84-87 vs 88 front suspension (Page 5/10)
Bloozberry FEB 03, 06:27 PM

quote
Originally posted by Will:
[Tilting the front crossmember] dramatically improves the driving experience, but reduces caster and everything that goes along with that. I'm working on adjustable upper control arms to get my caster back.



Can you be more specific? What's the theoretical purpose and what aspect of the driving experience is improved?


quote
Originally posted by Silicoan86:
I'm thinking the discrepancy between those spec sheets on the pre-88 cars is due to them being measured with different wheel options.



Possibly, but for something as simple to check as this it'd be better to find the specs on the steel wheel and come up with conclusive numbers rather than speculate.
Bloozberry FEB 03, 07:03 PM

quote
Originally posted by David Hambleton:

I have the factory '84 SE wheels on that car; the factory '88 Formula wheels on that car and '88 Formula wheels on my '86 Coupe that came with steel wheels.

Are there any effects on suspension/handling geometry among the factory supplied wheels when swapped among any year car?



I finally found the specs on the 13" wheels... they're 13 x 5.5 ET42. Knowing this, then the scrub radius would be as follows on '84-'87 cars if the following wheels were installed on the front:

Read in two columns: Installed Wheel / Scrub Radius:

14 x 5.5 ET 42 steel / 47 mm
14 x 6 ET 35 Hi Tech Aluminum / 54 mm
15 x 6 ET 37 Lace Aluminum ('88 front) / 52 mm
15 x 7 ET 30 Lace Aluminum ('86-'87 front & rear, '88 rear) / 59 mm

This is assuming the overall tire diameters are roughly the same as the P185/80R/13's installed on the 13" rims. Rather eye-opening isn't it? It's no wonder the 40 mm (or 35 mm) scrub radius on the '88's is noticeable.

(Edit: corrected my math... it's been a long day shovelling snow.)

[This message has been edited by Bloozberry (edited 02-03-2015).]

Silicoan86 FEB 03, 07:38 PM

quote
Originally posted by Bloozberry:
I finally found the specs on the 13" wheels... they're 13 x 5.5 ET42. Knowing this, then the scrub radius would be as follows on '84-'87 cars if the following wheels were installed on the front:

Read in two columns: Installed Wheel / Scrub Radius:

14 x 5.5 ET 42 steel / 47 mm
14 x 6 ET 35 Hi Tech Aluminum / 54 mm
15 x 6 ET 37 Lace Aluminum ('88 front) / 57 mm
15 x 7 ET 30 Lace Aluminum ('86-'87 front & rear, '88 rear) / 64 mm

This is assuming the overall tire diameters are roughly the same as the P185/80R/13's installed on the 13" rims. Rather eye-opening isn't it? It's no wonder the 40 mm (or 35 mm) scrub radius on the '88's is noticeable.



If we're assuming the overall tire diameter is the same, wouldn't it be:

14 x 5.5 ET 42 steel / 47 mm
14 x 6 ET 35 Hi Tech Aluminum / 54 mm
15 x 6 ET 37 Lace Aluminum ('88 front) / 57 mm 52 mm
15 x 7 ET 30 Lace Aluminum ('86-'87 front & rear, '88 rear) / 64 mm 59 mm

It's still a very significant difference to the '88. And as I mentioned, so many people run brake upgrades that add another 10mm to the equation, which is rarely compesated for in wheel choice.

[This message has been edited by Silicoan86 (edited 02-03-2015).]

Bloozberry FEB 03, 08:31 PM
Ooops I goofed. Thanks for catching that Silicoan86. I'll edit my original post so that no one accidentally uses the wrong numbers.
LornesGT FEB 03, 09:46 PM
Can 7 mm make that much difference? If changing to a wider tire and trying to compensate for it, is the wider tire changing something beside more friction and harder slow speed turns?

[This message has been edited by LornesGT (edited 02-03-2015).]

Will FEB 03, 11:15 PM

quote
Originally posted by Bloozberry:

Can you be more specific? What's the theoretical purpose and what aspect of the driving experience is improved?




Brake dive can be basically eliminated, but at the expense of reducing caster to almost nothing.
Bloozberry FEB 04, 09:06 AM

quote
Originally posted by LornesGT:
Can 7 mm make that much difference?



To answer that, I'll repeat the first sentence I posted in this thread: "Are you looking for subjective seat-of-the-pants opinions or objective numbers?" Some people add 3" spacers on the front of their cars, or 10" wide wheels with very low offsets to make their wide-bodied car "look" right. Most of these people won't complain about compromised handling (some won't even notice) because for them appearance is prime. So put on whatever wheels you want and if you enjoy the ride, forget about the nitty-gritty details that some of us enjoy discussing and trying to perfect. It's kind of like asking whether 610 horsepower is really any better than 590. You know the difference is there even if only a very few will ever be able to take advantage of it.


quote
Originally posted by LornesGT:
If changing to a wider tire and trying to compensate for it, is the wider tire changing something beside more friction and harder slow speed turns?



That's a bit of a loaded question.

Easy answer: No, unless you count more drag. It's only when you change the location of the center of the tire contact patch by changing the rim offset that other things change.

Complicated answer: No, but while you're not changing anything other than more friction, adding more friction can change things such as suspension dynamics (ex: location of the traction center), stress on mechanical components (ex: greater potential braking, acceleration, and lateral forces on fasteners and bearings), and operating characteristics (ex: likelihood of hydroplaning). How's that for taking a simple question and making it complicated?
wftb FEB 04, 09:20 AM
I have an article in one of my car mags where they took a subaru BRZ to a track to play around with tires .The subie stock comes with low rolling resistance tires that are not great on the skidpad or the track .So they put on high performance summer tires in the same size as stock and the improvement was huge , close to 5 seconds a lap faster than OEM tires and big improvement on the skid pad .So thinking that more should be better , they went to a wider tire , same brand .Skid pad went up to close to 1G but the lap times went down to only a little better than stock .The straight away speeds were down considerably because the stock engine could not over come the increased friction .Think of that before you put huge tires on a low powered car .(edited to change larger tire to wider tire , sorry for the confusion )

[This message has been edited by wftb (edited 02-04-2015).]

masospaghetti FEB 04, 02:39 PM

quote
Originally posted by wftb:

I have an article in one of my car mags where they took a subaru BRZ to a track to play around with tires .The subie stock comes with low rolling resistance tires that are not great on the skidpad or the track .So they put on high performance summer tires in the same size as stock and the improvement was huge , close to 5 seconds a lap faster than OEM tires and big improvement on the skid pad .So thinking that more should be better , they went to a larger tire , same brand .Skid pad went up to close to 1G but the lap times went down to only a little better than stock .The straight away speeds were down considerably because the stock engine could not over come the increased friction .Think of that before you put huge tires on a low powered car .



In this case it was probably the extra weight of the wheel and tire combination that was causing the reduction in performance, not the wider tire causing extra friction.

Larger wheels and wider tires generally weigh more, and rotating mass has a big effect on performance, both acceleration and cornering.

I wonder how much difference using the 88-lace style wheel would be on a pre-88 suspension, if it would be noticeable.
wftb FEB 04, 06:11 PM
They did not change the wheel size , just went with a wider tire .I will see if I can find the article .I corrected my earlier post .

[This message has been edited by wftb (edited 02-04-2015).]