tcsracing1

My 1991 now has a set of 18" RH wheels.

We also installed big reds up front.

Noticed that the fronts wheels will lock up under hard braking.

Would the ABS in the 1991 be sensitive to tire diameter or big red upgrade?

urquattro20Vt

I'm no expert but I sure would be surprised. Really I don't see how it would know...it's just comparing rotating speed of each wheel, no?

Brandon
'91 911 Turbo
'00 Audi S4 highly mod'd DD

Vince964T

Strange. Got same setup, big reds, 18s 235s front tyres, either Tropheos, Cup back in the days or Cup2s and I dont lock... Crap ABS but not locking. smthg's wrong

Doms964TurboII

Not if its working correctly

bweSteve

your R34 relay might be bad too. Should check that one. Plenty of threads on abs & r34.

=Steve

heliolps2

From my Experience with my 993 it did,

Factory called for 255/35/18's
I installed 285/35/18's and it triggered my ABS light, I cleaned all my sensors and replaced relays, nothing fixed it, I went back the Factory size tire and the ABS light was gone.

Metal Guru

Contamination and corrosion of the caliper pistons or collapsing rubber lines are also a possible cause. They act as inadvertent bias valves. The brake fluid pressure will achieve equilibrium so when it can't flow to the rears any more it will increase flow to the front.

tcsracing1

it was the fuse..... my bad...

heliolps2

Thank you for the update

bweSteve

Fuse? ... or the R34 relay (post # 5 above) ?

cobalt

The ABS computer for the C2 and turbos are all the same. Changing tire size shouldn't impact it unless you mess with rolling dia.