"Wide" tires on narrow rims?

[T540]

I need to replace the tires on my '82 Van Diemen.

I t has 6" wide front and 8" wide rear rims, both 13" diameter.

I'm thinking of fitting 7" wide fronts (7.0x20.5/13) and 9" wide rears (9.0x22.0/13).

The car is in a "formula libre" category so not running normal FC tire sizes is OK.

Any thoughts or comments on the suitability of using tires 1" wider than the rims would be appreciated.

The other option available to me is 6.0" or 6.5" wide fronts and 8.2" wide rears.

Thanks in advance.

[Wren]

Putting FC tires(7" front/8" rear) on 7" and 9" wheels is very common in FB. It works well with no issue. I think that it was someone at Hoosier who first recommended it.

[swifttiga]

(7.0x20.5/13) and 9" wide rears (9.0x22.0/13) That is the common set up here

[T540]

Are there any issues with the tires being 1" wider than the wheels?

[Wren]

There is no issue with the tires being one inch wider than the wheels. When the wheel is wider than the tire, it can be hard to seat the bead, but there are no problems in use.

[JerryH]

The tire sizes you mention are the ones used on FC cars. There is also an 8 in rear option......which works better on some cars......depending on the weight distribution.

They work ok on 6 and 8 rims......but a little better on 7 and 9 rims.

You could also run the 6 in FF front with the 8 in rears.

Jerry Hodges
JDR Race Cars

[S Lathrop]

Check with the manufacturer as to what rim the tire is designed to fit.

The down side of putting a wide tire on a narrow rim is that the tread will crown, not be flat on the ground. The performance of the tire mayl be significantly degraded.

[Purple Frog]

When Hoosier started offering the 8" bias rear for FC cars most of the field converted.

Less rolling resistance.
Less aero drag.
Less weight to accelerate/decelerate.

I know it improved my car, especially at high speed tracks (Road Atlanta, Daytona, RRR,etc.)