Board logo

Live axle or IRS
Mark RSP - 20/10/18 at 09:56 PM

I have a choice of a live axle or an IRS chassis
What are the pro's and cons of both ,It will have a bike engine for a power unit
Mainly i will be using the car for fun on the road

richard munnis - 20/10/18 at 11:33 PM

Personally I would go for irs rear axle have had both and still have a bec with irs for hills much more progressive rear end and better range of diffs if you decide to go for 1000cbrr type engine 3.54 is lowest in a live axle and no use for 1000cbrr type engine

jeffw - 21/10/18 at 06:00 AM

Ultimately IRS will be better however, a badly setup IRS car will try and kill you at every corner whereas a Live Axle car can't really be badly setup.

I remember speaking to someone who prepped a lot of customers kits for IVA/did work on them and he said he always dreaded the first test drive in a IRS car which a customer had built as he never knew what is was going to do, he was quite happy to jump in a live-axle car because they always did pretty much what they were meant to.

owelly - 21/10/18 at 06:56 AM

I aimed for the best of both......De-dion.

Sam_68 - 21/10/18 at 08:31 AM

quote:
Originally posted by owelly
I aimed for the best of both......De-dion.


Or the worst of both, depending on which way you look at it.

If you're a glass-half-empty man:
De Dion is not quite as light overall as either live axle or IRS, not quite as low unsprung weight as IRS, and doesn't (usually) prevent the partial transmission of a bump at one wheel to the wheel on the opposite side... so not quite as good grip or ride as true IRS.

If you're a glass-half-full man:
De Dion provides the predictable geometry of live axle with almost the unsprung weight of IRS (so better ride and grip than live axle).

You can actually design live axle/de Dion systems so that a bump at one wheel doesn't transmit any variation in load to the other wheel, but it's not common practice and most designs don't achieve it.

...All of which is irrelevant for the OP, if he's building the car indicated in his profile, 'cos Raw don't offer a de Dion version of the Striker.

In which case, the answer is unequivocally IRS, if you're intending road use.

perksy - 21/10/18 at 08:46 AM

My experience of them is that the IRS rides & handles better (if its been set up correctly) but if your chasing weight reduction then go live axle

That said, iv'e been in live axle cars that handle really well


Depends what your aiming for really, I'd of thought for a bec you'll be aiming for as low an overall weight as possible?

AdamR20 - 21/10/18 at 08:56 AM

Live axle for me. I've had BEC live, BEC IRS, CEC live and CEC IRS cars before. It's the weight that makes the difference IMO, around 50-60kg by my reckoning.

Sam_68 - 21/10/18 at 09:05 AM

For those recommending live axle, it's worth re-iterating Richard's point above, that you'll be limited on gearing (and even 3.54 and 3.77 English axles were like hen's teeth, last time I looked... although you can buy the CWP's from people like Burton).

One of the things I dislike about BECs for road use is that the gearing is almost always too short - the constant high cruising revs grate on my nerves. This may not bother you, but bear in mind that with a live axle you'll be looking a very under-geared 'screamer'.

Mike Bentley - 21/10/18 at 09:35 AM

IRS
as some of the others say you can get the diff ratio low enough

I had a Sylva Phoenix with a 919 carb'ed fireblade engine and a I think it was 3.08 : 1 diff out of a diesel sierra the gearing was great. I could drive it smoothly around the streets and race it in the RGB plus I managed 130 mph flat out (once only just to see)
Plus it accelerated well.

I loved that car and still not sure why I sold it.

Mike Bentley - 21/10/18 at 09:40 AM

PS
I've had a fisher fury with cross flow and live axle, and now have a locost with cross flow and live axle.

I think the handling is good with either IRS or Live with the IRS being a bit more of a supple ride.

With the IRS you have the option of adjusting the rear TOE to your taste

jossey - 21/10/18 at 09:42 AM

For road riding irs is much better. My westfield live axle used to move around on roads with a camber.

Track wise my westfield was great handling and never felt different from my Avon irs.

That said for resale irs gets more normally. Especially in westfield cars.

Hope that helps.

AdamR20 - 21/10/18 at 09:44 AM

3.54 diff isn't that rare (if anyone wants a genuine Ford CWP set for £220 give me a shout) and with a CBR1000 and 205/60r13 or 195/50r15 tyres gives about 128mph top end, perfect IMO. Wind noise is louder than engine at motorway cruise anyway!



[Edited on 21/10/18 by AdamR20]

Mark RSP - 21/10/18 at 04:27 PM

How do i find out what diff i have got as i have a cosworth sierra diff and an english axle, can i find out without taking them apart

Sam_68 - 21/10/18 at 05:18 PM

You can do it by carefully rolling the car forwards and counting revolutions of the propshaft to revolutions of the road wheels.

Don't try to do it by jacking the car and rotating the wheels, though, as if you have an open diff it will give false results

Edited to add: if it's just diffs/axles, and there are no tags or markings, you can do the same thing by counting turns of the input and output shafts, but make sure that both output shafts turn exactly the same number of revolutions.


[Edited on 21/10/18 by Sam_68]

Mark RSP - 21/10/18 at 05:22 PM

Sam both live anxle and cosy diff are out of the car as i haven't started to build it yet

Sam_68 - 21/10/18 at 05:23 PM

Sorry, yes... just realised that and edited my post above.

Sam_68 - 21/10/18 at 05:27 PM

... and it's not that big a deal to take the backplate off a Sierra diff and count the teeth on the CWP, of course.

Bit more of a pain with the English axle, as you need to extract the driveshafts first, but you can still do it without upsetting the clearance on the CWP, which is the main thing to worry about .

Mark RSP - 21/10/18 at 05:43 PM

Thanks Sam

peter030371 - 22/10/18 at 11:34 AM

I have had a live axle Striker and now an IRS Striker. The IRS is setup sensibly with the proper equipment and so much better to drive on the roads than the live axle ever was. Its much more stable over changing road conditions, pot holes, leaf debris etc. Go IRS IMHO