Track vs Tire Width, Front

[ONROADYNO]

What are the Pro's & Con's of reducing a front track 1" - 2" each side to fit a wider front tire?

Vehicle specs: approx. 3300lb, 60" track Australian Holden 1971 - 74.
very similar to 2nd gen Camaro.

Thankyou

[Schwartz Perf]

What will narrowing the front track width help in your situation? I am not familiar with their front suspensions.. But usually wider wheels/tires will run into sway bars, control arms, or even struts/shocks. Unless those items are also getting narrowed, then I don't see anything being solved by moving just the track width.

-Dale

[ONROADYNO]

Thankyou for your response.

My aim is to fit wider front tires without fouling the front fenders and keeping a good scrub radius and a good camber curve.

So basically if I had a choice of a weld in front clip what would be better?
57" with 315 tires or 60" with 275mm.

Thankyou

[mitch_04]

I'm pretty sure I saw Ron Sutton write that he will always take more track width vs tire size, but I don't remember in which thread it was in.

[Ron Sutton]

Originally Posted by ONROADYNO

Thankyou for your response.

My aim is to fit wider front tires without fouling the front fenders and keeping a good scrub radius and a good camber curve.

So basically if I had a choice of a weld in front clip what would be better?
57" with 315 tires or 60" with 275mm.

Thankyou

What would your rear tire size and track width be?

[dontlifttoshift]

57" and 315s

[ONROADYNO]

Ron, I would like to run 335/345 rear tires and the track can be varied to the best option.
Basically the standard body is 74" wide (total width including fender lip) with a standard track of 60.2" and wheelbase of 111".
I understand this is possibly a simplistic question without having all the knowledge, but would like to know the feasibility so when reading your "Sticky" I can relate it to the car I plan to modify. (my avatar is the 1971 - 74 Holden HQ)

Thankyou

[LXSS350]

There is a reason why all modern cars have maximum track width within their bodies dimensions. You don't see deep dish wheels on any modern or exotic car. With older cars however suspension engineering was not so well advanced. As far as width vs track the two are not mutually exclusive because of the physical limitations of the suspension and dimensional limitations with your design (car).

Always go maximum track with maximum width rims and tyres that will fit and not foul. You then get rims made to suit and many brands such as Forgeline will make them to the offset to fit between your design chassis limitations.

Of course if you want to keep the 70's look of deep dish wheels then you can also get rims built to suit such offset, but it will not be maximising the your geometry benefits you have available within the physical body limitations.

Its the leverage principle as you increase the wheel centre away from the mounting point you are putting more stress on your bearings under load. Obviously geometry is not a light subject with simple answers as so many things come into play. However in basic theory without all the semantics of specific chassis suspension fouling the Max rubber contact on the road is the same regardless of the offset of your wheels. So if handling is priority then the modern design of max track is always superior. If it was not we would see 2014 vettes, vipers, ferrari's, lambos etc all with deep dish wheels.

[Ron Sutton]

Originally Posted by ONROADYNO

Thankyou for your response.

My aim is to fit wider front tires without fouling the front fenders and keeping a good scrub radius and a good camber curve.

So basically if I had a choice of a weld in front clip what would be better?
57" with 315 tires or 60" with 275mm.

Thank you

Howdy,

Three things ...

1. The very basic answer ... assuming you're looking for optimum track or autocross performance ... would be to go with the 315s ... and run them as wide as the body will allow ... or wider if you're ok "fouling the fenders".

2. But there is more to it than that. Both adding grip with wider tires & narrowing the track width will increase the car's roll angle ... so you'll need to address that. All kinds of factors affect this ... CG height, roll center, spring & sway bar rates, etc.

I run the TRS-FLLD-RLLD calcs in advance & achieve the target front & rear roll angles by choosing the best package of spring rates, sway bar rates & roll centers.

Another key factor is the front to rear track width relationship. In case new people drop in on our conversation, track width is center of tread to center of tread. Tread width is outside tread to outside tread (not the sidewall).

Adjusting the front to rear track width relationship is a tuning tool … if the track width is adjustable … or a tuning challenge if it is too far biased on one end and NOT adjustable.

While there are exceptions to almost every rule, I typically don’t want to see the track width difference more than 1"-1.5” on either end. Even that can be a challenge if it the difference is the wrong direction.

Within reasonable differences making the front track width wider than the rear … or the rear wider than the front can be a practical tuning tool. Making the front track width wider than the rear = tightens the car … too much makes it push. Wider rear track width than front track width = frees the car … too much makes it loose.

Put simply, regardless of what is going on at the other end …
a. Moving the front tires out tightens the car.*
b. Moving the front tires in frees the car.*
c. Moving the rear tires in tightens the car.
d. Moving the rear tires out frees the car.

*Note: Adding spacers to the front hubs, increases the scrub radius. So when I can use either adjustable LCA’s … or simply replace the LCA’s for the track width I want … that is how I prefer to do it, versus adding wheel spacers to the front. I have used wheel spacers in the front many, many times. It’s just not my preferred method. Sometimes racing class rules dictate the decision.

A LOT of racers use small (1/8” to 1”) wheel spacers to tune … and in fact, many design & build their rear end & front hub combination with spacers as a part of it, so they can be removed to go “in” if needed … and of course, go “out” with more spacer as needed.

For cars I design, the lower control arms use adjustable threaded ends to allow up to 3/4” width change per side … 1.5” total track width adjustment, without affecting the scrub radius.

I like to start with the rear end with spacers that can be removed & of course, spacers can be added, for a 1” adjustable track width range in the rear. As far as spacers go, I prefer to use them on the rear end only, so as not to affect the scrub radius.

Additional tips: For cars with “high travel/low roll” suspension strategies, the front to rear “track width split” favoring the front works best. For cars with “low travel/high roll” suspension strategies, the front to rear track width split favoring the rear works best.

If the car is already “designed & built” … and the track width is wider in the front, that will “contribute” to the car being tight/pushy a degree. If the track width is a narrower in the front, that will “contribute” to the car being free/loose to a degree. I use the word contribute, because there are a lot of other suspension & geometry factors affecting the grip at each end of the car. If the track width is not adjustable at either end, you will need to tune with roll center, springs & sway bars to balance the car.


3. I think your math is incorrect. If you can run 275's with a 60" track width (and have the desired tire clearance with the fender) ... then if you put 315's on with the same tire clearance with the fender ... I think the math works out to a track width around 58.425".

Best wishes !

[ONROADYNO]

Will need time to process all your information Ron.
I suppose the word "tuning" or "development" come to mind.
Thanks again