Hi, im building an VortX and have an full set of 13x7" et24 CXR.

Im thinking of going up to 8" in the rear.
Is that an clever idea?

Tyres will be slicks for track and 888īs on the road.
Will have two setīs of rimīs.

Swaybarīs...anybody made a set for the vortx...any experience in that department on this chassie??

Car will have an strong track focus but bearable on the street.

We call swaybars anti roll bars.
Light weight cars with a low centre of gravity are better off on the road without anti roll bars. Lotus elise doesn`t have an anti roll bar.
On the track where it is smother it may be benificial.
Darren

I think only a very few manufacturers do make them but for there own specific kit cars, i wouldnt invest in one as unless it is specificly designed for your car it can make handling worse through reducing almost all dynamic camber. As far as I am aware the road car reason for having ARB's is to allow the fitment of a softer suspension setup(damper and spring) to be fitted as they havent got to control the roll as much. Maybe a stiffer coilover setup would be a better option that you can tweak far more easily?

The addition of anti roll bars is in my opinion a must for anyone who is half serious about handling on circuit. For road use I simply wouldn't bother.

It's very important though to make sure the strength of the bars fitted are the correct strength for the car. A correctly specified ARB should allow for a softer setup on the car, whilst still giving the driver good feedback and a direct feel, and also giving wheels the independence they need, so there is a lot to get right.

I am in the process of tweaking my front ARB now which I'm sure will have great results.

As for 8" wheels at the rear, it depends which engine you are planning on fitting. If you are looking for more grip from wider wheels then you won't get any more.

What is it you are trying to achieve with wider wheels? A 205 profile is fine for most cars, which will fit comfotably on a 7" rim. I think you would struggle to get heat into anything wider unless it's well over 200bhp!

Re ARB.
I would have them adjustable with knife brackets (well...if thats the word).
See pic.

Re engine: 2008 Hayabusa

The car will be track oriented (circuit) and i prefer track performance over posh street cruising.

My idea of having 8" rears is that it would accomodate slightly wider rubbers and let me use slightly softer compound to generate more grip without overheating.
I could be really wrong here...as if i canīt achieve heat in the rubber itīs just an waste of time...

To fight chassie roll by uprated spring will also cost grip as well as yaw ...as i never raced any car and especially an MNR VortX i donīt know what is helpful to produce even, hot laps.

As an ex bike racer i do know that lack of adjustment in handling can be very frustrating.

So...
Who races or push HARD with their vortX and gone down the road of chassie set-up improvment and willing to share their findings.

Frosty: Thanks for ARB input. Re tyres, i donīt want to be fine...i want to be FAST! If itīs an 0,2 sec to gain by using the "right" tyre with on track i will go for it. But if itīs an total waste..then i will not.

HiCost: I hear you We wanna go fast!

Basset: Who tested adjustable ARBīs on the VortX Super and ditched it? I do understand what you mean, but if nobody even tested it on the later chassies (mine is an late 2008 built Super).



[Edited on 30/10/09 by Triggerhappy]
Rescued attachment krankS.jpg

I'm pretty sure Matthew Lewis runs ARBs on his V8 Vortx, which is the only one racing frequently in the UK as far as I'm aware.

Just for your info Darren both the Elise & Exige run front ARB's, the higher spec models use 3 position adjustable ones.
Regds
Ian

Triggerhappy, it's good to see someone serious about handling.

I'm really not sure how much testing the MNR boys on here have done, but in principal the same theories apply to most of the cars on this board.

I think you're best off sticking to 7 inch rear wheels initially, because these will typically take anything between a 175 to a 225 tyre which is a massive range.

I have heard of people going from a 205 to a 225 and just not being able to heat them at all, so even 10mm makes a big difference on a light car.

If you go for 8 inch however, you are limited to 215 upwards. You would gain no extra grip, in fact you would lose it if you found you couldn't get them as warm as the fronts. You would probably find the need to run the rears a few PSI lower than the front to find the heat again.

Your problem will be heat management, and what you do to the front you do to the rear. You certainly wouldn't find a car running different compounds front and rear, so you would find a really soft tyre might work well at the rear, but the narrower front would just get overworked on the same tyre. This would really make ironing out handling problems difficult.

A 205 rear suits my 2007 Busa Westfield very well indeed. The good thing is that on a 7 inch rim I could go to a 225 if I wanted, which would make a massive different in heat management.

I would suggest 7 inches all round, or 7 inch rear and 6 inch front wheels.

I'll be changing my front wheels down from 7 to 6 inches soon to give better effective range there also.

** edited to say changing my front wheels down to 6 inches **

[Edited on 30/10/09 by Frosty]

hi
i've been using my mnr on track (only) for a year now and spent a lot of time on testing what could be the best.
IMO, 205 tyres are enought for bike engined car (althougt i have 8" because next year i'll fit a rotrex and 215 tyres)
re ARB, MNR chassis are very stiff, and to be efficient, front need to be quite hard and it is good to get a little "rolling effect" at rear.i haven't tried to fit soft spring with ARB yet but it works very well with no front/rear ARB .(better than my MK indy fitted with front and rear ARB)
but i'm sure it well worth trying!
cheers
antonio

Frosty: I hear you...iīll mabye rest a bit on the 8" issue. Again, car is not yet finished so no real hurry. But iīll try to get it so close to fast as possible as early as possibly. And if there is an collective knowledge that bring me (and anybody else) there its great.

Antonio: GREAT to hear from you (VortX driver).
Are you having an fully rosejointed car?
Are you using slickīs or R-tyres?
Have you tested differnt casters, spring rates etc. As i understand most 7īs have pretty much steering. Iīs not very clear but are you having ARBīs or plan to get an set done?
What have you tested and how did the car react?

hi
re wheels, a 8" rim will be fine for a 205 rear tyre.(should say it will fit perfectly)
my car is not fully rosejointed, since i bought a rt, but replace front wishbones with rosejointed to allow accurate settings.
till now, i've been using 888 tyres, but i'll go for slick next year.
i've tried a lot of different setings re-geo and i have now found a very good geo (thank you greg!)although the car oversteer a little bit on slow corners.
i've not tried ARB for the moment.i will try just to be sure, but i don't think it's needed, as i said the car is stiff enouht, even with soft spings.
you should start as it is, and see how you feel.
here are my settings:
ride height 75MM front
115 rear (chassis rail under fuel tank)
-1.8 front camber
-2 rear camber
1mm (each) toe out front
1mm(each) toe in rear
front caster 4.2 degrees
front springs 150lbs
rear 175lbs+helpers
hope that helps