Radial Wets / Crossply Slicks

[Craig Powers]

I have just spoken to BMTR about wets for my OMS2000m 1100cc.

I was exploring the use of slightly more durable compounds rather than the A45 (f) / A91 (r) that I run as slicks. This idea was floated by a fellow competitor based on resistance to aging (curing).

There is also the suggestion that the thread pattern is slightly more stable due to the harder compound.

One suggestion from BMTR is to run radial wets in an A15 compound. Apparently these can be run satisfactorily with little or no camber, as one would do with a crossply.

Does anyone have any experience in this area?

Craig Powers

[whimsy]

Hi Craig,

Can't say I have any experience of using harder compound wets, but I do have a couple of thoughts.

Wouldn't the downside of extra durability just be less grip? Granted A15 isn't massively harder than A91 and the conventional wisdom (which I know is what you are challenging!) is to use the softest rubber available in the wet. Of course once the track starts drying that's another issue, and even if you can run a 3rd intermediate set there is probably no perfect solution to changing conditions.

Is the aim is to preserve the wets (ie have improved resistance to ageing) so you don't have to buy a new set as often? Which brings me on to something I've heard, but haven't had a chance to confirm or otherwise. I'm told you can't cut radial slicks into wets. Can't see why as the rubber used on the radial carcase is the same as on the crossply!! And if you can, then the path I've always taken is to have slicks I'm replacing cut into wets periodically so that the wets don't become unusable with ageing. Having only recently moved to radial wets I haven't yet got to the stage of needing to replace them so I hope you CAN cut slick to wets!

Radial wets are massively better than cross ply wets, but I'm puzzled why a change of compound from A91 to A15 should mean any alteration to camber requirement. The tyre construction remains the same and I'd always thought it was the sidewalls in particular that set the need for negative camber? Also the very significant negative cambers being bandied around for use with radials a few years ago seem to have diminished significantly as people found that in practice, for hill climbing, they weren't necessary. I've been using 1.5 degrees negative at the front which isn't a huge amount.

Don't know if this is of any help but it might trigger one or two thoughts!

Andy

[CNHSS1]

Whimsy
regarding the radial wets and camber, do you run radial or crossply slicks? Reason i ask is that i thought that crossplies needed near zero camber/toe and yet radials liked lots of camber to 'work', requiring two 'setups'.
how are the radial wets much better? i assume the patterns the same, so water clearing should be identical as is the compound, so must be the carcass. Are the radial sidewalls softer/less stiff?

sorry for all the Qs, havent bothered with wets up until now, always thought slicks are good in the damp and that if its really wet the cars best on the trailer but am tempted to give full wets a go with views to our british summer

[Craig Powers]

Unfortunately the 'paddock advice' came to me indirectly so I didn't manage to discuss with the two originators. The actual advice was to use F3 or F.Renault wets (I can't recall which). Of course we could be taking this totally out of context; their advice may be solely based on the availability of cheap 2nd hand tyres! Nevertheless a call to BMTR seemed worthwhile. BMTR dismissed the F3 / F.Renault suggestion but did put forward the radials suggeston. More below....

Originally Posted by whimsy

Wouldn't the downside of extra durability just be less grip? Granted A15 isn't massively harder than A91 and the conventional wisdom (which I know is what you are challenging!) is to use the softest rubber available in the wet.

The BMTR advice was interesting because it implied that tread patterns on very soft compunds can distort to the detriment of grip. None of this is quantified or scientifically justified, of course. However BMTR say that there are hillclimbers out there doing this.

Originally Posted by whimsy

Is the aim is to preserve the wets (ie have improved resistance to ageing) so you don't have to buy a new set as often?

<Snipped out section re: cutting radial slicks towets. Discussed by others

I was just being totally open minded about the advice. By the time I get to the end of the season my slicks are fairly knackered and the rears are heavily worn, so there isn't much rubber to cut into. I certainly need new wets because mine are rock hard. Plus cutting tyres is a pain, so buying a set of pukka wets seamed a good idea.

Originally Posted by whimsy

Radial wets are massively better than cross ply wets,

Good news.

Originally Posted by whimsy

but I'm puzzled why a change of compound from A91 to A15 should mean any alteration to camber requirement. The tyre construction remains the same and I'd always thought it was the sidewalls in particular that set the need for negative camber?

Yes it is the difference between crossply and radial construction that affects the static camber requirement, not the compound. Sorry if my original post was confusing. Crossplies should be run with very little or no camber. Radials need quite a lot of negative static camber to pre load the tyres. Don't ask me for a detailed explanation. Its not my topic, but I can repeat facts parrot-fashion just like most of the paddock experts

Originally Posted by whimsy

Also the very significant negative cambers being bandied around for use with radials a few years ago seem to have diminished significantly as people found that in practice, for hill climbing, they weren't necessary. I've been using 1.5 degrees negative at the front which isn't a huge amount.

Also interesting. Helps explain why a wet radial can be run with crossply cambers.

[James Williams]

I have been told you can't cut Radial slicks into wets, but don't understand why? I haven't done it based on this advice. If anyone has any experience of cutting radial slicks into wets, I would be interested to know!

I haven't mixed Crossplies with Radials, I have always thought it best to be on one or the other on both slicks and wets. Sorry Craig, I haven't really helped you there, but a good thread where we might all learn a little.

[Craig Powers]

Originally Posted by James Williams

I have been told you can't cut Radial slicks into wets, but don't understand why? I haven't done it based on this advice. If anyone has any experience of cutting radial slicks into wets, I would be interested to know!

I haven't mixed Crossplies with Radials, I have always thought it best to be on one or the other on both slicks and wets. Sorry Craig, I haven't really helped you there, but a good thread where we might all learn a little.

Feedback to this earlier tread...

I am very pleased that I went with BMTR's suggestion of using Avon crossply slcks and Avon radial wets.

The wets were essential wear at Elvington this weekend and they gave excellent grip levels in very challenging condtions. It was very difficult to get the car off the line, but once rolling the car felt good, the tyres cleared the standing water very well and grip levels were quite remarkable for the conditions.

The compunds are A15. The fronts are moulded and the rears are hand cut from slicks (which covers James' query, above)

I am using typical crossply suspension set-up i.e. little or no static camber and I left the new Anti-Roll bars at their dry setting. There seemed no reason to change the bars; the car was fairly neutral, but with mild oversteer in places.

Craig Powers
OMS2000m ZZR1100

[whimsy]

For CNHSS1 - I've run both crossplies and radials - AND a mixture of the two! My experience is relevant to a lightweight single seater (300kgs) and a 210bhp engine, which is relevant because maximum benefit from radials seems to come to cars that are heavier, with more downforce and more power. At my car's weight / power I think the benefit from radial slicks is marginal.

I ran originally with both crossply slicks and wets, but found that against the opposition whilst I was comfortably ahead of other crossply users in the wet (the car was excellent in the wet), I was miles behind radial wet users. So I eventually bought a set of radial wets, and without changing the cambers or toes, hey presto, I posted much faster times.

Interestingly the tread patterns normally cut into crossplies by BMTR are different from the radial pattern, but in my case I'd had the radial pattern cut into my crossply wets. As the compound is the same the difference in performance must be down to the tyre construction. I think in the wet camber is probably less critical because the loads on the tyre are far less than in the dry - though I'm guessing here.

In the dry I've run all crossply, radial front and crossply rear (the crossply gives more notice of impending breakaway than the radial) and all radial (current set up, done as much for gearing effect from tyre size and squareness of tyre (22 inch rears crossplies tend to have a curved tread and reduced footprint area at correct inflation pressures)). The mixed set up has been used to great effect by Brodie Branch +Darren Luke (I understand) and (definitely) by James Blackmore (although he too has now gone to radials all round). Once I put radials on the front I did increase static camber from zero to 1.5 degrees negative, but I left the rears unchanged at zero.

As to whether the radial sidewalls are softer or stiffer - I don't know! Inflation pressures are higher than crossplies which suggests softer.

For James - I wonder if the reason we're told you can't cut radial slicks into wets has anything to do with maximising BMTR revenue.............

Andy

[Craig Powers]

Originally Posted by whimsy

e
As to whether the radial sidewalls are softer or stiffer - I don't know!

I have always been told that radial sidewalls are more compliant than crossply, whuch surprises me because I have received new crossply tyres which are squashing up to save shipping space. I've never seen anyone do that to a radial. They seem very stiff.

Bizarre.

********
I did see the item below posted on a F1 forum by one of our fellow competitors whose name is 'MrT' on that forum.

"Radials have more compliant side walls and a stiff tred section, and contact patches are maintained, in general, more consistently... I run cross ply slicks on our hillclimb single seater, and have heard that the radial versions to produce better peak grip but are quite edgy, they don;t slide as much and give up very quickly. Peaky slip curve as the graph below shows..

<image as attachment>

As I run in hillclimbs, where one mistake means you loose its important to have a drivable car, and therefore the crossplys I think are our best option."

[whimsy]

Crushing crossplies down to save space when transporting has been common practice, but BMTR warn against doing that to radials - presumably because it could damage the tyre.

I'm not sure whether the curves shown in the graph are representative of the tyres we use, but they do illustrate the general point that although radials have a higher max cornering force they give up suddenly in comparison to a crossply when you reach the limit. I think this is less of an issue if your car is properly balanced (ie both ends tend to give up at the same time), but when getting a new car set up, or as a newcomer, I think crossplies are definitely a better (safer) bet.

And having said that guess who is putting radials on a his new car ............

Andy

[Craig Powers]

Originally Posted by whimsy

I ran originally with both crossply slicks and wets, but found that against the opposition whilst I was comfortably ahead of other crossply users in the wet (the car was excellent in the wet), I was miles behind radial wet users. So I eventually bought a set of radial wets, and without changing the cambers or toes, hey presto, I posted much faster times.
Andy

Excellent post Whimsy. Just the sorted of experience that I was looking for. I will definitely explore the idea of wet radials now.

btw, I am running -1/4 deg neg on the front and zero camber on the rear of my OMS 1100 and I intend to keep these 'dry' settings.

Craig Powers