Upgrading Wheel Size

[Guest]

I have a '77 Regal that currently sports 15X7's? and would like to go up to 17 inch rims. <P>Current tire size is 215/70/15s, and according to a tire calculator I can put on 245/50/17s without affecting the speedo. <P>Will I encounter any rubbing problems with this size??? <P>Thanks<P>Scanlon<BR>

[NTX5467]

A couple of things to consider --<P>First, go into something like <A HREF="http://www.tirerack.com" TARGET=_blank>www.tirerack.com</A> and find some tires of the desired size. Then go to the "specs" area for that particular tire model and see what the "section width" measurement is. With that total width dimension, compare what it is to your current tires and see how much wheel well area will be consumed and if anything will hit the suspension.<P>Second, find out what the backspacing is on the wheels you want to use. This is the dimension from the inner mounting surface to the inside edge of the rim. Also, notice where the center of the tire will be (side to side). This way, you can see where the inside of the tire and wheel will be in comparison to where they are with the stock wheel. Now, get the same back spacing measurements from your existing stock wheel and determine where things will be with the projected tire/wheel combination. Don't forget to consider the upper edge of the fender and also with the front wheels turned to each extreme of turning. It could be that a wheel that fits great in the straight ahead position might hit the inner fenders when fully turned one direction or another (due to the wider section width and tread).<P>Third, there is a lot of camber change in those GM front suspensions as the wheels turn from right to left and vice versa. Putting a really wide tire/wheel on there will put a lot of stress on those short sidewalls and could even raise the edges of the tread off of the ground during tight turning maneuvers. Similarly, with those short sidewalls, the rims and tires will be much more vulnerable to holes (potholes) in the road as there's now basically no height in the sidewall to absorb these things. A wheel could also be bent plus cutting the sidewall.<P>Also, those wider treads are much more suceptible to hydroplaning on wet roads. Even that tread has deep grooves when new, it's like taking a wide piece of cardboard and wiping it against the water--what water can't escape between the grooves will be trying to lift the tire from the pavement. The wider tires might not corner any better than a similar 60 series tire due to the wide and narrow contact patch on the ground.<P>This brings up another side issue, if you need a new wheel a few years down the road, the aftermarket typically is always chaning their product lines. It's possible that a new wheel to match what you get could be discontinued from the manufacturer.<P>Just because everyone's getting 17" wheels and tires doesn't mean they are the best thing to have. But do be advised of some of the reasons to NOT get them. Your current wheels you have will support P245/60R-15 sizing (basically the old G60-15 tire size that came on the Skylark GS cars of the earlier times. That's a pretty wide tire without the same degree of problems with the size you're mentioning. Adding a set of those tires to your existing wheels will be much less expensive too!<P>It's your money, just be an informed shopper.<P>NTX5467

[Guest John Chapman]

To continue in the same vein...<P>Those 'stiff' short sidewalls will also transfer a lot of lateral load to the suspension. This may easily be more than the design limit. Then there's the wear factor of your front end, unless you've gone completely through it. Remember, when these cars were designed, 1.0G cornering was pretty much unheard of and production tires were a big part of that limitation. Now, 25 years later, you can buy it at the Chevvy dealer.