzXk-A7Avw (please ignore the off-tarmac event and focus on tyre deformation and contact patch movement).

[DougMilliken]

A recent video of the tyre under load makes me question the accuracy and effect of our static scrub...

If you have tire force & moment data, you could look at the overturning moment data (Mx) to put some numbers on the tire deflection seen in the video.

[BillCobb]

Finally, method in the madness.

Here's what we are talking about:

http://www.youtube.com/watch?v=nmo_dkNZIHM

Tires can have a large or small positive or negative Mx just going down the road straight. Then load, slip and camber can knock around all the geometric settings. This means you design for it rather that pick a number out of your ... Since these cars are known to attempt high lateral force levels. you ought to factor in this key player. Your driver will appreciate the effort (hey, that's a pun).

[DougMilliken]

Originally posted by BillCobb:
http://www.youtube.com/watch?v=nmo_dkNZIHM

(turn volume down before playing!!)

The TTC DVD includes videos on Calspan TIRF...but with no sound track.

[swong46]

There is a lot of talk about front scrub radius, but what about the rear? does it even matter?

[PatClarke]

Of course it matters!!! Think about it.

Pat

[Fyhr]

Originally posted by PatClarke:
Of course it matters!!! Think about it.

Pat

The only trick you need to convince Pat is: Large toe-base (say 100mm), large mechanical trail (mmm, self aligning goodness! (100mm) and give it a horribly large rear scrub (100mm?) for an acceptable solution. Then extrapolate this down to, hey we run zero rear scrub (we did) a smaller mechanical trail (why not reversed?) and you can easily allow yourself a nice easy to package 10 mm toe base!

But in all seriousness, refer to the videos above, calculate how your forces are affected by changing scrub and what you need to do to cope with those changes and you will be close to both a solution and answers to keep design judges happy. Remeber to read this too: http://www.formulastudent.de/d...ness-and-compliance/