Traction/tire slip @ Bonneville

[bvilletom]

The slippage you noticed from the time slip, tachometer and calculated speed was more this year because of the very wet & crappy conditions we raced in. I have raced at Bonneville for more than 40 years with small HP cars. Usually you have about 2 to 3% slippage, which is common. On the day it rained, you were pushing 3/4" or so standing wave of brine and slush water ahead of EACH tire which not only made the car go slower but also made the traction poor. This is why the big HP cameros and roadsters all add a lot of weight. In racing for a one mile run, the weight may make you slower than the slippage does. For the one mile distance, it is a one mile DRAG RACE, the faster the 1/2 mile speed is, the faster the mile speed will be.

Your car will be faster at the Mohave mile or ECTA because it is racing on a smooth surface with excellent traction.

bvilletom
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bvilletom
36hp Challenge record holder New Age 126.236mph

1970 Porsche 914/6 – 2 liter LSR record holder
1992 Metro Sedan – 1 liter LSR records
1987 Chevy Turbo Sprint – under construction

[bajamike560]

So the skinny tires and proper weight is in order for a good run on wet salt. Same skinny tires for a bit dryer conditions?

Mike
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[Alstrup]

I´m not sure I wanna try 125 mph in the rain, even on skinny tyres

I am aware of what is normal to use on the salt. But I can´t stop thinking that a slightly wider rear tyre SHOULD improove traction, - at a cost, I know. But the goal is to find where it aids and when it is too much.

I would say going from f.i. 165 to 185 should´nt hurt drag that much, but could improove traction quite a bit.

T

[Teeroy]

We ran 185's, spun them lots. Never did try to lower pressure in the rear for a run.
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[36hplandspeedracer]

[36hplandspeedracer]

Excuse me Alstrup, I meant Denmark,.

My aopologies.

Burly

[Alstrup]

Accepted

OK. In my mind the track was "dry" most of the time, this year excluded. So I did not understand that part fully. That changes the picture.

I have been out there, but never during spedweek, yet.

But since we are aquainted to snow it might be worth looking into some of the M&S tyres on the market today (if that is legal to use out there)
I´m sort of a "Nokian" guy when it comes to winter tyres. But last year my tyre guy convinced me to try the new (2011) Hankook I*cept WR, because he wanted my view on them and the fact that they were 15% lower price than the Nokian counterpart. (I had the option of returning them if I did not like them) - I have to admit that Hankook has really picked up on tyre quality over the last few years, overtaking older brands like Toyo, Falken, Good Year and to some extend Bridgestone. These I*ceptWR tyres perform just as good as the older Nokian WRA3.

If that kind of tyre is allowed I would take a serius look at the new Nokian Hakkepellitta 7 (with out the spikes though) - havent seen or tried it myself yet. But from what I hear it is awesome. AND Nokian has just broken the World record with landspeed on ice with them.

Food for thought.

T

[36hplandspeedracer]

Interesting concept Alstrup.

To run in the 130 MPH Club of the USFRA the tires must be H speed rated or greater(some exceptions are allowed for 36hp Challenge VW's running under 100 MPH-S rated are OK for them!). The tires must be in very good conidition(no sidewalll cracks) and mounted using metal valve stems and caps.

The major problem we experience today when using speed rated tires designed for use on the street is they are almost all low profile and wide, exactly what we would prefer not to run! Some reasonable speed rated options have been found but they are few and far between and for that reason, most VW Challenge racers have stepped up to the plate and installed race approved "Front Runner" style tires from different manufacturers on both the front and rear wheels. The only caution is, do not try to drive them on the streets since they have unusual handling characteristics when cornering and are not safe for street use!

Burly

[slalombuggy]

I understand your concept Alstrup. And I had considered using snow tires last time I came down. Then I found some Goodyear frontrunners.

The only problem I can see is that this year my front tires (165/45/15 Federal Formosa's) packed solid with salt. Now I can't tell if they did this while doing a run or on the return road at a relatively slower 60mph but the tread (almost full tread) was packed and there was probably 1/2" of salt built up on them making them VERY heavy.

My biggest concern would be the tire growing so heavy it would pull itself off the rim at speed, not exactly a good thing I know that's why they make us pump our tires up so much.

I think I heard someone say that at speeds over 100mph the tire starts to stretch so much that the air pressure will drop considerably, it sounded like by almost half. But I could have misheard this. If someone can correct this pleasae do.

brad

[Alstrup]

Hmm. The packing might be an issue. I did´nt think of that, and have no idea how the tyres would respond to salt. That would have to be tested. - On the other hand, M&S tyres are more soft in the compound, so there is a good chance that the packing would loosen itself from the tyres as soon as G force begins to play a role.

The low profile, or lack of such is a problem that needs to be looked into. If the brakes are 68- on one could use lightweight BMW ally wheels (They look a little like a VW wheel.) in 16", so the total rotating mass was kept equal.
If it is pre 67 the options are..... not that many, unless one is a little creative. But hey, that´s where the fun is.

T

PS. Come to think of the packing issue again. I do think the tyres will clean themselves when speed picks up. I draw a parrallel to snow just below 0. Such snow will also pack in the threads when the wheel is turning slow. But as soon as the speed increases the tyre cleans itself. Salt, somewhat different in material should behave the same way, maybe loosen at a slightly higher speed.

Winter tyres do have a slightly higher drag compared to summer tyres. So the trick will be to find the sweet spot where you can charge harder in the beginning of the course (reducing spin) and maintain or improove top speed at the end due to less spin with the amount of power present.

[36hplandspeedracer]

Alstrup, what (width, bolt pattern and offsets) of the BMW wheels you refer too. Are they 4 bolt with the same pattern as 68 and newer VW's?

By chance do you have a photo of the BMW wheels?

Thanx for your input.....................

Burly

[TomSimon]

Hi Burly, just thinking outside the box for a bit; What about a narrow spec formula vee tire (race slick)? But a set that has been custom grooved with a tire iron, midget and sprint car style? Seems if USFRA and SCTA rules allowed the F-vee slick, a stiff sidewall race tire good for, um, 150mph I assume, a guy could come up with whatever custom tread he wanted, while still having a fairly narrow footprint for high lbs/sq inch on the salt.

[bajamike560]

[Roadcow]

Burly is out of town but will be back tonight or tomorrow morning.
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[slalombuggy]

Mike, we can run any tires as long as they are speed rated for the class. At least H rated for the 130 Club V rated for the 150 Club. Formaula V tires would work. I ran front runners on the rear of the buggy

The "problem" with them is they are 4.5 inches wide and are a flat contact patch for road racing and I think would give greater resistance than front runners that are a more domed tread design. As far as grooving them. They have very little rubber on the tread area so the grooves would be very shallow. I don't know if they would be deep enough to be effective. Might be worth a try though. I have some contacts I can get them through fairly cheap.

brad

[bajamike560]

Thanks for the info Brad.
As far as grooving goes, I think a little is better than nothing right? Just need to figure out the proper pattern for single purpose tires.
Need someone to try this theory and give feedback.

Mike
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[36hplandspeedracer]

Jut got home and Matt Guzowski ran them in the 130 Club on his Formula V (naturally) and I think Tom Bruch has used them at Bonneville. Again, "Speed Rated" are the key words and most racing tires are rate for speed but I do not know where FV tires fall into on the H,Z and other speed ratings.

Anyone out their know?

Burly

[Alstrup]

[36hplandspeedracer]

Both look good Alstrup. Thanx.......................

Burly