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PeterRaymond
17-11-07, 05:41
I run what is aproximately a Lotus Seven, although the engine has been moved back and towards the passenger side of the car. It now has 58% of the weight on the rear wheels, IRS, at least 5000 ft-lb/degree chassis stiffness and it's powered by a 250hp Cosworth YBM. It weighs around 1460 lbs (660 Kg) with driver. It would be lighter, but I run it in the US in the SCCA Solo D modified class and minimum weights were recently raised.

SCCA Solo is what is called autocrossing in the US, but I guess that's not what it would be called there. We get three timed runs of around 50 seconds through a course set with traffic cones on a level paved surface. It's a different course for every event. Because we are not lapping continuously we have some of the same problems you have hill climbing. We want the tires to work as quickly as possible, we want as much grip as possible, but we don't want tires so soft that they overheat and go away.

So, that's the back ground. I am looking for a recomendation for an Avon tire compound. In particular, our National Championship is run each year in September and the temperatures have been on the cool side. Also, the surface does not have a huge amount of grip and isn't getting the Hoosiers that most people run up to temperature. We can share the car with a co-driver, which gets the runs closer together and we typically put insulated covers over the tires between runs to hold heat in, but that doesn't seem to be enough.

How soft should I go? I also have a choice of two different tire sizes. The smaller is 7.5 x 20.0-13 front and 10.0 x 22.0-13 rear. The larger is 10.0 x 20.0-13 front and 12.0 x 23.5-13 rear. I like the smaller size, because it narrows the car by inches, but I also like the larger size because, well bigger is better. Getting the tires warm with the larger size is just that much more difficult though.

A feeling for how consistant the tires and the different compounds are would be apreciated too.

I can't imagine any source for better answers to my questions, so thanks in advance!

Peter Raymond
Near Denver Colorado, USA

Radical
17-11-07, 17:02
Hi Peter,

I've seen some video clips of Solos and there are some clubs here that are trying them. It is closest to what we would call an Autotest, although autotests here generaly include reversing. Without the reversing does make it similar to a very tight Hillclimb or Sprint.

I have tryed Hoosiers in the past and can comfirm that you will see a dramatic improvement if you switch to the Avons. You could contact BMTR, I am sure they could give some advice on which compound.

Personaly I expect that you could go the A91 (the second softest), but probably better to go one grade harder with the A15, which is still excellent from cold, but should give longer life.

Angus

PeterRaymond
18-11-07, 06:30
Thank you for the reply.

My first event was in '78, but I missed the era in the US when reversing was included, although I have heard stories. Our speeds have also drifted upwards over the years, but most street licensed cars will spend most of their time in 2nd gear. Top speeds in my class reach up to perhaps 110 kph on some courses. We really don't have straightaways though, so the tires don't do any cooling between turns.

I had been thinking of either A15, or A91, but I didn't want to prejudice the answer. I didn't really have the nerve to go to A45, but I did give some consideration to what looks like a new compound: A89. I copied the below from the Avon web site.

A15 Soft compound for hillclimb slick and single seater circuit wet applications.
A91 Soft compound for hillclimb slick, single seater and sidecar circuit wet applications.
A89 Very soft compound for hillclimb slick and wet applications. Special order only.
A45 Ultra soft compound for hillclimb slick and wet applications. Special order only.

Peter Raymond

MikeBeattie
18-11-07, 19:35
Peter
I assume yours is a LONG distance question to a SHORT distasnce problem :)

If folk are not getting their Hoosiers up to heat, I'd go for the 89s or even the 45s, and probably the 45s on the front, as the rears will gain heat more quickly.

I ran 45s on a Jedi as fronts on Irish hills ( typically 60-70 secs) and sprints (100secs) without an issue, those were at speeds well in excess of what you are doing. We ran 5 runs in a day. Yes it is a much lighter car but there were never any tyre performance problems.

I would reckon that it is unlikely that 45s will overheat and "go off" during your run. How many events are you hoping to do on one set of tyres? It is unfortunately the way that the fresher tyres are, the better they perform, so if you want to be competitive you may need to budget for more replacement sets :)

PeterRaymond
22-11-07, 05:56
Peter
I assume yours is a LONG distance question to a SHORT distance problem :)

>> Yes, exactly!

If folk are not getting their Hoosiers up to heat, I'd go for the 89s or even the 45s, and probably the 45s on the front, as the rears will gain heat more quickly.

I ran 45s on a Jedi as fronts on Irish hills ( typically 60-70 secs) and sprints (100secs) without an issue, those were at speeds well in excess of what you are doing. We ran 5 runs in a day. Yes it is a much lighter car but there were never any tyre performance problems.

I would reckon that it is unlikely that 45s will overheat and "go off" during your run. How many events are you hoping to do on one set of tyres? It is unfortunately the way that the fresher tyres are, the better they perform, so if you want to be competitive you may need to budget for more replacement sets :)

>> We may get more heat in our tyres than one would first think. With the softest Hoosiers, which I have heard are only a little softer than A11s, we do sometimes overheat tyres. With 2 drivers on abrasive surface I've had to cool tyres off between runs. In this situation though, the runs are close enough together that there is time between runs to adjust the belts and replace the seat to switch from one driver to the other, but not much more than that.

>> Why do the tyres sometimes heat that quickly? Possible reasons are perhaps actually related to the fact that the speeds are lower. Most higher speed courses include straightaways, so some of the heat gained in a corner is lost on the straight. Also, the lower speeds mean lower gearing and more rear wheel torque, which tends to work the tyre somewhat harder.

>> I think I'm moving towards using 2 different compounds. One for "normal" events and a second for, in particular, our National Championship, where the surface does not heat the tyres as well and where the weather tends to be cool.

>> I may be able to get away with being a little conservative, since I don't have to have the perfect tyre, just a better tyre than anyone else in the class.

>> I generally use multiple sets in a year, in particular a fresh set for Nationals, but what's really expensive is experiments!

Thanks for all comments,

Peter Raymond

Steve Wilkinson
22-11-07, 12:46
I've seen some video clips of Solos and there are some clubs here that are trying them. It is closest to what we would call an Autotest, although autotests here generaly include reversing. Without the reversing does make it similar to a very tight Hillclimb or Sprint.
Angus

Autosolo in the States is bigger than in the UK. Events in the UK use Motorway Service station car parks whilst some of the Stateside events are in massive car parks at Malls. Speeds in the UK rarely exceed 40 mph whilst in the States they are a lot faster - more like a Sprint! In the UK the cars used are all road registered whilst in the States they also use race cars - Formula Fords, Sports Libre, Single Seaters etc.
All Autosolos feature just forward only 'gates' but there are high penalties for clipping the cones. It is a fast developing 'sport' in the UK and hopefully there will be regional championships in 2008 and possibly a National Final.

:cool:

Radical
22-11-07, 23:07
I agree and from the vids I have seen and our comments about having to cool the tyres, I still think that the A15 would be the best allrounders, I have never seen or heard anyone using the A89s so cannot comment, but definitely expect the A45 to be too soft for most of your events. Possibly A40 (91) for the straighter ones but expect to have to shave them clean after the runs as I expect they will grain.