What do you BEC chaps have in your Locost?

english live axel in a sylva strika ZX9r

On a track, both are similar in performance and this reasoning is why many S7s use live axles - it's also simpler and cheaper. However, the fact is, many/most owners don't drive on the track which makes this argument much less valid due to ride quality. If (and it's not guaranteed) unsprung weight on an IRS rear end is 1/2 that of a live axle, the ride will be twice as nice. "Nice" means if the car bounces 1" over a given bump with a live axle, the IRS version will bounc only 1/2" over the same bump. This is an enormously improtant issue with a car meant to be fun... it makes the difference between a "30-minute car" and a "Two-hour car." Said another way, it's far more pleasent to drive and as a result you will drive it more. Having the car bound across bumps with the driver's jaw clinched so he doesn't bite off his tongue isn't fun.

*If* a very light live axle can be obtained, great. But more then likely it'll be an extremely over-engineered, over weight, assembly. Before you build the car you can, with a bit of research, find what the unsprung weight of each will be, and make a more educated decision.

Better yet, get a ride in a live-axle S7 on some real-world roads. Now get a ride in an IRS S7 on the same road to see how they compare. It really comes down to you.

Trawling through the Lotus 7 forums I found this.

Live axle full of oil 45kgs

Total de Dion set-up 70kgs

Bearing in mind that the de Dion diff weighs 25kg (Sierra) it clearly shows that the difference in unsprung weight is negligible.

You need a well located live axle!

But you also need to add to the diff weight half the driveshaft weight, as they are not totally unsprung weight. Also, a proper IRS will have much better unsprung weight than either.

As an owner of a Live axled car, I agree with what kb58 says, on track there is little advantage with either, but on bumpy roads my live axle is far worse than my mate's (IRS) Megablade.

Chris