First impressions with 20" style 87s on 3.0 5 speed manual

[crystalworks]

Originally Posted by e39_touring

Revisiting this, and PropellerHead was right-on. I swapped out the Bridgestone runflats for non-RFT Continental DWS, and boy what a difference! The small-imperfection harshness is practically gone, and the car feels more nimble again.

I weighed the runflat tires coming off at 38.6 lbs front and 43.2 lbs rear.

Replacement tires weigh 28.9 lbs front and 33.3 lbs rear with more tread - a savings of 10 lbs per corner!

I also noticed a considerable weight savings when switching tires from the Dueler run flats to non. And that's even with increasing the tire size. I went to 285/40/20 up front and 325/35/20 out back. I like taller side walls.

[bcredliner]

Going from 18 to 20" 87s will improve handling due to wider footprint and improved turn-in. The heavier weight of 87s in straight line acceleration difference might mean losing a .1 in a quarter mile. The heavier weight increases sprung weight and is negative impact on handling. Taller sidewalls allow the tire to rollover more which improves ride but is also a negative impact to cornering.

The most negative result of this combination is the increased tire diameter. The greater diameter increases the effective diff ratio. Higher effective diff ratio will reduce straight line acceleration and slower road course times due to less acceleration out of corners.

Other than appearance, wide 18" rims and low profile soft tread tires would be better when complimented with heavier swaybars to reduce body roll, lowering it-lowering center of gravity, and spacers to widen the stance. HD shocks might be better but some I have tried made the X ride to hard on the street and X is not fun to drive as it was also very skittish- hard to keep in a straight line. Any combination is improved with an alignment that sets toe and camber for best handling. A stock X5 understeers too much which means at limits the front will break loose first, slide out from under it. Focus of handling improvements should be too reduce understeer toward a neutral condition.

Coilovers are great if one is tracking a lot but require a lot of testing and adjusting at each venue to get much more out of them. For tracking I would add a strut tower brace and camber plates.

If not tracking I don't think coilovers are a good value. A good set up without them will result in cornering capability that if pushed to the limits on the street is way too dangerous to ones self and others.

Before doing anything best practice is to do a complete suspension rebuild to start from an out of the showroom handling.

[PropellerHead]

Originally Posted by e39_touring

Replacement tires weigh 28.9 lbs front and 33.3 lbs rear with more tread - a savings of 10 lbs per corner!

That's GREAT! Glad to hear you're having a better experience now.

That's what this board is all about!