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Discussion in 'Car Talk' started by Azfalt Raser, Jan 29, 2016.
Can someone explain to me the benefits of scrub tires vs sticker tires?
I guess not.
Disclaimer - I'm not personally an expert and probably missed something glaringly obvious but here goes...
There's a few reasons why it might be beneficial to scrub a tyre. First up is the result of the manufacturing process. I'm not sure if this has been addressed in some manufacturers tyres or not so may actually be something that's not an issue with some (race) tyres though is something you may have noticed if you've ever had brand new tyres on a road car.
Many tires and their treads are produced using a moulding process and of course the tyres have to come out of that mould. A releasing agent is applied to the mould to stop both the tyre sticking to the mould and to help in the release of it from the mould. Due to the fact this is in direct contact with the rubber as it's pushed into mould inevitably some of the agent becomes embedded in the surface of the tyre, changing the properties of the compound and resulting in reduced grip until that part of the surface is scrubbed away leaving only the true tyre compound exposed. A quick Google search on this for road tyres shows a value sometimes as high as 500 miles of normal driving before it's completely gone.
In racing terms this would be much much less due to the relative softness of the tire and the higher loads applied to it and the fact that different agents and treatments for removal may be applied before the tire is used. I don't have data for this but given the short runs people have traditionally done in qualifying sessions it's likely more 1-2 laps.
A second (more racy) reason is to avoid/reduce cold graining which happens when a tyre is put under stress and load before it reaches it's full and correct operating temperature. In short it's a shearing of the compound between the layers/sections of the tyre which can produce a rippling effect or tearing of the surface which in turn reduces the available grip. This is why this type of graining is often worse in cold/wet conditions where temperatures are lower and sliding of the tyre is inevitable. scrubbing the tyre involves putting it through a heat cycle without over stressing it.
The reason this works (which is conjecture on my part based on watching racing, listening to drivers and the third reason...) is it hardens the compound at the surface of the tyre. Loading the tyre whilst heating it without shearing the surface is likely to compact the upper layers of the tyre resulting in a more dense arrangement of the compound and thus reducing the likelihood of shearing when the tyre is put under load without being at racing temperature, for instance at a race start or after a pit-stop. (more research needed here I think). I do have some reference pulled from he web regarding that from the Avon Tyres site where they explain their recommended scrubbing in procedure for tyres. It also includes information for what to do when scrubbing is not an option. http://www.avonmotorsport.com/resource-centre/user-advice
A third reason I know of is purely strategic and could be seen relatively often in F1 during the Bridgestone/Michelin days where teams on marginal strategies would put tyres through a series of heat cycles to effectively harden the compound at the tyre surface and extend their potential stint length giving them options such as making less pitstops or extending a middle stint to allow a driver to push hard during his first and last stints. Of course the scrubbing in process would also deal with any releasing agent issues before going racing.
This does not seem to be done on the Pirelli rubber they run today and can probably be explained by differences in compound and tyre manufacturing process coupled with the fact that everyone runs the same selection and in general without refuelling in pitstops if it's a two-stopper for one team it's a two-stopper for most teams so wearing tyres less probably provides a greater advantage than preparing them to be worn more.
They are the reasons that immediately sprung to mind, there may be more and my knowledge of tyre compound reactions under load is able to be tattooed on my pinky but it should give you a start for more research if you're interested. It's be nice if someone with a more intimate knowledge of tyre tech could chip in an lend some info.
Thank you for the explanation!
I edited my post to shorten it. But....below is the rest of my original post.
I used to use Yokohama A008R & BF Goodrich R1 tires. I had the option of having them heat cycled from the retailer. When new, my tires felt greasy and slippery. I ran a few laps, then let the tires cool, then ran afew more laps..... on and on. As time went on, I noticed grip increased.
I was watching an old Champ Car race (yes I'm that old) and they talked about teams saving "Sticker Tires" for all out speed. They also "scrubbed" a certain number of tires for the race.
If going by the same principle as my BF Goodrich tires, I just found it odd that the champ car slicks
would be faster without being "scrubbed in" - something I didn't really question before.
It must be due to the fact that those slicks didn't abide by the same principles.
Essentially, for my purposes, heat cycling the tires increased the longevity.
So scrubbed tires, I suppose were used for the standard and/or long stints, where as the sticker tires were used for all out speed for a limited number of laps - say the final 10-15 laps of a race or however long the "short stint" would be.
From what I see on tv now adays, I'm thinking that no longer holds true for certain tire types/manufactures.
It's been many years since I was in motorsports and I guess I forgot alot.
But, your explanation sounded very familiar.
Thanks for responding.