Wider 911 Wheel Track

mikesin · 04-30-2002, 02:02 AM

Hello : Are there any wheel alignment boffins out there who can assist a small problem I have ? I have "inherited" my sons unfinished project 911 USA Carrera. It is a 1975 model with 81 3.0Litre motor fitted. It is now converted to right hand drive with all correct parts. No problems in this aspect.

He has equipped the car with new widebody guards, as in 930, widened the wheel track of front and rear wheels and lowered the whole car. The centreline of the front wheels has been increased by 40mm each side with solid machined spacers, the back track is much less concern at this moment. I understand the rack and pinion assembly has been re-positioned to keep bump steer correct but the Carrera struts have not been changed.

My problem is that I am not convinced the car can be made to drive properly as the scrub radius or alignment will now be quite different. Presently it drives shockingly but I know it has not had a wheel alignment. I am confused by the fact I see comments that widening the wheels (track ?) gives the 911 better roadholding. At this moment I want to determine if it is even worth doing an alingment job or should I be looking to correct something else first.
Anyone help ?
Mike.
Brisbane, Australia.

Colby · 04-30-2002, 05:00 AM

How low did he lower it? Measure from the center of the wheel to the fender lip, both front and back.

USA spec: 26.5" front, 26" rear.
Euro spec: 25.5" front, 25" rear.

MANY of us have gone even lower than euro spec. However, then you need bump steer spacers. Other than that, lowering usually only helps handling, not hurts it.

Also, you say he widened the track. What size tires is it running?
Many of us again widen the track for better handling. This too should only help handling. If you have way bigger tires on one end, you can get excessive oversteer/understeer. But if he's following the typical turbo setup many of us use (which it sounds like he is), then it should be fine.

At this point, I would say get an alignment. That makes a huge difference.

Also, ask him if he changed the shocks, torsion bars, or sway bars. These will effect handling a lot as well.

Colby

Colby · 04-30-2002, 05:02 AM

One more thing: if you widen the front with spacers, you probably should do the same to the rear. Otherwise 1) the rears will fill the wheelwells and the fronts won't (which will look tacky) and 2) it can adversely effect handling.

Colby

mikesin · 04-30-2002, 12:58 PM

Hi Colby : Thankyou for responding.
The front track is currently 1440 approx and the rear is 1485 approx. The front tyres are 235/40 ZR/17 and the rear 265/40ZR/17. The height to the centre top of the fender wheel arch is 24.25 inches.

The wheel arches are filled and the car looks great It just handles like cr*p. The suspension was originally setup for autocross in the US and these low profile tyres my son has fitted would have you believe there was no springing at all. I have not yet had a chance to determine what size the torsion bars actually are but it does have new Bilstiens although again I don't yet know a model number for these.

Look forward to your comments.
Mike

Colby · 04-30-2002, 01:09 PM

Yes, 40 series tires do give you a stiff ride (but great handling).

I run 225/45/17 and 255/40/17 so your setup isn't too far off from mine.

The ride height is quite low (assuming you took those measurements from the rear), but that only effects how often you scrape, not how harsh the ride is.

My guess is the Bilsteins you have in there are the sport models (green) not the softer yellow ones.

Torsion bars are likely stiffer than stock too.

How exactly does it handle like cr*p? Is it just how stiff it rides that bothers you? That is a side effect of GOOD handling. Perhaps he has it setup to handle better than you would want. If that's the case, you can convert it back to smaller torsion bars and softer shocks (there will be many ppl on this list willing to trade their stockers plus cash for yours).

Also try raising the height a little. At that height, even with rack spacers it's likely to have some bump steer.

Colby

widebody911 · widebody911's Garage

I thought the yellow ones were the stiffies.

Quote:

Originally posted by Colby
My guess is the Bilsteins you have in there are the sport models (green) not the softer yellow ones.

marcesq · marcesq's Garage

With that tire set up, I would be willing to bet that there are 22mm torsion bars in the front and 28s or 29s in the rear. All good for handleing, and controling rear end squat, but not good for bumps in the road.

Maybe a kidney belt would help

mikesin · 05-01-2002, 12:41 AM

Re : handling like - "badly" :-)

At the moment the ride is harsh. Understabdable given the tyres. As above I don't yet know what torsion bars are in but yes it has green shockies.

Directional stability is the problem. The car is skittish and one cannot lose concentration for a moment, just around town. I expect that most of this is because it needs a wheel align job but my original concern above was about the scrub radius. The camber and castor can be adjusted easy but the widening forces the scrub radius to be incorrect. The contradiction in this is that I see spacers for sale promoting better handling and I see respondants to my query all of the opinion that the widening is not a problem but yet I know the scrub radius has been compromised.

I don't wish to race the car so am not concerned about the last nth of tractability. I just want a drive not not requiring absolute attention to keep on the road.

Can anyone talk to this scrub radius problem ?

Does anyone have a view on the fact that the widening causes much greater loading on the wheel bearings and axles.

Does anyone know why the 911 and 930 front struts have a different part number ? I note the wheel bearings are the same.

As soon as I can I will check the torsion and anti roll bars and let you know about these.

Keep it coming guys. I am gratified by the response.
Thanks,
Mike.

Colby · 05-01-2002, 04:57 AM

I am familiar with scrub radius, but I do not see why you are so concerned about it... Assuming it's the same on both sides, it usually does not adversely effect handling.

Wider, aggressive tread tires are notorious for wandering a little, especially "tracking" ruts in pavement, etc. That's a small price to pay for the better handling of wider tires, and the effect is usually nominal. It sounds like your alignment is way off, either caster, camber, or toe being "off" (maybe set ideal for racing, but poorly for street manners) could allow the front to feel like it wanders.

Overall, your 911 has a suspension setup that many of us strive to acheive. Yes, there are some prices you pay for ultimate performance. But what you're describing doesn't sound right. Harsh ride, common; wandering, something's not right. I would start with an alignment. I wouldn't suspect the larger tires just yet.

Colby