Tire sizes / Handling, Need a pros thoughts Options

[ruby914]

I got a 911 front end and a set of 7 & 8 x 16'' 5 lug fuchs for my WRX914, not from the same car.
The Fuchs had a set of used tires that I have not yet replaced.
The front tires 205/55 had heavy wear on the inside tread when I got them.
The rears are 225/50
After doing an alignment I found the steering heavy and didn't center out from a turn.
If do a tight U-turn, best I can explain it, it feels like the tires are buckling over them selves or washing out?
I added a little more toe-in to help the centering but no change.
My first question: Would that wear on the inside tread make the steering heavy and not straiten out?

So, I need new tires.
Here is my delima...
On my other stock 914, I have 195/50 x 15 and really like the feel, very light, low and quick response with the smaller diameter tires.

The WRX914 will be a daily driver.
1st, I wonder if new tires will correct all the current problem?
2nd question, I think of going a step lower profile to 225/45 and 205/45. Does this choice sound reasonable?
But there is something else I feel I must consider.
When the turbo kicks in, in 2nd gear ( 914 transaxle ) if I am pushing it on a curved freeway on-ramp or if the street is a little damp it breaks loose easy.
So, I think of 245/45's in the rear and 205/50 up front.
But that is not doing much in keeping the diameters lower.
This is the tire size calculater I have used http://www.1010tires.com/TireSizeCalculato...p?action=submit
Is there any option that I have missed?

BTW
I now have GT flares sheet metal screwed to my car marked for trim and welding.
I have one uninstalled set of 21mm wheel spacers and I think I will need one more set, maybe the same offset.
I think, I should get my new tires worked out before I look at the spacers again.

[messix]

who did the alignment?


it sounds like you need some more caster [tilt the strut towards the back of the car]

the wear on the inside on the tire could be too much camber [the strut tilted in at the top mount] or too much toe in [edit, brain fart, should be too toe out to cause inside tire wear] .


turning tight under acceleration will cause understeer. be carefull dialing this out as at higher speed you will find you will have dramatic oversteer [ass end coming around].

[mepstein]

How old are the tires? Age can make a big difference. Even with some tread left, the rubber could be shot.

[Mike Bellis]

The different feel can be atributed to the change in scrub radius caused by the wider offset of the new wheels. More caster may help a little. Driving and getting used to it will help also.

http://en.wikipedia.org/wiki/Scrub_radius

[ruby914]

About 8 months ago, I did the alignment myself.
I used the dimensions from the Haynes manual.
I used 8'x 1" alum. channel, off the bead of the tire and marks on the ground, to set the toe.
A level to set the to set the camber.
I don't remember paying with the caster.
I just took a look, the struts are all the way forward. I will pull it back and see if it makes a differences.

The tires are old and used from PO 911, can't use the wear pattern for reference to my alignment.
But, with a good alignment it would effect handling. Like too much camber I would think.

The scrub radius is something I didn't know about. Good link, Thanks.

To remove the garbage in garbage out effect, I think the more important question now is the new tire size?
I just don't find a tire combo that I am completely happy with.

[J P Stein]

I just took a look, the struts are all the way forward. I will pull it back and see if it makes a differences.

Nuff said.

[John]

Your alignment is way out of whack.

Moving the struts back will make a big difference. You will need to get a real alignment done. Sure I have seen the string thing done to set toe, and I have seen camber set with precision angle finders, but I have yet to see a reasonable way to set caster without a decent alignment machine.



Centering usually comes from caster. Caster is adjusted by moving the top of the front struts forward and backward. Typically 914's take all the caster they can get. 6+ degrees is what you are looking for. This typically has the front struts shoved as far BACK as possible.

Tire wear on the inside edges is usually caused by excessive negative camber. On 914's you want some negative camber. Camber is adjusted by moving the tops of the front struts sideways with respect to the direction of the car. Moving the top of the strut toward the center gives more negative camber.

Toe is adjusted by turning the tie-rods in and out.

In the rear, all that is adjusted is camber (adding or removing shims) and toe (pivoting the trailing arms fore and aft).


New tires should help out significantly. Dry, hard cracked tires will have little grip. However, soft sticky tires may not last long.

Don't stand on it in when the road is just damp. Oils on most roads tend to make a damp road a lot more slick than a WET road.

[brp986s]

How much (gulp) does a laser alignment rig like that cost?

[ruby914]

I have asked for a laser alignment unit for Christmas. (IMG:style_emoticons/default/piratenanner.gif)
For now, I moved the struts all the way back and it felt better. Yes, one extreme to the other. "914's take all the caster they can get. 6+ degrees" and I felt I wanted more.
I didn't feel the shuttering on U-turns today, still not centering as well as I would like but until I get tires... this seems ok.

I went looking for the 224/45, 205/45 and 245/45 tires today, just to see them next to the car.
I had no luck finding them. Seems they are not popular sizes. Is anyone else running these on there conversion?
Am I too off track with this choice?

[John]

How much (gulp) does a laser alignment rig like that cost?

The alignment stands/turntables were not included. I built them for my first alignment machine. (sourced from E-Bay). The problem with my first alignment machine was age. I could no longer get anyone to calibrate it. My second alignment setup (as seen here) was also purchased used. This one, however, was totally refurbished by an authorized service center and came complete with new wheel clamps and a reconditioned Dell PC.

It wasn't too bad considering that I do all my alignments (we have many vehicles) and I can get it set up exactly like I want it, and I don't have to go through the hassle of putting the race car on a trailer to take it someplace then have to go back later to pick it up. You won't find a whole lot of alignment shops that take the time to really get the settings just right. I probably should start doing alignments for others, but don't seem to have the time. (It was about half the cost of a decent 911 engine rebuild)

[J P Stein]

I put an autocross alignment on my Mr.2 a while back and it was then a PITA to drive on the street......it followed every groove, rut, camber change & hump in the road.

The shop up the street does all of my cars & aligns the car exactly (while I watch) as I ask him and gives me a print-out when done. I knew the Mr2 was gonna feel pretty crappy on the road so it was no surprise. The point here is that a "competition alignment" is not going to be your friend on the street. If you're gonna do your own alignment you'd better have a set up like John's....bring around $5K to the party...a bunch more if new equipment. Anyone that thinks they can set the thrust angle with strings is dreaming. Sure, I set a rough alignment on my car but then took it up to Carl's for *adjustment*. 100 bucks well spent, IMO, once a year. (IMG:style_emoticons/default/biggrin.gif)

The OPs thread doesn't contain enough data for selecting a tire size....with that in mind, a 205/50(pick a wheel size) is about all that will fit under stock 914 fenders.

[messix]

I put an autocross alignment on my Mr.2 a while back and it was then a PITA to drive on the street......it followed every groove, rut, camber change & hump in the road.

The shop up the street does all of my cars & aligns the car exactly (while I watch) as I ask him and gives me a print-out when done. I knew the Mr2 was gonna feel pretty crappy on the road so it was no surprise. The point here is that a "competition alignment" is not going to be your friend on the street. If you're gonna do your own alignment you'd better have a set up like John's....bring around $5K to the party...a bunch more if new equipment. Anyone that thinks they can set the thrust angle with strings is dreaming. Sure, I set a rough alignment on my car but then took it up to Carl's for *adjustment*. 100 bucks well spent, IMO, once a year. (IMG:style_emoticons/default/biggrin.gif)

The OPs thread doesn't contain enough data for selecting a tire size....with that in mind, a 205/50(pick a wheel size) is about all that will fit under stock 914 fenders.

JP he has flares on it!!!!


geez old man read his post why don't you!!!!! (IMG:style_emoticons/default/slap.gif) (IMG:style_emoticons/default/happy11.gif)

[John]

I put an autocross alignment on my Mr.2 a while back and it was then a PITA to drive on the street......it followed every groove, rut, camber change & hump in the road.

The shop up the street does all of my cars & aligns the car exactly (while I watch) as I ask him and gives me a print-out when done. I knew the Mr2 was gonna feel pretty crappy on the road so it was no surprise. The point here is that a "competition alignment" is not going to be your friend on the street. If you're gonna do your own alignment you'd better have a set up like John's....bring around $5K to the party...a bunch more if new equipment. Anyone that thinks they can set the thrust angle with strings is dreaming. Sure, I set a rough alignment on my car but then took it up to Carl's for *adjustment*. 100 bucks well spent, IMO, once a year. (IMG:style_emoticons/default/biggrin.gif)

The OPs thread doesn't contain enough data for selecting a tire size....with that in mind, a 205/50(pick a wheel size) is about all that will fit under stock 914 fenders.

Well, you did get my meaning when I stated approx half a decent 911 engine rebuild.....

A bunch more if new equipment... (IMG:style_emoticons/default/smile.gif) (this may be a big understatement) The sky is the limit when it comes to new alignment equipment. With my setup (including scales), I can get repeatable and accurate settings each time. It was a bunch of money, but I know it is right and if economic times means looking for a different way to generate income, I may open shop.

[J P Stein]

JP he has flares on it!!!!


geez old man read his post why don't you!!!!! (IMG:style_emoticons/default/slap.gif) (IMG:style_emoticons/default/happy11.gif)

Well, excuuuse me! My CRS syndrome is acting up.....again, I think

So, what is your answer to the man's question?

[ruby914]

(IMG:style_emoticons/default/icon_bump.gif)
Let me try to clarify my question.
I have 5 lug 7'' & 8'' x 16'' Fuchs rims. They now have Bridgestone Potenza RE750 225/ 50 R16 and 205/55 R16 tires.
I am interested in going lower profile. The only option I have found is Falken FK-452 225/45 R16 and 205/50 R16 but the front tires would be .050 larger dia than the rear.
It is not a lot but they are larger, seems too weird.
Is there any other lower profile tire option for this rim set? (IMG:style_emoticons/default/confused24.gif)

[messix]

JP he has flares on it!!!!


geez old man read his post why don't you!!!!! (IMG:style_emoticons/default/slap.gif) (IMG:style_emoticons/default/happy11.gif)

Well, excuuuse me! My CRS syndrome is acting up.....again, I think

So, what is your answer to the man's question?

well a 245 tire is nearly 8-9" of tire patch on the road, you would need a very soft rubber compound to conter the lower contact pressure per square inch of patch.

a 40 series tire is about the minimum to run on the road with out worry of side wall damage. [you will still have to avoid every pothole].

[wndsrfr]

I'm running 7's & 8's x16 on mine and have had a blast with the Dunlop Star Specs that I got from tirerack. I started the summer with 205/55's on front and 225/50's rear. After getting into some threshold braking and turn-in weakness at DE's I went for a square setup with 225/50's front and rear & am very happy with that. I was also looking for a lower profile set to help with the too tall gearing (stock) but instead went with a gear change flipping 5th to 3rd, 3rd to 5th and putting in a "S" for the new 4th, so it's now A/F/KA/S/Z and it's like a new car!

[SirAndy]

The different feel can be atributed to the change in scrub radius caused by the wider offset of the new wheels.

I doubt that's the problem. I run wheels and tires much wider than his in the front and the steering feels anything but heavy.

I think the clue is in the recent alignment ...
(IMG:style_emoticons/default/popcorn[1].gif)

[ruby914]

I'm running 7's & 8's x16 on mine and have had a blast with the Dunlop Star Specs that I got from tirerack. I started the summer with 205/55's on front and 225/50's rear. After getting into some threshold braking and turn-in weakness at DE's I went for a square setup with 225/50's front and rear & am very happy with that. I was also looking for a lower profile set to help with the too tall gearing (stock) but instead went with a gear change flipping 5th to 3rd, 3rd to 5th and putting in a "S" for the new 4th, so it's now A/F/KA/S/Z and it's like a new car!

This is what I was looking for.
With 7's & 8's x 16, 205/55's & 225/50's seem to be the only options, nothing lower profile seems balanced.
I am surprised, I am yet to find anyone running any lower profile tires with this rim combo.

[ruby914]

The different feel can be atributed to the change in scrub radius caused by the wider offset of the new wheels.

I doubt that's the problem. I run wheels and tires much wider than his in the front and the steering feels anything but heavy.

I think the clue is in the recent alignment ...
(IMG:style_emoticons/default/popcorn[1].gif)

Thanks Andy
More caster solved one problem.
I am happy with my rough alignment for now, until I get new tires.
A combo of more tire on the ground (compared to my 195/50 x 15 on the other car) and scrub may be all I feel.
I also have the steering column from the WRX in the car that changed the geometry just a little.
I don’t think the WRX column is an issue but after tires I will fine tune the alignment and address any other issues.
I think my first battle is tires