Urethane tyre treatment

Squeezing out those last few tenths

Urethane tyre treatment

Postby wixwacing » Mon 18 May, 2009 12:13 am

Urethane tyres have been around for some time now but their limitations have and are becoming apparent. Firstly I'd like to dispel some myths. Urethane is NOT pure rubber. It is predominantly plastic and as such has a few niggling traits. The first is that after having been on a wheel for some time (days/weeks/months) it can loose its elastic fit. This will manifest itself as a tyre which keeps peeling off the rim in tight corners where it never used to. Secondly, tyres with a low profile are a candidate for peeling off from new fitting simply because, if they have been moulded from an original, there isn't enough tyre depth to generate a good elastic fit. Lastly, their grip levels come at a price. The 'Shore' system of measuring their softness is an indication of potentially how much grip they can give but unlike rubber, the low elastic characteristics will let you down somewhere along the line.

Now this isn't an attack on urethane tyres, far from it. I use urethane tyres almost exclusively for painted board racing and am very happy with their performance! But I do have to be careful of what tyre I'm fitting to what rim. When I am picking a tyre for a model I try to get the right wheel ridge width and the right tyre sidewall depth but... I tend to go for a noticeably smaller tyre. This almost ensures that the tyre's reduced elasticity is still enough to keep it on the wheel. I am also inclined to get a slightly narrower tyre than the wheel normally takes for reasons I will explain later. Having said this, I have a compartment box with about thirty varieties of urethane tyres in it, so I can sit beside the track and get the best tyre for the conditions.

Next up is where are they appropriate?? Urethane have their uses and they are almost never of any use on plastic track. Why?? 'mine are brilliant' I hear you say. What I want to here is that they are brilliant in hard competition on plastic, Why. On plastic track, a poor rubber tyre can be improved on with a urethane tyre because of its softness. But urethane is plastic. Plastic on plastic is not a good combination and time and again I have fitted urethanes to a model for plastic track racing and have found that in non magnet conditions they can be slippier than a good soft rubber tyre e.g., Slot.it P4's and 6's, Ninco sports tyres and even BRM and NSR tyres. With traction magnets they improve and are fine up to a point .... but once again, a good rubber tyre goes beyond that point and when pressed hard, on plastic, a urethane tyre will let you down time and again in a tight corner.

So what? well, Urethane is best suited to painted board and is hard to beat if set up right. Rubber can get close but a well prepared urethane tyre will win on average. The first thing to do is get a tyre that fits the rim snugly and there is a little resistance to get them to fit. If there isn't, then they'll need to be glued and as we all know, like some other things, it's a messy business!! So. Tyre fit comes first. Now, a fresh urethane has a 'tacky' outer skin and this is only a skin. Low, wide models will take advantage of this and will be highly drivable. Narrow tracked cars like classic sports cars may well be inclined to tip over with the extra grip, which is no fun. Extra weight will put constraints on a model’s acceleration and braking and on a short club circuit this may have to be the trade off against not deslotting.

To reduce the tipping moment you can sand off the skin and run on the 'meat' of the tyre. This will reduce tipping tendency but will suffer a slight loss in traction. Another trade off! On low flat models, narrower tyres can actually generate more straight line speed than wider tyres. This is because the weight of the model is acting on a smaller surface and there is greater pressure on the track contact point. There may well be a cornering issue where the tyres will need to be sanded for maximum profile but also the outer edges will need to be slightly beveled to reduce the tipping moment here. So sanding seems to be almost inevitable. What are we going to do about it??

If you are running urethanes on coarse or medium grip plastic surfaces, it may well be best to sand the tyres with an 80 or 100 grit paper. This seems to help the tyre find a bit more grip in the corners without unduly affecting the model's straight line performance. Rubber tyres too seem to behave better on the likes of Ninco and SCX / Classic Scaley once they have had a coarse sanding. On semi smooth tracks like Carrera and Scalextric Sport it may well be better to run soft rubber. If you are going to run urethanes then it could well be better to sand them with a 400 grit paper to give them a better chance.

If you are going to race on urethane's preferred surface, that is, smooth painted board, then you need to true the tyres on 600 grit or higher sand paper. I have heard of people using 1200 grit but I'm not sure if this is myth or not. They definitely like the smoother paper, and after a couple of races, sand them again, they'll like it even more! But don't forget, as they get thinner, they will start to loose their elastic grip of the wheel!!

Finally, there is one more thing to watch out for. If other races are treating their tyres with CRC or WD40 or Chux wipes or the skin of a road kill possum then beware. Urethane is not impressed by oil on the driving line. You will find your model has even less grip than you were hoping for. The oil will coat the tyre and it will be a poor performer until such time as you can clean it off with a residue free solvent! I have found urethanes to be the tyre of choice for the start of racing and by half way through the evening I have had to change to soft rubber because of the build up of oil on the track, great for rubber, but not for plastic.

One last pointer, what is the easiest way to identify a urethane tyre?? When you sand it, it will give off a white or pale grey powder, unlike natural rubber, which ALWAYS gives off a black residue. Well, I hope this all makes sense. Let me know if you disagree and we'll race it out somewhere!
Image

When I'm not racing slotcars,
I'm out in the back yard, burning food!!

When I win, it's because of my talent, not my car or my controller!
User avatar
wixwacing
Marshal!!!
 
Posts: 1891
Joined: Thu 10 Jul, 2008 8:22 pm

Re: Urethane tyre treatment

Postby ddyke » Mon 12 Oct, 2009 2:45 am

Those were my findings as well. Here is a tidbit that I discovered. If you cast your own tires, cast them in two stages. In the first casting cast them in a hard shore urethane like Reoflex 40 or 50. Grind them down and make them round then put them back in the mold and cast/recap them with reoflex 20. You can keep recasting them as they wear.

Dan
Scrappy Dan
When I'm not eating food or sleeping, I'm down in the basement, wrecking slot cars!
ddyke
Pitcrew
 
Posts: 48
Joined: Wed 16 Jul, 2008 1:22 am
Location: Westside of Cincinnati: The Baddest Part of Town

Re: Urethane tyre treatment

Postby wixwacing » Tue 13 Oct, 2009 10:24 pm

Is this the original slotcar 'Retreads'???!!
Image

When I'm not racing slotcars,
I'm out in the back yard, burning food!!

When I win, it's because of my talent, not my car or my controller!
User avatar
wixwacing
Marshal!!!
 
Posts: 1891
Joined: Thu 10 Jul, 2008 8:22 pm

Re: Urethane tyre treatment

Postby Deslotted » Wed 14 Oct, 2009 7:36 pm

Not sure if they're the original retreads.
When I was a kid and too poor to afford new scalextric tyres when they went hard, My brother and I used to coat them in a layer of silicone sealer that We pinched from the old mans shed. Used to stay on for about 10 minutes I reckon, before they threw it off. :lol:
User avatar
Deslotted
Team Strategist
 
Posts: 149
Joined: Thu 01 Jan, 2009 7:25 pm
Location: West Oz

Re: Urethane tyre treatment

Postby ddyke » Thu 15 Oct, 2009 5:08 am

I am retreading urethanes with a softer compound of the same. You can do it at least twice - I have done than many. I am going to try originals later when I get more material.
Scrappy Dan
When I'm not eating food or sleeping, I'm down in the basement, wrecking slot cars!
ddyke
Pitcrew
 
Posts: 48
Joined: Wed 16 Jul, 2008 1:22 am
Location: Westside of Cincinnati: The Baddest Part of Town

Re: Urethane tyre treatment

Postby denny » Sun 12 Nov, 2017 9:12 pm

I found as well as others I raced with ,when you run on a NInco track most tyres need to be brand new .Ive ruined brand new MJKs by truing them. Foamies seem to be the only tyre that will run well for a while on Ninco .Ninco track eats tyres ,I was also told Nincos gone under anyone heard anything ?
denny
Engine Tech
 
Posts: 99
Joined: Thu 23 Sep, 2010 5:58 pm

Re: Urethane tyre treatment

Postby denny » Sun 12 Nov, 2017 9:46 pm

Now I remember why I came here LOL

How do you treat Silicon tyres for a smooth painted track .Ill be #@&^%$# if I can get my XB to handle on them.

WIX it must be the Possum Piss soaked into the road kill ,that stuff is sticky as ,don't ask how I know LOL
PS NInco tyres make good barriers because they don't work as tyres on any surface .
denny
Engine Tech
 
Posts: 99
Joined: Thu 23 Sep, 2010 5:58 pm


Return to Tuning Tips

Who is online

Users browsing this forum: No registered users and 1 guest

Untitled Document
Image hosted by Photobucket.com
Image hosted by Photobucket.com

Image hosted by Photobucket.com

Image hosted by Photobucket.com

Image hosted by Photobucket.com
Image hosted by Photobucket.com

Image hosted by Photobucket.com
Image hosted by Photobucket.com



































































































































Image hosted by Photobucket.com