Home made Urethane tires - additives

[cdub]

Not sure where the right place to post this question is on HRW, so I'm dropping it here.

I've made a few attempts at casting my own Urethane tires. I've tried Smooth-On Vytaflex 40 shore and 20 shore, and use their black pigment to dye them.

I've had success with 3D printing tire molds, a few different ways. However, I haven't been satisfied with the grip of the tires. The 40 Shore tires seemed to have almost a slick surface to them. If you dragged them across the track by hand there was no adhesion at all. So I went softer and tried the 20 Shore. The 20 Shore tires perform a little better on the car, but still feel slick to me.

Does anyone have any additives to put into the Urethane to get them to develop some level of adhesion when cured?

[docdoom]

Try wet sanding them and make sure the track is clean.

[KK Racing]

Hi cdub

Do about a 1,000 laps with your 40 shore tires before evaluating the performance. Depending on what you ran before you likely have a build up of other rubber, silicone and urethane compounds on your track surface and quite often the reaction between all of these can be detrimental to grip. Some will obviously disagree but allot of us find 40 -50 shore tires to be the most effective on wood tracks, not sure what surface you are running on. Try cleaning the track and like I said do about 1,000 laps before giving up on or evaluating any of your current formulas. Urethane tires crosslink and mature over time as well not to mention your first pulls from new molds may be part of the problem as well. Post curing both your molds and tires may also help if they are new. If you are using silicone molds try washing them with dishsoap and water and allowing them to fully dry before pouring your next batch. If your using Urethane molds try using less release agent or using it every other batch. Best of luck and let us know how this progresses.

Cheers
KK

[OXO cube]

i found too much dye in the mix made them slick
some commercial urathanes have a very slight translucent look to them
the dye is very concentrated and only a tiny tiny tiny amount is needed

i cast some without dye and found them miles better on my scally sport track
but the dye gives them the desired look

and as stated above , truing and a clean track are invaluable

Kev

[cdub]

Wow, thank you everyone for all the insights.

I have no idea how much dye I was using, but I'm certain it was too much. I was just adding dye until the urethane looked black.

I will comment that I've had a lot of trouble with the 20 shore tires breaking apart when I put them on a wheel. Sometimes they break in the process and other times they let go the next day, just due to the stress. I wouldn't make 20 shore tires again. I may rethink my mold strategy too. I have a lathe now, so I could potentially machine aluminum positives and make silicone molds from them. That would be neat.

[HO RacePro]

I'm curious -- is it possible to paint urethane? If you just paint the sidewalls you might be able to omit dying the tires entirely.

Ed Bianchi

[Michael Squier]

If you could, I would go for white walls. Hmm, might have to try that on something.

[Backintheslot]

Give them a true or a scuff, treat and clean them with 91% Isopropyl Alcohol. 40 shores when the car is too tight, 20 shores when the car is too loose.

[RichD]

When my club used urethane tires we found that they needed to be polished to get their best grip. The polishing was done by running a car on a skid pad for hours.

[GT40 Racer (DM)]

I true my home made urethanes - I start with around 240 grit paper to do the leg work, I then switch to 400 or 600 grit to fine tune and finish off with 1200 or 2000 grit to polish them up. Use water at all stages to keep them cool - more water at the polishing stage.
Before racing I usually give them a spin with 1200 grit.

I have run on Scalextric plastic track for a while now. So can't comment on how they grip on that surface.

[Fathead59]

Ok , I have a Tire Razor , is there a way to keep the tire cool while truing them ?

[Fathead59]

Also , if this is the wrong forum to ask this question , please feel free to move it to the correct place

[OXO cube]

running low & slow , keeping tyres cool and the lighter fluid trick are for rubber (afaik)
the lighter fluid helps with cooling and with the grinding

urethane tyres are very easy to grind and do not need lighter fluid , or to be ground a low speed
grind using increasingly fine grits ( no need to go extra extra fine ), then i polish with a rag and iso alcohol
they will come up real shiny and will give great grip when polished as mentioned above by RichD

Kev

[Fathead59]

Thanks for the info

[Phil Kalbfell]

Do not use any mineral based products on Eurethane tyres.
Did you allow them to cure for several days before using them.
I just add enough pigment to Colour the tyres, just a small amount on a popsicle stiring stick.
The two different Shore hardness can be used to make 30 shore if you want to try thrm
I usually sand using water on various wet and dry paper.
Also what other tyres are you comparing these to?

[cdub]

Typically, I'm taking a new car and removing the magnets. So, I take a car that runs okay with magnets, and then take out the magnets.

Then I'm putting on aftermarket tires. Usually either Ortmann or Paul Gage. I have also done home made tires, hence the initial post, and have found my homemade tires don't have nearly the grip the aftermarket tires have. They are basically no better than the stock tires.

I will need to order fresh Urethane as all mine has spoiled in the pots, which I expected.

Smooth on offers Vytaflex in Shore hardness 30, so I think I'm going to try that this time.

I'm also going to use way less dye, and try a little red dye as well.

With regards to cleaning urethanes, yes I agree with the concensus of avoiding any mineral oil based products. I have been using original formula Windex with great results. This was advice given to me on another forum.