DIfferent sized wheels....effects on suspension?

Well, I was talking about the effects on the suspension of street-legal automobiles in general, but my particular vehicle is a 1983 grand marquis sedan, sorry about the missing info.

Nic

Thanks for the info. If I changed wheel diameter, I would keep the tire diameter the same. I figure if I went with a wheel of the same width, and a diameter 1 inch smaller, but keeping the tire diameter the same, they might just wear a little more quickly.

Am I anywhere near correct in this assumption?

If the total diameter of the wheel/tire combo, the contact patch width, and the offset (dimension of the mounting flange versus wheel centerline) all remain the same, tire wear characteristics would mostly remain unchanged. If the wheel diameter is decreased and the aspect ratio of the tire (sidewall dimension) is increased a corresponding amount, the increased sidewall may smooth the ride somewhat. On the flip side of the coin, a taller wheel and shorter aspect ratio may make the ride rougher. With the tire absorbing less of the road surface changes and instead feeding them into the suspension (the rough ride), the suspension may be compromised in its ability to keep the tire properly in contact with the road as the suspension cycles. This would have a negative impact upon tire wear, but it is not likely to be very noticeable.

Mark

So, of all the cases we've discussed here... it looks like if I do change anything, the best (other than an identically measuring wheel) would probalby be to get 14" diameter wheels, with the width equal to the original, offset equal to the original, OD of the tire the same as original, and contact patch width (I'm not a tire expert... is this the width of the part that is in contact with the road?) the same as the original.

And in doing that, I might benifit from a slightly smoother ride.

Thanks alot marky, you've been very helpful.

Nic

I just got to thinking again.... I have to make sure the wheel clears braking parts.

centerline)

Yeah, I knew that changing the total diameter will cause accuracy issues with those gauges. That's probably about the first thing I thought of actually, since I knew I didn't want to have to change any gears out for them. I've looked at a few styles of wheels, I think that even with an inch smaller diameter than the original wheels, they would still look pretty good. I think they would look worse to INCREASE the wheel size. But, I'll ahve to get under and look/measure and make sure the brake parts will clear. I'm sure the rotors/drums will, but I"m not sure about the calipers on the front.

Thanks, once again.

Nic

that some individuals

A very valid concern regarding brake parts. And then there's the fact that some individuals may find a 14" wheel to be somewhat odd-looking on such a large car. All this is not to say that increasing the offset a half inch positive and increasing the total wheel/tire diameter an inch is going to make your vehicle a hard-to-drive maintanance nightmare, but from an engineering standpoint, yep, it's pretty hard to change anything from stock dimensions without some degree of degradation. On a non-handling related point, I should mention that a change of the total diameter of the wheel/tire on the rear of the car will render the speedo/odo progressively inaccurate. And contact patch is the 'footprint' of the tire on the road.

Mark...

With tyres and rims, there is a equation that dosnt change the running diameter of your rims. like 205/65 x 15 should go down to 215/60 x 14 and

225 /55 13 thus keeping teh outside diameter of the tyres to that of a 13 inch rim. It also allows the stock brakes to be used, as the inward dish of the rim is of normal distance and dosnt put the speedo out at all..