In board or out board brakes.

[Jay Laifman]

I don't know the best sub forum to ask this.

We just bought an Elva Mk VI that has front and rear discs. We understand that the original cars came with drums all around - but the last factory Mk VI had front discs, so the historic racing groups allow front discs.

I think though that we need to convert the rears back to drums. Originally the drums were inboard.

Does anyone know if the historic racing groups care if the drums are inboard or outboard based on originality?

I'm assuming that for the racer's sake that in board is preferred since it is unsprung weight, and having them inward reduces their effect because of the leverage based on where they are on the axle.

Now of course I have to figure out all the parts I'm going to need for that conversion, and how hard it is to find them.

[Mike Bell]

Jay, I’m guessing that the requirement for an FIA ‘Historic Technical Passport’ doesn’t come into the equation? If it were mine, and even if I didn’t need the above HTP to be able to race it, I would keep the car period correct. So either with drums all round or disc front, inboard drum rear. In the U.K. having drums all round can put the car in a different class to cars equipped with discs, so can be worthwhile. That may not apply in the US!

Obviously as the owner you can make any modifications you want, but personally, I’m always thinking of how saleable the car would be if I changed something fundamental. If fitting outboard rear drums, would it then be a major change for a subsequent owner if they wanted to change to period inboard?

[Jay Laifman]

Correct, no FIA.

We have been reading the rules from our local groups and looking at what is showing up at races. Including VARA and SVRA. It looks like sometimes there are a wide array of very correct cars, and full classes. Other times it looks like the turnout is much looser and they almost let anyone run what they brung. Maybe I'm misinterpreting those later races, and they still are sticklers for details.

This sort of raises an observation. We've been going to the Monterey Historics almost annually for literally decades, and other races as well. It sure seems to us that the classes have gotten thinner. In part, I think it's because as years have marched on, "historic" racing cars have gotten newer and newer. So either room has to be made for the new cars, or racers are gravitating towards some of the newer cars. Cars are put in the same run group that aren't even close. With these thinner groups, that's why we might see less stringency at some of the races. I guess though that this nothing new, and has been happening since the first historic race!

[Jay Laifman]

And, FWIW, I was just looking at pictures (I don't have the car yet) and realized that the drums become sprung weight when inboard. So wouldn't it always be better to be inboard when it can be?

[Mike Bell]

Originally Posted by Jay Laifman

And, FWIW, I was just looking at pictures (I don't have the car yet) and realized that the drums become sprung weight when inboard. So wouldn't it always be better to be inboard when it can be?

Yes, unsprung weight is the wheel/tyre, upright, brake if ‘outboard’ etc. Sprung weight is all the car at the inboard end of the suspension arms or whatever. That is why inboard brakes were preferred, as they reduced the unsprung weight. So definitely the best option on a race car if practical. Check out the Lotus 72 F1 car with inboard (driveshaft driven) front brakes....

[mstets]

There is a trade-off between unsprung weight and cooling, of both brakes and gearbox. On our Chevron based Can Am car our brake temps were fine on relatively high speed tracks like Road America and Mosport but cooked the rears (and CV joints) at Mid Ohio, resulting in DNF. I think that cooling is why inboard brakes are not seen much today.


Just an anecdote which may have little relevance to your Elva.