Large Scrub Radius

[marcin]

My team wants to use electric hub motors and these will pertude 40mm outside the wheel with a 100cm diameter.

The issue is they will conflict with the pull rod/pushrods.

So proposing to move the suspension pivots at the wheel further out, creating a large scrub radius.

Would anyone think a scrub radius is of 80mm-90mm extremely detrimental?
I know it will increase steering effort but by how much? Undrivable?

[marcin]

My team wants to use electric hub motors and these will pertude 40mm outside the wheel with a 100cm diameter.

The issue is they will conflict with the pull rod/pushrods.

So proposing to move the suspension pivots at the wheel further out, creating a large scrub radius.

Would anyone think a scrub radius is of 80mm-90mm extremely detrimental?
I know it will increase steering effort but by how much? Undrivable?

[thewoundedsoldier]

I doubt it would be too detrimental. Formula student is all about compromises. Your car will still be driveable.

Out of curiosity, what is your mechanical trail like? If you keep the trail under control, I think you will be fine.

As is often said in these forums, getting the car built on a quick schedule to get seat time is more important than fine tuning the theoreticals ahead of the fact.

[RobbyObby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by marcin:
with a 100cm diameter.
</div></BLOCKQUOTE>

Rollin on 40's are we?

[Dash]

Better start hitting the gym if you want to finish endurance.

[Rotary Sprocket]

As long as your scrub radius is within the tire contact patch the car will be driveable.

[BillCobb]

If these motors are high torque at low speed and the tire peak to slide ratio is high, you are going to need traction control. Otherwise, you will have a severe case of transient torque steer. That means the car will get stuck in a hunt for wheel spin. It will have a severe divergent pull to one direction and can rapidly switch from one direction to another. A "knuckle buster" for sure and a chance to break some critical parts in the steering system if not managed.

Try it out on a V8 FWD car by spacing the wheels. You'll get the idea really quick.

[Adambomb]

BillCobb is right...even if the steering effort was worked out the torque steer would be gaawwwd awful.

Although remember, offset isn't the only thing you can play with to get the scrub radius you want...

[Adambomb]

Hmm, reply coming soon...blocked because I accidentally typed a prolonged "gawd awful" using three w's. http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif Hell with it, here it is again:

BillCobb is right, even if you got the steering effort OK the torque steer would be gawd awful.

Just remember, there's other ways you can get the scrub radius you want than just playing with offset...

[Homemade WRX]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Dash:
Better start hitting the gym if you want to finish endurance. </div></BLOCKQUOTE>

That's nothing a little clutch, skinny pedal and flick of the wrist can't help solve http://fsae.com/groupee_common/emoticons/icon_razz.gif