My tire supplier said that front tires could now be as wide as the rears on FF's. Anyone else hear this? Would it be a good idea?
Mark
Tires
My tire supplier said that front tires could now be as wide as the rears on FF's. Anyone else hear this? Would it be a good idea?
Mark
1990 Van Diemen, the Racing Machine, CM AutoX, 2016 Frontier
You can try to make a street car into an autocrosser or you can do a lot less work and make a race car into a great autocrosser
Mark, in road racing, a lot of guys are using small tires on the rear (fronts on the rear). In FF, the rim size is dictated, not the tire size, so you can use any tire that will fit the rim.
As for a wider front, I have used a FC tire (7 X 20).
Dave,Originally Posted by Dave SanF 50
Are the road racers using FF or FF fronts for the rear or a different tire normally used in another class?
If so, what size? If they are 20 inch diameter that means significant rear suspension adjustment or modification just to raise the car one inch plus all the setup changes.
In any case I think the second place Runoff's car (Bill Valet) used the standard size Hoosier size and compound used in the F1600 Pro Series since the car was setup for them and, due to fuel pump or whatever issues during testing and qualifying he never got enough runs to dial in the car to different tires. FYI Bill won the Pro Series.
Mark,
I think the road racers are using narrow rears for tracks like Road America to reduce drag. Obviously not an issue for autox. Hoosier has tended to narrow the cantilever rear over the years for the road racers by the way. That is also at least part of the reason the road racers use the six inch front.
Dick
Who just had a new set of 7 inch fronts and normal cantilever rears mounted!
I can't see any advantage to a wider front tire for autocross, Mark. Your car already has good balance and that is with the rear bar full soft, basically. I also wonder what it might do to turn in and transient response, as the current tire seems to have just about a perfect sidewall profile or rim/section width relationship.
Mark: Was your tire supplier suggesting narrower rears to match the normal fronts as I assumed from what some road racers are doing? Not increasing the fronts to match the rears? As far as I know (Hoosier Tom and pictures) autocrossers are still using 7 X 20 fronts and the 22.5 cantilever rears.
Thanks!
Dick
Thanks for all the responses. The supplier was suggesting wider fronts. I believe based on something he heard somewhere, not his experience. A local formula Mazda guy has wider fronts than we run, so I was wondering about it. He is not that much faster than we are even with 70 more hp. I agree with Mike about the balance being good with the current tires. I hope I get all 4 new tires before the next event in one week.
Mark
1990 Van Diemen, the Racing Machine, CM AutoX, 2016 Frontier
You can try to make a street car into an autocrosser or you can do a lot less work and make a race car into a great autocrosser
Dick, Mark, et al
Regarding the same size tires F&R.
In the UK, the same size Avon threaded tire is used at all four corners. So VDs, being designed and built for the UK market have their roll centers and camber growth curves designed around the same size tire F&R. Swifts, being home grown, were designed for the cantilever, larger racing slick rears (7.5X22.5X13). The smaller rears are one way of getting the roll centers, rake, camber, etc back to where the designers intended.
See this ad in the FF classified. Note the tire sizes used.
[IMG]file:///C:/DOCUME%7E1/Owner/LOCALS%7E1/Temp/msohtml1/01/clip_image001.gif[/IMG]HOOSIER R25B 20.5X7.0-13 used
FOR SALE
USED
one set of qty 4
20.5x7.0-13 C2500 R25B
scuff, plus 18 laps
one set of qty 4
20.5x7.0-13 C2500 R25B
scuff, plus 13laps plus 5 laps
Can ups, at your expense,
or can deliver to Blackhawk, MC School, SCCA events,
or other Cendiv Tracks
___
FFCoalition.com
Marc Blanc
a wise FF prep guru told me. "Do what the car wants"
hard part is figuring out just what the car wants.but it's fun trying stuff
a wise FF prep guru told me. "Do what the car wants"
hard part is figuring out just what the car wants.
Here, here, Mark I'm coming back next week and we are going to be on the fast track of getting your car up to speed.
Ben
New tires must have worked; my car ran 1,2 and 6 fastest time(3 drivers) yesterday
Also would have been 2 and 3 for PAX(fun run times).
It was not quite as neutral on the new tires, back to fiddling with suspension.
Here is a link to a forum with video of Ben's best and my last run. http://www.baautox.com/forum/index.p...start=0&rid=26
Mark
1990 Van Diemen, the Racing Machine, CM AutoX, 2016 Frontier
You can try to make a street car into an autocrosser or you can do a lot less work and make a race car into a great autocrosser
I ran the wider FC front tires for the past dozen years. From what I could tell, most of the CMod national grid also ran the wider front tire.
For RR many racers are running the front tires at the rear in order to cut down on drag. If the car is set up for this, they seem to do pretty well.
Jim
I wish I understood everything I know.
fronts on the rear
One other aspect of using a front size tire on the rear of a FF is it gives one the same effect on the overall final drive ratio as using a lower gear ratio or CWP. For example, if you are using 22.5" tall tire (~70.7" circumference) and switch to a 20.5" tall tire (64.4" circumference), that is a ~9% reduction. If your first gear topped @ 50 mph with the 22.5" tire, you will now top out @ ~45.5 mph with the shorter tire. Almost the same result as going from a 10:31 to a 9:31, which is a 10% change.
Also, the fronts are cheaper than the rears, so you save money. LOL
In addition to the gearing change and lower initial cost, the shorter rear tires have several other effects.
o They reduce the rear unsprung weight by 10 lb
o They reduce the rear tire rotary inertia considerably
o They reduce aero drag
o They affect the suspension geometry
o They require big setup and CG location changes
o They are easier to drive
The last one is because the sidewall stiffness is the same front and rear. On turn-in, the cantilever rear tires take a fair amount of time and distance to deflect before they start producing much lateral force. That rotates the car and makes it feel like it's loose while the rear sidewalls are building deflection. With the same tires on both ends, it responds like a normal car.
Here is an indication of the setup changes required to rebalance a FF with the same tires on both ends.
Last edited by Neil_Roberts; 04.16.12 at 2:15 PM. Reason: Add link
Neil,
Do you have any idea whether or not the small rears are viable for autocross compared to the standard size? I spoke with Bruce Foss of Hoosier at the Pro F1600 race at VIR on Friday and he indicated that the small rears are only an advantage on tracks with long straights like Road America.
Also, I wonder is the typical CM early to late 80's suspension (mostly rocker or even outboard) could make the setup changes (I haven't read your notes yet . . .).
Thanks,
Dick
I'm sure they are viable, but I'm not sure if they have the potential to be faster. I'm going to try it and see, mostly to reduce the setup differences between autox and club racing. Another example of that is tires. Since the R25B compound appears to be durable enough for club racing as well as autox, I hope to run the same tires everywhere.
The only major obstacle to running the short rear tires with rocker or outboard suspension might be running out of droop travel. Longer shock tops may be required.
Even in solo, on a hot day the R25B can get greasy. We wind up watering them between runs. I would think they'd only work on a road course in very cool weather.
I wonder, once you get the balance right, how well the 7" tire will put down power coming out of tight corners at solo speeds?
By the way, I'm only halfway through the book but I'm really enjoying it so far!
Don
Don, very interestingly, I used to run my F5/FMod both on R25b and prior R25a and prior R25 tires. The R25b/a/* will get a bit greasy on hot days on the track toward the end of a race. On a hot autox the car would get surprisingly slipper on the R25b/a/* tires requiring watering between drivers. I have yet to really understand this phenomenon, but the tires are more usable hot on track than autox in my opinion. Not that either is bad, mind you. It seems somehow the sudden grip difference is more notable in autox than the constant change that occurs in club racing on that tire.
jim
Single driver cars also?
Asphalt and concrete?
Thanks!
Dick
On a hot (90 deg F +) sunny day, even single drivers need to spray their tires. On a road course the tires would cool significantly on the straights, but I would have thought that the tire temps in the long turns would get higher than ours do. No data, just going on the fact that road racers usually use harder compounds than us.
Don
Thanks! When you get to the section titled "Reshaping the Friction Circle", that will tell you how to improve power application. Lowering the tire pressure from the optimum for cornering will improve longitudinal grip.
It's worth knowing that the longitudinal grip of a bias ply tire is a lot more camber sensitive than a radial is. So, minimal static camber is helpful in that regard.
Also, changing the rear toe setting is a great way to find the best compromise between inside wheelspin and power oversteer. The reason that this works is that more toe in reduces the inside rear tire slip angle compared to the outside rear, so it has more of its longitudinal capacity available to combat wheelspin. If your inside rear tire goes up in smoke at the exit, more toe in will help. If you have too much toe in, the result will be power oversteer. The more toe you run, the tighter the turn radius is that you have optimized the setup for. Formula SAE teams have been known to run 1/2" of rear toe in due to the extremely tight courses and the small wheelbase to track width ratio that most of them have.
[QUOTE=Neil_Roberts;341390]I'm sure they are viable, but I'm not sure if they have the potential to be faster. I'm going to try it and see, mostly to reduce the setup differences between autox and club racing. Another example of that is tires. Since the R25B compound appears to be durable enough for club racing as well as autox, I hope to run the same tires everywhere.
Neil, I got 142 runs on my 25b's. I calculated that at around 150 miles. Maybe tires last longer road racing. Doesn't seem like much more than 4 30 min races. I have read that road racing eats up tires, I think in some book about thinking fast
Mark
1990 Van Diemen, the Racing Machine, CM AutoX, 2016 Frontier
You can try to make a street car into an autocrosser or you can do a lot less work and make a race car into a great autocrosser
A question for those who know: How does the R25B compound compare to the old R25 in terms of service life and heat sensitivity?
I noticed that when the R25 tires were new, they were grippy all the time. As they got older, the grip when they were hot stayed about the same, but they had to get hotter before the grip came in. During my last autox, they didn't come in until halfway through my last run. That worked out to a service life of 12 minutes, spread over about 1.5 years. Maybe that was more a factor of calendar time than heat cycles.
The R25B stays grippier longer than the R25A did. And I'm pretty sure that I felt the B's staying at a high level of grip longer than the A's.
Mark's experience doesn't match mine (14 years in my Citation, which I sold last October), plus 2 National Championships (not trying to brag, just offering credentials). After 40 runs, the tires (A's AND B's) were well degraded in terms of grip. But I'd keep running them at local events and when I got to 70 or 80 they were pretty bad. I once ran a set of tires to 105 runs and that was due to extreme racing poverty. But those tires were completely useless and not any fun at all.
After that, my co-driver and I agreed that we are in this not only for the competition but for the joy of driving ... and old tires detract from enjoyment. So we decided to not go much past 60 runs. Full tread but tired tires, both in terms of butt feel and durometer readings.
Jim
I wish I understood everything I know.
Neil, what Jim said. Also a lot depends on many variables like pavement, ambient temp, car set up, driver style, etc. etc.
from the other thread on tires:
On the "how long are R25's sticky?" Both myself and a local ex DP driver think you have 2 months from the time the mold release is broken. For autocross is seems to be a time thing more than a run thing. As they age, they turn into R35, R45 and eventually R60 equivalent compound. You can get a lot of runs out of an R60
From my track side service days: a customer had been running the same set of Yokohama 008's for 4 years and they still had tread left. He purchased a new set of Hoosiers and picked up at least 4 to 5 seconds a lap at Summit Point. He was grinning from ear to ear about the grip and sensation. not so happy they didn't last like the Yokohama 008's
It will be interesting to see how the 60 day experience Ted V has seen plays out for me. I broke the mold release with a total of 6 (3 cw and 3 ccw) laps around a 30 ft ID "skid pad" (a center circle in my asphalt driveway) this weekend without getting the tires to temp or even close to it. Literally just scuffed the mold release off and most of the residual glue from the stickers.
The first event will be the Evo Shootout in Charlotte this weekend on sealed asphalt. Runs will range from a minimum of 6 to a maximum of about 11 (complicated PAX based qualification and then runoff system). Then about 8 weeks later they will run at the Blytheville Pro Solo and Tour.
Single driver. Tow on an open trailer from Raleigh.
FYI: Durometer info - Brand new 25B's at about 75 degrees duro around 50. 2 year old 25B's with less than 50 runs duro a few points higher max. No real grip falloff data since the first event on the old tires was under perfect 80 - 90 temps on a high grip asphalt site and the last events were on somewhat cooler days on a lower grip site. I was REALLY impressed with my first exposure to 25B's. We will see what happens with this new set.
Edit to add: I've never corded a set of slicks. In the old days with 25's they were long gone before then. I was inactive for the 25A's and have only limited experience so far with the 25B's.
Dick
CM 85
Just guessing here, but perhaps this is how the R25B is able to endure club racing. I ran used GY R430 tires for the school and saw faint evidence of cords at the end of each day. As my level of effort approached 10 tenths, the amount of marbles flying off my tires increased dramatically. Perhaps the higher wear rate on the track continually exposes fresh rubber, and the thinner tread gains and loses heat faster.
Neil,
WOW. Is that typical for "hard" GY's? The Pro F1600 guys running Hoosier 45B's can get multiple weekends from a set with 2 races per weekend as I recall.
I think it is common for autocrossers to see hardly any wear on the front Hoosiers (even back in the 1990's) other than inside edge with more neg camber/ackerman than "normal". Therefore, most of the wear is on the rears which then start to go off which loosens the car enough that between the looseness and the times degrading we know it is time for new tires. Some guys will buy 2 sets of rears for each pair of fronts. Also, at some events we come back with OPR (other people's rubber) and/or expansion strip tar on our front tires. I don't know if the guys who use tire softening treatments ever cord the tires.
Dick
Neil,
FYI there are lots of tire closeups in Dennis Valet's Pro F1600 photos. Note how often the mold lines are still visible on the tires. The tires are Hoosier 45B but marked for the pro series.
Dick
I don't believe durometer readings as an indication of a tires ability to grip. I'm sure everyone will agree Hoosier Autocross compound works better than the road race compound at an autocross, and cold weather road racing. I have seen the A compound read higher the the R compound on new tires in the warehouse. Build dates on both sets not that old either.
That was my rather subtle point . . .I should have bought a set just for "anti rain insurance"
Dick
CM 85
Not so sure about the 60 days from scuff in thing. I use last years Nationals tires (with 13 runs) as good NT tires the following spring. I wrap my tires with black pallet wrap in grid, and store them in a dark corner of my basement when I'm not at a race. Typically get two big events (Nationals, National Tour or Div Championship) out of a set (24-30 runs), then use them for Divisional Series or local events up to 50-60 runs. I've gone as high as 100 runs at a test 'n' tune. Good for high slip angle car control / looking ahead practice, but not terribly fast. When we first switched to Hoosiers in '03 (don't remember what the compound number was back then) they did tend to burn up the rear tires first and the car would get looser over time. Later (maybe '05?) they went to a narrower front tire for a while and those tended to get chewed up quickly. Today's C2500 R25B tires seem to age very evenly front to rear on my car.
Don
Don (or anyone),
Thanks for update! Questions on the pallet wrap:
1) Does the wrap make the car more likely to slide on the trailer? What type of trailer surface and tie downs? I have Rhinoliner on an open trailer and tiedowns from suspension to D rings.
2) Do you have to jack the car to wrap the tires? (I cannot think of any other practical approach).
Also, how do you preserve rain tires? I'm planning on replacing my roughly 12 year old unused molded rains this summer and have to deal with transporting tires on the open trailer.
Thanks,
Dick
Hmmm. I have been using a durometer for 15 years on Hoosiers. It has always been an accurate indicator of a tire's grip.
Whenever I had two sets of Hoosiers in my garage, I'd durometer them. Without fail the older, more used set were a higher durometer reading than the newer set.
Furthermore, when applying a tire softener like "FV Traction Compound", the changes would make themselves apparent. This difference showed itself very quickly. Or let the tires sit a week or two and the changes were still there.
Because the rears usually go off before the fronts, the balance of the car gets loose. When I softened both ends equally, the balance would remain loose because. But when I used the durometer to keep one end from getting too soft, the balance was good.
And although there was no one number to shoot for with durometer readings, there was a general range that always showed up when the tires were getting used up. And when they hit another number, the tires were junk.
Re-reading Ted's post, I see he is referring to street tires. I have no experience durometering street tires and it could be that the harder rubber of a street tire (including the R street compound) might be a poor candidate for durometer use.
Despite the popular opinion that durometers are useless, I'll continue to use them and hopefully once again attain the modest success I've experienced.
Of course, YMMV.
Jim
I wish I understood everything I know.
Jim,
Thanks for the input. What sort of durometer "point spread" is significant? i.e. a couple of points, 5 points, 10 points? Also do the tires need to be a a standard ambient temp, presumably in the shade?
After seeing your post this morning I compared my brand new tires with the 2 year old set and also the never used old rain tires . . . all at about 60 degrees F. The new versus old slicks, especially the rears, have a bigger spread than when warmer. Plus the old rears seem to have different readings at different points on the tread surface. I have not done a comprehensive analysis since "my head" will require new tires after no more than 3 NT's or Pro's in any case, and probably just 2. With only 2 sets of wheels that means the older set won't be around very long in any case. Fresh rains will have their own set of wheels.
Dick
Trying to catch up on what folks have learned in the last 10 years so I have fewer reasons/excuses.
Tiled linoleum, straps over the rear tires into D-rings in the floor, sliding not an issue unless both rear tires lose air.
Yes. I bring a single stand to grid, jack up the rear of the car and put the stand under it, then leave the jack under the front of the car to clean and wrap the tires.
I do the exact same thing to my rain tires, except they were brand new in 2004. Every couple of years I give them a coat of tire softener, which makes them softer. Not sure if it makes them grip in the wet? Better than rock hard I think, but probably nowhere near as good as new ones. Last time I ran all three runs in the rain on rains was at the 2005 Divisional Championship, and some guy in an '88 Reynard smoked me that day. Not sure if it was my driving, or if my car setup is just not well suited to running in the pouring rain. Rains were relatively fresh then, and he was running the same type, so I don't think they were the problem.
Don
Hi Dick,
Since everyone's durometer may be off from other durometers, I don't use the readings to compare against other guys' durometers. Just my own. My durometer will read in the high "40s" when measuring new tires, scrubbed. 50s is fine. 60s is getting old. 70s are only good for practicing car control as Don put it so well. But I try not to go to an important event with something out of the 50s.
Having said that, your observation that readings change from spot to spot on the tread are right on. Side to side and circumferential. And when I've subjected tires to too much negative camber actually had higher readings on the inside (by 10 points or more).
Circumferentially I've also seen readings that vary by 10 points or more. Usually I'll take about 20 to 30 measurements. On any particular tire I'll see the vast majority within 4 or 5 points of each other and then some that are off by 10 points or more ... both higher and lower. I'll toss the outliers and average the rest and write all of that down.
I have to admit that there have been times (not too often) when the durometer readings were simply frustrating. But most of the time they made sense overall.
I find this useful for keeping track of tires along with the usual recording of events and runs taken. Sometimes a set of tires last longer than others while another set might go quickly. I like referencing my record of durometer readings to the other records. I can compare site surfaces, heat cycles, etc.
I've taken 100+ runs on newish tires at a test and tune and then the next week, despite all those runs happening in only one day (one heat cycle?), the tires will be crappy. The durometer bears that out and I won't bother with them anymore other than for a laid back, relaxing local event where if you finish behind a stock Mini, no one will care (well, maybe not behind, but too close). Now, even without the durometer all of us could have figured that out. So maybe I'm just a obsessive compulsive and need to satisfy my affliction with yet one more tool.It's just kind of interesting to me to keep this information.
The bottom line for me is that it allows me to rest easy over whether a set of tires I want to use at an important event are going to work reasonably well. If I was rich, I'd just buy 5 or 6 sets of tires a year and give my lightly used ones to you for free Dick (shipping costs on me!).
Jim
I wish I understood everything I know.
Don and Jim,
Thank you both (again) very much!
Jim, I'm "rich" in name only
Dick
CM 85
[QUOTE=Jim Garry;341779]Hi Dick,
The durometer bears that out and I won't bother with them anymore other than for a laid back, relaxing local event where if you finish behind a stock Mini, no one will care (well, maybe not behind, but too close). Now, even without the durometer all of us could have figured that out. So maybe I'm just a obsessive compulsive and need to satisfy my affliction with yet one more tool.
Jim, You must be talking about me, who has an affliction? I ordered one.
Does it make any difference if you test tires cold or hot?
Mark
1990 Van Diemen, the Racing Machine, CM AutoX, 2016 Frontier
You can try to make a street car into an autocrosser or you can do a lot less work and make a race car into a great autocrosser
my bad
I mis-spoke in post #7. The Avon tire used by the UK does have different sizes, F&R. So Sorry for any inconvenience this may have caused.
ACB10
Modern Formula Ford all weather tyre, the ACB10 was orginally developed in 1993 as the world Formula Ford contract tyre. Today the ACB10 continues to be the tyre of choice for most Formula Ford 1600 championships in UK, Europe, South Africa, Australia and New Zealand.
The ACB10 was launched as a ground breaking product that removed the need for buffing to increase performance. The tyre shows a constant performance level throughout its life.
Standard Formula Ford specifications are:
6.0/21.0-13 (spec - 8317)
7.0/22.0-13 (spec - 8319)
These are the only specifications to carry the 'Formula Ford' designation on the sidewall
Also available as a road legal version, the ACB10 sport.
Dave,I mis-spoke in post #7. The Avon tire used by the UK does have different sizes, F&R. So Sorry for any inconvenience this may have caused.
ACB10
Modern Formula Ford all weather tyre, the ACB10 was orginally developed in 1993 as the world Formula Ford contract tyre. Today the ACB10 continues to be the tyre of choice for most Formula Ford 1600 championships in UK, Europe, South Africa, Australia and New Zealand.
The ACB10 was launched as a ground breaking product that removed the need for buffing to increase performance. The tyre shows a constant performance level throughout its life.
Standard Formula Ford specifications are:
6.0/21.0-13 (spec - 8317)
7.0/22.0-13 (spec - 8319)
These are the only specifications to carry the 'Formula Ford' designation on the sidewall
Also available as a road legal version, the ACB10 sport.
sorry for the noobish kind of question, but what do they mean by buffering a tire to increase performance?
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