Home 
Home Search search Menu menu Not logged in - Login | Register

 Moderated by: Greg Fletcher
New Topic Reply Printer Friendly
Oversteer  Rating:  Rating
AuthorPost
 Posted: 05-17-2009 04:20 pm
  PM Quote Reply
1st Post
Dakota123
Member
 

Joined: 03-20-2009
Location: Colorado USA
Posts: 126
Status: 
Offline
I'm in the middle of replacing my suspension bushings.  The rears are out and I'm waiting on the replacements.  (By the way, not to speak for Greg but at this time he is out of the Superpros but has something akin to the Metalastiks available.)

Anyway, while I'm sure the bushings were indeed worn, they didn't look that bad, and that has me a little concerned:  I was getting a bit of oversteer in fast sweepers that I'm now afraid won't be cured by the bushing replacment. 

So, is oversteer just a characteristic of the Jensen Healey experience? 

Thanks for the insight.

Mike

Back To Top PM Quote Reply  

 Posted: 05-17-2009 06:39 pm
  PM Quote Reply
2nd Post
dwalls1
Member
 

Joined: 04-11-2008
Location: Bloomfield, New Mexico USA
Posts: 204
Status: 
Offline
Hope somebody that knows will check in on this, as I have wondered about some of the same issues myself. Thanks for posting.

Back To Top PM Quote Reply

 Posted: 05-17-2009 11:57 pm
  PM Quote Reply
3rd Post
Jensen Healey
Super Moderator


Joined: 03-11-2005
Location: San Anselmo, California USA
Posts: 977
Status: 
Offline
Check out this website:

http://www.automotion.co.nz/News/news-details.asp?NewsID=53

Kurt

Edit: The usual fixes include:

Add a front sway bar. (or remove the rear bar if you have them)

Increase rear tire pressure. The JH 24psi recommendation leaves a lot of room for changes! I run 30 psi at all 4 corners on 205/60 13 tires. The sidewalls are sloppy at lower pressures.

Put stickier tires on the rear. I run summer only compound. Freaky lack of grip in the wet!

Stiffer front shocks than rear shocks.

Take everything out of the boot including the jack. Remove the spare tire.

 

 


 

Last edited on 05-18-2009 03:17 pm by Jensen Healey

Back To Top PM Quote Reply  

 Posted: 05-18-2009 07:06 am
  PM Quote Reply
4th Post
subwoofer
Member
 

Joined: 04-01-2008
Location: Sandefjord, Norway
Posts: 583
Status: 
Offline
This book holds a lot of information on how suspensions work, and is a good read. It does not offer any silver bullets, but rather let's you start to figure out what is going on and gives pointers to what to change and why.

http://www.amazon.com/How-Make-Your-Car-Handle/dp/0912656468

--
Joachim

Back To Top PM Quote Reply

 Posted: 05-19-2009 02:24 pm
  PM Quote Reply
5th Post
Judson Manning
Member


Joined: 03-14-2005
Location: Atlanta, Georgia USA
Posts: 406
Status: 
Offline
What?  I thought the whole idea of a sports-car was for it to always have wildly uncontrollable oversteer???? or is that just indicative of 911s? hmmmm

A dead rear shock (my third set of Spax) and too much rear bar were the cause of my regular off-course excursions at Roebling a few years ago.  The standard open diff makes recovery pretty much impossible at speed.  Of course, recovery became extremely easy when I slapped on a set of 8.5" slicks!

For a street car tires will make the biggest difference, the problem is availability.  At $54 The Sumitomo is great, but the compound is just too hard for driving at the limit.  I really wish BFG, Kumho, et. al. still made their DOT approved quasi-racing tire in our size...

Back To Top PM Quote Reply  

 Posted: 05-19-2009 03:31 pm
  PM Quote Reply
6th Post
jgreen
Member
 

Joined: 01-28-2007
Location:  
Posts: 58
Status: 
Offline
Wait a Minute..... I thought you were working on your next Jensen Healey upgrade to handle over/understeer resulting from drivers not being able to handle the all the excess power from one of your rebuilt engines. It's ESP ( electronic stabilty control) in a Jensen Healey. I think it would only take a few hundred hours for you to retrofit a BMW system... ;) ;) ;)

John

Back To Top PM Quote Reply

 Posted: 05-19-2009 04:27 pm
  PM Quote Reply
7th Post
Jensen Healey
Super Moderator


Joined: 03-11-2005
Location: San Anselmo, California USA
Posts: 977
Status: 
Offline
Hi Judson, the Toyo R888 is still available at a few places. Get some before the're gone! It's a DOT approved track day tire UTOG 100.

I was shocked to see the Sumitomo was the only 205/60 at the Tire Rack. The West Coast Nationals will be in Carson City NV this fall and I dont want to drive over the Sierra with these summer only tires.

This issue may force me to move to 15" wheels. Of course they will stop making 15" tires if I do that!

Kurt

Edit: I found some 205/60-13 all season Cooper Gt's at summitracing.com.

Last edited on 05-22-2009 03:50 am by Jensen Healey

Back To Top PM Quote Reply  

 Posted: 05-19-2009 05:41 pm
  PM Quote Reply
8th Post
Greg Fletcher
Administrator


Joined: 03-11-2005
Location: Lake Nacimiento, California USA
Posts: 421
Status: 
Offline
I must say the Dynamic Stability Control in my Z3 Coupe has probably saved me more than once, that's what I call a functional upgrade!

The SuperPro bushings (all part numbers in stock at this time) won't solve your problems but will certainly help and point you in the right direction. These combined with a quality set of shocks and tires will transform the car from the stock set up. As Judson mentions, just switching from a stock 5.5 inch wide tire to say a 6 inch width with something like a Minilite wheel will provide another level of improvement.

I've just about finished up my field testing of the dead-stock Jensen Healey suspension & shocks on 13242 (I think they call it "dead" because that's what happens to you when you don't upgrade). I'm astonished that anyone could actually drive a car like this at any kind of speed! It's most frightening!

Back To Top PM Quote Reply

 Posted: 05-20-2009 02:47 pm
  PM Quote Reply
9th Post
Jensenman
Member
 

Joined: 04-14-2005
Location: Columbia, South Carolina USA
Posts: 156
Status: 
Offline
The J-H's rear suspension link geometry is set up to give roll understeer, yet the car will oversteer. That means there's something else that causes this problem.

The biggest single cause of the J-H's oversteer: excessive rear roll stiffness. This comes mainly from the stock rubber bushings binding. What happens: as the body rolls in a turn, the bushing's rubber does not slide, it twists. The further it twists, the more resistance, just like any type of spring. The more resistance, the more likely the inside rear tire will come off the ground and voila: oversteer. A rear sway bar will make this worse, as will anything else that keeps the rear axle from 'articulating' under the car. Stickier tires can help with this but are not the true answer.

Urethane bushings are another partial answer, but to be effective the bushings for the top of the axle must be replaced as well. For a long time, they weren't available in urethane, I believe they now are. When installing the urethanes, grease the dickens out of them but do not use chassis grease; use either Energy Suspension's sticky urethane grease or dielectric silicone grease. Be sure to lube the flat faces as well as the steel tubes. This is very important; urethane is a 'sticky' plastic and will bind if not lubed, thus bringing back the oversteer issue.

Urethanes still have one problem: as the control arms move, the sleeve needs to move in two directions at the same time. Urethane is hard enough that it still adds a good bit of resistance to this two way motion. For 95% of street driving, this will not be an issue. The rear will be more predictable up to the very limit but will still come around when seriously provoked.

For the great majority of driving (99%) a combination of urethane bushings and stickier tires will be more than sufficient. That last 1% would mean spherical bearings or rod ends instead of the rubber and that is a difficult and pricey thing, I would put it at 4 cases on Greg's 'vino' scale.

EDIT: If you are looking for a reasonably priced truly sticky street tire, you could do a lot worse than the Falken Azenis RT615. They have a 200 treadwear rating, unfortunately the smallest size is a 195/60-14 and that one probably will be gone in a few years as sales drop. Currently that one sells for ~$70 each. If someone is planning to go to 15's anyway, they have a 205/50-15 that should fit under the fenders well (always assuming correct wheel backspacing, etc). That size usually goes for ~$95. It is not the worlds' greatest rain tire, though.

The supply of DOT approved race tires and other 'streetable' performance oriented 13" tires is rapidly drying up, unfortunately.

Last edited on 05-20-2009 08:33 pm by Jensenman

Back To Top PM Quote Reply  

 Posted: 05-20-2009 04:29 pm
  PM Quote Reply
10th Post
Dakota123
Member
 

Joined: 03-20-2009
Location: Colorado USA
Posts: 126
Status: 
Offline
Jensenman, thanks for that valuable post.  IMO Greg should consider that one for the Garage section.  That is exactly what I was hoping for (not that the other posts weren't helpful as well).

I'm hoping to have enough time this evening to finish getting 10628 back together with SuperPros.  It will be interesting to see what the results are.

Mike

Back To Top PM Quote Reply

 Posted: 05-20-2009 05:48 pm
  PM Quote Reply
11th Post
subwoofer
Member
 

Joined: 04-01-2008
Location: Sandefjord, Norway
Posts: 583
Status: 
Offline
A word of advice if you haven't installed this kind of bushing before:

Installing the Superpros with a vice, I found that what looked really easy in the instruction video turned out to be really difficult the first time.

Make sure you lube well, then use the stem of a large screw driver to help get the first end of the bushings into the hole. Apply some (quite a lot actually) of pressure to the side of the bushing that wants to pop out by using the screw driver as a crow bar. Just in case I didn't express this in an understandable way: The screw driver does not go through the hole you are trying to get the bushing into, and don't use the tip of the screw driver anywhere near the bushing.

Took me 45 minutes and a lot of sweat to get the first one in, then the next five took 2 minutes each...

--
Joachim

Last edited on 05-20-2009 05:51 pm by subwoofer

Back To Top PM Quote Reply  

 Posted: 05-20-2009 05:57 pm
  PM Quote Reply
12th Post
Dakota123
Member
 

Joined: 03-20-2009
Location: Colorado USA
Posts: 126
Status: 
Offline
They are in and actually I did use the vice method -- I think you may have mentioned it in another thread.  Worked like a charm.  As you said, correct positioning and a little side force on the protruding bits as needed helps immensley.  Very satisfying when it goes 'pop' as it comes out the other side.

Mike

Back To Top PM Quote Reply

 Posted: 05-20-2009 07:52 pm
  PM Quote Reply
13th Post
Jensenman
Member
 

Joined: 04-14-2005
Location: Columbia, South Carolina USA
Posts: 156
Status: 
Offline
I have the pre-Superpro bushings in the rear of my car, they were made as a two piece split bushing. Those just about jumped in by themselves.

Back To Top PM Quote Reply  

 Posted: 05-20-2009 07:56 pm
  PM Quote Reply
14th Post
subwoofer
Member
 

Joined: 04-01-2008
Location: Sandefjord, Norway
Posts: 583
Status: 
Offline
The inner, lower front bushings were like that, simplest ever to install. Wonder why they didn't make the rear ones like that? Could be a matter of production costs, coming to think of it. Cheaper to handle half the number of items.

--
Joachim

Back To Top PM Quote Reply

 Posted: 05-25-2009 09:30 pm
  PM Quote Reply
15th Post
Dakota123
Member
 

Joined: 03-20-2009
Location: Colorado USA
Posts: 126
Status: 
Offline
As an update, the SuperPros are in, and most of the oversteer is gone.  Despite my fears that the old bushings weren't really the root cause, this project was a huge success.

I replaced the original Girling shocks with the KYB Gas-Adjust (KG5552, not sourced from Delta) and these I'm not as crazy about.  They're not terrible, and most of the time they are fine, but on sharp bumps they introduce a bit of an extra kick.  Maybe I'm getting old, but I don't care for it.  (And yes, I only tightened the suspension bolts when the weight was back on the suspension.)

So, I'm going to go back to a twin-tube, low-pressure design and see if I like that better.

Thanks again to all for your input.

Mike

Back To Top PM Quote Reply  

 Posted: 08-17-2010 01:41 am
  PM Quote Reply
16th Post
jdenglish
Member
 

Joined: 02-11-2009
Location:  
Posts: 78
Status: 
Offline
Kurt,
I'm a little late on this post.  I have 15" wheels and 4 new Falken Azenis 205/50/15 R615K's to be put on this week.  I'll start at 30 psi.  Take off goes the rear sway bar?

Back To Top PM Quote Reply

 Posted: 08-17-2010 02:58 am
  PM Quote Reply
17th Post
Jensen Healey
Super Moderator


Joined: 03-11-2005
Location: San Anselmo, California USA
Posts: 977
Status: 
Offline
If you have a problem with oversteer you'll have to deal with it. Wait untill you get it on the road.

I run the front and rear bars with gas Koni's and have no issues.

Kurt

JH 13148

Back To Top PM Quote Reply  

 Posted: 08-17-2010 03:00 am
  PM Quote Reply
18th Post
jdenglish
Member
 

Joined: 02-11-2009
Location:  
Posts: 78
Status: 
Offline
The first road test will be to Grass Valley

Back To Top PM Quote Reply

 Posted: 08-17-2010 03:53 pm
  PM Quote Reply
19th Post
Jensen Healey
Super Moderator


Joined: 03-11-2005
Location: San Anselmo, California USA
Posts: 977
Status: 
Offline
You mean the Jensen West Coast Nationals August 26- 29th??

Back To Top PM Quote Reply  

 Posted: 08-17-2010 04:17 pm
  PM Quote Reply
20th Post
jdenglish
Member
 

Joined: 02-11-2009
Location:  
Posts: 78
Status: 
Offline
Yes, we plan to drive up Saturday morning.

Back To Top PM Quote Reply

Current time is 04:53 pm  
> Jensen Healey & Jensen GT Tech > Suspension > Oversteer Top




UltraBB 1.172 Copyright © 2007-2011 Data 1 Systems