Switching from Bias Plys to Radials

Don Kraftson

Don Kraftson

Active member
Last year at the Runoffs I spoke to a few drivers and Hoosier regarding switching to radials. At that time. it seemed like the upside, even if we got the set up right, would be minimal. And there was a downside in potentially screwing the handling up.

This year it seems as though cars and drivers with radials are achieving even higher heights, while there are some sticking to bias plys who are continuing to do well. So I have some questions for those who have made the change (and who are willing to share) to see if it might be worth investing the time and money to go to radials.

1. How many sessions did it take you to get the set up right?
2. What changes did you make (camber, toe, springs and anything else)?
3. Have they improved your fast lap time or just the longevity of consistent fast laps?
4. Do they take longer, shorter or same to warm up?
5. Have they caused any scary moments while driving or are they comfortable?
6. Do they have a different life span?
7. What do you do if it rains?

Thanks very much.
 
Hello Don - Here is what I know, which is not much compared to anyone that may have run them all last year. At least it is info from a front engine rear drive roadster like yours.

1. How many sessions did it take you to get the set up right?
Don't have it right yet and have done 8 sessions. We are getting close but there is more work to do
2. What changes did you make (camber, toe, springs and anything else)?
We have changed camber, toe, springs and bars so far. Pressures are next
3. Have they improved your fast lap time or just the longevity of consistent fast laps?
We have not gone faster with them yet, but I think we will eventually
4. Do they take longer, shorter or same to warm up?
For me they seem to take a little longer, but are similar in that regard
5. Have they caused any scary moments while driving or are they comfortable?
No scary moments, but they are so different that it took a while to feel that I had tires under me that I could trust. I do trust them now and in fact they seem more forgiving in that I was able to throw the car sideways to avoid a spinning car in front of me and could still save it. I don't think that I could have done that with the bias plies.
6. Do they have a different life span?
They seem to wear like iron so far and thrive on abuse
7. What do you do if it rains?
Don't know yet. I do know that I won't be changing springs and camber.

I think that eventually they will be faster both in top speed and lap times, but have not seen that yet. For my car with a live axle rear the issue will be whether we can get around not being able to plug in some rear camber. That has the potential of being a show stopper.
 
I doubt if there are many still running a stock lever arm suspension in HP as we are, but I wonder if the very limited adjustability of this setup would make the radials a waste of time (and money!).

James Wiley
#72 HP Midget
Atlanta
 
James -

Can you shim the front for a few degrees of negative camber? (I'm not very Sprite-savvy wrt such details) I'd think that's the main adjustment required vs bias. As Mr Bartell notes, the bigger trick may be what to do in the rear....
 
Don I'd love to give you a more complete answer but unfortunately just don't have much time on them yet. After scrubbing in two different sets, I had only 3 laps trying to get to speed before started having unrelated problems.

I will say that I *added* two degrees of camber to my setup (front and rear) and still need slightly more in the front, after looking at the tread wear.

I'll also say the car feels pushy on the throttle, so I don't have the shocks dialed in yet and may need less front spring or bar.

Personally I love the feel as they feel grippy and quite predictable.

Hopefully someone with a lot more time on them will chime in...
 
1. How many sessions did it take you to get the set up right?
Not really sure yet. I think you can get somewhat close right out of the box, but there is fine tuning to do based on your car/driving. If you start getting into spring rate changes, it takes a little bit longer.
2. What changes did you make (camber, toe, springs and anything else)?
Camber (3°-3.5° front, 2.5° rear), springs and a lot higher tire PSI according to Hoosier
3. Have they improved your fast lap time or just the longevity of consistent fast laps?
tough to say, but I've been close at two tracks this year and broke a lap record at Buttonwillow, where I had raced last year. They are very consistent over a race. Hard to do a back-to-back comparison because of the set-up differences.
4. Do they take longer, shorter or same to warm up?
Longer to get up to temp
5. Have they caused any scary moments while driving or are they comfortable?
No. My problems at last years Runoffs were a result of a binding in the suspension that was giving inconsistent ride height measurements - and confusion. I f'd it up.
6. Do they have a different life span?
I used tires from last years Runoffs all year for four races and didn't see a drop in grip. I haven't been able to use up a set yet.
7. What do you do if it rains?
stick on the bias ply rains and see how they feel. Not sure what to expect. Hoping for radial rains

On the solid rear axle camber limitations, Hooiser reminded me that IT guys have been using their radial DOT tire with same suspension for years.
The radials should have less rolling resistance, an ability to withstand more heat/abuse and have a longer life span. I've heard that you need a different driving style, but I'm not sure I know what that is or how to change the way I drive. When I'm driving them I don't ever worry about abusing (sliding) them, but I was conscious of that with the bias-ply's.
I don't see going back to the bias ply tires, seems like the radials are the future.
 
My expierences with the Hoosier radials after 2 seasons on a front strut, independent rear, rear drive LP contemporary car: They come in right away-no waiting-for the first 6 or so heat cycles. Even after 15 cycles (the most I have tried) they still have acceptable grip after getting up to temp. Still lots of tread rubber left at that point even on abrasive tracks with a 2650# car.

Can't say my flyer lap times have improved by huge amounts--just that I get more flyers per session.

Car setup changes are going to depend on driving style and suspension design. With the bias tires on my car I couldn't get enough positive camber in the rear legally without bending or building control arms and now with radials -1 to -1.5 is great. Static front camber will work at -1.5 to -2.5 with 6+ positive caster. Spring rates ( and believe me I have changed them a LOT ) ironically are real close to bias setup. Minor changes in shock valving (personal desires).

I will never go back to bias--my car likes the radials--and I do too. As far as what I feel driving, I always felt like I was chasing the steering wheel trying to go fast in a corner with the bias tires. the radials require less corrective input and the car seems more free through a corner to me. Scary moments? NEVER( except on oil!)

Sam Moore
EP BMW Z3
 
So I'm still both an IT guy and Prod guy, how much different are these radial slicks than a Hoosier R6?
 
evanwebb":9uy5xsx2 said:
So I'm still both an IT guy and Prod guy, how much different are these radial slicks than a Hoosier R6?
Click to expand...
The Hoosier guy told me that the racing radials have nothing to do with DOT radials. They are a different breed. I don't know whether he was referring to the R6 or other DOT radials.
 
I've only ran on the 13's. I personally like them as they helped loosen my car up somewhat.

1. How many sessions did it take you to get the set up right?
--Tony Rivera and I ran them with the bias setup, took temps and adjusted negative camber until temps even across. About four five lap sessions.

2. What changes did you make (camber, toe, springs and anything else)?
Added negative camber front and rear based off tire temps. Changed out bump stops to softer and shorter ones in the front.

3. Have they improved your fast lap time or just the longevity of consistent fast laps?
Both lap times and longevity. Did some engine tuning as well that reduced lap times with little or no effect on tire wear.

4. Do they take longer, shorter or same to warm up?
I think they take about twice as long to warm up as the bias tire, but they are still drivable.

5. Have they caused any scary moments while driving or are they comfortable?
I'm running a stagger front to rear and the difference was a surprise the first fast turn or two.

6. Do they have a different life span?
They are lasting four times as long than bias tires did on the car.

7. What do you do if it rains?
They felt just as good in the rain as the bias tire, if not better. I still have the old rains and will use them without a setup modification.

I've run a T3 S2000 on R6's and they do not feel anything like the 13" radial slick.

James Rogerson
HP #66 Honda 84-87 Grocery getter.
 
I also forgot to mention that the Hoosier guy used a special tip on his pyrometer and told us that we were not getting accurate readings with our standard one. His readings were about 20 degrees higher because he said he was touching the steel belt. I don't know whether this is the sort of thing where you can calibrate your gauge and tip and just add for example 22 lbs to all readings and get the same as you would if you used the proper tip.
 
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