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Front tire offset/size vs road handling
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oprn
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PostPosted: Fri Sep 30, 2022 6:21 am    Post subject: Front tire offset/size vs road handling Reply with quote

I tried searching this on this site but came up with nothing. Maybe the wrong wording? I am not sure if anyone is interested in this subject but I thought I would share my experience to start it off.

My journey in this regard has been with a fiberglass street Buggy. First off - I know enough about cars and suspensions to understand that our rear engine air cooled cars were not the best at speed even in their prime. 50 years later and take 14.5" out of the wheelbase and you cannot expect an improvement!

My expectations were soundly rewarded in this car as it was genuinely squirrely on the highway at speed. So this is how the builder set it up: all stock ball joint beam with BF Goodrich 195/60SR14 tires on Chevy bolt pattern rims and 3/4" thick adaptors. Looked boss! Lots of offset, tires hanging out in the wind!

Ride was harsh, heavy to steer in a parking lot, bump steered bad, tried to follow every rut and ridge on the road and felt like it would be perfectly happy to swap ends in a heartbeat! I started with a temperature gun on the tire tread to optimize the tire pressures for best traction and wear. I ended up at 12 psi and most things improve somewhat with the biggest gain in ride quality.

Next was to replace the rusty front beam with an adjustable one (not narrowed) to lower the front of the car. Very little improvement and with the adjustment at the lowest setting the suspension now bottomed out on large bumps on the road causing the front wheels to bounce up and catch air time! Very unnerving! Raised it up some to fix that!

I knew that offset was my biggest enemy so the next step was to try and eliminate that. Empi disc conversion drilled Chevy/Porsche bolt pattern went on next. 3/4" of adapter gone! BIG improvement all around! (except for braking power which was worse, another day, another thread) Next was to get taller rubber so on went a set of 7" Porsche Fuchs with 215/60R15s on them. Ya, pretty wide but that is what I had on hand. Another big improvement in ride especially and handling, still a bit heavy in the parking lots.

Now for a more reasonable tire! I wanted to use these 7" Fuchs because I have them so thought the smallest tire would be a 185 but my tire guy talked me into 165/80R15s with the promise that if they didn't work for me he would give me a full refund! Wow! I love the results! The tires no longer hang out in the wind, they are covered completely by the fenders and the ride and handling are the best yet! Even the steering effort in a parking lot is way down! The only downside is that these 7" rims are now a bit vulnerable to curb rash so care needed on that front for sure!

This has all transformed the highway handling from sketchy and wearying to comfortable and confident. She is no Porsche but I feel confident that anyone could drive it now without any concern on my part.

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esde
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PostPosted: Sat Oct 01, 2022 10:13 am    Post subject: Re: Front tire offset/size vs road handling Reply with quote

A 165 on a 7" rim is far from ideal. But running the narrow tire has reduced the scrub radius in front, and reduced how much leverage the road has on your steering. That's always the balance we are fighting to find, Wider track stability or increased road feedback to the wheel; when does the benefit of one outweigh the other? Factor in a light, short wheelbase buggy, and things can get hairy with snap oversteer and such...
Did you consider finding narrow Fuchs for the front? And using the 165 in front with something bigger in back?
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oprn
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PostPosted: Sun Oct 02, 2022 6:57 pm    Post subject: Re: Front tire offset/size vs road handling Reply with quote

esde wrote:
Did you consider finding narrow Fuchs for the front?

Yes, I would rather have had 5.5" or 6" Fuchs on the front but those are the wheels that came on my parts 944 so I will use them until I find someone who wants to trade me a pair of genuine Fuchs 6" or narrower for these.
esde wrote:
And using the 165 in front with something bigger in back?

The rear is still running the 235/60 14" Chevy wheels and tires until I get the IRS from the 944 swapped over. Then it will get the 15" X 8" Fuchs from the rear of the Porsche with at least a 215 wide tire on them.
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slalombuggy
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PostPosted: Tue Oct 04, 2022 7:05 pm    Post subject: Re: Front tire offset/size vs road handling Reply with quote

With wheel adapters the scrub radius is totally out to lunch and then add wide tires and you have a formula for a front end that hunts all over the road.

Dropping the front REALLY kills the caster angle which is the angle that gives all vehicles stability at speed. This is why adding caster shims is so important. And then if you do big and Littles for tires, you make the problem even worse.

The only time I ever had a problem with hunting was on a buggy I built to sell and I put some 225/50/15s on the front on 7" spokes with a 3" backspace and just about ended up in the ditch on the freeway. I swapped to 205/60s and everything was fine.

On my street car I have run everything front 205/45/15 008R Yokohamas to 185/70 cheapies with some radical alignment setups, the car has never been unpredictable in its handling, it's been sketchy as all hell when set up for auto-x but it's always been predictable and I have always pushed it over the edge to see what it would do. That car has been around more times than a dancehall girl on Saturday night.

On my street buggy I have a 3" narrowed beam, running one set of springs and the top arms joined with a 3/4"bar, disk brakes and 3.5" Centerlines with a 1" backspace, it's king and link so I use Formula Vee link pin bushings at give me 1* of negative camber, toe is set at 3/16" tie in and caster is 7* built into my chassis. At 140kph the car is as stable as a rock and I have momentarily let go of the wheel at 200kph on the track and it has gone arrow straight.
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oprn
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PostPosted: Mon Oct 17, 2022 6:12 am    Post subject: Re: Front tire offset/size vs road handling Reply with quote

I avoided the narrow beam thing and went with stock width. It has been my experience running stock VWs that they are already too narrow to fit the ruts in our highways from the great American boat anchors. I felt a narrowed beam would make this ridge riding tendency even worse.

What are your feelings about running a front sway bar on our Buggies. At present I have not put mine back on and really, I don't see much difference.
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PostPosted: Tue Oct 18, 2022 6:00 am    Post subject: Re: Front tire offset/size vs road handling Reply with quote

oprn wrote:
I avoided the narrow beam thing and went with stock width. It has been my experience running stock VWs that they are already too narrow to fit the ruts in our highways from the great American boat anchors. I felt a narrowed beam would make this ridge riding tendency even worse.

What are your feelings about running a front sway bar on our Buggies. At present I have not put mine back on and really, I don't see much difference.


I auto-crossed my car for 2 decades and I drive aggresively on the street with it....I like taking fast corners and changing lanes quickly, so for me sway bars (front and back) are manditory. On a basic go for ice cream cruise kind of buggy, maybe not so much, but I also feel my car is a lot more stable on the highway because of them, the car is a dream to drive at 75mph.

To me, two things contribute to poorly handling buggies, that are comonly done over and over.

One is giant steam packer tires that everyone seems to need to run, all I've found them to do is make the car hunt all over the road, especially in ruts.

And the second is a non working front suspension. Most guys never decrease the spring rates on the fronts of their cars and they are far too stiff for anything to work right.
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oprn
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PostPosted: Sun Oct 23, 2022 4:43 am    Post subject: Re: Front tire offset/size vs road handling Reply with quote

And that is why I don't miss the front sway bar. The front suspension is too stiff. I also made the mistake of putting a lowered beam in it when I should have gone with dropped axles to retain full travel. A lowered beam very much limits suspension travel. I suspect the stock shocks are bottoming out, shorter ones maybe?

I still have the stock front sway bar but the hardware was rusted through to mount it. I also have a 944 rear sway bar that I am planning to try.

How much actual highway driving does your Buggy get? Mine gets used 95% on the highway.
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PostPosted: Thu Oct 27, 2022 10:50 am    Post subject: Re: Front tire offset/size vs road handling Reply with quote

I can't imagine a front end is as f'd up as mine. Looks cool, but like mentioned with the wheel offset and scrub, the car digs to the left and drifts to the right...bad. 17x7 with 4" of backspace and a 6" narrowed beam just to pull the wheel in enough to clear the fender, I would not recommend. Neither would I suggest a pair of 205 tires pulled in to the point where it NEVER rides in any asphalt rut. And it will seem fine cruising down the highway until the edge of a tire grabs one side of a rut or the other and then it's not fine in an instant.

I've been considering changing it up. I appreciate you posting your results.
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slalombuggy
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PostPosted: Sun Oct 30, 2022 9:18 pm    Post subject: Re: Front tire offset/size vs road handling Reply with quote

oprn wrote:
And that is why I don't miss the front sway bar. The front suspension is too stiff. I also made the mistake of putting a lowered beam in it when I should have gone with dropped axles to retain full travel. A lowered beam very much limits suspension travel. I suspect the stock shocks are bottoming out, shorter ones maybe?

I still have the stock front sway bar but the hardware was rusted through to mount it. I also have a 944 rear sway bar that I am planning to try.

How much actual highway driving does your Buggy get? Mine gets used 95% on the highway.


If the suspension is too stiff with a swaybar, then it is too stiff without it. Get rid off a spring stack and run a sway bar. A suspension that can't move can't function. I've only run link pin front ends, so I've never had valljoints to limit my travel. I always size my shocks so that they will stop extending before they bottom out.

Probably 60% of my driving is highway or freeway driving
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PostPosted: Tue Nov 01, 2022 1:08 pm    Post subject: Re: Front tire offset/size vs road handling Reply with quote

did you install the caster shims?
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PostPosted: Wed Nov 02, 2022 5:33 am    Post subject: Re: Front tire offset/size vs road handling Reply with quote

My buggy was slammed (originally) all with adjusters. I had one set of caster shims. I knew nothing back then and I didn’t have enough caster. I would get an 80 mph wander. A very hard to describe wander. Like the rear was trying to pass the front and steering wouldn’t compensate. Turned out, I had zero caster. Two sets of shims fixed it, until I redid everything.
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PostPosted: Fri Nov 04, 2022 4:41 am    Post subject: Re: Front tire offset/size vs road handling Reply with quote

madmike wrote:
did you install the caster shims?

Yes.
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PostPosted: Fri Nov 04, 2022 4:53 am    Post subject: Re: Front tire offset/size vs road handling Reply with quote

slalombuggy wrote:
If the suspension is too stiff with a swaybar, then it is too stiff without it. Get rid off a spring stack and run a sway bar. A suspension that can't move can't function. I've only run link pin front ends, so I've never had valljoints to limit my travel. I always size my shocks so that they will stop extending before they bottom out.

Probably 60% of my driving is highway or freeway driving

Our closest town is only 4 blocks wide one way and 5 blocks wide the other so the only time we get any real city driving in is when we take a long trip.

A local chap (5 hours from us) did like you and pulled all the leaves out of one tube. He said it made the front too soft and it bottomed too easily taking the wiring off his signal lights and rubbing the bottom side of his fenders. I am thinking of just removing a few leaves from each tube.
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PostPosted: Sat Nov 05, 2022 12:00 am    Post subject: Re: Front tire offset/size vs road handling Reply with quote

oprn wrote:
slalombuggy wrote:
If the suspension is too stiff with a swaybar, then it is too stiff without it. Get rid off a spring stack and run a sway bar. A suspension that can't move can't function. I've only run link pin front ends, so I've never had valljoints to limit my travel. I always size my shocks so that they will stop extending before they bottom out.

Probably 60% of my driving is highway or freeway driving

Our closest town is only 4 blocks wide one way and 5 blocks wide the other so the only time we get any real city driving in is when we take a long trip.

A local chap (5 hours from us) did like you and pulled all the leaves out of one tube. He said it made the front too soft and it bottomed too easily taking the wiring off his signal lights and rubbing the bottom side of his fenders. I am thinking of just removing a few leaves from each tube.


Putting a sway bar on it or joining the top torsion arms with a steel bar like I did will stiffen up the front end a bit as both sides are effectively making use off the entire spring pack. I have never bottomed out my front suspension.

I build most of my caster into my chassis' orange car has 7* built in race car has 15*
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PostPosted: Sun Nov 06, 2022 8:34 pm    Post subject: Re: Front tire offset/size vs road handling Reply with quote

The through rod acts as a sway bar too does it not?
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PostPosted: Tue Nov 08, 2022 7:24 pm    Post subject: Re: Front tire offset/size vs road handling Reply with quote

oprn wrote:
The through rod acts as a sway bar too does it not?


No, not unless it's keyed into the torsion arms. Usually they just have threaded rod at the ends that keeps the arms from sliding out of the beam but let's them move independently.
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