Tire fit questions

[Brian]

I'm using modern tires for the first time, previously used dunlop vintage ford tires and now I'm using 13" bias Atlantic tires. I have a question about how these tires fit the wheels:

I first mounted up a set of take-off Avons. They went on the wheels "normally" - the beads seated with about 40 PSI and they didn't leak down to any great extent. Then I got a set of the new spec Hoosiers, again take-offs but with only about three short sessions on them. They practically fell onto the wheels, beads seated with about 10 PSI, and they didn't hold air. They leaked around the bead seat area, and they would bleed down about 5 PSI per hour.

Now I have a brand new set of Goodyears. they actually measure about 3/16" to 1/4"smaller in diameter than the Hoosiers at the bead, and I can't get the bead to seat with 40 PSI - just won't pop.

What's up with this? Are there known issues with bead fitment on these kinds of tires? I read somewhere that someone had a very similar issue with Hoosiers, and fingers just pointed from wheel manufacter to tire manufacturer, both said the other guy's product was out of spec.

How much pressure is too much to seat the bead? What tricks are there? I was thinking of heat-gunning the bead to try to expand it a bit, would 200 deg F be a problem?

Thanks, Brian

[Jim Garry]

Just from watching the tire guys mount my tires ....

Did you use some type of lubricant on the bead?
I've also seen them at times use pressures to seat the bead that made me leave the vicinity.

Jim

[EYERACE]

it sounds as if you're mounting them yourself by hand...bingo...lather those baby's up and the wheel surface too..... and stretch 'em a little with the tool when you must. if you're worried about the pressure to seat the bead then try this - leave the valve out of the stem as you air it up and then immediately remove the chuck when it sets to relieve the excess you just used. and also work/knead/flex/press the sidewall as you try to seat the bead

[Scott B]

The new Hoosier FA tires are specific for a 14 inch width for the rear wheel. What type and size of wheels are you using? The GY tires require a little higher pressure to seat the bead, but are safer at speed, as eyerace said, put a lot of soapy water on both the bead and the wheel and they go right on. I have been hand mounting race tires for more than thrity years with no problems.....so far.

Scott B

[Brian]

I am putting these tires on to 10" wide fronts and 12" wide rears. I know that the rears are a little narrow, but that's what I have - so I will see how they do. The new C3000 Hoosiers are 12" wide, and their tech guy said that they were fine on 12" wide tires when I called to ask. The GY rears mounted up fine but they do look a little funny. These are the original Monocoque two piece spun aluminium wheels from 1972, so I really want to run them. I can get new inner halfs made if I really need to, to bring them out to 14". The car is the NTM MK4 B/SR, btw.

The problem that I wanted feedback on is the diameter of the bead area on the tires. The Hoosiers are bigger than the GY's or the Avons. When I took the hoosier rears off, I didn't have to break the rear bead, the tire was loose on the rim, it slid right down by hand. the Avons were a bear to loosen up, they were quite tight on the same rim. The GY's that I just put on were also quite tight on the rear side of the rim, definitely needed air to push them down while the Hoosiers went down to the bead seating area by hand.

I was really quite hoping to be able to run the Hoosiers, because as I said I have 12" wide rear wheels and the Hoosiers are spec'd for that width wheel. But since all four of them didn't fit I am assuming that the bead diameter size is on purpose, not a flaw. But what have other people found?

I am using lube to try to seat the beads, BTW, and it's only the fronts that won't seat, I presume because the short sidewall reduces the sideways pressure from the air. Fewer square inches of sidewall equals less pressure from the pounds per square inch.

Thanks, Brian

[dennis]

As a Goodyear rep. I will say that 40 PSI is not the normal bead seat pressure for our tires. There are several things to consider here and I will try to catch them all. First, brand new wheels tend to be tougher to seat on because the safety bead on the wheel is at it's largest diameter. I t tend to wear down over repeated mountings. Another thing, do your wheels have a grip ring on them. By that I mean a small band, usually about 3/8th's of an inch of rough surface? It's sort of like a sandpaper feeling and some manufacturers put it on to help stop the wheel from spinning inside the tire. As to what pressure to take it to, we routinely take it to 60-80 psi. However once the bead pops we don't continue to add air but it is not uncommon to have to go higher than 40psi. If it becomes evident that one wheel is harder to seat on than another, check the wheel diameter, 9 times out of 10, the wheel will be slightly larger. Now for the safety speech, when we mount we use dishsoap and water mix to lube the beads. If the bead has problems we will use straight dish soap. I highly recommend however using a tire cage to air the tire up. I know that we don't at the track, and I'm sure OSHA wouldn't approve but our mounters have mounted a few thousand tires and will only go so far. Someone who doesn't know the sounds, feel and look of what is going on with airing tires up should use much more caution. If you have never seen what happens when a tire or wheel let go it's usually catastrophic and causing serious damage and harm. If you would like you can e-mail me at ds@competitiontire.com or call me at 610/375-6191 and I would gladly help in any way I can. You can tell it is Monday morning becuase I forgot to check where you are from. My ending advice, if you are uncomfortable doing this which by questioning you are, then let a professional do this one. If you are in the Northeast I would gladly do as a service and even point out what you need to look for when you are doing it yourself. Some of us consider that as part of the services we as dealers are supposed to provide. Good luck, Dennis....

[Jonathan Hirst]

Hi Brian

On seating the GY's -
Try a taut tie down around the center of the tire circumfrence when inflating (with lots of lube on bead and seat). On wider tires with short (stiff) sidewalls, the tire tread surface can crown and decrease the outward expansion of the bead. Restrict the crowning to drive more of the tire movement under pressure in the outboard direction.

Sometimes it was enough to get the bead to seat back in the Sasco days.

I've gone as high as 60 psi+ to seat a tire but always do it with the valve core out - especially if its on a period cast rim. It isn't the pressure as it is the snap of the bead against a weak flange. Lots of lube and just enough pressure to ease it onto the bead.

If that doesn't work and you are still using soap and water, try with some proper tire lube. It may make the difference. If you don't have any then I can bring some for you to the VARAC Film Night - or pass it along to a designated delivery person.

Apart from that - I see Dennis has posted from Competition Tire - they're the experts.

jon

[Brian]

Thanks Dennis and Jon...

I've mounted a lot of tires but all a lot narrower and taller than the atlantic fronts, so I was looking at this little thing getting fatter and fatter and wondering how much air is too much...and given that I was just using a normal tire chuck to air up the tire I was pretty close to whatever action I was going to see if something bad happened. Knowing that more pressure than I've used so far is commonly required is a big help. I'm getting a clip-on chuck, a long hose and I have a cage to put the tire into, so I will try again. The rears mounted up fine, and in fact one of the fronts popped at 45- 50 PSI, so the wheels seem not to be particularly oversize.

Dennis, any comment about my running your Atlantic rears on 12" wide wheels?

Thanks again, appreciate the advice.

Brian

[dennis]

I cannot comment on it to much. It will be a little tougher to put them on a smaller wheel since they are made for 14" wheels. Atlantic rears have never been the problem to mount however, watch the profile for rounded shoulders and rollover wear. The fronts do take quite a bit to inflate they are tight to most wheels. What kind of wheel are you using? I recall Techno brand to be the hardest to mount with a couple of others close behind. A strong word of caution about a previous post, NEVER, let me say it again, NEVER use a constricting band around the tire to inflate. It is one thing to use it to get the bead to catch the lip of the wheel but once the seal forms and air pressure begins to build constricting bands are dangerous. This is one of our cardinal sins in our business. I witnessed a drag racer at 7psi blow one and it cut straight through the side of his trailer. If you cannot get the bead to reach the rim there are rubber rings that you can get to mount on top of the bead. If need be I can find out where we got ours and let you know. That does not seem to be your problem though. Dennis....

[Jonathan Hirst]

Thanks for the clarification Dennis regarding constriction straps and sealing the bead versus seating it.

[Avon Racing Technical]

If it helps at all, I would just like to add that the size of wheel that we work to is as follows:- for a 13" rim, the bead diameter should be 329.4mm with a CIRCUMFERENCE tolerance of -0, + 1.2mm. For 15” rims, it should be 380.2mm with a CIRCUMFERENCE tolerance of -0, + 1.2mm. Sorry for the use of metric units, but that’s how it’s quoted. It is on this basis that we design our moulds and bead diameters.

The pump-rings that we use to get the bead to approach the wheel flange were made by a company called Tip-Top.

Best regards,


Pete