Wow! What a difference 11mm makes

[Dug Nichols]

I set up my '73 with Bilstein HDs, H&R Sport Spring, and ST 22/19 sway bars running on original stock rims. I (regrettably) opted for the Kumho 185/70's even though the CNC's had just come out. As compared to my square Mintgrun with Boge Sport, IE Stage 1, and 22/19 sways running older Yokohama 185/17's on Octavos, the handling of the '73 had SO MUCH BODY ROLL. Yep, different cars with largely different suspensions, but I was really surprised by how different they handled in the twisty ones.

 

Yesterday on the '73 I swapped the Kumhos onto a set of E21 Turbines I've had in the garage forever, primarily b/c I wanted to get the original steelies into rehab mode and made the excuse that trying this wheel option would also be an interesting experiment to see how it affects the handling. Yep, I know Turbines aren't a proper offset -- with the wheels sitting "too far" outboard which is not per the suspension design and can cause premature on the wheel bearings, fender rubbing ,etc.

 

But DANG, the difference in body roll on hard cornering is really night and day. With the wider wheel set on the pavement the car is very significantly flatter around the hard corners and is a dream to bang through corners. The '73 now feels very very close to my Mintgrun, which makes some sense as the Octavo's on Mint are somewhere in the ET19 offset range (and the Turbines now on the '73 are ET18). 

This has me curious what moving to a 14" or 15" rim with proper 02 offset will do as comparison. Keep the flat stance on hard cornering as there's tire surface pushed further outside? Roll slightly more as the offset moves inboard slightly? I don't have 14's or 15's to try it out, but curious what the engineering minds say here.

[TobyB]

Spring stiffness

(yes, anti- roll bars are springs, but in your case they are a constant)

and suspension height

are the variables in your steady- state cornering suspension movement,

assuming your suspension mounting points are the same.

 

Suspension height because the 2002 roll centers wander all over the place

as the wheel moves up and down, both dynamically and statically.

 

t

likes about 5" at the rocker and about #350 springs with the relocated- pivot

Ireland front bar.

[Dug Nichols]

24 minutes ago, TobyB said:

Spring stiffness

(yes, anti- roll bars are springs, but in your case they are a constant)

and suspension height

are the variables in your steady- state cornering suspension movement,

assuming your suspension mounting points are the same.

 

Suspension height because the 2002 roll centers wander all over the place

as the wheel moves up and down, both dynamically and statically.

 

t

likes about 5" at the rocker and about #350 springs with the relocated- pivot

Ireland front bar.

What I wrote might be a little confusing, now that I re-read it. Here's what changed on my '73: rims only.

 

By changing only the rims (from '73 stock to E21 Turbines) I got remarkably different ride. (for the better in terms of body roll)

 

 

[visionaut]

Yep, wider track due to different wheel offsets.

Changing wheel diameter will not affect track, if they’re the same offsets.

[Tommy]

2 hours ago, Dug Nichols said:

What I wrote might be a little confusing, now that I re-read it. Here's what changed on my '73: rims only.

 

By changing only the rims (from '73 stock to E21 Turbines) I got remarkably different ride. (for the better in terms of body roll)

You also get much more steering effort when parking, potholes hit your hands ten times harder and grooves on road pull you towards ditch or another. But you need another test run in different circumstances to notice that. Compromises, that's life!

[d.hitchcock]

I've only ever driven my car on sticky 195/50-15s. I need to drive an 02 on stock-size rubber someday just to compare.

[Oldtimerfahrer]

2 hours ago, d.hitchcock said:

I've only ever driven my car on sticky 195/50-15s. I need to drive an 02 on stock-size rubber someday just to compare.

Find one with close to stock suspension, but sway bars front and rear with michelin xas mounted in 165 13...it will be interesting and not bad either.

Edited July 19, 2022 by Oldtimerfahrer
Spelling

[Senna27]

6 hours ago, Dug Nichols said:

I set up my '73 with Bilstein HDs, H&R Sport Spring, and ST 22/19 sway bars running on original stock rims. I (regrettably) opted for the Kumho 185/70's even though the CNC's had just come out. As compared to my square Mintgrun with Boge Sport, IE Stage 1, and 22/19 sways running older Yokohama 185/17's on Octavos, the handling of the '73 had SO MUCH BODY ROLL. Yep, different cars with largely different suspensions, but I was really surprised by how different they handled in the twisty ones.

 

Yesterday on the '73 I swapped the Kumhos onto a set of E21 Turbines I've had in the garage forever, primarily b/c I wanted to get the original steelies into rehab mode and made the excuse that trying this wheel option would also be an interesting experiment to see how it affects the handling. Yep, I know Turbines aren't a proper offset -- with the wheels sitting "too far" outboard which is not per the suspension design and can cause premature on the wheel bearings, fender rubbing ,etc.

 

But DANG, the difference in body roll on hard cornering is really night and day. With the wider wheel set on the pavement the car is very significantly flatter around the hard corners and is a dream to bang through corners. The '73 now feels very very close to my Mintgrun, which makes some sense as the Octavo's on Mint are somewhere in the ET19 offset range (and the Turbines now on the '73 are ET18). 

This has me curious what moving to a 14" or 15" rim with proper 02 offset will do as comparison. Keep the flat stance on hard cornering as there's tire surface pushed further outside? Roll slightly more as the offset moves inboard slightly? I don't have 14's or 15's to try it out, but curious what the engineering minds say here.

 

Going to 14" or 15 wheels with wider tires will certainly give you more grip. I think what you're experiencing is a psychological lessening of the roll effect when you changed to the different wheels/tires. The amount of body roll is controlled by a combination of ride height, shocks, spring rates and sway bars. Simply changing the wheels/tires won't limit the amount of body roll. Although the increased grip, just may make it feel that way on the twisty roads. 

 

I went from completely stock suspension with 185/70R13 CN36s to Koni shocks, Eibach springs, Turbo front bar, Dinan adjustable rear bar, 195/50R15 Brigestone RE-71R tires, strut bar, LSD and adjustable camber plates. While my car now feels like it's on rails, photos reveal she's still got some of that body roll.

 

I'm pretty picky when it comes to handling and balance. Thankfully it's only taken me 35 years to get it right. ? 

 

 

[Dug Nichols]

5 hours ago, Tommy said:

You also get much more steering effort when parking, potholes hit your hands ten times harder and grooves on road pull you towards ditch or another. But you need another test run in different circumstances to notice that. Compromises, that's life!

Yep, definitely noticed the difference in all these. Also noticed how much nicer the stock ‘73 steering wheel is compared to the 320IS smaller wheel in my Mintgrun (with similar offset rims)