Rim Brakes

I know it’s been a while since we last posted, it’s been a busy time in both mine and Refined’s lives. Either way, look for the updates to start trickling back in, starting with this easy, but intriguing article push from Autoblog.

I read this article from the NAIAS on Autoblog the other day at work, and immediately started contemplating the application of a rim disc and caliper.  Both from the engineering perspective and practical perspective.

Engineering wise, as Mr. Abulsamid points out, this makes quite a bit of sense.  The lever arm for the braking action is much longer, and since torque= force* distance, thus making the force applied by the caliper that much more effective.  On a normal road going car this can mean lower unsprung – and overall -  weight for the same braking capability, whereas a vehicle that pushes the envelope a bit more could have much more braking power for similar weight.  This weight/performance gain is especially useful in what is slowly, or quickly depening on who you talk to, becoming a fuel economy driven world.

The big engineering negative that comes to mind is that even though the unsprung weight is being reduced, putting the weight further out increases the wheels rotational inertia. This makes the wheels harder to slow down or accelerate.  I haven’t looked at the equations in quite a while, nor am I going to look them up quite this second, so I’m not sure how much this trade off will affect driving dynamics.

On the more practical side of things, for someone who does his own work on cars, there seems to be a bigger issue than finding replacement rims – I’ve already acquiesced to that becoming a big expenditure if I buy any modern automotive conveyance *shakes fist and wishes for the return of steelies*.  If I have a flat out on the highway, and don’t want to or can’t call AAA, how many extra tools am I going to need to put on the spare tire.   Beyond that, will I lose braking performance or adversely affect my handling dynamics if the rim brake on the spare is smaller, or worse yet: non-existent?

I grant though, that this problem would probably be handled, and mitigated, by use of runflat tires, especially if they are going through the expense and trouble of designing such a braking system.