How do you measure your 1/8 tires?
 

When you guys take a tire measurement, do you take it on the inside or outer edge? Do you take tire taper into consideration?

Outer edge of tire.

Are you talking about the diameter or the shore rating (hardness) ?

I think he means Tire diameter.

Yes I do mean tire diameter. So the outer edge measurement is what you go by no matter what the taper is?

Typical rear tires of 1/8th are all pre-cambered for the max traction....we all run like -1 degree toward inside, when measuring the roll out or simply rear tires diameter, I was told only measure the most OUTER size, which is the bigger diameter as the rear tire diameter.

So would you ever true a tire because of excess taper or just when it has uneven wear?

Try search over at www.mytsn.net and see you can find Art. C's article about pre-cambered tires........I am not 100% technical about the reason behind it, but it is definitely due to the WIDTH of that rear tires and with 21 engine, having 1 degree pre-camber is a must have on all 1/8th.

From my short 1/8th expereince, after truing the tires with 1 degree......after couple weekend of racing, the rear tires will still kept at around 1 degree pre-camber untill they are too THIN to use.......but if your tires ended up even after you started with 1 degree, there must be something is not right on the CAMBER (suspension) setup......

All in all........having 1 degree pre-camber is a standard setup of the rear tires, just be carefull about truing it....since it is 1 degree tapered inward, and typical (I think all) truer, is truing the INSIDE (smaller diameter) of the tires first.........lets say if you need to true it to 67mm........your bit setup should be LOWER then 67mm at first........the way I do is, I setup HIGH first, and keep truing it untilll it reach 67mm at the OUTER edge of the tires. I am sure there is a better way to do that, but I have plenty of time to true tires...I like seeing those foam got shaving off........ :lol:

The reason for cutting the taper into the tires, has nothing to do with making the tire wider for more traction (the surface width does increase slightly but is insignificant). The taper/cone is necessary to induce tire scrub & thereby simmulate differential action. With the inside of the tire smaller, it has a different roll-out than the outer edge. This, induces scrub & keeps the car from 'locking' on a straight line, allowing for a smoother entrance into a corner. If you were to try running the tires flat, you would find that the car resists turning into a corner, then abruptly comes around.
I usually cut a 1.5 deg. taper on my rear tires. With the Hudy truer, you simply set the diameter & angle you want & cut the tire. When you are done, the largest diameter(outer part) of the tire matches the setting on the truer.

[QUOTE=duneland]The reason for cutting the taper into the tires, has nothing to do with making the tire wider for more traction (the surface width does increase slightly but is insignificant). The taper/cone is necessary to induce tire scrub & thereby simmulate differential action. With the inside of the tire smaller, it has a different roll-out than the outer edge. This, induces scrub & keeps the car from 'locking' on a straight line, allowing for a smoother entrance into a corner. If you were to try running the tires flat, you would find that the car resists turning into a corner, then abruptly comes around.
QUOTE]

Duneland, do you mean the while cornering, the outside edge of the outside tires run longer distance than the inner edge of the inside tires, and that creates more diff action which results in smoother turning? So the advantage of running precamber tires has nothing to do with maximizing contact patch on the straight and in the corner? What do u mean by "locking" on a straight line?

Doesn't precambered tires reduce the outside tire contact patch during cornering? How do u determine how much camber u true the tires?

How come 1/10 touring still runs better with precambered tires given the cars usually run with diff?

Thanks for all the responses guys! Very useful info for this newbie.

raceblast, the coned tire induces scrub while going straight (by virtue of the different roll-out outside v.s. inside of tire). The solid axle induces scrub during cornering (due to the need for the outside tire to rotate faster than the inside tire & being prevented from doing so by the solid axle). By inducing scrub(coning tire) while going straight, we actually reduce rear tration so it will be more in line with the amount of rear traction we will have in the corner (when the solid axle forces scrub). If you are running straight, with 0 camber and 0 pre-camber with a bare minumum of toe-in, the car has maximum rear traction. It will resist turning (good set up for drag racing), giving it a 'locked on a straight line' feel. Once the front tires have generated enough side force to overcome the resistance at the rear, the back end will swing around from the sudden change in the amount of traction (scrub induced by solid axle). Running with more toe-in, neg camber and pre-cambered tires, gives a more ballanced feel. From that standpoint, it simmulates a diff. Works in a completely different way though, so the reference may have been misleading.
With a diff-equipped tc, pre-cambering the tires is unnecessary, but may be advantageous. Depends on several factors---camber rise, amount of neg. camber, roll-center, track demands, driving style, etc.
On a solid-axle 1/8 car, pre-cambering the tire is requirement. On a diff-equipped 1/10 tc, it is an optional tuning tool.

Hi, I have a question. I want to cut my 1/8 tires with 6 mm split.

Front 68 mm - 0 deg. camber
Rear 74 mm - 1 deg. camber

But Im not sure , shall I measure the split with outer or inner side of the tire. Because of the camber I have different dimension on rear tires!
Should I cut the outer or inner side to 74 mm. Which is the right one for the right split.

as mentioned earlier, all diameter referrences are for the largest part of the tire. For split, you are compairing the largest part of rear v.s. largest part of front.

duneland, thnx for info.